PHE Hot and Cold film Heat Transfer Coefficents 4

[SamOntario]

Basic overall HTC equation 1/U= 1/Uh + t/K + 1/Uc

PHE operation data: Primary side in/out = 120/70 degC flow=50m3/h softened water at 12 BarG, Secondary side in/out = 60/85 degC flow=100m3/h softened water at 10 BarG.

PHE construction material is SS316 t=0.7mm thick, thermal conductivity is approximately K=0.67 W/m/K.

I am puzzled that PHE manufacturer sales engineers giving me U ranging from 4000 W/K/m2 to 9000 W/K/m2 with the above data. When I ask for Uc and Uh, they could not provide and making excuses such as proprietary data. Pls advise how I could determine Uh and Uc within reasonable accuracy?

Pls also advise how to conduct performance tests if the operational data are deviated from the above design data, thanks.

 

[zerok]

rmw

Thanks for the input.

sam

I did some runs for you based on the plate dimensions you provided:

- Chevron angle usually between 25 and 65°.

- plate gap from 3 to 6 mm.

Here's what comes out of it:

Overall heat transfer coefficients:

PHE1:

plate gap(mm) 3 4.5 6

Chevron angle

25 10718 7969 6380

45 9594 7714.5 5656

65 5527 3914 3031

PHE4:

plate gap(mm) 3 4.5 6

Chevron angle

25 11330 8571 6895

45 10270 7673 6126

65 6035 4296 3336

Like rmw said the plate gap can be calculated from the compressed plate pack length. Have a look at the drawings, it should be available.

Hope this helps.

regards

zerok

 

[SamOntario]

zerok,

Thanks. From your results, Chevron angles and gap thickness have dramatic influence on HTC. A well designed PHE will require only a 1/3 of a less well designed PHE. Are the above HTCs based on a pressure drop limit of around 0.6bar at the cold side?

I am surprised how little I know about PHEs. I always thought that the hot film coeficients have the dominating limiting factor in heat transfer when flow in the hot side is about 1/2 flow of the cold side, and overall HTC should normally not be more than 6000W/C/m2.

I need more reading on how the can be so dramatic. Any suggestions?

 

[rmw]

Sam,

Within each chevron angle group that zerok has done the different gap thickness causes the velocity to vary. You can see the profound effect of velocity on this type of exchanger.

rmw