Heat exchanger effectiveness

  • Thread starter cabellos2
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  • #1
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If I calculate a heat exchanger effectiveness of 0.5 does this mean the heat exchanger is only 50% efficient in its transfer of thermal energy? Therefore if the capacity of the heat exchanger chosen is based on Q, then would you need to select a unit double this to account for only 0.5 effectiveness?
 

Answers and Replies

  • #2
russ_watters
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No. By conservation of energy, any energy that is lost on one side must be gained on the other so in that way you would have to call them 100% efficient. But the effectiveness is actually just a measure of the ability of a heat exchanger to exchange temperatures. Ie, a perfect counterflow heat exchanger should be able to get the two fluids to swap temperatures (assuming the same fluid and mass flow rate). If you have a=50F air and b=90F air going through a perfect heat exchanger, you should get a=90F air and b=50F air out of it. 50% effective would give you 70F air out from both streams.
 
  • #3
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Ok I understand the effectiveness.

But suppose I have calculated a value of Q and this determines my selection of a heating capacity of a heat exchanger. Is it advisable to select an exchanger with a capacity slightly higher than this in the same way a 'safety factor' might be incorporated into a design problem?
 
  • #4
russ_watters
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It may depend on the application, but yes, you probably want a safety factor.
 

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