*Article* **Thermal Performance Analysis of a Double-Pass Solar Air Collector: A CFD Approach**

**Irving A. Chávez-Bermúdez 1, Norma A. Rodríguez-Muñoz 2, Eduardo Venegas-Reyes 3, Loreto Valenzuela <sup>4</sup> and Naghelli Ortega-Avila 2,\***


**Featured Application: The developed solar air heater can be applied in drying and space heating applications from 50** *◦***C to 90** *◦***C. The solar collector could be modular, so it can be coupled to a variety of processes.**

**Abstract:** Solar air heaters can reduce climate change by replacing conventional fossil fuel-burning technologies in drying and space heating applications. Concentrating solar technologies, such as compound parabolic concentrators, allow air temperatures up to 120 ◦C; however, it is desirable to improve their heat transfer to reduce the space requirements for their installation. In this work, a parabolic concentrator composed of a flat receiver designed to recover heat from the cover–receiver– reflectors cavity is analyzed, operating it as a U-shape double pass solar heater. With this operation, first, the air flows through the cavity, and then it is incorporated into the duct, where the dominant heat gain occurs due to the capture of solar radiation. Thus, four input–output configurations in the cavity were modeled through dynamic simulations to determine the influence of the inlet and outlet air flow positions on the solar concentrator outlet temperature. Therefore, the incorporation of the first pass has a contribution of between 36% and 45% in useful energy gain, showing that this appropriate and relatively simple strategy can be implemented to improve the thermal performance of solar air collectors, resulting in instantaneous efficiencies higher than 75%. However, the simulation results demonstrate that the position of the inlets and outlets does not significantly impact the efficiency and outlet temperature.

**Keywords:** solar energy; CPC; solar heating; solar drying; industrial process; solar air heater; space heating
