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negative heat transfer coefficient in contour

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Old   April 21, 2010, 09:48
Default negative heat transfer coefficient in contour
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sharad kumar
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Hi,
I wanted to ask that i am doing simlation of a ammonia containing shell and tube heat exchanger in 2-d in cfd..we have given the boundary condition as temperature of ammonia at inlet and the temperature of tube walls we have also given the inlet velocity of ammonia and also given a phase change of ammonia vapor into liquid by condensation near the tube walls.there is a flow of water inside the tubes..but at last we are getting negative heat transfer cofficient in contour in the heat exchanger...what can be the reason behind it and how to rectify it.

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Old   April 21, 2010, 09:58
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Quote:
Originally Posted by sharad_kumar101 View Post
Hi,
I wanted to ask that i am doing simlation of a ammonia containing shell and tube heat exchanger in 2-d in cfd..we have given the boundary condition as temperature of ammonia at inlet and the temperature of tube walls we have also given the inlet velocity of ammonia and also given a phase change of ammonia vapor into liquid by condensation near the tube walls.there is a flow of water inside the tubes..but at last we are getting negative heat transfer cofficient in contour in the heat exchanger...what can be the region behind it and how to rectify it.
The velocity is 0.8 m/sand the inlet pressure is 14 bar..ammonia inlet temperature is 363k..and the tube wall temperature is 300k.
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