The influences of major geometrical parameters on detailed radiative performance of a multi-tubular solar thermochemical reactor

The surfaces of a cavity receiver in solar reactors may receive non-uniform solar fluxes. As a result, the receiver is prone to thermal stresses, which can negatively affect its performance and durability. The current study investigates the distribution of solar flux in a 50 kW solar reactor (designed for methane dissociation) containing seven graphite tubes by using Monte Carlo ray-tracing (MCRT) method. In this work, the complex radiation path from the sun to the parabolic dish and then to the solar receiver, as well as the non-uniformity of the radiation flux inside the reactor, is taken into consideration. This study, also investigates the influences of three important parameters (tolerance between the locations of reactor and focal point, absorptivity of receiver inside walls, and receiver configuration) on the performance of the solar reactor. The results reveal that a horizontal-cylindrical cavity receiver can results in the greatest absorbed power and most uniform solar flux distribution, as compared to a vertical-cylindrical, a cubic, and a spherical receiver. It is also observed that the total absorbed power and the uniformity of solar flux distribution increase with increasing the reflectivity of the inside walls. Furthermore, the results indicate that the reactor should not be placed more than 5 cm away from the focal point of the parabolic concentrator; otherwise, it experiences a substantial performance drop. The paper discusses in detail the reasoning for the mentioned observations.