8 replies to this topic

[Maabdolat]

Hi......

 

I am trying to design H&T exchanger in ERD software, but i only know the duty and tube side flows, pressure, temp.... but do not know the shell side pressure drop....

 

so, kindly guide me how i can design an exchanger, when i know only duty......

 

 

regards,

[Steve Hall]

When designing an exchanger the usual practice is to specify a maximum allowable pressure drop. Rule of thumb is 10 psi (70 kPa), but it really depends on your process and utility capabilities. Parameters such as baffle cut/spacing, shell diameter, and tube pitch affect the shell-side pressure drop - and, of course, the heat transfer film coefficient.

[Maabdolat]

thanks for help......

 

but kindly guide me how to design or select Heat exchanger when i know only heat duty, process temperatures, flows,

 

while the coolant flow and pressure are unknown........

 

 

actually i have heat duty and process gas parameters but dont know the coolant parameters, so help out plz.... how to get coolant parameters, as Exchanger Design and rating software , requires coolant parameters in designing Shell and tube heat exchanger, ........

[srfish]

If you do not know the coolant inlet temperature then you have a big problem. If the coolant is water then it is customary to use an inlet temperature of 85 to 90 F. and a  maximum outlet temperature of 120 F.

[Maabdolat]

thanks again....

 

but sir, what would be effect of coolent pressure on heat exchanger desing.....

 

actually, i know all parameters of process fluid and coolent.. but dont know about the coolent pressure???

 

does varying coolent pressure may effect heat exchanger desing, if yes.. then how to find simulation of Heat exchnager in Exchanger Desing and rating (Aspen ERD)software with unknown inlet pressure of coolent and delta Pressure of coolent.......

 

 

regards,

[srfish]

You have not said for sure that the coolant is water. If it is water, Then the operating pressure is not going to affect the heat transfer unless the pressure is unusually low where the typical allowable pressure drop mentioned by Steve Hall couldn't be used.

[Maabdolat]

Actually sir, i want to design shell and tube exchanger in Aspen ERD, where the hot fluid is gas(SO3) and the cold fluid is also gas (SO3)...

 

I know all properties of both streams, except pressure drop across shell side as well as tube side......

 

how to design or what pressure drop should i take in designing for both shell and tube sides........

 

regards,

[Propacket]

Maabdolat

 

There are no rules of thumb when we dont know about the process. We cant recommend tube side or shell side pressure drop when we dont know where the outlet streams are going and how your downstream unit operation(s) will behave due to low or excess pressure drop. If there is no concern regarding downstream unit operations, you can go with a typical value of 10 psi. In case downstream unit operations are susceptible to pressure drop, analyze yourself what should be the best delta P figures.    

[srfish]

That is a good comment by Propacket. Since we found out that the tube-side fluid is a gas instead of a liquid, I suggest an allowable pressure drop of 3 to 5 Psi. This comes from an engineering tip in www.gulleyassociates.com.