The recirculation number in a pumped evaporator coil refers to the ratio between the total mass flow rate of refrigerant circulating through the evaporator and the mass flow rate of refrigerant that is actually evaporated during the heat exchange process.
Formula:
where:
Nr = recirculation number
m tot = total refrigerant mass flow rate circulating in the coil
m evap = mass flow rate of refrigerant actually evaporated
Physical Meaning:
If Nr =1 → all the refrigerant passing through the evaporator is evaporated (ideal condition, no recirculation).
If Nr >1 → a portion of the liquid refrigerant does not evaporate and is recirculated through the system to improve heat exchange efficiency and prevent local overheating.
Direct expansion systems: (the refrigerant is fully evaporated).
Pumped recirculation systems: can range from 2 to 10, depending on system design and control.
A higher ensures a more uniform refrigerant distribution within the evaporator and greater operational stability, but it also increases energy consumption for the pump.