The drying of vegetables and crops is one of the crucial processes that improve the usability ofthe products. Since drying is a method requiring high energy, different drying methodswere exploredto decrease energy utilization and increase drying efficiency(Atalay 2020).The sun is an indispensable source of obtainable energy (i.e., solar energy) for Earth. With the increasing energy demand, the environmental effect of fossil fuel consumption, and mounting concerns of higher fuel costs, solar-powered energy poses an affordable option that does not significantly contribute to CO2 and CO discharges and other contaminants(Vasquez et al. 2019).There are several solar drying systems: cabinet solar drying, solar greenhouse drying, direct solar drying, direct sun drying, indirect type solar drying,and mixed-mode solar drying(Singh et al 2020).Among all the available drying systems, sun drying is the conventional and the most adopted technique to dry and preserve farming products like grains, fruits, and vegetables in most countries. However, the drying methods adopted in the preservation process raise serious concerns about the lossesin the quality and quantity of the driedproducts(Pangavhane et al 2002).For example, in open sun drying, the exposure to the sun is inconsistent from the period before noon to sunset, and when directly exposed to sunlight, the essential oil compounds are not completely reduced while the exposure damages the required colour, texture, and fragrance of the food products(Bhardwaj et al 2019). Besides, the open environment may expose the products to dust particles, insects, flies, wind, humidification at night,affecting the quality of the dried productsand may subsequently affect the market value of the raw materials andfinal product(Ali mohammudi et al 2020).
The drying process requires a large amount of thermal energy as high latentheat is desired for water evaporation. Currently, convective dryingandfreeze-drying are the two broadly utilized methods of drying around the world. It requires both mechanical and electrical energy input(Ananno 2020).Compared to other drying methods, the solar dryer saves a large amount of energy and obtains a better-quality food product. Nevertheless, the intermittent impact of weather and climatic conditions has been significant obstructions to the successful utilization of sunlight for solar dryers. As a result, different solar drying systems are incorporated with thermalstorage materials to remove the reabsorbedmoisture content from the products (Komalafe et al 2018). In order to ensure a consistent pattern of drying, phase change materials (PCMs) are used in the drying system. In the daytime, the solar energy is stored and released in the evening by the PCM, wherein the PCM uses the stored thermal energy as sensible and latent heat energy (Azaizia et al 2020). Therefore, the material temperature remains higher than the ambient condition in the sensible heat storage system (Kumar et al 2017). The most commonly used PCMs are fatty acids, paraffin wax, Glauber’s salt, calcium chloride hexahydrate, sodium thiosulfate pentahydrate, and sodium carbonate decahydrate (Esakkimuthu et al 2013). The high specific heat, latent heat of fusion, high density, thermal conductivity, chemical inertness, and non-toxic nature are some of the properties considered while selecting PCM for drying applications (Shalaby et al 2014). In the daytime, the PCM is charged using solar energy for about 8 hours (based on effective sunlight exposure) and discharges the stored energy in the remaining period of the day(Arfaoui et al 2017). Paraffin wax can be used as a PCM in latent heat storage systems. It is a non-corrosive, low-cost material, and chemically stable below 500℃ with a minimal volume difference during melting (Baniasadi et al 2017). The solar dryers have been comparatively examined with and without different PCMs.Studies have revealed that after 2:00p.m. the drying air temperature in the solar dryer with PCM increased about 3.5 to 6.5℃which was more than the other casesi.e., systems without PCM (El khadraoui et al 2017).
The quality of the food product is a very significant characteristic to be evaluated after drying, and the visual appearance of the food product also changes during drying irrespective of the method of drying; some of the changes that occur in the product isbrowning, loss of nutrient, hardening, etc (Mohana et al 2020). However, the moisture content in the crop needs to decrease after the drying process. The extent of bacterial degradation can be significantly decreased by removing the moisture content.Therefore, it is feasible to accumulate adried-outfood product for an extended period(Bahari et al 2020). The methodology of solar drying is typically intended to meet specific drying attributes of farming products with an improved approach to energy utilisation. The payback time of the developed drying system can be shortened based because the driercan serve inthe winter as well as summer seasons. Consequently, the actual price of the dryer is cheap(Swami et al 2021).
Coconuts are one of the most popular farm products, wherein the popularity of the fruit is ascribed to its culinary use and several health benefits. Besides its surface processed for natural fibres, coconuts can also be treatedto obtain coconut milk, copra, and oil. In the cooking process, thewhole fruit is known to havecountless benefits (Sumarni 2021). Conventional drying methodsare used to reduce the moisture and dry the coconut for future use. However, the methods may induce undesirable characteristics to the dried product like shrinkage, toughening of thesurface, and colour changes, which have been reported to influence consumer acceptance(Jariyawaranugoon 2018).The idea of using the solar dryer has proved to be comparatively inexpensive and effective for the drying process. In a study on the solar drying of coconuts, the moisture content in the wet base (w. b.) decreased from about 52% to 8% in 62 hours. The moisture content of copra reduced using solar dryers is higher that of open sun drying (Padmanaban et al 2017). Recent research studies have highlighted an effective drying system using a solar dryer to decrease the absolute drying period and increase the drying effectiveness of agricultural products. Using PCMs can improve the drying characteristics and decrease the drying period of coconuts.The key objective of the research is to decrease the microbial content in the dried food product, reduce human intervention and avoid improper drying during winter. Naturally, solar drying can preserve the food crops by retaining the colour, taste, fragrance, and quality (Ayyappan 2018). The current studyattempts to determine the role of paraffin wax as an effective phase change material (PCM) in drying coconutsusing a solar dryer. The improvement in the quality and value of the dried-out products with and without PCM has also been investigated.