Experimental investigation of leakage flow in centrifugal blood pump

• Main Author: Aw, Chung Seng
• Other Authors: Chan Weng Kong
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/50188
• Institution: Nanyang Technological University

The study of leakage flow is crucial in designing centrifugal blood pumps. High volumetric efficiency is achieved when the leakage flow is low. However, low leakage flow cause formation of thrombus, while too high a leakage flow causes high shear to blood resulting in hemolysis. In this project, designing and fabrication of dummy impellers was first carried out. The blood pump test rig was checked and being serviced to ensure good working condition. Experiments were first conducted to establish the pump characteristics of the centrifugal pump with dummy impellers. Also, the ΔP of outer and inner radii of the volute was measured. Generally, the pump characteristics curves obtained show that pump head increased with factors like throttling of flow rate, increase in pump speed increases and increase in gap size. From the results, the highest gap size h = 0.50 mm has best performance. However, the magnitude of increase in performance was found to decrease with increasing gap size. Changing the gap size, pump speed and throttling of flow did affect the ΔP distribution similar to the overall pump characteristics curves. The ΔP at rear volute is lower than the front volute, at lower operating flow rate. At higher flow rate, the ΔP at rear volute higher. This is due to the difference in geometry of front and rear volute. Another set of experiments was performed to obtain leakage flow measurement of the centrifugal blood pump using auxiliary pumps to provide suitable operating conditions such that reverse flow could be observed. First, a two-pump in series was introduced; results showed that the auxiliary pump were not strong enough to create high ΔP measurements at the volute face. Then, it was modified to a four-pump in series; results showed that at the lowest gap size, h = 0.225 mm, the ΔP was found to have of the same range of pressure difference with the previous experimental result. Leakage flow of 2.8 -3.8 l/min would be expected if the pump has the same geometry and operating at the same speed of 2000 rpm. The leakage flow result was higher compared to the previous result. The results obtained were compared to the theoretical model. It was found that the relationship of ΔP with corresponding leakage flow rate did not behave linearly unlike the theoretical model proposed. For higher gap size, h = 0.40 mm, the experimental data was found to be close to the theoretical result. Finally, the results were used to compare to the previous CFX result. The result showed that the experimental leakage flow was much higher than the CFX result for all the gap sizes and was in agreement of each other.