Development of a Tray Dryer
Chapter One
SIGNIFICANCE /JUSTIFICATION OF THE STUDY
Literature and statistics together with the present global economic meltdown have all proved it beyond all reasonable doubt that with the rate of exploration and world consumption of crude oil, most of the countries of the world will be faced with starvation or shortage of crude oil as means of generating their foreign revenue, hence, even the world leading countries such as America, Japan, Great Britain etc have started embarking or revisiting their agricultural sectors as last resorts to augmenting their national economy. Nigeria as our country should not be left out in returning to agricultural sector irrespective of how mechanized or local it could be. Thus, the analysis and design of the grain dryer will serve as an antidote that will rekindle or reinforce our local farmers in terms of confidence in storage facility for preservation of grains rather than depending solely on an unpredictable sunlight for preservation of grain crops. In the same token, the designed grain dryer will help to minimize the unnecessary wastage of crucial grains that could have served as consumable (food or crops for planting seasons).
CHAPTER TWO
LITERATURE REVIEW
During the early era of our colonial master, Nigeria produces about 50 millions tones of grains annually. They produced grains such as rice, sorghum, wheat, beans, maize etc. Due to depreciation of technological advancement in agriculture and introduction of poor preservative system of the grain crops, this production decrease drastically. For the production, an average 10% is lost during post harvest operation between the field and consumption. This implies that about 5 million tones of food grain value go to waste. The major share of the loss occurs during storage of surplus stock. Among the various causes of loss, the most important ones is in proper drying before storage (5). The preservation of agricultural produce by drying is a long- established technique. Sun drying in the open, on mud plastered or concrete floors are the conventional method of drying grain and also cash crops. The drying period / time required in open sun for these crops ranges from 5 -45 days depending upon the crop to be dried. Unfortunately, weather conditions are likely to occur during the dried period and degradation in quality of the find produce therefore becomes unavoidable (2).
It is well-know that deterioration in quality caused by improper drying can not be eliminated until improve drying system based on mechanical dryers have been adopted. However for many reasons, these systems have not been adopted.
The range of industrial technologies used for food drying includes; tunnel dryers, spray, roller freeze and tray dryers. Tray dryers are the most suitable in terms of cost and output, for small and medium sized enterprises.
The term tray drying is normally refers to small industrial systems with some form of air heater and a fan to pass air over the product being dried although sun drying on trays or in solar dryers can also be called tray drying.
While small tray dryers are available from Europe and the USA, where they are used in pilot plants and Universities, their cost makes them unaffordable and uneconomic for producers in developing countries.
Practical Action (previously know as ITDG) recognized the need for small, controllable, powered tray dryers that could be constructed by engineers in developing countries mainly from locally available materials that were capable of producing high quality products. This has resulted in a range of tray dryers that can be manufactured at a lower price and there are now tray dryers, based on these designs in many countries with the greatest up-take of the technology in Latin America.
The key point to bear in mind when considering the local construction of such a dryer is to understand the basic principles involved and adapt them to local conditions such as the dimensions of local plywood sheet, common stock steel sizes, social conditions and fuel availability.
Tray dryer principles
The dryers are made of trays held in a cabinet which is connected to a source of air heated by gas, diesel or bio-mass such as rice husk. The air temperature is usually controlled by a thermostat which is normally set between 50 and 70OC. The air enters the bottom of the chamber below the trays and then rises, through the trays of food being dried, and exits from an opening in the top of the chamber. In the Practical Action systems the trays are designed to force the air to follow a longer zigzag route which increases the air/food contact time and thus improve its efficiency. This system also reduces back pressure which means that cheaper, smaller fans can be used.
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CHAPTER THREE
THEORY OF TRAY DRYER
DEFINITION/MEANINGOF DRYING
Drying is the procedure used to remove excess moisture from the grain to reduce the moisture to a level acceptable for safe storage or for commercial sales. Generally, the term refers to the removal of relatively small amount of moisture from a solid or nearly solid material by evaporation. Therefore, drying involves both heat and mass transfer operations simultaneously, in convective drying; the heat required for evaporating moisture from the drying product is supplied by the external drying medium, usually air. Because of the basic difference in the characteristics of grains in thin layer and deep bed, the whole grain drying process is divided into thin layer drying and deep bed drying. THIN LAYER drying refers to the grain drying process in which all grains are fully exposed to the drying air under constant drying conditions, that is, at constant air temperature and humidity.
Equilibrium Moisture Content (EMC)
Most of agricultural produce, especially the food grains absorb moisture or loose moisture from environment. At a particular condition, the moisture content of grain depends upon the temperature and relative humidity of the environments. If the vapour pressure of water present in grains is more than the vapour in the air, the water present in grain vaporizes and diffuses in the atmosphere.
Alternatively, if the vapour pressure of water present in grain is less than the atmospheric vapour pressure, grain will absorb moisture from atmosphere. This property of gaining or losing of moisture as per the atmospheric condition is termed as hygroscopicity.
The Moisture Content (M.C) attained by a grain with respect to a set of atmospheric temperature and relative humidity is the Equilibrium Moisture Content
E.M.C. in such condition; the grain moisture is in equilibrium with surrounding air.
CHAPTER FOUR
DESIGN ANALYSIS
Drying Performance
In design analysis, it is paramount that the designer bears in mind the following design factors as source of control to the design analysis work, these include among others, functionality of the equipment, strength of materials;
Dryer performance can hence be expressed in terms of various efficiency factors. However, the main efficiency to be considered in this project work is the Thermal Efficiency which could be defined as the ratio of the latent energy of the fuel (Kerosene) charged.
CHAPTER FIVE
Conclusion and Recommendation
Tray grain dryer has become a very useful equipment that needed to be designed for the definite quest for people (farmers) to dry and preserve grains and for other purposes for which grains must be dried.
Basically, the laboratory grain dryer was designed after consideration of the level of technology in the country is hence simplicity; affordability and efficiency were the major considerable factors for such grain dryer design. The grain dryer will therefore be very useful for today’s agriculturist for dying of farm produce. It can equally be used domestically for small confectionaries for household consumption.
The fuel being utilized here for the design analysis is easily affordable by all classes of farmers. The rate of wear and tear will be at its minimal level since the designed equipment has no moving parts thus making it to have a reasonable life expectancy. Finally, the design analysis of the grain dryer expresses/indicates the realities of the field engineering especially in heat and mass transfer.
The researcher hereby recommend that farmers only purchase a fabricated design grain dryer that has been incorporated with saturated vapour exhaust valve to maximize the aim/objective of this work.
REFERENCES
- ChapmanA.J “Workshop Technology” Edward Arrod Publishers Ltd.
- KeeyB, “ Introduction to industrial drying Operation” Pergamon Press Oxford, 1978
- NnolimN, “ Applied Heat and Mass Transfer” Cecta (Nig) Ltd. 1998.
- Rogersand Mayhein, “ Engineering Thermodynamic work and Heat transfer” 3rd Edition, John Wiley & sons, INC New York,
- SloanE “ Drying System and Equipment” Elbany 74, No 1, 1967.
- WeltyR “ Engineering Heat Transfer” ( SI Version) John Wiky & Sons, New York, USA 1980.
