Experimental Performance Investigation of Solar Dryer Using Flat Plate

Experimental Performance Investigation of Solar Dryer Using Flat Plate Collector

Dr.Krupal Prabhakar Pawar

Professor, Rajiv Gandhi College of Engineering, Karjule Harya, Takalidokeshwar

Abstract:

Solar Drying is one of the important processes required for the preservation of food and agricultural products. Bacterial growth and moisture are being removed in this process. It helps for preserving the food products for more long time. Solar drying is an effective method used for drying food products. The device used for the preservation of food products using solar energy is called a solar dryer or solar dehydrator. The solar dryer is classified based on the mode of drying, circulation of air, type, and arrangement of a cabinet of solar air collectors. The preserved raisin is a favorite dry fruit in India. Traditionally the drying of raisins mainly exposes natural sunlight and requires about 21 days. In this experiment, a comparative study between natural sun drying and solar drying using a flat plated collector dryer was performed from 29th March 2020 to 19th April 2020. The incident area of solar radiation on the collector was 0.9m2 which had a black rough surface aluminum plated absorber of 1.8m² area attached below the covered acrylic glazing used in the collector body. It was found that the latitude inclination of 19.5° had a maximum temperature of 69°C during 01:00 PM – 02.00 PM hours. As the result found that, drying of raisins in a natural way takes up to 21 days, and comparatively it takes 7 days to dry using the solar dryer. Thus the drying period is reduced by 14 days.

Keywords : Solar Drying, Raisins, Agriculture Products, Natural Sunlight.

I. INTRODUCTION

The drying of grapes to form into raisins usually relies on direct sunlight exposure. This drying method requires more periods and lower quality of dried products. The drying of grapes is usually conducted under low temperatures, and thus, the use of solar dryers for dehydrating grapes is one of the best alternatives. Due to energy crises, most of the food processing and food preservation activities in the industries are dependent upon non-renewable energy sources. It needs to check for alternatives for non-renewable and polluting fossil fuels. The use of renewable energy sources like solar energy is one of the best solutions for reducing the usage of non-renewable sources. The sun produces its energy by many thermonuclear reactions which creates a large amount of heat and electromagnetic radiation which is easily available throughout the earth. This solar energy is trapped by the heat exchanger devices called solar collectors. By comparing solar drying with traditional drying, solar drying has advantages such as better quality of food products, reduction in wastage of food products, the better market price can be achieved to the products, products can be protected against flies, rain, and dust, the product can be left in the dryer overnight during rain, since dryers are waterproof, prevent fuel dependence and reduces the environmental impact, It is more efficient and cheap 7.

The chosen raw material was grapes, which is a versatile spring crop. We have kept 500 grams of grapes in the tray for the initial experiment. Grapes required drying temperature ranging from 20°C to 60°C. The reason behind the selection of grapes as a raw material is the prices of dried grapes or raisins is much higher than the prices of fresh grapes available in the market, also per 100 gram of fresh grapes contains 81% of the water in it and the nutrition value we get is, 18% carbohydrates, 1% protein, 69Kcal energy and a moderate amount of vitamin K (14% of daily value) which can get from only 29 gram of split dried raisins (dried grapes), according to USDA (US department of agriculture) [1-3]. The effect of environmental conditions plays a vital role in the performance of solar dryers. The minimum temperature required to use the solar dryer system for processing food is 15°C 1. The performance is affected by the use of material quality such as Aluminium sheets at the inner side gives better results in drying of foods. It also acts as a good absorber 2. The moisture, solar radiation, wind speed, humidity are the parameters that decide the results. The addition of a fan/blower to introduce indirect forced convection will help to enhance performance as well as to reduce the heat loss during the operation 9. The flow of air at the inner side may be unidirectional or bidirectional which is generally affected by external air wind speed 8. While the shape and geometry of collectors are the research area in which work can be tested by changing parameters. However, the performance of solar dryers varies around 10-15% in terms of efficiency and the general achieved temperature range is 50+°C with 15-22% of Relative Humidity 11.

