Flow Measurement Device Thermal Diffusivity Correction
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Solution Overview
Problem
Existing flow measurement devices inaccurately correct flow rates due to variations in thermal diffusivity of measurement target fluids, as they rely solely on thermal conductivity for correction.
Innovation Solution
A flow measurement device with a heater and temperature sensor arrangement that corrects flow rates based on temperature differences, accounting for thermal diffusivity, specific heat, and viscosity, using a characteristic value obtained from temperature changes to improve accuracy across different fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flow rate correction is performed using only thermal conductivity, then the correction process is simple, but measurement precision deteriorates for fluids with varying thermal diffusivities
Solution Approach 1:
The patent changes the correction parameter from solely thermal conductivity to a composite parameter incorporating thermal diffusivity (α = k/(ρ·cp)). This is achieved by measuring both the temperature difference ΔT between heater and sensor, and the temperature change rate dT/dt, then calculating thermal diffusivity using the relationship α = (ΔT/Δt)·(L²/ΔT), where L is the distance between heater and sensor. This parameter change enables accurate correction for different gas types while maintaining a relatively simple measurement mechanism.
Solution Approach 2:
The patent introduces thermal diffusivity as an intermediary parameter that mediates between the measurable quantities (temperature difference and temperature change rate) and the desired correction factor. By measuring the temperature change rate dT/dt as an intermediary, the system can derive thermal diffusivity without directly measuring it, enabling accurate flow rate correction across different fluids.
2Measurement precision
If temperature sensor is placed close to heater for accurate temperature sensing, then measurement precision improves, but the sensor is affected by harmful factors from the heater
Solution Approach 1:
The patent employs periodic heating by alternating the heater between heating and non-heating states. During the heating phase, the heater raises the fluid temperature; during the non-heating phase, the heater is turned off and the temperature naturally decreases. The temperature sensor measures temperature at specific phases (when heater is on and when it's off), allowing accurate temperature difference measurement without continuous thermal interference. This periodic action separates the measurement moments from the interference source.
Solution Approach 2:
The system performs preliminary temperature measurement during the non-heating phase before the heater is activated. This preliminary measurement establishes a baseline temperature that is not yet influenced by heater thermal interference. By having this preliminary reference, the system can accurately calculate temperature differences caused by heating while minimizing the impact of continuous thermal interference on the sensor.
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
Enhances the accuracy of flow rate measurements for fluids with varying thermal diffusivities by incorporating a correction mechanism that accounts for multiple physical properties, reducing errors and improving sensing precision.
Implementation Method 1
a heater for heating the measurement target fluid
Implementation Method 2
a temperature sensor for sensing a temperature of the measurement target fluid
Implementation Method 3
the thermal diffusivity of the measurement target fluid also affects the sensor output
Data Source
AI summary
A flow measurement device includes a flow sensor that senses a flow rate of a measurement target fluid flowing through a main channel, a characteristic-value obtaining unit that includes a heater heating the target fluid and a temperature sensor sensing a temperature of the target fluid, and obtains a characteristic value of the target fluid, and a flow rate correction unit that corrects a flow rate of the target fluid calculated based on a sensing signal from the flow sensor using the characteristic value of the target fluid obtained by the characteristic-value obtaining unit. The heater and the temperature sensor are arranged parallel to each other in a direction orthogonal to a flow direction of the target fluid. The characteristic-value obtaining unit obtains the characteristic value based on a difference between the temperatures of the target fluid sensed by the temperature sensor before and after the heater temperature is changed.