Influence of Entrapped Air Pockets on Hydraulic Transients in Water Pipelines
Publication: Journal of Hydraulic Engineering
Volume 137, Issue 12
Abstract
The pressure variations associated with a filling undulating pipeline containing an entrapped air pocket are investigated both experimentally and numerically. The influence of entrapped air on abnormal transient pressures is often ambiguous because the compressibility of the air pocket permits the liquid flow to accelerate but also partly cushions the system, with the balance of these tendencies being associated with the initial void fraction of the air pocket. Earlier experimental research involved systems with an initial void fraction greater than 5.8%; this paper focuses on initial void fractions ranging from 0 to 10% to more completely characterize the transient response. Experimental results show that the maximum pressure increases and then decreases as the initial void fraction decreases. A simplified model is developed by neglecting the liquid inertia and energy loss of a short water column near the air-water interface. Comparisons of the calculated and observed results show that the model is able to accurately predict peak pressures as a function of void fraction and filling conditions. Rigid water column models, however, perform poorly with small void fractions.
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Acknowledgments
The authors gratefully acknowledge the financial support on this research from the National Natural Science Foundation of China (Grant No. NNSFC50979029).
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 137 • Issue 12 • December 2011
Pages: 1686 - 1692
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Oct 27, 2010
Accepted: May 18, 2011
Published online: May 20, 2011
Published in print: Dec 1, 2011
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