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convergency problem with the introdution of gravity in 2D modeling

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Hello everyone:

I'm modeling a CVD growth in a quartz tube furnace using chemical engineering model (chns+chcd). When there is no gravity considered, calculation converged easily.

When gravity was introduced as volume force in y-direction, I still could manage to solve it for chns only by increasing gravity from 9 = 0.1m/s^2 to 9 = 9.81m/s^2 gradually. However, when I want to include chcd in the solver, the results did not converge.

The geometry of the furnace is: tube with diameter of 2.5" and length of 45", both inlet and outlet have a diameter of 0.25". The growth wafer in the furnace is roughly 1cm^2. I did notice the size difference is huge and I used boundary layer mesh on the wafer surface to investigate the adjacent area.

To play around, instead a quarter inch inlet, I set the whole 2.5" diameter of the tube as inlet and the same for outlet. This time I can solve chns+chcd with gravity introduced but just up to g = 1m/s^2.

I have no clue what's going wrong and will highly appreciate any inputs.

Thanks and regards,
Zhong

0 Replies Last Post Jul 5, 2010, 2:39 p.m. EDT
COMSOL Moderator

Hello Zhong Li

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