Fabrication and Analysis of Vapour Compression System with Ellipse shaped Evaporator coil

ABSTRACT:

A refrigerator is machine which cool and maintain a body at a temperature below that of surrounding. Majority of refrigerator system works on vapour compression refrigeration system. This system consists of compressor, condenser, expansion valve and evaporator. The performance of the system depends upon these system components.
The main objective of the project is to increase the performance of the system by increasing the heat transfer rate through the evaporator. Heat transfer from the evaporator increased by the changing the shape of the evaporator and by extended surfaces. In view of the above it is proposed to fabricate the ellipse shaped evaporator coil and to carry out the experimental investigation on it evaluate it performance and to compare it with the existing evaporator in the vapour compression refrigeration system. In this experiment involves 165 Litres capacity of domestic refrigerator which in turn results the better performance than the previous one, and same results can be seen in the coefficient of performance.

INTRODUCTION

The vapour compression system is the most widely used refrigeration system in practice. This refrigeration system adopts the vapour compression cycle. This cycle requires the addition of external work for its operation. Basically it consists of four processes namely:

1).Isentropic compression

2).Constant pressure heat rejection

3).Isenthalpic expansion

4).Constant pressure heat addition

The ellipse shape coil is used in almost all small refrigeration systems. Vapour refrigerant enters the ellipse shaped evaporator coil and as it flows through the suction pressure, the pressure drops because of friction and acceleration of the refrigerant. Some of the liquid flashes into the vapour as the refrigerant flows through the coil. Once the ellipse shape coil has been selected and installed, it cannot adjust to the variations in discharge pressure, suction pressure or load. Compressor and expansion device must arrive at suction and discharge conditions such that the compressor pumps the same flow rate of the refrigerant from the evaporator that the expansion device feeds. The designer of a new refrigeration unit employing a ellipse shaped coil must select the bore and length of the coil so that the compressor and its components operate under balanced operating condition at the desired evaporator temperature.

OBJECTIVE AND SCOPE :

Objective and scope of the present work are

• To perform studies on the ellipse shaped evaporator coil of vapour compression refrigeration system with alternative refrigerant.
• To numerically simulate the helical ellipse shape coil to understand the vapour flow and heat transfer involved in the system.
• To study experimentally the effect of the coil diameter and the tube diameter on the performance of the vapour compression refrigeration system.
• To compare experimentally evaluated results with that obtained by numerical simulation.

The ellipse shape coil used as an expansion device in small capacity hermetic sealed refrigeration units such as in domestic refrigerators water coolers room air conditioners, especially in small capacity installations. It is a copper tube of small internal diameter and of varying length depending upon the application. The inside diameter of the tube used in refrigeration work is generally defreeze box aluminium. But here ellipse shaped coil .at the inlet of the coil in order to protect it from contaminants.
In its operation, the liquid refrigerant from the condenser enters the capillary tube. Due to the frictional resistance offered by a small diameter tube, the pressure drops, since the frictional resistance offered by a small diameter tube, the pressure inversely proportional to the diameter, therefore longer the ellipse shape coil and smaller its inside diameter, greater is the pressure drop created in the refrigerant flow, in other words, greater pressure difference between the condenser and evaporator is needed for a given flow rate of the refrigerant. The diameter and length of the ellipse shape coil once selected for a given set of conditions and load cannot operate efficiently at other conditions.

EXPERIMENTAL PROCEDURE
Experimental procedure, which is carried out during the experiment, is given below:
a) The vapour compression refrigeration is switched on
b) The required evaporator temperature is attained, by adjusting the expansion valve and maintained constant
c) The required degree of super heat is maintained by regulating the water flow rate and its temperature through the
evaporator.
d) The required condensing temperature and pressure are attained by varying the inlet flow rate of air.
e) The data acquisition system at frequent intervals

• Temperature at inlet and outlet for all the components.
• Pressure at the inlet and exit for all the components.

Parameters which affect the performance of the system are flow rate of refrigerant, flow rate of air, capillary inner diameter, tube length, capillary coil diameter, condensing pressure, sub cooling and evaporating pressure.

Reference and Download :

Fabrication and Analysis of Vapour Compression System with Ellipse shaped Evaporator coil

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