In systems where the same refrigerant passes through the low and high pressure stages, extreme pressure values and specific volume can cause some problems. In fact, when the evaporation temperature is very low, the specific volume of the refrigerant vapor in the suction of the compressor is high, which
implies a high capacity compressor. With respect to pressure, it can be stated that reduced values, below atmospheric pressure, can promote the intake of air and moisture through openings in the refrigerant piping. On the other hand, if a refrigerant is chosen such that the evaporation pressure is higher than atmospheric, the discharge pressure may assume high values to the extent that vessels and reinforced wall pipes are required. The solution to these problems can be a cascaded system. In this system, different refrigerants are used in the high and low pressure circuits, constituting two systems
independent refrigerators. The interface between the systems is a heat exchanger that operates as a condenser for a low temperature circuit and as an evaporator for the high pressure circuit.
