In a typical absorption refrigeration system, ammonia is used as the refrigerant because it possesses most of the desirable properties. It is toxic, but since the system has no valves or moving parts, there is very little chance of leak and also the total amount refrigerant charge itself is small. Liquid ammonia of refrigerant charge itself is small. Liquid ammonia evaporates in the presence of air / other gases, the lighter than gas the faster the evaporation. Since hydrogen is the lightest gas and is also non corrosive and insoluble in water it is used in the low side of the system. Water is used as the solvent because of its ability to absorb ammonia readily. If liquid ammonia is introduced at the top of the system as shown in figure, it flows into the evaporator and evaporates. Hydrogen passes upward in the evaporator counter flow to the liquid ammonia that falls from one level to another. The ammonia vapour and hydrogen leave the top of the evaporator and pass through the gas heat exchanger where they are warmed by the hydrogen flowing to the evaporator. Then they flow through the vessel on the left and into absorber. Weak aqua is introduced at the top of the absorber, absorbing ammonia as it passes counter flow through this unit. The hydrogen leaves the top of the absorber and flow through the heat exchanger on its way to the evaporator. The strong ammonia solution leaves the bottom of the absorber and flows into the generator at the lower right.