Based on the non-orthogonal multiple-relaxation time lattice Boltzmann method (MRT-LBM), natural convection in a porous square cavity with a pair of isothermally hot and cold blocks inside has been studied numerically in the current study. The influence of arrangements (Case1, Case2, Case3, Case4, Case5), spacing ratio (S) and size ratio (A) of the hot and cold sources and the Rayleigh number (Ra) on the heat exchange efficiency has been studied. The results show that different arrangements produce different heat transfer effects. Hot and cold blocks placed horizontally (Case1) and hot block located in the upper left corner while cold block located in the bottom right corner (Case4) have better heat exchange performances than other three cases since the flow directions of hot and cold fluids are closer to that of heat transfer. Then the influence of spacing between blocks and size of blocks on heat transfer rate is further studied in Case1 and Case4. The heat transfer performance is improved with A increasing. Additionally, the variation of heat transfer performance with spacing is related to the arrangement and size ratio of blocks. For Ra=104, 105 and 106, the best heat transfer characteristic can be obtained in Case1 when S=0.05 and A=0.20. For Ra=107, Case4 exhibits the best heat transfer effect when S=0.35 and A=0.20.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
