Experimental study of heat transfer characteristics in a 180-deg round turned channel with discrete aluminum-foam blocks

This work experimentally investigated the local and average heat transfer characteristics in a 180-deg round turned channel with discrete aluminum-foam blocks. The air was used as coolant. Several aluminum-foam blocks (0.90 porosity and 10 PPI pore density) were installed discretely in the 180-deg round turned channel with the square cross section. Total four kinds of test section, with various arrangements of aluminum-foam blocks, were employed. The results indicate that the local peak values of the Nusselt numbers would appear at the positions of the aluminum-foam blocks. The local Nusselt numbers of the upper and bottom walls were higher than those of the side walls in the straight ducts; while the local Nusselt numbers of the outer side wall were higher than those of others walls in the turn. The local Nusselt numbers of the inner side wall generally were the lowest values. Besides, the average Nusselt numbers of the present porous channels were 74-140% higher than that of the empty channel, suggesting the significant heat transfer enhancement of the aluminum-foam blocks. Furthermore, in the straight duct, the staggered aluminum-foam blocks could promote heat transfer more efficiently than the symmetric aluminum-foam blocks did. The average Nusselt numbers of Model 3 and Model 4 (the whole channel filled with aluminum-foam blocks) were 20-30% higher than those of Model 1 and Model 2 (only straight ducts filled with aluminum-foam blocks). It is noteworthy that the pressure drops of Model 1 and Model 3 test sections (vertically symmetric configuration) are much higher than those of Model 2 and Model 4 test sections (vertically staggered configuration) by 180-280%.