TimR wrote:
On Thursday, March 14, 2013 10:13:27 PM UTC-4, wrote:

C- Why engineers treat air to water heat exchangers using CONVECTION,

not mass transfer


Do chemical engineers consider mass flow and mass transfer to be very
different things? If mechanical engineers do, then that's either a
recent change or my memory has completely faded. I haven't actually done
this calculation in a long long time, I became a suit.

But anyway. The very FIRST thing a mechanical engineer does in analyzing
an air to fluid heat exchanger, after drawing the system boundaries of
course, is a Mass Balance. The second thing is an Energy Balance. The
third thing is an Entropy Balance. Normally all three are required for a
solution. Sometimes the Entropy Balance is called the Availability Balance.

The mechanism by which heat is carried away from a car radiator is the
flow of mass called convection. Convection can be forced or free in the
mechanical engineer's world, that may not be true for physicists, who knows?

I looked it up, my memory was correct. A car needs a good 3 tons of AC,
much like an average sized house.

All depends on vehicle size. Imagine a van. I don't think a small car needs
more than 2 ton.

Greg

gregz wrote:
TimR wrote:
On Thursday, March 14, 2013 10:13:27 PM UTC-4, wrote:

C- Why engineers treat air to water heat exchangers using CONVECTION,

not mass transfer


Do chemical engineers consider mass flow and mass transfer to be very
different things? If mechanical engineers do, then that's either a
recent change or my memory has completely faded. I haven't actually done
this calculation in a long long time, I became a suit.

But anyway. The very FIRST thing a mechanical engineer does in analyzing
an air to fluid heat exchanger, after drawing the system boundaries of
course, is a Mass Balance. The second thing is an Energy Balance. The
third thing is an Entropy Balance. Normally all three are required for a
solution. Sometimes the Entropy Balance is called the Availability Balance.

The mechanism by which heat is carried away from a car radiator is the
flow of mass called convection. Convection can be forced or free in the
mechanical engineer's world, that may not be true for physicists, who knows?

I looked it up, my memory was correct. A car needs a good 3 tons of AC,
much like an average sized house.

All depends on vehicle size. Imagine a van. I don't think a small car needs
more than 2 ton.

Greg

We most always had to use recirculate in the summer desert. Often barely
comfortable.

Greg

On 03/14/2013 07:13 PM, wrote:
On Mar 14, 8:58�pm, jim beam wrote:
On 03/14/2013 12:03 PM, dpb wrote:





On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. �Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. �It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

are you for real? �do you understand what you're reading? �if you think
that contradicts a single thing i said, you have a serious comprehension
problem.



This is a dual-loop, closed system forced convection heat transfer
problem. �No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. �there is one closed loop on an automotive engine
coolant system. �the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer


And citing a book cover on Amazon is not a scientific
reference.....


i'm not going to waste electrons stroking your masturbatory reality
avoidance - just read the freakin' book.


--
fact check required

On Mar 14, 8:29*pm, "
wrote:
On Mar 14, 3:18*pm, TimR wrote:









On Thursday, March 14, 2013 3:03:17 PM UTC-4, dpb wrote:

transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview

is available at

http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4

(Table 0-2.1) (and where they're covered in the book) is sufficient.

This is a dual-loop, closed system forced convection heat transfer

problem. *No mass transfer in the analytic meaning thereof is occurring.

To me it seems you are being unnecessarily pedantic. *It appears that the chemical engineering usage of "mass transfer" would not be correctly applied to this system. *I'm guessing because I'm not a chemical engineer, I'm a mechanical engineer. *Mechanical engineers do not have the same precise usage standard and very well might talk about mass transfer in this problem. *Certainly mass crosses the system boundaries at a high rate. *- Hide quoted text -

- Show quoted text -

Maybe we should back up to where this rat hole started.
The discussion was about whether paint color of the radiator
made a difference in heat transfer, which lead into a
discussion of how heat is transfered from the radiator.
We then had Jim Beam claiming that a car radiator does
not transfer heat to the air via convection, that it works via
mass transfer.

There are 3 modes of heat transfer, conduction, convection
and radiation, correct?
We're talking about how the heat leaves the car
radiator. *I say the vast majority, probably 90%+ is by
convection, that is the air moving through the radiator.
A small amount is by conduction, that is heat transfering
from the radiator to the surrounding metal that it's touching, etc.
And a small amount is leaving via radiation.

I think the essential hangup here is that JB refuses to accept
that convection can be natural or forced.

Do you agree that convection is the predominant heat
tranfer mode? *Or do you agree with JB that convection is
not involved? *And if you agree that it's via convection, then
I don't believe you'd find mechanical engineers approaching
this as a mass transfer problem.

I think he thinks (as I do) that convection refers to the buoyancy of
a fluid due to temperature differences.
Movement due to mechanical means is nothing to do with convection
Ergo "forced convection" does not exist. A misnomer. Assisted
convection exists.
It's about terminology.
A car "radiator" in fact radiates very little heat. Another misnomer.
These terms arose historically when people had little understanding of
what was going on and are best avoided as they confuse the simple
minded.

I would say that the majority of the heat transfer in an automobile
radiator is by conduction. The heat has to get from the water into
the metal and from the metal into the air.
Both air and water have to be moved mechanically because convection is
negligable.

On Mar 15, 2:13*am, "
wrote:
On Mar 14, 8:58*pm, jim beam wrote:









On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. *Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

are you for real? *do you understand what you're reading? *if you think
that contradicts a single thing i said, you have a serious comprehension
problem.

This is a dual-loop, closed system forced convection heat transfer
problem. *No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. *there is one closed loop on an automotive engine
coolant system. *the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? *If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer

And citing a book cover on Amazon is not a scientific
reference.....

These are misnomers. The terms have come into use through attempts by
salespeople to differentiate between normal and fan ovens.

