HEAT EXCHANGERS

HEAT EXCHANGERS

PHE-because

316L is not required in PHE because there are no weldings, but 316 instead of 304 can be useful in many applications. Brackish water can require 254 SMO while sea water requires Titanium!

 

#7 Gasket material is a weak point of PHE expecially in case of multipurpose use (like in Pharmaceutical). Try to find a gasket material suitable for different fluids is not so easy… Fluid Compatibility Charts

HEAT-EXCHANGERS

Wide range of materials is available Viton® Extreme, Aflas® TFE/P, Viton® FKM, EPDM P.C., Buna-n, Silicone, NBR etc. but if you are in trouble don’t hesitate to select  fully welded WPHE!

#8 Heat Recovery is one of the main reason to select a PHE rather than other type of Heat Exchangers: countercurrent flow, LMTD=1 possible etc.

The LMTD is defined by the logarithmic mean as follows:

where ΔT is the temperature difference between the two streams at end A, andΔT is the temperature difference between the two streams at end B. With this definition, the LMTD can be used to find the exchanged heat in  heat exchanger:

Where Q is the exchanged heat duty (in watts), Uis the heat transfer coefficient (in watts per kelvinper square meter) and Ar is the exchange area.

If duty is not District Cooling, industrial applications  cost/benefit  better ratio in PHE is usually when LMTD is equal to 5.

Therefore if Process Engineer is asking for LMTD 3  show always  LMTD 5 option: CapEx will result more convenient!

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