Elimination of the radiant component of measured liquid thermal conductivities

Experimental determination of the thermal conductivity of liquids requires to eliminate reliably thermal radiation heat transfer. Using an approximate calculation method such eliminations have been done on several liquids in a plane layer with a steady-state heat transfer by simultaneous conduction and radiation. The method, the admissibility of simplifications, and the results are discussed. It is demonstrated that the knowledge of the optical properties of the liquid is very important, especially that of the IR-absorption spectrum. As the quantitative accuracy of available spectra is not sufficient, such spectra have to be determined particularly. The calculation method has been used to eliminate thermal radiation from effective thermal conductivities measured on a liquid within several layers of different thickness, where convection heat transfer was not present. The resulting “pure” thermal conductivities are independent of layer thickness. Thus the validity of the calculation method is verified.