Subsea Electric Cooling via Partial Forced Convection
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Solution Overview
Problem
Subsea electric systems face inefficiencies in cooling due to high viscosity and low thermal conductivity of dielectric fluids, leading to limited cooling capacity and increased mechanical complexity, particularly in natural convection systems, which are costly and prone to premature aging of temperature-sensitive components.
Innovation Solution
A cooling arrangement that combines natural convection with forced convection using a pump to enhance the flow of dielectric fluid through a heat exchanger, allowing for the use of long coiled tubes and internal mixers, reducing pressure drop and heat transfer resistance, and incorporating redundant pumping systems for reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If natural convection cooling is used without a pump, then the system reliability is improved by eliminating pump failures, but the cooling efficiency deteriorates due to limited heat transfer capacity
Solution Approach 1:
The patent applies partial forced convection by using a pump only for the portion of dielectric fluid that flows through the heat exchanger, while the rest of the fluid circulation in the tank continues via natural convection. This selective application of forced convection enhances cooling efficiency where needed without requiring a complete active cooling system, thus maintaining good reliability while improving productivity.
2Stress or pressure
If the inner diameter of heat exchanger pipes is increased, then the pressure drop is reduced for natural convection, but the heat transfer from oil to inner tube wall deteriorates due to laminar flow
Solution Approach 1:
The patent changes the flow regime parameter by introducing forced convection through a pump, which increases the flow velocity and transitions the flow from laminar to turbulent regime. This parameter change allows the use of larger pipe diameters (reducing pressure drop) while maintaining good heat transfer efficiency due to enhanced turbulent mixing.
3Stress or pressure
If many parallel pipes are used to maintain sufficient oil-flow cross-section, then the pressure drop is kept low, but the device complexity increases due to large number of connections
Solution Approach 1:
The patent extracts the pumping function from the natural convection system and applies it selectively to the heat exchanger portion. This allows the use of fewer, larger-diameter pipes in the heat exchanger without requiring complex manifold systems with numerous connections, as the forced flow provides sufficient pressure to overcome the resistance of a simpler pipe configuration.
4Reliability
If dielectric fluid viscosity is high, then the electric insulation properties are improved, but the thermal conductivity deteriorates leading to poor heat transfer
Solution Approach 1:
The patent uses hydraulic principles by introducing a pump to force the high-viscosity dielectric fluid through the heat exchanger at increased velocities. This hydraulic approach overcomes the poor natural convection caused by high viscosity, enabling effective heat transfer while maintaining the beneficial high insulation properties of the dielectric fluid.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in efficient subsea cooling of electric components, reducing the aging of temperature-sensitive components, enabling a compact, cost-effective, and reliable cooling system with improved heat transfer efficiency and reduced mechanical complexity.
Implementation Method 1
a pump arranged to force a flow of the dielectric fluid through the first heat exchanger; wherein flow of the dielectric fluid in the tank is partially by natural convection and partially by forced convection generated by the pump
Implementation Method 2
The oil in the tank and in any oil-to-sea-water heat exchanger can be moved by natural convection
Implementation Method 3
a first heat exchanger located outside the tank and in fluid contact with the tank, and arranged to during operation be in thermal contact with sea water
Data Source
Figure 1~2
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Figure 5~6
AI summary
There is presented an arrangement for cooling components of a subsea electric system. The arrangement comprises a tank filled with a dielectric fluid. The tank comprises a first section and a second section. The arrangement comprises at least one first electric component located within the first section. The arrangement comprises at least one second electric component located within the second section. The arrangement comprises a first heat exchanger located outside the tank and in fluid contact with the tank, and arranged to during operation be in thermal contact with sea water. The arrangement comprises a pump arranged to force a flow of the dielectric fluid through the first heat exchanger. Flow of the dielectric fluid in the tank is partially by natural convection and partially by forced convection generated by the pump. The at least one first electric component generates more heat than the at least one second electric component. Within the first section the share of the flow by natural convection is greater than within the second section.