Experimental Investigation of Thermal Contact Conductance in a Bundle of Flat Steel Bars

Abstract

The phenomenon of thermal contact conduction in two-phase (fluid-solid) media determines many technological processes. An example of such a process is heat treatment of steel bars, when a heated charge has a form of a packed bundle. In order to determine the optimal heating curve it is necessary to have knowledge about the intensity of transfer through contact areas of the bars. This phenomenon is quantified by the thermal contact conductance hct. The article describes the methodology of determining the hct coefficient for bundles of flat steel bars. The starting point for the analysis is the measurement of the effective thermal conductivity kef performed for 5 × 20 mm and 10 × 20 mm bars. Individual samples of the same bars differed in arrangement. The analytical investigation used the concept of an elementary cell. This approach consisted in analysing resistances for individual heat transfer types: conduction, contact conduction and radiation. Based on the performed calculations it has been established that the value of the hct coefficient for the analysed samples is within the range 128–472 W/(m2 K). Changes of the hct coefficient in the temperature range 25–700 °C can be described with a second degree polynomial. It has been established that hct assumes maximum values in the temperature range from 300 °C to 400 °C.