Measurement of thermal conductivity of fluid by unsteady hot wire method

非定常 熱線法 에 의한 流體 의 熱傳達率 測定

A modified technique of the transient hot wire method to measure the thermal conductivity of fluid has been described in this paper. The thermal conductivity of fluid can be obtained by acquiring wire temperature as a function of time. Multiplication of the inverse slope of the temperature versus logarithm of time by an instrumental constant gives the thermal conductivity. The constant voltage was applied to Wheatstone bridge circuit. The wire temperature can be measured as a function of time precisely with the aid of the data acquisition system composed of a microprocessor and an analog-digital converter. The thermal conductivity of the electrically conducting fluid has been measured with the insulated hot wire coated by electrically non-conducting material. The effect of the coated insulation layer on the thermal conductivity has been examined, in which it is confirmed that the thermal conductivity of electrically conducting liquid can be determined by the transient coated hot wire method. Thermal conductivities of methanol, carbontetrachrolide, Freon-22 and glycerin have been measured at room temperature in the pressure from 0.1MPa to 35.1MPa. The experiment has been performed to compare the data from the bare and the coated wires, and the results are satisfactory.

본 연구에서는 고정밀 아날로그-디지탈 변환기와 마이크로 프로세서(micropr- ocessor) Intel 8085를 사용하여 비정상 아날로그(analog)신호를 왜곡이 없이 디지탈 량으로 직접 변환하여 자료처리하였다. 또한 비정상 열선법은 열선에 전류를 가하여 열선이 열원이며 동시에 온도계의 두 가지 역할을 하므로, 전기전도성이 있는 액체는 적합하지 못한 단점이 있다. 이를 해결하기 위하여 열선에 얇은 절록피복층을 입혀 전기전도성 액체의 열전도율을 측정할 수 있는 가능성에 대한 연구를 시도하였다.