Pulsed Reactant Gas Flow for Single-Cycle CVI/CVD Densification
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Solution Overview
Problem
Conventional CVI/CVD processes for manufacturing carbon/carbon brake disks face inefficiencies due to pore occlusion, requiring multiple cycles and costly machining to maintain gas flow, which slows down the densification process and leads to interior porous defects.
Innovation Solution
A method and system that pulsate the flow rate of reactant gases during the CVI/CVD process to disturb the boundary layer, enhancing mass transfer and allowing for densification in a single cycle by using a mass flow controller to adjust flow rates and preheat the gases, thereby improving infiltration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional isothermal CVI/CVD process is used, then the process is simple to operate, but the densification requires multiple cycles with machining interruptions, reducing productivity
Solution Approach 1:
The patent applies periodic action by pulsing the reactant gas flow at controlled intervals during the CVI/CVD process. The mass flow controller delivers gas in pulses rather than continuous flow, creating periodic disturbances that prevent boundary layer formation and maintain enhanced mass transfer throughout the densification cycle, enabling single-cycle completion
Solution Approach 2:
The patent implements dynamics by transitioning from static continuous gas flow to dynamic pulsed gas flow. The flow rate is continuously adjusted through pulsing sequences with varying pulse widths and intervals, adapting the mass transfer conditions throughout the densification process to maintain optimal infiltration without pore occlusion
2Quantity of substance
If continuous reactant gas flow is used, then the process control is simple, but boundary layer forms on porous structure surfaces, reducing mass transfer efficiency
Solution Approach 1:
The mass flow controller delivers reactant gas in periodic pulses rather than continuous flow. Each pulse creates a temporary flow disturbance that prevents boundary layer stabilization on the porous structure surfaces, maintaining enhanced mass transfer efficiency throughout the infiltration process
Solution Approach 2:
The patent changes the flow rate parameter dynamically through pulsing. The mass flow controller adjusts the gas flow rate between different levels during the cycle, creating varying flow conditions that disrupt boundary layer formation and enhance reactant gas infiltration into the porous structure
3Productivity
If high gas flow rate is used to enhance mass transfer, then infiltration efficiency improves, but pore occlusion occurs on exterior surfaces, requiring machining interruptions
Solution Approach 1:
The pulsed gas flow delivers high concentration reactant gas in intermittent bursts rather than continuous high flow. This periodic delivery maintains high infiltration rates during pulses while allowing brief intervals for pressure equalization, preventing exterior pore occlusion while achieving complete densification
Solution Approach 2:
The patent applies partial action by using brief pulses of high flow rate rather than sustained high flow. Each pulse delivers sufficient reactant gas to drive infiltration forward, but the intermittent nature prevents excessive gas accumulation that would cause pore occlusion on exterior surfaces
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 approach enables achieving commercially viable density in a single processing cycle, reducing costs and time by enhancing mass transfer and preventing pore occlusion, resulting in higher quality carbon/carbon parts with reduced defects.
Implementation Method 1
The gas diffuses into the stack of porous materials, driven by concentration gradients
Implementation Method 2
The preheater may heat the reactant gas to a defined temperature before flowing the reactant gas into the ID volume
Implementation Method 3
The reactant gas may form a boundary layer in proximity to an axially top surface and an axially bottom surface of the annular porous structure
Implementation Method 4
pulsing the reactant gas into the ID volume to disturb the boundary layer and enhance a mass transfer process
Data Source
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AI summary
A system and method for enhancing a diffusion limited CVI/CVD process is provided. The system may densify a porous structure by flowing a reactant gas around the porous structure. A mass flow controller (170) may be configured to pulse the flow rate of the reactant gas around the porous structure. The mass flow controller (170) may pulse the flow rate from a nominal flow rate to a first flow rate. The mass flow controller (170) may pulse the first flow rate back to the nominal flow rate or to a second flow rate. The mass flow controller (170) may pulse the flow rate between the nominal flow rate, the first flow rate, and the second flow rate, as desired.