FIXED-AREA EXPANSION EDVICES:A CRITICAL REVIEW

Fixed -area expansion devices are widely used in refrigerators air-conditioners, and heat pumps of up to 3.5kW capacity with variable operating conditions. A fixed -area expansion device falls into one of the three categories: an orifice, a short tube, and a capillary tube. The earliest studies on orifices began in 1900s,with the interest in metering fluid flow rate .The research on capillary tubes began to be active in 1940s.Shine then, the study of fixed-area expansion devices has been one of main activities in refrigerating. With the increasing need to replace the ozone-depleting CFC and HCFC refrigerants , refrigerators ,air-conditioners ,and heat pump system have to be redesigned to accommodate new replacement refrigerants so that research activities in fixed-area expansion devices have been intensified since early 1980s . This paper gives a detailed review of the literature on fixed -area expansion devices. The main topics include the mass flow rate through orifices, the mass flow rate through short tubes, rating capillary tubes, metastable flow, the friction factor and friction pressure drop, and mathematical solution of fixed-area expansion device.