DEVELOPMENT OF FORCED CONVECTION SOLAR ONION DRYER

Transcription

1 DEVELOPMENT OF FORCED CONVECTION SOLAR ONION DRYER PROJECT REFERENCE NO. : 37S0199 COLLEGE : SHRI MADHWA VADIRAJA INSTITUTE OF TECHNOLOGY, UDUPI BRANCH : MECHANICAL ENGINEERING GUIDE : DR. RAJA YATEESH YADAV STUDENTS : NARASIMHA PAI K KEERTHAN NAGARAJA ULITHAYA Keywords: Drying Chamber The drying chambers made of a highly polished plywood box held in place by angle irons. The material has been chosen since wood is a poor conductor of heat and it has smooth surface finish; heat loss by radiation is minimized. Cover Plate This is transparent sheet used to cover the absorber, thereby preventing dust and rain from coming in contact with the absorber. It also retards the heat from escaping. It is placed about 25.4 mm above the absorber. Common materials used for cover plates are glass, flexi glass, fibreglass, reinforced polyester, thin plastic films and plastics. Absorber Plate This is a metal plate painted black and placed about 25.4 mm below the cover to absorb the incident solar radiation transmitted by the cover thereby heating the air between it and the cover. In its plainest form, it is no more than a blackened metal plate exposed to the sun. Insulator This is used to minimize heat loss from the system. It is placed under the absorber plate. The insulator must be able to withstand stagnation temperature, should be fire resistant and not subject to out-going gassing; and should not be damageable by 1

2 moisture or insect. Insulating materials are usually fibreglass, mineral wool, Styrofoam and urethanes. Blower fan This is used to draw the atmospheric air into the solar flat plate collector. The air drawn by the blower fan will pass through the copper tubes, the higher density air will move to the lower density air, so that suction will be created at the atmospheric air entering side of the pipe. Therefore air enters continuously and the process continuous. Introduction: Onion (Allium cepa) is one of the most popular vegetable that form of daily diet. In India, onion is an important commercial crop. It is widely grown is different parts of the country. At present, India stands second larger producer of onion in the world, next only to China. Indian onions are famous for their pungency and are available round the year. At least 175 countries grow onions. The major onion producers are Maharashtra, Gujarat, Uttar Pradesh, Rajasthan, Orissa, Karnataka, Tamil Nadu, Madhya Pradesh and Bihar. Maharashtra ranks first in onion production with a share of (18%) in terms of productivity. After harvesting onions, they have to be dehydrated so that they can be stored for long period of time. The local farmers dry the onions using natural sunlight. Drying in natural sunlight is possible in areas where, in an average year, the weather allows onions to be dried immediately after harvest. The main disadvantages of drying in natural sunlight are, contamination, theft or damage by birds, rats or insects etc., Slow or intermittent drying and no protection from rain or dew that wets the product, encourages mould growth and may result in a relatively high final moisture content. India lies between the latitude of 7 N and 37 N and receive abundant amount of solar radiation through the year. Solar energy is a renewable source of energy which is available at free of cost. Hence in the present work, an attempt has been made to develop a Solar Onion Dryer. In the present model the air is heated by solar radiation and the heated air is made to flow through just harvested onions. Thus moisture gets removed from the onion and become dried. 2

3 Objectives: In this project an attempt has been made to develop a forced convection solar onion dryer. The objectives of the project work are To conduct an experiment of drying just harvested onions by using forced convection. To determine the moisture content removed from just harvested onions in forced convection solar dryer. To compare the results of moisture content removed by forced convectional method and onions dried by conventional method. To determine the difference in the efficiency obtained by forced convection method over conventional method. Methodology: A solar power is has low density per unit area (1 kw/m 2 to 0.1kW/m 2 ). Hence it is collected by covering a large ground area by solar thermal collectors. It absorbs solar energy as heat and this can use to heat the air or water or any fluid. The heated air can use to the any other work. In this project air is the working media, air is heated which is sucked from the atmosphere. In the onion dryer the liquid flat plat collector is used. Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar energy into heat energy. The heat is transferred to air passing through pipes attached to the absorber plate. Absorber plates are commonly painted with "selective coatings," which absorb and retain heat better than ordinary black paint. Absorber plates are usually made of metal- typically copper or aluminum because the metal is a good heat conductor. Copper is more expensive, but is a better conductor and less prone to corrosion than aluminum. The heated air from the pipes is send to the draying chamber where the onion kept layer by layer. The heated air will absorb the moisture from the onion and is fed to the atmosphere naturally there is no extra feeding mechanism is needed because the hot air is continuously fed. The onion is drayed in the chamber because of hot air and later which is taken out layer by layer. A blower fan is added to draw the atmospheric air because when the air passing through the hot pipe the density will increase. The higher density air will move to the lower density air. So that suction created at the atmospheric air entering side of the pipe. Therefore air enters continuously and process continuous. The required temperature of the onion drying is 65 C 3

4 which is obtained from the setup so onion can dry. It can be kept to the long-time compared to the natural drying. Drying Chamber Solar Panel Blower Fan Pipe Hoses Figure 1: Forced Convection Solar Onion Dryer 4

5 Results and calculation: Details of onion: Harvested on -13 th April 2014 Harvested place: Honnavara, Uttara Kannada Dist. Location of Drying: SMVITM, Bantakal Figure 2 Fresh Harvested Onions Determination of moisture content removed M wb = {(M t -M d) / M t } x100 Trial 1: Date of drying: 14 th April 2014, 10 am Date of readings taken: 15 th April 2014, 12.30pm By Conventional Method Initial mass, M t = 938 g Final mass,m d = 918 g M wb = {( ) / 938} x100 = 2.13 % 5

6 Using Solar Drier Initial mass, M t = 938 g Final mass,m d = 912 g M wb = {( ) / 938} x100 = 2.8 % Figure 3 Onion dried using conventional method (trial 1) 6

7 Figure 4 Onion dried using solar drier (trial 1) Trial 2: Date of drying: 16 th April 2014, 10 am Date of readings taken: 17 th April 2014, 12.30pm By Conventional Method Initial mass, M t = 855 g Final mass,m d = 835 g M wb = {( ) / 855} x100 = 2.33 % Using Solar Drier Initial mass, M t = 855 g Final mass,m d = 828 g M wb = {( ) / 855} x100 = 3.16 % 7

8 Figure 5 Onion dried using conventional method (trial 2) Figure6 Onion dried using solar drier (trial 2) 8

9 Conclusions: In the present work, an attempt has been made to develop a forced convectional solar onion dryer. From the result obtained the following conclusion can be made 1. For the given location and for a given period of time, moisture content removed in the solar onion dryer is higher compared to conventional drying. 2. Onion dried using the solar onion dryer is more attractive and helps the farmers to get more profit from the consumers. 3. Since the onions are dried in the close chamber by supply of hot air, it is free from theft, animals, birds, mist, etc. 4. Efficiency is more in this method. 5. Time required for drying is less. 9