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-   -   Temperature rise at a boundry condition (http://www.cfd-online.com/Forums/fluent/28768-temperature-rise-boundry-condition.html)

Rodrigo July 31, 2001 17:48

Temperature rise at a boundry condition
 
Hello, Im working on a chimney, gases from combustion of natural gas mix with air, its a multiphase model, the boundry condition is velocity inlet. The gases come in at 450[K]. The near wall treatment is wall function. When I obtain a converged solution, the max temperature is 490 [K]. The first cells adjacent to the velocity inlet have a temperature distribution, starting from 450 at the boundry and 483 at the end of the first cell !!This cannot be because the wall functions should only modify cells that are near walls.

Can anyone tell me what im doing wrong?

marc whale August 1, 2001 04:40

Re: Temperature rise at a boundry condition
 
Are you sure that wall standard is the right choice ( check y+ value on the wall, if under 6 better two-zone if 30-60 good wall std. Wall function do modify cell temperature that are near the wall, it depends on the dimension of the cell compared to reynolds value ( and the temperature of the wall obviouly ). If you use "node value" in contour window you should see the temperature changing inside the cell. What temperature you set for the wall ( are there shadow walls ? ) ??? check that !

Rodrigo August 1, 2001 14:55

Re: Temperature rise at a boundry condition
 
The y+ for wall functions is all right at the walls, my problem is in the boundry condition.

At the velocity inlet, the gases obey my input temperature of 450, but in the same cell in direccion normal to the boundry condition, this value rises.

Evan Rosenbaum August 2, 2001 12:08

Re: Temperature rise at a boundry condition
 
Maybe I'm missing something, but what BC did you use for the wall. If you have an inlet temp of 450K and a wall temp of 500 K, I wouldn't be surprised that the fliud temp increases as it flows downstream.

Rodrigo August 2, 2001 14:39

Re: Temperature rise at a boundry condition
 
The heat flux at the wall is 0 with a temperature 300, so the temperature should go down, not up.

marc whale August 3, 2001 10:04

Re: Temperature rise at a boundry condition
 
Can it be a problem due to diffusion at inlets ? there is a cortex command that let you remove the diffusion at inlets ( I don't remember where in the manual is the instruction, but I am sure there is ). Give it a try and let me know Marc


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