Reconsideration of the transient line heat-source technique. Analytical discussion on the influence of natural convection.

In this paper, weak natural convection effects in the transient hot wire method of liquid thermal conductivity measurement are analytically investigated. Precise numerical calculations are performed using the FDM, concerning the slow natural convection liquid flow around a single thin hot wire and the distribution of the modified temperature term due to the flow. Then, the time dependencies of the apparent thermal conductivity, including the natural convection effects, are shown for various measuring conditions. The error in measurement are also shown for the case where two hot wires, having different lengths, are set in the Wheatstone bridge circuit to decrease the edge effects. It is shown, as a result, that slight natural convection effects appear, even during short periods of measurement, where the effects on accuracy had been considered negligible.