environmentally conscious design & manufacturing (me592) date: march 27, 2000 slide:1...

Environmentally Conscious Design & Manufacturing (ME592)

Date: March 27, 2000 Slide:1

Environmentally Conscious Design & Manufacturing

Class 10: Air Quality 1

Prof. S. M. Pandit



Agenda

Air quality and manufacturing Definitions Standards set by EPA Aerosols

» Impact on health» Particle motion ?» Removal



ManufacturingProduct{Quality, Economics}

Environment{Solid / Liquid / Aerosols / Gases / Energy}

Integrated View

Material,Energy

Wastes (Material / Energy) Product

Air Quality and Manufacturing



Particulate matterexposures to particles smaller than those that were being regulated by EPA - lodge deeply in the lungs and - cause premature deaths and respiratory problems

EPA regulations in Manufacturing - Health

• Need for revision of 25 year old standards




Process 1 .. n

Aerosols and Dust

Manufacturing Facility

Aerosols / Dustto Environment

Aerosols / Dustsettling inside




Aerosols: Suspensions of solid or liquid particles in a gas (usually air).

• The particulate portion of an aerosol is referred to as Particulate Matter or PM.

• Particulate Matter is a generic term applied to chemically heterogeneous discrete liquid droplets or solid particles.

• The metric used for describing PM is the micron, or micrometer.

• The PM in an aerosol can range in size from 0.001 to greater than 100 microns in diameter.

Aerosols - Definitions



Particulates are generally categorized based on size:

• Coarse Particles are larger than 2 microns in diameter • Fine Particles are between 0.1 and 2 microns in

diameter • Ultrafine Particles are less than 0.1 micron

Most aerosol particles are polydisperse -- they have a wide range of particle sizes that must be characterized by statistical measures. In some cases, such as with an ink jet printer, it is desirable to have a monodisperse aerosol with particles of equal size.

Aerosols - Definitions



Solid-Particle Aerosols:

• Dust: formed by mechanical disintegration of a parent material -- size range from submicron to visible

• Fume: produced by condensation of vapors

or gaseous combustion products -- less than 1 micron

Aerosol Terminology



Liquid-Droplet Aerosols:

• Mist: formed by condensation or atomization -- size range from submicron to 20 microns

• Fog: visible mist (high particle concentration)

Aerosol Terminology



Solid/Liquid particle aerosols:

• Smoke: visible aerosol resulting from incomplete combustion -- less than 1 micron

• Smog: photochemical reaction products, usually combined with water vapor -- less than 2 microns

Aerosol Terminology



Primary (health-based) PM standards revision• New annual PM2.5 standard set at 15 micrograms

per cubic meter (µg/m3) and • New 24-hour PM2.5 standard set at 65 µg/m3.

EPA is retaining the current annual PM10 standard of 50 µg/m3 and adjusting the PM10 24-hour standard of 150 µg/m3 by changing the form of the standard.

EPA Standards - Revision



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EPA is revising the secondary (welfare-based) standards

- Identical to the primary standards.

• PM2.5 and PM10 standards, combined with the Clean Air Act-required regional haze program, will provide

• Protection against the major PM-related welfare effects

• Visibility impairment• Soiling and • Materials damage.




What are the PM Effects of Concern?

The characteristics, sources, and potential health effects of larger or "coarse" fraction particles (from 2.5 to 10 micrometers in diameter) and smaller or "fine” particles (smaller than 2.5 micrometers in diameter) are very different.

Coarse particles come from sources such as windblown dust from the desert or agricultural fields and dust kicked up on unpaved roads by vehicle traffic.

Health Effects - 1



Fine particles are generally emitted from activities such as

industrial and residential combustion and from vehicle

exhaust.

Fine particles are also formed in the atmosphere when

gases such as sulfur dioxide, nitrogen oxides, and volatile

organic compounds, emitted by combustion activities, are

transformed by chemical reactions in the air.

Health Effects - 2



Coarse particles

- Accumulate in the respiratory system and

aggravate health problems such as asthma.

Fine particles

- Penetrate deeply into the lungs, are more likely than

coarse particles to contribute to the health effects (e.g.,

premature mortality and hospital admissions)

Health Effects - 3



These recent community studies find that

adverse public health effects are associated

with exposure to particles at levels well below

the previous PM standards for both short-term

(from less than 1 day to up to 5 days) and

long-term (from generally a year to several

years) periods.

Health Effects - 4



• Premature death

• Increased hospital admissions and emergency room visits (primarily the elderly and individuals with cardiopulmonary disease)

• Increased respiratory symptoms and disease (children and individuals with cardiopulmonary disease such as asthma)

Health Effects - 5



•Decreased lung function (particularly in children and individuals with asthma); and

•Alterations in - Lung tissue and structure

and in - Respiratory tract defense mechanisms.

Health Effects - 6



The forces acting on an aerosol

particle in still air are:

• Gravitational Force, W

• Bouyancy Force

• Drag Force

Motion?



Bouyancy Force

According to Archimedes' Bouyancy Principle, the bouyant force exerted on a floating body is equal to the weight of the fluid displaced by the body. The Bouyancy Force exerted on a spherical particle is:

where is the gas density.

Motion ?



Drag Force Sir Isaac Newton derived the general equation for the resistance force on a spheremoving through a gas while investigating the ballistics of cannon balls. Newton theorized that a sphere must push aside a volume of gas equal to the projected area of the sphere times its velocity. The general form of Newton's resistance equation is:

Motion ?



Drag Coefficient

The coefficient of drag, ,is dependent upon

Reynold's number (Re). For flow around a sphere,

there are three regions for the drag coefficient: the

Stoke's Law region, the Transition region, and

Newton's Law region.

Motion ?



• Settling velocity of particles

Motion ?



Aerosol Particle Deposition Mechanisms

There is a general misconception about how air filters work, i.e., that they work like a microscopic sieve. Particles are simply trapped due to its large size relative to the sieve. This is not the case for most types of air filters. Instead, aerosols are captured via collision and attachment to fiber surface.

Removal



There are five mechanisms by which an aerosol particle

can be deposited on a fiber:

• Interception

• Inertia impaction

• Diffusion

• Sedimentation

• Electrostatic attraction

Removal



Interception

Interception occurs when particles do not depart

from the streamlines. The inertia or Brownian

motion of particles is negligible. Particles following

streamlines arrive at the fibers and get

"intercepted" on the fiber surface.

Removal



Inertia Impaction

This occurs when particles cannot adjust to

the "sudden" change of streamlines near

fibers, and, due to inertia, depart from the

streamlines and impact on the fiber surface.

Removal



Diffusion

Diffusion occurs when smaller particles

having Brownian motion hit the surface of

the fibers. Flow is dictated by the

concentration gradient

Removal

environmentally conscious design & manufacturing (me592) date: march 27, 2000 slide:1...

Documents

manufacturing product

pandit slide

removal slide

aerosols impact

integrated view material

health particle motion