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#41
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PrecisionMachinisT writes:
Ignore the entire concept of latent heat if its convenient to you then.... Haven't ignored anything. (Regardless, I suspect you mean sensible heat.) Point being is the heat was already added or subtrcated from the sytstem before or after the phase change took place. The heat initially present in the water itself, or something intimately in contact with it, will vaporize very little water, and in practice the ambient heat will not flow in quickly (the vacuum being an insulator). And this only applies to free water. Ordinary vacuum dessication does not work for water bound in something like a silica gel dessicant, or entrained in the oil, or hydrating contaminants. A lot of people have been taught the pseudo-scientific myth that "water boils in a vacuum" in some magic sense that it doesn't in the atmosphere. The truth is that water vaporizes in a vacuum or in the atmosphere the same way: *only* because you add heat. In the same sense, water doesn't boil at 212 deg F, it boils because you add more heat after it is at 212 deg F. Another related myth is that if *you* were put into a vacuum, your body would explode or your "blood would boil". Pure bunk. Another popular (and yes, even in the HVAC trade) myth is "saturation" of air with humidity, that the moisture is carried or dissolved in the air, and that it "saturates" like a solution of salt in water. |
#42
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"Richard J Kinch" wrote in message . .. PrecisionMachinisT writes: Ignore the entire concept of latent heat if its convenient to you then.... Haven't ignored anything. (Regardless, I suspect you mean sensible heat.) Point being is the heat was already added or subtrcated from the sytstem before or after the phase change took place. The heat initially present in the water itself, or something intimately in contact with it, will vaporize very little water, and in practice the ambient heat will not flow in quickly (the vacuum being an insulator). And this only applies to free water. Ordinary vacuum dessication does not work for water bound in something like a silica gel dessicant, or entrained in the oil, or hydrating contaminants. A lot of people have been taught the pseudo-scientific myth that "water boils in a vacuum" in some magic sense that it doesn't in the atmosphere. The truth is that water vaporizes in a vacuum or in the atmosphere the same way: *only* because you add heat. In the same sense, water doesn't boil at 212 deg F, it boils because you add more heat after it is at 212 deg F. Another related myth is that if *you* were put into a vacuum, your body would explode or your "blood would boil". Pure bunk. Another popular (and yes, even in the HVAC trade) myth is "saturation" of air with humidity, that the moisture is carried or dissolved in the air, and that it "saturates" like a solution of salt in water. Obviously then , some part of "Im done, your a ****wit and my opinion still stands" has apparently still escaped your attention. Bye bye idiot troll......... -- SVL |
#44
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"PrecisionMachinisT" wrote in message ... "Jake" wrote in message news:CDwNe.48754$084.28178@attbi_s22... PrecisionMachinisT wrote: "DiDo" wrote in message news:BMrNe.128$IG2.84@trndny01... It is possible! how? well while water boils at low pressures but it ALSO FREEZES and once it get frozen it does not boils any more. Frozen water changes directly from the solid into the vapor phase under low pressure conditions, due to a phenomena known as 'sublimation'.....IOW, no "boiling" is needed. http://www.newton.dep.anl.gov/askasc.../chem03598.htm -- SVL Sam, I think Dido is talking about when you have a evap coil exposed to other cold temps within a running freezer.. a common occurence in the commercial world. This is what the man meant, I believe. Jake, Doesn't matter--next time it snows, watch your outside temp real close, and take note of any period over several days, or perhaps up to a week where the temp stays constantly below freezing....notice that the snow 'just kinda dissapears'....given enough time, it will eventually dissapear altogether, without ever reaching a temp above freezing, and without rain falling on it, etc.....now note that this process speeds up considerably at pressures below atmospheric. -- SVL This is Turtle. i see the example all the time with ice cub trays all the time. Fill a ice cube tray with water and let them freeze real good and then keep them in the freezer for 1 years. You will come back and find all the ice gone out of the ice cube tray. I call it freezer evaperation or called freezer burning the ice. This dehydration takes all the moisture out of food product and is called freezer burn. TURTLE |
#45
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wrote in message ... On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch wrote: I am not sure where you live but it is about 600 degrees F warmer than "space " on earth, even in the winter. There is plenty of available heat to sublimate water. Repeat after me: temperature is not heat. Repeat after me, a gas at a given temperature (ambient air) is heat. See cat...notice cat has a tail....pull on cat's tail........ Repeat until bored. -- SVL |
