1.0 INTRODUCTION 1.1 Background Information The power from the sun intercepted by the earth is approximately 1.8 x l0ll MW (Wikipedia 2009). This makes it one of the most promising unconventional energy sources. Solar energy is available in abundance in most parts of our country throughout the year and, so, the drying of various agricultural products in open sunlight is an age-old practice. The sun has produced energy for billions of years and this energy is in form of the sun’s rays (solar radiation) that reach the earth. Solar energy can be converted into other forms of energy such as heat and electricity. The angle of insolation (Incoming Solar Radiation) of the sun is different at different locations on earth because the earth is split into three main regions: polar, temperate and tropical. Since the earth is a sphere, the middle is more direct to the sun, unlike the other regions. So, the sun would "give" the heat to the tropics, closer to the equator, faster and later spread to the other regions, where it takes some time to heat them up. Drying of fruit and vegetables is one of the energy intensive processes in the food processing industry and a promising method of reducing post harvest losses. Escalating prices and shortages of conventional fuels have lead to an increased emphasis on using solar energy as an alternative energy source, especially in developing countries [1]. The legislation on pollution and sustainable and ecofriendly technologies has created greater demand for energy efficient drying processes in the food processing industries. Drying practices for chalk, particularly in Nigeria, are largely traditional, which. In traditional drying, the produce is spread on an open floor under sun, which has limitations like dust contamination, spoilage due to rains, insect infestation etc. Moreover, as there is no control over the drying rate, the chalk may be over dried, resulting in discoloration, loss of writing qualities 2 and sometimes even complete damage. The moisture content and the temperature at which chalk should be dried is always fixed, which is possible only in controlled drying. 1.2 A Brief History of Drying Large-scale continuous drying of foods began in the 1940’s and in 1945, the first conveyor dryer for foods was manufactured. By 1956, the first continuous dryer for breakfast cereal in the United States had been manufactured (Aeroglide, 2006) and by the 1950’s (Nyrop, 2007), the development and supply of complete spray dryers, for industrial drying had begun. Alternative air dispensing and atomization techniques were incorporated in the drying systems in the 60s, a period which also witnessed the development of flash and fluid bed dryers. According to Pier (2007), the 70’s saw the development of the Regenerating desiccant type air dryers which were designed largely due to the vulnerability of railway pneumatic systems to water condensation (which was as a result of the cooling compressed air). Allgemeiner (1955) stated that, as at 1869, chalk slurries were still being dried using the power of the sun and wind. However, by 1906, chalk plants construction had begun and had incorporated dryer drums, screening machines and several other machines which made the drying process faster. Development of various solar devices for thermal applications such as water heating, space heating, drying, cooking and power generation, however, began during the last century. Chalk is a soft white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It is formed under relatively deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores (Wikipedia 2009). Relatively, chalk is resistant to erosion and also because it is porous it can hold a large volume of underground water. Chalk has been quarried since pre-history, serving as a building 3 material and marl for fields. For instance, in Southeast England, den holes are a notable example of ancient chalk pits. The chalk group is a European stratigraphic unit deposited during the late cretaceous period; it forms the famous white cliffs of Dover in Kent, England. The champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage (Wikipedia, 2009). Chalk board, which necessitates the use of chalk as its writing material, could be dated back to 1801 when teachers and schools had no means of presenting information to roomful students all at once, no means of presentation of concepts and historical overviews for the entire class to view, grasp and discuss. Supplies of pencils and paper were often in short supply or unaffordable for making mass copies; hand outs too were a rarity, since the teachers had to hand a set for each of their students. The expense of material and the individual attention required by such presentation methods caused small class enrolment and slowed down instructions. The history of solar energy stretched back into the dim recesses of pre-history, perhaps as far as the clay tablet era in Mesopotamia when the temple priestesses used polished golden vessels to ignite the altar fibres. In 1615, Salomon de Caux published a description of a working solar “motor”. He used a number of glass lenses mounted in a frame that concentrated the Sun’s rays on an air tight metal chamber partially filled with water. The sunlight heated the air, which expanded and forced the water out as a small fountain (Aden B. Meinel, 1976) Solar ovens appear in the literature, as described by the English astronomer John Herschel, son of the famous astronomer Sir William Herschel. John Herschel constructed a simple device for practical use on his expedition to the Cape of Good Hope in 1837. His oven was simply a black box that was buried in sand for insulation and had a double layer glass cover that allowed 4 sunlight to enter and prevented heat from escaping. The oven was used by Herschel’s staff to cook meat and vegetables for the dinner table of the expedition. (Aden B. Meniel, 1976). In 1875, Mouchot made a notable advance in the solar collector design by making one in the form of a truncated cone reflector. The spherical or parabolic mirror arrays of his predecessors had focused all the light at one small sport in space where the absorber was placed. The earliest attempts to convert solar energy into other forms revolved around the generation of low-pressure steam to operate steam engines. According to Wikipedia (2009), solar energy is the radiant light and heat from the sun that has been harnessed by humans since ancient times using a range of even-evolving technologies. Solar energy (solar power) technologies can provide electrical generation by heat engine or photovoltaic means. A partial list of application would include space heating and cooling through solar architecture, portable water through distillation and disinfection, daylighting, hot water, thermal