3 replies to this topic

[Wendy]

Hi all,

I'm a bit embarrassed to ask...Im not sure I fully understand the definition of the term "pinch temperature" when dealing with heat exchangers. I used the resources I have and the search engines but still don't feel like 100% understand. Is it the closest temperature between the cold and hot curves? or is this the internal pinch temperature?

Your help is greatly appreciated.

[joerd]

You're right, the pinch temperature is where the smallest temperature difference occurs between the hot and the cold curves. If this is not at one of the ends (inlet or outlet) it is also called an internal pinch.

[USR]

To add more..i would like to say with reference to heat exchanger effectiveness...for a heat exchanger the maximum heat transfer is said to have taken place when the fluid of minimum heat capacity(could be the hot or cold fluid)is heated(or cooled)to the inlet temperature of the other fluid....(i hope its clear that am talkin for a counterflow Hx)
But this is not practically possible as it would require an infinite surface to do this....hence the closest temperature is what is seeked....so u may get a hot end pinch when cold fluid is heated to the inlet temp of hot fluid...or a cold end pinch when hot fluid is cooled to the cold fluid inlet temperature...

[eirik]

But what if the pinch is internal and not placed at any end? I understand why a heat exchanger is effective if the pinch is placed at the cold/hot end but I experience often that the pinch is internal. Isn't it logical that the pinch should be designed to be at the cold/warm end?

I know this thread is old, but I still hope anyone has something to add

To add more..i would like to say with reference to heat exchanger effectiveness...for a heat exchanger the maximum heat transfer is said to have taken place when the fluid of minimum heat capacity(could be the hot or cold fluid)is heated(or cooled)to the inlet temperature of the other fluid....(i hope its clear that am talkin for a counterflow Hx)
But this is not practically possible as it would require an infinite surface to do this....hence the closest temperature is what is seeked....so u may get a hot end pinch when cold fluid is heated to the inlet temp of hot fluid...or a cold end pinch when hot fluid is cooled to the cold fluid inlet temperature...