Original scientific paper https://doi.org/10.2298/TSCI190602459SThis study deals with the performance evaluation of a simple low-cost greenhouse dryer using energy and exergy analysis. Drying experiments were conducted under the open Sun and in greenhouse dryer with two different cover sheets of ultra violet polyethylene and drip lock under passive mode and active mode for two vegetables with medicinal values: ivy gourd (coccinia grandis) and turkey berry (solanum torvum). Thermal efficiency, exergy efficiency, and improvement potential were evaluated and presented. The experiment showed that performance of the greenhouse dryer was better than the open sun drying. Thermal efficiencies were up to 30.64% and exergy efficiency values were up to 0.09% and the maximum values were obtained during the drying of ivy gourd with the drip lock sheet under active mode. The results showed that this dryer could be used for drying agricultural products at low cost by the farmers in order to produce value added products from their harvested products.Drying or dehydration of food products decreases the moisture in the products to reduce weight, for easy transportation and increase shelf life. Traditionally agricultural products have been dried under the open Sun. It is a simple and economic process but has a lot of disadvantages, like depending on weather, slow process, loss due to birds, dust and other contamination. Best quality of dried products can be achieved with industrial hot air dryers, but it requires a huge amount of energy. Approximately 9.25% of the available energy in the developed countries is being consumed by drying process [3]. So, new cost and energy effective systems are essential to reduce the energy consumption. The objective of a drying system is to supply more heat to the product than available in the ambient [4]. It needs a proper thermodynamic analysis of a drying system.Energy and exergy analysis using First and Second law of thermodynamics should be performed for finding out the energy interactions and thermodynamic behavior of a drying system [5]. The analysis of a dryer should provide a quantitative measure of inefficiencies for a designer to design better systems [6]. The exergy analysis delivers suitable information to select the appropriate design and operational procedure for better performance [7].Exergy is the maximum work attained from a stream of matter, heat or work as it comes to equilibrium with a reference environment [8]. By carrying out exergy accounting in smaller and smaller subsystems, we are able to draw a map of how the destruction of exergy is scattered over the engineering system [9]. The lesser thermal efficiency of drying systems, higher price of fossil fuel and electricity and the GHG emitted from drying systems increase the importance for exergy analysis of drying systems [10]. Various exergetic indicators used in food industry are absolute exergy loss, exergetic efficiency, improvement potential, exergy destruction ratio, entropy generation, and cumulative exergy loss. Grass...

In the present work the drying characteristics and proximate analysis of turkey berry (Solanum torvum) were analyzed under open sun drying and greenhouse drying with two different glazing materials (UV Polyethylene sheet and Drip lock sheet) under passive and active modes. The drying rate under different modes of drying are 18.73g/h in drip lock greenhouse active mode,12.50 g/h in UV polyethylene sheet greenhouse active mode,15.22 g/hin drip lock sheet greenhouse passive mode, 11.84 g/h in UV polyethylene sheet greenhouse passive mode and 10.65 g/h in open sun drying. Twelve mathematical models were chosen to determine the drying characteristics of Turkey berry. From the statistical analysis it is found that Modified Henderson and Pabis model is the best drying model describing thin layer drying characteristics of turkey berry in both open sun drying and green house drying. The goodness of the fit achieved is based on the values of coefficient of determination(R2), sum square error(SSE), root mean square error(RMSE) and reduced chi square (?2).From the proximate analysis of dried turkey berry it is found that more amount of carbohydrate is retained in UV polyethylene greenhouse dryer under passive mode. In drip lock greenhouse dryer under passive mode the retention of vitamins such as protein, vitamin C and ash content showed a positive sign. In drip lock greenhouse dryer under active mode the retention of calcium, iron and dietary fibre is found to be high. Finally it is observed that more amounts of nutrients are retained in greenhouse drying than in open sun drying.