Heat Exchanger Tube/Shell side Pressure Drop
Heat Exchanger Tube/Shell side Pressure Drop
(OP)
I have to calculate the velocity of CW in tubes and the pressure drop in the tube/shell side of several heat exchangers. I used www.processassociates.com but I can't get the value of pressure drop. An example: An heat exchanger with 4 tube passes, 1232 tubes, 6m each tube length and ID of 23.3mm with a flowrate of 238 m3/h of CW (density 993.184 kg/m3 and viscosity of 0.0010565 Pa.s. The calculated velocity is 0.503392 m/s (checked by myself), Reynolds Re= 11026.512(too) and pressure drop of 60.370 mbar (??). I need to know the equation for calculate this pressure drop. I think my error is on tube length. What is the correct formula to calculate tube side pressure drop and the tube legth to consider? Another...formula to shell side pressure drop?





RE: Heat Exchanger Tube/Shell side Pressure Drop
I am not trying to answer your query.
I just followed the same steps,
your velocity and reynolds no. are correct.
But I get pressure drop of 246mbar for same confiuration.
Please check.
I feel the exchanger has very low tubeside velocity, shouldnot be less than 1.1 m/sec to have self cleaning.
Regards,
Saa
RE: Heat Exchanger Tube/Shell side Pressure Drop
RE: Heat Exchanger Tube/Shell side Pressure Drop
Thanks a lot and regards
AndreChE
RE: Heat Exchanger Tube/Shell side Pressure Drop
The value from www.processassociates.com probably doesn't take into account return losses.
AndreChE
RE: Heat Exchanger Tube/Shell side Pressure Drop
Thanks for letting me know return losses are also so significant
Regards,
SAA
RE: Heat Exchanger Tube/Shell side Pressure Drop
Did you recalculate deltaP? Still with 200-300 mbar? Have you followed Kern, Process Heat Transfer method? I'm with 70,6mbar and I think this is the correct value but it could be some mistake in my calculation.
Regards,
AndreChE
RE: Heat Exchanger Tube/Shell side Pressure Drop
For correct calculation of pressure drop and velocity of gas flow with taking into account of the tube length try to use the materials of papers:
"On static head in the pipe flow element"
http://arXiv.org/abs/physics/0301070 and
"Saint-Venant –Wantzel’s formula modern form"
http://arXiv.org/abs/physics/0302038
for prediction of flow regime (laminar turbulent)you may be use
the result of work: "The laminar flow instability criterion and turbulence in pipe"
http://arXiv.org/abs/physics/0303071
Sincerely
garyloz
RE: Heat Exchanger Tube/Shell side Pressure Drop
1) entering plus exiting the exchanger = 1.6 velocity heads (use the velocity in the pipe leading to and from the exchanger)this is usually negligible.
2) entering plus exiting the tubes = 1.5 velocity heads * number of tube passes (use velocity in the tubes)
3) end losses in tubeside bonnets and channels = 1.0 velocity head * number of tube passes (use velocity in the tubes)
**A velocity head = deltaH = (velocity)^2 / (2g) where deltaH is head loss in feet of fluid. See Perry's for further info OR Crane's tech paper 410.
***The three losses described above are additive to the loss you determine from the flow through the single tube using average velocity through one tube.