Thermal Anemometer Flow Meter Liquid Droplet Error Correction
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Solution Overview
Problem
Thermal anemometer type flow meters are sensitive to liquid in gas streams, leading to inaccurate measurements due to liquid contacting the sensor probes, which causes cooling or vaporization, resulting in high readings and errors in vapor and liquid mass flow calculations, especially in wet gas flows.
Innovation Solution
Operating thermal anemometer probes at different DeltaT temperatures, with a high DeltaT probe reducing the effect of liquid droplets and allowing for accurate measurement of vapor mass flow, and using dual DeltaT sensors to correct for errors by calculating heat loss components from both probes, enabling accurate determination of vapor and liquid mass flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If thermal anemometer probes are used to measure gas flow, then measurement accuracy and response speed are improved, but measurement precision deteriorates when liquid droplets are present in the gas stream
Solution Approach 1:
The measurement system is segmented into multiple probes operating at different DeltaT levels. Instead of using a single probe that is overly sensitive to liquid droplets, the system divides the measurement function across multiple probes with different temperature differentials, allowing the overall system to achieve both speed and precision by combining results from high-speed but less-accurate probes and high-accuracy but slower probes.
Solution Approach 2:
The system changes the operating parameter (DeltaT) of the thermal anemometer probes to different values simultaneously. By operating probes at multiple DeltaT levels (e.g., high DeltaT for reduced liquid sensitivity, low DeltaT for high sensitivity), the system can measure both vapor mass flow accurately and maintain fast response, resolving the contradiction between speed and precision through parameter variation.
2Measurement precision
If thermal anemometer probes operate at high DeltaT to reduce liquid droplet effect, then measurement precision improves, but the ability to detect liquid mass flow deteriorates
Solution Approach 1:
The measurement function is segmented between multiple probes with different DeltaT settings. Some probes operate at high DeltaT to measure vapor mass flow accurately with reduced liquid interference, while other probes operate at low DeltaT to detect liquid mass flow. The system then combines these segmented measurements to obtain both vapor and liquid mass flow information simultaneously.
Solution Approach 2:
The multi-probe system achieves multi-functionality by enabling simultaneous measurement of both vapor mass flow and liquid mass flow using the same sensor array. The high DeltaT probes provide vapor flow measurement capability while the low DeltaT probes provide liquid flow detection capability, making the overall system universal for measuring both phases without requiring separate measurement systems.
3Adaptability or versatility
If liquid droplets contact the sensor probes, then the sensor responds to the liquid, but measurement precision deteriorates due to cooling and vaporization effects
Solution Approach 1:
The system changes the temperature differential parameter of the probes to mitigate liquid droplet interference. By operating at high DeltaT, the probes are less susceptible to cooling and vaporization effects from liquid droplets, maintaining measurement precision. The system accepts that liquid response varies with DeltaT but uses this parameter control to achieve accurate vapor flow measurement despite liquid presence.
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 significantly reduces measurement errors caused by liquid presence, allowing for precise characterization of wet gas flows, including vapor and liquid mass flows, and steam quality, with high accuracy and reliability.
Implementation Method 1
a probe or element is heated above the stream temperature and the heat loss from the heated element is monitored by following some property of the heated element and correlating this property with the stream velocity
Implementation Method 2
any liquid contacting the sensor probes will cause a high reading due to the cooling of the anemometer by thermal conduction to the liquid
Implementation Method 3
cooling of the anemometer by thermal conduction to the liquid or vaporization of the liquid as it impacts the surface of the heated portion
Data Source
AI summary
A method is provided to operate a thermal anemometer flow meter to measure a property of a stream. The method includes measuring a first heat loss to the stream from operating at a first DeltaT above a temperature of the stream, measuring a second heat loss to the stream from operating at a second DeltaT above the temperature of the stream where the second DeltaT being greater than the first DeltaT. The method further includes determining the property of the stream based on the first and the second heat losses.