Thermal Mass Flowmeter Sensor Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional thermal mass flowmeters face challenges with low Signal-to-Noise Ratio (S/N) and poor thermal response due to the use of diode units with epoxy resin structures, which measure unintended temperature changes and have delayed thermal responses.
Innovation Solution
A thermal mass flowmeter design featuring separate temperature-sensing units and a heating unit on the outer peripheral surface of a capillary tube, utilizing thermistors or resistance temperature sensors with protective resins to enhance sensitivity and response, with the elements positioned closer to the capillary tube to reduce thermal resistance and noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diode units with epoxy resin structures are used for temperature sensing and heating, then the device structure is simplified and cost is reduced, but the Signal-to-Noise Ratio deteriorates and thermal response becomes delayed
Solution Approach 1:
The temperature-sensing unit and heating unit are separated into distinct components rather than being integrated in a single diode unit. This segmentation allows each component to be optimized independently - the temperature-sensing unit uses a thermistor with protective resin positioned close to the capillary tube for high S/N ratio, while the heating unit uses a resistive element positioned for effective heating, eliminating the compromise required by integrated diode units.
Solution Approach 2:
The protective resin is strategically positioned to cover only the necessary portions of the temperature-sensing element and heating element, with the resin thickness and coverage optimized locally. The temperature-sensing element is positioned with minimal resin coverage near the capillary tube to maximize thermal coupling and S/N ratio, while the heating element has sufficient resin coverage for protection without excessive thermal mass.
2Ease of manufacture
If diode units with epoxy resin structures are used for temperature sensing and heating, then the device structure is simplified and cost is reduced, but the thermal response speed deteriorates
Solution Approach 1:
Separating the temperature-sensing unit from the heating unit eliminates the thermal mass and thermal coupling issues of integrated diode units. The temperature-sensing unit can be positioned with minimal protective resin directly on the capillary tube, reducing thermal resistance and enabling faster response to temperature changes in the flowing fluid.
Solution Approach 2:
The thermal response speed is improved by changing the physical parameters of the protective resin layer - reducing its thickness and optimizing its thermal conductivity. The resin is applied only where necessary for protection, creating a thin thermal barrier that allows rapid heat transfer between the capillary tube and the temperature-sensing element.
3Speed
If temperature-sensing units are positioned closer to the capillary tube to reduce thermal resistance, then thermal response improves, but unintended temperature changes from the heating unit increase noise
Solution Approach 1:
The temperature-sensing unit and heating unit are positioned as separate components along the capillary tube rather than being co-located. This spatial segmentation allows the temperature-sensing unit to be positioned close to the capillary tube for fast response while being sufficiently distant from the heating unit to minimize exposure to its thermal field, thereby reducing noise from unintended temperature changes.
Solution Approach 2:
The asymmetric positioning of the temperature-sensing unit and heating unit along the capillary tube creates an optimized thermal measurement configuration. The temperature-sensing unit is positioned upstream or downstream at a distance that balances thermal response speed with noise reduction, while the heating unit is positioned to provide effective heating without directly heating the temperature-sensing element.
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 design achieves a higher S/N ratio and improved thermal response by minimizing unintended temperature changes and enhancing the sensitivity to fluid temperature changes, leading to more accurate flow rate measurements.
Implementation Method 1
a heating unit 12 is disposed in contact with an outer peripheral surface of the capillary tube 11... locally heating the fluid in the capillary tube 11 up to a given temperature by the heating unit 12
Implementation Method 2
each of the upstream-side and downstream-side temperature-sensing units includes a thermistor or a resistance temperature sensor which serves as a temperature-sensing element
Implementation Method 3
a thermistor or a resistance temperature sensor which serves as a temperature-sensing element
Implementation Method 4
When the fluid starts flowing through the capillary tube 11, the surface temperature distribution profile of the capillary tube 11 is displaced toward the downstream side in its entirety
Data Source
AI summary
Disclosed is a thermal mass flowmeter, which comprises a heating unit disposed on an outer peripheral surface of a capillary tube, and a pair of temperature-sensing units each provided as a separate component from said heating unit. The temperature-sensing units are disposed on the outer peripheral surface of the capillary tube at respective positions equally distant from the heating unit toward an upstream side and a downstream side of the capillary tube. Each of the temperature-sensing units has a structure in which a temperature-sensing element is covered by a protective resin molded around the temperature-sensing element. The temperature-sensing element consists of a thermistor or a resistance temperature sensor. The temperature-sensing element is disposed to be displaced to a contact surface of the molded resin with the capillary tube relative to a center of the molded resin.