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NCETSTM 2K14, MREC
Development of Solar Dryer for post harvest Treatment of Cereals -
Review
Sumit S. Dharmarao1
1
PG Stud...
NCETSTM 2K14, MREC
controllable, factors. From FAO report it is observe that
various commodities which are loss due to imp...
NCETSTM 2K14, MREC
1. Direct solar dryers. In these dryers, the material to be
dried is placed in a transparent enclosure ...
NCETSTM 2K14, MREC
The drying cabinet: The drying cabinet, together with the
structural frame of the dryer, was built from...
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this paper is about drying of cereals with help of solar dryer

Development of solar dryer for post harvest treatment of cereals by sumit dharmarao

  1. 1. NCETSTM 2K14, MREC Development of Solar Dryer for post harvest Treatment of Cereals - Review Sumit S. Dharmarao1 1 PG Student ,Department of Mechanical Engineering, Bramhadevdada Mane Institute Of Technology, Solapur, Maharashtra sumitdharmarao@gmail.com Abstract—although in many parts of India certain crops can be produced at certain period of year, the major part of the produce such as cereals & other crops are seasonal. Food produced in one harvest period lasts only for few weeks. This which must be stored for gradual consumption until next harvest and seeds must be held for next season crops. Also the market value of any crop tends to rise during off season. Therefore it is important to minimize losses and prepare the food for long lasting storage. This paper consist of various requirement of storage of cereals as cereals covers larger part of diet, for proper storage includes needs study of various properties of grains of cereals. This study shows that proper drying is required for proper storage, the solar dryer development details are presented in the paper. Index Terms— food storage, grain properties, post harvest, solar Dryer INTRODUCTION “Food waste” refers to food that is of good quality and fit for human consumption but that does not get consumed because it is discarded either before or after it spoils. Food waste is the result of negligence or a conscious decision to throw food away. Food loss is the unintended result of an agricultural process or technical limitation in storage, infrastructure, packaging, or marketing. [1] Technological limitations are basically faced by the developing nations such as India, Africa, Brazil etc. As per a news published in The Economics Times dated 12.Feb.2014 which is based on Food Corporation of India (FCI) replied RTI query asked by social activist Om Prakash Sharma in last few years 19,40,502 MT food cereals worth crores of rupees are wasted in India. The Food and Agriculture Organization of the United Nations (FAO) estimates that 32 percent of all food produced in the world was lost or wasted in 2009. This estimate is based on weight. When converted into calories, global food loss and waste amounts to approximately 24 percent of all food produced. “Food loss and waste” refers to the edible parts of plants and animals that are produced or harvested for human consumption but that are not ultimately consumed by people. Food loss and waste have many negative economic and environmental impacts. Economically, they represent a wasted investment that can reduce farmers’ incomes and increase consumers’ expenses. Environmentally, food loss and waste inflict a host of impacts, including unnecessary greenhouse gas emissions and inefficiently used water and land, which in turn can lead to diminished natural ecosystems and the services they provide. Grains may be lost in the pre-harvest, harvest and post- harvest stages. Pre-harvest losses occur before the process of harvesting begins, and may be due to insects, weeds and rusts. Harvest losses occur between the beginning and completion of harvesting, and are primarily caused by losses due to shattering. Post-harvest losses occur between harvest and the moment of human consumption. They include on-farm losses, such as when grain is threshed, winnowed and dried & losses along the chain during transportation, storage and processing. Important in many developing countries, particularly in India, are on-farm losses during storage, when the grain is being stored for auto-consumption or while the farmer awaits a selling opportunity or a rise in prices. There is probability of loss throughout the grain harvesting and agricultural marketing chains. During stripping of cereals (maize grain) from the cob, known as shelling, losses can occur when mechanical shelling is not followed up by hand-stripping of the grains that are missed. Certain shellers can damage the grain, making insect penetration easier. For crops other than maize, threshing losses occur as a result of spillage, incomplete removal of the grain or by damage to grain during the threshing. They can also occur after threshing due to poor separation of grain from the chaff during cleaning or winnowing. The major reasons stated are the un-proper drying & storing methods in our country for food losses.