Nanoporous Membrane Leak Detector for Hydrogen Helium Analysis
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Solution Overview
Problem
Existing sniffer leak detectors for mass spectrometric gas analysis have a low detection limit due to insufficient gas flow conductance, particularly for lighter test gases like hydrogen and helium, when using sintered ceramic membranes, which also allow heavier gases to pass through, degrading analysis accuracy.
Innovation Solution
A porous membrane with pore diameters matching the free path length of air at atmospheric pressure and room temperature is used, ensuring high conductance for light test gases while restricting heavier gases, with a high pore density and small wall thickness to achieve a molecular gas flow that enriches test gases in the vacuum, improving detection limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sintered ceramic membranes are used in the gas inlet, then gas flow conductance is improved, but heavier gases pass through along with test gases, degrading analysis accuracy
Solution Approach 1:
The patent employs a porous membrane with specifically controlled pore diameters (0.001-0.1 μm) to achieve selective gas transmission. The pore size is optimized to allow test gases (H2, He) to pass through while blocking heavier atmospheric gases, thereby simultaneously maintaining high gas flow conductance and analysis accuracy without the need for complex multi-stage filtration systems.
Solution Approach 2:
The membrane structure exhibits local quality optimization where the pore diameter is precisely controlled within a specific range (0.001-0.1 μm) to create selective permeability. This local structural characteristic enables the membrane to differentiate between light test gases and heavy atmospheric gases based on their molecular weights, allowing selective transmission that improves both conductance and measurement precision.
2Measurement precision
If pore diameter is reduced to restrict heavier gases, then analysis accuracy is improved, but gas flow conductance decreases
Solution Approach 1:
The patent optimizes the pore diameter parameter within the specific range of 0.001-0.1 μm to achieve the desired balance. This parameter optimization allows the membrane to maintain sufficient gas flow conductance while effectively restricting heavier gases, thereby improving analysis accuracy without excessively reducing gas flow. The pore size is carefully selected to exploit the difference in molecular weights between test gases and atmospheric gases.
3Productivity
If membrane pore density is increased to allow more gas flow, then gas flow conductance is improved, but heavier gases are less effectively restricted
Solution Approach 1:
The patent utilizes a composite membrane structure combining specific pore size characteristics (0.001-0.1 μm) with appropriate pore density to achieve both high gas flow conductance and effective gas separation. The composite nature of the membrane allows it to simultaneously provide sufficient open area for high conductance while maintaining the selective pore size characteristics needed to restrict heavier gases and ensure analysis accuracy.
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 configuration enhances the detection limit by preferentially allowing hydrogen and helium to enter the high vacuum, achieving a maximum high-vacuum pressure of 10^-4 mbar, thereby improving the sensitivity and accuracy of gas analysis.
Implementation Method 1
pores with a diameter that corresponds at most to the mean free path of air at atmospheric pressure and room temperature generate a molecular gas flow even at relatively high pressure
Implementation Method 2
The pore diameter of this membrane is less than or equal to the mean free path of air at atmospheric pressure and room temperature... The conductivity for the lighter test gases hydrogen and helium is particularly high, while the conductivity for the heavier gases, which are undesirable in the analysis, is low
Data Source
Figure 1~2
AI summary
A sniffing leak detector for sucking in and analyzing gas, including a sniffing probe for sucking in the gas, a gas-conveying pump connected to the sniffing probe, and a mass spectrometer connected to a vacuum pump for analyzing the sucked-in gas in a high vacuum. The gas flow through the sniffing probe is conducted along a membrane having gas-permeable pores. The membrane allows part of the gas to flow into the prevacuum of the vacuum pump for the mass spectrometric analysis of the gas in a high vacuum. The diameter of the pores is less than or equal to the free path of air at atmospheric pressure and room temperature in order to improve the detection limit of the sniffing leak detector.