Design and analysis of porous and solar thermofluidic systems: a computational fluid dynamics approach

Abstract

The passive and directional displacement of fluids is a highly desired characteristic in microfluidic and energy systems. The available energy that drives the fluids rises from changes in the relative contribution of surface and body forces. In this work, two different thermofluidic processes were analyzed: the directional and selective displacement of a nonaqueous fluid in porous media, and the development of a circular trough solar thermal cooker. First, the displacement of nonaqueous phase in a porous medium was mathematically modeled and experimentally validated. The concept of wettability capacity distribution (WCD) is introduced and applied to bulk porous media to passively influence directional spontaneous imbibition. The performance of the model was verified via experiments varying the interfacial tension, viscosity, permeability, and core materials and sizes. It was found that, while modifying the gravitational-to-capillary forces ratio (Bo>1×10-6) may contribute to asymmetrical oil production in hydromagnesite cores, the presence of a WCD play a major role in achieving this goal. In the second part, a passive circular trough solar thermal cooker was mathematically modeled and experimentally validated. A Monte Carlo-Metropolis algorithm was specified to estimate the optical efficiency of parabolic and circular geometries used to capture solar radiation. From the ray tracing simulations, the optical efficiencies were estimated in the range 72.4 % and 76.5 %, for circular and parabolic surfaces, respectively. The circular geometry was selected for the experimental prototype due to its lower production cost and technical requirements for construction. A computational fluid dynamics model was specified to determine the temperature profile of the cooking circuit. It was determined that the heat transfer fluid in the circuit can reach temperatures of up to 95 °C under ambient conditions (~850 W·m^-2·K^-1) in Monterrey, Mexico.