1-2 Heat Exchanger Configuration Question. 3

[Christine74]

In a 1-2 heat exchanger (one shell pass, two tube passes), is there any difference in the thermal performance if you make the first tube pass co-current and the second pass counter-current vs. making the first pass counter-current and the second pass co-current?

Are there any reasons to select one over the other?

Thanks,

Christine

 

[thermmech]

Theoretically it doesn't make any difference...

the exact location of the nozzles on the shellside may depend on other thing like the geometry of the tube bundle/shell/size of nozzles vs. the baffle spacing...

 

[itdepends]

The only possible reason I can think of is for the heating of highly viscous fluids that thin significantly on heating.

Then you may want to run the first pass counter current to heat the fluid as quickly as possible to drop the viscosity. This will marginally reduce pressure drop and increase the rate of heat transfer.

 

[25362]

As a matter of fact most shell and tube units have the shell inlet nozzle located near the channel outlet nozzle.

This would hardly signify in a true countercurrent mode of heat exchange since the multiple shell baffles would oblige the shell fluid to flow across tubes containing fluids inside both tube passes.

However, such an arrangement may tend to increase the temperature effectiveness,

[ε] = (t_in-t_out)_max[÷](t_h,in-t_c,in)​

c, cold; h, hot.