Accurate measurement of thermal conductivity of micro-quantity liquids by dielectric transient current method

The thermal conductivity of liquids is of a great significant parameter for engineering applications that require the use of liquids to enhance heat transfer. Although a number of experimental methods for measuring thermal conductivity of liquids have been reported, many of these methods have limitations in principle or accuracy for small amounts of liquids, particularly for some nanofluids with low thermal conductivity or high electrical conductivity. This paper presents a novel method for measuring thermal conductivity of micro-quantity liquid based on the modified thermal pulse method. The main principle of the measurement is based on fitting the changing characteristics of the thermal response current of a thin dielectric film thermally coupled to the tested liquid. The paper analyses the factors affecting the measurement range and accuracy of the technique through numerical simulations and experiments. The feasibilities and uncertainties of the proposed technique are discussed in relation to six typical samples including pure water, insulating oil and conductive nanofluids. The experimental results show that the method for testing the thermal conductivity of liquids has the advantages of low measuring time down to 10 ms, low fluid usage down to 60 nL, wide measurement range from 0.01 to 10 W/(m center dot K), good sample compatibility and high accuracy. It should be noted that the method is highly dependent on the thermal conductivity and thickness of the dielectric film, which limits the measurement range of the method.