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 claudia.h July 2, 2012 14:48

Problem with natural convection

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I tried to simulate the 3D natural convection flow in pipe with 45° angle to the horizontal. The ambient temperature is 30°C, so I set the Operating Temperature to 303 K. For operating density I used the density of the lowest occurring temperature of the fluid (1020 kg/m³ at 40°C).

The fluid is a polypropylene-glycol mixture and so I use a polynomial function for density, cp, lambda and viscosity.

I use the k-omega SST Model with the following boundary conditions:

Pressure Inlet:
Gauge Total Pressure: 0 Pa,
Specification Method: Intensity and Hydraulic Diameter
Thermal: Total Temperature 313 K

Pressure Outlet:
Gauge Pressure: 0 Pa
Specification Method: Intensity and Hydraulic Diameter
Thermal: Backflow Total Temperature 363 K

On the front side I use a Thermal BC with a Heat Flux of 250 W/m² and on the back side I use a thermal BC (convection) with a Heat Transfer Coefficient of 3 W/m²K and a Free Stream Temperature of 353 K.

When I visualize velocity vectors after simulation (after 1500 Iterations) then the velocity-vectors have the wrong direction (from outlet to the inlet) and that is impossible. It would be a great help for me if anybody has an idea could cause this phenomena. Thanks!