Face Mask - CFD design 

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As part of the united front against Covid, the barrier protection of PPE equipment (face masks) was a supplementary requirement to protection: Covid changed that. 

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Face masks have been accepted as a primary mechanism to the protection and spread of covid through airborne particles. As part of a development project a highly conforming mask was designed to provide barrier protection, analyses were performed to determine the fluid flow using a multi-layered four ply mask of Melt blown and Spunbond Non-woven polypropylene. 

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The Surgical face masks so often used in society today have the following hazards:

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1. Poor fitment: the face masks are not congruent at the interface to the human form increasing the hazard of airborne particles. When viewing the general public and in extreme cases of persons in small of stature often the ear loops are twisted to hold the face mask in position this can be seen.

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2. Environmental Hazard: the single use surgical face masks cause an environmental hazard both with being single use and non-biodegradable. 

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A functional design analysis was performed to define the mask requirements and associated part compliance to function. This prime focus being:

1. Ensure congruency to the wearer

2. Drive all breath through the mask with as minimal pressure drop as reasonably practicable.

 

A CAD model was generated that controlled congruency through a pre-formed shape using a four-ply structure (Functional Design Face Mask). Each material layer was measured for its pressure drop as a function of flow rate at a temperature of 34°C (exhaled breath temp.) using a differential pressure analyser. These data were then input into a CFD model defining porous media. (See Porous Material Characteristics).

 

A fluid volume was then defined around the manakin head and an exhaust flow of 0.0005 cubic metres per sconed representing exhalation. The model was then optimised to meet the goal criteria and plots of flow trajectories and pressure drops drove the design optimisation process.