Absorption Refrigeration Systems Basic Design

It is considered that the ARS is similar to the vapor-compression refrigeration cycle (using the evaporator, condenser, and throttling valve as in a basic vapor-compression refrigeration cycle), except that the compressor of the vapor-compression system is replaced by three main elements, an absorber, a solution pump, and a generator. Three steps, absorption, solution pumping, and vapor release, take place in an ARS.

In Figure 3.46, a basic ARS, which consists of an evaporator, a condenser, a generator, an absorber, a solution pump, and two throttling valves, is schematically shown. The strong solution (a mixture strong in refrigerant), which consists of the refrigerant and absorbent, is heated in the high- pressure portion of the system (the generator). This drives refrigerant vapor off the solution. The hot refrigerant vapor is cooled in the condenser until it condenses. Then the refrigerant liquid passes through a throttling valve into the lowpressure portion of the system, the evaporator. The reduction in pressure through this valve facilitates the vaporization of the refrigerant, which ultimately effects the heat removal from the medium. The desired refrigeration effect is then provided accordingly. The weak solution (weak in refrigerant) flows down through a throttling valve to the absorber. After the evaporator, the cold refrigerant comes to the absorber and is absorbed by this weak solution (i.e. absorbent), because of the strong chemical affinity for each other. The strong solution is then obtained and is pumped by a solution pump to the generator, where it is again heated, and the cycle continues. It is significant to note that the system operates at high vacuum at an evaporator pressure of about 1.0 kPa; the generator and the condenser operate at about 10.0 kPa.


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