Numerical Simulation Of Thermophysical Properties Measurement Technology Based On Transient Hot-Wire Method

Transient hot-wire method is a commonly used method for measuring thermal physical properties, it has been applied in powder, liquid, composite, porous media, the high temperature thermal conductivity of non-transparent and translucent solid materials measurement. In consideration of the characteristics of the unsteady state measurements of the transient hot-wire method, error estimation is always a key problem for this testing technology. The use of numerical simulation for error analysis of thermal conductivity measurement is uncommon in this kind of technology. Based on numerical simulation, measurement error of transient hot-wire method for thermal conductivity and various factors influencing the transient hot-wire method for thermal conductivity measurement were analyzed.This paper discusses the principle, mathematical model and the classification of transient hot-wire measurement, and then use the Fluent software to make a numerical simulation to obtain temperature distribution filed and temperature of monitoring points. The simulation values of thermal conductivity can be calculated by theoretical formula, the thermal conductivity measurement errors can be obtained by the simulation value compared with the set value. According to the principles and assumptions of the transient hot-wire method, different sample sizes, hotline radius and hotline heat capacity were selected for simulation to get the relative error of the thermal conductivity with different parameters.The results show that the temperature field distribution of numerical simulation is consistent with theoretical analysis. When other parameters are certain, the measurement error increases with the decrease of the sample size, the increase of hot-wire radius and heat capacity of the hot-wire, and the transient hot-wire method is more suitable for measuring the material with small thermal conductivity. When the sample dimensions (w × b) is larger than 16.5mm × 16.5mm, using the method of transient hot-wire to measure the materials whose 1.5 w/(m·K)<λ< 2.0 w/(m·K) the measurement error of thermal conductivity between simulated value and set value are less than 0.5%.When the hotwire radius ro=0.001mm, the increment of the thermal conductivity measurement error is very small, was only 0.029%, almost no change with the change of hotwire heat capacity. When the hotwire radius is less than 0.006mm, if the thermal conductivity of the test specimen λ=0.1W/(m·K), the increment of the relative error is very small, almost the same, and can be ignored. Therefore, using the method of transient hotwire to measure the thermal conductivity of materials, sample should be selected with larger size, the smaller radius and smaller heat capacity of hotwire to improve the accuracy of measurement. In this paper, the research for transient hot-wire testing technology in thermal and physical properties of error estimate provides the basic theoretical basis and reference.