HEAT TRANSFER IN GRILLE-SPHERE COMPOSITE PACKED BED: A NUMERICAL PARAMETRIC STUDY
Packed beds are used to enhance the heat transfer in heat-exchange devices, where the heat transfer coefficient may have a great influence on the whole efficiency of the energy system. Traditional randomly packed beds have high pressure drops while structured packed beds are hard to achieve, a grille-sphere composite packed bed was designed to combine the advantages of two types of traditional packed beds. In the grille-sphere composite packed bed where the fluid is heated by the spheres, the grille can not only change the flow field, but could also help to conduct part of the heat if the grille is conductive. The total heat flux in the grille-sphere composite packed bed is determined by several factors, such as the grille conductivity, the grille thickness and the inlet velocity. In the present study, we investigate the heat transfer characteristics in the packed bed by numerical simulation. And a parametric study is carried out to evaluate the contribution factor of the three influencing factors. Results show that, if the grille is conductive, the total heat flux will be promoted. In order to obtain the maximum heat flux, the conductivity of the grille should be neither too high nor too low and it is the same case for the thickness of the grille. Low velocity is always good for the improvement of total heat flux.