Choked Flow Isolator for Gas Chromatograph Noise Reduction
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Solution Overview
Problem
Gas chromatographs face interference from pressure fluctuations in the environment, which affect the accuracy of thermal conductivity detectors due to the sensitivity of these detectors to changes in gas pressure, leading to noise in measurements.
Innovation Solution
A choked flow channel is introduced downstream of the detector, where the gas flow becomes supersonic, preventing upstream propagation of pressure fluctuations and isolating the detector from environmental pressure changes, using a convergent-divergent nozzle or other structures that induce choked flow conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the detector measures thermal conductivity of the gas, then the sensitivity of the detector is improved, but the detector becomes sensitive to pressure fluctuations in the room, causing noise in measurements
Solution Approach 1:
A choked flow channel is introduced as an intermediary component between the detector and the environment. This channel creates a supersonic flow regime that acts as a barrier, preventing pressure fluctuations from the room from propagating upstream to the detector, while allowing the detector to maintain its sensitivity to thermal conductivity changes
Solution Approach 2:
The flow regime is changed from subsonic to supersonic by designing the choked flow channel with appropriate geometry (convergent-divergent nozzle). This parameter change in flow velocity creates a shock wave that blocks the transmission of pressure fluctuations upstream, isolating the detector from environmental pressure variations
2Device complexity
If the carrier gas is vented into the room, then the system operates simply, but pressure fluctuations from doors being opened and closed are transmitted back to the detector
Solution Approach 1:
The choked flow channel serves as a mediator between the carrier gas system and the room environment. It allows the gas to be vented simply into the room while simultaneously blocking the transmission of pressure fluctuations back to the detector, maintaining both system simplicity and noise reduction
3Productivity
If the gas is drawn through the chromatograph by a vacuum pump, then the system operates efficiently, but fluctuations in the pump pressure are transmitted back to the detector
Solution Approach 1:
The choked flow channel acts as a buffer between the vacuum pump and the detector. It allows the pump to operate efficiently at variable pressures while preventing these pressure fluctuations from propagating upstream to the detector, maintaining both productivity and measurement 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 solution significantly reduces errors caused by pressure fluctuations, enhancing the accuracy and reliability of gas chromatograph measurements by maintaining the detector's sensitivity only to the properties of the gas flowing through it.
Implementation Method 1
The fluid reaches a supersonic velocity at one point in the choked flow channel
Implementation Method 2
The fluid reaches a supersonic velocity at one point in the choked flow channel
Implementation Method 3
Gas chromatographs often utilize detectors that measure the thermal conductivity of the gas leaving the column
Data Source
AI summary
An apparatus and a method of making a measurement using the same. The apparatus includes a channel through which a fluid flows, a detector, and a choked flow channel. The detector measures a property of the fluid by generating a signal that depends on that property. The signal generated also depends on a pressure of the fluid in the detector. The choked flow channel receives the fluid at a first pressure after the fluid has been measured by the detector, and then transmits the fluid to a downstream location at a second pressure. The fluid reaches a supersonic velocity at one point in the choked flow channel. The choked flow channel may include a convergent-divergent nozzle or an orifice in a structure located in the choked flow channel.