Analyses of unsteady conduction-radiation heat transfer using unstructured Lattice Boltzmann method

This paper deals with the analyses of unsteady conduction-radiation heat transfer problem in 2-D irregular geometries using the Control Volume- Lattice Boltzmann Method (CVLBM for short). The energy and radiative transfer equations were discretized and a computer code was developed to solve the obtained algebraic equations. Using this code, different problems were numerically simulated and it was noticed that i) the results given by the CVLBM and the Control Volume Finite Element Method (CVFEM) are in good agreement, ii) compared to the blocked-off method, the CVLBM gives more accurate results and needs less number of control volumes, iii) the conduction to radiation heat transfer ratio depends not only on the medium properties (thermal conductivity and extinction coefficient) and temperature but also on the boundary conditions (wall emissivity, convective heat transfer coefficient, applied heat flux) and iv) for the unsteady problem, the conduction to radiation heat transfer ratio increases with time (from a value of zero) to reach a constant value at the steady state (SS). In addition, it was numerically demonstrated that the conduction to radiation heat transfer ratio can be estimated more precisely using the dimensionless number NCR=λβσTref3 than using the expression NCR=λβ4σTref3 used in all previous works.