The length and bending angle effects on the cooling performance of flat plate heat pipes

Abstract

The effects of length and bending angle on the cooling performance of flat plate heat pipes (FPHPs) were examined experimentally in this study. The length effect was explored with four lengths of 80, 150, 200, and 300mm; each FPHP was filled by acetone in cold condition to its optimum filling ratio. The bending angle effect was examined with four angles of 0°, 30°, 60°, and 90°, using the length of 200mm and the volumetric filling ratio of 31.4%. All FPHPs had the same cross sectional area of 50mm (width) by 2.5mm (thickness). Experimental results showed that by increasing the length from 80 to 150mm, to 200mm, and to 300mm, the minimum thermal resistance, Rth(min), increased by the factors of 2.4, 6.0, and 17.9, respectively from that of 0.103K/W of the 80mm FPHP. A rapid increase in Rth(min) occurred around the length of 150mm. For the FPHPs with lengths smaller than 150mm, Rth(min) could be smaller than 0.252K/W. The maximum heat transport capability Qmax decreased quickly from 109.5 to 49.6W (a factor of about 0.452) when the length was increased from 80 to 150mm, and then slowly decreased to the minimum value of 35W (a factor of about 0.318) for the length of 300mm. In contrast, the results of bending angles showed that by increasing the bending angle, the thermal resistance decreased; Rth(min) reduced by a factor of about 3.3 from 0.6207K/W of 0° bending to 0.1885K/W of 90° bending. The corresponding maximum effective thermal conductivity, Keff(max), increased from 1933.4 to 6365.6W/mK and Qmax increased from 45 to 85W. That is, a short FPHP preformed better than those of longer ones, and the thermal performance of FPHPs could be enhanced by proper bending.