energy for cooking and high temperature process heat for industrial purposes. Solar concentrating technologies such as the parabolic dish, trough and schettler reflectors can provide processing heat for commercial and industrial applications. The first commercial system was the solar total energy project (STEP) in Shenandoah, Georgia, USA, where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. Photovoltaics (PV) has mainly been used to power small and medium sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array. On large-scale generation, concentrating solar power (CSP) plants like SEGS have been the norm, but recently multi-mega watt PV plants are becoming common. Completed in 2007, the 14MW power station in Clark County, Nevada and the 20MW site in Benixama, Spain are characteristics of the trend toward larger photovoltaic power stations in the US and Europe. earth and stone.5 The first solar cell was constructed by Charles Fritts in the 1880’s. A legend claims that Archimedes used polished shields to concentrate sunlight on the invading Roman fleet and repel them from Syracuse. In all these systems a working fluid is heated by the concentrated sunlight and is then used for power generation or energy storage. shift time of use to off-peak hours and reduce overall heating goal requirement. . Calvin Fuller and Daryl Chapin created the Silicon solar cell in 1954. Thermal mass systems can store energy in form of heat at domestically useful temperatures for daily or seasonal durations. These materials are inexpensive. Phase change materials such as paraffin wax and Glavber’s salt are another thermal storage media. Massachusetts) was the first to use a Glauber’s Salt heating system in 1948. The concentrated light is then used as a heat source for a conventional power plant. researchers Gerald Pearson. These early solar cells cost 286USD/Watt and reached efficiencies of 4. Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine in 1866 and subsequent developments led to the use of concentrating solar-powered devices for irrigation.5-6% Concentrated sunlight has been used to perform useful tasks since the time of ancient China. Following the work of Russel Ohl in the 1940s. Well-designed systems can lower peak demand. readily available and can deliver domestically useful temperatures (approximately 640C). Although the prototype Selenium cells converted less than 1% of incident light into electricity. both Erust Werner Von Siemens and James Clerk Maxwell recognized the importance of this discovery. The “Dover House” (in Dover. Thermal storage systems generally use readily available materials with high specific heat capacities such as water. refrigeration and locomotion. Concentrating solar power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems.6 Solar energy can be stored at high temperatures.44 TJ in it 68m3 storage tanks with an annual storage efficiency of about 99%. . Limestone deposits develop as coccoliths (minute calcareous plates created by the decomposition of plankton skeletons) and accumulate to form sedimentary layers.15 inches (80 mm) long. allowing it to store 1. effectively using the grid as a storage mechanism.35 of an inch (9 mm) in diameter and 3. The solar too used this method of energy storage. Net metering programs give these systems credit offsets electricity provided from the grid when the system cannot meet demand. 1.04 percent to 40 percent. as they were originally called) using sticks of chalk because this method has proven cheap and easy. Lessons are often presented to entire classes on chalkboards (or blackboards. concentrates the calcium found naturally in seawater from . Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. excess electricity can be sent to the transmission grid. The energy is recovered when demand is high by releasing the water to run through a hydroelectric power generator. a tiny marine organism. a form of limestone.3. using molten salts. Pumped-storage hydro-electricity stores energy in form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one.1 Raw Materials The main component of chalk is calcium carbonate (CaCO3). 1.3 Chalk Production Processes Chalk used in school classrooms comes in slender sticks. Salts are effective storage mediums because they are low-cost. Plankton. With grid-tied systems. approximately . Primary crushing. titanium. breaks down large boulders. This is done in a kettle. generally by an open pit quarry method. is also quarried and pulverized. it also occurs disseminated in limestone. The limestone is then wetmilled with water in a ball mill—a rotating steel drum with steel balls inside to further pulverize the chalk. the limestone must be crushed. manganese. Chalk and dehydrated gypsum thus have similar origins and properties. alumina.2H2O). In less significant. Although great care is taken to eliminate contaminants when chalk is manufactured. The major difference in processing gypsum is that it must be dehydrated to form calcium sulphate. Next.3. amounts. arsenic and strontium may also occur.2 The Manufacturing Process To make chalk. fluorine. some impurities inherent to the mineral remain. potassium oxide. which is derived from gypsum (CaSO4 . limestone is first quarried. Pastels also contain clays and oils for binding. This step washes away impurities and leaves a fine powder. a large combustion chamber in which the gypsum is heated to between 244 and 253 degrees Fahrenheit (116-121 degrees Celsius). the gypsum . To further reduce the water. like limestone. 1. an evaporite mineral formed by the deposition of ocean brine. secondary crushing pulverizes smaller chunks into pebbles. This mixture produces sticks that write smoothly without smearing and draw better on paper than on chalkboards. and sulfur. sodium oxide.9 percent to between 5 and 6 percent.3 Dehydrating Gypsum Gypsum. Chief among these are silica. at which point its water content will have been reduced from 20. 1.3. copper. the major component of coloured chalk. and strong pigments. It is allowed to boil until it has been reduced by twelve to fifteen percent. phosphorus. iron. such as in a jaw crusher.7 which is then precipitated when the plankton dies. The base of pastel chalks is calcium sulfate (CaSO4). 4 Making White Classroom Chalk To make white classroom chalk. leaving calcium sulphate.8 is reheated to about 402 degrees Fahrenheit (204 degrees Celsius). the chalk factory usually grinds the materials again to render them smooth and uniformly fine. 1. After it has cured. almost all of the water has evaporated. Upon receiving chalk or calcium sulphate. designing space that naturally circulate air. convert and distribute sunlight. Solar technologies that can be broadly characterized as either passive or active are also being developed. 