The correct term would be "forced air circulation ovens"
Commercial ovens are identified as such.
http://www.powdercoating.romerpp.pl/...rculation.html

Without a fan, the correct term is "passive/natural air circulation".

Correct. Those are the ONLY three ways heat can move.

Jim Beam is saying that the heat transfer from the radiator is through a process called "advection". I looked up advection because I'd never heard that term before, and it's a word typically used in the weather sciences to discribe the transfer of heat, cold or humidity horizontally from one point to another as a result of air movement (typically, the wind).

To my way of thinking, the word "advection" wouldn't apply here because for there to be advection, there has to be air movement from one point to another. In the case of heat loss from a radiator, the car is definitely moving, but the air doesn't necessarily have to be moving. People drive cars on dead calm days too.

Here's what Wikipedia says about the word "convection":

"Forced convection:"
Main article: Forced convection

In forced convection, also called heat advection, fluid movement results from external surface forces such as a fan or pump. Forced convection is typically used to increase the rate of heat exchange. Many types of mixing also utilize forced convection to distribute one substance within another. Forced convection also occurs as a by-product to other processes, such as the action of a propeller in a fluid or aerodynamic heating. Fluid radiator systems, and also heating and cooling of parts of the body by blood circulation, are other familiar examples of forced convection."

Convection - Wikipedia, the free encyclopedia

Wiki also has a web page all about forced convection:

Forced convection - Wikipedia, the free encyclopedia

which describes forced convection as follows:

"Forced convection is a mechanism, or type of transport in which fluid motion is generated by an external source (like a pump, fan, suction device, etc.). It should be considered as one of the main methods of useful heat transfer as significant amounts of heat energy can be transported very efficiently and this mechanism is found very commonly in everyday life, including central heating, air conditioning, steam turbines and in many other machines."

Yes.

The heat loss from the radiator is primarily through forced convection, not mass transfer.

Jim:
If it's a dead calm day, and out on the highway a car is going 60 mph, and heat is lost from the car's radiator to that calm air along that highway, where do you see any mass transfer going on there?

On Thu, 14 Mar 2013 16:33:10 -0500, dpb wrote:

On 3/14/2013 2:18 PM, TimR wrote:
On Thursday, March 14, 2013 3:03:17 PM UTC-4, dpb wrote:

transport phenomena texts, Bird, Stewart, and Lightfoot. It's preview
is available at

http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/0470115394#reader_0470115394

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

This is a dual-loop, closed system forced convection heat transfer
problem. No mass transfer in the analytic meaning thereof is occurring.

To me it seems you are being unnecessarily pedantic. It appears that
the chemical engineering usage of "mass transfer" would not be
correctly applied to this system. I'm guessing because I'm not a
chemical engineer, I'm a mechanical engineer. Mechanical engineers
do not have the same precise usage standard and very well might talk
about mass transfer in this problem. Certainly mass crosses the
system boundaries at a high rate.

It isn't unnecessary nor pedantic either one imo.

If mechanical engineers didn't have precise definitions/usage then
they'd never get anywhere. That they do (get somewhere, that is)
implies a rigorous set of definitions.

There's mass flow but not mass transfer at work here.

The key point though, that the dominant heat transfer mechanism is
forced convection and the point to the naysayer was to show the table
that there _are_ precise meanings for the terms.

(Strictly speaking I'm not a ChE, either, I'm NucE w/ ChE minor
undergrad and Phys/NucSci grad... )

The discussions have been interesting but I'm still wondering just how
much, if any, the layer of paint reduces the effectiveness of the AC
condenser, or the engine radiator. I have to think that adding a
layer of anything to a "radiator" reduces it's ability to "let the
heat out". But how much? Surely if you picture a tube type radiator,
like some of the long looped tubes (without fins) used as power
steering or oil coolers it would seem logical to think that if you put
a nice thick coat of paint on them they would become a lot less
effective as an oil cooler. If you add the fins, and then paint the
whole surface area, same thing would seem like it would happen.

On Fri, 15 Mar 2013 02:56:31 +0000 (UTC), gregz
wrote:

TimR wrote:
On Thursday, March 14, 2013 10:13:27 PM UTC-4, wrote:

C- Why engineers treat air to water heat exchangers using CONVECTION,

not mass transfer


Do chemical engineers consider mass flow and mass transfer to be very
different things? If mechanical engineers do, then that's either a
recent change or my memory has completely faded. I haven't actually done
this calculation in a long long time, I became a suit.

But anyway. The very FIRST thing a mechanical engineer does in analyzing
an air to fluid heat exchanger, after drawing the system boundaries of
course, is a Mass Balance. The second thing is an Energy Balance. The
third thing is an Entropy Balance. Normally all three are required for a
solution. Sometimes the Entropy Balance is called the Availability Balance.

The mechanism by which heat is carried away from a car radiator is the
flow of mass called convection. Convection can be forced or free in the
mechanical engineer's world, that may not be true for physicists, who knows?

I looked it up, my memory was correct. A car needs a good 3 tons of AC,
much like an average sized house.

All depends on vehicle size. Imagine a van. I don't think a small car needs
more than 2 ton.

Greg

I've been looking into adding a unit and have found that most of the
underdash units are 15000 BTU. Some of the bus type units are 24000
BTU. I also found some info that suggests that most OEM factory units
are around 22000 BTU's. I also found info on the ratings of
compressors at various rpm. The smaller ones may only deliver 10,000
BTU's at 1000 rpm and max out at 20,000 at their peak. Some of the
larger ones will peak at around 25000 or a bit more. So it looks to
me like the most you can expect for a car is a bit more then 2 tons of
capacity. Still, that's a lot considering it would cool a 1200 sf
house.

