ZHANG+Xin-yi　FENG+Shou－ling

【Abstract】With the development of measurement technology，the basics and importance of thermophysical measurements are becoming more and more prominent.This article is the review of the development of thermophysical measurement technology in recent years.

【Key words】Thermophysical properties；Measurement

The thermophysical properties of the material are the physical properties related to the heat transfer process and the increase in heat content of the object directly，mainly include specific heat，thermal conductivity，thermal diffusivity，dissolution heat，thermal expansion coefficient，viscosity，surface emissivity，absorption rate，melting point， boiling point and so on.The thermophysical properties of material are related to the chemical properties，microstructure，porosity，humidity，pre-heat treatment，temperature and so on.Since the thermophysical relationship is related to lots of interrelated factors，the experiment is the only source to determine these thermophysical properties.

1 Periodic heat flow method

The periodic heat flow method was proposed by Angstrom for the first time in 1861.The temperature of the sample at any point in the sample is changed by the same period，and the thermal diffusivity is determined by measuring the amplitude and phase relationship of the two points in the sample.The periodic heat flow method has the advantages of short test time and simple calculation，and its thermal diffusivity measurement error is within ±5%.However，the method requires a sinusoidal or cosine wave for the propagation of the temperature in the sample，and it is difficult to obtain a more standard sine or cosine temperature wave in the experiment.

Zhou et al.[1-2]measurement of thermophysical properties of metallic materials by periodic heat flow method. Wang et al.[3]calculates the thermal conductivity based on the amplitude attenuation and phase lag generated when the signal propagates within the sample.Wang et al.[4] achieve the test system data acquisition and processing of the visualization function.

2 Laser pulse method

Laser pulse method is the application of a circular thin sample，one side with a pulse-shaped heater， according to the other side of the temperature changes with time to determine the thermal diffusivity，and then calculate the thermal conductivity.Laser pulse method has the advantages of many types of test materials，wide temperature range，fast speed，strong function，small sample size，simple shape and so on，but the actual process caused by heat loss effect，non-uniform heating effect， limited pulse time effect and so on， these effects caused by the error will be far more than the measurement error.

Wang P and other[5]overcome the shortcomings of two beam adjustment and data processing links，big error.Since then they have made by laser photoacoustic technique to measure the piezoelectric material defects principles and experimental methods[6]，and experimental method using the principle of laser photoacoustic backing material excitation technique measuring thermal diffusivity of the film[7].

3 Hot-wire method and transient hot-strip method

3.1 Hot-wire method

Hot-wire method is a uniform thin metal wire on the sample to be tested，the test is applied in the current hotline，to produce heat and radially conducted in a sample.Measure and record the temperature rise of the hotline itself with time or from the hotline at a distance from time to time changes in the temperature， and then calculate the thermal dissipation of the test sample according to the heat transfer mathematical model and the temperature change of the theoretical formula.The advantage is that it can measure the thermal diffusivity of solids，powders and liquids.The material to be measured may be isotropic or anisotropic； both homogeneous and nonhomogeneous.The disadvantage is that the measurement error is relatively large，and need to meet certain conditions： the measured medium infinite and uniform initial temperature；constant heating power；hotline infinite length infinity and so on.

Zhang L L and other[8]used hotline method to determine the thermal conductivity of wheat and rice.Luo X Q et al.[9]realize the thermal diffusion coefficient and thermal conductivity of dry pine board.Huang H J and other[10]tests thermal conductivity and thermal diffusion coefficient of two kinds of imidazole type ionic liquid in the range of 293 ～ 373 K. Lee J et al.[11]investigated the effects of particle size， particle and fluid type，temperature and volume concentration on thermal conductivity in ethylene glycol/Al2O3 nanofluids. Zhang T and other[12]non-sensitive contact resistance measurement of the volume of heat capacity， the measurement of porous insulating material sponge moisture and ice content，and will be extended to the porous material containing material before and after the volume of heat capacity changes in the determination of material quality.

3.2 Transient hot-strip method

Transient hot-strip method，proposed by Gustafsson[17-18]in the 1970s， has been widely used in the measurement of thermal conductivity of liquids，loose materials，porous media and non-metallic solid materials. After the tropical surface covered with a thin layer of insulation，it can also be used to measure metal materials.The method is applicable to a wide range，high precision and easy to implement.Hot-strip method is to held a very thin metal band in the middle of the sample to be tested or placed in the liquid，from a moment to a constant current heating metal belt，measuring and recording the tropical surface temperature response curve，and then the estimated thermal conductivity of the material.

Yu F[19]established an experimental device for measuring the thermal conductivity of nonconductive solid materials and loose materials.Wei G[20]and other simplified physical model reasonablely，analyzed systematically effects of the finite size of the sample on the thermal conductivity measurement accuracy，and studied for heating power of the hot-strip heating method.Luo[21]and other studied the minimum thickness of the material in the hot-strip method.

4 Plane heat source method

The plane heat source method is based on the law of the change of the temperature of the semi-infinite objects under the constant current boundary condition to measure the thermal diffusivity of the nonmetallic material，and the thermal conductivity of the material is measured simultaneously.The main advantages are that the experimental device is simple，the test cycle is short，and the thermal parameters such as thermal diffusivity，thermal conductivity and specific heat capacity are measured at the same time.But in this method，experimental data processing is complex and test accuracy improve hardly.

Wang Q[22]proposed a plane thermal source method that can simultaneously measure the thermal conductivity，thermal diffusivity and simultaneous estimation of the thermal resistance of the contact. Tian B[23] study on the thermal conductivity of graphite under different expansion conditions by plane heat source method.Zhou[24]developed a thermophysical measuring device for low thermal conductivity materials to determine the thermal conductivity and thermal diffusivity of eight refractory and ceramic fibers.Zhang H[25]and other measured thermal conductivity of the film.

5 Conclusion

Thermophysical properties are the basic properties of thermal research.With the continuous development of science in various fields and the continuous advancement of interdisciplinary field，thermophysical measurement technology is constantly improving.I believe that more new technical means will get more and better applications in the future.

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[責任編輯：田吉捷]