9 replies to this topic

[satank]

Hello All,

I operate heat exchanger in Hysys and it shows "ft correction factor is low".
What does this mean? How can I solve this problem?

Thank you in advance
Cherlean

[Donkencot]

cross temperature occurs...and Ft < 0.75...
It usually happened for Shell and tube HE 1-2

[Zauberberg]

It means that you have unreasonably close temperature approach for the selected exchanger type/geometry (it occurs usually with the TEMA E-shell which is the default shell type in HYSYS).

For simulation purposes, you can switch to the F-shell and avoid this issue. If the model is used for exchanger design purpose (i.e. getting the overall heat balance and fluid properties), you need to be very careful which type of exchanger you are going to select.

[sheiko]

Satank,

I have to recommend you reading this discussion: http://www.cheresour...heat-exchanger/

[satank]

Thank you for your replies

Edited by satank, 27 April 2011 - 10:47 AM.

[Elizabeth_I]

Guys, thanks for the posts!

[satank]

Hello guys,

I try to follow your suggestions in my process but it still have the same error.
Could you suggest me which variables I should adjust?
I am attached my hysys file to this reply.

Thank you in advance

Attached Files

•  ATR_HX.zip   120.12KB   163 downloads

[Zauberberg]

I don't know why the model is setup this way, as you use the hottest product stream to heat the 2nd coldest feed stream in series of exchangers. One would usually think of arranging the exchangers in a true counter-current pattern to get the maximum heat utilization.

Secondly, you have set the temperature profile unreasonably , i.e. getting a temperature cross in one of the exchangers due to improperly setting outlet temperature of the last 2 exchangers. I have put something like this for the outlet feed stream temperatures of all 4 exchangers:

Hex 1: 130 degC
Hex 2: 200 degC
Hex 3: 780 degC
Hex 4: 830 degC

and the model has converged. Of course, I don't know what are the true requirements of your system but you certainly can iterate further based on what are the required temperatures.

For changing an exchanger into an F-shell type, go to "Rating" tab, option "Sizing", and the under the "TEMA type" option chose "F" for the shell (middle column).

[satank]

Zauberberg,

Thank you for your help again. My purpose of this model is to heat the stream from 290K to 773K and cool the stream from 1083K to 664K by adding heat exchangers.

Satank

[Tareq]

Thanks for those who reply I was having the same problem~~


with my best Regards

Tareq

Edited by Tareq, 23 May 2011 - 05:55 AM.