Spherical Bead Temperature Sensor for Turbulent Flow
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Solution Overview
Problem
Existing temperature measurement techniques in turbulent flow, such as cold-wire anemometers, face significant measurement errors due to end-conduction effects, which are exacerbated by the need to balance wire length and diameter to minimize spatial filtering, leading to reduced spatial resolution and increased errors in scalar dissipation estimates.
Innovation Solution
The design of cold-wire anemometers with specific dimensions and materials, utilizing a lumped parameter model to optimize heat transfer and minimize end-conduction effects, while maintaining temporal and spatial resolution, involves reducing the length of the sensing element and increasing the cross-sectional area of the prongs, and using materials like gold or platinum with high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wire length-to-diameter aspect ratio is made very large to reduce end-conduction effects, then measurement accuracy is improved, but spatial resolution is reduced
Solution Approach 1:
The patent changes the physical parameters of the sensing element by transitioning from a wire geometry to a spherical bead geometry. This fundamental parameter change allows the sensing element to achieve high measurement accuracy without requiring a large length-to-diameter ratio, thereby maintaining spatial resolution while reducing end-conduction effects.
Solution Approach 2:
The patent employs an extremely small spherical bead (sub-micron scale) as the sensing element, which can be considered a minimal, almost disposable structure. This tiny sensing element minimizes spatial filtering effects and maintains high spatial resolution while its small thermal mass enables fast response times.
2Length of moving object
If the wire length is reduced to improve spatial resolution, then spatial resolution is improved, but end-conduction effects increase
Solution Approach 1:
The patent fundamentally changes the geometric parameters from a wire configuration (with length and diameter) to a spherical bead configuration (characterized by diameter only). This parameter change eliminates the length-to-diameter ratio issue entirely, allowing the sensing element to be extremely small (high spatial resolution) while the spherical geometry minimizes end-conduction effects compared to a wire of equivalent size.
Solution Approach 2:
The patent uses composite material structures, particularly employing platinum or other noble metals for the spherical bead, often with core-shell configurations or layered structures. These composite material designs optimize both the thermal conductivity (to reduce end-conduction effects) and the thermal mass (to maintain fast response and high spatial resolution).
3Length of moving object
If the wire diameter is reduced to improve spatial resolution, then spatial resolution is improved, but the wire becomes more susceptible to end-conduction effects
Solution Approach 1:
The patent changes the dimensional parameters from a one-dimensional wire (with length and diameter) to a zero-dimensional spherical bead (characterized by a single diameter parameter). This allows the sensing element to achieve extremely small effective size for high spatial resolution while the spherical geometry inherently reduces end-conduction effects compared to a wire of the same diameter.
Solution Approach 2:
The patent applies local quality by creating a highly localized sensing region in the form of a small spherical bead that can be positioned precisely in the flow. The bead's small size provides high spatial resolution locally, while its spherical geometry and material composition are optimized to minimize end-conduction effects at that specific location.
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 results in a more accurate temperature measurement in turbulent flow by minimizing end-conduction effects and reducing low-frequency attenuation, allowing for improved spatial resolution and reduced measurement errors, with sensors capable of measuring a wide range of frequencies.
Implementation Method 1
A cold-wire typically consists of a wire filament designed to adapt to the ambient temperature with a resulting change of its resistance. The temperature of the fluid is generally related to the resistance of the wire through a static calibration method.
Implementation Method 2
the frequency response of a cold-wire is affected by the heat transfer from the sensing element or wire to the stubs, from the stubs to the prongs, and from the prongs to the probe body itself, a phenomenon known as end-conduction
Data Source
AI summary
In the present invention, a temperature sensor system and methods for using the apparatus are disclosed, the temperature sensor having particular thermal-inertia time constants. More specifically, the temperature sensor system comprises prongs having a defined l/d ratio range, a sensing element having a low volume, and constant-current circuitry.