Re: Definition of heat [and S]

[brian whatcott <inet@INTELLISYS.NET>]

At 09:46 11/27/99 -0500, Ludwik wrote:
> /// we never know which part of dU, gained by an
> object, came in the form of d'Q and which came in the form
> of d'W. This is like not knowing which part of water in the
> Atlantic Ocean came from which river. ///
> Ludwik Kowalski

 I received a note the other day from a person who loves machines,
 about selecting water chillers.  He takes care of the steam plant
in a mill which is served by a 150kW steam generator (a 200HP boiler).

    He was interested in reducing the injurious on/off cycling
during the Summer's reduced steam demand. So he was considering
 absorption type commercial water chillers as an alternative to
ordinary air conditioning - because he could use hot water or waste
steam in this application.

His initial question was:
"How many pounds of steam (10psi) is a ton of air conditioning?"

This does indeed sound like one of those 'furlong per fortnight' deals
at first blush. He pointed me to a commercial URL with specs for
some absorption chillers.
For your interest, here is the data on the 10 ton chiller.

INPUT:
Hot water in: 190.4F
         out: 181.4F at 37.8 gall/min

COOLING WATER:
Water in: 85F
     out: 94F   at 64.2 gall/min

OUTPUT:
Chilled water out: 48.2F
           return: 57.2F at 26.4 gall/min with 5.5 psi drop.

You can see that the heat flows are 20,412 BTU/hr, 34,668 BTU/hr and
14,256 BTU/hr
 The specification calls for 170100 BTU/hr heat input for the 10 tons
of chilling ( 12000 BTU/hr)

In the course of digesting this information for the questioner, I came
 across a text book note which mentioned in passing, that in comparison
with gases which store considerable energy in compression, the liquids,
 being incompressible - almost, store little energy when compressed:
so that the contribution of heat versus work to thermodynamic energy
 is greatly towards heat in the case of liquids - such as this absorption
chiller, I suppose.

Certainly, it was notable that this ten ton unit called for a modest
60 watts of electrical control power. The sort of figure that gives one
hope of escaping the usual domestic gotcha in a utilitry outage:
if you have no volts, you have no gas heating or air conditioning.

All of which is a response to the suggestion that you can't know if
dQ or dW is responsible for dU.
   My response is; in the case of liquids and solids, you can make
 a very shrewd guess!



brian whatcott <inet@intellisys.net>
Altus OK