Mass Flow Controller with Flow Resistance Element for Gas Chromatography
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Solution Overview
Problem
Conventional gas chromatography (GC) devices face challenges in maintaining a constant mass flow rate through downstream columns with unknown geometry, dimensions, and temperature programs, especially when columns have complex geometries or are microfabricated, making it difficult to implement precise pressure programming and control.
Innovation Solution
A system comprising a small full-scale mass flow controller, a flow resistance element, and a pressure sensor that controls carrier gas flow to maintain a constant mass flow rate without needing detailed column characteristics, using a set point determined by the pressure sensor and flow resistance, allowing for operation across various column geometries and temperature programs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If calculated pressure programming method is used to control carrier gas flow, then constant mass flow rate can be achieved, but the method becomes difficult to implement when column dimensions are unknown or column geometry is complex
Solution Approach 1:
The patent introduces a flow resistance element as an intermediary component between the carrier gas source and the GC column. This element has known flow characteristics that can be used to calculate and control the mass flow rate without needing to know the column's internal geometry or dimensions. The flow resistance element acts as a mediator that simplifies the control problem by providing a reference with known properties.
Solution Approach 2:
The patent changes the control parameter from direct pressure control to flow resistance-based control. By using an element with known flow resistance characteristics, the system can determine mass flow rate through pressure measurements across the resistance element, without needing to know column dimensions or geometry. This parameter change enables universal applicability across different column types.
2Measurement precision
If calculated pressure programming is implemented, then chromatographic separation quality improves, but the method requires precise knowledge of column dimensions and temperature program
Solution Approach 1:
The flow resistance element serves as an intermediary that provides known flow characteristics, eliminating the need to know column internal characteristics. By measuring pressure drop across this known resistance, the system can infer flow conditions without losing information about column geometry or temperature program.
3Extent of automation
If conventional EPC system is used, then automated carrier gas flow control is achieved, but constant mass flow rate cannot be maintained across varying column conditions
Solution Approach 1:
The patent implements a feedback control mechanism where pressure measurements across the flow resistance element are continuously monitored. These measurements provide feedback about the actual mass flow rate, which is then used to adjust the carrier gas flow to maintain constant mass flow rate despite variations in column conditions. This feedback loop ensures both automation and reliability.
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 efficient and reproducible constant mass flow rate control in GC systems, independent of column geometry and temperature programs, facilitating advanced configurations like midpoint backflush and heart cutting, while maintaining chromatographic separation and detector sensitivity.
Implementation Method 1
A pressure differential is created across an inlet port and an outlet port of the flow resistance element
Implementation Method 2
A mass flow rate of the carrier gas to the downstream column system is controlled, without needing to know detailed characteristics of the downstream column and operating environment... A pressure differential is created across an inlet port and an outlet port of the flow resistance element
Data Source
AI summary
A device for providing a constant mass flow rate to a downstream column system of a gas chromatograph includes a small full scale mass flow controller that controls carrier gas to flow at a first mass flow rate and a flow resistance element, including an inlet port connected to a sample inlet, an outlet port connected to the downstream column system, and a pressure sensing port in fluid communication with the outlet port and the mass flow controller. A sample inlet pressure controller controls the sample inlet at a first pressure, and a pressure sensor measures a second pressure of the carrier gas at the pressure sensing port. A set point of the first pressure is determined as a function of the second pressure, flow resistance of the flow resistance element, and a second mass flow rate from the inlet port to the outlet port of the flow resistance element.