PIV pictures of stream field predict haemolysis index of centrifugal pump with streamlined impeller

Abstract

Previously it has been found by pump haemolysis testing that the flow rate has a remarkable effect on index of haemolysis (IH), while pressure head does not affect IH. Recent investigation with particle image velocimetry (PIV) technology has demonstrated that IH is directly related to the flow pattern of stream field in impeller vane channels. PIV is a visible approach showing the real flow status in the pump. The different positions of a tracer particle in two PIV pictures taken at 20 μs intervals decide the velocity value and direction. The velocity vectors of many particles draw the flow pattern of the stream field. The same pictures are taken at 2, 4 and 6 l min⁻¹ flow rates while the pressure head is kept unchanged at 100 mmHg; then the pictures are taken at 4 l min⁻¹ flow with different pressure heads of 80, 100 and 120 mmHg. Results reveal that the flow rate of 4 l min⁻¹ (IH = 0.030) has the best stream field, and neither turbulence nor separation can be seen. In other flow rates (IH: 0.048 – 0.082), there is obviously second flow. Meanwhile, no significant difference can be seen among the PIV pictures of different pressure heads pumped, which agrees with the results of haemolysis testing showing that pressure has no effect on pump haemolysis. It may be concluded that the haemolysis property of a centrifugal pump can be assessed approximately by PIV pictures, which are much easier to take than haemolysis tests.