Abstract :
This paper reports the design and development of an indirect, natural convection batch-type solar dryer fitted with North–South
reflectors. With the help of the reflectors the collector efficiency without load was enhanced from 40.0% to 58.5% under peak solar irradiation
conditions during a typical day in January in Bhavnagar, Gujarat, India. The corresponding computed values based on heat
transfer equations were 36.5% and 50.3%. The desired extent of drying (ca. 12%, wet basis) of ‘papad’ – a popular Indian wafer – could
be achieved within 5 h in this static dryer having 1.8 m2 area of the collector and computed loading capacity of 3.46 kg. The initial and
average values of the drying efficiency were 16.3% and 4.1%, respectively. The drying performance data could be fitted to the diffusivity
equation with effective diffusivity value of 3.9 10 9 m2 s 1. Despite the high collector efficiency achieved, the average drying efficiency
was low on account of under-loading of the dryer, as evident from the increase in drying efficiency to 13% in a smaller dryer loaded with
the same amount of wet papad.
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