Analysis of Combined Conduction-Radiation Heat Transfer In Multilayer Insulations

Modeling of the combined conduction-radiation heat transfer in multilayer insulation has been done. Governing equations of the problem are integro-differential and there is no exact solution for them. So numerical procedure with approximate solutions have been used. Main governing equations were energy equation and two-flux equations that respectively, using the finite volume and finite differences have been discretized. Numerical solution is validated with Ozisik’s solution and published experimental results. Total heat flux and effective thermal conductivity obtained via steady state results. Dimensionless temperature distribution and dimensionless radiative and conductive heat fluxes along sample thickness obtained. Near the hot boundary, dominating mode is radiation, so it is suggested that reflective screens to be located near hot boundary. For lower temperature differences, the dominating mode is conduction, so number of reflective screens does not influence effective thermal conductivity so much. In all steps of validation, the numerical results have good agreements with published data in references. Finally, as for radiation behavior along insulation thickness, it is suggested that just the foils near the hot boundary, to be coated with gold for sake of cost cutting. In addition, it is understood that layer density has an optimum value and this value does not changes if the boundary conditions and the material remain unchanged.