Modeling energy efficiency during dehydration process of cooked yam

Abstract

Studies on drying have focused on developing mathematical models and kinetics of drying crops, but literature is sparse on energy and exergy analysis of cooked yam used for instant-pounded yam flour production.  This work presents the effect of drying temperature and size on energy consumption during cooked yam dehydration, a major unit operation in instant-pounded yam production.  Cooked yam with uniform surface area but different thickness (5 mm, 10 mm, 15 mm,    20 mm, 25 mm and 30 mm) were dried in a cabinet dryer at varying temperatures (60^oC, 70^oC and 80^oC) and constant air velocity of 1.5 m s^-1.  During the drying process, parameters including inside chamber temperature, outside chamber temperature, ambient temperature, drying time and power output of the oven were recorded.  These data were used to calculate energy demand, energy input, energy output, exergy, anergy, work lost and energy efficiency according to standard equations.  Results showed that the energy supplied for drying increased with increasing yam size from 16,500 to 30,360 kJ, 13,860 to 27,720 kJ and 5,940 to 23,760 kJ at drying temperature of 60^oC, 70^oC and 80^oC respectively.  The actual energy utilized for drying (exergy) also increased as the size of the yam slice increased.  It increased from 14,963.96 to 27,533.76 kJ, 13,167 to 27,628.51 kJ and 5,768.10 to 23,681.58 kJ at drying temperature of 60^oC, 70^oC and 80^oC respectively.  Drying at 5 mm thick cooked yam at 70^oC gave highest efficiency of 92.68% whereas least efficiency of 85.84% was recorded when 30 mm thick cooked yam was dried at 80^oC.  It is not desirable to dry cooked yam whose thickness is less than 10 mm at 60^oC because the work lost would be relatively high work.  We recommend that the process should be optimized.

Keywords: Drying, Cooked yam, Energy analysis, Exergy efficiency, Instant-pounded yam flour