INTRODUCTION

The process of producing cold by artificial means may be called refrigeration. The term ‘refrigeration’ may be defined as the artificial withdrawal of heat, producing in a substance or within a space, a temperature lower than that which would exist under the natural influence of surroundings. In other words, the refrigeration means a continued extraction of heat from a body whose temperature is already below the temperature of its surroundings. In refrigeration, heat is virtually being pumped from a lower temperature to a higher temperature.

According to the second law of thermodynamics, the extraction of heat from a body at lower temperature to a higher temperature can only be performed with the aid of some external device. Such a device is called refrigerator. A refrigerator is a reversed heat engine or a heat pump which extracts heat from a cold body and delivers it to a hot body. The substance or medium which works in a heat pump to extract heat from a cold body and to deliver to a hot body is called a refrigerant.