A STUDY ON SOLAR DRYING SYSTEM FOR FISH PRESERVATION

Transcription

1 A STUDY ON SOLAR DRYING SYSTEM FOR FISH PRESERVATION R. Regupathi 1* and S. Balasubramanian 2 1* Assistant Professor of Basic Engineering, College of Fisheries Engineering, Tamil Nadu Dr. J.Jayalalithaa Fisheries University, Nagapattinam, Tamil Nadu, India. 2 Dean, College of Fisheries Engineering, Tamil Nadu Dr.J.Jayalalithaa Fisheries University, Nagapattinam, Tamil Nadu, India. ABSTRACT Solar fish dryer is a multi-purpose facility, which is of great importance to the economic growth of coastal area fisheries folk. Fish drying is essential for preservation in aquacultural applications. It is performed either using fossil fuels in an artificial mechanical drying process or by placing the fish under the open sun. An artificial mechanical drying method is costly and has a negative impact on the environment, while the open sun method is totally dependent on the weather. This paper presents the state of various designs of solar dryers are reported in the literature that are widely used today. The indirect, direct, and mixed mode dryers that have shown potential in drying agricultural, aquacultural products are discussed. Aside from identifying the active and passive mode solar dryers, we also highlight the environmental influence on solar energy (harnessing) that plays a vital role in the solar drying sector. The solar drying system utilizes solar energy to heat up air and to dry any food substance loaded, which is beneficial in reducing wastage of product and helps in preservation. Keywords: solar dryers, ambient temperature, fish, solar energy. 1. INTRODUCTION Solar fish dryer is a multi-purpose facility, which is of great importance to the economic growth of coastal area fisheries folk. Open drying is one of the methods used to preserve food products for longer periods. The heat from the sun coupled with the wind has been used to dry food product for preservation. High prices and shortages of fossil fuels have increased the emphasis on using alternative renewable energy resources. Drying of agricultural products using renewable energy such as solar energy is environmental friendly and has less environmental impact. Different types of solar dryers have been designed, constructed developed and tested in the different regions of the tropics and subtropics. The major two categories of the solar dryers are natural convection and forced convection. In the natural convection the airflow is established by buoyancy induced airflow while in forced convection the airflow is provided by using fan operated either by electricity, solar module, or fossil fuel. However, in rural areas maximizing the food production capabilities of small farmers is difficult. To rectify the problem, drying has become one of the main processing techniques used to preserve food products in sunny areas. But, traditional open sun drying has some disadvantages such as products are not protected against flies, rain and dust. For the past few years, scientists and researchers have been trying to find the best alternative to overcome this problem. They invented various kinds of solar dryers for food products and have continuously worked to improve these dryers. It yields better quality and nutritious dry fish. At present, researchers are finding ways to reduce the use of fuels in solar drying. In the conservation of agricultural/aquaculture products drying is an essential process. The supply and demand of energy is an important consideration in the drying sector. In this case, solar energy storage can minimize the gap between supply and demand. In many developing countries, cost-effective more efficient dryers play a vital role in substituting for the demand for fuel at steady state conditions. Solar drying is already being applied in the aquacultural sector with positive results and has very few barriers that can be improved. During the drying period, maximum efficiency, minimum moisture content at ambient temperature and humidity should be considered. Dryers have been developed and used to dry agricultural products in order to improve shelf life. Most of dryers either use an expensive source of energy such as electricity or a combination of solar energy and some other form of energy. Most projects of these nature have not been adopted by the small farmers, either because the final design and data collection procedures are frequently inappropriate or the cost has remained inaccessible and the subsequent transfer of technology from researcher to the end user has been anything but effective (Berinyuy,2004). The objective of this study is to present some of the basic types of solar dryer with a view of providing a better clue on their effectiveness in the drying of agricultural products. 137

