SOLAR TUNNEL FISH DRYER FOR SEASONAL APPLICATION IN THE PERSPECTIVE OF BANGLADESH

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1 Engineering e-transaction (ISSN ) Vol. 4, No. 2, December 2009, pp Online at SOLAR TUNNEL FISH DRYER FOR SEASONAL APPLICATION IN THE PERSPECTIVE OF BANGLADESH M. A. Wazed 1, M. T. Islam 2 and N. Uddin 2 1 Department of Engineering Design and Manufacture, University of Malaya (UM), Kuala Lumpur, Malaysia, 2 Department of Mechanical Engineering, Chittagong University of Engineering and Technology (CUET), 4349 Chittagong, Bangladesh awazed@gmail.com ABSTRACT Dry fish is one of the major export items of Bangladesh, a least developing country in south Asia. Most of the dry fish industries in the country are using direct sunlight for drying the fishes. The main objectives of this research are: i) to design and to fabricate a model type solar tunnel dryer like a solar air heater; ii) to analyze the effectiveness of the dryer; and iii) finally a comparison is performed with traditional method of sun drying. The authors have constructed a simple solar tunnel using locally available low cost materials. The collector surface temperature, duct temperature and ambient temperature, as well as relative humidity with definite time interval are measured. The maximum obtained surface and duct temperatures are 5253C and 3738C, respectively. The use of solar tunnel dryer leads to considerable reduction of drying time in comparison to the drying in direct sunlight. The fishes dried in the solar tunnel dryer are completely protected from rain, insects and dust. The quality of the dried fish in the tunnel dryer is better than the sun-dried products. Keywords: Solar dryer, drying fish, Bangladesh 1. INTRODUCTION Fish is an important component of the daily diet and the dried fish is an important source of protein in Bangladesh. Being a country of rivers and floodplains with a high potential of aquatic resources, fish plays a very important role in the daily life of many people in Bangladesh. The Bengali expression Mache Bhate Bengali, or Fish and Rice make a Bengali, illustrates this importance. Bangladesh produces 1,400,000 tonnes of fish annually mostly through inland capture fisheries and aquaculture (Graaf and Latif, 2002). Annual production of inland and marine fish (fresh) in Bangladesh is million metric ton and about million ton is used for internal consumption. Annual export of dried fish is about 1278 metric ton and Bangladesh earns about crore taka (local currency) as foreign currency and it ranks the third of the export of the country. In Bangladesh annual per capita consumption of inland and marine fish is 8.2 kg. Fish products account for 6% of the gross domestic product (GDP), 12% of export earnings and 70-85% of the animal protein intake in Bangladesh (Graaf, 2003). Freshwater fish account for more than 50 percent of dietary fish intake, and inland fisheries provide a source of employment to nearly 13 million people living in the floodplains. Drying of fish is mainly carried out by traditionally under open sun. Sun drying represents a low cost processing technique to preserve fish (Jain and Pathare, 2007). The traditional method used raised bamboo made platform in the coastal areas of Bangladesh. A substantial loss occurs in quantity and quality. To avoid the infestation due to insect and larva attack and for safe storage, commercial dried fish producers apply insecticides including DDT in fish. This fish is highly contaminated and creates broad spectrum of environmental and health hazards. Therefore, proper drying of fish is essential to save this valuable source of protein by reducing the spoilage. Figure 1 shows the fish production in Bangladesh. The quality of the dried products is the most important parameter in drying technology. Patil (1989) compared the quality of peppers after sun drying, polythene solar draying and solar cabinet drying. He found that the solar cabinet drying offers some advantages over direct sun drying in terms of better quality and faster rate of drying. Jayaraman et al. (1992) compared ascorbic acid retention in cauliflower, cabbage and bitter gourd dried by three different methods: i) directly under the sun, ii) under the sun in a black polythene tent, and iii) in a drying cabinet with three solar collectors. They reported that the direct exposure of these products to the sun decreased the quality factors like vitamin 73

2 retention. The use of solar energy in an indirect way may improve the quality of the end products. Figure 1: Fish production (marine and freshwater) in tones in Bangladesh (Source: FAO, FISHSTAT, 2007) Efforts were made to introduce polythene tent solar driers in coastal areas of Bangladesh. This dryer is effective in controlling insect larva. But, it does not provide any improvement in the performance of drying although the temperature inside dryer is 7-20C higher than the ambient temperature. The polythene tent solar drier thus suffers from the limitation due to extremely low buoyancy induced low airflow inside the dryer. The most promising option of solar drying appears to be a forced convection solar tunnel dryer. The temperature of food during sun drying is usually 5-150C above ambient temperature (Grabowski et