Quantifying the Influence of Air on the Capacity of Large Diameter Water Pipelines and Developing Provisional Guidelines for Effective De-Aeration Volume 1: Quantifying the Influence of Air on the Capacity of Large Diameter Water Pipelines
1177/1/04
March 2004

EXECUTIVE SUMMARY

1. Background and motivation

The geographically mismatch of the water demand centers and the water resources necessitate the transport of water over long distances and high elevation differences. On average water is transported about 350 km in South Africa (Basson, Van Niekerk & Van Rooyen, 1997). High energy costs and the increasing demand requires that the water transfer infrastructure should function optimally. To ensure operational effectiveness of pipelines they must be effectively de-aerated.

The influence of air on the capacity of pipelines has long been a cause for concern. The quantification thereof was, however, unknown and required investigation. The investigation of air in pipelines required a review of available literature, experimental work, field investigations and the development of provisional guidelines for optimal design to limit the negative effects of air.

2. Aims of this study

The aims of this study were to:

• Provide a literature review with regard to aspects related to air in water pipelines
• Conduct experimental and field work to establish to influence of air in pipelines and
• Compile a user guide for the design of effective de-aerated pipelines.

3. Research Findings

An extensive literature review has been conducted from which valuable information have been gathered and used in the design and set-up of experimental and field investigations.

The literature confirmed that flow velocity; air bubble size and the down slope of the pipeline are the main contributing factors, which determine whether the air can be removed hydraulically.

In the experimental work different air bubble sizes at different velocities and different pipe angles were tested to evaluate the available relationships predicting the required flow velocity to hydraulically transport air. New relationships were determined for different bubble sizes and operational conditions that can be used to determine the required positions where mechanical removal of air is required.