Results of research into technological process of fruit drying in the solar dryer

Abstract

The work addresses the issue of solving a scientific-applied task on the substantiation of operation modes of the solar fruit dryer in order to improve energy efficiency of the technological process of fruit drying for small amounts of fruit processed at private farms. We have explored the use of solar energy for fruit drying at the latitude of the location of Rivne oblast, Ukraine, which has the average annual solar radiation power of the order of 3.41 kW·h/m2 per daylight. This makes it possible to receive from 1.5 to 2.3 kW·h of energy per day from the air collector area of 1 m2. The series of analytical and experimental studies that we conducted has confirmed the possibility for a significant intensification of the process of fruit drying in the solar dryer. Compared with modern convective drying devices, the specific energy consumption when drying the fruit in the solar dryer is reduced by 3...3.7 MJ/kg. The degree of intensification grows by 3.3...12 times compared to drying devices of the mine and tunnel types. Such results were achieved by implementing the proposed design of a flat mirror concentrator, to enhance the slanting fluxes of morning and evening sun irradiation, and a heat accumulator, based on pebbles, for accumulating at night the excessive heat from the reserve source of energy. It was established that regardless of a blanching technique for fruit raw materials, the duration of drying in the solar dryer varies depending on physical parameters of the environment. In the process of drying, the experiments were carried out at a temperature of 289.15...333.15 K, and the duration of drying was from 50 to 74 hours. We have analyzed the effect of operational parameters on a change in the chemical indicators and quality of the dried fruit. Specifically, the content of vitamin C, which was 5.2 mg/% for pear, and 4.3 mg/% for apple. The acidity was 0.29 % for pear, and 0.46 % for apple. The content of dry nutrients was 87.5 % for pear, and 85.9 % for apple. The sugar content of fruit raw materials was 59.36 % for pear, and 57.8 % for apple.