Experimental investigation of leakage flow in centrifugal pump

• Main Author: Lim, Jason Han Wei.
• Other Authors: Chan Weng Kong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/54044
• Institution: Nanyang Technological University

Leakage flow study is vital in the design of centrifugal blood pumps. Having a good wash out within the pump at higher volumetric efficiency will prevent thrombus formation. However, excessive leakage flow is also undesirable as it may result in hemolysis. Therefore, a good combination of impeller’s rotational speed and clearance gap is essential. Experimental investigation had been conducted to determine the reliability of the blood pump test rig. A reverse flow was used in the experiment to investigate on the leakage flow behaviour produced. Experiments were carried out at four gap sizes and two rotational speeds with throttling actions to establish the pump characteristics. Results were obtained for pressure differences between the inner and outer radii of the impeller and leakage flow rate within clearance gap. Relationships between ΔP and leakage flow rate were plotted based on data obtained for each dummy impeller and pump rotational speed. Pressure distribution in the pump was analysed and it was observed that the front volute always shows a greater mean ΔP than the mean ΔP in the rear volute. This showed that the amount of leakage flow at the front volute is always higher. This was due to the fact that the original pump inlet is the pump exit for the reverse flow used in the experiment. For smaller gap size of 0.20 mm, the leakage flow produced was very small due to the friction generated within the pump. As gap size increases, decrease in friction generated allowed more flow into the clearance gap. Hence higher values of leakage flow rate were produced. Leakage flow rate obtained was compared to the data of theoretical leakage model. In comparison, theoretical data behaves linearly with ΔP while the experimental data for 1500 rpm did not show the same behaviour. This was due to the washout holes effect being neglected in the calculation of theoretical leakage flow rate. However, a linear behaviour was observed for 2000 rpm. A larger gap size of 0.5mm, the experimental data had a steeper gradient than the theoretical model. This showed that at higher pump speed of 2000 rpm and larger gap size, there was a better control over leakage flow rate.