Search

An analytical approach based on the linear potential theory is employed to enlighten the fundamental physics of atomization of droplets with an impinging sound wave, with a particular application in surface acoustic wave (SAW) atomization. When a plane sound wave, originated from the gas or the liquid side (resembling SAW), impinges on a liquid droplet, capillary waves are generated. It is shown that, for both cases, spatial phase-locking between the sound spherical modes and the free surface oscillations occurs. Hence, capillary waves will have the same spatial modes of the sound wave. The frequency spectrum analysis shows that the phase-locking causes two types of waves: the natural capillary waves with a wide range of frequencies, two to five orders of magnitude smaller than the impinging sound wave, and the forced wave, with a frequency equal to that of the sound wave. Since the instability of these surface waves leads to separation of droplets from the surface and the size of these droplets is correlated with the wavelength of the surface waves, this well explains the previous observations that droplets with a wide range of sizes are generated in the SAW experiments. Finally, a correlation is also proposed for predicting the atomized droplet size, which gives the size order for the generated droplets in SAW with good accuracy. The correlation could also suggest the possible size for remote atomization of the droplets by sound wave propagated in gas. [ABSTRACT FROM AUTHOR]

Erosion is a common problem in various parts of the pipeline industry. In this study, computational fluid dynamics is employed for analysis of pipeline erosion due to gas transported particles. Total removed volume and maximum erosion rate in different elbow geometries from 15 ° to 90 ° elbows, for a range of mass loadings are studied. Particle tracking is achieved using combination of Eulerian and Lagrangian methods. In the first stage, gas-solid flow is validated for both straight-pipe and elbow geometries. After that, the erosion model is validated with available data for a 90 ° , 76.2 mm diameter standard elbow. In the final stage, simulations for a range of elbow angles are performed for two different flow orientations: horizontal inlet and outlet flow directions (H-H flow) and the cases in which inlet flows are vertical and outlet flows either lie in the horizontal plane or make some angles with it (V-H flow). In addition to erosion rate, some important particle-wall impact-related variables such as impact speed, impact angle and impact frequency are presented for elbows with different configurations and angles. Results show that, in general, for a fixed inlet condition and bend geometry, maximum erosion rate in the V-H configuration is greater than that for the H-H orientation. However, total annual eroded volume in the H-H configuration is greater than that for the V-H case. In addition, in both V-H and H-H cases, for the range of mass loadings investigated, the maximum erosion rate increases steadily when the elbow angle increases from 15 ° to 90 ° but the rate of total eroded volume remains relatively constant for each value of sand rate. Results of this study are helpful in optimal selection of pipeline elbows for erosion protection. [ABSTRACT FROM AUTHOR]

A theoretical investigation of parametric excitation of liquid free surface by a high frequency sound wave is preformed, using potential flow theory. Pressure and velocity distributions, resembling the sound wave, are applied to the free surface of the liquid. It is found that for impinging wave two distinct capillary frequencies will be excited: One of them is the same as the frequency of the sound wave, and the other is equal to the natural frequency corresponding to a wavenumber equal to the horizontal wavenumber of the sound wave. When the wave propagates in vertical direction, mathematical formulation leads to an equation, which has resonance frequency equal to half of the excitation frequency. This can explain an important contradiction between the frequency and the wavelength of capillary waves in the two cases of normal and inclined interaction of the sound wave and the free surface of the liquid. [ABSTRACT FROM AUTHOR]

In this paper, a new model is developed to analyze a tilting pad bearing with 5 pads in a load-between-pad configuration in three dimensions. Isothermal Navier-Stokes equations with phase fraction equation for cavitation model are solved for 3D steady state simulation using the OpenFOAM package. Results show that with decrease in eccentricity, the difference between the 3D and 2D simulations increases. This is mainly due to the fluid inertia effects when entering the pads. Although applying the inertial boundary condition to the 2D model reduces the discrepancy, the difference in pressure distribution remains. Thus, at the lower eccentricity ratio, it is highly recommended to use 3D model in order to calculate pressure distribution precisely in tilting pad journal bearing. • Three dimensional steady state simulation of tilting pad journal bearing with 5 pads is performed. • Isothermal Navier-Stokes equations with additional phase fraction equation to model cavitation are used for simulation. • For high values of eccentricity, the results of 3D and 2D simulation match closely. • For low values of eccentricity, there is a noticeable difference between the 3D and 2D results for pressure distribution. • In 2D, inertial boundary condition reduces the discrepancy, however full 3D simulation is necessary for accurate results. [ABSTRACT FROM AUTHOR]

Laminar upward mixed convection in an inclined concentric straight annulus is studied numerically in this paper. The governing equations including for continuity, the three-dimensional Navier–Stokes, and the energy equations in cylindrical coordinates, are solved by means of a second-order finite-difference method based on the projection algorithm. To discretize conveniently, the governing equations in the annulus domain are obtained in cylindrical coordinates, using a uniform staggered grid. The Boussinesq approximation is employed to implement the natural convection term in the equations of motion. Developing hydrodynamic and thermal conditions are considered to survey the effect of different parameters such as the radius ratio, inclination, and Reynolds and Richardson numbers on flow field and thermal characteristics, while the outer wall is insulated and the inner one is at constant heat flux. It has been found that the heat transfer coefficient decreases as the inclination angle increases from the horizontal position. Also, a numerical relation is developed to predict the Nusselt number value, which is validated in the studied ranges. [ABSTRACT FROM PUBLISHER]

• Quality images for intermittent flow presented. • El Hajal-Thome map modified in low vapor quality region. • Intermittent flow divided to four subdivisions: Bubble, Transition, Slug with and without vapor entrainment. • Best heat transfer prediction by Thome correlation (MAE = 13%) in intermittent region. • A new correlation has proposed for intermittant flow with MAE = 10.4% This study investigates condensation of R141b in an 8 mm ID horizontal smooth tube. Condensation of R141b is conducted at an average saturation temperature of 40 ° C with mass fluxes ranging from 40 to 400 kg m−2 s−1. The plant runs with low vapor quality of refrigerant where intermittent flow is expected to be the dominant flow regime. Visualization images presented for intermittent flow regime. Observation results compared with four types of flow regime map and a modified version of El Hajal-Thome map is presented. Condensation heat transfer coefficient in intermittent zone is evaluated. Comparison between the available experimental data and the values predicted by the most popular and current correlations for condensation heat transfer in horizontal tubes are reported. Finally, a new correlation is proposed to predict condensation heat transfer coefficient within intermittent region. [ABSTRACT FROM AUTHOR]