- By adding a third fluid, an inert gas to the absorption system to balance the low – and high – side pressures of the system to function without a pump. Such system is called as three – absorption system.
- Thase systems have found widespread use in domestic refrigerators, particularly for mobile homes and recreational vehicles.
- The three fluids are a refrigerant, a solvent and an inert gas. The commonly used three fluid are
Inert gas: Hydrogen
- The strong ammonia solution from the absorber through heat exchanger is heated in the generator by a gas burner. During heating, ammonia vapors are removed from the solution and passed to the condenser.
- A rectifier or a water separator is fitted before the condenser. It removes water vapor carried with the ammonia vapors. So the dry ammonia vapors are supplied to the condenser. If these water vapors are not removed, they will enter into the evaporator where it will cause freezing and choking of the system.
- The hot weak solution left behind in the generator flows to the adsorber through the heat exchanger. This hot weak solution while passing through the exchanger is utilised in raising the temperature of the strong solution, which is passing through the heat exchanger from an absorber.
- The hydrogen gas permits the liquid ammonia to evaporate at a faster rate. During the evaporation, the ammonia absorbs latent heat from the refrigerated space. Thus it produces cooling effect.
- The mixture of the ammonia vapor and hydrogen is passed to the absorber. There ammonia is absorbed in water. The hydrogen raises to the top and flows back to the evaporator. This completes the cycle.
- This system cannot be used for industrial purposes, as the COP of the system is very low.