Hanif et al., 2014. Sci. Tech. and Dev. 33 (2): 63-67 * calm_tiger_hanif@yahoo.com PERFORMANCE EVALUATION OF A FLAT PLATE SOLAR COLLECTOR AS A DRIER FOR CHILLIES AND TOMATOES MUHAMMAD HANIF 1 *, MANSOOR KHAN KHATTAK 1 , MASOOD-UR-RAHMAN 1 , MAAZULLAH KHAN 2 , MUHAMMAD AMIN 1 AND MUHAMMAD RAMZAN 1 1 Department of Agricultural Mechanization, Faculty of Crop Production Sciences, University of Agriculture, Peshawar, Pakistan. 2 Nuclear Institutes for Food and Agriculture (NIFA), Peshawar, Pakistan. Abstract The research study was conducted to test the performance of a flat plate solar thermal collector as a drier. A 1.7 m 2 wooden box was developed, having a volume of 0.50 m 3 , which acted as insulation box for the solar thermal collector. In this box a V-corrugated steel sheet was placed at the center as an absorber, a 5.00 mm thick glass was used to cover the absorber. The solar thermal collector was connected to the drying box, having a volume of 48.50 m 3 . Performance of the solar collector was evaluated at seven different convective air flow rates (2.8, 5.8, 8.5, 11.7, 14.2 and 17.5 kg.min -1 ) from November 2011 to January 2012. The results showed that an increase in air mass flow rate significantly (P ≤ 0.001) increased the performance of the solar collector. The decrease in performance was also observed with the change of months of year. Drying environment was observed inside the drying box connected with the solar collector. The results obtained showed that performance of the solar collector was directly affecting the drying conditions inside the drying box. The temperature of the drying box for all air flow rates remained in the range of 40-45 o C and humidity of less than 10%. Samples of chillies and tomatoes were dried using drying chamber. Chillies took 23 while tomatoes took 19 hours to dehydrate completely. It was concluded that the solar thermal collector may be operated at high mass flow rates of air from 9:00 am to 4:00 pm to achieve maximum performance of the drier and optimum drying conditions for agricultural products to be dried in the drying box of the collector. Keywords: Solar energy, Flat plate, Solar collector, Performance, Efficiency, Air mass flow rates Introduction Solar energy has a great potential as renewable energy beside the hydro-electric and thermal energies. Pakistan is prosperous in renewable energy sources such as solar and bio energy but the scale of utilisation of solar energy has been very small as compared to the European countries, America and China. The nations must concentrate on the development of solar energy technology, like solar collectors and PV, to reduce energy deficiency in the upcoming future. Much of the area of Pakistan comes under the region of high solar intensity. The plains of Pakistan receive almost 700 w.m -2 of solar power. Peshawar (latitude of 34 o N and longitude of 71 o E) is receiving intense solar irradiance of 20 MJ. m -2 d -1 within annual total of 7000 MJ.m -2 (Hanif et al., 2012a). To conserve this huge amount of energy the best choice is the use of solar collectors. A solar collector is a device which helps in heating a medium such as air or water that can be used for drying and heating purposes. Solar collectors are mostly constructed by local farmers from locally available materials; hence they are of low performance. The key factor in constructing a solar collector is its performance in terms of efficiency to be determined. To overcome the energy crises in the agricultural sector, the only available source is solar energy. To conserve the available solar energy the use of flat plate solar collectors is the best technique for drying various fruits with minimum cost and time (Ahmed, 2011 and Hanif et al., 2012b). A flat plate solar collector with active heat flow having an efficiency of 35 to 45% is the best choice for drying various agro products. A number of research experiments have shown that on-farm flat plate solar collectors for agricultural use can be very economical source of heat energy for drying and water heating. Flat plate solar collectors with active heat flow give better solar dried products as compared to open sun drying. This facilitates farmers in early crop harvest, long term storage of fruits, and improvement in quality of valuable dried products free from dust and pathogens (Hassanain, 2009). Key parameters beside collector size that influence the performance of flat plate solar collectors are the forced air mass flow rates of the fluid flowing inside the collector and the ambient temperature around the collectors. Efficiency depends on the most favourable combination of temperature and air mass flow rates. Efficiency of solar collectors, used as a drier, must be confirmed when constructing a solar collector to see how much