2 2. LITERATURE REVIEW 1. Diemuodeke (2011) designed and fabricated direct natural convection solar dryer to dry tapioca in rural areas. A minimum of 7.56 m 2 solar collector area is required to dry a batch of 100 kg tapioca in 20 hours (two days drying period). The initial and final moisture content considered were 79 % and 10 % wet basis, respectively. The average ambient conditions are 32ºC air temperatures and 74 % relative humidity with daily global solar radiation incident on horizontal surface of 13 MJ/m 2 /day. 2. Mohanraj (2009) studied the performance of an indirect forced convection solar drier integrated with heat storage material is designed, fabricated and investigated for chilli drying. To maintain consistent air temperature inside the drier, heat storage material was enabled.the inclusion of heat storage material increases the drying time by about 4 h per day. The chilli was dried from initial moisture content 72.8% to the final moisture content about 9.2% and 9.7% (wet basis) in the bottom and top trays respectively. It is concluded that, forced convection solar drier is more suitable for producing high quality dried chilli for small holders. Thermal efficiency of the solar drier was estimated to be about 21% with specific moisture extraction rate of about 0.87 kg/kw h. 3. Hossaina (2006) designed and developed A Mixed mode type forced convection solar tunnel drier, to dry hot red and green chillies under the tropical weather conditions of Bangladesh.The dryer consists of air inlet, fan, solar module, solar collector, side metal frame, outlet of the collector, wooden support, plastic net, roof structure for supporting the plastic cover, base structure for supporting the dryer, rolling bar and outlet of the drying tunnel. Moisture content of red chilli was reduced from 2.85to 0.05 kg/kg(db) in 20 h in solar tunnel drier and it took 32 h to reduce the moisture content to 0.09 and 0.40 kg/kg (db) in improved and conventional sun drying methods, respectively. 4. Forson (2007) designed a mixed-mode natural convection solar crop dryer (MNCSCD) for drying cassava and other crops. A batch of cassava 160 kg by mass, having an initial moisture content of 67% wet basis from which 100 kg of water is required to be removed to have it dried to a desired moisture content of 17% wet basis, is used as the drying load in designing the dryer. A drying time of h is assumed for the anticipated test location (Kumasi; 6.71N, 1.61W) with an expected average solar irradiance of 400W/m2 and ambient conditions of 25 1C and 77.8% relative humidity. He concluded that a minimum of 42.4m 2 of solar collection area, according to the design, is required for an expected drying efficiency of 12.5%. 5. Bukola (2011) designed, constructed and tested the solar wind-ventilated cabinet dryer. Comparatively, drying with the solar cabinet dryer showed better results than open air-drying. During the period of test, the average air velocity through the solar dryer was 1.62 m/s and the average daylight efficiency of the system was 46.7%. The maximum drying air temperatures was found to be 64 o C inside the dryer. The average drying air temperature in the drying cabinet was higher than the ambient temperature in the range of 5 o C in the early hours of the day to 31 o C at mid-day. 80% and 55% weight losses were obtained in the drying of pepper and yam chips, respectively, in the dryer. 3. DESIGN APPROACH Heat is necessary to evaporate moisture from the material in the process of drying, and a flow of air helps in carrying away the evaporated moisture. Two basic mechanisms involved in the drying process. One is the migration of moisture from the interior of an individual material to the surface, and the other is evaporation of moisture from the surface to the surrounding air. Mumba (1995) states that drying is done either in thin layer drying or deep layer drying. Thin layer drying which is done for fruits and vegetables, the product is spread in thin layers with entire surface exposed to the air, moving through the product and in the falling rate region Newton s law of cooling is applicable. Most of the grains are dried in deep layer that can be considered as a series of thin layers. Here, the temperature and the humidity vary from layer to layer. The drying of a product depends on external variables such as temperature, humidity and velocity of the air stream is a complex heat and mass transfer process. Whereas, internal variables depends on parameters like surface characteristics, chemical composition, size and shape of products, and physical structure (porosity, density, etc.). The rate of moisture depends whether the material is hygroscopic or non-hygroscopic and movement from the product inside to the air outside differs from one product to another. The period of constant drying for most of the organic materials like fruits, vegetables, timber, etc. is short. It is the falling rate period in which is of more interest and which depends on the rate at which the moisture is removed. 4. AIR PROPERTIES The major factors/properties in determining the rate of removal of moisture are the capacity of air to remove moisture is principally dependent upon its initial temperature and humidity and the greater the temperature and lower the humidity the greater the moisture removal capacity of the air. It is important to appreciate the difference between the absolute humidity and relative humidity of air. The relationship between temperature, humidity and other thermodynamic properties is represented by the psychometric chart. The absolute humidity is the moisture content of the air (mass of water per unit mass of air) whereas the relative humidity is the ratio, expressed as a percentage, of the moisture content of the air at a specified temperature to the moisture content of air if it were saturated at that temperature. Fig 4.1 shows the changes when it is heated using the solar energy and then passed through a bed of moist product in condition of air. The heating of air from temperature to is represented by the line AB. The relative humidity falls from to during heating the absolute humidity remains constant at. As air moves through the material, it absorbs moisture from the dried material. Sensible heat in the air is converted to latent heat Under (hypothetical) adiabatic drying; and the change in the condition of air is represented along a line of constant enthalpy,. Air temperature decreases to, but both absolute humidity and relative humidity increase from and and from to, respectively. The difference between the absolute humidity s at C and B is, the absorption of moisture by the air. If unheated air is passed through the bed, the drying process would be represented by the line AD. Assuming that the air at D to be at the same relative humidity,, as the heated air at C, then the absorbed moisture would be, considerably less than that absorbed by the heated air. 138

