Final answer:
To change the specific capacity of an absorption refrigeration plant, an operating engineer should control the flow of steam to the generator and adjust the expansion valve, as these directly influence the refrigeration cycle capacity.
Step-by-step explanation:
In order to vary the specific capacity of an absorption refrigerating plant, an operating engineer should regulate the flow of steam to the generator, and adjust the expansion valve. This action controls the refrigeration cycle by varying the steam's energy input into the generator, which in turn affects the temperature and pressure of the refrigerant throughout the system. Regulating the flow of steam directly impacts the capacity of the refrigeration cycle since it determines the amount of heat supplied for the refrigeration process. Adjusting the expansion valve modifies the pressure drop of the refrigerant, influencing the evaporation temperature and thereby the cooling capacity.
The expansion valve serves a critical role in the system by controlling the rate at which the refrigerant is allowed to expand and consequently evaporate, cooling the space as needed. Conversely, operating parameters such as relief valves, NH2 pump speed, or absorber pump speed do not directly regulate the plant capacity in the same manner. Additionally, while the flow of water to the condenser impacts the removal of heat from the system, it is not primarily used to vary the plant's refrigerating capacity.