Thermal Mass Flow Meter for CO2 Concentration Monitoring
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Solution Overview
Problem
Current thermal mass flow meters lack an efficient method to determine the concentration of specific components in fluid samples without prior knowledge of the fluid's physicochemical characteristics, particularly for gases like CO2 in exhaled breath.
Innovation Solution
A device utilizing thermal mass flow meters measures the thermal conductivity of both a target fluid and a reference fluid with known composition, calculating the component concentration based on temperature differentials and flow rates, which enables continuous monitoring of CO2 levels in exhaled breath using a microfluid system with low production costs and efficient power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal mass flow meters are used to measure total mass flow rate based on heat transfer from a heated surface, then the measurement of fluid flow is achieved, but the determination of specific component concentration without prior knowledge of physicochemical characteristics is not possible
Solution Approach 1:
The patent segments the measurement process into two independent parallel channels: one for reference fluid with known composition and one for target fluid with unknown composition. Each channel has its own thermal mass flow meter, allowing independent measurement of thermal conductivity values. This segmentation enables the system to determine component concentration by comparing the target fluid measurement against the reference fluid measurement, eliminating the need for prior knowledge of the target fluid's physicochemical characteristics.
Solution Approach 2:
The reference fluid acts as an intermediary with known thermal conductivity and known component concentration. By introducing this intermediary substance through a dedicated reference channel, the system can indirectly determine the component concentration in the target fluid through comparison. The reference fluid mediates the measurement process, allowing the thermal mass flow meter to derive concentration information without requiring direct knowledge of the target fluid's properties.
2Measurement precision
If thermal conductivity measurements are performed on both reference and target fluids to determine component concentration, then accurate concentration monitoring is achieved, but the device complexity and production cost increase
Solution Approach 1:
The thermal mass flow meter is designed with multi-functionality, serving both as a flow rate measurement device and as a thermal conductivity measurement device. By measuring the thermal conductivity of both reference and target fluids through the same type of sensor, the system achieves accurate component concentration monitoring without requiring additional specialized equipment. This universal approach reduces production costs while maintaining measurement precision.
3Productivity
If continuous monitoring of CO2 concentration in exhaled breath is implemented using thermal mass flow meters, then real-time respiratory status evaluation is achieved, but energy consumption increases
Solution Approach 1:
The system performs preliminary calibration by measuring the thermal conductivity of reference fluid with known composition before or during target fluid measurement. This preliminary action establishes a reference thermal conductivity value that can be used for continuous monitoring of target fluid without requiring continuous recalibration. The pump system is designed to switch between reference and target channels efficiently, reducing energy consumption while maintaining continuous monitoring capability for respiratory status evaluation.
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 approach allows for accurate and continuous monitoring of CO2 concentration in exhaled breath, providing efficient evaluation of respiratory status with low production and operational costs, leveraging the linear correlation between thermal conductivity and component concentration.
Implementation Method 1
Thermal mass flow meters measure the total mass flow rate of the fluid based on heat transferred via convection from a heated surface to the fluid. The heat is transferred to a boundary layer of the fluid as the fluid flows over the heated surface.
Implementation Method 2
As different fluids have different thermal conductivities, the convective heat transfer differs between different fluids. For example, the thermal conductivity of ambient air at 25 degrees Celsius is 0.024 Watts per meter-Kelvin (W/[m * K]), whereas the thermal conductivity of CO2 at 25 degrees Celsius is 0.0146 W/(m * K).
Data Source
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AI summary
A device for measuring a concentration of a component in a target sample includes a flow chamber with a first channel that receives a reference sample having a known concentration of the component. The flow chamber also includes a second channel that receives the target sample having an unknown concentration of the component. A pump operates to pump the reference sample and the target sample at a same volume flow rate through the first and second channels, respectively. A thermal mass flow meter measures a thermal conductivity of the reference sample, a thermal conductivity of the target sample, or both.