Design, Construction, and Investigation of the Drying Equipment Using Solar Power for Bangladeshi Fruits and Vegetables

In underdeveloped nations where fuel and electricity are expensive, crop drying using solar power is a practical and affordable method of food preservation. For farmers in rural areas, it can be difficult or impossible to preserve fruits for later use without access to fuel and huge drying systems. Drying of potatoes in the sun is carried out with industrial dryers integrating solar power. This experiment shows how to design and optimize drying systems for usage in developing nations. A model of an industrial sun-drying system has been created and validated through experimental testing. The ambient temperature is between 28°C and 33°C, while the drying chamber’s temperature ranges from 30°C to 48°C at a flow rate of 1.8 m/s. The moisture content of the dried potato sample was 84.7% and 8.27% under loaded conditions and using only silica gel respectively. We use a photovoltaic (PV) solar panel-powered heating element coil in combination with solar energy that improves the efficiency of agricultural dryers.


Introduction
Due to biochemical interactions, many agricultural goods are susceptible to microbial and other spoilages because of their high moisture content.Dehydration or drying processes must therefore be carried out as preventative steps to lower the product's moisture level.Food is dried by removing its water content to prevent metabolic reactions and microbiological growth.The product's life is extended by drying, allowing for year-round availability.Open-air sun drying is one of the earliest and most wellknown methods for preserving agricultural products for an extended period [1][2][3].However, the enormous quantity of energy needed for these operations is often derived from traditional energy sources like fossil fuels.The use of renewable energy sources for drying is becoming increasingly important due to the depletion of fossil fuels and the rise in energy prices [4][5][6][7].The additional benefits of sun-drying systems include reduced energy, time, and size during drying operations, making the approach more effective and environmentally benign [8][9][10].Due to its abundance and accessibility, particularly for nations in the tropics like Bangladesh, it has also created a sustainable energy utilization with a lot of potential for a wide range of uses.The disadvantages of traditional open-air sun drying, such as contamination from dust, insects, birds, and animals, lack of control over drying conditions, and potential for chemical, enzymatic, and microbiological degradation due to extended drying durations, are all solved by solar-energy drying systems [11][12][13].Vegetables and fruits can be preserved by solar energy drying under hygienic, sanitary, and clean circumstances that the consumer may find acceptable.The procedure enhances product quality, saves time and energy, uses less drying space, increases process efficiency, and safeguards the environment [8], [9], [14].Suppose the hydrodynamic characteristics of the solar dryer are changed.In that case, it is predicted that the solar dryer might save around 780 USD/month and reduce carbon dioxide emissions by 6400 kg/month, according to an evaluation of the solar dryer's economics based on the payback period and CO 2 reduction [15][16][17].For many farmers and processors, generally in most developing countries, gridconnected electricity and supplies of other non-renewable sources of energy are unavailable, unreliable, scarce, or too expensive; this results in reduced expected profit due to unsuitable post-harvest processing [18][19][20].But even with all the benefits, it claims, a solar drier still depends on the weather.The drying process won't be effective in cloudy weather.In this study, a novel solar dryer is designed and experimented with its functionality.The flexibility of the drying process, made possible by the ability to change the temperature as required and hence manage the final moisture content of the product, is a significant advantage of solar dryers over conventional sun dryers.To eliminate the moisture, silica gel is also used in this task.To compare the efficiency of using a solar dryer versus drying in the open sun, the solar dryer's effectiveness factor was also investigated.Investigations were also conducted into the temperature distributions and the impact of solar radiation on the drying process.The effectiveness of a natural draft and its impact on the collector's drying rate and energy are to be evaluated.It uses an auxiliary heater powered by a rechargeable battery to support the solar dryer.The solar dryer will be able to function even in unfavorable weather with the addition of a backup heater.

