X. S. Ge

A convenient method of measuring the thermal conductivity of biological tissue

The basic principle of the thermal conductivity probe is described. Thin probes were developed based on this principle, with a reproducibility of 5.3% and relative error less than 6.0%. Each measurement can be completed in 90 s and the temperature increase can be controlled within 2 degrees C. Using the probes, the thermal conductivities of pig fat, meat, liver, kidney and live and dead snake head were measured and it was found that water content plays an important role in influencing the magnitude of the thermal conductivity of biological tissues. The probe can be used over a temperature range from -40 to 150 degrees C.

Effectiveness of the heat conduction reinforcement of particle filled composites

Based on a randomly mixed model, the effective thermal conductivity of particle filled composites is studied numerically with respect to the volume fraction of the particles and the ratio of the thermal conductivity of the particle to that of the matrix. Compared with experimental data and the estimations from other models, the proposed model seems to be well suited for predicting thermal conductivity. Some factors relative to heat conduction reinforcement are discussed. Improvement in the heat conduction performance will be limited if the thermal conductivity of the particle alone is concerned. The volume fraction of the particle should reach the critical value in order to significantly improve the effective thermal conductivity, which is in agreement with the percolation theory. Another crucial factor is the effective formation of particle chains for heat conduction reinforcement.

Randomly mixed model for predicting the effective thermal conductivity of moist porous media

A randomly mixed model is developed for the prediction of the effective thermal conductivity of a multi-phase system. The proposed model is based on the assumption that the smallest part of the phases is a cube, and all the cubes are randomly dispersed in the space. The effective thermal conductivity therefore can be found numerically from thermal conductivities and volume fractions of the components, using the principle of heat conduction in anisotropic media. The prediction does not depend upon empirical parameters and the algorithm is easy to perform in a personal computer. The validation of the proposed model is tested by several types of moist porous media with various porosities and degrees of saturation. Compared with the experimental data of the soils and building materials, the proposed model can give a fine prediction of the moist porous media for porosity less than 0.6. Finally, the deviations between the predicted and experimental results for high porosity are also analysed.

An improved hot probe for measuring thermal conductivity of liquids

To measure the thermal conductivity of liquids using a hot probe, it is necessary to minimize the disturbance caused by natural convection. With this in mind, two options are investigated in this work. One is to shorten the measurement duration; the other is to keep the power input (or the temperature rise of the probe) as low as possible. The measurement duration is studied using the three-ply composite heat transfer model, which includes the heater, the guard body and the measured sample. A resistance bridge is introduced to improve the measurement precision and the maximum temperature rise of the probe can be kept within 1 °C. According to the experimental results on liquid samples, the measurement time interval (MTI) is about 5–20 s, and the measurement uncertainty is about 3%. The thermal conductivities of dimethyl sulfoxide (DMSO) and its aqueous solutions have been determined using the proposed technique, and may not have been reported previously in the literature.

The measurement of thermal conductivities of solid fruits and vegetables

A thermal conductivity probe consisting of a heating cell, a thermocouple and a guard tube over the heating cell was developed and is described here. Analyses demonstrate that the guard tube acts as a thermal contact resistance. This resistance does not influence measurements of thermal conductivity significantly, but it must be considered in an accurate measurement of thermal diffusivity, especially when there is a gap between the heater and the guard tube. Calibration of the probe with glycerine in this work exhibits an accuracy of 1.4% for thermal conductivity measurements. The probe was used to measure the thermal conductivities of some solid fruits and vegetables. The sizes of both specimen and probe were analysed and their influences controlled to be under 1.0%. Each measurement was completed within two minutes and the temperature rise was less than under 6 °C. The water content of fruits and vegetables was found to be the dominant factor in determining their thermal conductivities. An empirical relationship between thermal conductivity and mass density is proposed based on the measurements. It is shown that this relation gives a deviation from experimental data of only 11%.

An improvement on the prediction of optical constants and radiative properties by introducing an expression for the damping frequency in Drude model

A method for predicting the optical constants and the radiative properties of metals and heat mirror films, by introducing an expression for the damping frequency in the Drude model, is described. The directional emissivity of aluminum predicted by this method agrees well with the classical experimental values given by Schmidt and Eckert. The prediction of the normal emissivity of indium–tin–oxide (ITO) heat mirror films is in agreement with our measured results. The directional emissivity of copper predicted using this method is reported. The calculated result of the spectrum normal emissivity of copper at 4 μm and 20°C is also given, which supports the measured result. The values for the directional emissivity of aluminum calculated by using various methods based on the Hagen–Rubens relation are reported, and the values do not agree with the experimental results.

Effective thermal conductivity of two-scale porous media

A two-scale model is developed for predicting the effective thermal conductivity of porous media. To account for the effects of the microstructure on the macroscopic conductivity, predictions from the one- and two-scale models are comparatively investigated. The results show that the microstructure can strongly affect the macroscopic conductivity, and the degree of the effects is related to the total porosity and the conductivity ratio of the components.

A Method of Determining the Thermophysical Properties and Calorific Intensity of the Organ or Tissue of a Living Body

A new method was developed to determine simultaneously the thermal conductivity, thermal diffusivity, specific heat, and calorific intensity of the organ or tissue of a living body either in vivo or in vitro with a thin hot probe. By using the method, the thermophysical properties and calorific intensities of a human palm and in vivo liver and a kidney, heart, brain, and foreleg and hindleg muscles of an anesthetized canine were measured. It is concluded that there are no significant differences in the thermophysical properties of organ or tissue of a living body either in vivo or in vitro. The measured thermophysical properties are in good agreement with those reported in the literature.

Simultaneous measurement of thermal conductivity and thermal diffusivity of solids by the parallel-wire method

An improved parallel-wire technique for simultaneous measurement of thermal conductivity and thermal diffusivity is presented. The deviation between experimental results and recommended (or another authors) values is less than 5% for fused quartz and refractory brick.

A method for measuring thermal radiation properties of semi-transparent materials

Films that are semi-transparent in the infrared are extensively used in solar energy applications and agriculture. For analysing the performance of such systems, it is important to know the thermal radiation properties of these films. Whereas transmissivity can be determined easily, measurement of emissivity poses a problem. The intensity usually consists of radiation emitted from the film and transmitted background radiation. In this paper a method for determining the hemispherical total emittance, reflectance and transmittance of semi-transparent films simultaneously is presented. It has the distinctive features of simplicity and high precision. The results for some transparent films are presented.