Typical efficiency values for concentric heat exchangers?

[VelocityGirl]

Ok, so I've finished all of my calculations, written most of my lab report and am finally at the discussion stage...but I can't find any typical efficiency values for concentric heat exchangers to compare my results with. HELP! If anyone knows where I can find these let me know, my report is due on Tuesday (29/11/11).

 

Cheers!

[Enthalpy]

I must understand it wrongly...

Nearly all heat lost by one fluid gets into the other. A tiny little bit of heat may flow into (or from!) the surroundings, but minimizing this is very easy.

So what do you call efficiency? I expect other numbers to characterize an exchanger, for instance watts per kelvin, or the pressure drop...

[VelocityGirl]

I meant to write "effectiveness", not "efficiency" Bit silly really! Yes generally other things would characterise it but I'm doing a lab report and am supposed to discuss this. It's ok now though, I found a graph of NTU against effectiveness and managed to read values from that to see if the results I had were within a decent range, they seem spot on

 

You said it's easy to minimize heat loss - how would you go about that? (I'm currently writing about this in my Discussion section!)

 

Cheers

[Enthalpy]

Depending on the temperature and the desired insulation...

A few rags;

Polyurethane foam, fitting the shape;

Glass wool, with a paper back at the low temperature;

A Dewar (usually not needed!)

Multi Layer Insulation in a Dewar (even less necessary)

 

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One funny idea with heat exchangers is that only technology limits their size.

 

That is, smaller exchange elements (tubes...) put the same area in a smaller volume, and decrease the distance heat crosses: more effective.

The pressure drop would increase with smaller elements, but you can make the individual flows shorter and connect them all in parallel, keeping the flow as easy.

This is what a lung does for instance: veins divide in smaller and smaller ones, down to short veinules and arterioles, which converge to arteries back.

 

One limit is the cleanliness of your fluids. Easier in a closed circuit!

The other limit is how you manufacture the exchanger.

 

There I describe a tiny exchanger made of thin electrolytic of catalytic nickel deposited on a tiny frame later dissolved:

http://saposjoint.ne...6&t=2051#p23419

interestingly, a research team in California recently used a similar process to make a "microlattice"

http://www.sciencefo...-microlattices/

 

Puzzling.

Edited December 3, 2011 by Enthalpy