1. By now. Passive solar technologies include selecting materials with favourable thermal properties. at which point it is removed from the kettle.4 Types of Chalk Dryer Having known that the most common type of chalk drying technique is sun drying. various types of dryer have been built which use electricity as their source of power. and shipped to the manufacturer. the manufacturer adds water to form thick slurry with the consistency of clay.1/2H2O + 11/2H2O The particles of chalk or calcium sulphate are now conveyed to vibrating screens that sift out the finer material. Cut into lengths of approximately 24. pumps and fans to convert sunlight into useful outputs. and referencing the position of a building to the sun. the sticks are next placed on a sheet that contains places for five such sticks. The slurry is then placed into and extruded from a die — an orifice of the desired long thin shape. The sheet is then placed in an oven. depending on the way they capture. the sticks are cut into 80 millimeters lengths.43 inches (62 cm). dried. where the chalk cures for four days at 1880F (850C). Active solar technologies use photovoltaic panels. packed in bags. Ca2SO4 .3.2H2O + heat = Ca2SO4 . . The ensuing fine chalk is then washed. design a mechanism that will convert the solar energy extracted to heat to dry the chalk. and (iv). Also. research and practical work on the chalk dryer has utilized electricity as its source of power supply . the box type dryer among different types will be concentrated on. harnessing solar energy and solar powered dryers for other processes apart from chalk drying (Ogunremi and Orimolade 2006). test the drying equipment for its performance. (iii). design and fabricate a dryer for chalk drying. using appropriate devices. (ii).6 Aim and Objectives of the Project The main aim of this project work is to develop a mechanism of powering of a chalk dryer using solar energy. . extract energy from the sun.9 1. In this study. The energy source is also limited to solar radiation out of several other sources that may exist. Locally available materials will be employed in construction and fabrication. driers for food conservation and preparation. little or no research has been done on the use of solar energy in powering chalk dryers. this study is limited to the design of chalk dryer. This project thus extends knowledge by adapting solarpowered dryers for drying chalk instead of food and also using solar energy source for the chalk dryer instead of electricity.7 Scope of the project Although different types of driers exist. 1. To the best of our knowledge. for example. The specific objectives are to (i).5 Statement of Problem A lot of work has been done on improvement of drying methods. 1. Hence.10 1. this work is set to develop a system which will efficiently utilize solar radiation from the sun and at the same time provide enough protection.8 Justification of the Project Literature reveals that over 50% of energy used in the sun drying process is being wasted and also that materials or things to be dried are subjected to contamination. . economical and environmental friendly. It opens with an examination of drying and the solar energy that is to be used. Solar heating systems used to dry food and other crops can improve the quality of the product. . thus improving the quality of life. coffee and other crops has proved to be relevant. 2. passive or natural-circulation solar-energy dryers and active or forced-convection solar-energy dryers. Two generic groups of solar-energy dryers can be identified. Therefore.0 Introduction This chapter focuses on the review of works that are germane to this study. viz. However. the use of solar thermal systems in the agricultural area to conserve vegetables. fruits.1 Solar Energy Drying Systems In many countries of the world.11 CHAPTER TWO LITERATURE REVIEW 2. details of construction and operational principles of the wide variety of practically realized designs of solar-energy drying systems reported previously is presented. Solar food dryers are available in a range of sizes and designs and are used for drying various food products. A systematic approach for the classification of solar-energy dryers has evolved. It is found that various types of driers are available to suit the needs of farmers. conversion and utilization in various fields and the chapter ends with a summary of our position on the respective outcomes. while reducing waste products and traditional fuel. A comprehensive review of the various designs. The latter part of the chapter is a survey of works done by scholars on solar energy collection. the availability of good information is lacking in many of the countries where solar food processing systems are most needed. selection of dryers for a particular application is largely a decision based on what is available and the types of dryers currently used widely. 2. Open sun drying of various agricultural produce is the most common application of solar energy. Coleman (1977) reported a solar energy apparatus for gathering and transmitting solar radiation to an energy storage area. The microwave energy is then transmitted to earth and converted to electrical power for distribution. such as air. Rom (1975). natural convection and forced convection type solar dryers have been developed for various commodities. Air or another gaseous mixture is flowed through the heating passage wherein solar radiation absorbed by the film is converted to thermal energy that is transferred to the gaseous stream. The other end of the optical fibre bundle is placed in the energy storage . The heating passage is surrounded on top by an insulating space. invented an apparatus for converting solar radiation to heat energy for heating gaseous stream.2 Solar Energy Collection and Conversion In the invention of Glaser (1973). Wide-angle lens apparatus is used to focus solar radiation on an end of an optical fiber bundle. With the objective of increasing the drying rate and improving quality of the products. in his work on solar energy. The other end of the optical fiber bundle is placed in the energy storage area and has a radiating device attached thereto to more efficiently remove the solar energy from the optical fibre bundle. to be used for heating or drying purposes. The air or other gaseous mixture is flowed through an elongated heating passage defined by plastic film formed of solar radiation absorbing or opaque (black) material and the film is inflated by the fluid pressure of the gaseous stream passing through. defined by the outer surface of the top portion of the opaque film and by an outer sheet of clear (solar radiation transparent) plastic film that is inflated into an expanded position by the gaseous insulating medium therein. solar radiation is collected