Degassed Boundary Layer Injection for Propeller Cavitation Control
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Solution Overview
Problem
Cavitation in hydraulic systems, such as impellers and propellers, leads to efficiency losses and material degradation due to the formation of vapor cavities and subsequent shock waves, limiting the speed of vessels and causing wear on surfaces.
Innovation Solution
Directing a partially degassed fluid towards the surface to form a boundary layer that increases the negative pressure required for cavitation inception, thereby reducing its occurrence, using a pulsed flow to maintain the boundary layer and control the degassing level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the shaft speed of impellers or propellers is increased to improve productivity, then the speed and efficiency of vessels improve, but cavitation occurs leading to material degradation and wear
Solution Approach 1:
The patent applies local quality by creating a boundary layer with different gas content characteristics at the surface of the impeller or propeller blades. This boundary layer has reduced dissolved gas concentration compared to the bulk fluid, which modifies the local cavitation behavior at the surface where it is most critical, allowing higher operating speeds without proportional increase in cavitation wear.
Solution Approach 2:
The patent changes the physical parameter of dissolved gas concentration in the fluid boundary layer by introducing a fluid with different gas content (such as degassed fluid or fluid with different gas composition). This parameter change increases the negative pressure required for cavitation inception, thereby reducing cavitation wear while maintaining high shaft speeds.
2Object-affected harmful factors
If hard materials are used to resist cavitation wear, then material degradation is reduced, but device complexity and manufacturing cost increase
Solution Approach 1:
Instead of changing the material properties of the impeller or propeller blades, the patent changes the physical parameter of the fluid boundary layer (dissolved gas concentration). This approach achieves cavitation wear resistance through fluid modification rather than material substitution, maintaining structural simplicity and avoiding the complexity associated with selecting and implementing hard materials.
3Object-affected harmful factors
If operating conditions are restricted to prevent cavitation, then cavitation wear is reduced, but productivity and vessel speed are limited
Solution Approach 1:
The patent enables higher shaft speeds by changing the parameter of dissolved gas concentration in the boundary layer fluid. This parameter change raises the cavitation inception threshold, allowing the system to operate at higher speeds without experiencing cavitation wear that would otherwise require speed restrictions.
Solution Approach 2:
The patent applies preliminary action by pre-modifying the fluid boundary layer before cavitation can occur. By introducing fluid with different gas content characteristics in advance, the system prepares the surface environment to resist cavitation inception, enabling higher operating speeds without subsequent cavitation damage.
4Object-affected harmful factors
If a boundary layer of degassed fluid is formed at the surface, then cavitation inception pressure increases and cavitation is reduced, but additional system complexity is introduced
Solution Approach 1:
The patent applies self-service by utilizing the natural convection and advection processes that occur in the fluid system to distribute the degassed fluid and form the boundary layer. The system leverages existing fluid flow patterns rather than requiring complex active control mechanisms, thereby achieving boundary layer formation with minimal additional system complexity.
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
Significantly reduces cavitation, improving the performance and efficiency of vessels, minimizing material degradation, and reducing noise associated with cavitation, allowing for higher operational speeds and reduced wear on surfaces.
Implementation Method 1
Cavitation is the formation of vapour cavities in hydraulic systems due to a consequence of forces acting upon the hydraulic system. Cavitation generally occurs when the local pressure falls sufficiently far below a saturated vapour pressure of a fluid
Implementation Method 2
directing a second fluid that is at least partially degassed towards the surface such that the second fluid is able to form a boundary layer at the surface
Implementation Method 3
The second fluid is periodically directed to the surface using a pulsed flow to form the boundary layer
Data Source
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AI summary
This disclosure relates to a system for reducing cavitation at a surface that moves relatively with respect to a first fluid. The system comprises a degasser configured to at least partially degas a second fluid. The system also comprises a reservoir in communication with the degasser and configured to house the at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface. The system is configured such that the directing of the at least partially degassed second fluid towards the surface forms a boundary layer at the surface. The boundary layer is adapted to at least partially increase the negative pressure required to initiate cavitation at the surface so as to reduce the occurrence of cavitation during such relative movement.