Research on Measurement Technology and Experiment of Thermophysical Properties of Phase Change Materials for Temperature Control
Supervisor:dai jing min xiao peng
With the development of science and technology,temperature control technology plays a very important role and has received widely attention,especially in the military field.For missiles used to attack targets,it is necessary for missiles to attack accurately without being detected.Therefore,surfaces of missiles are coated with electromagnetic wave absorbing material to prevent radar detection.During the missile flight,continuous friction with air will increase the surface temperature gradually.Thus,it is necessary to load temperature control components on the back of absorbing materials to keep the missile surface at a constant temperature so as to realize thermal infrared stealth.In the temperature control technology,phase change materials are widely used because of the advantages of stable phase change temperature range,high energy storage density and good chemical stability.Therefore,it is of great significance for the development of temperature control technology to study the phase change heat transfer characteristics and accurately measure the thermophysical properties of phase change materials.The research of temperature control components mainly includes the study of heat transfer process of internal phase change materials,as well as the measurement of thermophysical parameters such as thermal conductivity,phase change temperature and heat absorption.During the missile flight,the temperature control components may have different postures.The difference in the postures of the temperature control components will affect the heat transfer characteristics of internal phase change material.However,the research on the heat transfer of the temperature control components with different postures is currently very scarce.Besides,in order to test the performance of temperature control components,it is necessary to measure the thermophysical properties of temperature control components.Since the size of the temperature control component is large and the component is filled with solid-liquid phase change material,the methods and devices for measuring thermophysical properties of the component are also very scarce.Therefore,the theoretical and experimental research on the thermophysical properties of phase change temperature control materials has been carried out in this paper.The main research contents of this paper are as follows:(1)In view of the different positions of temperature control components after the missile is launched,a phase change heat transfer model of phase change material in a rectangular container with different inclination angles is established,and the phase change heat transfer characteristics of temperature control components with different inclination angles are analyzed.Considering the influence of contact thermal resistance on heat transfer during the heating process,the contact thermal resistance is corrected,so that the deviation between temperature monitoring points in simulation analysis and experimental temperature points is less than 7%.Furthermore,the non-linear relationship between energy storage time of phase change materials and inclination angles is revealed.Besides,in order to analyze the influencing factors of phase change heat transfer process,different levels of orthogonal test schemes are established.(2)Aiming at the thermophysical properties test of the temperature control components after missile launching,a method for measuring the thermal conductivity,phase change temperature and heat absorption of the temperature control component is proposed.Based on the basic principle of steady-state heat flow method,the thermal conductivity measurement method of temperature control component is established by calibrating the sensitivity coefficient of heat flow meter and contact thermal resistance between specimen and plates varied with temperature change,and the calculation model of thermal conductivity of phase change material in temperature control component is derived.Meanwhile,based on the calibration function of the calibration coefficient of the heat flow meter obtained by calibration experiment varied with temperature change,the calculation model of total heat absorption of phase change material in the temperature control component is established,and the judgment method of phase change temperature is provided.(3)In order to meet the requirements of thermophysical properties measurement of temperature control component products,a device for measuring thermal conductivity,phase change temperature and heat absorption of temperature control component product in a wide temperature range is developed.In this apparatus,two heating plates with the same structure are designed.The upper temperature limit of the cold plate is increased by using the convection and radiation heat dissipation method,which solves the problem of low temperature of the cold plate in steady-state heat flow method.Then,the thermal conductivity and the heat absorption of the temperature control component are measured.At the same time,according to selftuning results of PID parameters at different temperatures,a piecewise extremely constrained PID control method is proposed to reduce temperature overshoot.(4)Experiments are carried out with the thermophysical property measurement method and the designed apparatus proposed in this work,and the uncertainties of the testing results are analyzed.Through the test of the thermal conductivity of basic materials,the necessity of calibrating the sensitivity coefficients of the heat flow meter with temperature change in a wide temperature range is verified.Then,the thermophysical properties of n-docosane and erythritol in the container are measured,and the experimental results are compared and analyzed to verify the reliability of the method.Through the uncertainty analysis of thermophysical parameters for the phase change material in the container,the standard uncertainty of thermal conductivity test is better than 3.79%,the standard uncertainty of phase change temperature test is 0.3 °C,and the standard uncertainty of heat absorption test is 1.99%.