The Transient Model Of The Temperature-type Radial Heat Pipe And Experimental Research On Isothermal Characteristics

Isothermal is one of the important characteristics of the heat pipe, and theisothermal environment is important in engineering applications. A constanttemperature environment is necessary for calibration of temperature measuringdevices or the reproduction of Temperature Scales.In the area of semiconductormaterial growth, isothermal environment has a decisive influence on the quality ofmaterial growth. In the field of chemical industry, in order to prevent dew pointcorrosion need to control the wall temperature of the heat exchanger. There are manyways to create the isothermal environments, many scholars arouse great interest on thecombination of the isothermal features of the heat pipe and other areas.A radial heat pipe consists of two concentric pipes of different diameters attachedto each other by means of end caps, which create an annular vapor space between thetwo pipes. The radial heat pipe has several new features due to the new structure, suchas isothermal, high transmission performance and high heat transfer limit. Radial heatpipe has more advantages over axial heat pipe in aspects of isothermal. Because thegood performance in isothermal characteristics, radial heat pipe is applied to thegrowth of semiconductor material，standard blackbody, and temperature calibrationand soon. However, the radial heat pipes are more effective than conventional heatpipes and can be used in many applications including energy conversion systems,cooling of electronic equipments, air conditioning devices, heat recovery systems,furnace applications, high performance space applications, temperature and humiditycontrol, etc.This paper presents experimentally and theoretical investigation of the radial heatpipe behaviors in transient regimes and isothermal characteristics.First, the structure and characteristics of the Two-Phase Closed Thermosyphonwith working trap are described. A mathematical model to calculate thenon-steady-state startup process of the room temperature heat pipe is presented. Themodel is based on the special structure and use conditions of the room temperatureheat pipe. The steam temperature in tube only changes over time. This changecorrelation is calculated by numerical calculation and works as the temperatureboundary condition of the measurement trap. The temperature, velocity and pressuredistribution in the working trap are then solved by FLUENT. The main impact ofambient air to the thermometer well takes place at the orifice. Temperature is uniformat other locations. The comparison of the calculations and experimental date shows good agreement, and the maximum deviation is3.7K when the startup time is100s.And，simulation and experiments have proved that water fluid filling volume has littleeffect to the start-up performance of the heat pipe.Secondly, a simple, rapid mathematical model to calculate the non-steady-statestartup process of the radial heat pipe is presented in this paper. The model is based onthe special structure and using conditions of the radial heat pipe, the vaportemperature in heat pipe only changes over time. The startup performance of the heatpipe with variation input heat flux and the filling rate is analyzed. The results manifestthat the filling rate increased will reduce the maximum operating temperature of theheat pipe and shorten the startup time of the heat pipe. With the increase of input heatflux, the operating temperature increases and the time to reach the steady state of theheat pipe is added. The total thermal resistance of heat pipe decreases with theincrease of the input heat flux and filling rate. In addition, a condensation heat transfermodel is presented, the liquid film thickness and the local heat transfer coefficient ofthe inner wall surface is calculated.Finally, this paper presents experimentally investigation of the radial heat pipebehaviors in isothermal characteristics. In this paper, the effect of two parameters:different control temperature, the working fluid filling ratios were investigatedexperimentally. The results show that radial heat pipe not only has good isothermalperformance but also has good stability of the temperature. Moreover，the Radial heatpipe has a damping effect on the temperature fluctuations. In addition, theexperimental conclusions may provide reliable reference to the design of application.