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Hot Pinch and Cold Pinch

Hot Pinch and Cold Pinch

Hot Pinch and Cold Pinch

(OP)
Dear All!

Can you please help me to understand Hot Pinch and Cold Pinch temperatures. What is the relation between them and the minimum hot-stream outlet temperature possible?

This doubt came to me in light of doing an exercise in Hysys, where I encountered temperature cross problem, and it was suggested that we should go for more shells in case of temperature cross? I am not able to understand this relation too..
Can any one help?

Advance thanks to all!

Cheers
atm

RE: Hot Pinch and Cold Pinch

Heat transfer is limited by either: T1-t2 (hot end) or T2-t1 (cold end). Say hot pinch and cold pinch, or temperature approach.
T1 = Hot inlet temp
T2 = Hot outlet temp
t1 = cold inlet temp
t2 = cold outlet temp
Assume you are dealing with single phase on both sides

If you try to design for a very close "temperature approach", a conventional one-shell-pass may not work, as this is half co-current and half counter-current. Cross temperature limitation may occur. Watch for the MTD correction factor, this should be > 0.8.
In your case, if maximum heat recovery is of importance, you might try a fully countercurrent arrangement. This has an MTD correction factor = 1.
MTD: mean temperature difference.

RE: Hot Pinch and Cold Pinch

In such case, choosing TEMA F shell may be of help.
You can try to locate R. Mukherjee's article "Does your application call for F-shell heat exchanger", where it has been explained in details about temperature crosses and achieving maximum HEx duty.

Try this link: http://engineeredwriting.com/samples/040440.pdf

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