Solar Drying: Fundamentals,Applications and Innovations - National ...

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Visavale - Principles, Classification and Selection of Solar Dryers 1.7. THIN LAYER DRYING AND DEEP BED DRYING ........................................................ 12 1.7.1. Thin Layer Solar Drying .............................................................................................................. 12 1.7.2. Deep Bed Solar Drying ................................................................................................................. 13 1.8. SOLAR DRYING TECHNOLOGY ....................................................................................... 13 1.8.1. Classification of Solar Dryers .................................................................................................... 14 1.8.2. Applications of Solar Dryers ..................................................................................................... 16 1.8.2.1. Solar Drying of Agricultural Products........................................................................... 16 1.8.2.2. Solar Drying of Marine Products ..................................................................................... 18 1.9. WORKING PRINCIPLE ............................................................................................................ 19 1.9.1. Open Sun Drying (Osd)................................................................................................................ 19 1.9.2. Direct Solar Drying (DSD) .......................................................................................................... 19 1.9.3. Indirect Solar Drying (ISD)........................................................................................................ 20 1.9.4. Hybrid Solar Drying (HBD)........................................................................................................ 21 1.10. TYPES OF SOLAR DRYER ................................................................................................... 21 1.10.1. Passive Solar Drying Systems ................................................................................................ 21 1.10.2. Indirect-Type Passive Solar-Energy Dryers ..................................................................... 21 1.10.3. Direct-Type Passive Solar-Energy Dryers ........................................................................ 22 1.10.3.1. Solar Cabinet Dryers.......................................................................................................... 22 1.10.3.2. Natural-Circulation Greenhouse Dryers ................................................................... 23 1.10.4. Hybrid-Type Passive Solar-Energy Dryers ....................................................................... 25 1.11. ACTIVE SOLAR DRYING SYSTEMS................................................................................... 26 1.11.1. Indirect-Type Active Solar Drying Systems ..................................................................... 26 1.11.2. Direct-Type Active Solar-Energy Drying Systems ......................................................... 27 1.11.2.1. Absorption Dryers .............................................................................................................. 27 1.11.3. Hybrid-Type Active Solar-Energy Dryers ......................................................................... 28 1.12. SELECTION OF SOLAR DRYERS ........................................................................................ 29 1.12.1. Test case of solar drying at ICT Mumbai ........................................................................... 31 Solar cabinet drying of fish ............................................................................................................... 31 1.12.1. Economics of Solar Dryers ...................................................................................................... 40 1.12.2. Dynamic Methods of Economic Evaluation ...................................................................... 40 1.13. CONCLUSIONS ........................................................................................................................ 42 NOMENCLATURE ............................................................................................................................. 43 REFERENCES ..................................................................................................................................... 44 2 Drying of Foods, Vegetables and Fruits
Visavale - Principles, Classification and Selection of Solar Dryers 1.1. INTRODUCTION Preservation of fruits, vegetables, and food are essential for keeping them for a long time without further deterioration in the quality of the product. Several process technologies have been employed on an industrial scale to preserve food products; the major ones are canning, freezing, and dehydration. Among these, drying is especially suited for developing countries with poorly established low-temperature and thermal processing facilities. It offers a highly effective and practical means of preservation to reduce postharvest losses and offset the shortages in supply. Drying is a simple process of moisture removal from a product in order to reach the desired moisture content and is an energy intensive operation. The prime objective of drying apart from extended storage life can also be quality enhancement, ease of handling, further processing and sanitation and is probably the oldest method of food preservation practiced by humankind (Mujumdar, 2007). Drying involves the application of heat to vaporize moisture and some means of removing water vapor after its separation from the food products. It is thus a combined and simultaneous heat and mass transfer operation for which energy must be supplied. The removal of moisture prevents the growth and reproduction of microorganisms like bacteria, yeasts and molds causing decay and minimizes many of the moisture-mediated deteriorative reactions. It brings about substantial reduction in weight and volume, minimizing packing, storage, and transportation costs and enables storability of the product under ambient temperatures. These features are especially important for developing countries, in military feeding and space food formulations (vanArsdel, 1965). Drying in earlier times was done primarily in the sun, now many types of sophisticated equipments and methods are used to dehydrate foods. During the past few decades, considerable efforts have been made to understand some of the chemical and biochemical changes that occur during dehydration and to develop methods for preventing undesirable quality losses. The widest among drying methods is convective drying, i.e. drying by blowing heated air circulating either over the upper side, bottom side or both, or across the products. Hot air heats up the product and conveys released moisture to atmosphere. In direct solar drying called ``sun drying'' the product is heated directly by the sun's rays and moisture is removed by natural circulation of air due to density differences. Solar radiation in the form of solar thermal energy, is an alternative source of energy for drying especially to dry fruits, vegetables, agricultural grains and other kinds of material, such as wood. This procedure is especially applicable in the so-called “sunny belt” world-wide, i.e. in the regions where the intensity of solar radiation is high and sunshine duration is long. It is estimated that in developing countries there exist significant postharvest losses of agricultural products, due to lack of other preservation means. Drying by solar energy is a rather economical procedure for agricultural products, especially for medium to small amounts of products. It is still used from domestic upto small commercial size drying of crops, agricultural products and foodstuff, such as fruits, vegetables, aromatic herbs, wood, etc. contributing thus significantly to the economy of small agricultural communities and farms. Drying of Foods, Vegetables and Fruits 3
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