MODELING OF THIN LAYER DRYING OF CATFISH (CLARIAS GARIEPINUS) IN CONVENTIONAL AND HYBRID SOLAR DRYERS DURING THE WET SEASON

Thesis Overview

<p> <b>INTRODUCTION</b></p><p>&nbsp;Fish is one of the major animal protein foods available in the tropics. This has made fishery an important aspect of study. According to Olatunde (1989), in Nigeria, fish constitutes 40% of animal protein intake; unlike any other animal protein source with one problem of religious taboo or health hazard, fish is eaten across the country. Unfortunately, however, fish is one of the most perishable of all stable commodities, and in the tropical climate of most developing countries it will become unfit for human consumption within about one day of capture, unless it is subjected to some form of processing (Ames et al., 1999). According to Abba (2007), Nigeria has the resource capacity (12 million has inland water and aquaculture) to produce 2.4 million MT of fish every year with an estimated demand at 1.4 million MT which currently exceeds supply. Fish is highly perishable and can be stored only by proper refrigeration or drying. Most of the fishermen living at the coastal belt are below the poverty line; therefore, refrigeration is distinct dream to them. The only alternative available is drying (Senadeera et al., 2003) which is the most important techniques of food preservation (Menon and Muzumdar, 1987).&nbsp;</p><p>Drying is defined as a process of moisture removal due to simultaneous heat and mass transfer. It is classical method of food preservation, which provides longer shelf, lighter weight for transportation and small space for storage (Erteken and Yaldiz, 2004). To reduce the postharvest losses during drying and retain the quality of dried products, it is necessary to dry fish in an enclosed chamber, by preventing product from dust, insect, larva, birds and animals. Solar drying is a good alternative for fish farmers in Nigeria and other developing countries as the dryers can generate relatively high air temperatures and low relative humidity, both of which are conducive to improved drying rates. Solar drying is a form of convective drying in which the air is heated by solar energy obtained from the sun. However, it differs from sun drying in that a simple structure, with a collector is used to enhance the effect of insolation and minimizes loss to the surroundings. Sun drying is dependent on weather, temperature and relative humidity of the environment. While solar drying has many advantages over sun drying, as renewable energy sources and economical, particularly during energy crises, when the cost of fuel energy increases sharply (Saravacos et al., 2002). Drying kinetics of food is a complex phenomenon and requires simple representations to predict the drying behaviour, and for optimizing the drying parameters. The prediction of drying rate of agricultural materials under various conditions is important for the design of drying systems. Researches on the mathematical modeling and experimental studies had been conducted on the thin layer drying processes of various agricultural products (Abalone et al., 2004). However, little information is available on thin layer drying behaviour of fish. The study was, therefore, undertaken to evaluate the best drying models in describing thin layer drying of Catfish (Clarias gariepinus) in conventional and hybrid solar dryers during the wet season. <br></p><p> <b>MATERIALS AND METHODS&nbsp;</b></p><p><b>Study Area&nbsp;</b></p><p>The thin layer drying experiment was conducted in North eastern zone of Nigeria. Borno State is a state in north-eastern Nigeria. Its capital is Maiduguri (also known as 'Yerwa'), it lies within latitude 10°N and 14°N and longitude 11° 3 1 E and 14° 4 1 E and at an altitude of 280.0 m above sea level. Borno State which has an area of 61, 435sq. km is the largest state in the federation in terms of land mass. It has a two distinct seasons; rainy season with annual rainfall of about 600mm from July- October and a hot dry season from march-July. The dry season is preceded by a period (November- February) of Harmattan with very low temperature (N.M.A. 2015). Experimental Solar Dryers The orthographic projection of the convention solar dryer (CSD) used in this study, as shown in figure 1. The dryer consisted of three main compartments: the drying chamber, the collector area and the dryer stand. CSD uses only natural convention to remove moisture from the fresh fish and dry the product to a lower or safe moisture content level. <br></p><p> The hybrid solar dryer (HSD) orthographic projection is represented in figure 2. It is a base-like structure consisting of a solar collector, top drying chamber, absorber base, as well as natural convention air inlet units, a chimney for the exhaust of the moisture laden air at outlet and a stove with connecting duct which utilizes charcoal as fuel. The stove enhanced further drying during the rainy /cloudy days and when the sun had set to enhance further drying at night. The thermal profile of the dryers was also investigated using laboratory type, mercury-in-bulb thermometer (accuracy ±0.5°C) at the regular interval of one hour between the hours of 6.00 and 18.00 local time for a period of three days. <br></p><p> <img alt="Image result for Orthographic Projections of the Conventional Dryer"> <br></p><p> Sample Preparation and Drying Conditions Clarias gariepinus were procured from fishermen at the bank of Lake Alau, which is located 12km away from Maiduguri in Konduga Local Government Area of Borno State, Nigeria. The fish was transported in cold flask from the bank to the drying site, to retain its freshness and wholesome conditions prior to drying. The fish was prepared by washing thoroughly inside water, several times until it became clean, free of dirts and blood. The fish species of 2400g was weighed and divided into three equal parts of 800g each. The 800g fish was spread in thin layer and the three trays were placed in the drying chamber. The chamber was firmly closed to avoid escape of heat. Through the inlet, dry air enters the chamber, which was heated up by the collector, and the air move over the fish to remove moisture and the moist-laden air was raised and moved out of the chimney. Changes in fish weight were monitored throughout the experiment by weighing periodically using an electronic balance. Weighing of fish samples and temperature readings were carried out with respect to time as follows, 10,30,50… 240minutes (20minutes interval) and subsequent measurement and reading continued hourly until dynamic equilibrium moisture content was attained and drying terminated, the time taken was also recorded. Intermitted turning was also carried out on the fish to ascertain effective drying.&nbsp;&nbsp;<br></p>