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05/25/22 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

# Basic Laws of Gases and Particulates

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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 Presentation

### Text of Basic Laws of Gases and Particulates

• **Basic Laws of Gases and ParticulatesIdeal gas lawUnit of concentrationVapor pressure & partial pressureHumidity & psychrometric chartViscosityAerosol sizeAerosol size distributionSettling velocityBrownian motion and diffusion

• **Ideal Gas LawOther references:1. CRC Handbook of Chemistry & Physics2. Perrys Chemical Engineers HandbookP: pressureV: volumen: moleR: Ideal gas law constantT: TemperatureM: massMW: molecular weight: densityQ: volume flow rate : molar flow rate

• **Ideal Gas Law ConstantWhat 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?Avogadros number: 6.0231023 molecules/mole

At 1 atm and 25 oC, 1 mole of air has a volume of 24.5 L

• **Unit of ConcentrationSection 7.1.2

• **Concentration on a dry basisWater 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 wetvolume 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%

• **Vapor PressureThe pressure required to maintain a vapor in equilibrium with the condensed vapor (liquid or solid) with a flat surface at a specified temperature

• **

• **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?

• **Partial Pressure

• **Humidity in Air/Water MixturePsychometric Chart (Figure 1.3)Dry bulb temperatureWet bulb temperature: the temperature at which a thermometer with a wet wick wrapped around the bulb stabilizeshttp://www.usatoday.com/weather/wsling.htm The state of an air/water mixture is determined by pressure, temperature & humidityProperties of TDB of 40 oC and TWB of 30 oC?Why is TDB always higher than TWB?

• **http://howard.engr.siu.edu/staff1/tech/MET/ET401/LAB/psychro_carrier_si.jpg

• **ViscosityA measure of frictional force between fluid layers moving at different velocitiesAt 20 oC, the viscosity () of air is 1.8110-5 Pas (Ns/m2).The temperature dependence (on absolute temperature) is:What is the viscosity of air at 100 oC?(Valid between -70 to 500 oC)

• **Characterizing an Aerosol Particle How do we characterize a particle?Size, Shape, Density, Composition (toxicity, corrosivity, reactivity), Phase (liquid, solid)Coal fly ash particlesIron oxide particles from arc weldingWhy should we care the aerosol size?

• **Size Range of Aerosol ParticlesHinds, Aerosol Technology, 1999

• **Aerosol Size DistributionHow do we characterize particleS?Concentration:Number concentration by countingMass concentration by weight measurementSizeSpread Particle size distribution

• **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 10mDo 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 DistributionNumber distribution function

• **Settling VelocityIn settling, an aerosol experiences gravitational force (FG) and drag force (FD)

• **Brownian Motion & DiffusionThe primary transport mechanism for small particles (< 0.1 m); Important when transport distance is small: e.g. filter, airway in human lungBrownian motion: irregular wiggling motion of a particle caused by random bombardment of gas molecules against the particleDiffusion: the net transport of the particles from a region of higher concentration to a region of lower concentrationhttp://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html http://www.geocities.com/piratord/browni/Difus.htmlk = 1.38X10-23 J/K or 1.38X10-16 erg/K

• **Quick Reflection

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