Temperature Profiles in Heat Exchangers

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Temperature Profiles in Heat Exchangers

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

A Physics based Mean Temperature Difference?!?!?!
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Thermodynamics Heat Transfer Analysis of
Infinitesimal Heat Exchanger
Heat Transfer in an infinitesimal HX
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Synergism between HT TD
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For A finite HX
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For A finite HX
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Parallel flow configuration
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Counter flow configuration
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Capacity of A Finite Simple Heat Exchanger
A representative temperature difference for heat
communication
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Discussion on LMTD

• This LMTD is valid of simple tube in tube HXs
  only.
• LMTD can be easily calculated, when the fluid
  inlet temperatures are know and the outlet
  temperatures are specified.
• Lower the value of LMTD, higher the value of
  overall value of UA.
• For given end conditions, counter flow gives
  higher value of LMTD when compared to co flow.
• Counter flow generates more temperature driving
  force with same entropy generation.
• This nearly equal to mean of many local values
  of DT.

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Counter flow generates more temperature driving
force with same entropy generation.
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LMTD is nearly equal to mean of many local
values of DT
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The Problem of Sizing of A Heat Exchanger
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The Problem of Finding Capacity
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