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Robin

On 05/07/2020 20:03, wrote:
On Sunday, 5 July 2020 18:52:17 UTC+1, Robin wrote:
On 05/07/2020 12:58, Roger Hayter wrote:
Dave Plowman (News) wrote:
In article ,
Roger Hayter wrote:
tabbypurr@ wrote:
On Saturday, 4 July 2020 13:32:04 UTC+1, Roger Hayter wrote:
Max Demian wrote: On 04/07/2020 11:55,
Dave Plowman (News) wrote: In article
,
tabbypurr wrote: On Friday, 3 July 2020 11:19:23 UTC+1, Dave
Plowman (News) wrote: So you stand by his
claim that an electric convector heater is 100% efficient?
Just curious. I said some are, not all are. Oil
filled ones that overheat, glow red hot & catch fire may
have more heat output than input And
those that simply expand? As all will? It only expands
once. After that it is 100% efficient. And, of course, the
heat stored during expansion will be released when it cools down.
Obvious to everyone but Dave. Pressing a spring by expansion
then releasing it by unexpanding doesn't really do any work, it
just temporarily stores some energy. He'll never get it
though. He still thinks a resistor turning electricity to heat is
imposible.
NT

Of course in the spring case some of the energy is lost as heat, but in
the heater case none need be lost as mechanical work.

I'll say again. Nothing in this world is 100% efficient. Of course you can
approach it with some things. But never achieve it.

Why do you think that nothing is 100% efficient? The only reason for
believing this that I know of is a a thermodynamic one, and this does
not apply ot heat production as an endpoint. Though it certainly would
apply to heat *transfer*, but we are not talking about this.

Thermodynamics does not forbid 100% efficiency in the conversion /to/
heat. That does not mean it is easy to achieve /in practice/.

Rather a lot of texts (used to) state that 100% efficiency is /easy/ to
achieve. A common example they gave is a person pushing a box across a
flat floor at a constant speed. All the work is (they say) converted
into heat in the box/floor system. One of my undergraduate tutorial
tasks was to discuss that and some similar statements. My recollection
is points included:

where's the pressure suit to limit heat to that system alone (and even
then no vacuum is perfect)?

where are the insulated mittens if it's not the box/floor/person system?

what are the materials of the box and floor to guarantee there are no
endothermic reactions?

ditto as regards energy stored in defects in crystalline structures?

A better example IMO are the evolutions of Joule's paddle wheel
experiment - though even there I would question 100% conversion.

resistors do a fine job of it, if not overloaded. Wouldn't surprise me if there were a trillion of them out there.

My physics is well past its 40th anniversary of disuse so please remind
me how you have an electric current passing through as resistor with
/zero/ radiation and particle emission (taking account also of quantum
tunnelling). Please bear in mind that (1 - 10^-99) ain't 100%.

--
Robin
reply-to address is (intended to be) valid