# Operation Temperature for Boussimesq Approx

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 December 12, 2013, 12:16 Operation Temperature for Boussimesq Approx #1 Member   Tom Marquardt Join Date: May 2013 Posts: 34 Rep Power: 6 Hey guys, I'm trying to solve a natural convection melting problem. Boussinesq approximation is valid because ß*(T-T0)<<1. I'm not sure how to set the reference density rho(0) and temperature T(0). I have data regarding the density in solid (890kg/m³) and liquid phase (760kg/m³) and I know the melting temperature is 306 K. What would I use for operation temperature and density in this case? Might be a silly question but I'm not sure about this. Thanks for your help!

 December 12, 2013, 13:57 #2 Senior Member   Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 10 The Buossinesq model is valid when the temperature fullfill the condition delta T * thermal expansion coeff smaller than one. Beyond that you should be using a compressible model. Try setting your reference temperature to the mean of your expected temperatures. In a closed system, Tref shouldn't change your final solution (although higher buoyancy forces can cause stability issues). In an open system, Tref can be the ambient temperature, but you need to be careful not to induce false flows with very large body forces. The density is always an issue in fluent i usually use zero density or the density of the lighter phase (latter is suggested for multiphase flows)

 December 13, 2013, 04:14 #3 Member   Tom Marquardt Join Date: May 2013 Posts: 34 Rep Power: 6 Hey, thanks for your respond! I think I got your point but what does Try setting your reference temperature to the mean of your expected temperatures exactly mean? The initial temperature of the PCM is 295,13 K, the melting starts at 307K and the highest temperature possible will be the one of the Hot fluid stream melting the material with 325K. If I get you right, 325K would be the temperature to go, is this correct? Thanks!

 December 13, 2013, 07:09 #4 Senior Member   Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 10 That will be my start point!

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