Simple vapor absorption system Prof Dr M M

Simple vapor absorption system Prof. Dr. M. M. Nasr Mechanical Power and Energy Dept

Simple vapor absorption system In this system an absorber, a pump, a generator and a pressure reducing valve replace the compressor. • The low pressure refrigerant vapor leaving the evaporator enters the absorber where it is absorbed by the weak solution in the absorber. • Heat is removed in the absorber to increase the absorption capacity of solution. • The strong solution in the absorber is pumped to the generators. • The strong solution is heated in the generator during the heating the refrigerant vapors are driven off the solution and the weak solution flows back to the absorber.

• Two widespread absorption cycles currently in use are the lithium bromide (Li. Br) cycle and the ammonia-water (NH 3 -H 2 O) cycle. In the former, water acts as the refrigerant and Li. Br as the absorbent. In the latter, the ammoniawater solution is the refrigerant and water is the absorbent. The Li. Br cycle tends to be more common.

Aqua-Ammonia Vapor absorption system. • Here NH 3 is the refrigerant and H 2 O 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.

The function of the analyzer in the vapor absorption refrigeration system: The analyzer is a series of plated situated at the top of the generator. It traps the water vapor from entering the condenser. Ultimately it helps the pure ammonia vapor to enter the condenser. Actually, it helps to remove some unwanted water vapor particles to enter the condenser with NH 3 vapor. If these water vapors are permitted in the condenser, they might freeze in the expansion valve and the pipe may get choked. Function of rectifier The rectifier is nothing but a water-cooled condenser. It condenses the water vapor and some of the ammonia vapor and sends back to the generator. Elimination of the water vapor takes place in the condenser.

Maximum COP of ideal absorption refrigeration system • The ideal(max) COP of VARS system is equal to the product of efficiency of a Carnot heat engine operating between Tg and To and COP of a Carnot refrigeration system operating between To and Te

Maximum COP of ideal absorption refrigeration system Example: What is the COP of an ideal heatoperated refrigeration cycle that receives the energizing heat from a solar collector at a temperature of 70 o. C, performs refrigeration at 15 o. C, and rejects heat to atmosphere at a temperature of 35 o. C? • Neglecting solution pump work, Wp; the COP of VARS is given by: = 1. 47