and converted to microwave energy by a means on a satellite system maintained in outer space.12 Some very recent developments in solar drying technology are highlighted. solar radiation to be received in the interior space of the housing. A heat sink is advantageously utilized as a storage means for the solar energy thus gathered and transmitted. which has only one layer of glass for each face through which solar heat may pass and be collected upon a heat-collecting surface. A conditioning pump is provided within the apparatus to circulate conditioning air through both the collector and the heat retaining material within the housing. quickly release the heat to the surrounding fluid stream. presented an apparatus for collecting radiant energy and converting same to alternate energy form includes a housing having an interior space and a radiation transparent window allowing. Means are provided for passing a stream of fluid past the said window and for injecting radiation absorbent particles in the fluid stream.13 area and has a radiating device attached thereto to more efficiently remove the solar energy from the optical fibre bundles. The fluid stream particle mixture is heated until . for example. Specially designed and positioned ducts connect the collector to the interior of the housing in a manner such that air interchange between the collector and the interior of the housing is prevented except during operation of the conditioning pump. because of their very large surface area. Also. The particles absorb the radiation and. Hunt (1982) in his studies on energy collection and conversion. Utility pump means are also provided in the apparatus for withdrawing heat from the heat retaining material and circulating it through a remote building structure. storing and transmitting solar heat which includes an elongated rectangular insulated housing in which a quantity of heat retaining material is confined and a collector on the horizontal and vertical faces of the housing. so that heat is transferred from the collector to the heat retaining material. Keyes (1978) presents a self-contained apparatus for collecting. Both the collector and the interior of the housing are provided with appropriately positioned baffles to expose the conditioning air to all of the heat retaining material. In an aspect of the present invention properly-sized particles need not be vaporized prior to the entrance of the fluid stream into the turbine. The pipe was formed of a material that is substantially transparent to solar radiation.14 the particles vaporize. at least. The focal line for the linear lens should be substantially coincident also with the longitudinal axis . there was a linear focusing lens. which comprises a solar collector panel rotatably supported about a horizontal and a vertical axis and drive means for rotating the panel simultaneously about the two axes. for circulating a primary fluid heat transfer medium through separate collector sections of a solar receiver to recover solar heat. operating in different temperature ranges. Lenz (1989) provided a solar heat collecting apparatus. and through separate output heat exchangers to supply heat to a second heat transfer medium functioning as a working medium. the longitudinal axis of the pipe being substantially coincident with the focal line of the concave reflective surface. In addition. wherein each collector unit comprises an elongated trough member. with heat storage means being associated with each system for the purpose of satisfying the heat requirements of the working fluid and also to prevent cooling down of the collector during the time that little or no solar radiation is available. a concave reflective surface forming at least a portion of the interior surface of the trough and a fluid carrying pipe extending longitudinally within the trough member. Solar energy was absorbed and converted to thermal energy by means of. (1981). as the particles will not damage the turbine blades. in their studies on utilization of solar energy. The fluid stream is then allowed to expand in. Constantine et al. The collector panel comprises a battery of individual collector units. presented a process and system for economic utilization of solar energy. substantially covering and extending over the concave reflective surface. two systems. for example. a gas turbine to produce mechanical energy. directing the energy to a pre-determined region of the atmosphere located at a pre-established distance above a surface of the earth. The dryer was operated for 28 days from mid-April to the end of May 1996. presents a solar-powered window shade which consists of a venetian blind mounted within an interior of a frame of a window in a wall of a building.30C with a standard deviation of 8. modifying the distribution of solar radiation passing through a region to thereby concentrate the solar radiation at a pre-determined location on the surface. a substantial quantity of the concentrated solar radiation to produce heat energy. Also. At sunrise and all through the day. for converting solar radiation of sunlight into electrical energy. 2. the venetian blind will remain open to allow sunlight to enter through the window.60C within a 7-h period from 8:00h to 15:00h. the dryer attained an average temperature of 81. in his work on solar energy application. From hourly temperature considerations. Ampratwum and Dorvlo (1998) develop a solar collector in the form of a prototype solar cabinet dryer which was evaluated at no load as an air-heating system. Stirbl (1993) describes a system for collecting solar radiation by generating waveform energy.15 of the fluid carrying pipe. to help heat up the building. and absorbing at the location. a mechanism was placed on the venetian blind for utilizing the electrical energy to open and close it. controlling the energy directed to modulate an index of refraction of air in the predetermined region of the atmosphere to produce a pre-determined refraction index pattern in the region.3 Solar Energy Applications Corazizini (1995). to help retain the heat within the building. For the period of operation. it was determined that the rate of solar . the venetian blind remained closed to produce a thermal barrier. An apparatus was carried by the venetian blind. At sunset and all through the night. The temperature distribution in the plenum and also the drying rate of parchment coffee were determined.4 _C and the dryer could lower the moisture content of coffee beans from 54. (2006) give the development and testing of another type of efficient solar dryer. particularly meant for drying vegetables and fruit.10C. The temperature inside the plenum chamber could reach a maximum of 70. the product was loaded beneath the absorber plate. The performance was tested