[2] With a high moisture content, grain is susceptible to mould, heating, discoloration and a variety of chemical changes. Ideally, most grains should be dried to acceptable levels within 2–3 days of harvest.[3] The main cause of loss during drying is the cracking of grain kernels that are eaten whole, such as rice. Some grains may also be lost during the drying process. However, failure to dry crops adequately can lead to much higher levels of loss than poor-quality drying, and may result in the entire harvest becoming inedible. Adequate drying by farmers is essential if grains are to be stored on- farm and poorly dried grains for the market need to be sold quickly to enable the marketing-processing chain to carry out adequate drying before the grains become spoilt. One of the problems in assessing levels of post-harvest loss is in separating weight loss caused by the very necessary drying operations from weight loss caused by other,
  2. 2. NCETSTM 2K14, MREC controllable, factors. From FAO report it is observe that various commodities which are loss due to improper drying the loss is by weight & 100% = 1.3billion tones. Fig.1various commodities which are lost due to improper drying Grains are produced on a seasonal basis. In many places there is only one harvest a year. Thus most production of maize, wheat, rice, jawar, bajra etc. must be held in storage for periods varying from a few days up to more than a year. Drying & storage therefore plays a vital role in grain supply chains. For all grains, storage losses can be considerable but the greatest losses appear to be of cereals, particularly in India. Losses in stored grain are determined by the interaction between the grain, the storage environment and a variety of organisms. Hence there is need to develop proper/ suitable drying method for studyis undertaken & reported in following points. LITERATURE STUDY Sun Drying: Drying using the sun under the open sky for preserving low value foods and agricultural crops may be the most inexpensive and extensively used option since early times. Major disadvantage of this method is contamination of the products by dust, birds, animals and insects, spoiling due to rain, wind and moisture, and the method totally depends on good weather conditions. Further, the process is labor intensive, unhygienic, unreliable, time consuming, non-uniform drying, and requires a large area for spreading the produce out to dry. [4]. Drying using the sun under the open sky for preserving low value foods and agricultural crops may be the most inexpensive and extensively used option since early times.The current energy scenario clearly depicts that the available fossil fuel resources and its derivatives may not satisfy the future demands. The need for alternate energy resources is the need of the day. India is a tropical country and we receive solar radiation throughout the year for most of the days in a year(360 days in year)[5]. Our country is an agricultural country and the utilization of solar power for drying of agricultural produces is a boom to our country’s economy. Especially in rainy days without drying facilities a vast amount of agricultural produces gets wasted and it affects the farmer’s life.Most parts of the country receive mean solar radiation in the range of 5-7 kwh/m² and has more than 300 sunny days in a year. India is the fifth largest energy consumer. Use of Other Energies:India is experiencing an acute shortage of electric power that is likely to be worsening day by day which stresses the need for deployment of renewable energy resources to extenuate this energy crisis use of renewable energy sources in the form of solar, biomass, biogas, and wind energy must be done. Present Solar Dryers: In India most common method to dry the cereals is sun drying which has many drawbacks as mentioned above solar Dryer is just a method to avoid contamination of food with unwanted things.[6] As solar Dryer involves some problems like no drying during cloudy weather & at nights. Researchers & scientists have suggested Electro solar Dryer but countries like India which are facing deficiency of of electric power can’t go for such substitute, Another option available is hybrid solar Dryer which is combination of biogas & solar Dryer which increases cost & require separate set up of biogas plant.