3 Figure 4.1 Representation of drying process 5. CLASSIFICATION OF DRYING SYSTEMS Drying systems can be classified according to their operating temperature ranges into two main groups of high temperature dryers and low temperature dryers. However, dryers are more commonly classified broadly according to their heating sources into fossil fuel dryers (more commonly known as conventional dryers) and solar-energy dryers. Strictly, all practicallyrealized designs of high temperature dryers are fossil fuel powered, while the low temperature dryers are either fossil fuel or solarenergy based systems. 1. High temperature dryers High temperature dryers are necessary when very fast drying is desired. They are usually employed when the products require a short exposure to the drying air. Their operating temperatures are such that, if the drying air remains in contact with the product until equilibrium moisture content is reached, serious over drying will occur. Thus, the products are only dried to the required moisture contents and later cooled. High temperature dryers are usually classified into batch dryers and continuous-flow dryers. In batch dryers, the products are dried in a bin and subsequently moved to storage. Thus, they are usually known as batchin-bin dryers. Continuous-flow dryers are heated columns through which the product flows under gravity and is exposed to heated air while descending. Because of the temperature ranges prevalent in high temperature dryers, most known designs are electricity or fossil-fuel powered. Only a very few practically-realized designs of high temperature drying systems are solar-energy heated (Ekechukwu (1999)). 2. Low temperature dryers In low temperature drying systems, the moisture content of the product is usually brought in equilibrium with the drying air by constant ventilation. Thus, they do tolerate Intermittent or variable heat input. Low temperature drying enables products to be dried in bulk and is most suited also for long term storage systems. Thus, they are usually known as bulk or storage dryers. Their ability to accommodate intermittent heat input makes low temperature drying most appropriate for solar-energy applications. Thus, some conventional dryers and most practically-realized designs of solar-energy dryers are of the low temperature type say Ekechukwu (1999). 6. DESIGN METHODOLOGY 6.1 Types of solar driers Solar-energy drying systems are classified primarily according to their heating modes in which the solar heat is utilized. These driers can be classified into two major groups, namely: Active solar-energy drying systems (most types of which are often termed hybrid solar dryers); Passive solar-energy drying systems (conventionally termed natural-circulation solar drying systems). Three distinct sub-classes of either the active/passive solar drying systems can be identified namely: Direct-type solar dryers Indirect-type solar dryers Mixed-mode type solar dryers Fig 1. Types of Solar Dryers 139

4 Direct Solar Dryer Indirect Solar Dryer Mixed Solar Dryer Active Dryer Passive Dryer 1) Open Sun Drying The most common drying method involves spreading the fish into thin layers on trays, covering the mats with shadow, and exposing the product to wind and sun used in tropical and sub-tropical countries. For large amounts of products the open drying process is not suitable, processed by large firms. [8]Open sun drying depends on environmental conditions, such as solar radiation, wind, and other ambient conditions. Because of many detriments, it leads to the deterioration of the products, such as reduced quantity due to the wind, wastage, rainfall, and animal and anthropological impedance. Also, there is a loss due to various reasons such as rodents, birds, insects and micro-organisms. It can lead to considerably huge losses and it has very slow process. Here, the products dried under the open sun drying usually fail to reach international standard quality. With the awareness of inadequacies involved in this method, a more scientific method of solar-energy utilization for drying has emerged termed as controlled drying or solar drying. Fig 2. Open Sun Drying 2) Direct-type Solar Dryer It uses only the natural movement of heated air. It is a type of dryer in which solar radiation is directly absorbed by the product to be dried. A part of incidence solar radiation on the glass cover is reflected back to atmosphere and remaining is transmitted inside cabin dryer. It is also called natural convection cabinet dryer. It is also called as natural convection cabinet dryer. The quality of product is reduced since the solar radiation is directly fall on the product. This dryer comprises of a drying chamber that is covered by a transparent cover made of glass or plastic. Due to presence of glass cover unlike open sun drying and the absorption of solar radiation, product temperature increase and the material starts emitting long wave length radiation that is not allowed to escape to atmosphere. Hence the temperature above the product inside chamber becomes higher. 140

