Wael F. Saleh

A Hybrid Model to Predict the Onset of Gas Entrainment With Surface Tension Effects

The onset of gas entrainment in a single downward discharge, from a stratified gas-liquid region, was modeled. The discharge was modeled as a point-sink and Kelvin-Laplaces equation was used to incorporate surface tension effects. Consequently, a criterion to characterize the dip radius of curvature, at the onset of gas entrainment, was required. The dip geometry was experimentally investigated and a correlation was developed relating the dip radius of curvature to the discharge Froude number. The correlation was used in conjunction with the theoretical model. It was found that the predicted critical height demonstrated good agreement with experimental data with the three-dimensional point-sink approach, while poor agreement using the two-dimensional finite-branch approach was found. The inclusion of surface tension improved the models capability to predict the critical height, particularly at discharge Froude numbers below 1.

Modeling of the Onset of Gas Entrainment From a Stratified Two-Phase Region Through Branches on a Curved Surface

The present investigation is focused on the onset phenomena from a stratified two-phase region through a single branch located on a semi-circular wall, resembling a circular reservoir of a CANDU header-feeder configuration. Two different models have been developed, over the whole range of branch Froude number, to predict the critical height at the onset of gas-entrainment. The results showed that there is both a maximum and a minimum physical limit of prediction, which depends on the branch size and configuration. Also, at a distinct range of Froude numbers within the physical limits, the predicted values of both models collaborated to the same values. The critical height corresponding to the onset of gas entrainment was found to be a function of the branch orientation and Froude number. Three different experimental data sets at branch orientation angles of zero, 45, and 90 degrees were used to validate the present models. A good concurrence was illustrated between the experimental and theoretical values.

Experimental Investigation of Louver Cooling Scheme on Gas Turbine Vane Pressure Side

An experimental investigation has been performed to measure the cooling performance of the louver scheme using a two-dimensional cascade simulating the scaled vane of a high-pressure gas turbine. Two rows of an axially oriented louver scheme are distributed in a stagger arrangement over the pressure side. The effect of hole location on the cooling performance is investigated for each row individually, then the row interaction is investigated for both rows. The temperature distribution on the vane is mapped using a transient Thermochromic Liquid Crystal (TLC) technique to obtain the local distributions of the heat transfer coefficient and film cooling effectiveness. The performance of the louver scheme for each case is compared with that of two similar rows with a standard cylindrical exit at 0.9 density ratio. The exit Reynolds number based on the true chord is 1.5E5 and exit Mach number is 0.23. The local distributions of the effectiveness and the heat transfer coefficient are presented at four different blowing ratios ranging from 1 to 2. The louver scheme shows a superior cooling effectiveness than that of the cylindrical holes at all blowing ratios in terms of protection and lateral coverage. The row location highly affects the cooling performance for both the louver and cylindrical scheme due to the local pressure change and the variation of the surface curvature.Copyright

Droplet Vaporization in Turbulent Convective Flows With Temporal Variation of Pressure and Temperature

This paper presents a numerical model to investigate the effect of temporal variation of pressure and temperature on vaporization process of a single droplet exposed to a turbulent freestream of gaseous nitrogen. As a typical case, the evaporation rate and droplet life time of n-heptane droplet during adiabatic compression process and isobaric expansion process of a standard diesel cycle are investigated numerically. The numerical model is based on solving complete sets of time-dependent conservation equation of mass, momentum, energy, and species concentration in both gas-phase and liquid-phase. The turbulence terms in the conservation equations of the gas-phase are modeled by using the shear-stress transport (SST) model. The system parameters such as pressure and temperature at the beginning of fuel injection (i.e. represented by engine speed, RPM, and compression ratio, RC), and turbulence intensity are varied to provide a wide range of test conditions. To account for variation of temperature, variable thermo-physical properties, gas and liquid phase transients and radiation are considered. Also, the effects of high-pressure such as non-ideal gas behavior, solubility of gases into droplet and pressure dependence of gas- and liquid-phase thermo-physical properties are considered. Results of temporal variation of pressure and temperature are compared with those of isobaric and isothermal conditions.Copyright

A Hybrid Model for Predicting Gas Entrainment in a Small Branch From a Co-Current Flowing Gas-Liquid Regime

An analytical model was developed to predict the critical conditions at the onset of gas entrainment in a single downward oriented branch. The branch was installed on a horizontal square cross-sectional channel having a smooth stratified co-currently flowing gas-liquid regime in the upstream inlet region. The branch flow was simulated as a three-dimensional point-sink while the downstream run flow was treated with a uniform velocity at the critical dip location. A boundary condition was imposed in the model whereby the flow distribution between the branch and run was obtained experimentally and digital imaging was used to quantify the critical dip location through the dip angle. Three constant dip angles were evaluated in the model and results showed the dip height to have good agreement with experiments between angles of 50 and 60 degrees. The predicted upstream height, however, did not match well with the experimentally determined height due to the omission of shear and inertial effects between the upstream location and critical dip.Copyright

Co-Current Stratified Gas-Liquid Flow in a Horizontal Pipe With Discharging Branches

Experiments were performed in an adiabatic horizontal pipe with co-current stratified gas-liquid flow and a single discharge oriented at either 0, 45, or 90 degrees from horizontal. The study used air and water as the two fluid phases, operating at 312 kPa. The test section was scaled down from a typical CANDU header-feeder bank and used a pipe and discharge diameter of 50.8 mm and 6.35 mm, respectively. The objectives of the study were to provide quantitative two-phase measurements of the mass flow rate and quality at the pipe inlet, outlet, and discharge branch.Copyright

Investigation of the Onset of Gas Entrainment in Dual Discharging Oriented Branches on a Curved Wall With Stratified Flow Using Stereo PIV

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through header to the cooling channels, feeder’s tube, of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Stereoscopic Particle Image Velocimetry (3D-PIV) was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a quarter-circular wall configuration exposed to a stratified gas-liquid environment. The quarter-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45° and 90° degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc..) was done during dual discharge through the horizontal branch and the 45° or 90° branch from an air/water stratified region over a two selected Froude numbers in the horizontal branch while maintaining the Froude number in the other branch constant. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.© 2009 ASME

Experimental Investigation of the Two-Phase Phenomena in a Small Discharge Installed on a Large Pipe With Stratified Gas-Liquid Flow

Experiments were performed in a 50.8 mm diameter horizontal pipe with co-current stratified gas-liquid flow. A single, 6.35 mm diameter, downward oriented discharge was located at 1829 mm from the horizontal pipe’s inlet. Water and air, operating at a pressure of 312 kPa and adiabatic conditions, were used. The objectives of the study were to investigate gas entrainment in the discharge branch. Qualitative flow visualization of the two-phase entrainment flow structure was conducted, and measurements of the critical liquid height, two-phase mass flow rate, and quality, are provided. The results were compared with available correlations and showed good agreement with selected models.Copyright

Different Modes of Gas Entrainment Through Bottom Discharge Branch by Using Three Dimensional Particle Image Velocimetry System

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through small breaks in cooling channels of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Particle Image Velocimetry (PIV) in three dimension was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a semi-circular wall configuration during LOCA scenarios. The semi-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45 and 90 degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc.) was done during single discharge through the bottom branch from an air/water stratified region over a three selected Froude numbers. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.Copyright