Energy and Exergy Analysis of a Finned-Plate Solar Air Heater Using Thermal Storage System

Abstract

In this research an experimental study is conducted to analyze the thermal depending on first and second law of thermodynamics of a double pass solar air collector. To improve the thermal performance of such collector enhancement heat transfer technique were used by employing extended surfaces. Also, thermal storage material (Paraffin wax) was used to enhance the thermal performance in the case of sunset and cloudy days. Triangular longitudinal fins were added to the absorber plate to increase the heat transfer area, which led to increase heat transfer between air, and absorber plate. Four models of collectors were manufactured with different absorber plates which made from aluminum material. The first model, the flat plate was without fins and wax. In the second model, six longitudinal fins were placed perpendicular on airflow above the absorber plate and filled it with paraffin wax, the weight of 3.25kg. The third model, the longitudinal fins that incline of angle (45) were placed above the absorber plate. The length of the fins and weight of paraffin wax has the same values that used in the second model. The fourth model, six longitudinal fins were placed above the absorber plate and the same number of the longitudinal fins were placed under the absorber plate. The paraffin wax weight of 5.5 kg was used in this model. The experiments were repeated of all models after removing the paraffin wax and then the comparison has been made of all results. The dimensions of the collector in the present work are (122× 60× 25 cm). The experiments were carried out at the winter session in the climate of Iraq - Ramadi city longitude of (43.268) and latitude of (33.43). The five values of mass flow rates in the range (0.025 to 0.037) kg/s with PCM and three values in the range (0.027 to 0.037) kg/s without PCM have been used in the tests. The results with phase change material showed that the use of the fins above and under absorber plate (fourth model) gives good results compared to the other types. The highest temperature difference between inlet and outlet obtained during the day (15.9 °C) and highest temperature difference at sunset (4.4 °C). The highest thermal efficiency and exergetic efficiency were (293.02 %) and (99.47%) respectively. While the results without paraffin wax showed that the temperature difference increases II gradually until midday and then decreases gradually until becomes zero at sunset. Maximum temperatures difference obtained at the fourth type was (20.6 °C), whereas maximum efficiency and exergetic efficiency were (90.86 %), (43.08 %) respectively. A comparison has been made with previous works for thermal and exergetic efficiency with and without phase change material. The comparison showed good compatibility between results, the percentage of error does not exceed 3 %. The results proved that the paraffin wax was a good substance for storing heat and it enhances the thermal performance of double pass solar collector.