[7] There has no work done to build a more efficient solar dryer by adding principles of solar space heating which will useful in cloudy weather & even at time when there is no sun. As we know current scenario of world energy requirements & diminishing fossil fuels all over the world which forces us to choose the non traditional energy sources for completing our needs. In India about 60% of electrical energy is generated by using coal which is kind of fossil fuel .Today India is facing the energy crisis & the Dryers which run on electrical power and used for drying the cereals is not affordable by farmers also there are many villages in our nation which are still waiting for the electricity so the best option to dry out the cereals is to use solar Dryer, but again it has problem of non working in rainy, cloudy season and at nights. PROPOSED DRYER FOR FOOD DRYING Many researchers has provided the solution of combining the another energies along with solar energy like electrical, biogas, direct heating but they require auxiliary set up & another source to run it which results into the hike in capital cost of Dryer. There is another concept of solar space heating which must be looked to solve the above mentioned problem. In solar space heating floors, walls are designed to collect, store & distribute solar energy in the form of heat in sunny days and fortunately almost 320 days of year India has bright sunny days. PROPOSED SOLAR DRYER FOR FOOD DRYING A solar dryer is an enclosed unit to keep the food safe from damage from birds, insects, microorganism, pilferage, and unexpected rainfall. The produce is dried using solar thermal energy in a cleaner and healthier fashion. Basically, there are four types of solar dryers:
  3. 3. NCETSTM 2K14, MREC 1. Direct solar dryers. In these dryers, the material to be dried is placed in a transparent enclosure of glass or transparent plastic. The sun heats the material to be dried, and heat also builds up within the enclosure due to the ‘greenhouse effect.’ The drier chamber is usually painted black to absorb the maximum amount of heat. 2. Indirect solar dryers. In these dryers, the sun does not act directly on the material to be dried thus making them useful in the preparation of those crops whose vitamin content can be destroyed by sunlight. The products are dried by hot air heated elsewhere by the sun. 3. Mixed-mode dryers. In these dryers, the combined action of the solar radiation incident on the material to be dried and the air preheated in solar collector provides the heat required for the drying operation. 4. Hybrid solar dryers. In these dryers, although the sun is used to dry products, other technologies are also used to cause air movement in the dryers. THE DRYING PROCESS IN PROPOSED DRYER The process of dehydration consists of removal of moisture from the produce by heat usually in the presence of a controlled flow of air. Cereals are placed on flat bottomed trays that are placed into the dryer. The solar rays enter the cabinet through the cover material. Upon reaching the solar collector or tray surface, they are converted into heat energy, raising the inside temperature. The heat energy is transferred to the produce to be dried. The heated produce gives out water vapor and dries up. Gradually the heated moist air goes up and leaves the drying chamber through the air outlet at the high end of the drier. The efficiency of drying of the solar dryer is influenced by relative humidity in the air, the moisture content of the materials to be dried and their amount and thickness. The solar radiation intensity on the materials varies with seasons, time of the day, and length of exposure, ambient air temperature, and wind speed, which are important factors. Fig.2 General drying preocess DESIGN CONSEDERATIONS Points to be consider while designing the natural convection solar dryer system: 1. The amount of moisture to be removed from the given quantity of cereals 2. Harvesting period during which drying is needed 3. The daily sunshine hours for the selection of the total drying time 4. The quantity of air needed for drying 5. Daily solar radiation to determine energy received by the dryer per day and 6. Wind speed for the calculation of air vent dimensions. CONSTRUCTION OF PROPOSED DRYER Construction of mixed-mode solar dryer: The materials used for the construction of mixed-mode solar dryer were inexpensive and easily obtainable in the local market. Figure 2 shows the essential features of the dryer consisting of the solar collector (air heater), drying cabinets, and drying trays. Solar collector setup: The experimental setup is an open-flow loop that consists of a test duct with entrance and exit sections, a blower unit, control valve, orifice plate, and various devices for measurement of temperature, and fluid head. The flow system consists of an entry section, a test section, exit section, a flow meter, and a centrifugal blower. The setup consists of two identical wooden ducts: one is rough absorber duct and other one is smooth absorber duct. As shown in figure 3. The absorber plate which is made up of an aluminum sheet which is painted black to increase the absorbing capacity. Another absorber plate is roughed with strips to provide obstacle to the path of air to obtain the maximum temperature. The solar collector assembly consisted of airflow channels enclosed by transparent cover (glazing). The glazing is a single layer of 4-mm thick transparent glass sheet. The outlet of duct is connected to the orifice meter with an inclined manometer to measure the mass flow rate of air. The outlet of the orifice meter is connected to the inlet of the blower. The outlet of blower is connected to the inlet of the cabinet dryer. Fig.3 Mixed mode solar type
