Experimental evaluation of a solar cyclone reactor via particle image velocimetry

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 solar reactor window, wall, and exit. Especially when they accumulate at the reactor exit, agglomeration of these particles completely blocks the exit. Therefore, 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 make carbon particles fly in circles in the reactor instead of moving towards the exit all together at a time. In order to better understand and explain the flow dynamics inside the solar cyclone reactor, a prototype reactor was manufactured to test the concept and to analyze the flow via Particle Imagining Velocimetry (PIV). In this paper, design steps of this new solar reactor concept are given and a brief summary of the CFD simulations incorporating discrete ordinate radiation model (DO), species transport with volumetric reactions, and discrete phase model (DPM) for particles are presented. Then experiments focusing on the PIV analysis are described. To understand the flow evolution along the vortex line, several images in axial direction along the vortex line were captured. The results showed that when the main flow is increased by 25%, the vertical 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, which implied the horizontal twisting motion dominated the region due to the main flow, which could trapped the particles in the reactor for longer time. Furthermore, when the main flow was increased by 50%, the flow was a cyclone-dominated structure. During the vertical evolution along the vortex line, more vortices emerged between the wall region and core region, implying the energy was transfer from order to disorder. In summary, by appropriate selection of parameters, the concept of aero-shielded solar cyclone reactor can be an attractive option to overcome the problem of carbon particle deposition at the reactor walls and exit.