Composite Wick Design for Low Noise Particle Counting

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Solution Overview

Problem

Condensation particle counters (CPCs) experience high false-count rates, especially at increased sample flow rates, which is problematic for measuring low particle concentrations in cleanroom environments, as these false counts can be indistinguishable from real particle events and are not effectively reduced by existing technologies.

Innovation Solution

A composite wick design using multiple layers of porous materials, such as sintered plastic and Nytran ™< , is employed to manage the flow of working fluid and prevent the formation of noise particles, allowing for consistent ultra-low noise counts over extended periods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the sample flow rate is increased to improve measurement speed and productivity, then the productivity increases, but the false-count rate increases due to working fluid draining and bubble formation

Engineering Contradiction:

Improvesample flow rateVSAvoidfalse-count rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The wick is divided into multiple functional layers: a first porous material layer for primary fluid transport and a second porous material layer for fluid distribution and bubble suppression. This segmentation allows each layer to specialize in specific functions, enabling high flow rates while maintaining low false-count rates through coordinated operation of the layered structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The wick uses composite materials with different pore size distributions - a first porous material with larger pores for efficient fluid intake and a second porous material with smaller pores for controlled fluid release and bubble prevention. This composite structure enables the wick to handle high flow rates while suppressing the formation of noise particles that cause false counts

Inventive Principle:

Principle #40Composite materials

2Device complexity

If a single porous material wick is used to simplify the device structure, then the device complexity is reduced, but the false-count rate remains high due to inadequate fluid flow control

Engineering Contradiction:

Improvewick structureVSAvoidfalse-count rate

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the wick have different pore size distributions tailored to local requirements: the first porous material region has larger pores optimized for fluid intake from the reservoir, while the second porous material region has smaller pores optimized for controlled fluid release at the flow path interface, preventing bubble formation and droplet ejection

Inventive Principle:

Principle #3Local quality

3Object-affected harmful factors

If water-based working fluid is used to improve safety and environmental compatibility, then the harmful factors are reduced, but the false-count rate increases compared to alcohol-based fluids

Engineering Contradiction:

Improvetoxicity and environmental impactVSAvoidfalse-count rate

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The dual-layer porous wick structure is specifically optimized for water-based working fluids, using pore size distributions that leverage water's surface tension and capillary action characteristics to achieve stable fluid delivery without bubble formation, thereby enabling water-based CPCs to meet low false-count rate requirements

Inventive Principle:

Principle #31Porous materials

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 composite wick design significantly reduces false-particle counts to less than 0.02 counts per minute at 2.83 liters per minute, meeting stringent cleanroom requirements of less than six counts per hour, and maintains performance for over 30 days.

Implementation Method 1

A composite wick design using multiple layers of porous materials, such as sintered plastic and Nytran ™, is employed to manage the flow of working fluid

Methodology Applied

Scientific EffectCapillary action: Capillary Action

Implementation Method 2

The small particles are grown to a larger size by condensation, from a working fluid within the CPC, being formed on the particle

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentEP3532820B1Composite wicks for low noise particle counting

Publication Date: 2023.12.20 TSI INC

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AI summary

Various embodiments include composite wicks for ultra-low noise condensation particle counters (CPCs). In one embodiment, a composite wick includes a first porous material having a first pore density, with the first porous material further having a first surface and an opposing second surface. A second porous material is in fluid communication with the first porous material and has a first surface with an area substantially the same as an area of the first surface of the first porous material. The first surface of the second porous material is substantially in contact with the first surface of the first porous material. The second porous material has a pore density that is dissimilar the first pore density of the first material. The first material and the second material are configured to provide vapor from a liquid to a fluid-based particle counter. Other apparatuses are disclosed.