A Non-Steady-State Method of Measuring the Thermal Conductivity of Transparent Liquids

A plane source method has been developed for non-steady-state measurements of the thermal conductivity of transparent liquids. The plane source is realized by using an electrically heated metal foil, suspended in the liquid. The temperature distribution is described by using the concept of instantaneous heat sources giving a simple expression of the optical path, which is recorded with wave-front-shearing interferometry. The thermal diffusivity is determined simply by measuring the positions of the fringes, locating the points where the gradient of the optical path is constant and knowing the times between two subsequent exposures. The accuracy of the method, which is an absolute one, is demonstrated. The average deviation from the recommended values of the thermal conductivity was found to be 0.37%.