by adjusting the angle the dryer made with the horizontal either once. did not offer a significant advantage in terms of length of drying duration.90kW sqm-1 and over was maintained for about 6 hours. three.b. can accelerate the drying rate. The absorber plate of the dryer attained a temperature of 97. Tracking the sun. In this dryer.51kWsqm-1 to 0. The maximum air temperature in the dryer under this condition was 78. Sreekumar et al. The dryer has two compartments: one for collecting solar radiation and producing thermal energy and the other for spreading the product to be dried. This arrangement was made to absorb maximum solar radiation by the absorber plate.16 energy absorbed by the dryer ranged from 0.8% to below 13% (w.20C when it was studied under no load conditions. The dryer had six perforated trays for loading the material. Gikuru and Njoroge (2004) develop a small solar dryer with limited sun tracking capabilities and was tested. five or nine times a day when either loaded with coffee beans or under no load conditions. which prevented the problem of discoloration due to irradiation by direct sunlight. though allowing a faster rate of drying. Two axial flow fans. The dryer had a mild steel absorber plate and a polyvinyl chloride (pvc) transparent cover and could be adjusted to track the sun in increments of 150.) in 2 days as opposed to the 5– 7 days required in sun drying. The peak was reached at 11:00h and a high solar-energy rate of capture of 0. The dryer was loaded with 4 kg of bitter gourd having an initial moisture content of .93kW sqm-1. provided in the air inlet. 35.26 years. ‘present worth of annual savings’ and ‘present worth of cumulative savings’. The capabilities of these models were compared with experimental data obtained from available literature. Sitompul et al. This model also considered axial mass and heat dispersion in the fluid phase. The collector glazing was inclined at a particular angle. The drying cost for 1 kg of bitter gourd was calculated as Rs. for absorption of maximum solar radiation. and the final desired moisture content of 5% was achieved within 6 h without losing the product colour. then applied to simulate humidity and temperature profile of drying gas across dryers. So.52. which was much higher than the capital cost of the dryer (Rs. together with moisture content and temperature of grains. The life span of the solar dryer was assumed to be 20 years. and it was Rs. The dynamic twophase equations are solved numerically by finite difference with alternating direction implicit method algorithm. 17. . and it turned out be Rs. which was also very small considering the life of the system (20 years). The cumulative present worth of annual savings over the life of the solar dryer was calculated for bitter gourd drying.26. The quality of the product dried in the solar dryer was competitive with the branded products available in the market. under drying conditions such as temperature and absolute humidity of drying gas and moisture content of grains. 41. while it was 11 h for open sun drying. The simulation results showed that the dynamic of corn drying within the bed is well predicted by the two-phase model. 31659. the dryer would dry products free of cost during almost its entire life span. in the case of an electric dryer. 6500). The payback period was calculated as 3. namely ‘annualized cost method’. (2001) are concerned with heterogeneous modeling of deep-bed grain dryers based on a two-phase model by taking into account coupled heat and mass transfer within grains.17 95%. suitable to the location. A detailed performance analysis was done by three methods. Two modules were used. the photovoltaic modules receive approximately 0. on the roof top (350m above sea level) of the Department of Physics.996014.7Wm -2 in the wet season (April-October) to 480. biodiesel and some others. under very cloudy sky of 0.617168. the other was tilted at the latitude of the site. This can be achieved by changing the means of powering available chalk dryers that are mostly electric to solar-powered. The low values (and large fluctuations) of the hourly means recorded during the wet (monsoon) season are attributed to the important . University of Ilorin. the diurnal variations of net radiation have been studied by analysing one year data measured at a tropical station. in Nigeria (Jegede.18 The recent developments by engineers have unfolded the facts that. The solar energy is in abundance and is easier to tap than some other sources of power supply like gas. However.43 ° N.320N. 1996).8Wm -2 in the dry season (November-March).3±61. The study was carried out in June 2004. 4. the chalk dryer can be utilized with cost effective power supply.92m x 0.070 average clearness index (KT). This is confirmed by the R-square values of the linear least square regression analyses between the efficiencies of the modules and the cloudy sky radiation parameters. Osu (7. 2. While one of the modules was positioned flat. electricity. Also.4 Solar radiation Olopade and Sanusi (2008) studied the performance of PV modules under tropical sky conditions. Ilorin (8. each of 0.30m comprising 27 Solar cells. The maximum net daytime flux (which occurs around 14h local time) varies in the course of the year from 382. 4. while that of the flat module was 0. Nigeria.6±136.7-kWh/m2 average daily insolation of mainly diffuse radiation. Results and analyses show that.340E). The tilted module performs better by about 47% than the flat module.58 ° E). The R-square value of the tilted module was 0. the environmental benefits of the solar energy in comparison to petroleum based fuel and other sources should also be taken into consideration. The sun causes the air in the atmosphere to warm up. it generates a great amount of energy. Figure 2.. Richard L. The daily amplitude of the net radiation is larger for the dry season (maximum in November) than it is for the wet season (minimum in July). which is very pronounced in the tropical areas of West Africa. A lag of about 2 hours is observed between the times when the maxima of the air temperature and the net radiation courses occur over the area. Major patterns of winds are due to the earth's rotation about its axis and the day-night cycles of solar heating and subsequent cooling. setting temperature differentials that generate wind. Radiation from the sun catalyzes or directly supplies most of the natural energy systems on earth.5: The Sun and the Earth (Crowther.19 roles that the convective clouds and water vapour play in the atmospheric radiation budget. 2. Sustainable Design. Sun-Earth) .5 The sun The sun is a giant nuclear fusion reactor combining hydrogen to form helium. 