DESIGN AND CONSTRUCTION OF A REFRIGERATING UNIT

Thesis Overview

1.0 INTRODUCTIONRefrigeration is the process of lowering the temperature of a substance below that of its surrounding. Refrigeration is the practical application of the first and second law thermodynamics. Comprehensive understanding of the basic principles of thermodynamics is crucial for full understanding of basic operation of refrigerator. The first law states that the energy can neither be created nor destroyed. If energy of 2.5J appears in one forms it appears in another without a corresponding decrease of energy on the other form. The second law states that no system can receive heat at a given temperature and reject it at a higher temperature without receiving work from the surrounding heat always flow from Warner to cooler body. Through consideration of these laws, the ideal refrigeration cycle are considered. The carnot cycle is reversible and consist of adiabatic compression witherma rejection of heat, adiabatic expansion and wothermal addition of heatl the carnot cycle is unattainable ideal which serves as a standard of comparison and it provides a convenient guide to the temperature that should be maintained to achieved effectiveness. The efficiency or coefficient of performance (C.O.P.) of a carnot cycle depends on the temperature at which heat is added and rejected.Therefore,
C.O.P = T1
T2 – T1
Where T1 = Evaporation temperature
T2 = Conducting temperatureIn actual refrigeration there will be issues causing C.O.P to be less than that for ideal cycle. The basic methods of refrigeration like the mechanical refrigeration ejector (steam jet) refrigeration absorption refrigeration uses similar process for obtaining refrigeration effect. That is evaporation in the evaporator, condensation in the condenser, the main difference is in the way used refrigeration being done. The most compression. The cycle efficiency can be ignored in a number of ways.1. Multistage system: When evaporation and condensing temperature (pressure) difference is large, it is prudent to separate compression into two stages. The use of multistage system open up the opportunity to use flash gas removal and inter cooling as a measure to improve performance of the system.2. Cascade system: This appears in situation where the evaporating temperature is very low (below 600c). the refrigerant is used to achieve the cooling. The liquid with low boiling points are used as refrigerants.
1.1 SCOPE OFD THE PROJECTThe scope of this project is mainly concerned with the design and construction of a refrigerating unit that has a very performance level and with the cost of fabrication lower than that of existing prototypeA good refrigerator is one that has all the basic components of compressor, condensers, fan motor, copper tubes and other. This project must apply all the principles of refrigeration.