Temperature Insensitive Mass Flow Controller with Heat Sink
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Solution Overview
Problem
Mass flow controllers with thermal flow sensors experience inaccurate readings due to temperature changes in gases or gas mixtures, leading to undesired reactions.
Innovation Solution
A mass flow controller design incorporating a capillary tube with a heat sink and thermal sensing element, where the heat sink is used to control the temperature of the gas flowing through the capillary tube, maintaining it at a stable temperature to prevent unwanted reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gas temperature is increased to improve mass flow rate measurement, then the thermal flow sensor becomes more sensitive, but the gas may undergo undesired reactions leading to inaccurate readings
Solution Approach 1:
The flow line is divided into multiple sections: a first flow line section where temperature is controlled to prevent reactions, and a second flow line section where the gas is heated for measurement. This segmentation allows different temperature conditions in different zones to simultaneously prevent harmful reactions and enable accurate measurement.
Solution Approach 2:
A bypass flow line is introduced as an intermediary path that allows a portion of the gas to bypass the heated measurement section. This intermediary bypass line prevents the entire gas flow from being exposed to high temperatures, thereby preventing undesired reactions while still allowing measurement of the main flow.
2Reliability
If a bypass is introduced to control gas temperature, then temperature sensitivity is reduced, but device complexity increases
Solution Approach 1:
The bypass flow line is merged with the main flow line at the outlet end, creating an integrated system where the controlled temperature flow and the measurement flow combine. This merging approach reduces the need for separate independent systems while maintaining temperature control functionality.
Solution Approach 2:
The bypass flow line serves multiple functions: it acts as a temperature control mechanism, provides a reference flow path, and enables the thermal flow sensor to operate at optimal temperature without exposing the entire gas supply to high temperatures. This multi-functionality reduces the need for additional dedicated components.
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 stabilizes gas temperature, reducing inaccuracies in mass flow rate readings and preventing undesired reactions, allowing for precise control of gases like B2H6, which would otherwise react at higher temperatures.
Implementation Method 1
a first heat sink internal to the housing in one embodiment that is coupled to the capillary tube, with the first heat sink being adapted to control the temperature of the gas in the capillary tube
Implementation Method 2
A thermal sensing element is coupled to the capillary tube
Data Source
AI summary
A temperature insensitive mass flow controller comprising a main flow line, a capillary tube coupled to the main flow line across a bypass a thermal sensing element coupled to the capillary tube and a mass flow controller housing adapted to at least cover the capillary tube. A first heat sink has been coupled to the mass flow controller internal to the mass flow controller housing and coupled to the capillary tube. The heat sink being adapted to control a temperature of a gas in the capillary tube.