[seefd]

hi..im trying to solve a double tube heat exchanger problem and validate it with the experimental value in which the flow inside inner tube (hot water) is turbulent and the flow in the outer tube (cold water) is laminar

so in the "viscous" tab in defining models, which option should i select; whether laminar or k epsilon??

i tried solving it considering it as turbulent as a whole and selected k epsilon, but on doing so the outlet cold temperature went beyond the value of outlet hot temperature by some decimals...why is it so????
but the value of the outlet hot temperature was comparable with the experimental...why is this happening??

also i tried solving it as fully laminar, but now the cold outlet temperature was exactly same to the experimental but the hot outlet temperature was much higher than the real hot outlet temperature. why this happens??
please help

also please tell how can i solve such a problem quite accurately....


please post and help..

thanking in advance.....

[Amir]

Hey,
you can set specific zone in FLUENT as laminar zone when the solver is set as k-epsilon for example.
define->BC->fluid zone->.... toggle on laminar zone
in such problems (heat transfer) it's better to use node based gradients.