Entrapped Air Removal by Hydraulic Means in Gravity Water Systems in Small Diameter Pipelines

Abstract

Gravity water delivery systems are common around the world to transport water without the use of external energy. The systems’ inadequate design and operation tend to form entrapped air bodies in downward pipeline lengths. Entrapped air generates considerable energy losses when there are no air admission-expulsion valves or due to valve failures. Air removal by hydraulic means has been modeled under various pipeline diameters, downward slopes, and air volume conditions. However, no generic entrapped air removal models exist, and the study in small diameters (≤50 mm) is limited. Most of the models reported in the literature were obtained for diameters greater than 50 mm, presenting notorious discrepancies among each other. In this research, the entrapped air removal in small diameter pipelines was studied (12.7, 15.875, 19.05, 25.4, 31.75, and 38.1 mm), highlighting the importance of the joint study of the air bubbles’ removal by the turbulent action of a hydraulic jump downstream of an air body and the consequent removal of remaining entrapped air by a hydrodynamic thrust. Potential models were found for the air bubbles’ removal for different pipeline diameters and downward slopes. Linear relationships were found between the dimensionless air removal parameter and the pipeline’s downward slope.