The terms liquid recirculation and liquid overfeed are sometimes used
interchangeably and refer to the practice of delivering a greater rate of liquid
refrigerant to the evaporator than evaporates. So at the exit of the coil a mixture
of liquid and vapor flow out of the evaporator, as shown in Fig. 8.1. If there is
desire to differentiate between liquid overfeed and liquid recirculation, it might
be that liquid overfeed applies to the coil, while a liquid recirculation system
incorporates the additional equipment to accommodate the overfeeding of
the coil.
The overfeed operation contrasts to regulating with a controlled expansion
valve the liquid flow rate to the evaporator so that it precisely matches the rate
of evaporation.
The flooded evaporator, discussed in Chapter 6 and arbitrarily not included
in the category of liquid recirculation, also operates in a liquid-overfeed manner,
resulting in no superheat at the outlet of the evaporator. Flooded evaporators
are supplied with high-pressure liquid like DX coils. Those configurations
classified in this chapter as liquid recirculation have a central liquid-vapor
separator capable of serving multiple evaporators. Furthermore, the liquid
recirculation is forced by either mechanical pumps or by gas-pressure pumping