04-01-2013, 01:54 PM
INFLUENCE OF ELECTRONIC EXPANSION VALVE ON THE PERFORMANCE OF WINDOW AIR CONDITIONER RETROFITTED WITH R407C
ABSTRACT
The object of this experimental study is to investigate the effects of the expansion devices on the performance of a one TR window air conditioner retrofitted with eco friendly alternative refrigerant R-407C. The widow air conditioner applying the expansion devices of a capillary tube, thermostatic expansion valve and electronic expansion valve is tested by varying condenser temperature from 400C to 550C, while maintaining evaporator temperature at 60C. The R 22 capillary tube system is utilized as baseline unit for the performance comparison with the R-407C system. The capacity for the R407C EEV system is higher by 10.1% at full charge condition than that for the R22 capillary tube system. The capacity for the R407C EEV system is higher by 10.2% at full charge condition than that for the R407C TEV system. The COP of R407C EEV system is higher by 15.4% and 12.3% than that of R407C capillary tube and thermostatic expansion valve respectively. The final result show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve and capillary tube.
INTRODUCTION
Refrigeration systems are employed in wide variety of industrial and domestic applications, for example metal manufacture, food preservation, ice cream manufacture etc. Air conditioning is a necessity for efficient functioning of human beings, for the efficient functioning of certain sophisticated equipments or for a particular industrial process or for the storage of commodity for long periods without getting spoiled.
The concept of air conditioning is developed with the advancement of technology and the need for comforts. As the concept of life is changing and the maximum time of the modern man is spent in the office or at home, the need of air conditioning has gradually increased and is becoming a necessity rather than a luxury. In tropical countries where the conditions are extreme, the air conditioning is all the more important as without air conditioning it would be difficult to survive, be it in summer or winter
VAPOUR COMPRESSION REFRIGRATION SYSTEM
A vapour compression refrigeration system is an improved type of air refrigeration system in which a suitable working substance termed as a refrigerant, is used. It condenses and evaporates at temperatures and pressures close to the atmospheric conditions. The refrigerants usually used for this purpose are ammonia, carbon dioxide and sulphur dioxide. The refrigerant used does not leave the system but is circulated throughout the system alternatively condensing and evaporating. In evaporating, the refrigerant absorbs its latent from brine (salt water) which is used for circulating it around the cold chamber, while condensing, it gives out it latent heat of the circulating water of the cooler. The vapour compressing refrigeration system is, therefore is a latent heat pump, as it pumps its latent heat from the brine and delivers it to the cooler.
CAPILLARY TUBE
The capillary tube is a fixed restriction-type device. It is a long and narrow tube connecting the condenser directly to evaporator. The pressure drop through the capillary tube is due to the following factors:
1. Friction, due to fluid viscosity, resulting in frictional pressure drop.
2. Acceleration, due to the flashing of the liquid refrigerant into vapour, resulting in momentum pressure drop.
ELECTRONIC EXPANSION VALVE
The advantages of an electronic superheat controller are obvious. The evaporator is always optimally filled with refrigerant. Even with large load variations, which mean an extremely wide range of partial-load operating conditions, exactly the right amount of refrigerant can be injected.
This is done by constantly sensing the actual superheat value in the evaporator by means of a pressure transducer and a very sensitive temperature sensor and conveying this information to the controller in near real time. With this information, the controller can act to achieve an optimally low superheat level.