Transcript Environmentally Conscious Design & Manufacturing ME592E-1

Environmentally Conscious
Design & Manufacturing
Class 10: Air Quality 1
Prof. S. M. Pandit
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Agenda
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Air quality and manufacturing
Definitions
Standards set by EPA
Aerosols
» Impact on health
» Particle motion ?
» Removal
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Air Quality and Manufacturing
Integrated View
Material,
Energy
Manufacturing
Product
{Quality, Economics}
Environment
{Solid / Liquid / Aerosols / Gases / Energy}
Wastes (Material / Energy)
Product
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Air Quality and Manufacturing
EPA regulations in Manufacturing - Health
• Need for revision of 25 year old standards
Particulate matter
exposures to particles smaller than those
that were being regulated by EPA
- lodge deeply in the lungs and
- cause premature deaths and respiratory
problems
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Air Quality and Manufacturing
Aerosols / Dust
settling inside
Aerosols and Dust
Aerosols / Dust
to Environment
Process 1 .. n
Manufacturing Facility
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Aerosols - Definitions
Aerosols: Suspensions of solid or liquid particles in a gas
(usually air).
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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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Aerosols - Definitions
Particulates are generally categorized based on size:
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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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Aerosol Terminology
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Aerosol Terminology
Liquid-Droplet Aerosols:
• Mist: formed by condensation or atomization -size range from submicron to 20 microns
• Fog: visible mist (high particle concentration)
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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EPA Standards - Revision
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Micrograms / cubic meter
EPA Standards - Revision
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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EPA Standards - Revision
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 1
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 2
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 3
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)
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 4
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 5
• 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)
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Health Effects - 6
•Decreased lung function
(particularly in children
and individuals with
asthma); and
•Alterations in
- Lung tissue and structure
and in
- Respiratory tract
defense mechanisms.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Motion?
The forces acting on an aerosol
particle in still air are:
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Gravitational Force, W
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Bouyancy Force
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Drag Force
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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 r is the gas density.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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:
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Motion ?
• Settling velocity of particles
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Removal
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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Removal
There are five mechanisms by which an aerosol particle
can be deposited on a fiber:
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Interception
Inertia impaction
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Diffusion
Sedimentation
Electrostatic attraction
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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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.
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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Removal
Diffusion
Diffusion occurs when smaller particles
having Brownian motion hit the surface of
the fibers. Flow is dictated by the
concentration gradient
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000
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