Properties of Gases

1. Properties of Gases Reading: Chap 1.5-1.7, 10, 8.5 • Ideal gas law • Unit of concentration • Vapor pressure & partial pressure • Solubility • Energy • Humidity & psychrometric chart • Cooling Aerosol & Particulate Research Laboratory

2. 82.057 8.314 8.314 8.314 Ideal Gas Law Other references: 1. CRC Handbook of Chemistry & Physics 2. Perry’s Chemical Engineers’ Handbook Aerosol & Particulate Research Laboratory

3. Is 1 g/cm3 SO2 equal to 1 ppb 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”? Unit of Concentration Aerosol & Particulate Research Laboratory

4. Pv in mmHg and T in oC(if Table 9.2 is used) (Saturation) Vapor Pressure Time to reach equilibrium How does vapor pressure change if the temperature increases? 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 Aerosol & Particulate Research Laboratory

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6. 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? Aerosol & Particulate Research Laboratory

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8. Partial Pressure: 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 Saturation Ratio (or relative humidity for water) 4 moles of N2 1 mole of O2 @ 1 atm 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? Can you predict the weather at dawn? Aerosol & Particulate Research Laboratory

9. Solubility Henry’s Law: the concentration of a gas dissolved in solution is proportional to its partial pressure at a constant temperature H or H: pressure/ mole fraction in liquid H1: mole fraction in vapor/ mole fraction in liquid Is H a constant at a given temperature? Aerosol & Particulate Research Laboratory

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11. Energy Why is energy important in APCD? • Heat Capacity: the amount of energy required to raise the temperature of the substance by 1 oC. Which one requires more energy to raise 1 oC? Water or copper? • Specific Heat Capacity (Cp or Cv): heat capacity on a unit mass basis (also a molar basis for gas) • Enthalpy: the difference of energy compared to that at reference temperature (25 oC or 60 oF) – see Table B.7 • For liquid like water, the latent heat (HL, energy of vaporization) also needs to be included. How much energy can we extract from 2 kg of air cooling from 100 to 50 oC? (Table A.1 next page) Aerosol & Particulate Research Laboratory

12. Handout Aerosol & Particulate Research Laboratory

13. Humidity in Air/Water Mixture • The state of an air/water mixture is determined by pressure, temperature & humidity • PsychrometricChart (Figures B.3 & B.4 or Handout) • 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 Why is TDB always higher than TWB? Properties of TDB of 40 oC and TWB of 30 oC? If a stream of moist air is cooled and humidified adiabatically from TDB of 40 oC and TWB of 30 oC to TDB of 32 oC, how much is the change of water per pound of dry air? Aerosol & Particulate Research Laboratory

14. http://howard.engr.siu.edu/staff1/tech/MET/ET401/LAB/psychro_carrier_si.jpghttp://howard.engr.siu.edu/staff1/tech/MET/ET401/LAB/psychro_carrier_si.jpg Aerosol & Particulate Research Laboratory

15. Cooling Q: Why is cooling of exhaust necessary? Q: What options do we have? • Dilution with ambient air (pros & cons?) • Mass balance and energy balance • Injection with water: remember to add latent heat for vaporization (pros & cons?) Q: What is the dilution air flow rate needed (in cfm at 90 oF) to cool 50,000 acfm of air from 1200 oF to 500 oF? Aerosol & Particulate Research Laboratory

16. Heat Exchanger: large U-tubes to transfer heat to ambient air (water) by convection and radiation (pros & cons?) H1: rate of heat given off by hot fluid H2: rate of heat absorbed by cold fluid Hx: rate of heat exchanged U: overall heat transfer coefficient A: heat transfer area DTLM: log mean temperature difference Aerosol & Particulate Research Laboratory

17. When only one flow is gas? When both flows are gases? ho: heat transfer coef. (outside tube) hi: heat transfer coef. (inside tube) xw: tube wall thickness km: tube thermal conductivity Values can be found in Table 8.8 and reference books. Why can double pane windows reduce energy consumption (heating & air conditioning) better than single pane windows? Aerosol & Particulate Research Laboratory http://accentcountryhomes.com

18. Quick Reflection Aerosol & Particulate Research Laboratory

19. Dilution with Ambient Air Energy balance and mass balance Heat capacity definition Density definition Aerosol & Particulate Research Laboratory

20. For a common air pollution scenario where pollutant concentration is dilute, gas heat capacity can be assumed to be the same as air heat capacity The density of gas depends on the temperature Plug (3) & (4) into (1) and (2) Aerosol & Particulate Research Laboratory

21. Cancel rair and regroup terms Use (5) in (7), it becomes Use (6) in (8), it then becomes Aerosol & Particulate Research Laboratory