Convective Solar Dryer with a Wood Waste Backup Heater for Dehydration of Food

Appropriate technology for the conversion of solar radiation to thermal energy is vital for food dehydration. Commercial producers of dried foods need reliable drying technologies for continuity technologies for continuity of production. However, solar radiation is not available whenever it is needed to drying. This limitation discourages many of these producers from investing in solar technologies, including dryers. Consequently, it is necessary to improve the system design to promote the application of solar dryers. In the present study, a natural convection solar dryer with an integrated thermal mass and sawdust backup heater has been designed and constructed, the dryer was tested in three modes of operation by drying twelve batches of fresh pineapples (ananas comosus): solar, biomas and solar-biomass, meteorological conditions were monitored during the dehydration process and both fresh and dried pineapple slices analyzed for vitamin C and ash content. Results show that the solar mode of operation was slowest (five days) in drying the samples, with the solar biomass mode being fastest (3 days) under the prevailing meteorological conditions (which were generally unfavorable from January through July). Samples were successfully dried even under rainy conditions, with moisture content dropping from 669% to 11% (on dry basis db) when the dryer was operated in the solar-biomass mode. This level of moisture content is suitable for safe storage and distribution of the dried fruit. It was also found that 26% to 44% of the vitamin c was retained in the dried product, ash content varied between 0.5% and 0.6% (on wet bassis, wb), with no significant difference between ash content (db) in fresh and dried samples, this shows that there was very little or no food contamination arising