Experimental investigation of leakage flow in centrifugal blood pump
Tay, Wen Bin
Date of Issue2014
School of Mechanical and Aerospace Engineering
The study of leakage flow is essential in the design of a good centrifugal blood pump. A good wash out at high volumetric efficiency will prevent thrombus1 formation, while excessive leakage flow results in undesirable hemolysis2. To design a good centrifugal blood pump, a good combination of the impeller rotational speed and clearance gap is necessary. Experimental investigation had been carried out to determine the leakage flow characteristics of the test rig, which is essentially a scaled up model of the centrifugal blood pump. The reverse flow method was used to better determine the leakage flow rate. The experiment was conducted using 4 different clearance gap sizes at 2 different rotational speeds. Results for the pressure differences between the inner and outer radius of each tapping points, the pump head and leakage flow rate were obtained and were plotted into ΔP versus leakage flow rate graphs for analysis. The results showed that leakage flow rate increases as gap size increase due to a decrease in frictional effects, which also causes the total mean ΔP to decreases as gap size increases. The mean ΔP at the front volute was also noted to be consistently higher than the mean ΔP at the rear volute. This indicates a higher leakage flow rate at the front volute as compared to the rear volute and is due to the effects of reverse flow as the original pump inlet is now the pump exit. Experimental leakage flow results were also compared against the theoretical predictions. After comparing, it is observed that both the experimental results and theoretical predictions of leakage flow rate behave linearly with ΔP. However the difference between the experimental results and theoretical predictions increased significantly as the clearance gap sizes increase due to the effects of the inertia effects between the volute wall and fluid. The theoretical predictions had not taken into consideration the effects of the inertia effects. The modified theoretical predictions which take into consideration the inertia effects and pressure differences across different angular positions managed to better predict the leakage flow rate values and thus reducing the difference between experimental results and predicted values.
Final Year Project (FYP)
Nanyang Technological University