Abstract:
Solar energy is an important renewable energy source. The flat-plate collector is the simplest and one of the most effective means of collecting solar energy for use in systems that require thermal energy at comparatively low temperatures. Although, flat-plate solar collector is a very important equipment in food preservation sector, appropriate performance evaluation is still not carried out in Sri Lankan conditions as far as air heating is considered. Designing of a solar collector with optimum performance is advantageous for absorbing solar radiation for receiving high thermal energy. The present study was focused to select the suitable roughness for the absorber plate of the solar collector. The size of the newly designed solar collector was 700 mm wide and 1200 mm long. Gravel sieved through 20 mm mesh was used as the roughness material, a corrugated Amano sheet with 0.45 mm thickness was used as an absorber plate of the solar collector and plywood sheet with polystyrene layer was used as insulating material. Transparent glass cover with 5 mm thickness was used as solar radiation receiver. Four types of absorber plates with different surface roughnesses such as 300, 550 and 850 gravel per m2 and a surface without gravel as a control were experimentally evaluated. The temperature and relative humidity of inlet and out let of the solar collector was measured during 30 minute intervals. Air flow rate and solar radiation were measured using anemometer and pyranometer, respectively. Observed data were statistically analysed using ANOVA by Software SAS to test the for significance of experimental results. Temperature of solar collector was increased with increasing surface roughness of the absorbing plate. While the highest out let temperature of the collector was observed with 550 gravels per m2 lowest outlet relative humidity was observed in the absorber plate without gravel. The results revealed that surface roughness affects the performance of solar collector. Solar collector with the medium roughness recorded the highest outlet temperature.
