[Stoves] Differences in stove testing

[Bond, Tami C]

Ron,
Wonderful!

(By the way, I am not so much looking for examples from other fields. Examples from combustion field would be fine—even preferable.)

a.   On 3 pages as a part of a USGS annual document from 1907.

Who could be unhappy with a book entitled “A study of four hundred steaming tests”?! Extremely delightful.

Indeed this book gives “boiler efficiency” as heat divided by (Heat of fuel minus Heat in ash).
The context for this term can be found in the glossary on page 183— Throughout the text they refer to it as code item 72* (with a star). This is defined as “the ratio of the heat absorbed by the boiler to the potential heat of combustible ascending from the grate” — i.e. how good the boiler is at absorbing the heat offered to it.

So, the “boiler efficiency” here is very similar to what Baldwin called PHU, percent heat utilized (as Crispin has just reminded us). It looks like this book was focused on determining the capacity of boilers to absorb heat, very much like PHU. But this measure is not the overall efficiency, as Baldwin points out— it is a measure of how good the heat transfer is, and the extensive discussion of other efficiency definitions throughout the book makes that clear.

b.  A book from 1915  Engineering Thermodynamics   By James Ambrose Moyer, James Park Calderwood    Again a page with the idea of subtraction shows up

OK. The efficiency of steam engines does contain a subtraction in the denominator. Here, heat provided as steam to an engine is measured as (I’m paraphrasing) mass flow times (L + Cp (Tin - Tout)) where L is the latent heat, Cp the specific heat. It is pretty standard to have a reference temperature for sensible heat. You could label the temperature in the sensible heat Eout, energy out. But recall that I’m looking for something specific: a case where a system’s *benefit* is an output and still subtracted from the denominator.

My problem with these two is that I think you are looking for examples from other fields.  I have no doubt there are dozens of other books using this equation in the succeeding century.

It should be not difficult to find them, then.

2.    Not mentioned last night, but I also found these:
(I’m not going to buy books either)

c.  Also an expensive text (Exergy: Energy, Environment and Sustainable Development;   By Ibrahim Dincer, Marc A. Rosen)
where there is a subtraction in the denominator (p 253);  the University of Illinois may still be a main resource on Exergy (with an x - not Energy)

...3.   I also found some possible benefit on talk on the differences between “efficiency” and “effectiveness” - with at least one author claiming the latter is to be preferred.  Maybe the “denominator equation” is effectiveness.

I was able to get this in our library. Your guess was correct that it was presenting an exergy efficiency— the book is primarily about exergy analyses. Jim also sent me a nice paper on a Second-Law analysis of char production which contains the “denominator equation” to calculate an exergy efficiency.

The terms “exergy”, “availability” (I don’t know about “effectiveness”) are associated with a Second-Law analysis (rather than First-Law analysis) of the system. The assessment of thermal efficiency comes from the energy-balance (First Law) analysis. Second-Law analysis, you may remember from introductory thermo, is an analysis of the transfer one *could* have gotten with 2nd-Law constraints. There are indeed people who prefer and advocate for the 2nd-Law analysis which can also give useful information. BUT— and this is important— nobody confuses a thermal efficiency with an exergy efficiency, nor presents an exergy efficiency as a thermal efficiency.  The exergy efficiency can be calculated and provide useful information to the analyst— but it is NEVER presented as a thermal efficiency.

So, in candidates with denominator subtraction, we have (1) a heat-transfer efficiency, (2) an efficiency using sensible heat where subtracting a reference state is not only common but requisite, (3) an exergy efficiency from a Second-Law analysis. I *still* have yet to see a *thermal* efficiency where one actually removes *chemical energy* from the control volume and subtracts it from the denominator— but I am sure that if anyone can find one, you can.

Thanks for all your research!! Much appreciated.

Tami


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T. C. Bond - Nathan M. Newmark Distinguished Professor - John D. and Catherine T. MacArthur Fellow 2014
U of Illinois: Civil & Environmental Engineering - Atmospheric Sciences (Affiliate) - Women & Gender in Global Perspectives (Affiliate)
publish.illinois.edu/humanenvironments<http://publish.illinois.edu/humanenvironments>; www.hiwater.org<http://www.hiwater.org>

The only problem worth solving is the problem of how we govern ourselves. — Karl Schroeder, Degrees of Freedom

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