Multiscale simulation of energy transfer in concentrating solar collectors of solar power system

In this keynote lecture the multiscale simulation of heat transfer and fluid flow problems is presented in detail focusing on the simulation of heat transfer process in concentrating solar collectors (CSCs) of solar power system. Six sections are included. In the first section the meaning of multiscale problems is briefly introduced. From numerical point of view the multiscale problems are divided into two categories: multiscale process and multiscale system; In the multiscale process different governing equations and different numerical methods should be used for different regions and numerical solutions should be coupled at the interface. A typical multiscale process is the mass and heat transfer in a PEMFC. For the multiscale system the same governing equation and the same numerical method are used at different regions. The cooling process by air stream in a large data center is a typical multiscale system. In the previous studies for the multiscale processes emphasis is manly concentrated on convective-diffusive heat transfer process. The focus of the present lecture will be put on the radiative-convective-diffusive process occurred in CSCs. In the second part of the lecture introduction to four kinds of solar collector used in CSCs are presented. They are the parabolic trough solar collector (PTSC), the linear Fresnel reflector (LFR), the central receiver collector (CRC) and the solar dish collector (SDC). It can be seen that their common function is to collect the radiation from the sun, concentrate the solar energy and re-radiate the energy to a target where some kind of heat transfer surface is located to absorb the concentrated energy and transfers the energy to some working fluids. Especially, from the heat transfer point of view, the whole photo-thermal conversion process in all these receivers is a very complex coupled radiation-convection-conduction process where the heat source comes from the solar radiation carried by countless microcosmic photons (Fig.1) .