[mehyan]

hi everybody,


I have been trying to simulate a double pipe heat exchanger using ansys CFX15. inner tube is used for hot water flow and outer is used for cold water flow.
in defining boundary conditions both hot and cold inlet is defined in terms of mass flow rate (both have the sane mass flow rate). and then interfaces is determined.
both inner and outer tubes have same hydraulic diameter.
when the calculation is finished the following results was obtained:

temp-cold- outlet= the correct result
temp-hot -outlet= the correct result
inner tube heat transfer coefficient =the correct result
inner tube Re number = the correct result
outer tube Re number = the incorrect result
outer tube heat transfer coefficient= the incorrect result


i think outer tube incorrect Re number causes incorrect result in outer tube heat transfer coefficient ,


but the question is that why the outer and inner tube Re number should not be the same whereas the hydraulic diameter, mass flow rate and fluid type in both domain is the same and also temperature changes are not considerable ?

(i have the same problem on fluent)



Kindly help me.

Thanx