On Mar 15, 3:15*am, harry wrote:
On Mar 14, 8:29*pm, "
wrote:





On Mar 14, 3:18*pm, TimR wrote:

On Thursday, March 14, 2013 3:03:17 PM UTC-4, dpb wrote:

transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview

is available at

http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4

(Table 0-2.1) (and where they're covered in the book) is sufficient..

This is a dual-loop, closed system forced convection heat transfer

problem. *No mass transfer in the analytic meaning thereof is occurring.

To me it seems you are being unnecessarily pedantic. *It appears that the chemical engineering usage of "mass transfer" would not be correctly applied to this system. *I'm guessing because I'm not a chemical engineer, I'm a mechanical engineer. *Mechanical engineers do not have the same precise usage standard and very well might talk about mass transfer in this problem. *Certainly mass crosses the system boundaries at a high rate. *- Hide quoted text -

- Show quoted text -

Maybe we should back up to where this rat hole started.
The discussion was about whether paint color of the radiator
made a difference in heat transfer, which lead into a
discussion of how heat is transfered from the radiator.
We then had Jim Beam claiming that a car radiator does
not transfer heat to the air via convection, that it works via
mass transfer.

There are 3 modes of heat transfer, conduction, convection
and radiation, correct?
We're talking about how the heat leaves the car
radiator. *I say the vast majority, probably 90%+ is by
convection, that is the air moving through the radiator.
A small amount is by conduction, that is heat transfering
from the radiator to the surrounding metal that it's touching, etc.
And a small amount is leaving via radiation.

I think the essential hangup here is that JB refuses to accept
that convection can be natural or forced.

Do you agree that convection is the predominant heat
tranfer mode? *Or do you agree with JB that convection is
not involved? *And if you agree that it's via convection, then
I don't believe you'd find mechanical engineers approaching
this as a mass transfer problem.

I think he thinks (as I do) that convection refers to the buoyancy of
a fluid due to *temperature differences.

Anytime anyone thinks like you do, that's a pretty
good indication that they are probably wrong. You've
demonstrated that you're the village idiot over and over
again. You just did it again. What you "think" convection
means isn't relevant. How it's defined and used does.



Movement due to mechanical means is nothing to do with convection
Ergo "forced convection" does not exist.

Wrong.


A misnomer. *Assisted
convection exists.
It's about terminology.

Which you obviously do not understand and instead
of educating yourself, here you are making a fool of
yourself again.


A car "radiator" in fact radiates very little heat. Another misnomer.
These terms arose historically when people had little understanding of
what was going on and are best avoided as they confuse the simple
minded.


That would be you.




I would say that the majority of the heat transfer in an automobile
radiator is by conduction. *The heat has to get from the water into
the metal and from the metal into the air.
Both air and water have to be moved mechanically because convection is
negligable.- Hide quoted text -

- Show quoted text -

Wrong yet again.

On Mar 14, 10:34*pm, TimR wrote:
On Thursday, March 14, 2013 10:13:27 PM UTC-4, wrote:

C- Why engineers treat air to water heat exchangers using CONVECTION,

not mass transfer

Do chemical engineers consider mass flow and mass transfer to be very different things?

Why do you answer a question with a question and try to
take this even further off point? I posed a few very simple,
yes or no questions that go directly to the point of the discussion:


There are 3 modes of heat transfer, conduction, convection
and radiation, correct?
We're talking about how the heat leaves the car
radiator. I say the vast majority, probably 90%+ is by
convection, that is the air moving through the radiator.
A small amount is by conduction, that is heat transfering
from the radiator to the surrounding metal that it's touching, etc.
And a small amount is leaving via radiation.


Do you agree that convection is the predominant heat
tranfer mode? Or do you agree with JB that convection is
not involved?


The above is the core of the issue.

On Mar 14, 11:44*pm, jim beam wrote:
On 03/14/2013 07:13 PM, wrote:





On Mar 14, 8:58 pm, jim beam wrote:
On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

are you for real? do you understand what you're reading? if you think
that contradicts a single thing i said, you have a serious comprehension
problem.

This is a dual-loop, closed system forced convection heat transfer
problem. No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. there is one closed loop on an automotive engine
coolant system. the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? *If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer

And citing a book cover on Amazon is not a scientific
reference.....

i'm not going to waste electrons stroking your masturbatory reality
avoidance - just read the freakin' book.

--
fact check required- Hide quoted text -

- Show quoted text -

My reality avoidance? Citing an entire book on Amazon about
mass and heat transfer proves nothing about your contention that
convection is not the primary heat transfer mechanism in a water
to air heat exchanger, ie a radiator.

And if forced convection is not convection, maybe you can
explain why there are convection ovens in kitchens? I have
two. A regular oven does not have a fan. A convection oven
does. When you set it to "convection bake", the fan comes
on to circulate the air. Capiche? I suppose your answer is
to tell the oven makers to read a book on Amazon.....

Your central error here is that you insist that convection can
only be natural, not forced. If you have the page of that book
on Amazon that says dpb and I are wrong on that, just give
us the page.... The fact that the village idiot, harry now agrees
with you should be enough to make you reconsider your
position.

On Mar 15, 3:26*am, harry wrote:
On Mar 15, 2:13*am, "
wrote:





On Mar 14, 8:58*pm, jim beam wrote:

On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. *Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient..

are you for real? *do you understand what you're reading? *if you think
that contradicts a single thing i said, you have a serious comprehension
problem.

This is a dual-loop, closed system forced convection heat transfer
problem. *No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. *there is one closed loop on an automotive engine
coolant system. *the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? *If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer

And citing a book cover on Amazon is not a scientific
reference.....

These are misnomers. *The terms have come into use through attempts by
salespeople to differentiate between normal and fan ovens.

The correct term would be "forced air circulation ovens"
Commercial ovens are identified as such.http://www.powdercoating.romerpp.pl/...ven_with_force...

