ANSI HI 9.6.7:2015 pdf free download – Rotodynamic Pumps – Guideline for Effects of Liquid Viscosity on Performance
9.6.7.1 Summary
Viscosity is one of the properties that characterizes all fluids. The performance of a rotodynamic pump varies with the viscosity of the pumped fluid. If the viscosity of the pumped fluid differs (is higher) significantly from that of water (which is the basis for most published performance curves), then the pump performance will differ from the published curve. For simplicity, the term viscous fluid is used within this document. In this context, viscous fluid is meant to describe a fluid with a viscosity greater than that of water, not to imply some fluids are not viscous. Head (H) and rate of flow (Q) will normally decrease as viscosity increases. Power (P) will increase, as will net positive suction head required (NPSH3) in most circumstances. Starting torque may also be affected. The Hydraulic Institute (HI) has developed a generalized method for predicting performance of rotodynamic pumps on Newtonian liquids of viscosity greater than that of water. This is an empirical method based on the test data available from sources throughout the world. The HI method enables pump users and designers to estimate perfor- mance of a particular rotodynamic pump on liquids of known viscosity, given the performance on water. The proce- dure may also result in a suitable pump being selected for a required duty on viscous liquids. Performance estimates using the HI method are only approximate. There are many factors for particular pump geometries and flow conditions that the method does not take into account. It is nevertheless a dependable approx- imation when only limited data on the pump are available and the estimate is needed.
Since the release of the previous version of this standard, use of computational fluid dynamics (CFD) by pump designers for simulation and optimization of the performance of rotodynamic pumps has dramatically increased. The code, expertise, and calculated outputs of this tool have greatly improved with maturity. Today’s pump design- ers are finding CFD a valuable tool in the pursuit of high-performance hydraulics. However, little effort has been expended in the study of fluids other than water. The expectations are that this tool could add insight and increase the knowledge of the dynamics of pump flow with viscous fluids and lead to improved design in this application. It is the desire of the HI Effects of Liquid Viscosity on Rotodynamic Pump Performance Committee that CFD simula- tions of viscous fluids on pump performance would be an area of future research. Correlations of simulation results to the methodology offered in this standard and further test validation would be beneficial for the fluid handling industry. Theoretical methods based on loss analysis may provide more accurate predictions of the effects of liquid viscosity on pump performance when the geometry of a particular pump is known in more detail. This document explains the basis of such theoretical methods. Pump users should consult pump manufacturers to determine whether or not more accurate predictions of performance for a particular pump and viscous liquid are available. This document also includes technical considerations and recommendations for pump applications on viscous liq- uids.