#46
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On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT"
wrote: wrote in message .. . On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch wrote: I am not sure where you live but it is about 600 degrees F warmer than "space " on earth, even in the winter. There is plenty of available heat to sublimate water. Repeat after me: temperature is not heat. Repeat after me, a gas at a given temperature (ambient air) is heat. See cat...notice cat has a tail....pull on cat's tail........ Repeat until bored. See cow. See cow udders. Pull cow udders. Get milk. If cow only have one udder, get cream. Click here every day to feed an animal that needs you today !!! http://www.theanimalrescuesite.com/ Paul ( pjm @ pobox . com ) - remove spaces to email me 'Some days, it's just not worth chewing through the restraints.' 'With sufficient thrust, pigs fly just fine.' HVAC/R program for Palm PDA's Free demo now available online http://pmilligan.net/palm/ |
#47
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wrote in message news If cow only have one udder, get cream. Bull. -- SVL |
#48
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1 On Sun, 21 Aug 2005 02:15:25 -0500, Richard J Kinch wrote: The truth is that water vaporizes in a vacuum or in the atmosphere the same way: *only* because you add heat. In the same sense, water doesn't boil at 212 deg F, it boils because you add more heat after it is at 212 deg F. Then you're all wet. -----BEGIN PGP SIGNATURE----- Version: PGP 7.1 iQA/AwUBQwjejAIk7T39FC4ZEQIO9QCguHSRV5tUO06ZeIVnzzonnE DuqsEAnjJ1 Imv1in/cDv3fIdImpY7Mj8dN =ZMXn -----END PGP SIGNATURE----- -- -john wide-open at throttle dot info |
#49
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wrote in message news On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT" wrote: wrote in message .. . On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch wrote: I am not sure where you live but it is about 600 degrees F warmer than "space " on earth, even in the winter. There is plenty of available heat to sublimate water. Repeat after me: temperature is not heat. Repeat after me, a gas at a given temperature (ambient air) is heat. See cat...notice cat has a tail....pull on cat's tail........ Repeat until bored. See cow. See cow udders. Pull cow udders. Get milk. If cow only have one udder, get cream. "I think I'll go wash up..." Click here every day to feed an animal that needs you today !!! http://www.theanimalrescuesite.com/ Paul ( pjm @ pobox . com ) - remove spaces to email me 'Some days, it's just not worth chewing through the restraints.' 'With sufficient thrust, pigs fly just fine.' HVAC/R program for Palm PDA's Free demo now available online http://pmilligan.net/palm/ |
#50
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"TURTLE" wrote in message .. . "PrecisionMachinisT" wrote in message ... "Jake" wrote in message news:CDwNe.48754$084.28178@attbi_s22... PrecisionMachinisT wrote: "DiDo" wrote in message news:BMrNe.128$IG2.84@trndny01... It is possible! how? well while water boils at low pressures but it ALSO FREEZES and once it get frozen it does not boils any more. Frozen water changes directly from the solid into the vapor phase under low pressure conditions, due to a phenomena known as 'sublimation'.....IOW, no "boiling" is needed. http://www.newton.dep.anl.gov/askasc.../chem03598.htm -- SVL Sam, I think Dido is talking about when you have a evap coil exposed to other cold temps within a running freezer.. a common occurence in the commercial world. This is what the man meant, I believe. Jake, Doesn't matter--next time it snows, watch your outside temp real close, and take note of any period over several days, or perhaps up to a week where the temp stays constantly below freezing....notice that the snow 'just kinda dissapears'....given enough time, it will eventually dissapear altogether, without ever reaching a temp above freezing, and without rain falling on it, etc.....now note that this process speeds up considerably at pressures below atmospheric. -- SVL This is Turtle. i see the example all the time with ice cub trays all the time. Fill a ice cube tray with water and let them freeze real good and then keep them in the freezer for 1 years. You will come back and find all the ice gone out of the ice cube tray. I call it freezer evaperation or called freezer burning the ice. This dehydration takes all the moisture out of food product and is called freezer burn. Also it can be freeze dried... Joseph TURTLE |
#51
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On Sun, 21 Aug 2005 14:19:42 -0700, "Joseph"
