In a cascade system, the evaporator of the high stage is the condenser for the low stage (see Chapter 2). Construction of this heat exchanger will be a com­bination of the design factors for evaporators and condensers, and no general rules apply apart from these. The intercooler of a two-stage or compound sys­tem de-superheats the discharge gas from the first stage so that it will not be too hot on entering the high stage. In practice, it will leave the intercooler only slightly superheated above the interstage saturation point. The normal fluctua­tions in an operating system may lead to actual condensation at times, but is not so intended.

The small condensing surface required by a domestic appliance such as a deep-freeze may allow the use of the outside metal skin of the appliance itself as a surface condenser. In such a construction, the condenser tube is held in close mechanical contact with the skin, so that heat is conducted through to the outside air, where it is lost by natural convection. This system is restricted to a few hundred watts.

Posted in Refrigeration and Air Conditioning