Gravitational Field Axial Grooved Heat Pipe Heat Transfer Experiments

An experimental investigation of thermal characteristics of trapezoidal axial grooved heat pipe (AGHP) is presented in this paper. The material of tested AGHP is aluminium alloy and the working fluid is pure ammonia. The effects on thermal performance of heat pipe inclination, cooling methods and heat source number and distribution mode are analyzed.The results are obtained in terms of axial temperature distribution, axial temperature difference, heat transfer capacity, total heat resistance, equivalent heat transfer coefficients of evaporator section and condenser section, etc.Experimental results indicate that firstly thermal characteristic of heat pipe with bottom-heating mode is much better than that with above-heating mode. With the same amount of heat input at the evaporator section, the working temperature and axial temperature difference are much lower for bottom-heating mode heat pipe. At the water cooling mode, the equivalent heat transfer coefficients of evaporator and condenser section with bottom-heating vertical mode are respectively the 1.5 and 2.5 times than that of horizontal mode. The total thermal resistances of heat pipe at above-heating mode, horizontal, bottom-heating mode are decreased with the order of ten.Secondly, heat transfer capacity can be greatly enhanced with water cooling compared with air natural convection cooling. For vertical orientation with bottom-heating mode and horizontal orientation, the heat transfer capacity with cooling water are respectively the 5.9 times and 1.2 times than that with air natural convection cooling.Thirdly, heat source amounts have less influence on the heat transfer capacity compared with the cooling modes. The heat transfer capacity unnecessarily can be enhanced with the addition of heat sources. It also depends on heat pipe orientation and heat sources distribution mode. To horizontal orientation heat pipe with double heat sources, the end-middle distribution mode is much better than end-end distribution mode because the heat transfer capacity of the former increase by 31.5% while the latter decrease by 25.8% compared with that under single heat source at air cooling mode. To vertical orientation heat pipe with double heat sources, the maximum heat transfer capacity of end-middle distribution mode and end-end distribution mode respectively increase by 14.3% and 5.2% than that with single heat source at air cooling mode.In addition, the flow performance of this kind of axial grooved heat pipe is also involved. At water cooling mode, the vapor and liquid pressure drop is not more than 1Pa, indicating excellent axial temperature uniformity.