Robert C. Bowden

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.

Co-Current Gas-Liquid Smooth-Stratified Flow in a Horizontal Reduced T-Junction Including Wavy and Slug Regime Transition Boundaries

Experiments were performed in a horizontal reduced T-junction using a branch diameter of 6.35 mm and an inlet pipe diameter of 50.8 mm. The inlet length was 1.8 m and three branch orientations were tested at 0, 45, and 90 degrees down from the horizontal. Water and air, operating at 206 kPa, were used to provide an adiabatic two-phase environment. Both fluids flowed co-currently within the inlet towards the branch in the smooth-stratified regime. Results demonstrate the relationship between the interface height and the inlet and branch two-phase quantities, including the inlet superficial liquid and gas velocities, and branch two-phase mass flow rate and quality. In certain instances transitions to wavy-stratified or slug regimes were observed and these limits are quantified for each branch orientation. Flow visualization was used to identify the initiation of two-phase flow in the branch, including the onsets of gas and liquid entrainment. The critical height at the onset of gas entrainment was quantified as a function of the single phase liquid branch Froude number for the 45 and 90 degree branches, respectively. The branch quality results were scaled using the critical height and showed good agreement with selected models.

Experimental Investigation of Two-Phase Flow in a Multi-Branch Reduced T-Junction With Co-Current Stratified Gas-Liquid Flow

Experiments were performed in a horizontal reduced T-junction using a branch diameter of 6.35 mm and an inlet pipe diameter of 50.8 mm. The inlet length was 1.8 m, and three branch orientations were tested at 0, 45, and 90 degrees from horizontal. Air and water, operating at 206 kPa, were used to provide a two-phase environment. Both fluids flowed co-currently within the inlet towards the branch in the smooth-stratified regime. Flow visualization was used to identify the onset of gas entrainment. The critical height at the onset of gas entrainment was quantified as a function of the single phase liquid branch Froude number for the 45, and 90 degree branches, respectively.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