Performance of Novel Portable Solar Drying Technologies for Small and Mid-Size Growers of Specialty Crops Under Indiana Weather Conditions
Abstract
Solar drying of specialty crops like fruits and vegetables is widely used for product quality preservation, shelf-life extension, and adding value towards marketing purposes. Drying involves heat and moisture transfer from the product, thus it reduces costs of transportation and storage due to the decrease in volume and increase in nutrient density of the dried product. Therefore, it is one the of the most important unit operations for minimally processed foods among small and midsize farmers, processors and even large food processors. Moreover, drying is an energy-intensive operation that represents between 10% to 15% of the total energy consumption by food industries. While open-air sun drying of crops is the most commonly used method in the world especially by small and mid-size growers, there is a lack of commercial solar drying technologies available for use by these growers. Additionally, a lot of the research conducted on various types of experimental solar dryers are mostly based on experimental drying practices, without mathematical considerations of the drying kinetics, and minimal evaluation of final product quality in comparison with the common open-air sun drying method, which is affected by contamination from external factors such as dust and other foreign matter. Quality and drying kinetics affect the efficiency/performance of the dryers, and not considering them can increase production cost, and reduce the profit of the operation. Thus, the use of models for predict drying behavior, and effects of the drying methods on product quality are needed as engineering aspects for the evaluation of drying technologies and their improvement. The overall goal of this thesis was to study the performance of two related portable multipurpose solar dryers, DehytrayTM and DehymeleonTM, in comparison to open-air sun drying by drying tomatoes, apples and mint under West Lafayette, Indiana weather conditions. Thin layer drying tests were conducted on tomato slices, apples slices and mint leaves, with three temperatures [24°C (75°F), 35°C (95°F) and 54 °C (130°F)], and an airflow velocity of 1 m/s to determine the drying kinetics of these products during diurnal drying cycles typical for solar and/or open-air sun drying. Subsequently, field drying tests were conducted for tomatoes slices, apples slices and mint leaves with the two solar drying technologies (DehymeleonTM and DehytrayTM) and open-air sun drying using uncovered Dehytrays as the control. The average temperatures achieved for these technologies were 45°C (113°F), 60°C (140 °F) and 27°C (80.6 °F) for the DehymeleonTM, DehytrayTM and open-air sun drying, respectively. Moisture diffusivity were in the order of 10-4 to 10-9 (m2 /s) for the different methods, depending directly on the product, temperatures and air flow inside the drying chamber. Quality attributes (color, vitamin C and microbial growth) were measured before and after the field drying tests. Color difference (ΔE) for DehymeleonTM solar dryer showed the least variation compared with the fresh products. However, for the DehytrayTM ΔE increased due to the impact of its higher temperature and direct sunlight exposure that led to Maillard reactions and caramelization in the case of tomatoes and apples slices. Additionally, vitamin C (Ascorbic acid) content for tomatoes and apples slices was affected for the high ranges of temperatures reached inside the Dehytray™.
Degree
M.Sc.
Advisors
Ileleji, Purdue University.
Subject Area
Agriculture|Nutrition|Design|Alternative Energy|Agronomy|Atmospheric sciences|Energy|Food Science|Mathematics
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