Without a fan, the correct term is "passive/natural air circulation".- Hide quoted text -

- Show quoted text -

http://en.wikipedia.org/wiki/Convection

Convection is the concerted, collective movement of ensembles of
molecules within fluids (e.g., liquids, gases) and rheids.

The term convection may have slightly different but related usages in
different scientific or engineering contexts or applications. The
broader sense is in fluid mechanics, where convection refers to the
motion of fluid regardless of cause.[2][3] However in thermodynamics
"convection" often refers specifically to heat transfer by convection.
[4]

Additionally, convection includes fluid movement both by bulk motion
(advection) and by the motion of individual particles (diffusion).
However in some cases, convection is taken to mean only advective
phenomena. For instance, in the transport equation, which describes a
number of different transport phenomena, terms are separated into
"convective" and "diffusive" effects, with "convective" meaning purely
advective in context.

Forced convection:
In forced convection, also called heat advection, fluid movement
results from external surface forces such as a fan or pump. Forced
convection is typically used to increase the rate of heat exchange.



Moron.

On Friday, March 15, 2013 3:15:19 AM UTC-4, harry wrote:
I think he thinks (as I do) that convection refers to the buoyancy of

a fluid due to temperature differences.

Movement due to mechanical means is nothing to do with convection

Ergo "forced convection" does not exist. A misnomer. Assisted

convection exists.


Well, that would be wrong, but it is an understandable mistake.

You're focusing on the movement of the fluid.

Convection refers to the movement of the HEAT, not the fluid. Moving air, water, or any other fluid can carry more heat away. As far as the heat transfer is concerned, what causes the fluid to move is not relevant.

Heat transfer class, at 0800 in the morning after I'd worked the night shift (yuck) covered free and forced convection, transient and steady state. Four chances to get it wrong.

In one sense, convection IS also conduction. The transfer of the heat from the exchanger metal to the boundary layer of the fluid is conduction. This is normally ignored as it is not the limiting factor.

Of course, those who say a radiator doesn't radiate are correct.

On Mar 15, 8:44*am, TimR wrote:
On Friday, March 15, 2013 3:15:19 AM UTC-4, harry wrote:
I think he thinks (as I do) that convection refers to the buoyancy of

a fluid due to *temperature differences.

Movement due to mechanical means is nothing to do with convection

Ergo "forced convection" does not exist. A misnomer. *Assisted

convection exists.

Well, that would be wrong, but it is an understandable mistake.

You're focusing on the movement of the fluid.

Convection refers to the movement of the HEAT, not the fluid.

Wrong again. Fill a beaker sitting on a burner with water.
Use a pipette to put a few drops of blue dye at the very bottom.
Heat it and watch what happens. The blue dye water starts rising
via CONVECTION.



Moving air, water, or any other fluid can carry more heat away. *As
far as the heat transfer is concerned, what causes the fluid to move
is not relevant.

Heat transfer class, at 0800 in the morning after I'd worked the night shift (yuck) covered free and forced convection, transient and steady state. *Four chances to get it wrong.




In one sense, convection IS also conduction.

No it's not.



The transfer of the heat from the exchanger metal to the boundary layer of the fluid is conduction.

That's true.



*This is normally ignored as it is not the limiting factor.

Of course, those who say a radiator doesn't radiate are correct.

No, that's wrong too. It does radiate, it's just that if it's
a car radiator, home heating radiator, etc radiation is not the
main and most significant heat transfer mechanism.
Convection is.

On 3/15/2013 6:28 AM, wrote:
On Mar 15, 3:26 am, harry wrote:
On Mar 15, 2:13 am, "
wrote:





On Mar 14, 8:58 pm, jim beam wrote:

On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

are you for real? do you understand what you're reading? if you think
that contradicts a single thing i said, you have a serious comprehension
problem.

This is a dual-loop, closed system forced convection heat transfer
problem. No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. there is one closed loop on an automotive engine
coolant system. the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer

And citing a book cover on Amazon is not a scientific
reference.....

These are misnomers. The terms have come into use through attempts by
salespeople to differentiate between normal and fan ovens.

The correct term would be "forced air circulation ovens"
Commercial ovens are identified as such.http://www.powdercoating.romerpp.pl/...ven_with_force...

Without a fan, the correct term is "passive/natural air circulation".- Hide quoted text -

- Show quoted text -

http://en.wikipedia.org/wiki/Convection

Convection is the concerted, collective movement of ensembles of
molecules within fluids (e.g., liquids, gases) and rheids.

The term convection may have slightly different but related usages in
different scientific or engineering contexts or applications. The
broader sense is in fluid mechanics, where convection refers to the
motion of fluid regardless of cause.[2][3] However in thermodynamics
"convection" often refers specifically to heat transfer by convection.
[4]

Additionally, convection includes fluid movement both by bulk motion
(advection) and by the motion of individual particles (diffusion).
However in some cases, convection is taken to mean only advective
phenomena. For instance, in the transport equation, which describes a
number of different transport phenomena, terms are separated into
"convective" and "diffusive" effects, with "convective" meaning purely
advective in context.

Forced convection:
In forced convection, also called heat advection, fluid movement
results from external surface forces such as a fan or pump. Forced
convection is typically used to increase the rate of heat exchange.


Let me take a shot at in a different way. If you have a gas/liquid the
density of the g/l is determined by the size of the molecules. It seems
to me that adding energy to a molecule would would increase its size and
make it less dense than the surround molecules in your g/l. When there
is gravity, the lighter molecules would tend to migrate to the top of a
container and if collected and cooled to a temperature below
that of your existing g/l, those cooled molecules would have less energy
thus less density than the g/l and would tend to migrate toward the
bottom of your container. If you are a PhD and this is wrong thinking
don't howl at me because it's a SWAG made from observation and
could be totally wrong and too simplistic. ^_^

TDD

On Mar 15, 9:42*am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/15/2013 6:28 AM, wrote:





On Mar 15, 3:26 am, harry wrote:
On Mar 15, 2:13 am, "
wrote:

On Mar 14, 8:58 pm, jim beam wrote:

On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. *Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient..

are you for real? *do you understand what you're reading? *if you think
that contradicts a single thing i said, you have a serious comprehension
problem.