Experimental setup
The experimental prototype test rig consisting of a solar collector, a drying chamber, a solar panel, a chimney, an axial fan, an electric motor, a battery, and a control panel was developed in the Mechanical Engineering Department at the Military Institute of Science and Technology (MIST), Bangladesh.The solar collector was fabricated with locally accessible materials and comprised of a base, MS sheet, glazing material, an absorber, air intake and air outlet holes, a reflector, an insulator (polyethylene foam), and a glass cover plate.The CAD design of the solar dryer is shown in Fig. 1 and the numbers are denoted as 1.Solar Collector, 2. Control panel, 3. Chimney, 4. Drying chamber, 5. Glass cover and 6.Solar panel.These are fastened inside a 1.25 m × 1 m rectangular enclosure made of plyboard.The rectangular box as a solar collector (810 mm x 760 mm x 260 mm) is protected by an MS sheet and the protection plate is attached to the top side of the box and is made of toughened glass with a thickness of 0.006 m.To capture the most radiations, the absorber plate is made of a 0.8 mm galvanized iron sheet and is darkened.

Figure 1. The CAD design of the assembled solar dryer
This plate is anchored 0.050 meters from the ground.A layer of polyurethane (PU) foam that is 0.025 m thick is used to insulate the rectangular box from all sides except the top surface.The entire box is positioned on the iron framework, angled at 30 degrees with the ground, and facing north-south.This unique type of heat exchanger converts solar energy into heat.A fluid receives energy from a distant radiant energy source.Flat plate collectors are frequently utilized for applications needing less than 80°C [21], [22].Compared to concentrating type collectors, flat plate collectors are mechanically simpler and require less care [23][24][25].The main structure of the drying chamber is constructed of low-cost ply board that is 0.019 m thick and this enclosure is typically a box of 1.00 m × 0.60 m × 0.60 m.It was insulated and covered at all sides with 0.025-m-thick polyurethane foam to minimize heat losses.An intake connector pipe was installed at the bottom of the enclosure to take heated air that is hotter from the collector.Inside the drying cabinet, two drying trays are available for uploading the drying goods.The distance between each of the two trays is 0.12 meters.Each drying tray covers an area of 0.85 m 2 and is made of stainless-steel wire mesh with a size of 0.002 m.The trays were kept on a wooden block that was fastened to the cabinet's interior sidewalls.The option of moving the trays inside the cabinet has been kept for simpler removal of the trays during product loading or unloading.

Figure 2. Assembled Solar dryer
The dryer's loading door on the back side is made to make loading and unloading foods easy to examine dried items.A control unit with a temperature controller for the operation of the auxiliary heater was implemented to measure the ambient temperature, the solar collector temperature, and the drying chamber temperature and compare it with the set value.Fig. 2 presents the actual experimental setup of the prototype assembled system.

Experimental procedure
The experimental tests were carried out under outdoor conditions during July and August 2021.Based on hardness, color, and size consistency, samples of potatoes were sorted and chosen.They were cleaned by giving them a thorough wash in tap water, rinsing them with distilled water, and finally wiping them down with absorbent paper.After two minutes of pretreatment in boiling water, the water was drained from the cleaned potatoes.Using a potato slicer, the potatoes were cut into 3mm-thick slices.The sliced potatoes were placed on a wire mesh tray and put into the drying chamber.The initial weight of potatoes was 0.750 kg and the final weight was 0.115 kg.The data (Dry bulb temp, relative humidity of air) were taken from 9.00 to 16.00 hours and the absolute humidity was calculated from the psychometric chart.The control panel thermostat controlled the drying chamber's temperature.Data Logger, Anemometer, Pyranometer, Hygrometer, and temperature indicator are used for measuring.The investigations analyze a drying chamber's thermal characteristics for varied air distributions.The dryer's efficiency describes its entire thermal performance, considering the effectiveness of the drying chamber, solar collector, and any other system additions.The following formula, which is defined by , was used to determine the efficiency of the manufactured hybrid dryer where Qe = Quantity of heat used in evaporating moisture, A = area of solar collector, t = drying time, s, and I = Average Solar intensity, W/m 2 .The drying rate is the amount of evaporated moisture over time [26], denoted by where Mi = mass of the sample before drying, Md = mass of the sample after drying, and t = drying period.
Moisture content is one of the crucial criteria used to assess a dryer's performance.Both the overall weight of the material to be dried and the Quantity of solid weight existing in the material can be used to determine a substance's moisture content.The following equation gives the moisture content on a wet basis Peak solar radiation occurred between 11.30 and 14.00 hours.

