Numerical Simulation and Experimental Study of Natural Convection Flow in a Test Bench for Solar Air Heaters

Abstract

This paper is intended to check the thermal convection flow during a new solar air heater (SAH) test bench, which is conducted in the LASEM laboratory. In fact, the applied system includes two-passage heater solar air separated by an absorber. On the other hand, a glass piece is connected to the box prototype via a pipe. Then, the piece of the glass is attached to the front side of this device in which an absorber is inserted. Moreover, two circular holes are made on the same face of the box prototype. The first is an entry hole through which hot air goes inside, and an exit hole through which air is released into the surrounding area. The study was conducted using the Navier-Stokes equations associated with the k–ω turbulence model through the use of the newly released Ansys 17.0 software to characterize the aero-thermal structure of our new system operating in natural convection. In these conditions, it has been observed that the hot zone created on the mirror side receiving the solar radiation generates an ascendant movement. It goes from the bottom to the top and enters the box prototype. The same phenomenon is also created in the box where the airflow coming from the solar heat escapes into the environment. This movement created between the hot zone of the solar heat and the box prototype is also imposed in the cold zone of the solar heat on the heat-insulating side. In these conditions, the air movement is however from the top to the bottom. Indeed, the acceleration of the air velocity at the inlet of the solar heat is due to the change of the section which is more reduced by comparison to the rest of the air circulation duct. Based on our experimental results generated in a two-passage solar air heater connected to the box prototype, the computational approach and the simulation results were validated. By referring to the classic solar air heater with one passage, the energy efficiency measured in the same conditions was enhanced and presented the efficient one with an improvement of about 27%. Finally, the numerical results are compared to our experimental results and those obtained by the authors. The comparison proved a good agreement.