Numerical modelling of sample–furnace thermal lag in dynamic mechanical analyser

Abstract

Due to dynamic nature of processes taking place during the experiment (chemical reaction and physical processes, heat flow, gas flow, etc.) the results obtained by thermal methods may considerably depend on the condi- tions used during the experiment. Therefore, whenever the results of thermal analysis are reported, the experimental conditions used should be stated. In this paper we have studied the heat transfer from the furnace to the sample and through the sample during dynamic mechanical analysis measurements. Numerical modelling of the heat transfer was done using an own computer program based on the heat conduction equation, solved numerically applying the finite difference methods. The calculated values of the thermal lag between the furnace and the sample were compared with the values experimentally determined on samples of a com- posite polymeric energetic material (double-base rocket propellant). Also, the temperature distribution within the sample as a function of the heating rate was analysed using the same numerical model. It was found out that using this model and temperature dependent heat transfer coefficient, experimentally obtained values of the thermal lag between the furnace and the sample can be satisfactory described. It was also shown that even at slow heating rates, such is, e.g. 2 C min -1 , the thermal lag between the furnace and the sample can reach several degrees, while the thermal gradient within 3-mm thick rectangular sample can reach 0.4 C.