wrote: wrote in message news On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT" wrote: wrote in message .. . On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch wrote: I am not sure where you live but it is about 600 degrees F warmer than "space " on earth, even in the winter. There is plenty of available heat to sublimate water. Repeat after me: temperature is not heat. Repeat after me, a gas at a given temperature (ambient air) is heat. See cat...notice cat has a tail....pull on cat's tail........ Repeat until bored. See cow. See cow udders. Pull cow udders. Get milk. If cow only have one udder, get cream. "I think I'll go wash up..." I guess that can wait for an udder day. Shoulda wore gloves. Click here every day to feed an animal that needs you today !!! http://www.theanimalrescuesite.com/ Paul ( pjm @ pobox . com ) - remove spaces to email me 'Some days, it's just not worth chewing through the restraints.' 'With sufficient thrust, pigs fly just fine.' HVAC/R program for Palm PDA's Free demo now available online http://pmilligan.net/palm/ |
#52
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1 See cow. See cow udders. Pull cow udders. Get milk. If cow only have one udder, get cream. "I think I'll go wash up..." I guess that can wait for an udder day. Shoulda wore gloves. Now you are in for a real teat. -----BEGIN PGP SIGNATURE----- Version: PGP 7.1 iQA/AwUBQwj3mAIk7T39FC4ZEQIg+gCeOJleXpVn84fHEmoKKKx74A qePXoAoOL5 YiIqi2zXsbkKjEjvLeO8Cl7g =zaPo -----END PGP SIGNATURE----- -- -john wide-open at throttle dot info |
#53
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"~^Johnny^~" wrote in message ... -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 See cow. See cow udders. Pull cow udders. Get milk. If cow only have one udder, get cream. "I think I'll go wash up..." I guess that can wait for an udder day. Shoulda wore gloves. Now you are in for a real teat. Nice tits at this site: http://www.nice-tits.org/ -- SVL |
#54
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wrote:
Repeat after me, a gas at a given temperature (ambient air) is heat. Air = heat. Oxygen = heat. Nitrogen = heat... Learn something new every day around here. Nick |
#55
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On Mon, 22 Aug 2005 16:01:53 -0400, wrote:
On 22 Aug 2005 08:46:05 -0400, wrote: Air = heat. Oxygen = heat. Nitrogen = heat... Learn something new every day around here. At least they're not = 'coolth' :-) Excuse me, I have to go get a breath of fresh heat now .... If that air, nitrogen and oxygen is anything but 0 degrees Kelvin it has heat. That is why we have "AIR" conditionoing in the first place. For the purposes of this silly argument, water in the system will actually be touching the metal or in the oil, both excellent conductors of ambient heat. If the water is trapped in the dessicants of the dryer, who cares?, That should be in the trash by now and a new dryer in the system. If you are not replacing your dryers you are certainly a hack. Click here every day to feed an animal that needs you today !!! http://www.theanimalrescuesite.com/ Paul ( pjm @ pobox . com ) - remove spaces to email me 'Some days, it's just not worth chewing through the restraints.' 'With sufficient thrust, pigs fly just fine.' HVAC/R program for Palm PDA's Free demo now available online http://pmilligan.net/palm/ |
#56
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wrote:
Repeat after me, a gas at a given temperature (ambient air) is heat. Air = heat. Oxygen = heat. Nitrogen = heat... Learn something new every day around here. If that air, nitrogen and oxygen is anything but 0 degrees Kelvin it has heat. That is why we have "AIR" conditionoing in the first place. Oh, you meant it CONTAINS heat... Nick |
#57
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Thank You
Mr. Richard J Kinc For explaining to some of these VUSIS and I say to some because when arrogance superseded the ignorance there are some people that will not except truth or the facts. It does not metter how had you may try Sorry I am not that patient Good Luck from Dido "Travis Jordan" wrote in message .. . papaya wrote: if you only pull 500 microns of vacuum for your customer, you are not getting all of the water out and are going to be making hydrochloric acid for them, so they can buy a new unit from you, Mr. Con Artist. Most manufacturers installation instructions say evacuate to 350 microns, then insure that the vacuum holds for at least a minute after closing off the vacuum pump. Their instructions (and their warranty) are good enough for me. |
#58
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Richard J Kinchwrote:
PrecisionMachinisT writes: A lot of people have been taught the pseudo-scientific myth that "water boils in a vacuum" in some magic sense that it doesn't in the atmosphere. The truth is that water vaporizes in a vacuum or in the atmosphere the same way: *only* because you add heat. In the same sense, water doesn't boil at 212 deg F, it boils because you add more heat after it is at 212 deg F. Nothing pseudo-scientific about it. I have boiled water with ice. Here is how: take a glass flask with an indentation in the bottom, add a little water. You may want to add boiling chips to make the effect more gradual. Attach a cork with a rubber hose to the top to vent. Put it on a bunsen burner and boil, just to get the steam to drive all the air out. Remove heat and clamp the rubber hose. Let it cool. Invert, add ice to the depression, and watch the cool water boil, not with the addition of heat, but with the addition of ice. I have boiled water down to 60 degrees F with this technique. What is