Qingzhi Hou

Emptying of large-scale pipeline by pressurized air

AbstractEmptying of an initially water-filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air-water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water-air “tail.” Measured discharges, water-level changes, and pressure variations along the pipeline during emptying are compared using control volume (CV) model results. The CV model solutions for a nonstratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure, and water level. But by considering water-column mass loss due to the water-air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air...

Improved One-Dimensional Models for Rapid Emptying and Filling of Pipelines

Improved one-dimensional (1D) models ? compared to previous work by the authors ? are proposed which are able to predict the velocity, length and position of the liquid column in the rapid emptying and filling of a pipeline. The models include driving pressure and gravity, skin friction and local drag, and holdup at the tail and gas intrusion at the front of the liquid column. Analytical and numerical results are validated against each other, and against experimental data from a large-scale laboratory setup.

An Improved 1D Model for Liquid Slugs Travelling in Pipelines

An improved one-dimensional (1D) model — compared to previous work by the authors — is proposed which is able to predict the acceleration and shortening of a single liquid slug propagating in a straight pipe with a downstream bend. The model includes holdup at the slug’s tail and flow separation at the bend. The obtained analytical and numerical results are validated against experimental data. The effects of the improvement and of holdup are examined in a parameter variation study.Copyright

ACOUSTIC RESONANCE IN A RESERVOIR - DOUBLE PIPE - ORIFICE SYSTEM

Acoustic resonance in a two-pipe system is simulated with four different models for the periodic excitation. Analytical solutions are provided in full for the three linear excitations. Exact numerical results are presented for the nonlinear excitation. The influence of a large-diameter supply pipe (instead of a constant-head reservoir) on the systems fundamental frequencies and mode shapes is studied. The peculiar behaviour of wave reflection at an orifice is fully explained.

Acoustic Resonance in a Reservoir-Pipeline-Orifice System

The fundamentals of oscillating flow in a reservoir-pipe-orifice system are revisited in a theoretical study related to acoustic resonance experiments carried out in a large-scale pipeline. Four different types of system excitation are considered: forcing velocity, forcing pressure, linear oscillating resistance and nonlinear oscillating resistance. Analytical solutions are given for the periodic responses to the first three excitations. Analytical and numerical results for the large-scale pipeline are presented and some peculiarities are discussed.

Analytical solutions for liquid slugs and PIGS traveling in pipelines with entrapped gas

Liquid slugs have a relatively low mass and can therefore - when they occupy a full cross-section of a pipeline - be accelerated to very high velocities by means of pressurized gas. When entrapped gas pockets are present, pressures and temperatures may become dangerously high. Simple models and analytical solutions are derived and used to predict transient velocities, pressures and temperatures. The models have a generic character as they also describe the basics of breaking surface waves impacting on a wall, and pigs and bullets propelled by compressed gas.

Analytical and Numerical Solution for a Rigid Liquid-Column Moving in a Pipe With Fluctuating Reservoir-Head and Venting Entrapped-Gas

The motion of liquid filling a pipeline is impeded when the gas ahead of it cannot escape freely. Trapped gas will lead to a significant pressure build-up in front of the liquid column, which slows down the column and eventually bounces it back. This paper is an extension of previous work by the authors in the sense that the trapped gas can escape through a vent. Another addition is that the driving pressure is not kept constant but fluctuating. The obtained analytical and numerical solutions are utilized in parameter variation studies that give deeper insight in the systems behavior.

An Improved One-Dimensional Model for Liquid Slugs Traveling in Pipelines

An improved one-dimensional (1D) model—compared to previous work by the authors—is proposed, which is able to predict the acceleration and shortening of a single liquid slug propagating in a straight pipe with a downstream bend. The model includes holdup at the slugs tail and flow separation at the bend. The obtained analytical and numerical results are validated against experimental data. The effects of holdup, driving pressure and slug length are examined in a parameter variation study.

Acoustic Resonance Experiments in a Reservoir-Pipeline-Orifice System

Acoustic resonance in liquid-filled pipe systems is an undesirable phenomenon that cannot always be prevented. It causes noise, vibration, fatigue, instability, and it may lead to damage of hydraulic machinery and pipe supports. If possible, resonance should be anticipated in the design process and be part of the hydraulic-transients analysis. This paper describes acoustic resonance tests carried out at Deltares, Delft, The Netherlands, within the framework of the European Hydralab III programme. The test system is a 49 m long pipeline of 206 mm diameter that is discharging water from a 24 m high reservoir through a 240 mm 2 orifice to the open atmosphere. The outflow is partly interrupted by a rotating disc which generates flow disturbances at a fixed frequency in the range 1.5 Hz to 100 Hz. In previous studies [1, 2] a similar system was analysed theoretically. Herein experimental data are presented and interpreted. Steady oscillatory behaviour is inferred from pressures measured at four different positions along the pipeline. Heavy pipe vibration during resonance was observed (visually and audibly) and recorded by a displacement transducer.