A numerical study on particle tracking and heat transfer enhancement in a solar cavity receiver

The thermochemical dissociation of natural gas into hydrogen and carbon involves the presence of solid phase carbon particles. In addition to the produced carbon, carbon particles can be seeded to the process as a catalyst which act both as a heat transfer enhancing medium and nucleation site for the dissociation reaction. However, presence of discrete phase particles imposes various challenges such as deposition on solar reactor walls and windows, and clogging of the exhaust. Meticulous reactor-receiver design optimization is therefore required and is presented in this study. The Discrete Phase Model (DPM) was implemented in a numerical CFD model to track injected carbon particles in a Lagrangian framework. Validation of the model was done with respect to available experimental data and showed similar deposition phenomena on the reactor window. A parametric design study was performed taking into account flow rates, particle size, particle loading and receiver geometry. Use of a finer particle size distribution demonstrated the ability of the flow to entrain more particles to the exhaust and reduce deposition on the bottom wall of the cavity. Three design iterations on an existing 1 kW solar cavity receiver were proposed, depicting an increase of at least 6.5% on the outlet gas temperature and 4% on the overall average gas temperature within the receiver. Results of this study highlighted the importance of flow configuration, flow parameters and particle size on the deposition and heat transfer inside solar cavity receivers. Outcome of this study can serve as a reference for solar reactor design involving presence of particulate media.