Influences of Miscible and Immiscible Oils on Flow Characteristics Through Capillary Tube—Validation of Calculation Model

A capillary tube is widely used as an expansion device for small refrigeration cycles. This series of papers discusses the influence of mixing refrigeration oil with the refrigerant on the flow through the capillary tube. In the first report, the mass flow rate and temperature and pressure distributions are examined experimentally when miscible or immiscible oil is mixed with refrigerant. In this study, a theoretical model is developed to estimate the influence of oil on the properties of refrigerant/oil mixture and on the mass flow rate. The theoretical model for the miscible combination is also applicable to the immiscible one, since the immiscible oil mixes homogeneously in the liquid phase in the capillary tube. The mass flow rates in both cases of miscible and immiscible combinations are calculated within an error of ±5% in comparison to measured data. In the immiscible combination, however, the model tends to underestimate the mass flow rate slightly as the oil concentration becomes larger than 0.1.

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