Theoretical Investigation of R600a Flow Characteristics in a Capillary Tube Used in Refrigeration Systems
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Abstract
This research presents a theoretical investigation of the flow characteristics of R600a refrigerant through a small-bore tube, commonly called to as a capillary tube.The developed mathematical model is based on the homogeneous flow, accounting for the phase change of R600a along the capillary tube. The refrigerant enters as a subcooled liquid, transitions to a saturated liquid, then to a saturated liquid–vapor mixture and finally accelerates to sonic velocity at the tube outlet. The model was validated by comparison with previous studies, showing excellent agreement. The results indicate that as the mass flow rate increases, the pressure of R600a drops sharply. In addition, increasing the capillary tube diameter or the degree of subcooling necessitates a higher flow rate to maintain a constant pressure drop. Conversely, a rougher inner tube surface requires a lower flow rate, with the effect being more pronounced in larger-diameter tubes.
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