Can this be done with a heat exchanger?

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Discussion Overview

The discussion revolves around the feasibility of using a plate heat exchanger with differing flow rates on the primary and secondary sides while maintaining the same temperature difference (delta T) across both sides. The conversation includes considerations of energy conservation, specific heat capacities, and the implications of fluid properties.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether it is possible to have different flow rates with the same delta T, suggesting that conservation of energy implies they must be the same.
  • Another participant confirms the initial query about the impossibility of differing flow rates under the same delta T and seeks advice on how to explain this to the customer.
  • A different viewpoint suggests that if the temperatures of the fluids were significantly different, varying flow rates could yield identical temperature drops due to the temperature dependence of specific heat.
  • Another participant raises the question of whether the same liquid is used on both sides, indicating that differing specific heat capacities could allow for the same delta T with different flow rates.
  • A participant agrees with the notion that the close delta Ts imply they are effectively the same, reinforcing that differing fluids might allow for different flow rates.

Areas of Agreement / Disagreement

Participants express disagreement regarding the possibility of different flow rates with the same delta T, with some asserting that conservation of energy rules this out, while others suggest conditions under which it might be feasible, particularly involving different fluids or significant temperature differences.

Contextual Notes

Participants discuss the implications of specific heat capacities and the nature of the fluids involved, but there are unresolved assumptions regarding the properties of the fluids and the specific conditions of the heat exchanger setup.

Who May Find This Useful

Individuals interested in heat exchanger design, energy conservation principles, and fluid dynamics may find this discussion relevant.

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A customer of mine came to me asking for a price on a plate heat exchanger for water. The data he brought me was the following:

Primary side: 1,9 l/s and 12/16 C.
Sec. side: 2,4 l/s and 14/18 C.

I was just wondering if it is even possible to have different flows when the delta T is the same on both sides...?
 
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No, conservation of energy requires that they be the same.
 
Thx, good to get that confirmed. Any tips on how I can easily explain this to him so that he "gets it" ?
 
If the temperatures of the fluid were drastically different it would be possible for different flowrates to give identical drops in temperature as specific heat is temperature variant. However, in this case the temperatures are so close that specific heat is in effect constant.
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http://www.cfdengineer.com.
 
Is it the same liquid on each side? If the specific heat capacities are different you might get the same Delta T with different flow rates.
 
I agree with doc.

I am not an engineer, just a Mechanical contractor. The Delta T's you listed are so close, they are in effect the same. If the fluids were different, then maybe. But you deltas are so close...
 

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