Computational fluid dynamics and particle image velocimetry characterization of a solar cyclone reactor

Solar thermal cracking of methane produces two valuable products, hydrogen gas and solid carbon, both of which can be used as a fuel and as a commodity. During the course of this two-phase phenomenon, carbon particles tend to deposit on the solar reactor window, wall, and exit. When they accumulate at the reactor exit, the agglomeration of these particles completely blocks the exit. This problem has been the major issue preventing solar cracking reactors from running continuously. To address this problem, a cyclone solar reactor was designed to enhance the residence time and allow carbon particles to rotate in the reactor instead of moving towards the exit inlarge particle groups together. A prototype reactor was manufactured to test the concept, to better understand and explain the flow dynamics inside the solar cyclone reactor and to analyze the flow via particle image velocimetry (PIV). Advanced measurement and computational techniques were applied to build the prototype reactor. Computational fluid dynamics (CFD) analysis employing discrete phase model (DPM) was used to predict the particle transport phenomenadel (DPM), whereas PIV was applied for the experimental part of the work. To understand the flow evolution along the vortex line, several images in the axial direction along the vortex line were captured. The results showed that when the main flow was increased by 25%, the axial velocity components became larger. It was also observed that the vertical vortices along the vortex line showed stronger interaction with outward fluid in the core region. This implied that the horizontal twisting motion dominated the region due to the main flow, which could trap the particles in the reactor for a longer time. Furthermore, when the main flow was increased by 50%, the flow displayed a cyclone-dominated structure. During the velocity evolution along the vortex line, more vortices emerged between the wall region and core region, implying that the energy was transferred from order to disorder. In summary, by appropriate selection of parameters, the concept of an aero-shielded solar cyclone reactor can be an attractive option to overcome the problem of carbon particle deposition at the reactor walls and exit.