Flow In Circumferential Direction Research Articles

2D computational investigation into transport phenomena of subcooled and saturated flow boiling in large length to diameter ratio micro-channel heat sinks

This study computationally investigates into the transport phenomena and heat transfer mechanisms associated with subcooled and saturated flow boiling of R-134a in large length to diameter micro-channel heat sinks. A two-dimensional computational model has been developed for analysis of the interfacial behavior of flow boiling that widely changes from bubbly to annular flow in micro-channel. OpenFOAM based 2D CFD solver was developed by using the volume of fluid method and Lee phase change model, enabling nucleate boiling occurs within the single-phase flow, to solve the transport equation for interface tracking. The conjugate heat transfer at the solid and liquid interface has been considered for the channel wall temperatures, which were compared with experimental results for assessing accuracy of developed CFD model. The high-speed images of flow boiling at multiple locations along the micro-channel were compared with flow patterns acquired from the computational simulation and showed an overall good agreement, which is verified by comparing with the void fractions estimated by the empirical correlations. The measured experimental data were also compared with the simulation results and showed good agreement for limited cases those without dry-out occurrence. The accuracy of two-dimensional CFD simulation in predicting the annular flow under asymmetric heating condition is compromised by excluding the flow along the sidewall which redistributes the flow in circumferential direction. The nonuniform film evaporation at the top and bottom side of the channel precipitates the pseudo dry-out leading to unexpected temperature rise and erroneous thermal responses. In spite of the successful simulation of coexisting subcooled and saturated flow boiling for limited cases without dry-out, this study unveils the causes and mechanisms that limit accurate 2D CFD simulation for widely varying two-phase flow in micro-channel heat sinks.

Discussion on back-to-back two-stage centrifugal compressor compact design techniques

Design a small flow back-to-back two-stage centrifugal compressor in the aviation turbocharger, the compressor is compact structure, small axial length, light weighted. Stationary parts have a great influence on their overall performance decline. Therefore, the stationary part of the back-to-back two-stage centrifugal compressor should pay full attention to the diffuser, bend, return vane and volute design. Volute also impact downstream return vane, making the flow in circumferential direction is not uniformed, and several blade angle of attack is drastically changed in downstream of the volute with the airflow can not be rotated to required angle. Loading of high-pressure rotor blades change due to non-uniformed of flow in circumferential direction, which makes individual blade load distribution changed, and affected blade passage load decreased to reduce the capability of work, the tip low speed range increases.

Pattern formation around interacting bodies in rotating fluids

The interaction of bodies like spheres and disks in rotating fluids leads to novel flow structures. The primary swirling flow in circumferential direction is superimposed by a secondary motion in the meridional plane. The flow is visualized by introducing ink through a hole in the center of the axes and distributed radially in the central plane between the interacting bodies. The flow structure depends on the shape of the bodies, their geometrical arrangement and the Reynolds number given by the rotational speed. The observed flow structures gave rise to further investigations with PIV-measurements and numerical simulations.

Experimental and numerical study of rotating magnetic field driven flow in cylindrical enclosures with different aspect ratios

Azimuthal velocities of the rotating magnetic field driven flow in a cylindrical container are measured in two different experiments for different aspect ratios (height/radius) of the container and different strengths of the magnetic field. The measured velocities are compared with the calculated ones. A good agreement between the experimental and numerical results is obtained. This validates the experimental techniques, the computational approach, and also the time-averaged model widely used in calculations of RMFdriven flows. It is shown that the average angular velocity normalized by the square root of the magnetic Taylor number grows linearly for the aspect ratios exceeding 1, and non-linearly for smaller aspect ratios. It is shown also that when the magnetic field is sufficiently large, the average angular velocity grows proportionally to the Hartmann number or proportionally to the square root of the magnetic Taylor number. It is shown that the dependence of the average angular velocity on the aspect ratio can be roughly approximated by a power of the ratio radius/height. 1. Introduction. Rotating magnetic fields (RMFs) are widely used in metallurgical and crystal growth technologies for controlling the melt flows and heat and mass transfer characteristics [1–3]. The rotating magnetic field induces a time-averaged azimuthal force, which drives the flow in circumferential direction. In its turn, non-uniform rotation of the liquid induces the azimuthal flow. All three components of the flow affect the heat and mass transfer processes thus yielding a powerful tool for flow and heat and mass transfer control. The RMF-driven flows have been intensively studied during two recent decades both experimentally and numerically (see [2–18] and references therein). In spite of the large number of numerical studies of the RMF-induced flows, there are only few experimental investigations [2–9]. Most of experimental studies examine the influence of RMF on the temperature field or on the properties of grown crystals [2, 8–11], so avoiding the study of the flow field itself. There are very few attempts to measure the fluid velocities directly [3, 7, 14]. In the present study we report direct measurements of the azimuthal velocities of the RMF-driven flow in cylindrical containers of different aspect ratios (height/radius). The measured velocities are compared with the results of calculations, which, in their turn, are performed by two independent approaches. In this way we perform cross-validation of the experimental methodology with the calculations. The main set of results of the present study consists of the experimentally measured and numerically calculated dependencies of the azimuthal velocity in different radial and axial cross-sections of the container on the parameters of the RMF inductor and the geometry of the cylindrical container. A good agreement between the experimental and numerical results provides a rigorous experimental