U-Shaped Mass Flow Sensor Layout for Zero Point Stability
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Solution Overview
Problem
Mass flow meters and controllers experience zero point fluctuations due to thermal siphoning phenomena when fluid flows vertically, especially in miniaturized systems where increasing tube length or adding heaters is challenging, leading to accuracy issues.
Innovation Solution
A mass flow sensor with a U-shaped flow path and thermal resistors wound around straight portions, along with a heat dissipating portion made of high thermal conductivity material, is used to stabilize temperature distribution and reduce zero point fluctuations by balancing heat dissipation across the sensor elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tube length of the sensor tube is increased to suppress thermal siphoning phenomenon, then zero point stability is improved, but device size increases which conflicts with miniaturization requirements
Solution Approach 1:
The invention applies local quality by introducing a heat dissipating portion with high thermal conductivity material specifically at the position where thermal siphoning occurs (near the sensor elements), rather than uniformly increasing the entire tube length. This localized heat dissipation structure suppresses thermal siphoning phenomenon and stabilizes zero point without requiring overall device enlargement, thus resolving the contradiction between reliability and device size.
2Reliability
If a heater is added to prevent thermal siphoning phenomenon, then zero point stability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The invention merges the heat dissipating function directly into the existing sensor tube structure by providing a heat dissipating portion made of high thermal conductivity material in contact with the sensor tube. This integrated approach eliminates the need for separate heater components while achieving thermal siphoning suppression, thus improving zero point stability without increasing device complexity or manufacturing difficulty.
3Reliability
If the U-shaped opening is arranged horizontally to suppress thermal siphoning, then zero point stability is improved, but heat balance between sensor elements deteriorates due to heat dissipation by the main body block
Solution Approach 1:
The invention applies asymmetry by strategically positioning the heat dissipating portion on only one side of the sensor tube (the side opposite to the second thermal resistor). This asymmetric heat dissipation configuration compensates for the heat loss to the main body block, restoring the heat balance between the two sensor elements while maintaining the horizontal U-shaped opening arrangement that suppresses thermal siphoning phenomenon.
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
The solution effectively reduces zero point fluctuations, ensuring accurate flow rate measurements even in vertical fluid flow configurations by maintaining heat balance and preventing temperature differences between sensor elements.
Implementation Method 1
a first thermal resistor wound around any one of the straight portions, a second thermal resistor wound around the straight portion around which the first thermal resistor is wound
Implementation Method 2
a heat dissipating portion provided so as to be in contact with the flow path tube on the side opposite to the second thermal resistor across the first thermal resistor
Implementation Method 3
the fluid heated by the sensor element rises in the sensor pipe, joins the main flow path (so-called bypass portion), the fluid cooled in the main flow path drops, and flows back into the sensor pipe
Data Source
AI summary
A mass flow sensor is provided with reduced zero point fluctuation, and a mass flow meter and a mass flow controller using the mass flow sensor, the mass flow sensor comprising a U-shaped flow path passage in which a fluid flows from first end to a second end, having a bottom portion and two straight portions connecting the bottom portion to the ends, a first thermal resistor wound around one of the straight portions, a second thermal resistor wound around the same straight portion as the first thermal resistor and provided away from the first thermal resistor toward the second end, and a heat dissipating portion provided so as to be in contact with the flow path passage on the side opposite to the second thermal resistor across the first thermal resistor.