Thesis Abstract

<p>&nbsp;                   <b>ABSTRACT</b>&nbsp;</p><p>&nbsp;The solar drying system utilizes solar energy to heat up air and to dry any food substance loaded, which is not only beneficial in that it reduces wastage of agricultural produce and helps in preservation of agricultural produce.Based on the limitations of the natural sun drying such as exposure to direct sunlight, liabilty to pests and rodents lack of proper monitoring, and the escalated cost of the mechanical dryers, a solar dryer was therefore developed to cater for this limitations. This project presents the design and construction of a domestic passive solar dryer, the dryer is composed of solar collector (air heater) and a solar drying chamber containing rack of three trays both being integrated together. The air allowed in through air inlet is heated up in the solar collector and channeled through the drying chamber where it is utilized in drying (removing the moisture content from the food substance or agricultural produce loaded). The design was based on the geographical location which is Abeokuta and meteorological data were obtained for proper design specification. . The dimensions of the dryer was 94cm x 45cm x 101cm/ 20cm (length x width x height). Locally available materials were used for the construction, chiefly comprising of wood (gmelina), polyurethane glass, mild steel metal sheet and net cloth for the trays. The optimum temperature of the dryer was 60.5o C with a corresponding ambient temperature of 34.50o C. The mass of water removal of 199.9g and 153.6g in cassava and plantain respectively using the solar dryer was achieved as against 156.8g and 125.3g in cassava and plantain respectively using the sun drying method and indicating 43.1g and 28.3g difference respectively, for ten slices of cassava and plantain dried over a particular day. The rapid rate of drying in the dryer reveals its ability to dry food items reasonably rapidly to a safe moisture. <br></p>

Thesis Overview

<p> <b>1.0 INTRODUCTION&nbsp;</b></p><p><b>1.1 Drying&nbsp;</b></p><p>Drying is an excellent way to preserve food and solar dryers are appropriate food preservation technology for sustainable development. Drying was probably the first ever food preserving method used by man, even before cooking (Alamu et al., 2010). It involves the removal of moisture from agricultural produce so as to provide a product that can be safely stored for longer period of time. “Sun drying” is the earliest method of drying farm produce ever known to man and it involves simply laying the agricultural products in the sun on mats, roofs or drying floors. This has several disadvantages since the farm produce are laid in the open sky and there is greater risk of spoilage due to adverse climatic conditions like rain, wind, moist and dust, loss of produce to birds, insects and rodents (pests); totally dependent on good weather and very slow drying rate with danger of mould growth thereby causing deterioration and decomposition of the produce. The process also requires large area of land, takes time and highly labour intensive. In order to protect the products from above mentioned disadvantages and also to accelerate the time for drying the products, control the final moisture and reduce wastage through bacterial action, different types of solar dryer can be used (Exell 1980; Fohr and Figueredo 1987; Ghazanfari and Sokhansanj 2002; Janjaia et al., 2008; Khalil et al., 2007, Roa and Macedo 1976; Ting and Shore 1983; Yaldyz and Ertekyn, 2001). With cultural and industrial development, artificial mechanical drying came into practice, but this process is highly energy intensive and expensive which ultimately increases product cost. Recently, efforts to improve “sun drying” have led to “solar drying”.&nbsp;</p><p>Solar dryers are specialized devices that control the drying process and protect agricultural produce from damage by insect pests, dust and rain. In comparison to natural “sun drying”, solar dryers generate higher temperatures, lower relative humidity, lower product moisture content and reduced spoilage during the drying process. In addition, it takes up less space, takes less time and relatively inexpensive compared to artificial mechanical drying method. Thus, solar drying is a better alternative solution to all the drawbacks of natural drying and artificial mechanical drying. The solar dryer can be seen as one of the solutions to the world’s food and energy crises. With drying, most agricultural produce can be preserved and this can be achieved more efficiently through the use of solar dryers.&nbsp;</p><p>Solar dryers are a very useful device for:</p><p></p><p></p><ul><li>&nbsp; Agricultural crop drying.&nbsp;</li><li>&nbsp;Food processing industries for dehydration of fruits and vegetables.&nbsp;</li><li>&nbsp;Fish and meat drying.&nbsp;</li><li>Dairy industries for production of milk powder.&nbsp;</li><li>Seasoning of wood and timber.</li><li>&nbsp; Textile industries for drying of textile materials, etc.&nbsp;</li></ul><p></p><p></p><p>&nbsp;Thus, the solar dryer is one of the many ways of making use of solar energy efficiently in meeting man’s demand for energy and food supply, total system cost is a most important consideration in designing a solar dryer for agricultural uses. No matter how well a solar system operates, it will not gain widespread use unless it presents an economically feasible alternative to other available energy sources.&nbsp;</p><p><b>1.2 Some Background to the Drying Concept&nbsp;</b></p><p>&nbsp;The idea of using solar energy to produce high temperature dates back to ancient times. The solar radiation has been used by man since the beginning of time for heating his domicile, for agricultural purposes and for personal comfort. Reports abound in literature on the 18th century works of Archimedes on concentrating the sun’s rays with flat mirrors; Modern research on the use of solar energy started during the 20th century. Developments include the invention of a solar boiler, small powered steam engines and solar battery, but it is difficult to market them in competition with engines running on inexpensive gasoline. During the mid 1970’s shortages of oil and natural gas, increase in the cost of fossil fuels and the depletion of other resources stimulated efforts in the United States to develop solar energy into a practical power source. Thus, interest was rekindled in the harnessing of solar energy for heating and cooling, the generation of electricity and other purposes (Leon, et al., 2002).&nbsp;</p>