What is the working principle of an absorption refrigeration system?

Solar energy can be converted more efficiently to heat than mechanical or electrical energy, the use of vapor absorption cycle with solar energy to be the best solution at present time.

absorption
Solar absorption refrigeration system

It consists of the following collector:

  1. Solar flat plate collector
  2. Generator
  3. Absorber with absorber pump
  4. Condenser
  5. Evaporator
  6. Expansion valve
  7. Pressure reducing valve
  8. Rectifier
  9. Regenerator

The most common combinations of working fluids employed in the absorption systems are ammonia (refrigerant) – water (absorbent).

Flat plate solar collector

A solar collector is a special kind of heat exchanger that transforms solar radiant energy (heat) into fluid (water/air). Flat plate collectors are designed for applications requiring energy delivery at moderate temperatures, up to 100* C. They are always mounted in a stationary position and do not require tracking of the sun and require only little maintenance.

The flat plate collectors are universally used for absorption refrigeration systems because of the greater simplicity of construction and lower cost.

Working principle

  • The low-pressure pure ammonia vapor leaving the evaporator enters the absorber where it is absorbed by cold water in it.
  • While absorbing, the pressure in the absorber comes down which tends to draw more ammonia vapor from the evaporator.
  • While absorbing more ammonia vapor, the temperature of the solution (rich solution) rises, and the heat thus formed in the absorber is removed with help of a cooling water arrangement.
  • The strong aqua ammonia from the absorber is pumped into the generator through the regenerator (heat exchanger) to raise the temperature of the strong solution by the return hot weak solution from the generator.
  • The regenerated strong solution of ammonia in the generator is heated with the help of a heating coil of a solar flat plate collector.
  • The heat transfer from the solar collector to the generator leads to the separation of ammonia vapor from aqua ammonia leaving behind the hot weak aqua solution to the absorber through a properly adjusted pressure reducing valve.
  • On the other hand, the separated high-pressure ammonia vapor passed to the condenser through a rectifier.
  • A rectifier or a water separator removes water vapor carried with the ammonia vapors and drains back to the generator.
  • High-pressure ammonia vapor is condensed in the condenser by using an external cooling source to high-pressure liquid ammonia.
  • This liquid ammonia is passed to the expansion valve and then to the evaporator where heat transfer from the refrigerated space causes vapourization of the ammonia (refrigerant). Thus it produces a cooling effect.

Advantages

  1. Free heat energy from the sum
  2. Operation cost is minimized
  3. Suitable for locations where electrical power is not readily available
  4. Used to keep various medicines cool for extended lengths of time.

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