Inline Virtual Impactor Flow Accelerator for Aerosol Separation
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Solution Overview
Problem
Conventional aerosol sampling systems face challenges in efficiently separating coarse and fine particles, particularly due to issues with particle rebound, re-entrainment, and maintenance requirements in inertial impactors, and the complexity of virtual impactor geometry makes alignment and performance inconsistent.
Innovation Solution
An inline virtual impactor design featuring a flow accelerator and stabilizer member within a cylindrical housing, creating an annular flow passage, and an aspiration section to separate aerosol particles into minor and major flows based on size, with adjustable cutpoint Stokes number and flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oil or grease is applied to the collection surface of a real impactor to retain large particles, then large particle retention improves, but fine particle loss increases due to fibrous particles causing inadvertent collection
Solution Approach 1:
The patent extracts the harmful interaction between fibrous particles and the oiled surface by eliminating the collection surface entirely. Instead of collecting particles on a surface, the virtual impactor uses a slot through which particles pass, removing the source of fine particle contamination while maintaining large particle separation through inertial effects in the flow path.
Solution Approach 2:
The patent introduces an intermediary fluid stream (the gas flow through the slot) that mediates particle separation without requiring direct contact between particles and a collection surface. The gas flow carries separated particles away, preventing the fibrous particle contamination issue while maintaining separation efficiency.
2Reliability
If conventional virtual impactor geometry is used with complex alignment requirements, then particle separation can be achieved, but device complexity and alignment difficulty increase
Solution Approach 1:
The flow accelerator member serves multiple functions simultaneously: it accelerates the gas stream, defines the slot geometry, and acts as one of the separating surfaces. This multi-functionality reduces the number of separate components and simplifies alignment requirements compared to conventional virtual impactors that require precise positioning of separate acceleration and collection elements.
Solution Approach 2:
The patent merges the flow accelerator and flow stabilizer members into a single integrated structure with the slot formed between them. This combination simplifies the overall geometry and reduces alignment complexity while maintaining the necessary flow characteristics for effective particle separation.
3Productivity
If real impactors are used for pre-separation, then large particle removal is effective, but maintenance frequency increases due to dust accumulation and particle rebound
Solution Approach 1:
The virtual impactor design allows the slot to self-clean by maintaining gas flow through it, preventing dust accumulation that would otherwise require manual cleaning. The continuous flow regime prevents particles from adhering to the slot surfaces, eliminating the maintenance issues associated with real impactor collection surfaces.
Solution Approach 2:
The patent uses pneumatic flow through the slot to achieve particle separation without mechanical contact or collection surfaces. The gas flow dynamically clears particles from the separation region, eliminating the need for mechanical cleaning mechanisms and reducing maintenance requirements compared to real impactors.
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 inline virtual impactor effectively minimizes large particle carryover, reduces maintenance needs, and achieves stable flow separation with improved alignment, enhancing the efficiency of aerosol sampling and powder processing by producing a zero-defect fine fraction.
Implementation Method 1
a flow accelerator member disposed in an upstream portion of the outer housing... creates an annular flow passage between the flow accelerator and the outer housing
Implementation Method 2
the principle of operation for inertial impactors is that an aerosol stream is accelerated in a nozzle and impinges upon a collection surface... Particles in the aerosol stream having sufficiently high inertia will impact upon the collection surface while the other particles will follow the airflow out of the impaction region
Data Source
AI summary
An inline virtual impactor comprising an outer housing having a housing inlet, a housing inner surface, a major flow outlet and a minor flow outlet; a flow accelerator member disposed in the upstream portion of the outer housing; and a flow stabilizer member disposed within the outer housing downstream of the flow accelerator member, wherein the disposition of the flow accelerator creates an annular flow passage between the flow accelerator and the outer housing, and wherein a flow divider that is at least partially downstream of the flow stabilizer member effects splitting of the flow stream entering the housing into major and minor flows. The minor flow comprises primarily particles having a size greater than a cutpoint size and the major flow comprises primarily particles smaller than the cutpoint size. The inline virtual impactor may further comprise an aspiration section located upstream of the flow accelerator member.