Segmented Bypass Capillary Tubes for High Flow Mass Flow Control
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Solution Overview
Problem
High-flow mass flow controllers face challenges in maintaining laminar flow and optimal pressure drops across capillary tubes, leading to non-linear flow measurements and suboptimal operating conditions for thermal sensors, especially at flow rates above 100 to 200 standard liters per minute.
Innovation Solution
The design incorporates a bypass with multiple capillary tubes and segmented pressure drops, allowing the thermal sensor to be positioned across specific pressure drops to divert gas flow, thereby maintaining linear proportionality and reducing pressure drops to optimal levels for accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high-flow tubular bypass with many tiny capillary tubes is used, then high flow rates can be handled, but the pressure drop becomes too large and flow becomes non-linear at flow rates above 100-200 SLPM
Solution Approach 1:
The bypass is divided into multiple parallel capillary tube bundles instead of using one long bypass with many tiny tubes. This segmentation reduces the pressure drop while maintaining laminar flow and linear proportionality between sensor flow and main flow, enabling accurate measurements at high flow rates above 100-200 SLPM.
2Measurement precision
If the bypass length is increased to maintain laminar flow, then flow linearity is improved, but the pressure drop increases beyond optimal levels for thermal sensors
Solution Approach 1:
The bypass is segmented into multiple parallel capillary tube bundles, each with optimized length and diameter. This configuration maintains laminar flow and linear measurement characteristics while reducing the overall pressure drop to optimal levels for thermal sensor operation.
Solution Approach 2:
The capillary tube parameters (length, diameter, number of tubes) are optimized to achieve the desired balance between maintaining laminar flow for linear measurements and reducing pressure drop to optimal levels for thermal sensor operation.
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 ensures accurate and linear flow rate measurements across high flow rates, maintaining optimal operating conditions for thermal sensors and reducing pressure drops, ensuring reliable mass flow control.
Implementation Method 1
the flow of the gas through these capillary tubes is laminar, so that the pressure drop across the bypass 1110 is linearly proportional to the flow
Implementation Method 2
a thermal sensor 1130, that is used to measure a mass flow rate of a gas passing through the MFC 1100. The thermal sensor 1130 does this by measuring the flow rate through a sensor tube 1120
Data Source
AI summary
Mass flow meters and mass flow controllers that include mass flow meters are disclosed. A mass flow meter includes a main flow path for a gas, and a bypass with a length, L, within the main flow path. The bypass includes a continuous flow section including a plurality of continuous capillary tubes that each have a length, L. The bypass also includes n flow segments forming n−1 spaces within the bypass where n is greater than or equal to 2, and each of the flow segments has a plurality of capillary tubes. The mass flow meter also includes at least one thermal sensor including a sensor tube, and the sensor tube is positioned across at least one of the flow segments to divert a portion of the gas around the at least one of the flow segments and provide a measured flow signal in response to the diverted portion of the gas.