Miniature Differential Pressure Flow Sensor for Cryogenic Environments
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Solution Overview
Problem
Conventional Pitot tubes used for measuring fluid flow velocity are not miniaturized, leading to issues with robustness, sensitivity, and frequency response, especially in extreme conditions and cryogenic applications, where they are prone to damage and have limited ability to measure fast velocity variations due to dead volume and small diaphragm area.
Innovation Solution
A miniature fluid flow velocity sensor utilizing a stack with a pressure-sensitive diaphragm extending to the tip, sealed cavities for differential pressure measurement, and a detector for capacitance or resistance variation, allowing increased diaphragm area without increasing invasiveness and minimizing dead volume for improved sensitivity and frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the diaphragm area is increased to improve sensitivity, then the sensitivity is improved, but the diameter of the outer tube increases and the dead volume increases, limiting the frequency response
Solution Approach 1:
The patent transitions from a conventional lateral diaphragm arrangement to a longitudinal diaphragm arrangement that extends along the flow direction. This dimensional reorientation allows the diaphragm area to be increased without increasing the outer tube diameter, as the diaphragm now utilizes the length dimension rather than the radial dimension. The diaphragm extends from the tip region toward the base of the probe, maximizing area while maintaining a compact cylindrical profile that preserves frequency response characteristics.
Solution Approach 2:
The patent embeds the pressure-sensitive diaphragm within the probe structure such that it extends longitudinally inside the outer tube. The diaphragm is positioned and secured within the probe body, with its sensing surface exposed to the fluid flow through the tip opening. This nested arrangement allows the diaphragm to be integrated into the probe's internal volume, maximizing its area without increasing the external dimensions of the probe.
2Measurement precision
If the diaphragm is made very flexible to achieve reasonable sensitivity, then the sensitivity is improved, but the diaphragm may break in extreme conditions, especially for large flow velocity or upon cryogenic cool-down
Solution Approach 1:
The patent specifies that the diaphragm be made from elastomeric material with carefully controlled durometer hardness between 20 and 40 Shore A. This parameter optimization balances flexibility for pressure sensitivity with sufficient mechanical strength for robustness. The patent also specifies gauge thickness between 0.002 and 0.006 inches, creating an optimal thickness range that provides adequate flexibility while preventing breakage under extreme conditions.
Solution Approach 2:
The patent employs composite construction by bonding the elastomeric diaphragm to rigid support structures (such as metallic or ceramic rings) at its edges. This composite approach combines the flexibility and pressure sensitivity of the elastomeric material with the mechanical strength and dimensional stability of the rigid support, creating a diaphragm assembly that is both sensitive and robust against extreme conditions.
3Measurement precision
If the probe is miniaturized to measure superfluid turbulence, then the measurement capability for microscopic length scale is improved, but the robustness decreases and the probe is prone to damage
Solution Approach 1:
The patent applies different material properties and structural characteristics to different regions of the probe. The diaphragm region uses soft, flexible elastomeric material for pressure sensitivity, while the outer tube and support structures use rigid, strength-oriented materials. The tip region is minimized for measurement precision, while the body portion provides mechanical strength. This local differentiation allows the probe to be miniaturized for measuring superfluid turbulence while maintaining robustness through strategically placed structural reinforcement.
Solution Approach 2:
The patent specifies optimized parameter ranges for miniaturized construction: outer tube diameter of 0.5-3.0 mm, diaphragm thickness of 0.002-0.006 inches, and durometer hardness of 20-40 Shore A. These parameter changes enable the probe to achieve the small dimensions needed for superfluid turbulence measurement while maintaining sufficient mechanical strength and pressure sensitivity through carefully controlled material and geometric parameters.
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 sensor provides enhanced sensitivity and frequency response, protecting the diaphragm from transient overpressures while maintaining sensitivity to small pressure changes, enabling accurate measurement of fluid flow velocity and turbulence, particularly in cryogenic environments.
Implementation Method 1
a detector configured to measure a parameter representative of the differential pressure between the first and the second cavities
Implementation Method 2
The first cavity is entirely sealed, except at the tip of the stack, so as to be under a stagnation pressure during operation of the fluid flow velocity sensor, and wherein the second cavity is opened so as to be under a reference pressure
Data Source
Figure 1~2B
Figure 3~4
Figure 5~6
AI summary
The invention relates to a fluid flow velocity sensor using a differential pressure measurement and comprising a stack (200) having a tip (230) pointing in a first direction, said stack comprising first and second plates (210A-210B) arranged in parallel one another along the first direction; and a pressure-sensitive diaphragm (220) arranged between the first and second plates (210A-210B) along the first direction, said pressure-sensitive diaphragm (220) being spaced apart from the first plate (210A) by a first cavity and from the second plate (210B) by a second cavity, wherein the first cavity is entirely sealed, except at the tip (230) of the stack, so as to be under a stagnation pressure during operation of the fluid flow velocity sensor, and wherein the second cavity is opened so as to be under a reference pressure during operation of the fluid flow velocity sensor. The fluid flow velocity sensor further comprises a detector configured to measure a parameter representative of the differential pressure between the first and the second cavities.