Nozzle-Baffle Converter Surface Roughness to Prevent Sticking
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Solution Overview
Problem
Electro-pneumatic converters based on the nozzle/baffle plate principle face dynamic controllability issues at output pressures close to the initial pressure due to Bernoulli effects, which cause the baffle plate to stick to the nozzle, leading to hysteresis-influenced characteristic curves and unreliable control.
Innovation Solution
An adjustable electro-pneumatic converter is designed with a baffle plate and nozzle edge surface roughness that promotes turbulent airflow when the nozzle is closed, using a proportionality factor between the nozzle edge width and surface roughness depths to prevent laminar flow and counteract Bernoulli forces, ensuring dynamic control even at high output pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the baffle plate is designed to completely close the nozzle aperture, then the output pressure can reach the full initial pressure value, but the baffle plate sticks to the nozzle due to Bernoulli effects causing negative pressure and laminar flow
Solution Approach 1:
The invention applies different surface qualities to different components: the baffle plate is given a smooth surface (Rz ≤ 1.6 μm) while the nozzle aperture edge is given a rough surface (Rz ≥ 1.6 μm). This local differentiation of surface quality prevents laminar flow and Bernoulli effects at the critical interface where the baffle plate meets the nozzle edge, eliminating sticking while maintaining control reliability.
Solution Approach 2:
The invention changes the surface roughness parameter of the nozzle aperture edge to Rz ≥ 1.6 μm, which fundamentally alters the airflow characteristics from laminar to turbulent. This parameter change disrupts the negative pressure generation mechanism of Bernoulli effects, preventing the baffle plate from sticking to the nozzle while allowing the system to maintain reliable control.
2Manufacturing precision
If the baffle plate and nozzle surface have very low surface roughness for tight closing, then the system achieves good tightness, but laminar flow occurs causing Bernoulli effects and baffle plate sticking
Solution Approach 1:
The invention applies different surface qualities to different components: the baffle plate is given a smooth surface (Rz ≤ 1.6 μm) while the nozzle aperture edge is given a rough surface (Rz ≥ 1.6 μm). This local differentiation of surface quality prevents laminar flow and Bernoulli effects at the critical interface where the baffle plate meets the nozzle edge, eliminating sticking while maintaining control reliability.
Solution Approach 2:
The invention converts the potentially harmful rough surface (which would normally prevent tight closing) into a beneficial feature by applying roughness specifically to the nozzle aperture edge. This localized roughness disrupts laminar flow and eliminates Bernoulli effects, transforming what would be a defect into a solution that prevents sticking while the baffle plate's smooth surface ensures adequate sealing.
3Ease of operation
If the baffle plate is kept away from the nozzle to avoid sticking, then dynamic controllability improves, but the system loses tightness and cannot achieve full output pressure
Solution Approach 1:
The invention applies different surface qualities to different components: the baffle plate is given a smooth surface (Rz ≤ 1.6 μm) while the nozzle aperture edge is given a rough surface (Rz ≥ 1.6 μm). This local differentiation of surface quality prevents laminar flow and Bernoulli effects at the critical interface where the baffle plate meets the nozzle edge, eliminating sticking while maintaining control reliability.
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 effectively reduces Bernoulli forces, preventing the baffle plate from sticking to the nozzle, allowing for reliable and dynamic control of output pressure, especially at pressures near the initial pressure, by ensuring turbulent airflow and maintaining system tightness.
Implementation Method 1
a baffle plate is moved by means of an electromagnetic transducer system
Implementation Method 2
The system is supplied with a constant initial pressure Pv via a restrictor
Implementation Method 3
The output pressure can be adjusted by adjusting the baffle plate and thus controlling the air flow through the exhaust nozzle
Implementation Method 4
The baffle plate and the nozzle edge surface are designed so that the air flows turbulently between them when the nozzle aperture is closed by the baffle plate to a gap less than 30 μm wide
Implementation Method 5
Bernoulli effects occur with such electro-pneumatic converters: The fast and essentially laminar flowing air, which escapes between the nozzle and the baffle plate, leads to a negative pressure and thus, due to the force resulting from the negative pressure, potentially to the baffle plate sticking to the nozzle
Data Source
AI summary
An adjustable electro-pneumatic converter or transducer based on the nozzle/baffle plate principle is proposed. A defined roughness (Rz) of the baffle plate surface can prevent the occurrence of Bernoulli forces at output pressures close to the initial pressure, i.e. when the exhaust nozzle (140) is almost completely closed by the baffle plate (100). The system thus becomes more dynamically controllable under these conditions. Such a converter can be used to control any consumer system, e.g. air power amplifiers for electro-pneumatic positioners.