Relative humidity vs. time under no load
At one-hour intervals between 0900 hours to 1600 hours, the solar dryer's drying chamber's relative humidity was plotted against time on a graph, shown in Fig. 5.At first, it appeared that the relative humidity was the same throughout.The relative humidity started to drop as the air in the chamber began to heat up.At 1400 hours, the drying chamber's humidity was at its lowest, 53%.

Testing under loaded conditions and using a backup heater
To determine the maximum temperature, moisture content, and drying rate, the prototype was set under an unloaded and loaded dryer condition.The test was carried out in two days, and the results were averaged.The solar collector alone was first evaluated.
The trial started at 9.00 hours when the ambient temperature was 28.5°C.Fig. 5 (a) shows the changes in the temperature levels.At 14.00 hours, the maximum average for the ambient temperature, the solar collector, and the drying chamber were 33.5°C, 49.4°C, and 42.1°C, respectively.On the other hand, for unloaded conditions, the maximum average for the ambient temperature, the solar collector, and the drying chamber were 33°C, 48.3°C, and 48°C, respectively.This result shows that for the underloaded condition, the temperature at ambient and the solar collector was lower but in the drying chamber was higher than the loaded condition.The dryer is hottest about mid-day when the sun is usually overhead.The backup heater was used for the temperature measurement.Data collection took place over two days, with the findings averaged.The test was conducted on August 27 th and 28 th , 2021, at 18.00 hours, with a 30°C ambient temperature.The temperature fluctuations are depicted in Fig. 4 (b).At 20.30 hours, it was noted that the drying chamber's temperature was 39°C.The calculated drying rate was 0.09 kg/hr using equation no. 2 and the moisture content was 84.7% using equation no. 3.

Testing using silica gel
This testing was carried out to determine the moisture loss using only the silica gel in a loaded dryer condition without using a solar collector, which is illustrated in Fig. 6.The test was carried out in two days, and the results averaged.After 5 hrs of the process, it was shown that moister content was 8.27% and the drying rate was 0.012 kg/hr using equation no 2 and 3 respectively.
where, Qe = Quantity of heat used in evaporating moisture, L = 0.81m, W = 0.76m, A = L×W, I = 327.75w/m², t = 7 hrs.The drying efficiency was found to be 24.44 %, indicating a rather effective use of solar radiation in drying the product.Solar drying improves the quality of dried goods by improving nutrient retention, physical appearance, antioxidant qualities, and sensory and product acceptance scores.Fig. 7 shows a photograph of sun-dried potatoes compared with modified potato slices.

Conclusions
To study the drying behavior of potato slices, a solar dryer that uses photovoltaic (PV) solar panels to power the heating element, axial flow fan, and battery charging system was built.The findings showed that the solar-energy dryer could generate temperatures as high as 49.4°C and 42.1°C in the collection and dryer chambers, respectively.The highest ambient temperature for drying in the open sun was 33.5°C under loaded conditions.The calculated average drying rate was 0.09 kg/hr.To make highquality, shelf-stable dried potato slices, the cycle's duration had to be shortened, and the drying temperature was comparatively raised to 49.4°C.The temperature reached 49.4°C, which is perfect for drying fruits and vegetables.The study proves that the prototype agricultural dryer using solar power is the most suitable drying equipment for Bangladesh.

Acknowledgment
The authors are grateful to the members of the Department of Mechanical Engineering, Military Institute of Science and Technology (MIST) for supporting and providing laboratory facilities to carry out this research.

Figure 3 .
Figure 3. Variation of Solar radiation at different timeAs recorded from the weather station, the incident solar radiation with output voltage is shown in Fig.3for two full days of sunlight exposure.Triplicate experiments were conducted for each procedure to show the average radiation levels.The solar radiation levels were generally similar amongst separate

Figure 4 .
Figure 4. Variation of Relative Humidity with operating hours.

Figure 5 .
Figure 5. Variation of temperature using a backup heater

Figure 6 .
Figure 6.Moister is removed using silica gel 3.5.Dryer Efficiency and Comparison of Product Quality The performance of the solar dryer was evaluated in terms of several efficiency parameters as the thermodynamic properties.Using equation no. 1, the efficiency of the dryer is  =  ×× = 24.4%(4)

Figure 7 .
Figure 7. Photograph of sun-dried potatoes compared with modified dryer potato slices