A surge drum of a flooded system is used to...

The surge drum in a flooded refrigeration system serves a dual purpose, which makes the option combining both functions the correct answer. One primary function is to separate vapor from liquid refrigerant, allowing for efficient suction gas management. In this process, the heavier liquid refrigerant settles at the bottom of the surge drum while the vapor rises to the top. This separation is crucial because it ensures that only vapor enters the suction line and compressor, preventing liquid refrigerant from causing damage or inefficiencies during the compression process.

Additionally, the surge drum manages "flash gas" from the make-up liquid. When liquid refrigerant experiences a sudden drop in pressure upon entering the surge drum, some of it can evaporate, forming "flash gas." The surge drum allows this gas to be collected efficiently while also ensuring that the remaining liquid can be reused or circulated in the system.

Together, these functions highlight the importance of the surge drum in optimizing the overall operation of a flooded refrigeration system, ensuring both the efficiency of the vapor compression process and effective liquid management.