happening is that cooling the glass on top causes most of the remaining steam to condense, establishing a decent vacuum. Lowering the pressure over the water lowers the boiling point, so the water now boils. You have said repeatedly that one must add heat for sublimation to occur. That is not true. Sublimation and evaporation both proceed by the same mechanism. Pour water on the floor, and it will evaporate without addition of heat, unless the relative humidity is 100%. Sublimation happens, too, just starting from the solid instead of liquid phase of water. What is happening microscopically is related to the the kinetic energy of the molecules. Temperature is not heat, as you pointed out. But they are related. Temperature is defined to be proportional to the random translational kinetic energy per molecule of the material. Heat transfer is equal to the change of the random translation kinetic energy plus rotational and vibrational kinetic energy plus changes in potential energy. So any substance above absolute zero contains heat, and its molecules have a distribution of kinetic energies. When a molecule on the surface achieves an atypically large kinetic energy from collisions with its neighbors, it reaches escape velocity. If the substance is a liquid, we call it evaporation. If it is a solid, we call it sublimation. There is always a reverse process of capture from the atmosphere. But the process is usually slower. The temperature of the surface determines the escape rate. The partial pressure of water in the surrounding atmosphere determines the capture rate. In a perfect vacuum, the capture rate is zero, and the net effect is evaporation or sublimation. |
#59
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rick1matthews wrote:
Pour water on the floor, and it will evaporate without addition of heat... It's more accurate to say that the heat required to evaporate the water (about 1000 Btu/lb) comes from the surroundings, ie this evaporation cools the floor, the air, and so on. Nick |
#60
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"rick1matthews" wrote in message ... Richard J Kinchwrote: PrecisionMachinisT writes: A lot of people have been taught the pseudo-scientific myth that "water boils in a vacuum" in some magic sense that it doesn't in the atmosphere. The truth is that water vaporizes in a vacuum or in the atmosphere the same way: *only* because you add heat. In the same sense, water doesn't boil at 212 deg F, it boils because you add more heat after it is at 212 deg F. Nothing pseudo-scientific about it. I have boiled water with ice. Here is how: take a glass flask with an indentation in the bottom, add a little water. You may want to add boiling chips to make the effect more gradual. Attach a cork with a rubber hose to the top to vent. Put it on a bunsen burner and boil, just to get the steam to drive all the air out. Remove heat and clamp the rubber hose. Let it cool. Invert, add ice to the depression, and watch the cool water boil, not with the addition of heat, but with the addition of ice. I have boiled water down to 60 degrees F with this technique. What is happening is that cooling the glass on top causes most of the remaining steam to condense, establishing a decent vacuum. Lowering the pressure over the water lowers the boiling point, so the water now boils. Julius Sumner Miller would be proud : ) You have said repeatedly that one must add heat for sublimation to occur. That is not true. Sublimation and evaporation both proceed by the same mechanism. Pour water on the floor, and it will evaporate without addition of heat, unless the relative humidity is 100%. Sublimation happens, too, just starting from the solid instead of liquid phase of water. What is happening microscopically is related to the the kinetic energy of the molecules. Temperature is not heat, as you pointed out. But they are related. Temperature is defined to be proportional to the random translational kinetic energy per molecule of the material. Heat transfer is equal to the change of the random translation kinetic energy plus rotational and vibrational kinetic energy plus changes in potential energy. So any substance above absolute zero contains heat, and its molecules have a distribution of kinetic energies. When a molecule on the surface achieves an atypically large kinetic energy from collisions with its neighbors, it reaches escape velocity. If the substance is a liquid, we call it evaporation. If it is a solid, we call it sublimation. There is always a reverse process of capture from the atmosphere. But the process is usually slower. The temperature of the surface determines the escape rate. The partial pressure of water in the surrounding atmosphere determines the capture rate. In a perfect vacuum, the capture rate is zero, and the net effect is evaporation or sublimation. |
#61
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wrote on 8/25/2005 8:37 AM:
