Effect of Reynolds number on performance of a small centrifugal pump

A study of a small centrifugal blood pump has been made to address the effectiveness of traditional pump affinity laws and the influence that viscous effects, as characterized by the Reynolds number, have on the pump performance. This was investigated both experimentally and numerically on models of a small implantable centrifugal blood pump, which has an impeller diameter of 46 mm with a log spiral volute. In the experiments, the Head-Flow curves were determined for speeds between 500 and 3000 rpm and for two different viscosity fluids. It was found that lower Reynolds number flows did not adhere to conventional pump affinity laws, whereas higher Reynolds number flows scale very effectively according to pump affinity laws. The numerical study consisted of comparing the generated head and internal flow field of the pump scaled based on traditional affinity laws with and without consideration of the Reynolds number. Like the experimental results, the numerical simulations indicate that consideration of the Reynolds number is necessary to insure accurate scaling in this small pump. INTRODUCTION In industrial sized machines, pump affinity laws are often used to predict the performance of one turbomachine based on scaling to another geometrically similar machine. Buckingham Pi analysis of pump flow equations leads to three dimensionless parameters necessary to guarantee the dynamic similarity of the flow through any two geometrically similar pumps. Three commonly chosen parameters are given as Π1=Q/(νD), (1) Π2=nQ/(gH), (2) Π3=Q/(nD). (3) Π1 is a type of Reynolds number. Π2 is the specific speed, and Π3 is the specific capacity, usually denoted Φ. A fourth term, which is not independent of Π2 and Π3, is commonly used instead of Π2. This group is similar to the head coefficient, is given as