Rotating Machine Cooling via Rotor Cavities and Annular Flow
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Solution Overview
Problem
Existing rotor cooling systems for electric motors face challenges in efficiently managing heat without increasing machine mass, especially at high speeds and varying ambient conditions, and often require additional cooling elements that add weight and size.
Innovation Solution
A rotor cooling system featuring radial protrusions with cavities and an annular space between concentric shafts, where a fluid path allows coolant to flow through the cavities and annular space, enhanced by magnetic segments and a seal to maintain a pathway for efficient heat transfer, and optionally using baffles to control flow resistance and heat transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the size of the rotor and stator are selected so that heat transfer may occur through use of a gas in the air-gap between the rotor and stator, then heat transfer is improved, but the mass and volume of the machine increase
Solution Approach 1:
The cooling system is nested within the existing rotor structure by forming cavities inside the rotor core and shaft, allowing coolant flow paths to be integrated without adding external cooling components that would increase mass and volume
Solution Approach 2:
A liquid coolant is introduced through the hollow stationary shaft and circulated through cavities in the rotor core and radial protrusions, using fluid-based heat transfer to remove heat from the rotor without requiring increased air-gap convection that would demand larger dimensions
2Temperature
If the rotor is flooded with a dielectric fluid such as oil to cool the rotor, then heat transfer coefficient increases, but churning losses become high at high speeds
Solution Approach 1:
Instead of flooding the entire rotor cavity with fluid, the cooling system segments the coolant flow into specific cavities within the rotor core and radial protrusions, allowing controlled coolant circulation that reduces fluid agitation and churning losses while maintaining effective heat transfer at the heat-generating surfaces
Solution Approach 2:
Coolant is directed specifically to locations where heat is generated ( rotor core and radial protrusions with magnetic segments) rather than flooding the entire rotor, providing localized cooling that reduces unnecessary fluid movement and energy losses
3Temperature
If additional cooling elements are added to the rotor to improve cooling efficiency, then heat removal is enhanced, but the device complexity and mass increase
Solution Approach 1:
The cooling function is merged with the structural components of the rotor by forming cavities within the rotor core and radial protrusions, and by using the hollow stationary shaft as part of the cooling fluid path, thereby integrating cooling functionality into existing structural elements without adding separate cooling components
Solution Approach 2:
The hollow stationary shaft serves dual functions as both a structural support element and a coolant delivery conduit, while the radial protrusions serve both magnetic/structural purposes and provide coolant flow paths through their cavities, reducing the need for dedicated cooling components
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 design enhances heat removal from the rotor, maintaining internal temperatures within safe limits, enabling higher power density without increasing machine size or mass, and allowing for effective cooling even at high speeds and varying conditions.
Implementation Method 1
Heat is thus transferred from the rotor to the oil, and then removed from the oil via natural convection, forced convection, or liquid cooling
Data Source
AI summary
An electrical machine comprising a rotor is presented. The electrical machine includes the rotor disposed on a rotatable shaft and defining a plurality of radial protrusions extending from the shaft up to a periphery of the rotor. The radial protrusions having cavities define a fluid path. A stationary shaft is disposed concentrically within the rotatable shaft wherein an annular space is formed between the stationary and rotatable shaft. A plurality of magnetic segments is disposed on the radial protrusions and the fluid path from within the stationary shaft into the annular space and extending through the cavities within the radial protrusions.