Experimental Research On Heat Transfer Performance Of Heat Pipe With Spiral Liquid Suction Core

Heat pipe has been applied to ventilation system for its superior thermal conductivity,isotherm and variability of heat flux.It can exchange indoor and outdoor air and achieve the purpose of preheating fresh air.Because of its high cost and complex manufacturing process,it has not been widely used.In this Paper,the horizontal and triangular heat pipes are designed with high thermal conductivity copper as pipes,copper spring as wick and water as working medium,and the performance of heat pipes is explored through experiments.Firstly,the isothermal and thermal conductivity of a horizontal heat pipe with a length of 300 mm,a diameter of 10 mm and a wall thickness of 1.5 mm at different wind speeds（1-8 m/s）and inclinations（0°,30°,60°,90°）were investigated.The results show that with the increase of wind speed and inclination,the isothermal and thermal conductivity of the heat pipe are enhanced.Compared with the way of increasing the wind speed,the inclination has a greater impact on the performance of heat pipe.Secondly,a 300 mm long copper spring with pitch of 1.5 mm and 0.75 mm was inserted into the horizontal heat pipe as the core,and a group of coreless horizontal heat pipes were set for comparison.Under the conditions of absolute pressure of 1×10^-1Pa、1×10^-2 Pa、1×10^-3 Pa、1×10^-4 Pa,the three heat pipes are filled with 30%,50%and 70%liquid respectively.The results show that the horizontal heat pipes with spiral core structure have better thermal conductivity and average temperature than those without core,and the horizontal heat pipes with pitch of 1.5 mm have lower heat transfer temperature difference and thermal resistance than those with pitch of 0.75 mm.The heat transfer and equivalent thermal conductivity are larger.When the vacuum degree is the same,the optimum filling rate of horizontal heat pipe is about 50%,too low or too high filling rate will lead to the decline of heat pipe performance.With the same filling rate,the improvement of vacuum will significantly optimize the thermal conductivity of horizontal heat pipe,making its thermal resistance smaller and equivalent thermal conductivity larger.Finally,this paper designs and manufactures a triangular loop heat pipe with no liquid storage device,no liquid reflux pipeline and interchangeable position of evaporation condensation section.The triangular heat pipe with circumference of 600 mm,diameter of10 mm and wall thickness of 1.5 mm was tested.The wick is a copper spring with 150 mm length and 1.5 mm pitch.When the absolute pressure in the tube is 1×10^-2 Pa and 1×10^-4 Pa,the heat pipe is filled with 30%and 50%liquid respectively.During the process of heating power increasing from 6 W to 33 W,the temperature change shows that with the increase of heating power,the heat transfer temperature difference,heat transfer capacity and equivalent thermal conductivity of the triangular heat pipe increase,and the thermal resistance decreases.In addition,the optimum filling rate range of the triangular heat pipe can be increased by increasing the vacuum degree.After exchanging the position of evaporation condensation section,the heat transfer performance is basically unchanged.