Vapour Compression Refrigeration & Vapour Absorption Refrigeration

Vapour Absorption System/Machine (VAM) is kind of refrigerating machine that uses the absorption phenomena instead of compression process as being used in conventional machines.

refrigeration

In this case, material (for e.g. Water) is sent through tubes into Evaporator where Refrigerant (Let say Water) is poured over the tube. Since vacuum is maintained in the evaporator and boiling point of liquid decreases as the pressure decreases so the refrigerant after taking heat from the water in the tubes gets evaporated and becomes vapour. Now, this vapour is then absorbed by Absorbent in Absorber which is generally hygroscopic (affinity to water) in nature. So we have now dilute absorbent. Generally, LiBr is used as absorbent. Now we have to recharge the LiBr i.e., we need to get the LiBr back to concentrated form. So for that, we pass the dilute LiBr through Generator using Absorbent Pump where dil. LiBr is heated to higher temperature so that water gets separated because the absorption capacity of LiBr decreases with increase in temperature and decrease in concentration. Now the LiBr gets concentrated and sent back to the Absorber. Now the refrigerant is in steam state so to get back the steam to water, we pass it through the Condenser where is looses heat to Cooling water and again sent to Evaporator by Referigerant Pump.

This is the cycle that is followed in Vapour Absorption Cycle.

Evaporator->Absorber->Generator->Condenser->Evaporator….

This mechanism is used in Chillers where we have to use the waste heat coming from some other plant.

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