Learning Forum

[mchombly]

Good people of ANSYS Learning Forum,nI have a 2D axisymmetric model i.e. a rectangle. On the bottom edge I am applying a constant heat flux (505253 W/m2), on the same edge I am applying an emissivity of 0.47.nUsing the Stefan-Boltzman Law I can approximate the temperature on that edge to be 2086K, which is roughly what I get when simulated.nNow I place a radiation boundary condition on the opposite edge of the rectangle, and run the simulation again. When I run the simulation using a material with high thermal conductivity (i.e k = 164 W/m.K) the temperature difference across the boundary is drastically reduced and the maximum temperature approximately 1300K. When I run the simulation with a low thermal conductivity (i.e k = 6 W/m.K) the temperature difference is much larger and the maximum temperature is approximately 1700K.nMy understanding is that the heat flux should always be applying an initial temperature of approximately 2086K on one side of the rectangle, and the thermal conductivity should only affect the temperature on the other side of the rectangle.nIs it possible to set the heat flux and temperature of the rectangle at the same time so I can control the starting point for the temperature change across the material?nAny advice/help/literature would be greatly appreciated.nThank you for your time!n

[Karthik Remella]

Hello,nNo, you will not be able to specify both heat flux and temperature on the same boundary. When you specify one, the other automatically falls out as the solution.nI'm not 100 % sure if I understand your geometry completely. But, if you have a thermally conducting slab of rectangle and you specify the same heat flux, a thermally conducting slab will see a smaller temperature difference compared to the same slab made out of a material which is a poorer conductor of heat (low thermal conductivity). This is because as the thermal conductivity increases, the effective thermal resistance across the slab decreases and therefore, you see a smaller temperature difference across it.nI hope this helps.nThanks.nKarthikn

[mchombly]

Good Afternoon Karthik,nThank you for responding to my question. The geometry is a 2D-axisymmetric model and therefore when applying the boundary conditions I effectively have a rectangle.nCould you please clarify if the following is correct: If I apply a uniform heat flux on one edge of my rectangle, regardless of the thermal conductivity of the material, the temperature as a result of that heat flux should be same (i.e. if I apply a heat flux of 505253 W/m2 the temperature should be the same on that edge if I ran a simulation with a material of K = 6 or K =164), the only thing which should change is the temperature difference between the two edges.nThanks, I look forward to your response.n

[Karthik Remella]

Hello,nTo answer your question regarding applying the same heat flux on the same edge for two different materials - the temperature is not going to be the same. The final edge temperature is the result of the overall heat balance in your system (conduction + convection + radiation - if any). Because the thermal conductivity is changing the overall thermal resistance in your body, you will likely get a different temperature. nThanks.nKarthikn