DESIGN AND DEVELOPMENT OF AN INTEGRATED EARTH AIR HEAT EXCHANGER CUM EVAPORATIVE COOL (EAHE-EC) STORAGE STRUCTURE FOR FRESH PRODUCE

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Date
2023
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ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI-110012 2023
Abstract
ABSTRACT Design and Development of an Integrated Earth Air Heat Exchanger cum Evaporative Cool (EAHE-EC) Storage Structure for Fresh Produce Conventional air-conditioned storage systems are more energy intensive, which requires consistent supply of electricity. Apart from this, it is costly and not suitable in remote areas where electricity is almost inaccessible. Therefore, in the present research work, an integrated earth air heat exchanger cum evaporative cool (EAHE-EC) storage structure was designed and developed to store fresh produce at the farm level. For the design of any storage system, it is necessary to know the effect of storage temperature and time on the respiration rate of fresh produce. The respiration rate of fresh tomato (cv. Avinash-2) and mango (cv. Langra) fruit was generated at temperatures 10, 20, 25, 30, and 35°C using the closed system method. The measured data were used to develop mathematical models, namely regression function and enzyme kinetics model. The applicability of the model for the prediction of respiration rate was verified at 17°C storage temperature and showed good agreement with the experimentally measured respiration rate. Among both models, the enzyme kinetics model was found to be the well-fitted model to forecast the respiration rate of tomato and mango fruit. The integrated EAHE-EC storage structure works based on the combined principle of geothermal energy and adiabatic cooling. It comprises a storage room, earth air heat exchanger, and evaporative cooling systems. The storage room is made of single-wall heatinsulated hollow bricks and polyurethane foam (PUF) roof panels. The EAHE unit consists of 0.09 m inner diameter PVC (Polyvinyl chloride) pipes with a buried length of 38 m and buried at a depth of 1.5 m in flat land. The evaporative cooling unit comprises a mainframe, cooling pads, pad holders, and a water supply unit, including a water pump, water storage tank, dripper pipes, and flow rate control valves. The cooling performance of the developed EAHE-EC system was evaluated at three different air velocities (4 to 6 m/s), water flow rates (0.032 to 0.096 kg/s), and thickness of the cooling pad (50 to 150 mm). These independent parameters were optimized using Box- Behnken Design (BBD) under Response Surface Methodology (RSM) in Design-Expert Software. The corresponding optimum values for maximum temperature drop (16.80°C) 138 and humidity rise (70.85%) within a range of input variables were found to be 4 m/s air velocity, 0.065 kg/s water flow rate, and 150 mm thickness of the cooling pad. The effectiveness of the developed EAHE-EC system for its capability to extend the shelf life of fresh commodities was studied by assessing the effect of storage conditions (ambient storage and EAHE-EC system) on each postharvest quality parameter of tomato and mango fruit. Based on the retention of the overall quality and microbial load till the end of the storage period, the shelf life of tomato and mango fruit stored inside the EAHEEC system was recorded as 21 and 12 days, respectively, which was 2.5-3 times higher than ambient storage (9 and 4 days). The extra shelf-life gained by tomatoes and mangoes inside the EAHE-EC system can provide a sufficient buffer period for farmers for retailing and marketing. Keywords: Regression function, Enzyme kinetics, Arrhenius equation, Integrated cooling system, Earth air heat exchanger, Evaporative cooling, Postharvest quality, Shelf-life extension.
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