MEMS Thermal Time-of-Flight Gas Meter for Accurate Mass Flow
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Solution Overview
Problem
Current gas metering technologies for natural gas are limited by their mechanical measurement principles, which are sensitive to temperature and pressure changes, and lack precision in measuring thermal values, leading to revenue losses and inaccurate tariffs, especially when dealing with varying gas compositions.
Innovation Solution
A utility gas meter utilizing MEMS thermal time-of-flight sensors with dual sensing elements for in-situ measurement of volumetric flowrate and heat value, capable of compensating for temperature and pressure variations, and equipped with a MEMS gas composition sensor for accurate gas composition analysis, enabling gas composition independent mass flow and thermal property measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical metering technologies are used for natural gas measurement, then the metering system is simple and cost-effective, but the measurement precision deteriorates due to sensitivity to temperature and pressure changes
Solution Approach 1:
The patent replaces mechanical metering technologies with thermal time-of-flight sensing technology. The microheater generates a temperature pulse that propagates through the gas flow, and temperature sensors detect the pulse arrival time. This thermal field-based measurement method eliminates the mechanical moving parts that are sensitive to temperature and pressure changes, providing accurate measurement of thermal conductivity and specific heat for calculating heating value.
Solution Approach 2:
The patent measures thermal conductivity and specific heat by generating temperature pulses and detecting their propagation characteristics through the gas flow. By measuring the time response and temperature distribution, the system calculates thermal properties that are then used to determine the heating value of natural gas. This parameter-based approach provides precision independent of traditional mechanical measurement limitations.
2Measurement precision
If volumetric metering is used for natural gas tariff calculation, then the metering system is simple, but the accuracy of tariff calculation deteriorates because actual consumption is thermal value not volume
Solution Approach 1:
The patent integrates multiple measurement functions into a single device: the microheater and temperature sensors simultaneously measure thermal conductivity and specific heat of the natural gas. These two thermal properties are then used to calculate the heating value (thermal content) of the gas. This multi-functional approach enables accurate thermal value measurement without requiring separate offline analysis equipment.
Solution Approach 2:
The system performs self-measurement of thermal properties directly at the metering location. The microheater generates temperature pulses that propagate through the flowing gas, and the temperature sensors detect the pulse characteristics. The controller automatically calculates thermal conductivity and specific heat from these measurements, enabling the device to determine its own measurement parameters without external intervention or complex offline analysis.
3Measurement precision
If offline gas analysis with complicated instrumentation is used to measure thermal values, then the measurement accuracy is high, but the device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the essential measurement function from complex offline gas analysis systems. Instead of using complicated instrumentation for offline thermal value measurement, the system incorporates a microheater and temperature sensors directly into the metering device. This extraction enables on-line measurement of thermal conductivity and specific heat, providing accurate thermal value data without the complexity and cost of traditional offline analysis equipment.
Solution Approach 2:
The patent uses a simplified thermal pulse propagation model to replicate the measurement capability of complex gas analysis systems. By measuring the time response and temperature distribution of a thermal pulse through the gas flow, the system calculates thermal conductivity and specific heat using established thermal diffusion equations. This copying approach achieves accurate thermal property measurement with a much simpler device configuration than traditional offline analysis instrumentation.
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 provides accurate, real-time measurement of gas thermal values and mass flowrate, independent of gas composition, ensuring fair tariffs and reducing revenue losses, while being compact and compatible with existing infrastructure for seamless installation and remote data transmission.
Implementation Method 1
a temperature pulse generated by the microheater will be disposed in and closely coupled to the fluid to be measured. By measurement of the time response of the temperature registered by the sensor elements
Implementation Method 2
the measured thermal conductivity and specific heat are not the same as the thermal values of natural gas... the time differences are measured between a microheater and sensors placed close-by at a micrometer scale
Implementation Method 3
Time lag approach for measuring fluid velocity... the time differences are measured between a microheater and sensors placed close-by at a micrometer scale. By comparing the thermal responses of the sensors and the time lag of the heat transfer from the microheater to the sensor
Implementation Method 4
Measurement of thermal conductivity and specific heat... both thermal conductivity and specific heat could be obtained... the measured gas thermal conductivity and specific heat can be converted to the HHV (high heat value) of natural gas
Data Source
AI summary
An electronic utility gas meter using MEMS thermal time-of-flight flow sensor to meter gas custody transfer mass flowrate and an additional MEMS gas sensor to measure the combustion gas composition for the correlations to the acquisition of gas high heat value simultaneously is disclosed in the present invention. The meter is designed for the applications in the city utility gas consumption in compliance with the current tariff while metering the true thermal value of the delivered gases for future upgrades. Data safety, remote data communication, and other features with state-of-the-art electronics are also included in the design.