Hello,

 

I have a project where i need to design a heat exchanger (HE) to reduce the temperature of hot air. The hot air comes in at 700K with a pressure of 1300Kpa, it will come out of the HE with the same pressure but how do i calculate its exit temperature?

 

I know it has something to do with the HE Efficiency, which i do not know how to find. HELP!

Hey,

 

We need a LOT more parameters before this answer can be found... but first: where the hell do you get 1300 KPa (13 bar) of pressure at 700 K (427 deg C)??

And what do you want to do with the heat?

 

- You need to choose the 2nd fluid in your heat exchanger. If something cools down, something else heats up. A common choice is water or steam (or both, meaning you make steam from water).

- Then you need to choose the exit temperature (yes, you can CHOOSE that). Alternatively, if you already have the heat exchanger, you must know the "heat exchanging surface area", and preferably the type of material. You can calculate one with the other.

- Then you must also determine if your flows are turbulent or laminar. For this you need to know the flow of both fluids.

 

I believe that's all for a first approximation.

 

This is an engineering question, or possibly a physics question. I have reported this thread and asked it to be moved.

 

Finally, there is no need to abbreviate heat exchanger into HE. It does not make you look more scientific, and using such abbreviations will only get you into trouble when somebody doesn't understand it.

An old, but still very good, book on the topic of heat exchanger design is "Process Heat Transfer" by D. Q. Kern. If you can find a copy, have a look. That should have everything you need.