II. EXPERIMENTAL SETUP

The experimental model consists of major components like flat plate collector and drying chamber which are connected by the flexible pipe for the transfer of drying high-temperature air from the collector to the drying chamber. A flat plate collector is designed as per a multi-stage pattern to achieve more heat and it consists of layers of insulator and absorber in it, which are air securely covered by an acrylic sheet to convey solar radiation to the absorber. The drying chamber cabinet is isolated with insulator material and contains two trays of size 600 mm X 600 mm for carrying food hub for drying. For measurement purposes Arduino based smart data logging system is used which contains DHT22 & DHT11 respectively temperature and humidity sensors have a range of Temperature -40°C to 100°C and humidity 0% to 100% which are further connected with Arduino UNO motherboard and 16 X 2 character Alphanumerical display for showing the temperature and humidity values of sensors which kept in locations of a setup like Temperature & humidity at ambient, Temperature & humidity at absorber surface of collector, Temperature & humidity of air exhaled from the collector, Temperature & humidity inside the drying chamber[1-3]. The RTC (Real-time clock) device is used to indicate and manipulate the temperature and humidity data concerning time. The SD card logger is used to store the daily data of temperatures and humidity at different conditions. The model is programmed as per auto ON & OFF of the system from 10.00 AM to 06.00 PM. This study is conducted to examine the thermal characteristics of the solar dryer with a flat plated collector.

A. Flat plated Solar Air Collector

The flat plate solar air collector consists of components like a layer of insulation material, charcoal black painted absorber plates, airflow passages, acrylic glass, and coating material.

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Fig.1 Flat Plated Solar Air Collector

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Fig.2 Solar Collector with Absorber Surface

The cabinet body of the flat plate solar collector is made up of wooden plywood of inner sizes of 1500 mm X 600 mm X 120 mm and has a thickness of 12mm. The material for insulation of the collector body is polystyrene foam sheet and Aluminum foil having lower thermal conductivities as 0.033 W/mK & 0.06 W/mK respectively used to reduce the heat loss.

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Fig.3 Solar Air Collector Insulation

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Fig.4 Complete Assembly of Setup

The absorber element used for absorbing solar radiation is the rough texture of an aluminum sheet of 0.5 mm thickness in a conical harmonic shape for providing more surface area for absorber plates. These absorber plates are painted black with charcoal-activated paint. The important material used in the collector body is the acrylic glass sheet of thickness 3 mm. The solar collector is mounted and supported on a heavy-duty mild steel structure which is durable and adjustable concerning latitude angle and can be set up into standard angles like 15°, 20°, 35°, 40°, 45° as per investigating performance at different latitude angles.

B. Drying Chamber

The drying chamber cabinet is constructed from wooden plywood material to reduce heat losses. The dimensions of the drying chamber are 600 mm X 600 mm X 600 mm with a thickness of 12 mm. The drying chamber is insulated by polystyrene foam sheet and aluminum foil from the interior to reduce heat losses. Two trays made up of meshed steel structures are used inside the drying chamber to contain food products for the drying process. Both trays are placed at 250 mm distinct from each other. The drying chamber is constructed with a chimney at the top for sweeping out humid air from the drying chamber. The collector and the drying chamber are connected utilizing a flexible pipe of diameter 2 inches.

C. Fans (Air Exhauster)

A pair of DC fans are used as the end of each stage is used in solar collectors having discharge 35 CFM and having a total power rating of 12V 0.18 W of each fan. The velocity of air can be controlled with the help of a DC regulator.

II. METHODOLOGY

The performance investigation is carried out in two experimental procedures. In the first experiment, an amount of 500 gram fresh grapes were kept directly in an open atmosphere for drying. This study is based on a daily record of the amount of weight drop and change in color of the grape converting into perfect raisins. The second experimental project model of a solar dryer which consists of a flat plated multi-stage air flowing collector and drying cabinet chamber is tested by using a measured amount of fresh grapes of 500 grams which were kept in the solar dryer for testing and investigation of weight drop i.e. moisture removal. The experiment is conducted from 10.00 AM to 06.00 PM for a few couple of days. To achieve a steady-state condition the trial of experimental measurement is started one hour before the actual measurements were taken. Daily at the end of the day, the color appearance and the weight drop were recorded. During the trial of the experiment temperature and humidity at ambient condition, temperature and humidity at absorber plate, temperature, and humidity at collector air discharge, and temperature and humidity at dryer chamber are measured and recorded by the smart Arduino system and further saved into an SD Card. Temperatures and humidity were measured using DHT22 & DHT11 digital sensors which were further connected to the data logging system and LCD screen for continuous monitoring of data points. The velocity of the flow of air is regulated by the fan controller and measured by the anemometer. Also, the pyrometer is used to measure solar radiation.