This is a dual-loop, closed system forced convection heat transfer
problem. *No mass transfer in the analytic meaning thereof is occurring.

comprehension problem. *there is one closed loop on an automotive engine
coolant system. *the other is wide freakin' open.

--
fact check required- Hide quoted text -

- Show quoted text -

Do you still deny that convection is the primary energy
transfer mechanism in a car radiator?

Do you still deny that convection can only exist if it's
natural convection? *If the answer to the above is yes, please
explain:

A - Convection ovens, which use a FAN . I have two
here so I know they exist.

B- Why numerous references, some of which have
been cited, talk about natural and forced convecton.
I have yet to see your reference that says convection
can only be natural, ie without a fan or pump.

C- Why engineers treat air to water heat exchangers using CONVECTION,
not mass transfer

And citing a book cover on Amazon is not a scientific
reference.....

These are misnomers. *The terms have come into use through attempts by
salespeople to differentiate between normal and fan ovens.

The correct term would be "forced air circulation ovens"
Commercial ovens are identified as such.http://www.powdercoating.romerpp.pl/...ven_with_force...

Without a fan, the correct term is "passive/natural air circulation".- Hide quoted text -

- Show quoted text -

http://en.wikipedia.org/wiki/Convection

Convection is the concerted, collective movement of ensembles of
molecules within fluids (e.g., liquids, gases) and rheids.

The term convection may have slightly different but related usages in
different scientific or engineering contexts or applications. The
broader sense is in fluid mechanics, where convection refers to the
motion of fluid regardless of cause.[2][3] However in thermodynamics
"convection" often refers specifically to heat transfer by convection.
[4]

Additionally, convection includes fluid movement both by bulk motion
(advection) and by the motion of individual particles (diffusion).
However in some cases, convection is taken to mean only advective
phenomena. For instance, in the transport equation, which describes a
number of different transport phenomena, terms are separated into
"convective" and "diffusive" effects, with "convective" meaning purely
advective in context.

Forced convection:
In forced convection, also called heat advection, fluid movement
results from external surface forces such as a fan or pump. Forced
convection is typically used to increase the rate of heat exchange.

Let me take a shot at in a different way. If you have a gas/liquid the
density of the g/l is determined by the size of the molecules. It seems
to me that adding energy to a molecule would would increase its size and
make it less dense than the surround molecules in your g/l. When there
is gravity, the lighter molecules would tend to migrate to the top of a
container and if collected and cooled to a temperature below
that of your existing g/l, those cooled molecules would have less energy
thus less density than the g/l and would tend to migrate toward the
bottom of your container. If you are a PhD and this is wrong thinking
don't howl at me because it's a SWAG made from observation and
could be totally wrong and too simplistic. ^_^

TDD- Hide quoted text -

- Show quoted text -

Yes, that's the essence of the idea of how fluids move
via natural convection. Except that it's not the size of the
molecules
that changes, it's the spacing between them. The more energy
they have, the more they are bouncing around, the more
space between them.

On Mar 15, 12:02*pm, "
wrote:
On Mar 15, 3:15*am, harry wrote:









On Mar 14, 8:29*pm, "
wrote:

On Mar 14, 3:18*pm, TimR wrote:

On Thursday, March 14, 2013 3:03:17 PM UTC-4, dpb wrote:

transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview

is available at

http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4

(Table 0-2.1) (and where they're covered in the book) is sufficient.

On Mar 15, 12:28*pm, "
wrote:
On Mar 15, 3:26*am, harry wrote:









On Mar 15, 2:13*am, "
wrote:

On Mar 14, 8:58*pm, jim beam wrote:

On 03/14/2013 12:03 PM, dpb wrote:

On 3/14/2013 10:02 AM, jim beam wrote:
On 03/14/2013 06:01 AM, wrote:
On Mar 13, 9:10 pm, jim beam wrote:
On 03/13/2013 10:45 AM, Vic Smith wrote:

On Tue, 12 Mar 2013 18:50:58 -0700, jim beam wrote:

this said however, this is not a radiative system, it's a mass
transfer system. ...

It's a simple pump and fan aided heat exchanger, not a "mass transfer
system."
...

because that's what it is, technically speaking. it's not
convection in
the traditional sense - it's forced transfer of a medium typically
characterized by its mass.

Mass is not being transfered across the system boundary.
Only heat. Yes, water flows in the engine cooling system and air
flows through the radiator, but no water is transfered into
the air and vice-versa.

that's deliberate obfuscation. air [mass] is transferred within the
greater body of itself. that's why "mass transfer" is used to describe
the process which for free bodies is otherwise known as "convection" or
forced systems, "advection".
...

Not, hardly. *Read the introductory chapter of the granddaddy of all
transport phenomena texts, Bird, Stewart, and Lightfoot. *It's preview
is available at
http://www.amazon.com/Transport-Phenomena-Revised-Byron-Bird/dp/04701...

The first few paragraphs of Chap 0 and the table of processes on p. 4
(Table 0-2.1) (and where they're covered in the book) is sufficient.

On 03/13/2013 09:47 PM, Pavel314 wrote:
snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. I can accept that
under-the-hood is a hostile environment, but the disparity in price
seems too large.

On Mar 16, 12:43*pm, cjt wrote:
On 03/13/2013 09:47 PM, Pavel314 wrote:
snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. *I can accept that
under-the-hood is a hostile environment, but the disparity in price
seems too large.

