CONSTRUCTION OF A PORTABLE REFRIGERATOR

ABSTRACT

This project write up focuses on the construction and analysis of a portable cooling system with compressor capacity of 105W. The principles of improving the operation of a cooling system, choice of materials, various methods used in the construction and recommendation for advancement where duly treated. As the cooling system composes of mechanical and electrical parts, a lot of efforts were made to discuss the various stages and sequences of assembly. Stating a quite number of safety rules which must be adhered strictly by anybody who may embark on the project in future to achieve a satisfying result. With due consideration that we are in the modern age of refrigeration due to the gradual destruction of the ozone layer, refrigerant R134a (1,1,1,2-tetraflouroethane) was used. The entire system was tested and the condenser and evaporator temperature recorded 32oC and -4oC respectively. The results gotten from revealed that (i) the rate at which water cools in the system reduces as water reaches its freezing point (ii) the performance of the refrigerator is affected by the amount of load stored in it. The C.O.P (coefficient of performance) of the system was calculated and found to be high 6.33. Aprea et al (1996) reported that vapour compression refrigeration systems are widely used for cold storage, domestic and super market refrigeration because of its high coefficient of performance.

CHAPTER ONE

1.0 INTRODUCTION

A portable refrigerator is simply a refrigerator fitted with rollers at its ends so that it can easily be moved to any direction with little application of force. Here, the mechanical refrigeration has to do with the production of a machine that controls a temperature lower than atmosphere temperature. This involves the removal of heat from a low temperature level and rejecting it to a relatively higher temperature level.

Naturally, heat flows from a body at a higher temperature to body at a lower temperature. But in the reverse case, an external energy or work input is required. The carrier substance used to transport heat is called a refrigerant. Therefore, refrigerator is the reversed heat engine cycle.

Refrigeration is accomplished by various methods, such as: the vapour compression system, absorption system, and steam jet refrigeration cycle. In this project only the vapour compression system of refrigeration shall be discussed as it was the method adopted to accomplish the project.

Refrigeration contributes to the raising of standard of living of different races. Although refrigeration is primarily an application of thermodynamics, but advances have made refrigeration in recent years to grow into so many phrase where we need technicians, craft persons, engineers, scientists, and others from phases of engineering to pool skills and knowledge in the design, manufacturer and operation of the refrigeration system. A good knowledge of thermodynamics and properties of refrigerants is required before the complete cycle analysis can be made.
The application is limitless. The most common and readily recognized ones are found in the preservation of food and chilling of our drinks and water especially during the hot and dry season.

1.1 IMPORTANCE OF PROJECT

The importance attached to this project is to achieve a fast cooling system with little or no adverse effects on the food tissues, the flavor, freshness and natural nutrients of food materials. The construction intention is based on reduced cost, longer life span, fast freezing techniques, compactness, and portability and so on. We also employed the use of refrigerant that has no effect of man and his environment. However, the refrigerant that was used in this project does not enhance the ozone layer’s depletion.

While taking the specification on the size, we also put into consideration the items that are to be cooled or preserved. Also the cabinet dimensions and compressor capacity also considered.

The essential design parameters of the portable refrigerator are as follows:

i. Compressor

ii. Capillary tube

iii. Condenser

iv. Evaporator

v. Thermostat

vi. Refrigerant

vii. Rubber seal

viii. Drier

ix. Relay and overload

x. Aluminum sheets

xi. Lagging materials

xii. Lubricating oil

xiii. Plywood

xiv. Vegetable basin

xv. Valve

xvi. Hinges

xvii. Rollers

1.2 NATURE OF THE STUDY

The design for contemporary refrigerator is based on two basic laws of physics: first, that heat flows from warmer material to cooler materials and never the reverse; second, which decreasing the pressure of a gas also decreases its temperature. In the refrigeration systems typically include a compressor, a condenser, an expansion valve (capillary tube), and an evaporator. All components interconnected to form a fluid circuit. Cooling is accomplished through evaporation of a liquid refrigerant under reduced temperature and pressure.

The raw material in refrigerators today consists of several basic components: the exterior cabinet and door, the inner cabinet or liner, the insulation inserted between the two, the cooling system, the refrigerant, and the fixtures. The cabinet and door are made of aluminum or steel sheet metal that is sometimes pre-painted. The inner cabinet is made of sheet metal, like the outer cabinet, or of plastic, but in this study, the researcher(s) used wood. The insulation that fills the gap between the inner and outer cabinets consists of foam. The components of the cooling system (compressor, condenser) are made of aluminum, copper, or an alloy.

1.3 OBJECTIVE OF THE PROJECT

The main objectives of this project are to achieve the following purpose:

a. To construct a portable domestic cooling equipment that can be easily be moved to any convenient position.

b. To construct a cooling system that is efficient with little or no complexity in maintenance.

c. To construct a cooling system with low cost

d. To construct a cooling system with reduced weight and size.

1.4 SCOPE AND LIMITATION OF THE PROJECT

Portable mobile refrigerator as its name entails is for domestic application and to some extent for commercial purpose due to its fast freezing nature and mobility.

While the limitation of this mobile cooling system is basically on its specification in terms of size, capacity and area of need in terms of power source. Based on this specification, the equipment is not congruent for industrial use, where large refrigeration unit are more ideal.

REFERENCES

American society for heating: Fundamental Handbook, Refrigeration and Air Conditioning for Engineers (1977) Ashrae publishing U.S.A (p.272).

Anderson, Oscar Edward (1953). Refrigeration in America; a history of new technology and its impact. (Princeton): Published for the University of Cincinnati by Princeton University Press. Pp. 5-6

Aprea, C., Mastrullo, R. and Rossi, F.D., Behaviour and performances of R502 alternative working fluids in refrigerating plants. International Journal of Refrigeration, Vol. 19(4), (1996), pp. 257-263

Burstall, Aubrey F. (1965). A history of Mechanical Engineering. The MIT Press.

D. P. Wilson and R. S. Basu (1988). “Thermodynamic Properties of a New Stratospherically Safe Working Fluid – Refrigerant-134a,” ASHRAE Trans. 94 pt. 2.

Freiberg and Susanne (2010). Fresh: A Perishable History (1st Havard University Press Pbk. Ed.). Cambridge, Mass. Belknap. Pp. 20-23

Neuburger, Albert (2003). The Technical Arts and Science of the Ancients. London: Kegan Paul. P.122

Offor, I. C. lecture notebook on refrigeration cycle. Departmental of Mechanical engineering, federal polytechnic Oko, Anambra State.

R. K. Rajput: Engineering Thermodynamics. Fourth edition.
www.r744.com/everythingR744

Y.V.C. Rao (2003). An Introduction to Thermodynamics (2nd ed.). University Press.