TP24-26 Lessons Learned in Cooling Tower Pump Intake Design

Physical modeling has long been used for final design, optimization, and Hydraulic Institute compliance of pump intake structures. Cooling water pumps are a critical component of any cooling tower design, and they are particularly sensitive to the transition from basin to intake. This paper shares our experience in modeling hundreds of cooling tower pump intakes and discusses the pros and cons of several different types of transitions including vertical step, sloped floors and recessed configurations. Case studies are presented which show the sensitivity to minor details and the importance of considering the intake transition early in the tower siting and design and how these minor details can significantly impact pump performance.  This paper takes a look at four issues associated with the transition between the cooling tower and the pump intake. The first is a closer look at the vertical step and sloped ramp transitions. The second is a closer look at stop log support walls, an intake design feature common in seawater intakes but also encountered in cooling tower applications. The third is a less common but very problematic issue resulting from bay walls which do not extend the length of the pump intake causing separation induced water level oscillations. Discussion on how this occurs and can be prevented is presented. The fourth is a discussion on choked flow conditions occurring when the design low water level is set below the critical depth at the entrance to the pump bays. This paper presents a synopsis of several recent physical model studies and a review of recurring problems associated with common intake design features. The results of several model studies are presented to demonstrate the negative impacts that these common intake features have on approach flow conditions. The intent of the paper is to provide the design engineer some additional guidance not offered in industry guidelines or standards with the hope of avoiding common problems which can be costly and difficult to remediate after the intake has been constructed.