Friction factor correlations for perforated tubes at low injection rates

Abstract

Perforated tubes are widely used in industry for various applications. A special application arises when there is fluid injection into the perforated tube. Such cases arise when perforated tubes are used for horizontal oil well drilling and French drains. The behaviour of the flow under these conditions has led to the development of correlations, which consider the effects of the perforations and injection process. However, there are few friction factor correlations in literature, which consider the increased kinetic energy at the perforated tube outlet caused by fluid injection and acceleration. The current study reports experimental correlations for determining the friction factor of perforated tubes when the additional kinetic energy from the injection process is considered. The friction factor measurements were conducted in copper tubes with an internal diameter of 20.8 mm and a wall thickness of 1 mm at three nondimensional pitches of 0.375, 0.75 and 1.5. A perforated length-to-diameter ratio of 40:1 was used for the perforated tubes. A perforation row contained seven small perforation holes with a diameter of 1.5 mm spaced evenly around the perimeter of the tube. These perforation rows were staggered row to row, resulting in triangular perforation patterns. Water was used as a test medium with Reynolds numbers at the tube outlet ranging from 20 000 to 60 000. The injection ratio was varied from 0 to 5% to obtain a total of 135 unique combinations of perforated tube friction factor data at different injection ratios, Reynolds numbers and nondimensional perforation pitches. The experiments were condensed into friction factor correlations, which allow perforated tube parameters to be optimisation for minimising pressure losses encountered in draining operations. Copyright