Final answer:
The 'C' in the formula C = Fd1 represents the pressure-relief device's discharge capacity in BTU/minute, which is a measure of the amount of heat it can safely discharge to prevent over-pressurization.
Step-by-step explanation:
The rated discharge capacity of the pressure-relief device or fusible plug for a refrigerant-containing vessel is determined by the formula C = Fd1. The "C" in the formula represents the capacity in terms of BTU/minute. This unit of measure indicates the amount of heat that the pressure-relief device can safely discharge per minute to prevent over-pressurization, which could lead to vessel failure or explosion. The pressure-relief device is thus a critical safety component in systems where refrigerants are used, such as air conditioning and refrigeration systems. This measure helps ensure that the device will release refrigerant at a rate sufficient to prevent excessive pressure build-up within the vessel.