basic laws of gases and particulates
DESCRIPTION
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. Ideal Gas Law. P : pressure V : volume n : mole - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/1.jpg)
04/24/231
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
![Page 2: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/2.jpg)
04/24/232
Ideal Gas Law
Other references:1. CRC Handbook of Chemistry & Physics2. Perry’s Chemical Engineers’ Handbook
TRnQPTRMWP
TRMWM
TRnVP
P: pressureV: volumen: moleR: Ideal gas law constantT: TemperatureM: massMW: molecular weight: densityQ: volume flow rate : molar flow raten
![Page 3: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/3.jpg)
04/24/233
Ideal Gas Law Constant
82.057
8.314 8.314
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: 6.0231023 molecules/mole
At 1 atm and 25 oC, 1 mole of air has a volume of 24.5 L
![Page 4: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/4.jpg)
04/24/234
Unit of Concentration
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”?
Section 7.1.2
![Page 5: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/5.jpg)
04/24/235
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 dryCO2 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%
![Page 6: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/6.jpg)
04/24/236
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
TCBATPv
)(log Pv in mmHg and T in oC (if Table 9.2 is used)
(Saturation) Vapor PressureTime to reach equilibrium
How does vapor pressure change if the temperature increases?
![Page 7: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/7.jpg)
04/24/237
![Page 8: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/8.jpg)
04/24/238
What is the vapor pressure of water at 20 oC? If the measurement is conducted on Mars (the atmospheric pressure is about 0.006 atm), what will be the value?
![Page 9: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/9.jpg)
04/24/239
Partial Pressure
)100( )(
SRHTPPSv
a Supersaturation: S > 1 (RH > 100%)
Saturation Ratio (or relative humidity for water)
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
Taa PyP ya: mole fraction of component “a” in the mixture in the gas phasePT: total pressure of the system
After a shower at dusk, the temperature starts to drop. How do PV and Pa change correspondingly?
1 mole of O2 @ 1 atm
4 moles of N2
How much is PO2?
![Page 10: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/10.jpg)
04/24/2310
Humidity in Air/Water Mixture
• 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
http://www.usatoday.com/weather/wsling.htm
• The state of an air/water mixture is determined by pressure, temperature & humidity
Properties of TDB of 40 oC and TWB of 30 oC?
Why is TDB always higher than TWB?
![Page 11: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/11.jpg)
04/24/2311http://howard.engr.siu.edu/staff1/tech/MET/ET401/LAB/psychro_carrier_si.jpg
![Page 12: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/12.jpg)
04/24/2312
Viscosity• A measure of frictional force between fluid layers
moving at different velocities
At 20 oC, the viscosity () of air is 1.8110-5 Pa·s (N·s/m2).The temperature dependence (on absolute temperature) is:
74.0
1
212
TT
What is the viscosity of air at 100 oC?
(Valid between -70 to 500 oC)
![Page 13: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/13.jpg)
04/24/2313
Characterizing an Aerosol Particle How do we characterize a particle?
• Size, Shape, Density, Composition (toxicity, corrosivity, reactivity), Phase (liquid, solid)
Coal fly ash particles Iron oxide particles from arc welding
Why should we care the aerosol size?
![Page 14: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/14.jpg)
04/24/2314
Size Range of Aerosol Particles
Hinds, Aerosol Technology, 1999
![Page 15: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/15.jpg)
04/24/2315
Aerosol Size DistributionHow do we characterize particle”S”?
• Concentration:– Number concentration by counting– Mass concentration by weight measurement
• Size• Spread Particle size distribution
Dis
tribu
tion
func
tion
![Page 16: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/16.jpg)
04/24/2316
Type of Size DistributionEx. A system containing spherical particlesNumber Concentration: Mass Concentration:100 #/cc 1m & = 1.91g/cm3 10-10 g/cc 1m1 #/cc 10m 10-9 g/cc 10m
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
Num
ber d
istri
butio
n fu
nctio
n
Mass Distribution
Mas
s di
strib
utio
n fu
nctio
n
![Page 17: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/17.jpg)
04/24/2317
Settling Velocity
Microscopy, Settling velocity, Light scatteringHow do we determine the particle size?
FG=mg
t=0V(t)=0
FG=mg
t=V(t)=?
FG=mg
t>3V(t)=VTS
FD=3V(t)dp
FD=3VTSdp
In settling, an aerosol experiences gravitational force (FG) and drag force (FD)
When they are equal to each other, there is no more acceleration.
mgdVFF ppGD 3
18
2gdVV ppTSp
How to get a larger settling velocity?
![Page 18: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/18.jpg)
04/24/2318
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
http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html
http://www.geocities.com/piratord/browni/Difus.html
p
c
dkTCD3
Stokes-Einstein Equation for Diffusion Coefficient How to get a
larger diffusivity?k = 1.38X10-23 J/K or 1.38X10-16 erg/K
![Page 19: Basic Laws of Gases and Particulates](https://reader033.vdocuments.mx/reader033/viewer/2022052604/568150b2550346895dbecf78/html5/thumbnails/19.jpg)
04/24/2319
Quick Reflection