Absorption Refrigerator - Single Pressure Absorption Refrigeration

Single Pressure Absorption Refrigeration

A single-pressure absorption refrigerator uses three substances: ammonia, hydrogen gas, and water. At standard atmospheric conditions, ammonia is a gas with a boiling point of -33°C, but a single-pressure absorption refrigerator is pressurised to the point where the ammonia is a liquid. The cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused.

The cooling cycle starts with liquefied ammonia entering the evaporator at room temperature. The ammonia is mixed in the evaporator with hydrogen. The partial pressure of the hydrogen is used to regulate the total pressure, which in turn regulates the vapour pressure and thus the boiling point of the ammonia. As the ammonia boils in the evaporator it pulls heat from the refrigerator's interior and provides the cooling required.

The next three steps exist to separate the gaseous ammonia and the hydrogen. First, in the absorber, the mixture of gases enters the bottom of an uphill series of tubes, into which water is added at the top. The ammonia dissolves in the water, producing a mixture of liquid ammonia solution and hydrogen. The gaseous hydrogen collects at the top of the absorber, while the liquid ammonia solution flows to the bottom.

The second step separates the ammonia and water. In the generator, heat is applied to the solution to distill the ammonia from the water. Some water vapor and bubbles remain mixed with the ammonia. This water is dried out in the final separation step, done in the separator, by passing it through an uphill series of twisted pipes with minor obstacles to pop the bubbles, allowing the collected water to drain back to the generator.

Finally the pure ammonia gas enters the condenser. In this heat exchanger, the hot ammonia gas is cooled to room temperature and hence condenses to a liquid, allowing the cycle to restart.