Influence of thermal and flow conditions on the thermal stresses distribution in the evaporator tubes

Abstract

In the article are presented results of thermal and flow numerical analysis of the working conditions of three smooth waterwall tubes, connected by fins, which are heated with different heat fluxes. The analysis is carried out using a numerical model, which allows determining the distribution of the temperature of working fluid flowing through waterwall tubes and distribution of the temperature in cross-section of these tubes. The temperature is calculated in every finite element of fluid or tube in every time step depending on current thermophysical parameters of the fluid and metal from which were made the tubes and fins. On the base of the temperature distribution obtained with the use of the numerical algorithm, it is possible to determine the thermal stress distribution in tubes and fins, which are connecting them and determine where the maximum values of the thermal stresses occur. The analysis for three neighboring waterwall tubes allows determining the stress differences in tubes and fins, in the case when the external tubes are heated with lower heat flux and the internal tube is heated with higher heat flux – this is the case that corresponds to the thermal conditions occurring in the supercritical combustion chamber wall.