M Ayub Hossain
Senior Scientific Officer
Farm Machinery and Postharvest Process Engineering Division
Bangladesh Agricultural Research Institute, Joydebpur, Gazipur-1701
M Arshadul Hoque
Scientific Officer
Farm Machinery and Postharvest Process Engineering Division
Bangladesh Agricultural Research Institute, Joydebpur, Gazipur-1701
A prototype of hybrid solar dryer was developed for drying of fruits, vegetables, spices and medicinal plants. It consisted of a flat-plate concentrating collector, an auxiliary electric heater and a drying unit. The dryer was tested during March to June 2008. Temperature in the dryer was higher than the ambient temperature and it could be maintained as desired using temperature controller. Reflected solar radiation was found about 57% of global solar radiation. The dryer was tested for drying of red chilli, Shatamuli (Asparagus racemosus L.) and Basak (Adhatoda vasica L.) leaves. Moisture reduction was higher in solar dryer than that of open sun drying. It took about 25 and 32 hours to reduce the moisture contents of chilli from 75 to 10% (wb) in the solar dryer and sun drying method, respectively. The capacity of the dryer was to dry about 20 kg of fresh chilli per batch. Drying rate was found higher for sliced than splitted and whole samples of Shatanuli. Blanched Shatamuli and Basak leaves dried faster than non-blanched leaves. Colour of Basak leaves decreased significantly after drying. By water blanching significant amount of green colour could be retained.
Basok, collector, dryer, drying capacity, colour, shatamuli, solar,
Postharvest and Agro-processing
1. To design and fabricate a dryer prototype
2. To test the performance of the dryer for drying of different crops
Whole Basak (Adhatada vasica L.) leaves were dried in the dryer and open sun using blanching and non-blanching conditions. Some of the Shatamuli (Asparagus rocemosus L.) roots were splitted longitudinally, some were sliced into 2-3 mm pieces and some were kept as whole root and dried them with blanching and non-blanching conditions. To compare the performance of the dryer with that of sun drying, control samples were also placed on trays in a single layer beside the dryer in the open sun. Drying was started after completion of the loading, usually at 09:00 h and discontinued up to reach the final moisture content of the product. Weight loss of both the samples in the solar dryer and the control samples in the open sun were measured during the drying period in day time (09:00 to 17:00 h) at one hour interval with an electronic balance. In the afternoon, after 17:00 h, the samples in the solar dryer were kept in the dryer and the collector was covered by reflector and the control samples were kept in the same place with a perforated cover on it so that air can easily move on and around the samples. Next morning, at 09:00 h the cover of the dryer and also the cover from the control samples were removed and subjected to dry by solar radiation. The ambient air, collector air, drying air (on different trays), inlet air and outlet air temperatures were measured at one hour interval. A lux meter was used to measure the global solar radiation and total radiation (global+ reflected from reflector) during the day time drying period. After completion of drying, the dried samples were collected, cooled in a shade to the ambient temperature and then sealed it in the plastic bags.
Research Report
Temperature in the dryer was higher than the ambient temperature and it could be maintained as desired. Reflected solar radiation was found about 57% of global solar radiation. Moisture reduction was higher in solar dryer than that of open sun drying. It took about 25 and 32 hours to reduce the moisture content of chilli from 75 to 10% (wb) in the solar dryer and sun drying method, respectively. The capacity of the dryer was about 20 kg of fresh chilli per batch. Drying rate was very slow for whole sample of both blanched and non-blanched Shatamuli. Blanched Basak leaves dried faster than non-blanched leaves. Drying rate of samples dried in the dryer was higher than those of sun drying method. Colour of Basak leaves decreased significantly after drying. By water blanching significant amount of green colour could be retained.
Journal, Report/Proceedings