Working Principles of VCRS-Mechanical Engineering

You might ask what are the components of VARS that makes it different from VCRS. Well, the need for the compressor is eliminated in the vapor absorption system. The compressor is replaced by a generator, a pump, and an absorber. So the basic components of a basic Vapor absorption refrigeration are-

• Generator
• pump
• absorber
• condenser
• evaporator
• expander or throttling device

And some other components like rectifier, analyzer and heat exchanger.

Vapour Absorption Refrigeration System Schematic diagram

Remember that in NH3-H2O – ammonia is the refrigerant and water is the absorber but the LiBr-H2O water is the refrigerant and LiBr is the absorber. Most of the time in the interview board you will be asked about the refrigeration and air conditioning interview questions.

In this case, we are demonstrating the Aqua-Ammonia Vapor absorption system. Here NH3 is the refrigerant and H2O is the absorbent. In VA refrigeration system the requirement of the compressor is fulfilled by using an arrangement consisting of an absorber, a pump, and a generator. However, more elements are added to improve the performance of the system. The elements condenser, evaporator and expansion valve are all same for VC and VA cycles.

First, evaporator passes the refrigerant vapor to the absorber (In this case ammonia vapor). NH3 has a property of mixing with the cool water promptly. So, in absorber ammonia mixed with water is known as strong NH3-Water solution. With the help of a pump, this strong solution moves towards the generator where the solution is heated and NH3 is liberated from the water and collected on the top of the generator with high pressure. In the VC system, the function of the compressor is to compress the refrigerant vapor and increase its pressure. Here in VARS, the generator is doing the same. Hence, the function of the compressor is already achieved. Likewise, the refrigerant vapor with high pressure goes to condenser and liberates heat and ultimately becomes liquid. The liquid is collected in a receiver tank and then moves through the expansion valve. Here it is expanded, moves towards the evaporator and collects heat and becomes vapor and the cycle continues.

The solution exchange in generator and absorber also runs in a cycle. Now, what happens in the absorber and generator. With the help of a pump, the strong solution is transferred to the generator. In the generator, heat is supplied and separated ammonia is ready for the next step. The solution in the generator is thus called a weak solution. This weak solution comes back to the generator with the help of a return duct. For example, the heat exchanger is used to cool the weak solution, otherwise, the water of the absorber will be heated.

This type of refrigeration cycle is used where exhaust heat is available. Extra or unused heat can be used to run the generator. For developing solar refrigeration system this type of arrangement is very useful. But you might be thinking that here electrical is used to run the pump. But still, the running the cost is less in Vapor absorption system than Vapor compression cycle because the energy used in pumps is very less in comparison to that of a compressor.