with passive solar dryers . As a result , the drying time and solar collector area of an active solar dryer are reduced by three times and 50 %, respectively .
Figure 1 : Conventional sun drying process of shrimp paste .
The problem with this method is that it requires a large open space and is also dependent on the availability of effective sunshine . More seriously , it is susceptible to contamination by foreign materials . In the context of today ’ s food production , it is considered to be less hygienic and of lower quality .
PHYSICS OF THE SOLAR DRYING SYSTEM
As an alternative to conventional open solar drying , a more systematic solar drying system is introduced by incorporating the elements of renewable energy and economic viability . Various types of solar drying systems have been designed , tested , and developed worldwide , and these systems exhibit varying degrees of technical performance . These solar drying systems can be classified into three different categories : small , medium and large scale dryers . The design of a solar dryer is based on the physics of heat transfer and the mode of air movement ( i . e . active or passive ), exposure to insulation , direction of air flow , arrangement of the dryer and the status of solar contribution .
In a passive solar dryer , solar heated air is circulated through the products by natural convection due to buoyancy forces and / or a result of wind pressure . On the other hand , the air flow through an active solar dryer is optimised using a blower or fan ( i . e . the forced convection system ). Hence , the capacity and the reliability of the active solar dryers are increased considerably compared
Small Scale Solar Tray System Based on the fundamental process of solar drying physics , the solar tray dryer is made from glass and the solar collector is made of black painted iron plate which was recently discovered to be an efficient heat collector ( Suherman , et al 2018 ). The selected material has the properties of heat collectors . The dryer uses trays or similar product holders to expose the products to heated air in an enclosed space . The tray holds the products inside a cabinet or similar enclosure and they are exposed to heated air . Figure 2 shows the schematic diagram of a typical solar tray dryer . The main advantage of tray dryers are their handling simplicity and low capital cost . But they have the disadvantage of non-uniform products drying at different locations within the system . As a consequence , the product trays in the dryers must be rotated to improve the uniformity of drying .
Figure 2 : A typical solar tray dryer .
Medium Scale Solar Dryer Tunnel System To cater for a larger scale of dried seafood production , a medium scale solar dryer system , such as a solar tunnel dryer , is used . This design is relatively larger in size and more complex in design compared with a solar tray dryer . As shown in Figure 3 , it consists of a solar collector
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