Single Effect Absorption Refrigeration Systems

As stated earlier, in ARS, an absorber, generator, pump and recuperative heat exchanger replace the compressor. Like mechanical refrigeration, as shown in Figure 3.49, the cycle begins when high-pressure liquid refrigerant from the condenser passes through a metering device (1) into the lower-pressure evaporator (2) and collects in the evaporator pan or sump. As before, the flashing that occurs at the entrance to the evaporator cools the remaining liquid refrigerant. Similarly, the transfer of heat from the comparatively warm system water to the now-cool refrigerant causes the latter to evaporate (2), and the resulting refrigerant vapor migrates to the lower-pressure absorber (3). There, it is soaked up by an absorbent lithium-bromide solution. This process not only creates a low-pressure area that draws a continuous flow of refrigerant vapor from the evaporator to the absorber, but also causes the vapor to condense (3) as it releases the heat of vaporization picked up in the evaporator. This heat—along with the heat of dilution produced as the refrigerant condensate mixes with the absorbent—is transferred to the cooling water and released in the cooling tower. Of course, assimilating refrigerant dilutes the lithium-bromide solution and reduces its affinity for refrigerant vapor. To sustain the refrigeration cycle, the solution must be reconcentrated. This is accomplished by constantly pumping (4) dilute solution from the absorber to the generator (5), where the addition of heat boils the refrigerant from the absorbent. Once the refrigerant is removed, the reconcentrated lithium-bromide solution returns to the absorber, ready to resume the absorption process. Meanwhile, the refrigerant vapor liberated in the generator migrates to the cooler condenser (6). There, the refrigerant returns to its liquid state as the cooling water picks up the heat of vaporization carried by the vapor. The liquid refrigerant’s return to the metering device (1) completes the cycle.


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