6: The tilt of the earth remains constant at 23.6 Sun's Apparent Movement The earth rotates around the sun. the path of the radiation through the horizon lengthens and the intensity of the radiation decreases.20 A great amount of energy is absorbed by the earth's surface itself. as well as by the oceans.47o as it revolves around the Sun. The path of the earth around the sun is . The energy absorbed by the plants is converted into food energy and from the oceans. Figure 2. The angle of the sun and its intensity on earth is affected by location of the place on the surface of the earth. This causes the sun to "rise" and "set". Also. plants and buildings. at a high elevation. During the day. 2. the length of atmosphere that solar radiation passes through varies with the time of day and month of the year. the amount of atmosphere that the solar rays have to travel through is lesser and therefore the energy content is somewhat higher. evaporation causes the hydrologic conversion cycle. The length of the atmosphere that the solar radiation has to pass through determines the amount of radiation that reaches the earth's surface. the sun is directly overhead and radiation travels through least amount of atmosphere enroute to the earth's surface. As the sun moves closer to the horizon (sunset). (The Passive Solar Energy Book by Mazria Edward) Because of the earth's tilt and rotation. the greater the energy. From literatures that have been reviewed (Olopade and Sanusi (2008). consisting of water droplets or ice crystals constitute a major factor. Kuku and Salau (1985)) there is an average value of 700wh/m2solar radiation in Ile-Ife. The intensity is further reduced on overcast days.21 a slight ellipse. 1990. back-scattering predominates.000 watts/square meter (295 Btu/hour/ square foot) on a bright clear day (Kaplan 1985). The availability of solar radiation for technological application is determined. they are characterized by a wavelength inversely proportional to their energy . to a large extent. sunlight reaching the earth is a mixture of direct (unscattered) and diffuse (scattered) radiation. . As the earth orbits around the sun. radiation is scattered either forward or backward. Thus. Depending on the depth and number of layers of the cloud. which attenuate the solar flux. and thick stratus can reflect up to 70% incident radiation (Monteith and Unsworth. Beyond the earth's atmosphere the intensity of sunlight is about 1. 1976).470 from the vertical to the plane of the earth's orbit around the sun. Clouds. At sea level the intensity is reduced to approximately 1. by clearness of the sky. When the depth is substantial. The axis is tilted 23. The solar flux is attenuated by a number of factors before its final reception on earth. Passage through the atmosphere depletes the intensity due to absorption by the various gases and vapors in the air and by scattering from these gases and vapors and from particles of dust and ice also in the air.350 watts per square meter (429 British thermal units [Btu] per hour per square foot).the shorter the wavelength. mainly by scattering (Fagbenle. The solar rays reach the Earth's surface after being attenuated by the atmosphere. Meinel and Meinel. Made up of elementary particles called photons. 1990). it rotates on its axis that extends from the North pole to the South Pole every 24 hours. The top section of the solar dryer was the reflector area. top collector and bottom drying chamber.6 mm thick ply wood.1: Solar-aided chalk dryer with the thermocouple .1. Experimental set up The experimental set up. 3. Plate 3. The body of the dryer was made of 65x55x1. The reflector used was made with mirrors gently positioned on plywoods of equal sizes and positioned at 300 to the vertical with each side of 55 cm at the bottom. The height of the absorber region was 65. consists of the solar-aided chalk drier provided with mirror reflector tilted at 00 and 150 to the dryer (Appendix 1 and 2). shown in Plate. A 4 mm doubled clear glass which was glued together and allowed to get dried for 24 hours was mounted on the top of the dryer as a glazing plate.1.22 3.5 cm and that of the back portion was 80cm when the reflector is tilted at 150.0 Methodology 3. Basically. The reflector was designed in a way such that the angl at which it is to the dryer can be varied for Ile-Ife (latitude 7 0281 ). All the sidewalls and bottom wall has plywood as insulators. the developed dryer consists of three parts: the reflectors. The material used to make the tray was wood and chicken wire.1: Side sketch of chalk dryer showing distance between trays Stand .23 Air holes of area 0. Four rows of holes. and the distance between holes was 4 cm. And the trays were arranged one above the other. Reflectors Tray 1 Air outflow 15cm Tray 2 Air inflow Fig 3. facilitated the exhaust of warm moist air from the dryer. The individual rows were separated a distance of 6 cm. The size of the single tray was 0.5 m2.1. having 5 holes per row.197 m3. See template 3 for details. It consists of two trays to load the material to be dried. and it was located underneath the glazing plate. The diameter of an individual hole was 5 mm. The distance between the consecutive bottom and top of trays was 15cm as shown in Fig 3.125m2 was provided in the front and under the dryer for air flow through the drying chamber. The total volume of the drying chamber was 0. The temperature readings were taken every 30 minutes. two types of studies were carried out on the solar dryer. The two trays were loaded with chalk having an initial moisture content on 95%. The ambient temperature. Various measuring devices were used to investigate the effects of the environmental and operating parameters on the performance of the dryer. the outlet holes were kept. used for the drying tests.2 kg in each tray. During the study. The temperatures of the ambient.001 g). Chalk. The total quantity loaded was 8.2. The weight of the chalk being dried was recorded every 1 h. Basically. All the experiments were conducted from 10:00 am to 3:00 pm. 3. Samples of products in the dryer were weighed at 1 hr intervals using a a weighing balance (±0.24 3.2. is the most popular blackboard . First was when reflector was tilted at 00 and the other when at 150.4kg. were monitored using the thermocouple.1. absorber plate temperature. Obafemi Awolowo University Ile-Ife Nigeria (70 281 latitude). Test of the dryer with reflectors at 00 to the dryer The experiment was conducted for 5 hrs to measure the maximum temperature achieved by the absorber plate of the dryer and the drying cabinet. the moisture content of the sample was determined by comparing the weight of an already dried sample with a sample that has just been moulded. The performance of the system was continuously monitored during the mid periods of the month of March 2010. At the end of the drying process. The relative humidity of the atmosphere was obtained by using the Sling psychrometer to get the wet and dry bulb temperature and checking the psychrometric chart. Experimental procedure The experiments were conducted in the Solar Laboratory of the Department of Mechanical Engineering. tray temperatures in the drying chamber. etc. 4. absorber plate and dryer trays were recorded every 30 mins during the study period. It can also be used in Snail rearing as it is known to contain calcium which is good for Snail shells. These are abundantly available in Ogun State. Test with reflectors tilted at 150 to the dryer All parameters were monitored as described above except that the reflectors were tilted at 150 (Fig 3.4 kg of chalk was loaded in the dryer. especially in rural area institutions. It is manufactured from Limestone. 