al., 2006) Fish is a very important foodstuff in developing countries, due to its high protein content and nutritional value. Temperature is a very important factor for accelerating the process of spoilage. The spoilage reactions connecting on the death of the fish proceed at very rapid rate. Fresh fish contains up to 80% of water. It is highly perishable material and having a short storage life (Bala and Mondol, 2001). When moisture content is reduced to 25%, contaminating agents cannot survive and autotypic activity is greatly reduced. However, to prevent mould growth during storage, moisture content must be reduced to15%. Typical species of fish can generally withstand at temperature range of 45-50C before proteins are denatured or cooking starts. In Bangladesh, each year a large quantity of fish and fish products are spoiled due to lack of proper preservation and storage facility particularly during the peak season of harvesting. Moreover, fishermen do not get legitimate return of their harvest during the peak period for lack of preservation and transportation facilities in the coastal areas of the country. Even sometimes they just have to abandon the spoiled as it becomes unfit for human consumption. Whatever the amount of picks, it receives no value until the consumer consumes as a food. Proper drying of freshly collected fish can minimize the amount of fish spoiled. It is estimated that about 30% (about 307,500 MT) of the freshly harvested fish is spoiled every year due to lack of proper preservation facility. About 40% (71,750 MT, dry weight) of the remaining harvested fish is dried. Among the dry fishes about 60% (43,050 MT) contaminated by both insects and insecticides and they are not fit for human consumption. The conventional sun drying system has limitations to control the drying process and parameter, weather uncertainties, high labor factors, drying areas, insect infestation, control of dust and other foreign materials and so on. However, open sun drying is widely practiced in tropical and subtropical countries to preserve agricultural products, where solar radiation is convenient (Szulmaver, 1971) and where it is abundant, inexhaustible, and environmental friendly (Basunia and Abe, 2001). A straight forward steady state analysis has been adopted to evaluate the performance of different solar dryers by using simple basic energy balance equations by Joshi et al. (2004). The empirical results for the same are shown in Gewali and Ramchandra (2004). The literatures show that the solar tunnel dryer is the most efficient one. The authors would like to refer the readers to Sharma et al. (2009) and Ramana (2009) for a comprehensive review on the solar dryers. Figure 2: Average values of hourly solar radiation and ambient temperatures 74

3 Bangladesh is a tropical country and the solar radiation is abundant and inexhaustible throughout the year (Figure 2). The average temperatures and rainfall is much higher for April-October of a year (Figure 3). Therefore, the solar drying would be the best option for Bangladesh. Also the literatures show that the solar tunnel dryer is the most efficient among the available options. Hence the authors are highly motivated towards this research. In this article the authors fabricated a solar tunnel dryer like a solar air heater, analyzed its performance and compare with similar work. bacteria and enzymes. Any reduction in the temperature prior to processing will maintain the quality of the fish for longer. Fish can be kept cool by covering it with clean, damp sacking and placing it in the shade. Although this method is simple and requires no special equipment, the fish still begins to deteriorate within a few hours. An alternative is to pack the fish with ice. This is an effective method and preserves the fish for a longer period of time. Freezing is another method for cooling fish. This technique provides long-term preservation, but it is relatively expensive in terms of equipment and operating costs. It is not recommended for the majority of small-scale fisheries Cured Fish Products Curing involves the techniques of drying, dry salting/brining (soaking in salt solution) or smoking. These may be used alone or in various combinations to produce a range of products with a long shelf- life. For example: Figure 3: Monthly average temperature and rainfall in Bangladesh 2. PRESERVATION OF FISH The different techniques of fish preservation are discussed in this section Cooked Fish Cooking provides short-term preservation of fish and it usually allows for few days before any deterioration becomes noticeable. Different methods are used for cooking fish but the principle of the processes is similar. The flesh of the fish softens, enzymes become inactivated and the process kills many of the bacteria present on the surface of the fish. Boiling and poaching both involve cooking the fish in hot water whereas frying uses hot oil. They are very simple and require no more than basic-household equipment and are therefore suitable for small-scale production Cooled/Frozen fish The spoilage of fish is directly related to temperature. Up to 40ºC, The higher the temperature, the faster the spoilage. Above 40ºC the generated heat will destroy Drying Smoking Drying Brining