Vapour Compression Refrigeration Cycle

Table of Contents

Summary3

Introduction3

Objectives5

Equipment and Instrumentation5

Procedure9

Theory11

Observations and Results13

Discussion14

Conclusion15

References16

Appendix17

Vapour Compression Refrigeration Cycle

Summary

The Vapor Compression Refrigeration cycle is a simple four stage process that cools a small enclosed area to a temperature lower than the surroundings. During the cycle, a refrigerant removes heat from the enclosed space and dissipates it to the surrounding air. The Evaporator draws heat from the space as the cold liquid-vapor refrigerant evaporates. The Compressor increases the pressure of the vapor, which increases the temperature above that of the surrounding air. The Condenser then releases heat to the surroundings as the hot vapor refrigerant condenses. This saturated liquid passes through the Expansion Valve, abruptly lowering the pressure and initiating the auto-refrigeration effect. This drops the temperature of the refrigerant and begins a new cycle.

Introduction

One of the most important parameters of air quality is its relative humidity (ratio of the actual amount of moisture in air to the maxi-mum amount that could be present at a given temperature). Relative humidity of air can be reduced to a required level by cooling the air, condensing out excess moisture and re-heating air to the re-quired temperature. A refrigerator can be used to extract heat from the air stream and release it to atmosphere.

The thermodynamics of the vapour compression refrigeration cycle shown in Figure 1. From the end user's point of view, the basic assessment of performance of a refrigerator is the ratio of heat extracted from the low temperature source (here: air to be cooled) to the work input into the compressor. This ratio, called the Coefficient of Performance (COP), will be determined in the experiment.

Figure 1: Refrigeration cycle applied to air conditioning

Figure 2: Schematic diagram of the Air Conditioning Unit

Objectives

The object of this experiment is to study the performance of a vapour compression refrigeration cycle (as applied to cooling and dehumidification of air).

Equipment and Instrumentation

Atmospheric air enters through the calibrated intake orifice upstream of station "A". The air mass flow rate can be calculated from:

Since there will be no re-circulation of air in this experiment, dry and wet temperatures 3 and 4 of the air at station "B" should be identical to station "A", which presents a good opportunity to check and comment on the accuracy of the instrumentation.

Electric pre-heaters and injection of steam from the boiler will be used in this experiment between stations "B" and "C" to bring the air stream at station "C" to the conditions of a simulated warm and humid climate. The state point of air at Station "C" can be determined from the wet and dry thermocouple readings 5 and 6.

Air then passes to station "D" through the evaporator section of the refrigerator, where it is cooled and excess moisture is condensed out. The state point of air at Station "D" can be determined from the wet and dry thermocouple readings 7 and 8.

Downstream from there are electric heaters which can be used to re-heat the air to the required temperature and reduce its relative ...