III. RESULTS AND DISCUSSIONS

A. Thermal Performance of the Device

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Graph No.1 variation of temperature present at the atmosphere, temperature inside the collector body, temperature at the absorber surface, and temperature inside the drying chamber.

Graph No.1 represents the variation of time concerning temperature present in the atmosphere, the temperature inside the collector body, temperature at the absorber surface, and temperature inside the drying chamber on the first day of drying. (29th March 2020) which is typically a sunny day. Exactly at 10.00 AM, the drying of grapes is started. After 30 minutes, the temperature rise in the drying chamber is observed. The temperature inside the drying chamber is noted maximum from 03.00 PM to 03.30 PM as 41°C.

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Graph No.2 shows the variation of solar radiation incident on flat plate collector on 29th march 2020, it is noted that the peak radiation amount is 673 W/m2 from 12.30 PM to 01.00 PM.

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Graph No.3 variations of relative humidity (%) present at atmosphere and present inside the drying chamber concerning time.

As shown in Graph No. 3 the relative humidity at the beginning of the drying test was almost the same. The incident solar radiations during the start were 660W/m2 and the recorded atmospheric temperature was 33.3°C. After a time of 2 hours, solar radiation is raised with 13W/m2 which results in a reduction of humidity inside the drying chamber by 4%. After 04.00 PM the humidity in the atmosphere raised by 18% in just two hours, but it does not raise the humidity and moisture content inside the drying chamber. Due to heat trapped by the collector body and absorber surface, the dehumidification continued and reached up to 7% relative humidity.

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Graph No.4 variation of solar radiation incident on flat plate collector daily at 02.00 PM.

Graph No 4 shows radiation incidents on solar collectors. As per the Nashik, the altitude collector is set at the angle of 190. Which gets maximum solar radiation in collectors. In experimental processes, solar radiation gets an increases on a sunny day.

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Graph No.5 temperature at atmosphere and temperature inside the drying chamber of solar dryer daily at 02.00 PM

Graph No. 5 shows the variation in temperatures in ambient temperature and inside the drying chamber during the period of grapes drying in the solar dryer. As shown in the graph, on 29th March, 1st April and 4th April, due to cloudy weather the temperature gradient between the drying cabin and atmospheric temperature was low as 1.8°C, 2.6°C, 2.4°C but during the sunny days like 30th March and 3rd April the temperature difference between the drying cabin and atmospheric temperature was 3.8°C to 4.2°C.

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Graph No.6 Relative Humidity at atmosphere and Relative Humidity inside the drying chamber of solar dryer daily at 02.00 PM.

Graph No. 6 shows relative humidity in the atmosphere and inside the drying chamber. Reading takes at 02.00 PM every day. On 1st April 2020, humidity is high. Humidity, as compared to the atmosphere, is less in the drying chamber which increases the moisture removal rate.

B. Drying Behavior of the Device

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Graph No. 7 Daily variation in moisture content using the solar dryer and without using the solar dryer (Conventional method)

Graph No. 7 shows the daily variation of moisture content of two groups of grapes in which one is kept inside the solar dryer and the other is dried conventionally. As compared to natural drying the solar drying required 7 days for complete drying. In natural drying quantity and quality is low due to uneven drying processes.

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Graph No.8 variation of temperature and weight of raisins concerning days (Conventional drying)

Graph No. 8 shows that the conventional method of drying grapes takes 21 days to convert into raisins. The initial moisture content of grapes was 81%. As the moisture content of grapes reduces, the weight is also reduced. The sample weight of the grape bunch was 500 grams which was reduced up to 110 grams. At this stage, it is converted into perfect raisins since the weight drop was stopped after 110 grams.

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Fig.5 shows the weight drop from 500 grams to 110 grams and physical and aesthetical changes of grapes.

IV. CONCLUSION

A flat plated indirect type flat plate collector solar dehydrator was developed to investigate the performance of drying grapes. The following conclusions have been drawn from the results: Temperature inside the drying chamber cabinet is remains higher than the ambient temperature. The result of grapes drying is shown that the mass of 500-gram grapes converted into 110 grams of perfect raisins. The maximum output temperature of 59°C can be achieved. The average thermal efficiency of the solar dryer using a flat plate collector is 9.14%.

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