3. For the drying tests. The freshly moulded chalk was placed in the dryer after being allowed to solidify for 30 minutes in the mould.2) for the same number of hrs.2: Side sketch of chalk dryer showing reflectors tilted at 15 0 Stand .25 writing materials in Nigeria.2.2. pieces weighing 8. Reflectors 150 Tray 1 15cm Tray 2 Air inflow Fig 3. 91 (Reflective Insulation Manufactures Association April 1999). 4.26 4.3 1 1. Variation of temperature in the solar dryer and ambient temperature with Time when reflector is are at 00 to the dryer.3 11 11. Test of the dryer with reflector tilted at 00 The parameters monitored.1. 65 60 Temperature 55 50 45 40 35 30 25 10 10. against time Tray 2 temp.3 3 Time Open sun drying temp.1a.3 12 .3 2 2. 4.30 pm. RESULTS AND DISCUSSION 4. The maximum temperature monitored in the inner wall was 650C. The high temperature of the inner wall was due to the coating of a black gloss paint. . In this study. The maximum tray temperature in the dryer was monitored as 550C at 2. The average relative humidity was 75% which ranges from 80% at 10am to 55% at around 3pm. which was at 2:30 pm.00 12. such as ambient temperature and temperature in the solar dryer are shown in Fig.1a the experimental time period was from 10:00 am to 3:00 pm. against time Tray 1 temp. the reflectors were placed directly on the dryer and not tilted throughout the experimental period. against time Fig. which has an absorptivity of 0. 00pm 34 1.15 4.00 4.06 The temperature reading of the chalk under open sun drying tends to fluctuate within the period of experiment within a range of 31 to 360C and the peak which is 360C was obtained at 2.20 4.30am 32 12 noon 32 12.00 4.00 3.00pm while Tray 2 reached its peak at2.05 4.1.30pm 34 1.14 4.12 4.00am 33 11. It was observed that the temperature rise of the dryer wall above ambient air was in the range of 23 – 290C during the study period.30am 31 11.02 4.30pm 36 3. We suspect that it takes some little period of time for tray 2 to attain the chamber temperature than tray 1.20 4.30pm 33 2.14 4.02 4.15 4. Tray 1 reached its peak temperature at 2.03 4. The samples were collected from the different trays to analyze the uniformity of drying.10 4.4 kg of the chalks was calculated as 2043 kJ/batch. This might have been because of the evaporation of surface moisture at the . and then it started to decrease.12 4. Temperature and mass properties (reflector at 00 to the dryer) Avg RH =75% Time Ambient temp 32 10am 10.99 3.27 Table 4.30pm. This could have been as a result closeness of tray 1 to the top of the dryer which is the entry point of solar rays than tray2.20 4.30pm. The solar energy required for removal of the moisture content from 8.10 4.00pm 35 Tray 1 Temperature Tray2 Wall(Tw) Tw -TA Tray1 45 43 45 46 49 52 55 58 59 58 57 41 40 43 45 47 47 48 50 52 55 54 4. Drying was very fast in the initial hours of operation.18 4. The fluctuation in temperature could have been as a result of periodic cloud cover on the sun and wind effects which tend to reduce chalk temperature.13 4.2 4.10 4.08 4.05 4.10 4.98 55 54 57 59 61 60 62 60 62 65 63 23 23 24 27 29 26 28 27 28 29 28 Mass of chalk Tray2 Sundrying temp 4.13 4.00pm 34 2. A slight difference of tray temperature in the drier was noticed even though they follow the same pattern.02 4.12 4.13 4. and it was found that the reduction in moisture content of Tray 1 is slightly higher than that of tray 2.16 4. 25 4. 4.3 12. but the entire moisture was removed from the product loaded in the solar dryer in the second day itself.43% to the final value of 17. The moisture content of the chalk was reduced from an initial moisture content of 21.00 3.09% for Tray 1and 17.50% for tray 2. Reduction of moisture content of chalk with Time when reflector is at 00 to the dryer .1b.00 12.10 4.05 4. It was known that as the moisture content of the product is reduced.20 Mass (kg) 4. 4.50% for tray 2 and 19% for open sun drying within an effective drying time of 5 hrs as shown in Fig. The result obtained was compared with chalk dried in the open sun. 17.3 11 11.28 beginning of the process. more energy might be required to evaporate the same amount of moisture from the product. We suspect that the dryer continued the removal of moisture content during the late periods of the day.09% for tray 1.3 3 Time Mass of Open sun drying against Time Mass of Chalk in tray1 against time Mass of Chalk in tray2 against time Fig.3 1 1.15 4.1b. The moisture content at the of end of the experiment when the reflectors are placed at 00 to the dryer was 17.95 10 10. 4.3 2 2. 3 2 2.00 12.3 1 1. radiation incident on inner wall of the dryer.2a. . Test with reflector tilted at 150 to the dryer In this experiment. 4. 4. Variation of temperature in the solar dryer and Open air sun drying with Time when reflector is at 150 to the dryer. ambient temperature and rise in tray temperatures inside the dryer above the ambient temperature are shown in Fig.3 11 11.2. against time Tray 2 temp against time Fig.29 4. against time Tray 1 temp.3 12 .4 kg of freshly cast chalk to study its drying behaviour. The dryer. The rise in tray temperature varied from 9 0C to 190C during 10 am to 3pm.2a. with solar radiation when the reflector was tilted at 150 to the dryer. The average relative humidity of the air at the time of experiment was 75%.3 3 Time Open sun drying temp. the dryer was loaded with 8. 55 50 Temperature 45 40 35 30 25 10 10. 