Flow Structure of Supersonic Jet From a Straight Micro-Tube

In the case of micro-channels, the boundary layer is formed on the walls and it plays a role of a wall of a converging and diverging nozzle. Then, the outlet Mach number is beyond unity even if the tube is straight. Therefore, in the present study, the successive incident and reflected shock waves on underexpanded state jet from a straight micro-tube whose diameter ranges from 150μm to 500μm were visualized by Schlieren and Shadowgragh methods. The stagnation pressure ranges from 597 to 963 kPa. The flow characteristics on supersonic jet at the micro-tube outlet were also obtained. Also, it is confirmed that Mach number at a straight micro-tube outlet is beyond unity since the shock wave generates from the needle and the Mach number fluctuates in the jet. The experimental correlation for the distance from the micro-tube outlet to the Mach disk as a function of the ratio of stagnation pressure to ambient back pressure was proposed and compared with available correlations in literature.