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Means to Increase Heat Transfer from an ESP Motor

IP.com Disclosure Number: IPCOM000028994D
Publication Date: 2004-Jun-10
Document File: 3 page(s) / 14K

Publishing Venue

The IP.com Prior Art Database

Abstract

• Disclosure:

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This is the abbreviated version, containing approximately 47% of the total text.

Means to Increase Heat Transfer from an ESP Motor

·        Disclosure:

This invention relates to a means to increase the rate of heat transfer from a submersible electric pump motor to the fluid flowing past the motor.

·        Background:

Electric submersible pumps (ESP) are widely used to pump water and oil from well bores.  ESP’s used in the petroleum industry are typically constructed as combined unites wherein a long (20 feet or more), small diameter (7.25 inches or less) electric motor is directly connected to and drives a similar long, small diameter, multi-staged centrifugal pump.  The ESP is lowered into the well bore and submerged in the fluid being pumped.  The pumped fluid flowing over the outside of the motor cools the electric motor.  Typical ESP motors operate at high power densities and without this cooling they are quickly damaged by overheating.

When the fluid being pumped has a low viscosity, a high specific heat and a high thermal conductivity (such as light oil, water or water cut oil) adequate cooling is seldom a problem.  When the fluid has a high viscosity, a low specific heat and a low thermal conductivity (typical of highly viscous crude oils), the ESP motor is forced to operate at a much higher temperature in order to reject internally generated heat.  This high operating temperature reduces motor life and results in short run times.

Heat transfer, from the motor’s outside surface to the fluid flowing last the motor, occurs according to the question:

Q = hc A (Ts – Tf)

Where:   Q = rate of heat transfer

              hc =   rate of transfer coefficient

               A = surface area

               Ts = temperature of surface

               Tf   = temperature of fluid

For a given amount of heat generated by the motor, increasing the surface area and/or

the heat transfer coefficient can lower the surface temperature.  The heat transfer

coefficient represents the complex interaction of the fluid’s thermophysical properties,

the temperature differentials, the velocity of flow and, to a lesser extent, the geometry

of the flow path.

         The thermophysical properties of a fluid, at any given temperature, are relatively fixed

         and unalterable.  Increasing the velocity of flow has only a small effect upon the heat

         transfer coefficient of highly viscous fluids.  This leaves increasing the surface area as

         the most promising way of lowering surface temperatures of ESP motors operating in

         highly viscous fluids.

            The addition of “cooling fins” to a heat transfer surface is a widely used means of increasing

         the surface area.  The design criteria, predictability of performance and effectiveness of cooling

         fins have been widely investigated and are indisputably established.  The most effective cooling

         fins are re...