Flooded-refrigerant evaporators

Flooded refrigeration systems are a version of the closed-cycle design that may reduce operating problems in some appHcations. In flooded systems, the refrigerant is circulated to heat exchangers or evaporators by a pump. Figure 11 shows the flooded cycle, which can employ any of the simple or compound closed-refrigeration cycles. 

EVAPORATOR, FLOODED - Evaporator containing liquid refrigerant at all times. 

Refrigeration evaporators could be classified according to the method of feed as either direc t (diy) expansion or flooded (hquid... 

This formulation applies both to the use of a semi-continuous cycle with an expansion valve and to a discontinuous cycle (such as that in the solar refrigerator) using a flooded evaporator in which the warm condensate must first cool itself before it can cool the load. 

Operated in this manner, the shell-and-tube type is a flooded evaporator (see Figure 7.3) and has oil drainage pots if using ammonia, or a mixture bleed system if the refrigerant is one of the halocarbons. The speed of the liquid within the tubes should be about 1 m/ s or more, to promote internal turbulence for good heat transfer. End cover baffles will constrain the flow to a number of passes, as with the shell-and-tube condenser. (See Section 6.4.)... 

Chilling of brines for pre-cooling will generally be in shell-and-tube evaporators. The Baudelot cooler within the pressure vessel may be cooled by flooded or dry expansion refrigerant, or by brine. 

Refrigeration compressors which will probably be used on flooded evaporators (R.717 and the larger machines generally) will be rated with the suction at saturated conditions, since there will be little or no superheat in practice. Compressors for dry expansion systems may be rated at a stated amount of superheat, commonly 8 K. 

Fig. 11. Liquid recirculation in a flooded system where A = refrigerant circulated through coils as brine, B = direct expansion coils, C = flooded evaporators, andD = special heat-exchanger designs.

The unit will be of flood type that will cool the products as they are conveyed into the channel filled with water. The products will be dropped into the channel filled with water at one end and picked up at the other end. The channel can be as wide as 3 m and as high as 90 cm. The water is to be circulated and cooled by the evaporator section of a lefiigeratioii syslem. The refrigerant temperature inside the coils is to be -2°C, and the water temperature is not to drop below l°C and not to e.xceed 6°C. 

FLOOD BACK - The condition of liquid refrigerant returning, usually from an overfed evaporator, to the compressor through the suction line. 

SYSTEM, FLOODED - A system in which only part of the refrigerant passing over the heat transfer surface is evaporated, and the portion not evaporated is separated from the vapor and recirculated. 

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