Study On Heat Transfer Performance And Dynamic Characteristics Of Rotating Heat Pipe

With the development of industrialization,the heat dissipation problem of rotating parts is becoming more and more prominent.Rotating heat pipe is a high performance heat transfer element driven by rotating centrifugal force.However,the research on rotating heat pipe is not enough at present,which limits its application in the field of heat dissipation.Therefore,it is of great significance to study the heat transfer performance of rotating heat pipe for promoting the application of rotating heat pipe.In this paper,an axial rotating heat pipe using water as a working medium was designed and manufactured,of which the inner surface is shape of cylinder.A rotating heat pipe test bench was set up,and the influences of rotating speed,liquid filling ratio,heating power and cooling temperature on the heat transfer performance of the heat pipe were obtained with the thermal resistance as the evaluation index.The ethanol rotating heat pipe was made as the control group,and the influence of working medium on the heat transfer performance and law was compared and analyzed.A visual experimental platform was designed to preliminarily explore the influence of rotating speed on the flow pattern of working medium.In this paper,the steady-state heat transfer performance and dynamic characteristics of heat pipes were studied.The dynamic characteristics include temperature fluctuation,start-up process and failure phenomenon.(1)Under the steady-state condition,the temperature of the evaporation section of the heat pipe is higher,followed by the temperature of the adiabatic section,and the temperature of the condensing section is lower.The temperature difference of the adiabatic section is smaller,which reflects the good temperature uniformity of the heat pipe.Under the same experimental conditions,the wall temperature of the ethanol heat pipe is higher than that of the water heat pipe,and the heat transfer performance is worse than that of the water heat pipe.The thermal resistance decreases monotonically with the increase of heating power and cooling temperature,and the influence on the condensing section are more obvious,while the thermal resistance of the evaporating section does not change significantly,the thermal resistance of the condensing section decreases gradually with the increase of heating power.The variation trend of heat pipe thermal resistance with rotating speed is different under different liquid filling ratios: When the liquid filling ratio is 26.1%,the thermal resistance of the heat pipe increases monotonically with the increase of the rotating speed.When the filling ratio is 65.3%,the thermal resistance decreases monotonously with the increase of the rotating speed.When the liquid filling ratio is39.2%,the monotonicity of thermal resistance with the change of rotating speed is related to the heating power,and the monotonicity increases at low power and the tendency increases first and then decreases at high power.The inert gas degrades the heat transfer performance of the heat pipe,and its influence is mainly concentrated in the condensing section With the increase of heating power and cooling temperature,the influence of inert gas on the performance of heat pipe is gradually weakened.(2)The temperature fluctuation of the heat pipe will occur under specific working conditions,especially when the speed is zero.At high heating power,the temperature fluctuation is periodical,and the fluctuation frequency increases with the increase of heating power.The phenomenon of temperature fluctuation is integral.At the same time,the peak of the temperature wave in the evaporation section corresponds to the trough of the adiabatic section and the condensation section.When the heat pipe rotates,it is more conducive for the heat pipe to start-up.During the process of heat pipe start-up,the temperature of the evaporation section changes greatly,while the temperature of the condensing section and the adiabatic section changes little.The starting phenomenon of ethanol heat pipe is obvious at zero rotation speed,but that of water heat pipe is not obvious.(3)The rotating heat pipe is easy to fail,that is,the temperature of the evaporation section of the heat pipe rises rapidly,and the heat pipe cannot work normally.The filling ratio has a great influence on the failure: The heat pipe failure is more likely to occur when the liquid filling ratio is 13.6%,and it is more likely to occur when the heating power is high and cooling temperature is low when the liquid filling ratio is 26.1%.No failure was found at 39.2% and 65.3% filling ratios.The influence of rotating speed on heat pipe failure is irreversible,irreversibility means that the failure still exists when the speed is adjusted to the original normal speed after failure.The influence of cooling temperature on heat pipe failure is hysteretic,when the heat pipe is rotating,the cooling temperature can be lowered to keep the lower limit of normal operating temperature lower than the cooling temperature that fails when the heat pipe is rotating at zero speed.High speed will inhibit heat pipe failure,for example,the ethanol heat pipe can work normally under the condition of low speed,but it is easy failure when the speed is about 770 RPM,increasing the speed can make the heat pipe return to the normal state.(4)Visualization experiments show that the rotating speed will affect the flow pattern of the liquid working fluid in the heat pipe.When the rotating speed is 659 RPM,the working fluid flow pattern belongs to the stratified flow stage,and when the rotating speed is 770 RPM and 841 RPM,it belongs to the partial annular flow stage,when the rotating speed is as high as 1080 RPM,it belongs to the annular flow stage.