Calculating Temperature Change for Heat Exchanger

[matt621]

Hello,

After the last post I completely changed the system. I now have a new system. Based on the feedback from last time I increased the time in contact with the block significantly. And I have made it a two stage unit.

Here are the parameters for the first stage. An Aluminum block. (assume typical 6061) Assume the block is held to 32F and it picks up no new heat (it will but I have another exchanger in a 32F or below water bath of significant capacity. So I'm 99.9% sure I can keep it at 32F.)687Square Inches of total surface area. (Total mass of the block is about 7#s.)The air running in between the plates (assume each plate is half the surface area).The air is 100F, and anyone molecule of air is in close proximity of one of the plates for 3 seconds. And by very lose proximity assume .06" or closer.Can we calculate how much the drop in temperature will be for the air with just these parameters?If we need something else, what would that something else be?

Currently the plates are smooth and I know I can get better transfer if I rough them up, however I also have a flow issue for the air,so any increase in the roughness of the surface of the block will result in a loss of flow of the air between them.)

Based on the answer here, I may not even need the 2nd stage but if I do I think I can approx it close enough to start working on it.

Thank you very much.

 

[Nidum]

If we need something else, what would that something else be?

A lot more information if you want a proper answer . To begin with please post a clear sketch showing the arrangement of block , plates and heat exchanger that you have and the actual flow path of the air .

 

[matt621]

I'm sorry, I'm unable to provide a sketch.

If you just imagine 2 plates parallel to each other, about 1/8" apart forming a channel for the air to go thru. (ends blocked so it creates a long thin tunnel for the air to pass.) The blocks will be kept at approx. 32F (or lower).

Based on the speed of the air, from the start of the channel/tunnel to the end the air will be in contact with the blocks/channel a min. of 3 seconds.

Maybe another way to put this is if a cubic mm of air @ 100F is put into contact with 1 sq mm for a min. of 3 seconds how much heat will be removed from the 1 cubic mm of air? ie, what temp will the air coming out of the other end be? (Assuming a semi smooth surface fo the al., ie, not polished, but what any standard milling process would produce.)

Thanks