An experimental evaluation of capillary tube-suction line heat exchanger performance with alternative refrigerants HFC-134a and HFC-152a

摘要

Worldwide environmental concerns have resulted in mandates that CFC refrigerants be replaced with alternative refrigerants. The most common refrigerant used in household refrigerators is CFC-12, and alternative refrigerants HFC-134a and HFC-152a are potential replacements;The capillary tube is the predominant expansion device found in household refrigerators. It is usually soldered to the suction line for three to five feet of length, thus, creating a simple counter-flow heat exchanger. Heat exchanger performance is characterized by both the refrigerant mass flow rate and a heat transfer effect, commonly referred to as effective subcooling;Capillary tube-suction line heat exchanger performance was experimentally evaluated with alternative refrigerants HFC-134a and HFC-152a. In accomplishing this task, a test facility simulating a household refrigerator was designed and constructed with the capability of controlling the appropriate operating conditions. Next, efficient experimental test plans were designed using statistical methods. Performance databases were then obtained with each refrigerant of an applicable range of heat exchanger geometries and operating conditions including; capillary tube inner diameter (0.026 to 0.031 in), capillary tube length (96 to 130 in), heat exchanger length (30 to 70 in), condenser temperature (85 to 132°F), evaporator pressure (16 to 26 psia), capillary tube inlet condition(15°F subcooled to 5% quality), and oil concentration level (0% to 3%);Measured mass flow rate ranged between 6 and 21 lbm/hr. Variables having the greatest effect on mass flow rate included condenser temperature, capillary tube inner diameter, capillary tube length, and inlet quality level. Measured effective subcooling level ranged between 25 and 60°F. Variables having the greatest effect on effective subcooling level included condenser temperature, heat exchanger length, suction line diameter, and suction inlet temperature;Heat exchanger performance prediction equations were developed for HFC-134a and HFC-152a, which were based on their respective databases. A general performance prediction procedure was also developed based on the HFC-134a results, and by considering the fundamental processes affecting mass flow rate and effective subcooling. Using the procedure, measured performance was successfully predicted for HFC-152a and CFC-12.