The relative low COP of transcritical CO2 systems caused by the throttle valve limited the further development. The replacement of a throttle valve with a turboexpander, an ejector or a vortex tube is leading to the way for improving the COP of a transcritical CO2 system. In this paper, a transcritical carbon dioxide refrigeration cycle with different expansion devices was analyzed theoreticall...

In many industrial equipment such as boilers and heat exchangers, the cylindrical tubes are exposed to the gas- liquid two phase flow. For any immersed body in flow field vortex shedding is created with a frequency that may be constant or variable, according to conditions such as flow rates, geometry of body, and etc. The failure will happen in the equipment, when this frequency is close to...

In this article, a Ranque–Hilsch Vortex Tube has been optimized utilizing axial angles for nozzles. Effect of nozzles angles on the flow behavior has been investigated by computational fluid dynamics (CFD) techniques. A finite volume approach with the standard k–ε turbulence model has been used to carry out all the computations. The dimensions of studied vortex tubes are kept the same for all m...

We investigate holographic optical tweezers manipulating micro-beads at a suspended air-liquid interface. Axial confinement of the particles in the two-dimensional interface is maintained by the interplay between surface tension and gravity. Therefore, optical trapping of the micro-beads is possible even with a long distance air objective. Efficient micro-circulation of the liquid can be induce...

In the present study, numerical investigations of a Francis turbine at model scale are performed. A part load operating point is selected for the analysis with a focus on the cavitating draft tube vortex rope. For three σ-levels, different aspects are investigated. First, the extension of the vapor volume is analyzed and compared to high-speed visualization recordings from the measurements. Fur...

In this paper, the behavior of shock wave discharged from the pipe end is studied. The shock wave is generated using the shock tube (MO-tube). The flow field while the shock moves downstream is visualized using shadow photography and schlieren photography. The propagation of shock wave and the phenomenon of the occurrence of second vortex ring are examined and discussed.

In this paper, the implicitly implemented LES method and fifth order bandwidth-optimized WENO scheme are used to make comprehensive studies on the interaction of vortex rings and shock waves of the MVG controlled flow at M=2.5 and Re θ θ θ θ =5760. The kinetic information of the vortex rings is carefully studied and provided. The interaction of the streamwise vortices and vortex rings are inves...

In order to decrease the fluid dynamic forces of the U-bent tube with a circular section and avoid the occurrence of fluid-structure interaction problems, three-dimensional simulations of fluid flows around the tubes are carried out. In the case that the axis of the curved tube with the circular section is prevented from being normal to the direction of the flows approaching the tube, the forma...