Critical flow devices, either venturis or nozzles operating at choked conditions, are popular as transfer standards and metering devices. Stagnation temperature and pressure upstream of the nozzle determine the flow rate, provided downstream pressure is low enough to ensure choked flow. Such devices are consistent and make excellent transfer standards for many laboratories. Introduces the concept of critical flow devices to the refrigeration industry, as well as provide basic tables for their use.

KEYWORDS: refrigerants, R12, R22, R502, refrigeration, nozzles, flow rate, venturi meters, temperature, meters.