Liquid Hydrogen Pump Impeller Fastener Thermal Expansion
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Solution Overview
Problem
Liquid hydrogen pumps face challenges due to a wide temperature range, leading to relative thermal expansion and excess stress, which can result in short operational life and thread unlocking.
Innovation Solution
An impellor assembly with a fastener that has an unconstrained length corresponding to the axial length of the impellor, allowing for differential thermal expansion between materials with different coefficients of thermal expansion, thereby maintaining clamping loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the pump operates across a wide temperature range from liquid hydrogen temperature to ambient temperature, then the pump can function in both cryogenic operation and warm storage/assembly conditions, but relative thermal expansion between components causes excess stress and thread unlocking
Solution Approach 1:
The patent applies parameter changes by selecting materials with different coefficients of thermal expansion for different components. The impellor is made from a material with a higher coefficient of thermal expansion than the shaft material, allowing each component to expand and contract at different rates during temperature transitions, thereby accommodating thermal stress without causing thread unlocking
Solution Approach 2:
The patent implements beforehand cushioning by designing the fastener with an unthreaded portion that acts as a stress-absorbing element. This unthreaded section provides a compliance zone that absorbs thermal expansion differences between the impellor and shaft, preventing the transmission of excessive stress to the threaded engagement portion and maintaining reliable thread locking across temperature cycles
2Strength
If the fastener is made entirely of threaded portions, then the fastener provides strong clamping force, but thermal expansion differences cause stress concentration at the thread roots leading to fatigue failure
Solution Approach 1:
The patent applies segmentation by dividing the fastener into distinct functional zones: a threaded portion for providing clamping force and an unthreaded portion for absorbing thermal stress. This segmentation allows each section to perform its specific function optimally - the threaded section maintains strong engagement while the unthreaded section acts as a stress-relief buffer during thermal cycling
Solution Approach 2:
The unthreaded portion of the fastener serves as an intermediary element between the threaded engagement zone and the clamped components. It mediates the thermal expansion forces by providing a compliant transition zone that prevents direct transmission of differential thermal stress to the thread roots, thereby reducing fatigue accumulation and extending service life
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 solution effectively maintains clamping loads across varying temperatures, preventing thread unlocking and reducing strain and fatigue, thus extending the operational life of the pump.
Implementation Method 1
the fastener and the impellor comprise a material having a first coefficient of thermal expansion and the shaft comprises a material having a second coefficient of thermal expansion, wherein the first and second coefficients of thermal expansion are different
Data Source
AI summary
An impellor assembly for a liquid hydrogen pump. The assembly comprises a shaft, one or more impellors mounted to the shaft, a fastener configured to engage with the shaft at a first engagement point and with the one or more impellor at a second engagement point to axially clamp the one or more impellor to the shaft, an axially unconstrained length of the fastener being defined by an axial distance between the first and second engagement points. An axial extent of a clamped portion of the one or more impellors corresponds to the axially unconstrained length of the fastener. The fastener and the impellor comprise a material having a first coefficient of thermal expansion and the shaft comprises a material having a second coefficient of thermal expansion, wherein the first and second coefficients of thermal expansion are different.