Performance of Plate Heat Exchanger 1

[teknomania]

Hi All,

I would like to develop a model to measure the performance of a plate heat exchanger (the model obtaining the return temperature and flow rate at the primary side according to the input values of supply temperature at the primary side and the supply and return temperatures together with the flow rate, the all last three at the secondary side). As input to develop the model, I only have the performance measures for different cases and the dimensions, both provided by the product company. Please check the attached Word document for the performance data.

Can any of you describe step-by-step the method to develop this model by basing on the performance data given by the product company?

More Details:
Water-to-Water heat exchanger
One pass in both primary and secondary side

Regards.

 

[IRstuff]

With all the calculators and calculations on the web, why are you doing yet another one?

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[dbill74]

Assuming you are transfer heat from water to water, the transfer to/from water can be calculated with Q = Constant * Flowrate * Delta T
For Q in BTUH
Cconstant = 500
Flowrate in GPM
and T in Faren. or Rankin.
such that Q = 500*GPM*Delta T (F)

Using the performance data you provided, a similar equation for kW, l/s and degrees C
Q = 4.1667*l/s*Delta T

Linking the 2 sides is the fact that Q_{primary side} = Q_{secondary side}

 

[teknomania]

IRstuff,

Normally I use the commercial software of "SSP Online Calculation Software" provided by the SWEP for sizing and performance calculation of the heat exchangers.

But this time I need to develop the model to obtain the performance (Tr and flow rate at the primary side) of the heat exchanger. It is because I will integrate this new model to one big simulation of a district heating substation in Matlab. So that is the reason.

Is there a way to follow LMTD and/or e-NTU methods to reach the main aim? Please explain in details. The information in internet is same. Couldn't reach an example how to calculate the performance of a plate heat exchanger.

Regards.

 

[georgeverghese]

There are 2 problems here

a) Boil down the given performance data to give primary side and secondary side heat transfer coeffs, from which it would be possible to calculate an overall U and match that with the exit temps listed for each side

b) Given the numerical expressions for primary and sec side coeffs, it would then be possible to calculate the overall U and get the corresponding stream exit temps by trial and error

You could save yourself a lot of agony for (a) by getting the numerical expression for the primary and sec side htc by asking the PHE vendor. The expression should be similar in configuration to that for the Nusselt or Ditus Boelter eqn. Else it may be possible to derive this yourself if you have the patience and a lot more time. Check that a skin to bulk viscosity ratio factor is included to improve accuracy if the fluid on either side is viscous at the appropriate skin temp.You may also confirm with the vendor that the LMTD corr factor F for plate heat HEX = 1.0 for the full range of hot side approach temps.

For (b), the trial and error approach for this would be approx as follow

i) Guess a trial value for the exit temp temp for either primary or sec sides

ii) Then, given that Qprimary = Qsec, compute the exit temp for the other side

iii) Then calculate the LMTD, now that you have all temps known for this trial run
For the given flows on each side, calculate the htc for each side given the expressions you've gotten from (a). Physical props for the stream should be computed using the mid temp value for the HX for this trial, if this HX is in linear single phase heating or cooling operation.

iv) Then compute U for the HX and apply a minimal fouling resistance as required, if necessary - for PHE, the fouling resistance usually is close to zero.

v) Then compute Qhex = UA LMTD

vi) Solution is reached when Qhex = Qprimary or Qsecondary. If not, use another trial value for the exit temp from either side and repeat (i) to (vi).

 

[teknomania]

Thak you georgeverghese.