5 Fig 3. Direct Solar Dryer 3) Indirect-type solar drying In an indirect solar dryer, at first the sun's heat is collected by the solar collectors and then it is passed onto the dryer cabinet, where the drying occurs. Goyal (1997) designed a reverse observer dryer based on this concept, shown in fig 4. Basunia (2001) says that the basic concept of reverse flat plate collector is used to dry food products in a solar cabinet-type dryer.the solar air that enters the chamber is heated and is then made to pass through over the wet crops. The air heaters are connected and a solar air heater is used to heat the air that enters the chamber. The heated air turns into warm humid air that passes through an outlet. This kind of dryer is better when compared to other dryers in terms of solving various equations based on energy balance. Also has better performance than other conventional cabinet type of dryers. Because of its low-cost requirements it is ideal for small farms. The dryer contains a flat plate collector, a drying chamber, thermally and acoustically insulated pipes that joined between the collector and chamber. This drying unit can still produce good quality products, under unfavourable weather situations. Fig 4. Indirect-type Solar Dryer 4) Mixed-mode type solar drying The mixed-mode solar dryer has no moving part that s why it is called the passive dryer. This kind of dryer requires energy from the sunrays that enters through the collector lustering. The sunrays are harnessed by trapping the heat of the air which is collected inside the chamber and the inside surface of the collector is painted black. The mixed-mode dryer is the best of the three because of the highest drying rate when compared to the three kinds of dryers. Simate (2003) discussed the basic concepts of mixed-mode solar dryers by involving computer modelling. Fig 5. Mixed-mode type Solar Dryer 141

6 USES OF SOLAR DRYING SYSTEM Solar fish dryer is a multi-purpose facility, which is of great importance to the economic growth of coastal area fisheries folk. Better Quality of Products are obtained. It Reduces Losses and Better market price to the products. Product can be left in the dryer overnight during rain, since dryers are waterproof. It is more efficient and cheap. It can be used for drying and preservation of fish without using conventional drying fuel such as kerosene, firewood, charcoal etc. Reducing conventional fuel demand can result in significant cost savings. Drying materials at optimum temperatures and in a shorter amount of time enables them to retain more of their nutritional value such as vitamin C. It is hygienic and healthier. Since materials are dried in a controlled environment, they are less likely to be contaminated by pests, and can be stored with less likelihood of the growth of toxic fungi. CONCLUSION This paper presents a study on the various types of solar dryers available today. Here, we discusses the types of the solar dryer which is beneficial than the sun drying techniques. For comparison of drying efficiencies of various driers, the dependence of the drying on the characteristics of product remains still as a problem. The classification illustrates solar dryer designs can be grouped systematically according to their operating temperature ranges, heating sources and heating modes, operational modes or structural modes. Three sub-groups of these dryers that differ mainly on their structural arrangement can also be identified, through integral or direct mode solar dryers, distributed or indirect-modes. This paper discusses low-cost drying technologies can be readily introduced in rural areas to reduce spoilage, improve product quality and overall processing hygiene. REFERENCES 1. Basunia,M., Abe,T., (2001) Thin-layer solar drying characteristics of rough rice under natural convection, Journal of Food Engineering, Vol.47, pp Bukola O.Bolaji., Tajudeen M.A. Olayanju., and Taiwo O. Falade.,(2011) Performance Evaluation of a Solar Wind- Ventilated Cabinet Dryer, The West Indian Journal of Engineering, Vol.33, Nos.1/21,pp Diemuodeke E. Ogheneruona., Momoh O.L. Yusuf., (2011) Design and Fabrication of a Direct Natural Convection Solar Dryer for Tapioca, Leonardo Electronic Journal of Practices and Technologies, ISSN ; No. 18, pp Ekechukwu, O.V., Norton, B., (1999) Review of solar-energy drying systems II: an overview of solar drying technology, Energy Conversion & Management, Vol.40, No.6, pp Forson, F.K., Nazha, M. A.A., Akuffo, F.O., Rajakaruna, H.,(2007) Design of mixed-mode natural convection solar crop dryers: Application of principles and rules of thumb, Kwame Nkrumah University of Science and Technology, Kumasi, Renewable Energy Vol. 32,pp Goyal R, Tiwari G. Parametric study of a reverse flat plate absorber cabinet dryer: a new concept. Solar Energy 1997;60: Hossaina, M.A.,and Bala, B.K., (2006) Drying of hot chilli using solar tunnel drier, Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute, Bangladesh Agricultural University, Mymensingh Mohanraj, M., Chandrasekar, P., (2009) Performance of a Forced convection Solar drier Integrated with gravel as Heat Storage material for Chilli Drying, Journal of engineering Science and Technology, Vol.4, No.3, pp Mumba, J., (1995), Development of a photovoltaic powered forced circulation grain dryer for use in the tropics, Renewable Energy, Vol. 6, No. 7, pp Narendra Rathore., Panwar, N.L.,(2011) Design and Development of energy efficient solar tunnel dryer for Industrial drying, Article in Clean Technologies and Environmental Policy, vol.13, pp Panwar, N., Kaushik, S., Kothari, S.,( 2012) State of the art of solar cooking: an overview, Renew Sustain Energy Rev, Vol. 16, pp Sandip sengar., Yashwant Khandetod., (2009) Low cost solar dryer for fish, African Journal of Environmental Science and Technology Vol. 3 (9), pp , 13. Simate I, (2003) Optimization of mixed-mode and indirect-mode natural convection solar dryers, Renew Energy, Vol. 28, pp