Thermal Flow Meter Slope Effect Correction via Prandtl Number
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Solution Overview
Problem
Conventional thermal flow meters experience measurement errors due to the thermosiphon effect, which is influenced by the attitude and pressure of the flow rate control device, as well as thermophysical properties of the gas, making accurate correction difficult.
Innovation Solution
A thermal flow meter that includes an upstream-side and downstream-side electrical resistance element, a sensor output generator, a slope effect estimator based on the Prandtl number, and a flow rate calculator to correct the slope effect, allowing for precise estimation and correction of the thermosiphon-induced errors without hardware modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the flow rate control device is vertically disposed, then the gas flows in a vertical direction, but measurement errors occur due to the thermosiphon effect
Solution Approach 1:
The invention changes the parameter used for correction from simple attitude angle (gyro sensor data) to include the Prandtl number, which characterizes the thermophysical properties of the gas. By incorporating this dimensionless number that reflects the ratio of momentum diffusivity to thermal diffusivity, the system can accurately predict and correct thermosiphon effects under various mounting orientations and gas types.
Solution Approach 2:
The invention replaces the purely mechanical/physical correction approach (gyro sensor-based attitude detection) with a computational fluid dynamics-based correction method. Instead of relying solely on mechanical orientation sensing, the system uses calculated parameters (Prandtl number) and empirical correlations to model and correct the thermosiphon effect, achieving higher accuracy without additional hardware.
2Device complexity
If correction is performed based only on attitude detection, then the system is simple, but correction accuracy is insufficient due to neglecting pressure and thermophysical properties
Solution Approach 1:
The invention introduces the Prandtl number as a key parameter for correction, transforming the correction approach from geometry-only (attitude angles) to physics-based (thermophysical properties). The Prandtl number captures the essential thermal and viscous characteristics of the gas, enabling accurate prediction of thermosiphon convection patterns without complex hardware modifications.
Solution Approach 2:
The invention uses the Prandtl number as an intermediary parameter that bridges the gap between simple attitude detection and complex fluid dynamics. This dimensionless number serves as a mediator that encapsulates the thermophysical behavior of the gas, allowing the system to achieve high correction accuracy through computational methods rather than direct physical measurement of complex flow patterns.
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 solution enables accurate correction of measurement errors caused by the thermosiphon effect, improving the precision of flow rate measurements by accounting for pressure and thermal conductivity effects, thereby enhancing the accuracy of flow rate control.
Implementation Method 1
An upstream-side electrical resistance element and a downstream-side electrical resistance element are provided at a portion on this sensor flow path where the internal flow path inside the block body is oriented in substantially the same direction as the flow direction of the fluid
Implementation Method 2
the voltage differential applied to each electrical resistance element changes in accordance with the flow rate of the gas flowing through the sensor flow path
Implementation Method 3
due to what is known as a thermosiphon effect, the zero-point output from the thermal flow meter shifts in accordance with the mounting orientation and the pressure of the sealed gas
Implementation Method 4
a value other than zero is output because of the convection generated within the sensor flow path by this thermosiphon effect
Data Source
AI summary
The present invention provides a thermal flow meter that includes a sensor flow path along which flows a fluid being measured, an upstream-side electrical resistance element provided on the sensor flow path, a downstream-side electrical resistance element provided downstream of the upstream-side electrical resistance element, a sensor output generator that, based on respective voltages that are output in accordance with changes in the upstream-side and downstream-side electrical resistance elements, generates a sensor output in accordance with the flow rate of the fluid being measured, a slope effect estimator that, based on at least a Prandtl number of the fluid being measured, estimates a slope effect that is generated in the sensor output in accordance with an attitude of the sensor flow path, and a flow rate calculator that corrects the slope effect from the sensor output, and calculates the flow rate of the fluid being measured.