Jet Pump Vibration Damping via Narrowing Clearance Flow Path
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Solution Overview
Problem
Existing jet pump designs in boiling water reactors face self-excited vibration issues due to clearance flow paths between the inlet mixer pipe and the diffuser pipe, which can lead to structural degradation and increased vibration amplitude, despite previous vibration restraint techniques failing to effectively address these issues without inhibiting thermal expansion or mechanical deterioration.
Innovation Solution
A jet pump design incorporating a self-vibration damping structure with a narrowing clearance flow path, where the outer pipe wall of the inlet mixer pipe gradually increases in diameter and the inner pipe wall of the diffuser pipe maintains a uniform diameter, creating a flow path resistance greater than fluid inertia force, thereby reducing self-excited vibrations without restricting thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a clearance is provided in the slip joint structure to accommodate thermal expansion, then the structural deformation due to thermal expansion is accommodated, but a clearance flow path is formed which causes self-excited vibration
Solution Approach 1:
A vibration damping structure is introduced as an intermediary element within the clearance flow path. This structure mediates between the need for clearance (for thermal expansion) and the harmful effect of clearance flow (vibration). The damping structure absorbs vibrational energy while allowing the clearance to remain open for thermal accommodation.
Solution Approach 2:
The clearance flow that causes vibration is converted into a beneficial damping effect. By strategically placing damping structures within the clearance, the flow path itself becomes a vibration control mechanism, transforming the harmful clearance flow into a useful vibration damping feature.
2Reliability
If vibration restraining structures are provided at locations away from the connection portion, then vibration is restrained, but the restraint effect decreases with distance from the connection portion
Solution Approach 1:
The vibration damping structures are placed locally at the connection portion between the inlet mixer pipe and diffuser pipe, where the vibration source is located. This local placement ensures maximum effectiveness while simplifying the overall structure, avoiding the need for distributed vibration restraining structures throughout the system.
Solution Approach 2:
Instead of placing vibration restraining structures away from the connection portion (conventional approach), the invention inverts the strategy by placing damping structures directly at the connection portion where clearance flow occurs. This inversion maximizes the restraint effect at the source of vibration.
3Reliability
If the inlet mixer pipe and diffuser pipe are press-contacted to eliminate clearance, then vibration is restrained, but the function of the clearance for accommodating thermal expansion is inhibited
Solution Approach 1:
The clearance space is segmented into functional zones: one zone allows thermal expansion movement, while another zone contains vibration damping structures. This segmentation enables the same clearance to serve dual purposes - accommodating thermal expansion while preventing vibration through the distributed damping elements.
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 effectively restrains self-excited vibrations in the connection portion between the inlet mixer pipe and the diffuser pipe, maintaining structural deformation accommodation and reducing the likelihood of vibration-induced damage, while simplifying the jet pump structure.
Implementation Method 1
creating a flow path resistance greater than fluid inertia force, thereby reducing self-excited vibrations
Implementation Method 2
creating a flow path resistance greater than fluid inertia force
Data Source
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AI summary
The present invention has an object to provide a jet pump, which can restrain self-excited vibration in a connection portion between an inlet mixer pipe and a diffuser pipe without inhibiting a structural deformation due to thermal expansion and the like. The jet pump includes: a slip joint structure connecting the inlet mixer pipe and the diffuser pipe to each other by inserting the inlet mixer pipe into an upper end opening of the diffuser pipe with a clearance left therebetween; and a self vibration damping structure configured such that when the clearance defined by an outer pipe wall of the inlet mixer pipe and an inner pipe wall of the diffuser pipe is widening or narrowing due to vibration of the inlet mixer pipe or the diffuser pipe, a flow path resistance inside a clearance flow path for pumped coolant water defined by the clearance is not smaller than a fluid inertia force all over the clearance flow path.