Моделирование охлаждения масла погружного электродвигателя с помощью теплообменника

Abstract

Submersible motors are part of submersible oil production pumps that convert electrical energy, which is supplied through a cable from VSD, into mechanical energy of pump rotation. Currently, in about 30% of cases, the failure of an electrical submersible pump is due to a failure of the submersible motor. One of the main causes of failures is overheating of the stator winding insulation. Overheating of submersible oil-filled electric motors occurs because more heat is generated inside the motor than is removed through its outer surface. To intensify the heat removal, it is proposed to connect a heat exchanger in series with the motor and to organize the circulation of the oil in a closed loop. Both in the submersible motor and in the heat exchanger, oil flows along the annular gap along the inner surface of the housing, the oil channel is closed through a hole inside the shaft. The aim of the work is to select such a configuration of the annular channel, in which its length would be minimal. Intensification of heat removal by increasing the speed of the coolant is not advisable, because requires the motor to be equipped with a powerful pump for pumping oil, which will become an additional source of heat. Therefore, it was decided to increase the surface area of the annular channel through which heat, through the body of the installation, is removed to the well fluid. A series of calculations was performed for heat exchangers with smooth walls, with fins (perpendicular to the flow direction), and with spiral grooves (which additionally increase the length of the trajectory of oil particles and the time of their thermal contact with the stacks of the heat exchanger body). Computational fluid dynamics calculations showed that heat exchangers made according to the first two design options removed less than half of the heat. According to the third option, the oil was cooled practically to the temperature of the well fluid with a heat exchanger length of about 10% of the submersible motor length.