Investigation the effect of porosity on the thermohydraulic performance of a solar air collector with perforated obstacles

Subject Areas : Renewable Energy

Amin Ghalenoei ¹ ( PhD student, Energy Conversion Department, Mechanical Engineering Faculty, University of Kashan, Kashan, Iran. )
Majid Sabzpooshani ² ( PhD, Energy Conversion Department, Mechanical Engineering Faculty and Energy Research Institute, University of Kashan, Kashan, Iran. *(Corresponding Author) )

Received: 2021-04-10 Accepted : 2022-08-31 Published : 2023-07-23

Keywords: Solar air heater, perforated obstacles, Pressure drop, thermal efficiency effective efficiency,

Abstract :

Background and Objective: Due to undesirable thermo-physical properties of the air, the solar air collectors do not benefit from the high thermal efficiency and need to be improved with the help of different methods. In this study, the effects of using various obstacles on the thermohydraulic performance of a collectors were examined experimentally and compared to the performance of a simple collector.    Material and Methodology: A solar air collector was designed, built and tested under the environmental conditions of Abadan city in Khuzestan province. Three different perforated obstacles with three hole sizes (3, 4 and 5 cm) were placed on the absorber plate. Measured parameters include the temperature of inlet and outlet air, absorber plate, pressure drop and solar radiation. Measurements were made for two different air flux (0.0218 and 0.0364 kg/s).   Findings: It has become clear that using various perforated obstacles increases the temperature difference between inlet and outlet air and subsequently their efficiencies compared to a simple conventional collector. It was also noted that in all cases, the increase in mass flowrate causes increasing the effective and thermal efficiency of system and decreasing the temperature difference between inlet and outlet air. Temperature difference in the best case (perforated obstacles with 3 cm holes) for each of the two flowrates increases twice compared to the simple collector. Also, the highest amount of average efficiency for two flowrates is 68% and 83% and the average effective efficiency is 28.4% and 34.1%.  Discussion and Conclusion: With the reduction of sizes of the holes in the perforated obstacles, the rate of heat transfer and subsequently the thermal efficiency of the collector will increase due to increasing the turbulence of the flow. This causes the pressure drop to rise up as well but also has a positive effect of increasing the temperature difference which dominates the negative effect of the pressure drop and eventually it becomes clear that there is a direct relation between increasing the effective efficiency with reducing the size of the holes.

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