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
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R: Ideal gas law constant
MW: molecular weight
Q: volume flow rate
: molar flow rate
1. CRC Handbook of Chemistry & Physics
2. Perry’s Chemical Engineers’ Handbook
Time to reach equilibrium
How does vapor pressure change if the temperature increases?Vapor Pressure
Pv in mmHg and T in oC(if Table 9.2 is used)
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?
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
4 moles of N2
1 mole of O2 @ 1 atm
(or relative humidity for water)
How much is PO2?
Supersaturation: S > 1 (RH > 100%)
After a shower at dusk, the temperature starts to drop. How do PV and Pa change correspondingly?Partial Pressure
Why is TDB always higher than TWB?
Properties of TDB of 40 oC and TWB of 30 oC?
At 20 oC, the viscosity () of air is 1.8110-5 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?
How do we characterize a particle?
Coal fly ash particles
Iron oxide particles from arc welding
Why should we care the aerosol size?
Hinds, Aerosol Technology, 1999
Mass distribution functionType of Size Distribution
Ex. A system containing spherical particles
Number Concentration: Mass Concentration:
100 #/cc 1m & = 1.91g/cm3 10-10 g/cc 1m
1 #/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 function
Microscopy, Settling velocity, Light scattering
When they are equal to each other, there is no more acceleration.
How to get a larger settling velocity?
In settling, an aerosol experiences gravitational force (FG) and drag force (FD)
How to get a larger diffusivity?Brownian Motion & Diffusion
k = 1.38X10-23 J/K or 1.38X10-16 erg/K