Figure 5 : A smart greenhouse dryer system
in the front section and a drying tunnel in the back section and the two sections are connected in series . Usually , the solar collector section is covered with transparent glass , polyethylene or polycarbonate sheets and the drying tunnel is covered with plastic sheets . Dry air is circulated over the product using fans . The marine products are placed on a number of trays inside the drying chamber . The products are uniformly dried in this type of dryer because variations in air temperature are minimal during the drying period ( Patil & Gawande , 2016 ). The air temperature can be kept almost constant by regulating the air flow rate inside the dryer .
Greenhouse Dryer To further improve the drying performance of the solar dryer tunnel system and borrowing the conceptual idea from greenhouse agriculture , a greenhouse dryer system has been developed . It is generally classified based on its structure ( i . e . dome type or roof even type ) and heat transfer mode ( i . e . passive / natural convection type or active / forced convection ). As illustrated in Figure 4 , the dome shaped greenhouse maximises the utilisation of solar radiation . The roof even greenhouse allows homogenous air mixing inside the dryer . The movement of air through the dryer and over the product takes place due to density difference of hot and humid air in passive mode and an external force produced by a fan or blower in the active mode ( Patil & Gawande , 2016 ; Prakash & Kumar , 2014 ).
Smart Greenhouse Dryer In parallel with the digital and big data era of IR 4.0 , the current greenhouse dryer can potentially be equipped with a smart sensing system and Artificial Intelligence ( AI ) capabilities to further improve the efficiency of the system . The conceptual design of the smart system is shown in Figure 5 . A thermocouple and a hygrometer sensor are used to measure temperature and humidity of the greenhouse dryer respectively . An anemometer is used to measure the air velocity at various positions . A pyranometer is used to assess the intensity of solar radiation around vicinity of the solar greenhouse .
For example , the air flow velocity can be automatically varied by adjusting the opening window of the air inlet and outlet based on the air velocity , temperature and humidity conditions
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