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The purpose of this study was to design, fabricate and test an agro-dryer for drying agro-commodities. Initially, a survey was conducted to identify which commodities are dried locally and what methods were adopted in drying. Thereafter, dryer designs in use in various parts of the world were reviewed and a suitable design was selected for the prototype. Main emphasis was given in designing a simple machine to be made from locally available materials and manufacturing technology. Information gathered from 200 respondents indicated that locally; cereals, legumes, condiments, fruits, vegetables, medicinal plants, hay and fodder, fish and meat are dried mostly in open air or under shade. Open air-drying was reported as the most common method of drying agro-commodities. The farmers were not happy with uncontrolled open air method and desired to design a simple and easy to use low cost dryer suitable for drying any gro-commodity in a clear or cloudy/ rainy day. A prototype dryer was designed that used both direct and indirect solar heat in conjunction with a provision for drying materials with solid fuels under inclement weather conditions. Initially, the dryer was tested under three drying modes (i) dryer alone (ii) Dryer with booster and (iii) open air-drying (as control) on chilies and rose flowers. Results indicated that dryer-booster combination removed the product moisture very quickly followed by dryer alone, while open air took double the drying time as compared to dryer modes. Having gained the confidence on the dryer performance, detailed tests were conducted to study the effects of four drying modes dryer alone, dryer-booster, charcoal heating and open air forced air convection (at night) tray shifting and material layer thickness on the dryer performance. Tests indicated that dryer alone removed 1.6 to 3.0% moisture/hour from chilies, cauliflower and green peas as compared to just 1% per hour in open air. However, from rose flowers, 5-10% m/hr was removed in dryer mode while open-air mode removed 3-4% m/hr. Thus the drying time required in dryer modes was more or less half of that required in open-air drying. Dryer modes under forced air convection (at night) removed significantly more moisture compared to open-air mode. Shifting of trays however, had no significant effect in first two days but on third and fourth day the effect was significant. Moisture removed from thick layer of commodities under forced air convection in dryer modes was significantly higher as compared to open-air mode. Charcoal heating was effective as the solar drying 90 kg of vegetables were dried using one bag of charcoal day in four days. Calculations on the calorific value and drying efficiency confirmed that four kg charcoal would deliver 5.3 MJ of energy / hour, and a 40 kg bag of charcoal was enough for one day. The farmer may use this option on a rainy or cloudy day. In a stacked tray arrangement, the top trays dried significantly faster than the trays placed below the top trays placed below the top trays. It was observed that in a stack of 4 trays, the top tray removed 36%, second tray 11% and third tray 4% more moisture compared to the tray placed at the bottom. Chilies at full load, when dried in open-air, required 40% more time as compared to the dryer modes. At part load, open air-drying took 75 to 133% more time as compared to dryer modes. In rose flowers 100% more time was required in open air required 50% more time under natural air convection as compared to dryer mode. Similar trend was noted in green peas and chilies in stack tests. Moisture removal from chilies cauliflower and green peas on daily basis indicated that cumulatively, 40% moisture escaped on first day, 69% on second day and 89% on third day in dryer modes whereas 30% on first day, 56% on second day and 76% on third day in open-air drying mode. Thus, the dryer modes removed significantly more moisture than the open-air mode. The temperature inside the dryer at high moisture ratio was less due to heavy moisture load inside the dryer. As the moisture ratio started decreasing with progress in dying process, thus the temperature simultaneously energized the drying process. Conversely, the relative humidity remained high inside the dryer at higher moisture ratio. As the drying process progressed, the moisture ratio decreased and consequently, the relative humidity dropped sharply to a minimum. Temperature and humidity showed a similar response in green peas and chilies. The rating of organoleptic materials dried in dryer with solar or charcoal heat was between good and excellent while the materials dried in open air were rated between poor and fair. Two models were developed to predict the rate of moisture removal with drying time. The empirical model based on the moisture removal time relationship yielded predication equations of logarithmic form that best fitted to the experimental values with R2 ranging from 0.91 to 0.99. Another mathematical model used moisture ratio time relationship, also yielded prediction equations of exponential form that also very accurately matched with the experimental results with R2 approaching unity. A simple dryer design is suggested for farmers with babul wood frame and a polyethylene sheet transparent cover. The cost of the suggested dryer is affordable, ensuring a better product quality.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Design, Fabrication, Performance Evaluation, Agro dryer , Drying Agro commodities, Dryer design, Open air method, Drying materials, Dryer alone, Dryer with booster, Open air drying, Drying time, Stacked tray arrangement, Empirical model, Rate of moisture, Moisture ratio, Solar drying system, Natural and forced convection dryers, Drying activities
Subjects:Agriculture & Veterinary Sciences(a) > Agriculture(a1)
ID Code:272
Deposited By:Mr Ghulam Murtaza
Deposited On:18 Jun 2006
Last Modified:11 Jun 2008 21:54

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