Development of a Solar Collector for Agricultural Products Drying

Development of a solar collector for drying agricultural products, particularly vegetables, was designed, constructed and evaluated. The primary objective of the study was to tackle the issue prevalent in many existing solar dryers, which are predominantly stationary and consequently fail to optimize their power output potential. Therefore, a solar tracking device was formulated and constructed to trace the sun's trajectory, ensuring the generation of the highest attainable power and increase the energy harvested and thereby optimizing the amount of energy received. The drying apparatus primarily comprises a solar collector, a solar tracking device, drying chamber and chimney The size of the collector considered was 1219 mm x 609 mm, comprising a single-layer glass with a thickness of 4 mm, a black-painted aluminum absorber plate measuring 2 mm in thickness, and an insulation material with thickness of 3 mm which was enclosed within a wooden casing. The drying chamber was made of highly polished wood frame and covered with plywood, consisting of three drying trays. A 200–W wiper engine that swings a collector configuration was adapted and this 200 watts motor wiper makes it possible for the collector to attain 1500 rotation in a full wipe. Equipped with a sensor that is calibrated to allow a track of 30 degrees in 120 minutes; in that way, optimum and down times are appropriately captured. In assessing the various conducted tests, the performance parameters considered for evaluation comprised temperature, moisture content of the produce, collector and drying efficiencies, drying period, and drying rate. The moisture content of okra experienced a reduction from 87 % (w.b,), 7.0 g H2O/g solids(d.b) to 13% (w.b), 0.1 g H2O/g solids(d.b) respectively and the moisture content of pepper experienced a reduction from 83 % (w.b), 4.89 g H2O/g solids(d.b) to 17 % (w.b), 0.03 g H2O/g solids (d.b) respectively in a span of two to four days. The drying rate for okra was identified to be 2.00 (g H2O/g solids)/h whereas for pepper it was 0.67(g H2O/g solids)/h. The collector efficiency was identified to be 25.24 % and Drying efficiency was also identified to be 28.67%. The drying curves, typical of thin layer type, produced during the drying process, followed definite pattern irrespective of the trays in the drying chamber. With the polynomial behaviour, their equations, typical of Okra was y = 0.3056x2  - 7.0526x + 43.633 and R2 were estimated highly with correlation coefficient (R2 ) ranging from 91 to 99%, and for Pepper as: y = 0.61x2 - 10.166x  + 46.168 and R2  values ranged from 83 – 94% - a measure of theoretical correctness. These high values ofcorrelation coefficients obtained from the drying curves bore reasonable closeness between the experiment and theory. In all, these 2nd order equation models of these curves, described the behaviour of the drying process. This work provided a good insight into what possibilities local technologies can do. The products of drying displayed showed good indices of acceptability, attainment of shelf-life moisture content, and showing aesthetic and commercial appeals.