Cavity receiver in solar tower concentrator usually experiences highly intense radiation. Due to asymmetric concentration of solar rays, non-uniform heat flux distribution occurs on the different parts of the cavity receiver. This non-uniform distribution leads to uneven thermal expansion and stresses in receiver, which affects the reliable operation and reduces life time of receiver parts. Therefore, it is necessary to reduce the non-uniformity of solar flux on the surface of the absorber tubes and different parts of the solar reactor. The aim of this study was to focuses on the distributions of concatenated solar flux over graphite tubes of a 50kW solar reactor, which was previously designed for methane thermal dissociation at the focus of a solar furnace. In this study, the absorbed solar power on the different parts of the reactor is determined by Monte Carlo ray tracing method. Moreover, the effect of aperture size and the absorptivity of receiver parts on the net magnitude and distribution of absorbed power in reactor are investigated. The results prove that the 16cm aperture absorbs the maximum power and leads to even better solar flux distributions. Replacing the absorbing walls by the reflective walls will also result in more power absorbed by the tubes and better uniformity of flux distribution around the tubes.

Gasification technology is an important part of clean coal technology. Further development of this technology requires understanding the processes and interactions of gas and solid fuel particles injected into the gasifier. In this study, a numerical simulation of an entrained flow coal gasifier has been investigated using experimental operating conditions. The reactions and kinetic parameters of the gasification process have been extracted using coal gasification data obtained from similar published papers. Comparison of the simulation results with experimental data and two other similar studies confirm the accuracy of the developed model. The focus of this study is on the accuracy of the models presented for the devolatilization process and the effect of the oxidizer change from oxygen to air on the gasifier performance. Four devolatilization models including chemical percolation devolatilization, single rate, Kobayashi and constant rate models have been investigated. The predicted trends of species changes are similar in different devolatilization models but the amount of produced syngas is somewhat different depending on the accuracy of each model. The Kobayashi and constant rate models predict the devolatilization rate lower than the other two models. The results obtained from the chemical percolation devolatilization model are more consistent with the experimental data compared to the other models but require higher computational times. The use of air oxidizing agents reduces the concentration of produced syngas rather than oxygen and hence reduces the gasifier efficiency.