The case is a equipment with a internal heat sources which going to heat the air, the air must be static and I have to consider a natural convection, also the heat transfer of the fluid.
Have I consider the fluid as solid? Just consider the thermal conductivity and/or the convection coefficient.
In the case of heat generating equipment surrounded by stagnant air there will be heat transfer due to natural convection. If you want to carry out CFD simulation of that natural convection you don't need to consider heat transfer coefficient of the equipment wall because your simulation will solve the governing equation for fluid flow and heat transfer directly and will provide you velocity and temperature distribution. In that case you need to consider air as fluid and it requires properties of air like thermal conductivity, density, specific heat, viscosity etc. But to replicate the amount heat generation you can do that many ways,
i) you can give volumetric heat generation in the equipment and solve the conduction equation inside equipment consider equipment as solid with a heat conductivity value,
ii) you can give amount of heat flux at the wall of the equipment by back calculating total heat generation inside that equipment.
You should not forget extra term due to gravity in momentum equation.
If you don't want to carry out CFD simulation of outside air, you can consider natural heat transfer directly at the outside wall of the equipment with bulk outside temperature of stagnant air. With that if you solve conduction equation of the equipment you will get the temperature distribution of the equipment.
Hi all!, thanks for your answers, I already know the heat generation inside the equipment, but the temperature reach levels of 4000°C that's physically impossible, the boundary conditions I used are: Stagnation inlet, outlet condition and heat source. really i don't known the thermal conductivity, so I consider an arbitrary value for the wall.
Arijit Mahapatra Mehdi Aliehyaei
You can consider the energy equation with an internal energy source, and remove the convection term since the fluid is static. In fact, this amounts to solving a conduction equation (transient or stationary) but in a fluid at rest. In this case, the finite differences or finite volume method are very easy to apply.
You can do simple calculation for the heat balance of the equipment. From that calculation you can back calculate temperature of the body equating amount of heat transfer by natural convection with amount of heat generation inside. You can proceed for this calculation assuming heat transfer coefficient around 5~10 W/m^2k. If you get temperature as reasonably higher than ambient temperature you should consider radiation of the wall if the the surface is not polished. After all these if you still get higher temperature then I think forced convection (by adding fan or something) is the next solution you may think.
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