Heat Exchager pressure losses

[joisy]

Hello All,

can you please advise the method/way to calculate dP across shell tube heat exchanger (operating with gas)

thanks,
Joisy

 

[TBP]

There are generic calculations to determine required surface areas of heat exchangers, but you really need data from individual manufacturers to figure the pressure drops for a specific model, in a given application.

 

[25362]

There are a series of books dealing with friction drops when in the shell side as well as when on the tube side, that I've seen in the past.
I'll mention: Fluid Flow and Heat Transfer by Akes L. Lydersen (John Wiley and Sons) besides Perry's Chemical Engineering Manual.
At the end you'll have to follow TBP's advice and get sufficient data from the manufacturer.
A visit to the internet could be of value, for example:

http://www.pfrengineering.com/new_page_1.htm

 

[lilliput1]

Don't forget presssure drop through the control valve, piping,fittings, valves, equipment etc. See if you can read the manufacturer's nameplate on the heat exchanger. Get model No. & Serial No. & call them up. Control valve PD would be minimum 50% of the HX PD.

 

[MariusChE]

You calculate it in exactly the same way as you would for a pipe (tube side, I mean). All that you now do is to divide the flow into the number of tubes and calculate the dP over any tube. The dP over any tube will be equal to the dP over all tubes. Remember that the flow is not isothermal and you must do some CTD or else...GUESS! You'll be ok. Good luck.

 

[joisy]

Yes, I did that. Thanks everybody. Should I have also used the inlet/outlet restrictions of the tube in dP calc, shouldn't I?

The result is almost two times bigger than one, recommended by Kern?! - dP=f Gt^2 L n/(2g Ro Di @t)

 

[MariusChE]

If your pressure drop is twice that of Kern then so be it! You have calculated it and your calculation is correct, so believe it. The inlet & outlet dPs are usually negligable, but if you want to calculate those then go for it. Remember that your heat exchanger is not going to be made EXACTLY the right sixe, it's going to be slightly bigger. You have to make sure that it's big enough to do the job.

 

[joisy]

The result much depends on inlet/outlet restriction due to relatively small diameter and length of tubing. I use equation where K=0.78 for entrance and 1.0 for the tube exit accordingly. this makes Kpipe=3.58 and Kin/out=1.78 - not the negligible value.