  4. 4. NCETSTM 2K14, MREC The drying cabinet: The drying cabinet, together with the structural frame of the dryer, was built from well-seasoned wood which could withstand termite and atmospheric attacks. An outlet vent was provided toward the upper end at the back of the cabinet to facilitate and control the convective flow of air through the dryer. The roof and the two opposite side walls of the cabinet are covered with transparent glass sheets of 4-mm thick, which provided glass. The dryer skeleton was formed with wood raised 200 mm from the ground. Drying trays: The drying trays are contained inside the drying chamber and are constructed from a double layer of fine wire mesh with a fairly open structure to allow drying air to pass through the food items. The three trays were separated with a gap of 100 mm. The orientation of solar collector: The flat plate solar collector is kept horizontally and oriented in such a way that it receives maximum solar radiation during the desired season of use. The best stationary orientation is south in the northern hemisphere and north in the southern hemisphere. Therefore, solar collector in this work is orientation facing south. OPERATION OF PROPOSED DRYER The dryer was a passive system in the sense that it had no moving parts. The sun rays entering through the collector glazing energizes it. The absorption of the rays is enhance by the inside surface of the collector that were painted black and the absorbed energy heats the air further weight loss occurred were known. The dryer performance was evaluated and comparison was made with the result obtained with natural drying process and by forced convection with smooth and rough absorber plate. CONCLUSIONS 1. A simple and inexpensive mixed-mode solar dryer was designed and constructed using locally sourced materials. 2. The hourly variation of the temperatures inside the cabinet and air heater is much higher than ambient temperature during the most hours of the day. 3. The temperature increase inside the drying cabinet was up to 60 to 80°C for most the hours in the noon time. The drying rate, collector efficiency, and percentage of moisture removed for drying cereals were 0.52 kg/h, 67.5%, and 88%, respectively. 4. The dryer exhibited sufficient ability to dry food items at a reasonable rapid time to a safe moisture level and simultaneously ensured a superior quality of the dried product 5. The drying of cereals in the open sun takes 7 to 8 days during clear sunny weather conditions. However, it only takes 3 to 4 days in the solar cabinet dryer under similar weather conditions. Also, the quality of dried grapes is remarkably better in cabinet dryer compared to open sun drying as the product is protected from dust and insects. 6. The dryer is easy to build and required only semiskilled laborer and limited facilities to fabricate. Thus, the dryer is suitable for use in urban as well as rural areas of the country. REFERENCES [1] Brian Lipinski & et all, “ Installment two of creating a sustainable food future reducing food loss & waste” World Resource Insitute [2] News based on RTI report published in Economics Times dated 12.feb.2014 [3] Harris, kentel L and carl J. lindblad, eds.- “ Post harvest drain loss assessment methods a manual of methods for evaluation of post harvest losses” American association of cereals chemists, 1976. [4] A report on “food processing in Bihar the road ahead ” IL&FS analysis; RAU and state government publications. Pp. 28-31 [5] “Krishidarshini 2014”, Mahatma Jothiba Fule krishi vidyapeeth, Rahuri, Maharashtra, India. [6] M.G. Campos “Good practices in grain Storage” 9th International Working Conference on Stored product protection, France 2007. [7] K gunkesaran, sannugam & P. suresh. “modeling & analytical Experimental study of hybrid solar dryer integrated with biomass dryer for drying” IPCSIT, vol.28 (2012), IACSIT, press, Singapore. [8] Paul artiuch & Samuel kornstein “ sustainable Approaches to Reducing Food Easte in India” MIT Independent activities period research project, February 2012 [9] Chandrakumar pardhi,and jiwanlal Bhagoria “ Development and Performance evaluation of Mixed mode solar dryer with forced convection” International Journal of Energy & Engineering 2013.
  • JOSHUAJEYANANTH

    Jun. 7, 2020
  • MwakaChileshe

    May. 30, 2020

this paper is about drying of cereals with help of solar dryer

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