1 reply to this topic

[xin]

Hi,

 

I am trying to design a heat exchanger that performs two duty, 1) to condense incoming steam 2) to further subcool the condensed steam

 

To be more specific, the incoming superheated steam is at 143deg C, the saturation temperature is 104 deg C, the outlet temperature of the subcooled condensate is 55 deg C

 

The cooling water in is 40 deg C, the cooling water out is 50 deg C. Counter- current flow.

 

I have worked out the LMTD for two different steps, but what would be the combined LMTD?  If I use 59.3degC as LMTD, I might undersize the heater, if I use 30.6 deg C as LMTD, I might oversize the heater, so what should I do?

 

 

Step 1 -Condensing               Hot End Cold End     104.4 104.4     50 40           LMTD 59.3 degC                           Step 2 - Subcooling               Hot End Cold End     104.4 55     50 40           LMTD 30.6 degC  

 

 

Thanks,

Christy

[Zauberberg]

There is a variety of related subjects discussed in details in D.Q. Kern's "Process Heat Transfer", particularly on pages 283-309, as well as in the Chapter 5, "Temperature".

 

Based on the description it seems that there are 3 distinctive zones in the exchanger: desuperheating, condensing, and subcooling.