# Natural convection with heat flux

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 March 22, 2007, 09:09 Natural convection with heat flux #1 Anton Guest   Posts: n/a Hello. Can someone help me? How can I compute a natural convection with such a boundary conditions as heat flux? Problem: there is a heater immersed in volume with liquid with defined heat flux density (w/m3). All the heat produced by heater can draw away by only one surface of the volume. I tried to define negative heat flux on that surface, but after solving I recieve a great temperatures in liquid such as 10^3. While the working temperature is about 300 K. Thank you.

 March 22, 2007, 19:29 Re: Natural convection with heat flux #2 Cristina Guest   Posts: n/a Hi! I'm working with natural convection too and I have read your message.I may help you. You have a heater immersed in a liquid volume. The heater is modeled as a solid with an internal generation(source term in material's menu??) and the liquid volume must be adiabatic except in one surface, in which you must especify another boundary condition, as example, temperature. Why did you try to define negative heat flux on a surface? Maybe I didn't understand your problem. Regards

 March 23, 2007, 08:18 Re: Natural convection with heat flux #3 Anton Guest   Posts: n/a Thanks for responding, Cristina! Yes, my heater has energy source term. The volume with fluid is a Dewar vessel so I thought that all energy (known quantity) produced by heater in this vessel must go away through only one, upper face, vented to atmosphere. Best regards

 March 28, 2007, 17:11 Re: Natural convection with heat flux #4 Seyed Farid Hosseinizadeh Guest   Posts: n/a Hey: Please check your meshes and your boundary conditions. Also apply the material property in correct way. It is laminar or turbulens and what is your Rayliegh number? Please be sure that your applied number for heat flux is correct. It must be per surface area. Otherwise, I guess this is not a complex problem. I will be so gald if I can do some help. Thanks/Farid

 March 29, 2007, 08:30 Re: Natural convection with heat flux #5 Anton Guest   Posts: n/a Hi! Thank you for your reply! Rayliegh number is about 3.6e8. I think, i defined all properties correct.. Density as boussinesq, thermal expansion coefficient 5.9e-3. Can i define a negative heat flux at all? maybe Fluent does not support such things?.. I recalculated heat flux form [w/m3] to -[w/m2], but Fluent writes that temperature is limited by 1.0000e0 or 5.0000e3. maube i should write UDF?

 April 2, 2007, 04:03 Re: Natural convection with heat flux #6 Ameya Guest   Posts: n/a I too am solving a problem on natural convetions. my rayleigh no is of the orefer of e10.Hence i have selected the laminar model. my model comprises a 3 fin horizontal base array. when i give a constant heat flux to the base of the array the temperature exceeds beyond limit. the mesh around the array i very fine around 5oo microns. please help asap thanx in advance regards ameya

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