Smoking Drying Salting Drying Salting Drying Smoking These techniques reduce the water content in the flesh of the fish, and thereby prevent the growth spoilage microorganisms Dried Fish The heat of the sun and movement of air remove moisture, which causes the fish to dry. In order to prevent spoilage, the moisture content needs to be reduced to 25% or less. It depends on the oiliness of the fish and whether it has been salted. Traditionally, whole small fish or split large fish are spread in the sun on the ground, or on mats, nets, roofs or on raised racks. Sun drying does not allow very much control over drying times, and it also exposes the fish to attack by insects or vermin and there are all possibilities of contamination by sand and dirt. Such techniques are totally dependent upon the weather conditions. The ideal is dry weather with low humidity and clear sky. 75

4 2.5. Salted Fish Most food poisoning bacteria cannot live in salty conditions and a concentration of 6-10 percent salt in the fish tissue will prevent their activity. The product is preserved by salting and will have a longer shelf life. However, a group of microorganisms known as 'halophytic bacteria' are salt loving and will spoil the salted fish even at a concentration of 6-10 percent. Salting requires minimal equipment, but the method used is important. Salt can be applied in many different ways. Traditional methods involve rubbing salt into the flesh of the fish or making alternate layers. The recommended levels of salt usage are percent of the prepared weight of the fish. However the concentration of salt in the flesh is not sufficient to preserve the fish, if it is not uniformly applied. A better technique is brining. It involves immersing the fish into a pre-prepared solution of salt (36 percent salt). The advantage is that the salt concentration can be more easily controlled and salt penetration is more uniform. Brining is usually used in conjunction with drying Smoked Fish The preservative effect of the smoking process is due to drying and the deposition of the natural chemicals of wood smoke in the fish flesh. Smoke from the burning wood contains a number of compounds, which inhibit bacteria. Heat from the fire causes drying, and if the temperature is high enough, the flesh becomes cooked. Both of these factors prevent bacterial growth and enzyme activity, which may cause spoilage. Fish can be categorized as: Cold smoking. In this method, the temperature is not high enough to cook the fish. It is not usually higher than 35ºC. Hot smoking. In this method, the temperature is high enough to cook fish. Hot smoking is often the preferred method. This is because the process requires less control than cold processing and the shelf life of the hot-smoked product is longer; because the fish is smoked until dry. Hot smoking consumes more fuel than the coldsmoking method. Traditionally, the fish would be placed with smoldering grasses or wood. Alteration, fish may be laid or hung on bamboo racks in the smoke of a fire Fermented Fish Fermentation is a process by which beneficial bacteria are encouraged to grow. These bacteria increase the acidity of the fish and therefore prevent the growth of spoilage and food-poisoning bacteria. Additionally, salt is used to prevent the action of spoilage bacteria and allow the fish enzymes and the beneficial acidproducing bacteria to soften (break down) the flesh. Fermentation is therefore the controlled action of the desirable microorganisms in order to alter the flavor or texture of the fish and extend the shelf life. 3. PERSPECTIVES OF THE RESEARCH IN RESPECT TO BANGLADESH Tropical area lying between the latitudes 350 north and south, which have at least 2000 hours of bright sunshine per year, are ideal for the utilization of sun energy. In Bangladesh, monsoon starts from June to September and the duration of cloudiness is more than 70% of the day. It may well be assumed that sunshine would prevail 200 hours annually in most of the parts of the country where the highest percentage would occur from the middle of September to the middle of April in a year. In such cases the use of solar tunnel dryer leads to considerable reduction of drying time in comparison to direct sun drying. The fishes being dried in the solar tunnel dryer are completely protected from rain, insect and dust. The fishes dried in the tunnel dryer are of quality-dried products as compared to sun-dried products. Thus, this study demonstrates the potentiality of solar tunnel drier for drying of fish in Bangladesh. The foremost intension of this research is to design and to fabricate a model type solar fish dryer to achieve the following specific objectives: i. To determine the effects of different pretreatment and drying parameters on the quality of dried fish. ii. To adopt and optimize the solar tunnel dryer suitable for drying of fish for Bangladesh for mass and medium scale commercial production. 76

