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ABSTRACT The objective of this study is to investigate the influence of geometrical parameters of a solar chimney, i.e., on the flow channel air gap, on the performance of a solar dryer in terms of thermal efficiency, drying efficiency, and dried product weight loss. Experimental outcomes showed the temperature inside the drying chamber increases as solar intensity increases, while relative humidity decreases. In the study sliced potatoes were selected to be dried. The average collector and chimney efficiency were found to be higher when a 10 cm air gap height was used instead of a 5 cm air gap height. After 8.5 h of drying, the moisture content of the 5 cm and 10 cm chimney air gap height differed by around 28%. Moreover, the temperature of the chimney absorber was found to be between 35.5-81 °C, with an average of 56.6 °C, which is roughly 13% lower than the collector absorber due to the solar chimney’s orientation. ABSTRAK Tujuan dari penelitian ini adalah untuk mengetahui pengaruh parameter geometri cerobong surya, khususnya ketinggian celah udara saluran aliran, terhadap kinerja pengering surya dalam hal ini efisiensi termal, efisiensi pengeringan, dan kehilangan berat produk kering. Hasil pengujian memperlihatkan bahwa temperatur di dalam ruang pengering meningkat seiring dengan meningkatnya intensitas matahari, sementara kelembaban relatif menurun. Dalam penelitian ini, irisan kentang dipilih sebagai objek pengering. Efisiensi kolektor dan cerobong rata-rata lebih tinggi pada kondisi celah udara 10 cm dibandingkan celah udara 5 cm. Setelah 8,5 jam proses pengeringan, kadar air pada kondisi celah udara cerobong 5 cm dan 10 cm berbeda sekitar 28%. Temperatur penyerap cerobong berada diantara 35,5-81 °C, dengan rata-rata 56,6 °C, yang berarti temperaturnya lebih rendah 13% dibandingkan dengan temperatur penyerap kolektor, sebagai akibat adanya orientasi cerobong surya.

Solar air collector is one of the main components of a solar dryer unit, which supplies the conditioned air for processing the perishable edible items. Various techniques have been employed to improve the thermal efficiency of the collector system, such as extended surfaces, packed beds, artificial roughness, etc., however, the cost of construction is higher. Therefore, this study was focussed on the collector efficiency enhancement using a chimney without applying the aforementioned. A single-pass solar air collector coupled with drying chamber and chimney was utilized for the experiments. The experiments were conducted in September. The average values of the solar radiation intensity, ambient temperature, temperatures inside the dryer, collector efficiency were graphically presented. The experimental data reported the maximum values of the outlet temperatures for the solar air collector with and without a chimney to be 52.8 °C and 57 °C, respectively. The collector thermal efficiency with and without the chimney was found to vary from 29.6% to 64.8% and from 26.9% to 44.8%, respectively. Furthermore, it was noticed that, with the chimney, the temperature inside the dryer showed uniform tendency.

The article investigates the thermal behaviour of a solar collector retrofitted with a natural draught unit. The objective of this work is to draw a comparative line between a system that is equipped with a circular vertical channel and the conventional one. The effectiveness of the solar heating system and how to further improve the prevailing system are examined in this study. The flat plate solar collector was used to assess the dynamics of the system. The Hottel–Whillier–Bliss equation was used to obtain the useful heat gain rate. The instantaneous collector efficiency was reduced by 22.84%. The net heat loss encountered with natural draught was augmented by 10.89%. The net pressure drop along the length of the collector was increased when a solar collector related to the circular chimney. The stagnant temperature of the collector with the natural draught was decreased by 3.20%. The heat loss to the surrounding was computed to be 33.94% of the net energy received by a solar collector connected with the circular stack. The Fanning friction factor for airflow was reduced in the system equipped with natural draught. The static pressure was marginally dropped at the inlet, whereas it was steeply increased at the outlet of the solar collector. The static pressure would be the same for both systems at collector length l = 0.84 m. The inference can be deducted from the comparative analysis that the air stream flow behind the collector plate and could provide better prospects for a collector unit equipped with natural draught at the exhaust end of the solar dryer. [ABSTRACT FROM AUTHOR]