First, it doesn't always cost $1,200 to fix a car AC. If it's a bad
switch or a corroded wire to the compressor it could be $100.
If it's leaking shrader valves, it could be $250.
Second, you're comparing the cost to repair something with the
price of a new cheap, mass market appliance built on a high volume
assembly line. If that $100 air conditioner had a compressor that
failed, shred metal bits, contaminating the whole thing, what do
you think it would cost to diagnose it, take it all apart, flush it,
purge it,
braze in a new compressor, recharge, test it, etc? It would be many
times the $100 it costs for it to begin with, so it just isn't done.
You can't
throw away the auto AC as a unit and get a new one, so you have to
deal with what's there. The factor in that half the system, ie the
evaporator, TXV valve, blower, etc is buried under the dash where
a lot of stuff potentially has to be removed if that part needs
repair.

Also, how much it cost to fix a car AC is highly dependent on
the parts used. Go to the dealer and pay for a new OEM
compressor, receiver/dryer, etc and it's a lot of money. Kind of
like buying a shelf or plastic part for a fridge. Use an
independent shopt that will offer a rebuilt compressor, aftermarket
parts, etc and the price can be hundreds less.

On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:
snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. I can accept that
under-the-hood is a hostile environment, but the disparity in price
seems too large.

It's mostly the labor costs. But parts can be costly too, compared to
a window unit. Window unit compressors are hermetically sealed with
the driving motor, cars compressors are belt driven. Pretty sure car
condensers are bigger and more costly. Don't know why.
Ever replace a car A/C compressor, condenser or evaporator?
Lots of labor digging them out and putting them in.
Pretty sure car A/C shops charge you for refrigerant, even if they
pulled yours for recycling.
But it mostly car mechanic manual labor vs automated factory labor.

On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:



On 03/13/2013 09:47 PM, Pavel314 wrote:

snip



I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.



I've recently been wondering the same thing. I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:

On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:



On 03/13/2013 09:47 PM, Pavel314 wrote:

snip



I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.



I've recently been wondering the same thing. I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. And the home unit also has a
blower fan that, in the car, is again, "free". Likewise, the duct
work in the car is "free". The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.

On Mar 16, 9:49*pm, Ashton Crusher wrote:
On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:





On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:

snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. *I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. *And the home unit also has a
blower fan that, in the car, is again, "free". *Likewise, the duct
work in the car is "free". *The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.- Hide quoted text -

- Show quoted text -

I see folks throwing out all kinds of numbers for how many btus
or tons a typical auto AC is, but I haven't seen a reference
that I'd call credible or rely on. And I'd bet the typical auto AC
isn't 3 tons.
It's probably more like half that. A car is a tougher environment
to cool than a house, but it's also a small volume. One thing that
suggest it's not 3 tons is the size of the equipment it takes to
get 3 tons of cooling. Anyone think for example the evaporator
in a car is anywhere near the size of one in a home 3 ton HVAC?

" wrote:
On Mar 16, 9:49 pm, Ashton Crusher wrote:
On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:





On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:

snip

I've always wondered why it costs $1,200 to fix a car AC but you can
buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. And the home unit also has a
blower fan that, in the car, is again, "free". Likewise, the duct
work in the car is "free". The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.- Hide quoted text -

- Show quoted text -

I see folks throwing out all kinds of numbers for how many btus
or tons a typical auto AC is, but I haven't seen a reference
that I'd call credible or rely on. And I'd bet the typical auto AC
isn't 3 tons.
It's probably more like half that. A car is a tougher environment
to cool than a house, but it's also a small volume. One thing that
suggest it's not 3 tons is the size of the equipment it takes to
get 3 tons of cooling. Anyone think for example the evaporator
in a car is anywhere near the size of one in a home 3 ton HVAC?

It's not designed for efficiency. My 2.5 ton home compressor is small
considering there is a motor in there. I recall in my air conditioning book
talk about vehicles. Big difference in full size vans vs small car.

Greg

On Sat, 16 Mar 2013 19:10:26 -0700 (PDT), "
wrote:

On Mar 16, 9:49*pm, Ashton Crusher wrote:
On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:





On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:

snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. *I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. *And the home unit also has a
blower fan that, in the car, is again, "free". *Likewise, the duct
work in the car is "free". *The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.- Hide quoted text -

- Show quoted text -

I see folks throwing out all kinds of numbers for how many btus
or tons a typical auto AC is, but I haven't seen a reference
that I'd call credible or rely on. And I'd bet the typical auto AC
isn't 3 tons.
It's probably more like half that. A car is a tougher environment
to cool than a house, but it's also a small volume. One thing that
suggest it's not 3 tons is the size of the equipment it takes to
get 3 tons of cooling. Anyone think for example the evaporator
in a car is anywhere near the size of one in a home 3 ton HVAC?

I posted on this a couple days ago without any citations. But here's
a paper that I was able to find and it's pretty much what I recalled
from several years ago when I went looking for the same info.
http://docs.lib.purdue.edu/cgi/viewc...9&context=icec

basically, the typical Auto AC compressor will run perhaps 6000-8000
BTU at idle speed. When you are cruising at high speed on a freeway
you can figure on between 20,000 to 30,000 BTU's depending on the type
of compressor. As I mentioned before, most add on system evaporators
are only 15,000 to 20,000 BTU capable and factory installed ones are
around 22-24,000. But that's only when the compressor can supply them
with enough freon. So at idle the system will only be as good as the
compressor is at idle speed.

there's an interesting article from 1969 here...
http://books.google.com/books?id=Eyo...epage&q&f=true

On Mar 17, 2:44*am, Ashton Crusher wrote:
On Sat, 16 Mar 2013 19:10:26 -0700 (PDT), "





wrote:
On Mar 16, 9:49*pm, Ashton Crusher wrote:
On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:

On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:

snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. *I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. *And the home unit also has a
blower fan that, in the car, is again, "free". *Likewise, the duct
work in the car is "free". *The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.- Hide quoted text -

- Show quoted text -

I see folks throwing out all kinds of numbers for how many btus
or tons a typical auto AC is, but I haven't seen a reference
that I'd call credible or rely on. * And I'd bet the typical auto AC
isn't 3 tons.
It's probably more like half that. *A car is a tougher environment
to cool than a house, but it's also a small volume. *One thing that
suggest it's not 3 tons is the size of the equipment it takes to
get 3 tons of cooling. *Anyone think for example the evaporator
in a car is anywhere near the size of one in a home 3 ton HVAC?