2b.1. The result obtained was compared with chalk dried in the open sun and it was discovered that at the end of the period of experiment. Reduction of moisture content of chalk with Time when reflector is at 150 to the Dryer .08 4.22 4.16 4.20 4. and it was found that the reduction in moisture in Tray 1 is slightly higher than that of tray 2.18 Mass (kg) 4. The average relative humidity was 52% which ranges from 70% at 10am to 43% at around 3pm.3 2 2.4 kg of product was calculated as 2043 kJ/batch.3 1 1.2b. Drying was very fast in the initial hours of operation.06 4.30% for tray 1 and 19. The samples were collected from the different trays to analyze the uniformity of drying.3 11 11.14 4.3 12 12.02 10 10. The solar energy required for removal of the moisture from 8.43% to the final value of 18.12% for both tray 2 and ambient.30 during the study period.The moisture content of the chalk was reduced from an initial moisture content of 21. within one day with an effective drying time of 5 hrs as shown in Fig.3 3 Time Mass of chalk in open sun drying against Time Mass of Chalk in Tray 1 against time Mass of Chalk in Tray 2 against time Fig. and then it started to decrease as also in the case of 4.04 4.12 4.10 4. chalks from tray 2 has the same moisture content as that of the ambient. 4. 4. 4. This could be as a result of low temperature values when compared to reading with reflectors at 00 or as a result of low relative humidity. 08 On a general note.1 and 4.10 4.30am 11.16 4.10 4.15 4.43% moisture in the present drier was only two days of a spread of 11 hrs and open sun drying (24hrs spread over three days) at Dara chalks.12 4.30pm 2.08 4.08 Sun drying temp 4. Arubidi Ile-Ife.30pm 3.06 4.2% reduction in moisture was) at an average of 43% relative humidity and average temperature of 630C was spread over eight drying days (Ezekoye and Enebe (2006)) . whereas the drying duration required for the reduction of 21.12 4.31 Table 4.00pm 1.10 4.2.20 4.16 4.2 the temperature variations shows a better performance of dryer when reflector is tilted at 00 to that at 150.17 4.2 4.13 4.14 4.00pm 2. from the temperature ranges of Experiment 4.2 4.30am 12 noon 12.19 4.13 4. Temperature and mass properties (reflector at 150 to the dryer) Avg RH = 52% Time 10am 10.20 4.10 4.00pm Temperature Mass of chalk Ambient temp Tray 1 Tray2 Wall Tw -TA Tray1 Tray2 29 30 30 32 31 32 30 31 32 33 33 39 40 39 41 42 45 47 49 50 52 50 38 38 38 39 42 43 45 44 43 47 45 39 40 40 42 42 46 50 50 56 58 56 10 10 10 10 9 14 20 19 24 25 13 4. the experimental data obtained at UNN Enugu state Nigeria for drying pepper (56.15 4.30pm 1.12 4.20 4. These indicates a good performance of the designed drier showing the effect of the use of insulation materials and reflectors.08 4.04 4.14 4. We suspect that this may be due to intensity of the sun being higher and staying longer at overhead. This could be as a result of the use of glazing plates on three sides of the dryer at UNN which may generate a high temperature but may tend to lose it more quickly.06 4.10 4.00am 11. .13 4. For comparison purposes.20 4.10 4. e.1 Recommendations -The mirror can be replaced with stainless steel to avoid the risk of breakage and maintenance. There is no need of carrying the chalks inside during the nights in order to avoid re-wetting since the dryer is sealed with glass and wood to protect the samples from dew and rain. The drying duration of the product was reduced considerably in comparison with traditional sun drying. 5. Moreover. one at a time. -The chalk dryer can be made single tray equipment or each tray should be used individually i. . which helps the writing quality of the chalk. the chalk could retain its original colour after the drying process. The experiments were conducted for drying chalk. Conclusions An efficient and economic solar-aided chalk dryer has been developed using locally available material in Nigeria and characterized. The product was loaded in the trays inside the dryer.32 5. The dryer can be enlarged for large-scale drying and commercial purposes by increasing the reflector and collector size. to maximize its operating efficiency for chalk drying. Reflective Insulation Manufacturers Association (RIMA) . National Aeronautics and Space Administration (NASA) 4. Interview with Mr Aderemi Awojobi. Interview with Mr Adaranijo of Dara chalk 2. on solar powered dryers 3.33 Notes 1. united states patent. Gikuru M. pages 269 – 280 Wikipedia free encyclopedia. November. 63-71. (1981). 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Method and apparatus for utilizing solar energy United states Patent. 2. pp. (1993) Method and apparatus for generating atmospheric solar energy concentrator. P. (2006).. S. F. 59.( 1995) Development of a solar powered window shade. Federal University of Technology. Widiasa I. S. united states patent. vol. .S.A. Journal of Applied energy.E. (1973) Method and apparatus for converting solar radiation to electrical power United states Patent 19.com Ezekoye B.M. M. Albert G. Vol. 1. No. Constantine D. Sitompul J.wikipedia. 74 (2006). Manikantan P. L. (1982) Radiant energy collection and conversion apparatus and method united states Patent.34 References Glaser E. Istadi. Rom F. C. Keyes J. pp. and Enebe O. Department of Physics. 7. Vijayakumar K. Arlington. Stirbl R.. H. C. Sreekumar A.223.265. J. Nigeria. 247–252. Lenz E.N. No. of Science and Technology. E. and Njoroge K. (2001) Drying Technology. Coleman R. 4. K. 650 pp. Dev. and Beckman W. April 1999. Addison-Wesley. Res. 1990. 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Applied Solar Energy: An Introduction. (2006) Design. Ogunremi A. A. 2008. Radiant Barriers and Radiant Control Coatings. Nigeria. New York. 00 3.05 4.14 4.00 4.13 4.2 4.15 4.00pm 34 58 2.12 4.12 4.02 4.98 4.20 4.13 4.99 3.13 4.20 4.00pm 34 33 58 1.16 4.30pm 36 57 3.30am 32 49 12 noon 32 52 12.14 4.20 4.00 4.08 4.12 4.10 4.02 4.02 4.06 80 78 72 73 74 73 73 73 73 68 55 .10 4. Temperature and mass (reflector at 00 to the dryer) Time Open(TA) Tray 1 32 45 10am 43 10.30pm 34 55 1. Humidity 4.10 4.18 4.03 4.30pm 59 2.05 4.15 4.30am 31 45 11.36 APPENDIX I Table of Relative humidity.10 4.00am 33 46 11.00pm 35 Temperature Tray2 Wall(Tw) Tw TA 41 55 23 40 54 23 43 57 24 45 59 27 47 61 29 47 60 26 48 62 28 50 60 27 52 62 28 55 65 29 54 63 28 Mass of chalk Avg RH =75% Tray1 Tray2 Open Rel. 08 4.10 4.13 4.20 4.08 .08 4.2 4.20 4.14 4.17 4.00pm 1.30pm 1.13 4.12 4.20 4.30pm 2.10 4.2 4.30am 11.00am 11.12 4.10 4.15 4.00pm 29 30 30 32 31 32 30 31 32 33 33 Tray 1 39 40 39 41 42 45 47 49 50 52 50 Temperature Tray2 Wall 38 38 38 39 42 43 45 44 43 47 45 39 40 40 42 42 46 50 50 56 58 56 Tw -TA Mass of chalk Tray1 Tray2 Open Avg RH = 52% Rel.19 4.16 4.13 4.37 Table of Relative humidity.10 4.08 4.04 70 65 55 54 52 52 52 45 45 43 43 4.10 4.10 4.30am 12 noon 12. Humidity 10 10 10 10 9 14 20 19 24 25 13 4.16 4.15 4. Temperature and mass (reflector at 150 to the dryer) Time Open 10am 10.14 4.06 4.06 4.30pm 3.12 4.20 4.00pm 2. 38 Appendix II Template 1: Solar-aided dryer (Reflector is at 00) . 39 S Template 2: Solar-aided dryer (Reflectors tilted at 150) . 40 Template 3: Solar-aided dryer when loaded with chalk . 41 Template 4: The Thermocouple . 42 Template 5: Psychrometric chart . 43 Template 6: Wet and Dry Bulb Thermometer . 44 Template 7: Drying Tray . 45 Template 8: Weighing Scale .