Gas Analyzer Probe Tube Thermal Lens Mitigation
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Solution Overview
Problem
The existing gas analyzing apparatuses face issues with measurement accuracy due to thermal lens effects caused by uneven temperature distributions, which can lead to fluctuations in the optical axis and unstable light reception, especially when analyzing high-temperature flue gases containing components like SOx and NOx, and require additional components like heaters and temperature control systems, increasing cost and complexity.
Innovation Solution
A gas analyzing apparatus is designed with a tube-like member and optical system that includes a blocking plate to prevent sample gas from entering the gap between the tube and the pipe wall, ensuring a continuous temperature gradient along the measurement light path, and a purge gas feed tube with a uniform inner diameter to prevent turbulent flow, thereby reducing thermal lens effects without the need for additional heating or temperature control systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If purge gas is fed into the probe tube to prevent optical system members from being exposed to high temperature sample gas, then the optical system members are protected from damage, but uneven temperature distribution occurs in the probe tube causing thermal lens effects and measurement accuracy deterioration
Solution Approach 1:
The probe tube is divided into two separate regions: a measurement region for sample gas introduction and a purge gas introduction region for optical system protection. This segmentation allows independent control of temperature conditions in each region, enabling protection of optical components without disrupting the temperature stability needed for accurate measurements.
Solution Approach 2:
A temperature control unit acts as an intermediary device that actively maintains uniform temperature distribution in the measurement region. This mediator compensates for the temperature unevenness caused by purge gas introduction, ensuring measurement accuracy is preserved despite the presence of cold purge gas in the system.
2Ease of manufacture
If a conventional probe structure with flange attachment is used, then the probe can be installed on the pipe, but gaps form between the probe and pipe allowing sample gas to enter and cool the probe tube causing thermal lens effects
Solution Approach 1:
The problematic gap region between the probe and pipe is isolated by extracting it from the measurement path. The measurement region is designed to be sealed and separated from the external environment, preventing sample gas leakage into the probe tube while maintaining the simple flange attachment structure for easy installation.
Solution Approach 2:
The sealing approach moves from a two-dimensional flange interface to a three-dimensional sealed chamber structure. By creating a closed measurement region that extends into the probe interior, the design prevents gas leakage paths that would otherwise exist at the flange interface, eliminating thermal lens effects while preserving installation ease.
3Measurement precision
If heaters and temperature control systems are added to maintain uniform temperature distribution, then thermal lens effects are reduced, but device complexity and cost increase
Solution Approach 1:
The system achieves temperature stability through self-service mechanisms rather than active heating. By introducing purge gas at controlled locations and utilizing natural convection and thermal isolation, the system maintains uniform temperature distribution in the measurement region without requiring external heaters or complex temperature control systems.
Solution Approach 2:
The cold purge gas, which initially causes temperature unevenness, is strategically introduced to create a temperature gradient that directs hot sample gas away from the optical system members. This converts the harmful cooling effect into a beneficial protective mechanism, shielding optical components from high-temperature sample gas while maintaining measurement region stability.
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 design enhances measurement accuracy by maintaining a stable temperature distribution, preventing thermal lens effects, and simplifying the installation process by eliminating the need for complex temperature control systems, while reducing costs and improving optical axis adjustment efficiency.
Implementation Method 1
measurement light emitted from a light source toward the gas is reflected by a reflector disposed at the tip of the probe, and hence concentration of components of the sample gas is analyzed based on information of the reflected measurement light
Implementation Method 2
it is possible to adopt a structure in which the purge gas is fed into the distal end portion of the probe tube B through a purge gas feed tube (not shown) disposed in the probe tube B
Data Source
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AI summary
A gas analyzer (100) for measuring a concentration of a sample gas flowing in a pipe (150) is provided. The gas analyzer comprises a tube-like member (115, 132) including a light path through which measurement light is emitted to a measurement region of a gas flowing in a pipe and/or through which the measurement light from the measurement region is received; an optical system (111, 131) for emitting the measurement light to the gas in the measurement region and/or receiving the measurement light from the measurement region; a purge gas feed tube (120, 136) having a hollow portion including a purge gas flow path for providing a purge gas (Pa) to the region between the optical system and the measurement region, and the optical path for the measurement light, the purge gas feed tube being provided inside of the tube-like member defining a first gap (144, 135) between it and an inner wall of the tube-like member; and a flange (116, 133) attached to a portion of an opening of the pipe side wall such that a second gap (155, 163) is defined between an outer circumferential surface of the tube-like member and an inner circumferential surface of the portion.