Heat Exchanger Rating and Estimation 2

[L7T]

I've recently made the jump from management to design so I'm a bit rusty on the basics, anyways heres my question:
We are looking at using an obsolete closed loop system (heat exchanger (HX), pump and expansion tank) to provide cooling to a new process. The known parameters are;
1. delta T across the new process
2. the flow rate of the process fluid (process fluid is on tube side of the HX)
3. the total heat to be removed by the HX
4. the cooling fluid inlet temperature to the HX (cooling fluid on shell side of HX)
5. HX configuration :counter current single pass
6. HX surface area and number of tubes

I am trying to determine if the heat exchanger has enough capacity to remove what I need it to remove. To apply the NTU-effeicincy calculations I need to know the overall heat transfer coeff. (U) which I don't know, as I only have the shell side inlet fluid temp. I can't apply LMTD methodolgy to determine U. I've contacted the manufacturer who has given me the overall U for a given set of design conditions, however these are drastically different from my operating conditions, so I suspect that I can not use the design U in my calcs as U depends on the operating conditions (at least I think it does). Is my only recourse to perform testing (install a heat source - inline heater)in order to confirm what the heat exchanger can remove or is there some other trick of the trade I can use ?

 

[thermcool]

I would recommend you to go for the experimental approach. It is possible to use the theoretical correlations for the calculation of the overall heat transfer coefficient but still like the manufacturer values they can be quite vague depending on the experimental conditions and the condition of the heat exchanger (fouling etc).

 

[djack77494]

I agree with thermcool. Your best indication on what the heat exchanger can do is data telling you what it IS doing. Technology and engineering companies and heat transfer textbooks use their own, often proprietary estimates of U, fouling factors, and other heat transfer parameters. But if you've got a running exchanger, that is definitely your best source of information.
Doug

 

[Ashereng]

I agree with thermcool also. Measure it.

This is an "obsolete closed loop system (heat exchanger (HX), pump and expansion tank)". Lots of things might have changed.

After your test, at least you now have actual data for your correlations going forward, like when you change the temperatures and flow rates of ... whatever.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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