5 4. EXPERIMENTAL SETUP The authors have designed and constructed a solar tunnel fish dryer. The size of this dryer is:- 180cm 90cm 100cm; Duct size 180cm 90cm 30cm; roof 25cm high; and slope 30º with horizontal (Figure 4). The dryer is fabricated using a corrugated GI sheet air-heating collector, a tunnel- drying unit and small fan to provide the required airflow over the product to be dried. These are connected in series. Both the collector and the drying unit are covered with polyethylene. Black paint is used as an absorber in the collector. The products to be dried are placed in Vertical and horizontal in the tunnel dryer. Glass wool is used as insulation material to reduce the heat loss from the dryer. The whole system is placed horizontally on a raised platform. Air at required flow rate is supplied by an AC fan. The power requirement to drive the fan is low. The cover is fixed like a sloping roof to prevent the dryer unit from rain. Solar radiation passes through the transparent cover of the collector and heats the absorber. Ambient air is forced through the collector. Heat is transferred from absorber to air in the collector. The heated air from collector while passing over the fish absorbs moisture from the fish. Solar radiation also passes through the transparent cover of the dryer and heats the fishes. This changes the drying rate and the temperature in the dryer. The solar tunnel dryer is installed at Chittagong University of Engineering and Technology (CUET), a public university in Chittagong, Bangladesh. The dryer was placed on a raised platform and it was not under the shade of trees or buildings from 9 a.m. to 5 p.m. The full scale experimental runs on solar dryer were carried out in the months of November December, 2008 and January, METHODOLOGY Important parameters affecting the performance of the dryer are measured. Mercury thermometer (0C to 100C) is used to measure the air temperature along the flow direction inside the dryer. The relative humidity of air is measured by using a Phychrometer (0C to 50C). Anemometer (speed range from 0.3m/s to 40m/s) is employed to measure the velocity of air at the outlet of the dryer. Weight loss of the fishes being dried is noted at a suitable interval with an electronic balance. The sun dried control samples are weighted as well. All these data are recorded at one-hour interval. The moisture contents are measured at the end of each run of experiments by air oven (model No.-979, China) method. Maximum air velocity is 0.5 m/s; temperature is not exceeding 52ºC and Moisture is within range 7 to 15% at least. Experimental drying runs were conducted on silver Jew (powa) fish. The fish was treated with salt and it was initially treated with dry salt (salt to fish ratio of 1:4) and stacked for about 16 hours before drying. This salt penetrates into the flesh and denatures the enzymes and destroys a major portion of the bacteria originally present on the flesh because of their sensitivity to salt. The inclusions inside the fishes were removed before salt treatment. A thick stick is inserted all through the fishes and then washed well. The drying was started usually at 9.0 am and discontinued at 4.0 pm for each day. To compare the performance of the tunnel drier with that of the sun drying, control samples of fish were placed on trays in a raised platform beside the drier. Both experimental and control samples were dried simultaneously under the same condition vertical and horizontal. 6. EXPERIMENTAL RESULTS Figure 4: Solar Tunnel Fish Drier The experiment was conducted in November December, 2008 and January, The relative humidity (RH), ambient temperature (T a ), Inlet 77

6 temperature of the duct (T din ), Outlet temperature of the duct (T dout ) and the surface temperature of the absorber plate (T s ) were measured. The variation of temperatures and relative humidity with day time has been studies. Figure 5 shows the variation of the ambient temperature, surface temperature, inlet & outlet temperatures of duct and relative humidity with day time for two different days. It is found that peak surface temperature of the drier is 58C at 13:00PM. The surface temperature increases up to 13:00 PM and then starts to decrease. collector. However, the drying air temperature decreases along the drying tunnel during the early phase of drying (9 a.m.) and then it becomes almost constant throughout the drier length. As a result the fishes were almost uniformly dried along the length of the dryer. Figure 5(b): Variation of Temperatures and Relative Humidity with Day Time (January 21, 2009) Figure 5(a): Variation of Temperatures and Relative Humidity with Day Time (December 17, 2008) During the time of experiment maximum relative humidity obtained 60% which is decreases with day time up to 12:30 PM, maximum ambient temperature obtained 30C at 13:00 PM, maximum inlet temperature of the duct obtained 3839C at 13:00 PM, maximum outlet temperature of the duct obtained 35C at 13:00 PM and maximum surface temperature of the collector plate obtained 58C at 13:00 PM. Whenever dust fall on the collector surface, the efficiency of the collector plate decreases gradually. So it should be care to clean the collector surface before start the drying process. It is most important to clean the collector surface every two or three hour s interval. The efficiency of the collector plate is at maximum when the surface of the collector is neat and clean. Figure 6 shows the variation of the air temperature along the length of both collector and dryer for different solar radiation for a typical