1. Basic Laws of Gases and Particulates
Ideal gas law
Unit of concentration
Vapor pressure & partial pressure
Humidity & psychrometric chart
Viscosity
Aerosol size
Aerosol size distribution
Settling velocity
Brownian motion and diffusion
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2. Ideal Gas Law P: pressure V: volume n: mole R: Ideal gas law constant
T: Temperature
M: mass
MW: molecular weight
: density
Q: volume flow rate
: molar flow rate
Other references:
1. CRC Handbook of Chemistry & Physics
2. Perry’s Chemical Engineers’ Handbook
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3. Ideal Gas Law Constant
82.057
8.314
What is the volume of 1 g-mole of air at 25 oC and 1 atm?
How many lb-moles are there for 380 ft3 of air at 60 oF and 14.7 psi?
Avogadro’s number:
6.0231023 molecules/mole
At 1 atm and 25 oC, 1 mole of air has a volume of 24.5 L
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4. Unit of Concentration Is 1 g/cm3 SO2 equal to 1 ppm SO2?
Section 7.1.2
Is 1 g/cm3 SO2 equal to 1 ppm SO2?
The annual standard of NO2 is 100 g/m3. What is the concentration in ppb?
Is “ppm” molar basis, volume basis or mass basis?
What’s the difference between “ACFM” and “SCFM”?
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5. Concentration on a “dry” basis
Water vapor is commonly present in a heated gas stream, e.g., combustion of a hydrocarbon fuel.
Water vapor can condense as temperature cools down. The amount varies and is very sensitive to temperature.
To prevent the variation, standards are written to correct to "dry" conditions when expressing concentrations.
volume basis wet
volume basis dry
CO2 18%
18%*(100/88) = 20.5%
H2O 12%
O2 10%
10%*(100/88) = 11.4%
N2 60%
60%*(100/88) = 68.2%
Total = 100%
(100-12)%*(100/88) = 100%
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6. (Saturation) Vapor Pressure
The pressure required to maintain a vapor in equilibrium with the condensed vapor (liquid or solid) with a flat surface at a specified temperature
(Saturation) Vapor Pressure
Time to reach equilibrium
How does vapor pressure change if the temperature increases?
Pv in mmHg and T in oC (if Table 9.2 is used)
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8. What is the vapor pressure of water at 20 oC
What is the vapor pressure of water at 20 oC? If the measurement is conducted on Mars (the atmospheric pressure is about atm), what will be the value?
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9. Partial Pressure ya: mole fraction of component “a” Saturation Ratio
The pressure that a gas (or vapor) in a mixture of gases would exert if it were to occupy the entire volume occupied by the mixture
ya: mole fraction of component “a”
in the mixture in the gas phase
PT: total pressure of the system
1 mole of 1 atm
4 moles of N2
How much is PO2?
Supersaturation: S > 1 (RH > 100%)
Saturation Ratio
(or relative humidity for water)
After a shower at dusk, the temperature starts to drop. How do PV and Pa change correspondingly?
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10. Humidity in Air/Water Mixture
The state of an air/water mixture is determined by pressure, temperature & humidity
Psychometric Chart (Figure 1.3)
Dry bulb temperature
Wet bulb temperature: the temperature at which a thermometer with a wet wick wrapped around the bulb stabilizes
Why is TDB always higher than TWB?
Properties of TDB of 40 oC and TWB of 30 oC?
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11. http://howard. engr. siu
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12. Viscosity
A measure of frictional force between fluid layers moving at different velocities
At 20 oC, the viscosity () of air is 1.8110-5 Pa·s (N·s/m2).
The temperature dependence (on absolute temperature) is:
(Valid between -70 to 500 oC)
What is the viscosity of air at 100 oC?
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13. Characterizing an Aerosol Particle
How do we characterize a particle?
Coal fly ash particles
Iron oxide particles from arc welding
Size, Shape, Density, Composition (toxicity, corrosivity, reactivity), Phase (liquid, solid)
Why should we care the aerosol size?
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14. Size Range of Aerosol Particles
Hinds, Aerosol Technology, 1999
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15. Aerosol Size Distribution
How do we characterize particle”S”?
Concentration:
Number concentration by counting
Mass concentration by weight measurement
Size
Spread
Particle size distribution
Distribution function
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16. Type of Size Distribution
Ex. A system containing spherical particles
Number Concentration: Mass Concentration:
100 #/cc 1m &  = 1.91g/cm g/cc 1m
1 #/cc 10m g/cc 10m
Do we have “more” 1 m or 10 m particles (i.e. are the majority 1 or 10 m)?
How will it impact the PSD we see?
Number Distribution
Mass Distribution
Mass distribution function
Number distribution function
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17. Settling Velocity How do we determine the particle size?
Microscopy, Settling velocity, Light scattering
How do we determine the particle size?
In settling, an aerosol experiences gravitational force (FG) and drag force (FD)
FG=mg
t=0
V(t)=0
t=
V(t)=?
t>3
V(t)=VTS
FD=3V(t)dp
FD=3VTSdp
When they are equal to each other, there is no more acceleration.
How to get a larger settling velocity?
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18. Brownian Motion & Diffusion
The primary transport mechanism for small particles (< 0.1 m); Important when transport distance is small: e.g. filter, airway in human lung
Brownian motion: irregular wiggling motion of a particle caused by random bombardment of gas molecules against the particle
Diffusion: the net transport of the particles from a region of higher concentration to a region of lower concentration
How to get a larger diffusivity?
Stokes-Einstein Equation for
Diffusion Coefficient
k = 1.38X10-23 J/K or 1.38X10-16 erg/K
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19. Quick Reflection
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