M. Mahbubur Razzaque

Bubble size in coalescence dominant regime of turbulent air–water flow through horizontal pipes

An experimental study was performed in a 25.4 mm ID pipeline to evaluate the development of the bubble size distribution in the horizontal flow of an air–water system. As the air stream enters into the flowing water stream through a T-injector, it breaks into bubbles with a log-normal size distribution. Because of the small water velocity (1–3 m/s) and small initial bubble size, coalescence, not breakage, plays the dominant role in the present study. The effects of average water velocity, air volume fraction and air injector diameter on the initial bubble size distribution and its evolution along the length of the pipe in the coalescence dominant regime are investigated. At larger water velocities, the log-normal bubble size distributions are also maintained downstream of the injector. At smaller velocities, the distributions deviate slightly from the log-normal pattern. For all distributions, the value of the ratio d99.8/d32 is about 2.2 and is fairly independent of average water velocity, pipe length, air volume fraction and air injector diameter. It is found that at large velocities of water, the prediction of dmax through Levich’s breakup theory agrees well with the experimental d99.8 values for air volume fraction up to 0.003.

Effects of Groove Orientation on Hydrodynamic Behavior of Wet Clutch Coolant Films

A steady-state Reynolds type equation with inertia consideration is solved numerically for a coolant film entrapped between a grooved separator-friction plate pair of a multidisk wet clutch arrangement at a particular instant of the disengaged state. Straight grooves with rounded, trapezoidal, and V-section at different angular orientations are considered and the effects of their geometry and orientation on viscous torque, flow rate, and axial force are presented. Among the profiles studied, the rounded one is found to be better. Grooves inclined with the flow direction cause less viscous torque and, hence, less power loss. The choice of orientation angle, β, to give a maximum outflow or inflow may be helpful for cooling by better convection. For wider radial span and large number of grooves, the minimum operating gap ratio is suggested to be around 2.0. Inertia effects may shift the optimum orientation angle by as much as 10 deg, even at a moderate value of gap Reynolds number.

Squeezing of a Porous Faced Rotating Annular Disk Over a Grooved Annular Disk

The squeezing process of a porous faced annular disk rotating against a grooved counterpart is simulated and a squeeze film equation is obtained considering permeability and grooving effects. The governing equations, derived for isothermal fluid film and no slip boundary condition at the permeable boundary, are solved numerically. Film thickness, viscous torque, squeeze time and viscous energy dissipation are calculated and analyzed for various values of permeability, facing thickness, groove geometry, orientation, applied load and speed. It has been shown that the angular orientation significantly affects the squeezing process. High values of permeability and applied load reduce the influence of orientation. For any permeability and groove geometry, the squeeze time as well as the energy dissipation is minimum for grooves with angular orientation in the range of 30° ∼ 60°. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

Effects of Grooving in a Hydrostatic Circular Step Thrust Bearing With Porous Facing

Effects of grooving in a porous faced hydrostatic circular step thrust bearing are investigated using a mathematical model based on the narrow groove theory (NGT). It is shown that enhancement of load capacity by grooving the step is possible at moderate level of permeability of the porous facing. Load capacity drops sharply with the increase of porous facing thickness. However, this drop in load capacity occurs mostly within a small thickness of the porous facing. Considering the coupled effects of permeability and inertia, it is recommended that the dimensionless step location should be 0.5–0.8 and the dimensionless step height should be less than five to take advantage of grooving. The groove geometric parameters such as groove inclination angle, fraction of grooved area and groove depth corresponding to the maximum load capacity are found to be the same for both with and without porous facing. However, with porous facing, the sensitivity of the load capacity on the groove parameters reduces. At high level of permeability, the effects of grooves may become insignificant because of high seepage flow through the porous facing.

Effects of permeability and surface roughness on the behavior of an oscillating viscoelastic squeeze film

Purpose – The purpose of this paper is to present a parametric study of the effects of permeability and surface roughness on the hydrodynamic force and the leakage flow rate in an oscillating squeeze film between a rigid surface and a rubber surface.Design/methodology/approach – The study is conducted numerically using a squeeze film model that incorporates the effects of viscoelasticity, permeability and surface roughness.Findings – It is seen that with increasing permeability of the porous rubber block, both the hydrodynamic force and the leakage flow rate decrease. Increasing center line average (CLA) of surface roughness height distribution decreases the leakage flow rate slightly but increases the hydrodynamic force. The decrease in the hydrodynamic force due to using permeable material in squeeze film may be compensated for by deliberately increasing the surface roughness. The effect of variation in frequency of system vibration may be minimized by using optimally selected permeable materials with r...

Effect of erodent particles on the erosion of metal specimens

This paper presents the experimental results of the measurement of erosion rate of carbon steel specimens in sand water slurry system in a slurry pot tester. Sylhet sand has been sieved to get three sizes of erodent particles; namely, less than 250 micron, 250 to 590 micron and 590 to 1190 micron. Experiments are done with three sand concentrations (10%, 15% and 20%). The rate of erosion of the carbon steel specimens is measured as the loss of weight per unit surface area per unit time under the dynamic action of solid particles. The eroded surfaces of the specimens are examined using Scanning Electron Microscopy (SEM) to visualize the impact of the slurry of various conditions. It is seen that irrespective of the particle size the rate of erosion increases with the increase of slurry concentration. This increment of erosion rate at high concentration is high for large particles. High erosion rate is observed in case of large sand particles. In case of small and fine particles erosion rate is small becaus...

Effects of Grooving in a Circular Step Thrust Bearing

Assuming narrow grooves and considering inertia effect, an equation for the pressure distribution in a grooved circular step thrust bearing has been derived. A parametric study has been performed to investigate the effects of step and groove geometry on pressure distribution, load capacity and lubricant flow rate. Three arrangements of the bearing surface have been studied and it has been found that the maximum load capacity is obtained by putting grooves only on the step. Inertia significantly affects the load capacity. To get increased load capacity with increase of inertia, the step inner radius should be larger than 0.45 times of the outer radius. For the most enhancement of hydrodynamic load, the groove inclination angle should be 135° with the direction of rotation and the depth should be twice the minimum film thickness.Copyright