experimental run. The temperature inside the collector increases along the length of the collector from the inlet of the Figure 6: Variations of air temperature along the length of solar tunnel drier for a typical experimental run Comparison of the moisture contents of fishes in the solar tunnel dryer with those obtained by the traditional method for a typical experimental run during drying is shown in Figure 7. The moisture content of salt treated fishes of a typical experimental run reached to 14.95% (w.b.) from 65.32% (w.b.) in 30 hours of drying in the solar tunnel drier while it took 38 hours of drying to bring down the moisture content of a similar sample in the traditional method. The faster drying of fishes inside the solar tunnel dryer is due to the fact that the fishes in the dryer received energy both from the collector and from incident solar radiation, while the control samples received energy only from incident radiation and lost significant amount of energy to the environment. 78

7 Figure 8 shows the comparison of moisture content (wb) with the similar work of Bala and Mondol (2001) in the month of November. Though the year is different, the environmental parameters do not fluctuate much. It is pellucid that the pattern of the line almost same, nevertheless there are variations in their values. dried fishes is assured. From the experimental results the following conclusion can be drawn: 1. The use of solar tunnel fish drier leads to a considerable reduction of the drying time than conventional sun drying. 2. In all the cases fishes dried in the solar tunnel dryer were completely protected from rain, insects and dust. The dried fishes were a high quality product. Figure 7: Moisture content reduction of fish (DV, SV) with time interval 3. This dryer is simple in construction and it can be constructed using locally available materials by the local craftsman. The solar tunnel dryer can be operated by a photovoltaic module independent of the electrical grid. The photovoltaic system has the advantage that the temperature of the drying air is automatically controlled by the solar radiation. The photovoltaic driven solar tunnel drier must be optimized for efficient operation. REFERENCES Graaf, G.D. and Latif, A. (2002). Development of freshwater fish farming and poverty alleviation: A case study from Bangladesh, Aquaculture Asia, 7(2), 5-7. Figure 8: Moisture content reduction of fish (DV, SV) with time interval ( to ) compared with Bala and Mondol (2001) ( to ) Proximate analysis of both fresh and dried fish was conducted and solar dried fish shows better quality. Chemical compositions of the dried fish represent the fact that the fish dried in the solar tunnel dryer was a good quality product for human consumption. In all cases the quality of fishes dried in the tunnel drier was a quality dried product as compared to sun dried. Thus, this study demonstrated the potentiality of the solar tunnel drier for drying of fishes in Bangladesh. 7. CONCLUSION After the design and fabrication of the solar tunnel dryer, its operations have been observed. Production of Graaf, G. D. (2003) Dynamics of floodplain fisheries in Bangladesh, results of 8 years fisheries monitoring in the Compartmentalization Pilot Project. Fish. Manag. Ecol., 10, Jain, D. and Pathare, P. B. (2007). Study the drying kinetics of open sun drying of fish, Journal of Food Engineering, 78, Patil, R. T. (1989), Drying studies on black pepper, J. Food Science & Technology, 26, Jayaraman, K. S., Gupta, D. K. D. and Rao, N. B. (1992). Solar draying of vegetables: Quality improvement using cabinet with multiple flat plate collectors and pretreatment, In: Drying of Solids, Ed. A. S. Mujzumder, International Science publications and Oxford & IBH publication Co., NY, USA, and 79

8 New Delhi, Mujzumder (1992). International Science publications and Oxford & IBH publication Co., NY, USA, and New Delhi, Grabowski, S., Marcotte, M. and Ramaswamy, H. (2006). Dehydrated vegetables: Principles and Applications, In: Handbook of Food Science, Technology and Engineering, 3, Ed. Y. H. Hui, CRC, Taylor & Francis Group. Bala, B. K. and Mondol, M. R. A. (2001). Experimental investigation on solar drying of fish using solar tunnel dryer, Drying Technology, 19(2), Szulmayer, W. (1971). From sun drying to solar dehydration I - Methods and equipments, Food Technology in Australia, 23, Joshi, C. B, Gewali, M. B. and Bhandari, R. C. (2004) Performance of Solar Drying System: A Case Study of Nepal, Journal of the Institution of Engineers, India (interdisciplinary panel), 85(2), Gewali, M. B. and Ramchandra, B. (2004). Solar drying technology packages developed at RECAST, Renewable Energy Technologies in Asia: A Regional Research and Dissemination Programme (RETs in Asia). Phase III, Final Report, Kathmandu, Nepal. Sharma, A. Chen, C. R. and Lan, N. V. (2009). Solar-energy drying systems: A review, Renewable and Sustainable Energy Reviews, 139(6-7), pp Ramana, M. M. V. (2009). A review of new technologies, models and experimental investigations of solar driers, Renewable and Sustainable Energy Reviews, 13(4), Basunia, M. A. and Abe, T. (2001). Thin-layer solar drying characteristics of rough rice under natural convection, Journal of Food Engineering, 47,