rick1matthews wrote: Pour water on the floor, and it will evaporate without addition of heat... It's more accurate to say that the heat required to evaporate the water (about 1000 Btu/lb) comes from the surroundings, ie this evaporation cools the floor, the air, and so on. Some of the heat comes from the surroundings in this example. Some comes from within the water itself. Key to this discussion is that no external source of heat is needed to evaporate water. Were a 70 degree F drop of water suspended (perhaps in a weightless environment) in a hard vacuum, which in turn is completely surrounded by shiny surfaces cooled to 100 milliKelvin, the drop would still evaporate. So where did the heat come to evaporate it? Statements were made earlier that water only boils when heat is added and that water only evaporates when heat is added. Neither statement is true. Water evaporates whenever the partial pressure of water in the surrounding atmosphere is so small that the capture of the water molecules from the air is less than the escape of water molecules from the surface of the water. The rate of escape is determined by the water temperature. The rate of capture is determined by the partial pressure of water. The water temperature at which the two are in equilibrium is called the dew point. If the water is cooler than the dew point, you get net condensation. If the water is warmer than this dew point, you get net evaporation. When air pressure is very low, the partial pressure of water can only be lower. Therefore the dew point must be quite low, so that 72 degree F water (or 35 degree F water, for that matter), is warmer that its dew point. Water molecules are always escaping, and there are few water molecules in the environment to balance the process. Hence, the water evaporates. The cooler it is, the slower it evaporates, but it does still evaporate. In a perfect vacuum, even a 1 Kelvin ice cube would eventually sublime way, though not in billion years. -- Rick Matthews |
#62
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Rick Matthews writes:
Statements were made earlier that water only boils when heat is added and that water only evaporates when heat is added. Neither statement is true. It is true in the sense that the heat content of the water itself can only evaporate a small portion of it. If you squirted warm water out of the Space Shuttle in orbit, some would flash to vapor but most of it would just wind up floating around frozen. The point is simply that vacuum itself does not evaporate water, it is heat, contrary to the popular notion. |
#63
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True, most of the water will freeze before evaporating. But
you also said: It *will not* sublime at all if there is no heat added, even in a perfect vacuum. which is not true. The ice will sublime in a perfect vacuum if it is above absolute zero, as long as there is any ice left. Change "at all" to "quickly" and I will agree with you. Rick |
#64
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Rick writes:
The ice will sublime in a perfect vacuum if it is above absolute zero, as long as there is any ice left. If it is above absolute zero, then it must have had some heat added. |
#65
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The thing you are missing is gravity. Ice is not going to "float
around" in that pipe. It will lay on the pipe (compressor, valves etc) and heat from the ambient air on the other side of the pipe will evaporate the water. Some of it will gain heat by this process, although much more slowly than one might expect or hope. Remember it takes a huge amount of heat transfer to vaporize water, and the vacuum is an excellent insulator. Parts of a glob of water in contact with the system will freeze and then tend to sublimate a thin layer of vapor to separate themselves from the heat source, instead of staying in intimate contact. And remember this doesn't work at all for water entrained in or bound to something else. Another practical problem in a AC system is that the water may trapped on the other side of 50 feet of of 3/8 inch tubing from the vacuum source, such as if the service connection is at the compressor on a split system with the water stuck up in the evaporator. The back pressure of a long thin line will spoil the vacuum on the other end. My point is simply to correct the common misconception among AC techs that if they pull a good vacuum on a system that it is guaranteed to be dry, because they believe "water boils in a vacuum" from seeing a high school science demonstration. The purpose of vacuuming an AC system is to remove non-condensibles, not to clean out contaminants like water. |
#66
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That does not follow.
Rick |
#67
Posted to alt.home.repair
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500 microns? - then you are a HACK!!
Summary judgment God. Glad to know asking means finished. You should run Nasa. You know everything based on one question. And you are polite. Never insulting, never profabe. What a guy
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#68
Posted to alt.home.repair
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500 microns? - then you are a HACK!!
Well put. Old school gentlemen who is an excellent teacher. I can tell you didnt read that in a book , and if applied and refined. Amen. Like the no name calling, shows confidence. 35 yrs tech., installer, engineer.
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