What is the basic working principle of Refrigerator?

A refrigerator works by compressing and expanding a fluid in order to effect a heat transfer from the medium being cooled to the atmosphere where it is allowed to dissipate. The basic system works as follows:

A fluid is compressed which causes it to heat up, this is pumped through a coil which transfers the heat of compression to the atmosphere or other fluid this cools the fluid in the system, the fluid is then expanded through an orifice where it cools even further as a result of the expansion (no heat transfer actually occurs, it's what "causes" the expansion), this then passes through another coil inside the refrigerator where it absorbs heat from the air inside the refrigerator, this heated fluid then passes back to the compressor where it is compressed again causing it to heat up again and the cycle repeats.