Development of a New Apparatus for Measuring Thermal Conductivities of Fluid Mixtures and Biological Fluids

该项目是为了开发一种测量气体和液体导热系数的新仪器而进行的。该装置的原理是基于理论上建立的等温球体稳定自由对流换热特性。设计了一种非常简单的装置，以珠状热敏电阻作为加热球。实验结果表明：(1)通过引入热敏电阻的有效直径和三个仪器常数，可以准确地估计热敏电阻与理想球体形状不同、热敏电阻中非均匀发热引起的温度分布不均匀以及导线的热损失所引起的各种影响。(2)对于液体和气体，样品容器的内径必须分别大于热敏电阻直径的30倍和40倍。(3)对空气、水、乙醇、甲醇和制冷剂R113的测量，本方法的误差估计在2%以内。(4)对水、乙醇、水-甲醇和R113-油三种二元液体混合物的导热系数的测量表明，该装置对于基础研究液体混合物的导热特性是有效的。

This project was performed to develop a new apparatus for measuring thermal conductivities of gases and liquids. The principle of the apparatus is based on the theoretically established heat-transfer-characteristics for steady free convection from an isothermal sphere.A very simple apparatus was devised with a bead thermistor as the heated sphere. From the tests with the apparatus, following results were obtained:(1) Various effects caused by the difference in shape between the thermistor and an ideal sphere, nonuniform temperature distribution due to heterogeneous heat generation in the thermistor and heat loss from lead wires can be accurately estimated by introducing an effective diameter of the thermistor and three apparatus constants.(2) Inner diameter of sample vessel must be larger than about 30 and 40 times of thermistor diameter for liquids and gases, respectively.(3) Inaccuracy of the present method is estimated to be within 2% from the measurements for air, water, ethanol, methanol and refrigerant R113, when the other physical properties are known.(4) The measurements of thermal conductivities of binery liquid mixtures of waterethanol, water-methanol and R113-oil show that this apparatus is effective to the basic study for characteristics of thermal conductivities of fluid mixtures.The measurement for biological fluids has been undertaken.