Gas Measurement Probe Shroud for Thermal Dispersion Accuracy
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Solution Overview
Problem
Existing gas flow measurement systems, particularly thermal flowmeters, face accuracy limitations at low and high velocities due to spurious heat losses and finite thermal resistance, respectively, and require additional components like laminar flow elements to extend measurement ranges.
Innovation Solution
A gas measurement system with a probe comprising a thermal dispersion type sensor and a reference thermistor disposed within a shroud, where the shroud controls gas flow past the sensors, mounted on an elongate member within a duct, and a microprocessor calculates and displays gas velocity and temperature, minimizing flow disturbances and enhancing accuracy across a broader range of velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal flowmeters are used for gas velocity measurement, then measurement capability is provided, but accuracy deteriorates at low velocities due to spurious heat losses and at high velocities due to finite thermal resistance
Solution Approach 1:
A shroud structure is introduced as an intermediary component between the thermal flowmeter sensors and the gas flow. The shroud with its rectangular entry area controls and conditions the gas flow before it reaches the sensors, reducing spurious heat losses and minimizing flow disturbances. This mediator enables accurate measurements across a broader velocity range by creating optimal flow conditions around the sensors.
Solution Approach 2:
The invention changes the physical parameters of the flow environment by introducing a shroud that modifies flow velocity distribution and thermal characteristics. The shroud creates a controlled flow regime with reduced turbulence and heat loss, effectively changing the operating parameters to extend the accurate measurement range from a narrow band to a broader velocity spectrum.
2Adaptability or versatility
If laminar flow elements are added to extend high velocity range, then measurement range is improved, but device complexity increases
Solution Approach 1:
The shroud structure serves multiple functions simultaneously: it controls gas flow distribution, reduces spurious heat losses, minimizes flow disturbances, and extends the measurement range. This multi-functional design achieves the capability previously requiring separate laminar flow elements without adding corresponding complexity, as the shroud integrates these functions into a single component.
3Ease of operation
If thermal dispersion sensors are positioned directly in gas flow, then measurement is enabled, but spurious heat losses increase at low velocities reducing accuracy
Solution Approach 1:
The shroud acts as a mediator between the thermal dispersion sensors and the gas flow. It conditions the flow to reduce spurious heat losses while maintaining sensor accessibility to the gas. The controlled flow regime created by the shroud ensures that heat transfer from the sensors is primarily due to convection from actual gas motion rather than parasitic heat loss mechanisms.
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 system provides accurate gas velocity and temperature measurements across a wider range of velocities by controlling gas flow through a shroud with a rectangular entry area, reducing spurious heat losses and thermal resistance limitations, thereby improving measurement accuracy and reliability.
Implementation Method 1
The rate of heat flow into the fluid from the sensor is directly proportional to the mass flow rate of the fluid
Implementation Method 2
A circuit senses the temperature response of the sensor as a function of the mass fluid flow rate
Data Source
AI summary
A gas measurement system comprising a probe (10), the probe (10) comprises a sensor circuit comprising a thermal dispersion sensor (23) and a reference thermistor (24), the thermal dispersion sensor and the reference thermistor are disposed within a shroud (20), the shroud partially enclosing the thermal dispersion sensor and the reference thermistor such that a gas flow through the shroud is substantially representative of the gas flow through a gas duct, the probe further comprises an elongate member (27) having an aerodynamic form, the shroud is mounted to the elongate member, the elongate member mountable within the gas duct, and a microprocessor for receiving a signal from the thermal dispersion sensor and the reference thermistor, the microprocessor calculating and displaying a gas velocity and gas temperature.