I posted on this a couple days ago without any citations. *But here's
a paper that I was able to find and it's pretty much what I recalled
from several years ago when I went looking for the same info.http://docs.lib.purdue.edu/cgi/viewc...9&context=icec

basically, the typical Auto AC compressor will run perhaps 6000-8000
BTU at idle speed. *When you are cruising at high speed on a freeway
you can figure on between 20,000 to 30,000 BTU's depending on the type
of compressor.

If that's true then there would be a 3 to 4X difference in cooling
capacity
between when the car is idling and when the car is at highway speed.
There is some difference, but it sure isn't 3 to 4x difference, not
IMO.
And if you put a thermometer in front of the cold air outlets, there
would have to be either a huge variation in the volume or the temp of
the air exiting based on engine RPM. Again, there is some slight
variation in temperature, but it's not 3 - 4x.







*As I mentioned before, most add on system evaporators
are only 15,000 to 20,000 BTU capable and factory installed ones are
around 22-24,000. *But that's only when the compressor can supply them
with enough freon. *So at idle the system will only be as good as the
compressor is at idle speed.

there's an interesting article from 1969 here...http://books.google.com/books?id=Eyo...opular+sci...- Hide quoted text -

- Show quoted text -

On Sun, 17 Mar 2013 04:47:00 -0700 (PDT), "
wrote:

On Mar 17, 2:44*am, Ashton Crusher wrote:
On Sat, 16 Mar 2013 19:10:26 -0700 (PDT), "





wrote:
On Mar 16, 9:49*pm, Ashton Crusher wrote:
On Sat, 16 Mar 2013 18:26:54 -0700 (PDT), TimR
wrote:

On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:
On Sat, 16 Mar 2013 11:43:54 -0500, cjt wrote:

On 03/13/2013 09:47 PM, Pavel314 wrote:

snip

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.

I've recently been wondering the same thing. *I can accept that

under-the-hood is a hostile environment, but the disparity in price

seems too large.

A car AC is a three ton unit.

A three ton unit for your house is likely to cost you about $4000 installed.

In fairness to the price disparity, the home unit also includes an
EXTRA motor to drive teh compressor (in the car the motor comes with
the car so it's "free") and the home unit also includes a condenser
fan this is similarly "free" in the car. *And the home unit also has a
blower fan that, in the car, is again, "free". *Likewise, the duct
work in the car is "free". *The extra cost to add AC at the factory to
a modern car is really pretty low, I'd bet the parts don't amount to
more then $500 and the extra labor perhaps $100.- Hide quoted text -

- Show quoted text -

I see folks throwing out all kinds of numbers for how many btus
or tons a typical auto AC is, but I haven't seen a reference
that I'd call credible or rely on. * And I'd bet the typical auto AC
isn't 3 tons.
It's probably more like half that. *A car is a tougher environment
to cool than a house, but it's also a small volume. *One thing that
suggest it's not 3 tons is the size of the equipment it takes to
get 3 tons of cooling. *Anyone think for example the evaporator
in a car is anywhere near the size of one in a home 3 ton HVAC?

I posted on this a couple days ago without any citations. *But here's
a paper that I was able to find and it's pretty much what I recalled
from several years ago when I went looking for the same info.http://docs.lib.purdue.edu/cgi/viewc...9&context=icec

basically, the typical Auto AC compressor will run perhaps 6000-8000
BTU at idle speed. *When you are cruising at high speed on a freeway
you can figure on between 20,000 to 30,000 BTU's depending on the type
of compressor.

If that's true then there would be a 3 to 4X difference in cooling
capacity
between when the car is idling and when the car is at highway speed.
There is some difference, but it sure isn't 3 to 4x difference, not
IMO.
And if you put a thermometer in front of the cold air outlets, there
would have to be either a huge variation in the volume or the temp of
the air exiting based on engine RPM. Again, there is some slight
variation in temperature, but it's not 3 - 4x.





There are a couple issues on this. A LOT depends on the temperature
and humidity of the air you are cooling down. A lot also depends on
whether the vehicle body has been sitting out in the sun baking or
not. My experience with my 92 explorer says there is definitely a
difference of 3x. But that's when it's 105 in the shade and it NEEDS
the full capacity. Then you can tell a huge difference between the
cooling at idle and at speed, it's like night and day. This is pretty
much true on almost every car out here in AZ. Now if you are talking
about the difference when it's 85 degrees then sure, it seems to be
working nearly as good at idle as at speed. But that's because you
don't need 20,000 BTU's to cool things off, you only need 10,000. At
speed the compressor is very possibly off more then it's on.

On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.

On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD

On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use it.


--
fact check required

On 3/17/2013 10:03 PM, jim beam wrote:
On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted
black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than
the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use it.



I own a small condensing unit from a vending machine that has steel fins
that I've used for years as a recovery system for refrigerant.
I purchased a new one a while back for an old Coke vending machine
and that new unit has steel fins. Many soft drink vending machines
have steel finned condensing units underneath them because they are
more durable and less likely to be damaged by the myriad environments
those types of machines wind up in. ^_^

TDD

On 03/17/2013 09:31 PM, The Daring Dufas wrote:
On 3/17/2013 10:03 PM, jim beam wrote:
On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since
this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare
aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted
black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than
the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use
it.



