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Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:1
Environmentally Conscious Design & Manufacturing
Class 10: Air Quality 1
Prof. S. M. Pandit
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:2
Agenda
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 Slide:3
ManufacturingProduct{Quality, Economics}
Environment{Solid / Liquid / Aerosols / Gases / Energy}
Integrated View
Material,Energy
Wastes (Material / Energy) Product
Air Quality and Manufacturing
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:4
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
Air Quality and Manufacturing
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:5
Process 1 .. n
Aerosols and Dust
Manufacturing Facility
Aerosols / Dustto Environment
Aerosols / Dustsettling inside
Air Quality and Manufacturing
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:6
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:7
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:8
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:9
Liquid-Droplet Aerosols:
• Mist: formed by condensation or atomization -- size range from submicron to 20 microns
• Fog: visible mist (high particle concentration)
Aerosol Terminology
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:10
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:11
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:12
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EPA Standards - Revision
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:13
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.
EPA Standards - Revision
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:14
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:15
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:16
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:17
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:18
• 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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:19
•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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:20
The forces acting on an aerosol
particle in still air are:
• Gravitational Force, W
• Bouyancy Force
• Drag Force
Motion?
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:21
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 ?
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:22
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 ?
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:23
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 ?
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:24
• Settling velocity of particles
Motion ?
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:25
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:26
There are five mechanisms by which an aerosol particle
can be deposited on a fiber:
• Interception
• Inertia impaction
• Diffusion
• Sedimentation
• Electrostatic attraction
Removal
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:27
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:28
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
Environmentally Conscious Design & Manufacturing (ME592)
Date: March 27, 2000 Slide:29
Diffusion
Diffusion occurs when smaller particles
having Brownian motion hit the surface of
the fibers. Flow is dictated by the
concentration gradient
Removal