Effects of geometrical parameters on performance of miniature centrifugal pump
Date of Issue2014
School of Mechanical and Aerospace Engineering
In this project, the effects of blade geometrical parameters on the performance of a miniature centrifugal pump are examined. Geometrical parameters such as blade angle, inner radius, blade thickness, blade number, volute outlet width, together with the flow coefficient are investigated. The performances of the pumps designed are analyzed theoretically, numerically and experimentally. Energy models including Euler head, slip loss, leakage loss, friction loss, blockage loss, diffusion loss and shock loss are considered in the theoretical analysis. 3-D numerical studies using a commercial software FLUENT showed that the results are consistent with theoretical results. Experimental studies on the pump characteristics and velocities in the impeller passage were performed. The numerical and theoretical results are consistent with experimental results. Numerical and experimental results showed that the traditionally designed impeller cannot operate at the design point because the pressure generated is negative. The impeller channel is short and the fluid does not have enough time to receive energy from rotating impeller. Modified models registered positive pressure generated. Theoretical results show that wall friction loss and tip leakage loss are negligible, while the slip loss is most significant. The blockage loss, diffusion loss and disk friction loss increase with flow rate, and decrease with the radius ratio. The leakage loss is significant when the radius ratio r1/r2 is larger than 0.4, and the shock loss should be considered when the blade angle β is smaller than 45˚. The leakage flow rate is 15% of the total flow rate when the radius ratio is 0.4 and is 52% when the radius ratio is 0.9. The shock loss is 9% of the theoretical head when the blade angle is 45˚ and is 70% when the blade angle is 30˚. The effect of flow coefficient is studied. This parameter is important in the design procedure, and the recommended value for macro-size pump is not suitable for miniature pumps. When the flow coefficient is varied for a given outer radius and operating speed, the maximum pressure generated is obtained at the optimum flow coefficient. Simulation results show the optimized flow coefficient is in the range of 1.47 to 2 for the 20 mm diameter model. The effects of blade angle, inner radius, blade number and thickness are investigated. With increasing blade angle, and decreasing blade thickness, the pressure generated is increasing. Optimized values of inner radius and blade number exist. According to the theoretical results, the optimum radius is 5.4 mm and 2.7 mm for 20 mm and 10 mm diameter models respectively. The optimum blade number is 13 for 20 mm diameter models while 11 for 10 mm diameter models. Two volute design methods, namely, Constant Mean Velocity (CMV) method and Constant Angular Momentum (CAM) method are compared. For the same impeller operating at the same rotational speed, the difference between them is negligible, because the energy losses are mainly due to the volute length. For the same volute height and outlet width, the difference in the volute length is only 1% for the two methods. The results obtained in the present study provide us guidelines on the design and performance study of miniature centrifugal pump.
DRNTU::Engineering::Mechanical engineering::Fluid mechanics