I own a small condensing unit from a vending machine that has steel fins
that I've used for years as a recovery system for refrigerant.
I purchased a new one a while back for an old Coke vending machine
and that new unit has steel fins. Many soft drink vending machines
have steel finned condensing units underneath them because they are
more durable and less likely to be damaged by the myriad environments
those types of machines wind up in. ^_^

TDD

i guess that would be a "specialty application". but how did you
determine their material? when you say "fins", do you mean the
grate-like arrangement at the back of a common refrigerator?


--
fact check required

On 3/18/2013 8:58 AM, jim beam wrote:
On 03/17/2013 09:31 PM, The Daring Dufas wrote:
On 3/17/2013 10:03 PM, jim beam wrote:
On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has
paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too,
some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since
this
is not floating out in space and merely "radiating" heat
passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't
have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare
aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted
black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than
the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and
the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are
galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use
it.



I own a small condensing unit from a vending machine that has steel fins
that I've used for years as a recovery system for refrigerant.
I purchased a new one a while back for an old Coke vending machine
and that new unit has steel fins. Many soft drink vending machines
have steel finned condensing units underneath them because they are
more durable and less likely to be damaged by the myriad environments
those types of machines wind up in. ^_^

TDD

i guess that would be a "specialty application". but how did you
determine their material? when you say "fins", do you mean the
grate-like arrangement at the back of a common refrigerator?



The condenser coil on the vending looks like a small radiator with a
fan. The condensing unit is usually underneath mounted on a steel base
with the compressor. The units can be slid out for servicing and or
replacement. Take a look under a Coke vending machine or glass door Coke
box and you may see the condensing unit. If you see a vender loading a
soft drink vending machine, the door will be open and the
condensing unit should be visible at the bottom. Ask the guy to point
out the condensing unit for you. ^_^

TDD

On Sun, 17 Mar 2013 22:31:45 -0600, The Daring Dufas
wrote:

On 3/17/2013 10:03 PM, jim beam wrote:
On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted
black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than
the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use it.

Gas tight joints are not required between fins and tubes. The tubes
are generally copper or tin-plated copper, with the find press fit to
the tubing.- not even soldered in many cases.



I own a small condensing unit from a vending machine that has steel fins
that I've used for years as a recovery system for refrigerant.
I purchased a new one a while back for an old Coke vending machine
and that new unit has steel fins. Many soft drink vending machines
have steel finned condensing units underneath them because they are
more durable and less likely to be damaged by the myriad environments
those types of machines wind up in. ^_^

TDD

On 03/18/2013 11:19 AM, wrote:
On Sun, 17 Mar 2013 22:31:45 -0600, The Daring Dufas
wrote:

On 3/17/2013 10:03 PM, jim beam wrote:
On 03/17/2013 07:58 PM, The Daring Dufas wrote:
On 3/17/2013 8:32 PM, wrote:
On Tue, 12 Mar 2013 19:11:44 -0600, The Daring Dufas
wrote:

On 3/12/2013 5:38 PM, Ashton Crusher wrote:
AC condensers (the part that's in front of the radiator) can be
purchased in bare aluminum or painted black. The purpose is to
transfer heat to the air. It seems to me that for maximum heat
transfer the best choice would be the bare aluminum. If it has paint
on it it seems like the paint would act as a thin insulation and
reduce it's effectiveness at transferring heat. Since so many of
these are painted there must be something wrong with my thinking OR
the insulating effect must be very very minimal.

The same question could be asked about the regular radiator too, some
are bare aluminum and some are painted black.

I have heard in the past some talk about "black bodies" but since this
is not floating out in space and merely "radiating" heat passively in
a vacuum but is also (mostly) losing heat thru the movement of air
over it's surface it seems like any surface coating that doesn't have
a very similar coefficient of heat conductivity would be detrimental
to that heat transfer.

Anybody know anything specific about the effect or non-effect of
the
paint? Is it a 'special' paint? Does it just look like bare aluminum
but it's painted with some clear paint so it's painted anyway?


According to what I learned in physics class, a dark object radiates
heat away better than a silver colored object. There is a classic lab
experiment where two identically sized containers with one painted
black
and the other white or silver are filled with boiling water and
the temperature drop is timed. The black container cools faster than
the
light colored container. ^_^

TDD
There comes a point where the better emissivity of the black and the
poorer conduction of the paint cancel out. I expect that where air
movement is adequate, the non painted unit would be more effective.
Where air movement is limited, the darker colour MAY help.

I believe the black paint is for protection.


I wouldn't discount that at all since I've seen a lot of corrosion
damage done to condensers that were made from aluminum. Interestingly
enough, the small condensing units that are under those soft drink
vending machines are often painted black even if the fins are galvanized
steel. ^_^

TDD


galvanized steel cooling fins??? are you sure or are you guessing?
steel's a poor conductor and it's much harder to make gas-tight joins as
easily as brass/copper/aluminum. i can't imagine why anyone would use it.

Gas tight joints are not required between fins and tubes.

true.


The tubes
are generally copper or tin-plated copper,

right


with the find

fins?


press fit to
the tubing.- not even soldered in many cases.

that's where i'm having the problem. steel is a poor conductor - it
makes more sense to have the tubes steel and the fine fins made of
copper or aluminum than the other way around.





I own a small condensing unit from a vending machine that has steel fins
that I've used for years as a recovery system for refrigerant.
I purchased a new one a while back for an old Coke vending machine
and that new unit has steel fins. Many soft drink vending machines
have steel finned condensing units underneath them because they are
more durable and less likely to be damaged by the myriad environments
those types of machines wind up in. ^_^

TDD



--
fact check required

The Daring Dufas posted for all of us...

And I know how to SNIP



But what if you use dark matter? o_O

TDD

I think this topic has gone into a black hole...

--
Tekkie