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Takeshi July 10, 2003 12:53

Heat transfer tube
I'd like to know an appropriate turbulent model for analysis of heat transfer tube used for heat exchanger. I'd like to know following characteristics.

Pressure drop, Heat transfer coefficient

The size of the tube is as follows:

Inner diameter: 2mm, Length: 500mm

The tube is very slim and long. I have to pay attention to cell size. Too small size cells can make analysis unstable? The tube may be dimpled to increase heat transfer coefficient. Wall temperature is fixed and fluid is water.

What do you think is the most appropriate turbulent model for this analysis? In my opinion, low Re k-e model may be appropriate because I need to cauculate near wall region with high accuracy to evaluate heat transfer coefficient.


allan July 11, 2003 10:08

Re: Heat transfer tube
regarding the low Re turbulence model, stictly speaking you will need a lot of cells, 20 node points in the boundary layer, however there is alterative, the hybrid wall function where the standard u+ y+ correlation is extended down to y+ approx = 1. This can be activated by setting c125=1, and you must select a low re turbulence model, but use a high re grid.

I found this in various release patches of star, but not in v3150A. If it's not there request a version from CD


Takeshi July 14, 2003 12:29

Re: Heat transfer tube
Thank you for your advise. What is c125=1?

allan July 14, 2003 13:36

Re: Heat transfer tube
c125 and others are control constants which allows beta features and other special controls to be set.

c125 is the one to switch on the hybrid wall functions. On the command line type:

rcon,125,1 and to deselect it



Takeshi July 15, 2003 10:44

Re: Heat transfer tube
Thanks! I'll give it a try.

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