Heat transfer in a conical cavity calorimeter for measuring thermal power of a point focus concentrator

A theoretical study of the heat transfer process that takes place in a special calorimeter of conical cavity named CAVICAL is presented. This instrument is used to measure the thermal power of a point focus solar concentrator system named DEFRAC, developed at the Center for Energy Research of the National University of Mexico. The DEFRAC concentrator has a power of 1.3 kWth and a very fine optical system. The calorimeter has a cavity opening of 8.24 cm2. A detailed heat transfer study was done using FLUENT code. The heat transfer processes taken into account for the analysis were the radiative energy absorbed by the inner cavity wall, the energy transfer from the outer cavity wall to the air by natural convection, the energy transferred by conduction through the inner metallic wall of the calorimeter, and by forced convection to the fluid in the cooling system. The calorimetric information gathered allowed determining the thermal power that the concentrator is able to capture. Temperature and velocity fields have been calculated for each of the thermal fluids considered inside of the calorimeter. The analysis gave thermal losses and measured the thermal efficiency of the device. The information generated is useful to further optimize the design of the calorimeter.