Redesign of a Multiple Heat Transfer Mode Charcoal Oven
Chapter One
OBJECTIVE OF THE WORK
The main objectives of this project work were as follows
- To redesign the charcoal oven.
- To fabricate the oven.
- To test the oven.
CHAPTER TWO
LITERATURE REVIEW
THEORY OF HEAT
Heat is energy in transit under the motive force of a temperature difference. Any theory should be able to explain the facts below;
- Heat lost by the hot body always equal to heat gained by the cold body
- The heat flow takes place from higher to lower temperature.
- That substance expands on heating.
- In order to change the state of a body from solid to liquid or liquid to gas without rise in temperature, certain amount of heat is required.
- When a body is heated or cooled its weight does not change.
According to the modern or dynamical theory of heat, Heat is a form of energy. The mean kinetic energy per molecule of the substance is proportional to its absolutes temperature.
HEAT TRANSFER AND ITS MODES
Heat transfer many be defined as the transmission of energy from one region to another as a result of temperature gradient. It takes place by the following three modes: (i) Conduction (ii) Convection (iii) Radiation.
Heat transmission in majority of real situations occurs as a result of combustion of the modes of heat transfer in a baking, heat transfer from the charcoal to the baking space and heat conduction through the oven walls. Heat always flows in the direct of lower temperature.
Heat transfer by Conduction
Conduction is the transfer of heat from one part of a substance to another part of the same substance, or from one substance to another in physical contact without appreciable displacement of molecules forming the substance.
In solid, the heat is conducted by the following two mechanisms:
- By lattice Vibration(the faster moving molecules or atoms in the hottest part of a body transfer heat by impacts some of their energy to adjacent molecules.
- By transfer of free electrons(free electrons provide an energy flux in the direction of decreasing temperature for the major portion of the heat flux except at low temperature. In case of gases, the mechanism of heat conduction is simple. The kinetic energy of a molecule is a function of temperature. These are in continuous random motion exchanging energy and momentum. When a molecule from the high temperature region collides with a molecule from the low temperature region, its loses energy by collisions.
- Fourier’s Laws of Heat Conduction
Fourier’s laws of heat conduction are an empirical law base on observation and states that the rate of flow of heat through a simple homogeneous solid is directly proportional to the area of the section at right angles to the direction of heat flow and to changes of temperature with respect to the length of the path of the heat flow. Mathematically, it can be represented by the equation.
CHAPTER THREE
REDESIGN AND MODIFICATION OF A MULTIPLE HEAT TRANSFER MODE CHARCOAL OVEN
MATERIALS AND MATERIAL SELECTION
A large number of materials are available for engineering applications. The choice of a material for a given application can determine, to a large extent, the ultimate success or failure and effective/efficiency of the system as it is the final practical decision in the design process. Hence in selecting the materials suitable for use in this work, the physical properties of the materials were used as the basic parameters guiding the selection. The factors, properties used include temperature unification, cost effectiveness, energy source and it’s compositions, mode of heat transfer (dominantly conventional), composition of materials to be baked, insulation and other considerations were raw materials availability, heat conductivity and resistivity, strength as may be required, rigidity, corrosion resistance, weight and other mechanical engineering properties (such as machinability, fatigue) , manufacturing requirements (such as fabrication method, tolerance, finishing) etc.
Material for Oven unit
The material selected for the oven body are three quarter inches square pipe mild steel metal for the frame and one and half millimeters thickness of mild steel sheet metal for the inner and outer covering of the oven with insulations in between.
CHAPTER FOUR
RESULTS
Experimental results
Having fabricated the oven it was tested in two different ways to determine the time it takes to raise the temperature up to the uniform temperature on both portion that can bake. The first procedure which was with regulating plate were presented as followed. In each way of testing they were a response time of 3minutes.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS CONCLUSION
CONCLUSION
In developing countries like Nigeria, where job opportunities are very scarce, it is not wise to allow the few operating ones to close down. Therefore, Based on the results obtained from the performance test carried out on the fabricated oven the set objectives of the research was achieved, the following conclusions can also be made:
- The height of the lower rack from the hot plate affected the uniformity of the temperature as observed in table 4.6.
- Further reduction of the area of regulating plate gave an appreciable result.
RECOMMENDATIONS
- The regulating plate should be cut in a sizable geometry to have a more comparable area.
- The surface of the ambient inlet holes should be covered with pipes of required diameter to reduce retardation of the air inflow due to insulation
- Caution should be taken during welding operation for proper squaring as it effect the complete sealing if the doors
- Further research is recommended to deduce a mathematical model for finding the area reduction and ease the operation of the system.
- The capacity of the combustion chamber should be increased to accommodate more fuel for longer operation period.
- An awareness campaign should be undertaken to encourage the use of oven.
REFERENCE
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