Refrigerant, also known as refrigerant, refrigerant and snow seed, is the medium substance in various heat engines to complete energy conversion. These substances usually increase their power by reversible phase transition (such as gas-liquid phase transition). Such as the steam in the steam engine, the snow in the refrigerator and so on. In general, when the steam engine is working, the heat energy of the steam is released and converted into mechanical energy to generate the original power; while the snow seed of the refrigerator is used to transfer the heat at the low temperature to the high temperature.