A review paper on Solar Dryer

The unpredictable rise and frequent scarcity of fossil fuel accelerated the continuous search for an alternative power source. Solar is one of the renewable and sustainable sources of power that attracted a large community of researchers from all over the world. This is largely due to its abundant in both direct and indirect form. As such the development of efficient and inexpensive equipment for the drying of agricultural and marine products using solar power evolved thereby improving the quality of the products as well as improving the quality of life. The use of solar dryers in the drying of agricultural products can significantly reduce or eliminate product wastage, food poisoning and at the sometime enhance productivity of the farmers towards better revenue derived. A solar crop drying system does not solely depend on solar energy to function; it combines fuel burning with the energy of the sun, thus reducing fossil fuel consumption. In this paper a review of the solar dryer is presented. The various design of the solar dryer is reported in the literature thus far is presented.. Introduction Open air and uncontrolled sun drying is still the most common method used to preserve and process Agricultural product.But uncontrolled drying suffers from serious problem of wind born dust, infestation by insect, product may be seriously degraded to the extent that sometimes become market valueless and resultant loss of and have to the food quality may have adverse economic effects on domestic and international market. Dryers have been developed and used to dry agricultural products in order to improve shelf life (Esper and Muhlbauer, 1996). Most of these either use an expensive source of energy such as electricity (ElShiatryet al., 1991) or a combination of solar energy and some other form of energy (Sesay and Stenning, 1996). Most projects of these nature have not been adopted by the small farmers, either because the final design and data collection procedures are frequently inappropriate or the cost has remained inaccessible and the subsequent transfer of technology from researcher to the end user has been anything but effective (Berinyuy,2004). The objective of this study is to present some of the basic types of solar dryer with a view of providing a better clue on their effectiveness in the drying of agricultural products. Advantages of Solar Drying System 1) Better Quality of Products are obtained 2) It Reduces Losses and Better market price to the products. 3) Products are protected against flies, rain and dust; product can be left in the dryer overnight during rain, since dryers are waterproof. 4) Prevent fuel dependence and Reduces the environmental impact 5) It is more efficient and cheap. Disadvantages of Solar Drying System 1) Quality of products are not obtained in some cases. 2) Adequate solar radiation is required. 3) It is more expensive Require more time for drying. Classification of Solar Dryer Solar dryers are available in a range of size and design and are used for drying of various agricultural products. Various types of Dryers are available in the market as per requirement of farmers. Primarily all the drying systems are classified on the basis of their operating temperature ranges that is High Temperature solar dryer and Low Temperature Solar dryer. Following criteria's are required for the classification of solar dryer:1) Air movement mode 2) Insulation exposure 3) Air flow direction 4) Dryer arrangement 5) Solar contribution 6) Type of fruit to be dried 1) Direct Solar Dryer It is a type of dryer in which solar radiation is directly absorbed by the product to be dried.it is also called as natural convection cabinet dryer since the solar radiation is directly fall on the product ,the quality of product is reduced. This dryer comprises of a drying chamber that is covered by a transparent cover made of glass or plastic. The drying chamber is usually a shallow, insulated box with air-holes in it to allow air to enter and exit the UmeshToshniwal, S.R Karale / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.896-902 897 | P a g e box .Fig. shows a schematic of a simple direct dryer (Murthy, 2009). Fig.1 Direct solar drying (Natural convection type cabinet drier) 2) Indirect Solar Dryer The solar radiation gained by the system is utilized to heat the air which flows through the product to be dried in this dryer. In this of dryer quality of product improved though drying rate increased. Heated air is blown through the drying chamber . At the top of drying chamber vents are provide through which moisture is removed. In indirect type of solar drying systems a better control over drying is achieved. Fig. describes another principle of indirect solar drying which is generally known asconventional dryer. Fig.2 İndirect solar drier ( Forced convection solar drier) 3) Forced Convection and Natural Convection Solar Dryer Forced convectionIn this type of dryer air is forced through a solar collector and the product bed by a fan or a blower, normally referred to as active dryer. Natural convection – In this dryer natural movement of air takes place thus called as passive dryers.The heated air flow is induced by thermal gradient. Fig.3 Classes of solar dryers and their drying modes (adopted from [11]) Solar Dryer Evaluation Methods: A review of evaluation methods and the parameters generally considered for evaluation of solar dryers was presented by [12],[13]; Table gives the summary of the parameters. Physical features of the dryer Thermal performance Quality of dried products Economics and other parameters