ABSTRACT
It’s been difficult for the traditional freezers to reduce the temperature of a material quickly enough to the required temperature; therefore, the plate freezer was introduced. This project deals on the design and development of a locally made plate freezer with a local voltage controller, which is aimed at increasing the cooling rate of the system. In this report, a plate freezer consisting of three plates connected in series but arranged in parallel and having a cooling load of 0.371kw is to be designed with the available materials. It is observed in the system that high cooling rate was achieved but the flow of the refrigerant takes some minutes to circulate throughout the system. The system still uses the necessary components required for effective work in the system, and the main source of cooling is the refrigerant. The refrigerant used is R-134a which is now found out in market as a replacement of R-12.
TABLE OF CONTENTS
Title page i
Declaration ii
Dedication iii
Certification iv
Acknowledgement v
Abstract vi
Table of content vii
List of Figures x
List of Tables xi
Chapter One: Introduction
1.1 Background of study 1
1.2 Statement of problem 3
1.3 Aim and Objectives 3
1.4 Justification of study 3
Chapter Two: Literature review
2.1 History 4
2.2 Development of the plate freezer 5
Chapter Three: Materials and methods
3.1 Plate freezer and selection of its components 7
3.2 Working principle of a plate freezer 7
3.3 Selection of plate freezer components 9
3.3.1 The compressor 10
3.3.2 The condenser 11
3.3.3 The evaporator 13
3.3.4 Capillary tube 13
3.3.5 The refrigerant 14
3.4 Methods 14
3.5 System design calculation 15
3.5.1 Chilling load calculation 15
3.5.2 Compressor capacity and design 17
3.5.3 Condenser capacity and design 18
3.5.4 Design of expansion device (capillary tube) 22
3.5.5 Evaporator design 25
Chapter Four: Testing/results and discussion
4.0 Experimental procedures 29
4.1 Results and discussion 30
Chapter Five: Conclusion and recommendation
5.1 Conclusion 34
5.2 Recommendation 35
References 36
Appendices 38
LIST OF TABLES
Table 4.1. Meat Temperature, Evaporating Temperature and Condensing Temperature with respect to increasing Time 32
LIST OF FIGURES
Fig 1. Theoretical vapor compression cycle 2
Fig 2. Evaporator Plates 8
Fig 3. Schematic drawing of the plate freezer 9
Fig 4. Diagram of a Compressor 10
Fig 5. The Condenser 12
Fig 6. A Graph of Meat Temperature against varying Time 33
Fig 7. A Graph of Evaporating Temperature against varying Time 33
Fig 8. A Graph of Condensing Temperature against varying Time 34
CHAPTER 1
INTRODUCTION
Freezers have become to be a house hold necessity since it was introduced in the late 1940s, food preservation is usually done by keeping the food inside chambers which has evaporator coils installed around it. This chamber is properly insulated from the surroundings by a casing.
The heat transfer takes place from the food to the freezer (chamber) surface through the air gap. But air is a bad conductor of heat so the freezing rate is low and time consuming. The freezing rate was increased by the development of a Plate freezer.
In the plate freezer there are two or more plates (depending on the manufacturers choice) through which the refrigerant expands. The food is placed between the plates. As the plates are in direct contact with the food, there is better heat transfer which increases the freezing rate.
Compared to the traditional method of freezing this method theoretically takes only a Quarter of the time required to bring 1 kg of meat from 30 ºC to -20 ºC, meaning the freezing rate is increased about four times. This is the crucial reason why plate freezers are replacing traditional freezing equipment’s. This research is bent on constructing a plate upright freezer using locally available materials.
1.1 Background of Study
Refrigeration systems operate on a series of consecutive thermodynamic processes that form a cycle that returns the working substance to the same state. A thermodynamic refrigeration cycle removes heat from a low-temperature object (refrigeration) and rejects it at a higher temperature. This cyclic process requires that work be input so that the second law of thermodynamics is not violated (Wark, 1983). The ideal refrigeration system is based on the concept of the reversible Carnot cycle. The Carnot cycle is a theoretical concept because it is ideal, which means that it is lossless, frictionless, and there are no temperature differences in heat exchange processes. None of these ideals can ever be achieved in practice. The Carnot cycle therefore provides a reference standard against which the performance of all other refrigeration cycles can be compared.
The refrigeration systems use a fluid known as refrigerant that absorbs the heat from low- temperature region and rejects it at higher-temperature region by undergoing a phase transition. Commonly used refrigerants are mostly harmful for environment. In a refrigeration system, the coefficient of performance (COP), which is defined as the ratio of rate of heat removal in evaporator to the mechanical work input to the compressor, provides an estimate of refrigeration process. An increase in the heat removal rate in the evaporator or a decrease in the compressor work shall thus be helpful in enhancing the COP of the refrigeration system
Fig 1. Theoretical vapor compression cycle
1.2 Statement of problem
The ability to reduce the temperature in the thermal center of an item to be refrigerated quickly enough to prevent at least significantly limit the growth of pathogens such as Salmonella which are injurious to human health is quite uncommon in most traditional freezers.
Due to the slow freezing rates in traditional freezer, a large amount of energy is mostly required.
1.3 Aim and Objectives
The aim of this project work is to fabricate a small-scale Plate freezer, so as to practically observe its freezing rate compared to that of a traditional freezer
This aim will be achieved through the following objectives
• Constructing a Plate freezer using locally available materials
• Addition of a voltage control device to safe guard the compressor in an energy surge.
1.4 Justification of study
This work is due to the need for Nigeria to adopt, in a much larger scale. The need for this country Nigeria to do so includes:
• Increase cooling rate
• Low power cost: Due to its freezing rate, lesser power is required to achieve adequate cooling/freezing.
• They occupy less space
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