Suction line frosting
When flooding of the evaporator takes place, frosting along the suction line will be evident. This is caused by the liquid refrigerant boiling off and reducing the temperature of the suction line. Frosting along the suction line can also occur when there is a pressure drop through the evaporator and the suction line temperature is reduced to below 0 °C.
With low temperature applications the returning suction vapour may be at a temperature well below 0 °C, resulting in suction line frosting. It is common practice to insulate suction lines of low temperature installations in order to overcome this problem.
Distributor refrigerant control
Some commercial evaporators are designed with series-parallel and parallel tubing circuits, which means that they have more than one refrigerant circuit. Refrigerant from a single outlet expansion valve is directed to the circuits by means of a distributor, which in most cases is part of the evaporator assembly. These exist in many forms; two types are shown in Figure 22.
A multi-outlet expansion valve can also be used to perform a similar func- tion, feeding two refrigerant circuits. Such a valve is shown in Figure 23.