Análise numérica do fenômeno de transporte em torno do motor de bomba centrífuga submersa

Abstract

Electrical Submersible Pumps (ESP) are mainly applied in lifting operations in deep water oil exploration. Due to its geometry, the elevated fluid itself cools the pump’s motor. Thus, a vertical annular flow is formed around the ESP motor. Since at different moments there is gas together with the elevated oil at various times, it is difficult to understand the thermofluidic phenomenon, as these equipment are installed on the seabed. It is widely known that the presence of gas causes undesirable phenomena for the pump, such as surging and gas lock. Gas can cause failure due to overheating (notably motor failure), causing huge losses to the industry. Given that this topic concerns a multiphase flow, the present work shows the mathematical demonstration for the two-fluid model, as well as analyses of the local conservation of thermal energy equations, for each two-phase pattern of interest. Other parameters of the existing transport phenomenon are introduced and analytically demonstrated. Such theories serve as a basis for understanding the numerical analyses performed using the Ansys Fluent. Two two phase simulations are executed with different liquid mass flow rates, having as their geometry the ESP motor prototype built at the Center for Studies in Oil and Gas Flow and Measurement (Nemog). This prototype is designed to obtain the highest possible dynamic similarity with the real prototype. For the numerical analysis, the Eulerian multiphase model is applied simultaneously with the Multi-Fluid VOF, in addition to other interfacial dynamics modeling. For the treatment of turbulence, the k − ω SST model is imposed for each phase. The simulations show the formation of the slug pattern and distortions that the presence of gas causes in the velocity of the liquid. Velocities up to 1.5 m/s are reached in the motor-shroud annular, causing high Reynolds numbers in different regions and showing that the treatment of the flow as turbulent is adequate. For a single-phase flow, the Nusselt number tends to a constant value of 2.70 regardless of the inlet flow rate. For a two-phase flow, this dimensionless is a function of the ratio between inflows and reaches approximately constant values in the region where both phases are present. Given the imposed boundary conditions, for the first simulation the Nusselt number tends to 43.1 while for the second simulation the value of 82.3 is obtained