Analysis of the R744 flow through the ejector ducts on the basis of visualisation procedure at the dedicated laboratory test rig

Development of the R744 technology is partially dependent on the highly efficient operation of the ejectors as one of the crucial components for the modern refrigeration system. Regarding these devices, the high-speed fluid flow coupled with mixing of vapour and partially evaporated liquid stream directly influences the ejector efficiency. The new knowledge of the aforementioned processes would be valuable for the device design using numerical models as well as an effective control of the overall system performance. The representative results from the laboratory refrigeration test rig which is dedicated for visualisation of the ejector mixing processes along suction nozzle, pre-mixing chamber and diffuser are presented in this study. The transparent section of the vapour/liquid R744 ejector ducts provided an access for visualisation of the R744 flow and mixing processes using high-speed camera and PIV techniques. Hence, the work consists of a brief description of the installation, visualisation procedures and the preliminary results. In particular, the selected on- and off-design operating regimes were described having regard the ejector performance factors and its correlation with the output of the visualisation procedure. Moreover, on the basis of the flow visualisation, the motive stream behaviour along pre-mixing chamber was described regarding that area as crucial for further mixing processes. Moreover, some of the flow characteristics recorded during the conducted studies were correlated with the numerical predictions obtained from various turbulence models.