Heat Transfer Behavior of the Boundary Layer Near Surfaces in Annular Flow of High Capacity Canned Motor Pump

Abstract

As significant fluid machinery, canned motor pumps are widely applied in industrial field. The typical characteristic of canned motor pump is that the fluid comes into the narrow gap and affects the performance of canned motor. The coolant flow in the narrow annular gap between rotor and stator cans belongs to Taylor-Couette-Poiseuille flow which has been investigated for a long time while the thermal design is a key function of internal narrow gap annular flow of canned motor. However, the temperature distribution prediction of canned motor deviates from the experiments, especially in the high-capacity canned motor due to the large shear rate of fluid and eddy-current loss of motor’s can. According to the researcher’s work, the significant work lies in the heat transfer coefficient that different researchers give various numerical prediction and experimental measurement. It brings big challenge in thermal design of high-capacity canned motor pump. In this paper, the author focuses on the reason why the heat transfer coefficient is remarkably lower than that other’s forecast. In this paper, the heat transfer behavior of the boundary layer near surfaces in the annular flow is investigated by using the commercial fluid dynamic (CFD) method. Firstly, the Naiver-Stocks (N-S) equations and energy conservation equation are employed for modeling the flow and heat transfer behavior, and the k-ω turbulent model is used for solving the flow control equations. Secondly, the fluid domain is described by a simplified geometrical model: two concentric cylinders with finite gap length. Thirdly, numerical approach is used to analyze the subject with tools of Solidworks, ICEM CFD and Ansys Fluent. Two parameters are analyzed in the research, namely the rotating speed and the wall heat flux, without considering the fluid viscous dissipation and thermal contact resistance. Numerical simulation results indicate that Taylor vortex exists in the flow regime, and the temperature distribution is affected by both the rotating speed and the wall heat flux, named thermal barrier effect under large heat flux condition. The thermal barrier effect lies in that the temperature gradient of interface decreases compared to the peak value of temperature gradient near the surface, so that the heat transfer coefficient is reduced remarkably. This effect leads to the temperature prediction deviates from the experiment measurement.