Learning Forum

[jaehun LEE]

i am working on a shell and tube heat exchanger. below figure is the geometry that I am using. (2D axisymmetric) through the inlet of the yellow part, hot air enters (atmosphere pressure). and in the middle, there are 4 black zones. they are baffle. on the other hand, through the inlet of the purple part, cool air enters. and it's pressure is 8barG. around 9bar. (including atmosphere pressure). and between yellow and purple zone, there is a solid zone which is pipe thickness

to simulate this configuration, two distinct pressure should be applied to different zone. so i set the operating pressure as 101325 Pa, which is the same as the atmosphere pressure. and give to the outlet gauge pressure 8barG. and inlet Supersonic/Initial Gauge pressure 8barG. (as i know this value is the initial value of inlet gauge pressure).

but as you can see maybe this cannot solve the problem well. this is the velocity U profile along the yellow part center line.

we cannot set the operating pressure 9 bar. because between the yellow part and purple part the pressure difference is 8bar.

 

could you give me some advice?

 

[Rob]

If the pressure drop in each zone is minimal, do you need to have a variable density? If not, you can set (for example) air to have a density of 4.5 kg/m3 if that's correct for 8 bar, and another air material in the tube at 1.18 kg/m3 to mimic atmospheric conditions. Pressure is just a driver for flow in most cases so we're only really worried about the difference over the domain. 

In CFX there's a flag somewhere to allow you to set two sets of operating conditions. I think it's detached zones or similar.