Calculation for correction factor LMTD in crossflow HEX?
Calculation for correction factor LMTD in crossflow HEX?
(OP)
Is there anyone who can tell me what the equation for the correction factor of a LMTD in a crossflow heat exchanger is? I only can find charts of this correction factor, but no equation...





RE: Calculation for correction factor LMTD in crossflow HEX?
t = tube
T = shell
i = in
o = out
LMTD = (Ti-to)-(To-ti)/ln[(Ti-to)/(To-ti)]
RE: Calculation for correction factor LMTD in crossflow HEX?
RE: Calculation for correction factor LMTD in crossflow HEX?
@ tickle: Thanks for your answer, I only need the correction factor for the LMTD, not the calculation for a MTD itself.
@ 25362: I need this formulas because I am working on a effectivity calculation for a specific crossflow heat exchanger and I would like to calculate the EMTD exactly. The charts I have are not precisely enough.
Both persons, thank you for your post!
RE: Calculation for correction factor LMTD in crossflow HEX?
RE: Calculation for correction factor LMTD in crossflow HEX?
RE: Calculation for correction factor LMTD in crossflow HEX?
If you do not want to use the set of curves available for the "F" factor (you will find them on the net) , I suggest you get a copy of the july 7, 1996, chemical engineering issue. Richard Turton is the author.
It contains formulas, involving a Bessel function that can be easily programmed, even in a spreadsheet.
It is also fairly easy to write a program, using a relaxation method (guess the temperature profile ; apply for each node or cell q=uA*true delta_t, and iterate).
You state the charts are not precise enough (??) . Could that mean that you are in an area where the effectiveness of your exchanger is very poor?
RE: Calculation for correction factor LMTD in crossflow HEX?
Tnx for your post siretb!
RE: Calculation for correction factor LMTD in crossflow HEX?
I have never seen data for F factors for crossflow, with 4 passes (unmixed/unmixed). There are charts for F charts for crossflow, 2 passes. Keep in mind that the hypothesis (mixed or unmixed) will alter the result, and that often the reality in in-between.
My feeling is that some simplification would be OK, unless you are in an area where the F factor gets much below 0.7.
If you do need some accuracy, again a relaxation method is easy to program.
If you need more, we'll need actual data to help more.
RE: Calculation for correction factor LMTD in crossflow HEX?