Prediction of the Impact of Fiber Polydispersity on Filter Efficiency

E P Prediction of the Impact of Fiber Polydispersity on Filter Efficiency David Vidal, Jean-Michel Tucny, François Drolet and François Bertrand URPEI – Dept. of Chemical Engineering - École Polytechnique de Montréal, C.P. 6079, succ. Centre-Ville, Montréal, Québec, H3C 3A7, Canada To better predict the capture efficiency and permeability of filters constituted of polydisperse fiber distributions, and thus design optimized high-performance air filters. VALIDATION ACKNOWLEDGMENTS CONCLUSIONS Contrary to classical theory, our simulations show that commercial standards can be reached by blending a relatively low amount of high performance (costly) fine fibres with coarser (cheaper) fibres. On the basis of these numerical results, we have devised a modified single-fibre theory, which is currently being evaluated with carefully designed experiments using model micro-sized glass fibers. Our modified single-fibre theory uses a semi-empirical parameter that takes into account the polydispersity of the fiber diameter distribution and is more appropriate than the equivalent diameter theory. Once validated, this new model could become a powerful design tool to determine the optimum fiber furnish for making high-performance filters. Air filtration consists in the removal of airborne particles by a porous (fibrous) filter through which the air is flowing. The air filtration market represents worldwide a multi- billion dollar market with an annual growth rate of around 5%. Today’s filtration market is driven by the need for products that deliver higher purity, greater efficiency and lower energy consumption at lower cost. HEPA filter N95 facemask AIR FILTRATION AND ITS MARKET FILTRATION THEORY OBJECTIVES METHODOLOGY 3-step numerical modelling 1. Create virtual filters using a stochastic deposition method 2. Compute air flow using lattice Boltzmann method Single-fibre theory Aerosol capture mechanisms (credit: LadyofHats) OPTIMIZING FILTERS P = + + ⇒ ,, ⇒ ,, , ⇒ ,, , =1− − 4(1−)ℎ Use finer fibers Use coarser fibers = −(1 − )/∆ : diameter of the fiber = eq for polydisperse cases : diameter of the aerosol : capture efficiency of the filter ℎ: thickness of the filter : permeability of the filter : volume fraction of coarse fibres : quality factor of the filter : coarse-to-fine fiber diameter ratio (bidisperse case) NOMENCLATURE 3. Calculate aerosol motion and capture by solving Langevin equation ⇒ and ℎ ⇒ Δ, ⇒ Fiber furnish Devise a correlation for predicting the quality factor : superficial air velocity P: pressure drop across the filter : capture efficiency of a single fibre : capture efficiency of a single fibre due to interception : capture efficiency of a single fibre due to Brownian diffusion : capture efficiency of a single fibre due to impaction : porosity of the filter RESULTS (CONT’D) 20 40 60 80 100 120 0.01 0.1 1 Model Prediction Experimental Result Comparison with single-fibre theory Comparison with experiments d p (m) Impaction, interception Brownian diffusion Hardwood, 90 g/m 2 , no pressing d p (m) Capture Efficiency (%) Capture Efficiency (%) ϕ = 87.4% d = 2 μm v f = 0.05 m/s h = 97 μm RESULTS d f = 1 μm v f = 0.05 m/s N95 standard Permeability & efficiency predictions for bidisperse filters Towards a modified single-fibre theory for polydisperse filters Virus Bacteria Bioactive agents, dust, etc… Previous model New model

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Poster presented at the 2015 Fiber Conference

Transcript of Prediction of the Impact of Fiber Polydispersity on Filter Efficiency

E P

Prediction of the Impact of Fiber Polydispersity on Filter Efficiency

David Vidal, Jean-Michel Tucny, François Drolet and François BertrandURPEI – Dept. of Chemical Engineering - École Polytechnique de Montréal, C.P. 6079, succ. Centre-Ville, Montréal, Québec, H3C 3A7, Canada

To better predict the capture efficiency and permeabilityof filters constituted of polydisperse fiber distributions, and thus design optimized high-performance air filters.

VALIDATION

ACKNOWLEDGMENTS

CONCLUSIONS

Contrary to classical theory, our simulations show thatcommercial standards can be reached by blending arelatively low amount of high performance (costly) finefibres with coarser (cheaper) fibres.

On the basis of these numerical results, we have deviseda modified single-fibre theory, which is currentlybeing evaluated with carefully designed experimentsusing model micro-sized glass fibers.

Our modified single-fibre theory uses a semi-empiricalparameter that takes into account the polydispersityof the fiber diameter distribution and is moreappropriate than the equivalent diameter theory.

Once validated, this new model could become apowerful design tool to determine the optimum fiberfurnish for making high-performance filters.

Air filtration consists in the removal of airborne particles by a porous (fibrous) filter through which the air is flowing.

The air filtration market represents worldwide a multi-billion dollar market with an annual growth rate of around 5%.

Today’s filtration market is driven by the need for products that deliver higher purity, greater efficiency and lower energy consumption at lower cost.

HEPAfilter

N95facemask

AIR FILTRATION AND ITS MARKET

FILTRATION THEORY

OBJECTIVES

METHODOLOGY

3-step numerical modelling

1. Create virtual filters using a stochastic deposition method

2. Compute air flow using lattice Boltzmann method

Single-fibre theory

Aerosol capture mechanisms

(credit: LadyofHats)

OPTIMIZING FILTERS

𝜂 = 𝜂𝐷 + 𝜂𝑅 + 𝜂𝐼

⇒ 𝜂𝑅 𝑑𝑝, 𝑑, 𝜙

⇒ 𝜂𝐼 𝑑𝑝, 𝑑, 𝑣𝑓 , 𝜙

⇒ 𝜂𝐷 𝑑𝑝, 𝑑, 𝑣𝑓 , 𝜙

𝐸 = 1 − 𝑒−4(1−𝜙)ℎ

𝜙 𝜋𝑑𝜂

Use finer fibers

Use coarser fibers

𝑄𝐹 = −𝑙𝑛(1 − 𝐸)/∆𝑃

𝑑: diameter of the fiber 𝑑 = 𝑑eq for

polydisperse cases𝑑𝑝: diameter of the aerosol

𝐸: capture efficiency of the filterℎ: thickness of the filter𝐾: permeability of the filter𝑚𝑐: volume fraction of coarse fibres𝑄𝐹: quality factor of the filter𝑅𝑐𝑓: coarse-to-fine fiber diameter ratio

(bidisperse case)

NOMENCLATURE

3. Calculate aerosol motionand capture by solving Langevinequation

⇒ 𝜙 and ℎ

⇒ Δ𝑃,𝐾

⇒ 𝐸

𝑄𝐹

Fiber furnish

Devise a correlation for predicting the quality factor

𝑣𝑓: superficial air velocity

P: pressure drop across the filter𝜂: capture efficiency of a single fibre𝜂𝑅: capture efficiency of a single fibre

due to interception𝜂𝐷: capture efficiency of a single fibre