Effect of 90° elbows on pump inlet flow conditions

Abstract

Abstract The use of 90° elbows upstream of a pump inlet can distort the approach flow resulting in spatial and temporal velocity variations and swirling flow that negatively affect pump performance and increase maintenance requirements. In order to attend these flow conditions, pumps have to be installed according to generally accepted standards such as ANSI/HI 9.8. (American national standard for rotodynamic pumps for pump intake design, Hydraulic Institute, Parsippany, 2012). However, in these standards, there is little information about the minimum distance between single and double 90° elbows and a pump. Therefore, this paper presents results for the pipe flow downstream of 90° elbows and its attendance to the standards at the inlet of pumps using Computational Fluid Dynamics (CFD). Prior to its application, the CFD model was validated by comparing the computed velocity profiles with experimental results downstream of a 90° elbow. It is found that it is necessary 3 to 16 pipe diameters from the elbow in order to reduce the swirling flow. The velocity distribution at a cross section was never uniform up to 50 pipe diameters downstream of the elbows. The temporal velocity fluctuation was always low. It is concluded that the specifications of downstream pipe lengths in the current inlet pipe flow standards are not sufficient to achieve the desired flow at the pump inlet.

Keywords

• CFD
• Swirl
• Velocity distribution