Two-phase flow, Quality, Plug flow, Instrumentation, Injection cycle
In order to control refrigeration cycles employing an injection system properly, it is important to detect quality of gas–liquid two-phase refrigerant in a two-phase region of the cycle. Although there are some techniques such as using a capacitance sensor or a X-ray beam scanning to measure a cross-sectional void fraction of the gas-liquid two-phase flow in a pipe, the measurement of the quality or flow rate of each phase is quite difficult since the liquid phase and gas phase of two-phase flow flowing in a pipe have different velocities in most cases. Meanwhile, the flow through a narrow tube becomes plug flow and the velocities of gas plug and liquid plug are almost the same. Therefore, the void fraction or quality of two-phase flow with plug flow in the narrow tube can be measured by detecting each plug length. Authors have examined the quality measurement of two-phase flow in the refrigeration cycle based on the plug flow characteristics. In previous studies, it was confirmed that the quality can be measured with an accuracy of about ±10% when the flow regime is plug flow in the narrow tube. However, the quality range where the flow regime becomes the plug flow is limited to the quality less than 0.1. In this study, multiple narrow tubes are installed with a gas bypass line to extend the quality range to be measured. Consequently, the measurable range of quality up to 0.8 was achieved with an accuracy of ±10%.