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Efficiency of (flat) thermal collectors? - Page 3

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Posted by azuredu on January 7, 2009, 9:34 am
 


No that's not what I have seen.

The light usually goes out of the tube before it widens the bright
line.

The bright line is given by a portion of the surface that concentrates
to the tube.

Use my method and check the light leaks. I bet that you'll have
surprises.

Posted by Morris Dovey on January 7, 2009, 11:08 am
 
azuredu wrote:

Come spring, I'll check with an IR thermometer by measuring the
temperature of the hot head at the ribs and at the points midway between
the ribs.

If the temperatures between the ribs meet operational requirements, it
won't be considered a problem - and if they don't meet requirements,
it'll be a simple matter to add support between the ribs.

Thanks for your input.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

Posted by azuredu on January 7, 2009, 11:21 am
 

The temperature does not tell the story at all. What you have to
measure is the thermal output. In calories or kwh or whatever other
energy unit. Then compare with the input to compute the optic
efficiency.

Well the input can more or less be guessed out if the sky is clear.
But measuring thermal output is the only way to tell people about the
efficiency of your collector.

Posted by Morris Dovey on January 7, 2009, 12:46 pm
 azuredu wrote:

All true, but I don't particularly care to talk about efficiency. What I
care about is *demonstrating* that an inexpensive solar engine is
capable of doing a useful amount of work.

All of the heat is used right where it's being produced and discarded a
fraction of a second later - there /is/ no thermal output except as waste.

Serious optimization may follow, but that's not the best use of my time
at this point in the project.

-----

BTW, you only get partial credit (perhaps 3 out of 10 points) because
Carnot cycle efficiency is determined /only/ by the temperatures:

    maximum efficiency = 1 - (Tc / Th)

where Tc and Th are the temperatures (in Kelvins) at the engine's cold
and hot heads.

Getting heat into the engine to maximize Th seems much easier discarding
it effectively to minimize Tc.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

Posted by separatus on January 6, 2009, 10:31 pm
 
I'll take a look. Always like seeing what others are up to!

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