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Design and Development of Solar Dryer for Food Preservation

S. Tabassum*
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

M. S. Bashar
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

M. S. Islam
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

A. Sharmin
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

S. C. Debnath
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

S. Parveen
Institute of Food Science and Technology, Bangladesh Council of Scienti?c and Industrial Research (BCSIR), Dhaka, Bangladesh

S. A. A. Khanom
Institute of Food Science and Technology, Bangladesh Council of Scienti?c and Industrial Research (BCSIR), Dhaka, Bangladesh

M. Khanam
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

Abstract/ Executive Summary:

Solar thermal energy is an alternative source of energy which can be used for drying vegetables, fishes, fruits or other kinds of material, such as wood. In Bangladesh, there exist significant post-harvest losses of agricultural products due to lack of the use of proper preservation system. Drying by using solar thermal energy can be an effective solution for this loss. As Bangladesh is situated in latitude 23°43’N and longitude 90°26’E, this is very much suitable to use solar thermal energy. To reduce the limitations of the natural sun drying e.g. exposure of the foodstuff to rain and dust; uncontrolled drying; exposure to direct sunlight; infestation by insects etc., two types of solar dryer (low cost solar dryer for small production and solar dryer for large production) were developed. The design was based on the geographical location of Dhaka, Bangladesh. The experiments were conducted to dry vegetables and fishes. The obtained results revealed that the temperatures inside the dryer were much higher than the ambient temperature. The rapid rate of drying proves its ability to dry food to keep in safe moisture level in a hygienic environment. Microbiological and nutritional values ensure a superior quality of the dried product also.

Keywords: Solar energy; Solar dryer; Insolation; Natural Circulation; Mixed-mode; Moisture

Location: Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Drier

Objectives:

The aim of this work is to focus on designing and fabricating simple direct natural convection dryers suitable for Bangladesh and it can be an attempt to solve the above mentioned problem. A brief design description, details of the experiments, evaluation the product quality with respect to microbiological test and nutritional value and the conclusion drawn are the prominent features of this work.

Methodology:

The basic theory of solar drying is utilizing incident solar radiation and converts it into thermal energy required for drying purposes. Basically, solar dryer contains different collectors which heat the air and heated air is then passed through the drying chamber to be dried. The latent heat of vaporization required to remove moisture from the product is provided by the hot air flowing through the dryer. The air flow through the dryer is an important factor in the drying process and is responsible for moisture transport by enhancing convective transfer of water vapor from the raw material to the dry surrounding air by outlet. In this study, two types of solar dryer have been designed, developed and analysed in different months: 1. Low cost solar dryer for small production 2. Due to low cost and simple operation and maintenance, this appears to be the obvious option and popular choice for drying of agricultural products at home. The dimension of this dryer is 0.91m length×0.76m width×0.61m height with tilted transparent top and is constructed with available materials readily available in Bangladesh like wood and transparent plastic. Since agricultural products which are mostly available in winter and maximum solar insolation getting around in 40° at that time, so the angle of heat collection is calculated as latitude plus 15 degrees that is 38°. It provides air inlet and outlet holes at the lower and back side respectively. The outlet vents are at higher level. Sun ray passes through the transparent plastic cover and heats the air inside the dryer. This heated air dries the agriculture products and moves out through the outlet vents. A direct mode natural convection solar dryer has been designed to receive and utilize maximum solar energy in a chamber. This solar dryer has been developed for quite large scale production. The dryer consists of three main parts: solar collector, drying trays and outlet chimney. The solar collector that acts as drying chamber has the dimension of 1.52m length×1.89m width ×0.91m tilted height. The drying chamber is tilted with transparent glass top so that the sunlight can pass through the glass and reach to all the drying trays. Inside the drying chamber there are three movable stainless steel mesh trays. The frame of each tray has been constructed by thai aluminum with dimensions of 1.52m length×0.55m width. Three tray holders made of angle of thai aluminum are set up in such a way to hold tray inside drying chamber. The lower holder is 0.15m above the absorber plate (made of blackened metal sheet) and the upper holder is 0.15m apart from transparent glass of the top. The distance between two adjacent tray holders is 0.30m. Transparent glass of 0.005m (i.e., 5mm) thickness is used on top and tilted parts of the dryer. The air from outside enters through the inlet air holes located at the base of absorber plate. It blows through the drying chamber and goes out from the chamber by using outlet vent shaped as chimney which is located on the upper side of the back edge. The dryer is set on four wheels to make it mobile. Field level studies were conducted at IFRD, BCSIR to demonstrate the potentiality of the solar driers for production of high quality solar dried vegetables, fishes and medicinal plants. Before drying, vegetables were processed. Potato and carrots were sorted to remove defects, washed and then sliced with sharp slicers into approximately 0.003m (i.e., 3mm) thick slices. They were weighted and placed on drying trays. Also another tray of vegetables was kept in open air to compare the effectiveness of the dryer. Before placing into trays, vegetables were weighted and moisture contents were determined. Testing was performed from October to December in the year of 2015. Ambient air and drying chamber temperatures were measured with digital thermometers. Solar radiation was measured with solar tracking system of Kipp & Zonen with pyranometer (SMP3-V), phrgeometer (CGR-3), pyrheliometer (SHP1), sunshine duration sensor (CSD3) and automatic sun tracker (SOLYS32). The sliced vegetables were sampled out periodically and the moisture content was measured by moisture analyzer. Measurements were done at 15 minutes intervals.

Source of Information: Bangladesh J. Sci. Ind. Res. 54(2), 155-160, 2019

Article Link (Online Journal): https://doi.org/10.3329/bjsir.v54i2.41672

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Different tests have demonstrated that solar driers are appropriate for production of quality dried fruits, vegetables, medicinal plants and fishes. In all the cases the use of solar driers leads to considerable reduction of drying time in comparison to open sun drying. Also the drier produces the good quality hygienic dried products. However, the drying time increases with the increase of humidity in the air. It also depends on the incident solar insolation. Solar driers are simple in construction, low cost and can be constructed using locally available materials.

Knowledge Management: Journal