Multilayer Porous Structure Characterization via Slip Flow Gas Permeation
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Solution Overview
Problem
Current methods for characterizing multilayer porous structures, especially heterogeneous ones, are either destructive or limited to small volumes, failing to accurately characterize each layer independently in a non-destructive manner.
Innovation Solution
A method and system utilizing a slip flow model that accounts for gas slip velocity at the gas/pore wall interface, measuring pressure evolution upstream and downstream, and fitting a gas flow model to determine properties of each layer, allowing for non-destructive characterization of multilayer porous structures with fluid communication between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tomography or observation techniques (scanning electron microscopy, mercury porometry) are used to characterize each layer, then measurement precision is improved, but the structure is destroyed and only a very small volume can be analyzed
Solution Approach 1:
The patent replaces mechanical/physical destruction methods (tomography, electron microscopy, mercury porometry) with a gas flow-based measurement system. By measuring pressure evolution during gas permeation and applying slip flow models, the system obtains layer-specific pore radius and hydraulic resistivity data without physically contacting or damaging the structure
Solution Approach 2:
The patent introduces gas as an intermediary substance to probe the porous structure. The gas flows through the layers, and its pressure evolution serves as a mediator to indirectly measure pore properties. This allows characterization without direct contact that would destroy the structure
2Productivity
If the slip flow model is applied to homogeneous porous structures, then productivity is improved by obtaining pore radius, but in heterogeneous multilayer structures the obtained radius is only globally representative and does not characterize each layer
Solution Approach 1:
The patent segments the multilayer porous structure into distinct layers (first layer, second layer, etc.) and develops separate characterization equations for each layer. By measuring pressure evolution at multiple time points and applying the slip flow model to each layer's contribution, the system obtains individual pore radius and hydraulic resistivity values for each layer rather than a single global average
Solution Approach 2:
The patent adds the temporal dimension to the measurement by monitoring pressure evolution over time during gas permeation. This time-dependent measurement approach, combined with the slip flow model, enables differentiation between layers based on their respective flow resistance characteristics, transforming a single-point measurement into a multi-dimensional characterization process
3Device complexity
If conventional flow models are used without considering slip velocity, then device complexity is reduced, but measurement precision deteriorates in rarefied gas environments where Knudsen number is between 10-3 and 0.1
Solution Approach 1:
The patent modifies the flow model by incorporating the slip velocity parameter at the gas-channel wall interface. The slip flow model introduces a slip velocity term that accounts for rarefaction effects when the Knudsen number is between 10-3 and 0.1. This parameter change enables accurate characterization of porous structures in the transition flow regime without requiring complex computational models
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
Enables precise and rapid characterization of multilayer porous structures, identifying layer properties such as pore radii and hydraulic resistivity without destroying the structure, and can detect random defects, with low gas consumption and independence from the nature of the gas used.
Implementation Method 1
a well-known rarefaction phenomenon is observed which is generally assimilated to slip on the scale of the continuous medium because it results in a jump in speed (dynamic slip) at the gas/channel wall interface. Consequently, a particularly used model is the slip flow model which takes into account a slip velocity at the gas/channel wall interface.
Implementation Method 2
The flow regime is usually determined by Knudsen's number, which is a dimensionless number defined by the ratio between the mean free path of the molecules making up the gas and a characteristic dimension of the gas flow in the structure. When the Knudsen number is between 10-3 and 0.1, the flow regime is in a rarefied medium.
Implementation Method 3
measure the time evolution of the gas pressure upstream of the porous structure and the time evolution of the gas pressure downstream of the porous structure
Implementation Method 4
flowing a gas through the pores of the porous structure
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
Method and system for characterizing in rarefied gaseous medium layers of a multilayer porous structure in which each layer comprises a set of pores and allows fluidic communication between the layers.