Comparative drying performance of Mackerel (Rastrelliger Kanagurta) in a solar tunnel dryer and an open-air raised drying rack

Abstract

A sand base solar tunnel dryer was fabricated at Gazi, Kwale – Kenya and its effectiveness in drying mackerel (Rastrelliger kanagurta) was compared to that of an open air drying rack. The dryer consisted of a collector, drying cabinet and a photovoltaic system. The collector was covered with UV stabilized polyethylene while the drying cabinet’s roof was made of glass. Direct Current fans, one for driving air in and another for extracting air were used. The drying rack measuring 10m by 1m made of mangrove poles with timber support for the nylon mesh on which the fish were laid. The starting weights of the mackerel were 95.0 ± 18.02g and 96.7 ±5.77g in the solar dryer and drying rack respectively. The net drying time was 28 hours over a period three days. There was a significant difference (p<0.05) in the rate of the mackerel’s weight loss in the solar tunnel dryer and on the drying rack. The moisture in the fresh fish reduced from 70.6%±0.9 (2.40kg/kg, db) to 14.5%±6.6 (0.17kg/kg, db) in the solar dryer and to 39.3%±3.4 (0.65kg/kg, db) on the rack. The drying rate constants for the solar and rack-dried mackerel were 0.0772 h-1 and 0.0436 h-1 respectively. Drying was more uniform with the solar tunnel dryer compared to the rack dryer with drying coefficients (R2) of 0.7544 and 0.4116 respectively. The mean temperature during the entire drying period was 57.6°C in the solar tunnel dryer and 35.6°C in the drying rack respectively. The mean humidity during the entire drying period was 46.4% in the solar tunnel dryer and 47.2% for the drying rack. This study provides information for design engineers in the food industry in the design and operation of post-harvest fish drying facilities using low cost solar energy systems