Research On Thermal Resistance Control Based On Semiconductor Thermoelectric Effect

Thermal resistance is a physical quantity that objects have a blocking effect on the heat transfer.The definition of thermal resistance is similar to that of electrical resistance.It is the ratio of the temperature difference on both sides of the thermal resistance to the heat flow through,and it is reciprocal to the heat transfer coefficient.Heat transfer can be enhanced by reducing heat resistance and weakened by increasing thermal resistance.Thus,the control of variable thermal resistance（VTR）is particularly important in practical applications,widely used in the temperature control,buildings,precision instruments,etc.The semiconductor thermoelectric effect mainly includes the Peltier effect and Seebeck effect,which can realize the mutual conversion between heat and electric.Variable thermal resistance is adjusted by controlling the input heat flow to achieving different thermal resistance.Compared with other forms of thermoelectric resistance,the variable thermal resistance based on thermoelectric effects has the advantages of small size,no mechanical structure,simple control and higher precision.In this paper,the regulation of variable thermal resistance based on semiconductor thermoelectric effect is studied theoretically and experimentally,and a balance compensation method for measuring thermal resistance is proposed and applied.The main research contents are as follows:Firstly,the thermal resistance network model of TE device is established theoretically,and the heat transfer of two thermoelectric effects of TE device is analyzed.Based on the thermoelectric effect,the VTR of self-powered and the VTR of extra-powered are proposed.The effects of the internal resistance Ri,the figure of merit Z,the temperature difference and the input heat flow P on the equivalent thermogenic resistance are studied.The VTR based on self-powered and extra-powered is related to the average temperature,the semiconductor material and physical size,which is increased with extra resistance and current.The vary of environmental temperature has no an obvious effect on VTR.The direction of VTR based on thermoelectric effect is given theoretically.To verify the VTR based on the thermoelectric effect,an equipment of researching the thermal characteristic of VTR is designed built.In the equipment,a double-plate heater is used to supply a constant heat flow and a TEC is used to achieve a variable temperature condition,which simulates practical working environment to obtain a regulation of VTR.The experimental results show that TEC-12706 has an obvious increasing thermal resistance when the extra resistance changing between0 and 20Ω.The scope of the VTR of self-powered is 2.15-3.8 K/W,the net value is 0.65.With the ambient temperature changing,the value of VTR is not an obvious variation.The curve of VTR of extra-powered is a linear and has a great influence on the input heat flow.According to the VTR characteristics and the principle of the steady-state method to measure thermal resistance,a balance compensation method is proposed to measure the thermal resistance.The VTR is used as the compensation unit.By controlling the VTR,the compensating side and the tested side can reach a symmetrical thermal balance state.Then the equivalent thermal resistance of the compensation unit is the thermal resistance of the tested object,and the thermal conductivity of the tested object can be obtained indirectly.In the experiment,the temperature difference sensor is installed to detect the heat balance state of the system.By controlling the input current or external resistance value of the variable thermal resistance,the signals of the two temperature difference sensors are equal.Fourier’s law can be obtained and the equivalent thermal resistance is equal to the tested thermal resistance when the system reaches a stable symmetric thermal equilibrium state.The balance compensation method is used to test the thermal resistance.It is necessary to obtain the fitting relationship between the equivalent thermal resistance R_effand the input current I or input resistance R_Lthrough test experiments.In the experiment,the thermal resistance of four plexiglass samples with different thicknesses was measured by the balance compensation method.After conversion,the average thermal conductivity of the four kinds of plexiglass was 0.24W/m·K,and the value referred to other literatures was 0.2W/m·K.The thermal conductivity of 95 alumina ceramics is28.7W/m·K in the experiment,and 22W/m·K in reference to other literature.The analysis error may be due to the small theoretical temperature difference due to the measured heat dissipation,which leads to the thermal conductivity obtained in the experiment slightly higher than the value in the literature,and the mechanical error caused by the system’s failure to reach the theoretical equilibrium state.The experimental error differs little from the literature value,and the obtained data are valid,which can confirm the feasibility of the balance compensation method for measuring thermal resistance.Based on the study of the thermoelectric effect of semiconductor thermal resistance,the balance compensation method is proposed to measure the thermal resistance.The method is demonstrated to be correct and feasible by the actual measurement.It is instructive to apply the balance compensation method in the field of thermal resistance measurement.