Cryogenic Magnet Compression Sleeves for Direct-Drive Pumps
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Solution Overview
Problem
Centrifugal pumps and turbines face challenges in efficiently pumping low-density cryogenic liquids like liquid hydrogen due to reduced differential pressure and potential damage from high rotational speeds and low temperatures, which can cause permanent magnets to crack or pulverize.
Innovation Solution
An axial direct drive design with annular permanent magnets arranged within compression sleeves, utilizing materials with differing coefficients of thermal expansion to maintain radial compression and prevent tensile stress, even at very low temperatures and high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If permanent magnets are used in directly driven pumps at high rotational speeds, then productivity and energy efficiency are improved, but the magnets are subjected to high centrifugal forces that can cause cracking or pulverization at low temperatures
Solution Approach 1:
The patent changes the physical state and mechanical properties of the magnet by subjecting it to cryogenic temperatures. This parameter change causes the magnet material to become more brittle and susceptible to centrifugal forces, creating the technical problem that the invention then solves through the compression sleeve mechanism.
Solution Approach 2:
The patent utilizes differential thermal contraction between the magnet and the compression sleeve materials when cooled to cryogenic temperatures. The compression sleeve is made of a material that contracts more than the magnet, creating a compressive force that counteracts the centrifugal forces during high-speed rotation.
2Productivity
If the pump operates at very high rotational speeds to compensate for low liquid density, then productivity is improved, but the centrifugal forces on permanent magnets increase causing potential failure
Solution Approach 1:
The compression sleeve acts as a counterbalancing mechanism that applies a compressive force opposite to the centrifugal force experienced by the magnet during high-speed rotation. This pre-compression ensures the magnet remains intact despite the high centrifugal loads.
Solution Approach 2:
The magnet is pre-compressed by the compression sleeve before operation begins. This beforehand cushioning creates a mechanical constraint that prevents the magnet from cracking or pulverizing when centrifugal forces are applied during high-speed operation.
3Loss of energy
If cryogenic temperatures are used to maintain liquid hydrogen, then energy efficiency is improved, but permanent magnets become more susceptible to mechanical failure
Solution Approach 1:
The invention exploits differential thermal contraction between the magnet and compression sleeve materials when cooled to cryogenic temperatures. The compression sleeve material is selected to contract more than the magnet, creating a compressive force that protects the magnet during subsequent high-speed operation.
Solution Approach 2:
The patent uses composite construction with the magnet embedded in a compression sleeve made of a different material with suitable mechanical and thermal properties. This composite structure allows the magnet to benefit from cryogenic temperatures while being protected by the compression sleeve's mechanical support.
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
The design ensures the integrity of permanent magnets by keeping them in a compressive state, preventing cracking or disintegration, thus enabling efficient pumping of cryogenic liquids at high rotational speeds without significant energy loss.
Implementation Method 1
The annular magnet ring is surrounded and radially bounded by an outer compression ring having an outer CTE that is equal to or greater than a magnet CTE of the permanent magnets, and surrounds and is radially bounded by an inner compression ring having an inner CTE that is equal to or less than the magnet CTE, wherein the outer CTE is greater than the magnet CTE, the inner CTE is less than the magnet CTE, or both. The permanent magnets are thereby radially compressed due to unequal thermal contraction of the permanent magnets and the inner and outer compression ring s when the inner and outer compression ring s and the permanent magnets are cooled by the process liquid.
Implementation Method 2
a plurality of stator coils contained within an interior of the stator housing and configured to be axially proximate the permanent magnets as they pass in proximity to the proximal face of the stator housing
Data Source
AI summary
An integral motor pump (IMP) or turbine (IMT) applicable to a low temperature process liquid, such as liquid hydrogen, includes an impeller having an annular ring of permanent magnets attached thereto passing in axial proximity to a plurality of stator coils. The magnet ring is radially bounded by inner and outer compression sleeves having coefficients of expansion (CTEs) respectively less than and greater than the CTE of the magnets. Unequal thermal contraction of the compression sleeves, when cooled by the process liquid, applies radial compression to the magnet ring, overcoming centrifugal forces and maintains the magnets in radial compression, thereby preventing fracturing or pulverizing of the magnets. The magnet ring can be a monolithic ring with alternating magnetic regions, a ring of closely abutting magnets, or a ring of discrete magnets surrounded by a barrier material having a CTE equal to the magnet CTE.