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GAS TRANSFER

GAS TRANSFER. M. B. Timmons, Ph.D. Biological & Environmental Engineering Cornell University Brian J. Vinci The Conservation Funds Freshwater Institute. Dissolved Gases - Fundamentals. Dry Air Components. Dissolved Gases - Fundamentals. The solubility of a gas (mg/L).

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GAS TRANSFER

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  1. GAS TRANSFER M. B. Timmons, Ph.D. Biological & Environmental EngineeringCornell University Brian J. VinciThe Conservation Funds Freshwater Institute Recirculating Aquaculture Systems Short Course

  2. Dissolved Gases - Fundamentals Dry Air Components Recirculating Aquaculture Systems Short Course

  3. Dissolved Gases - Fundamentals The solubility of a gas (mg/L) Recirculating Aquaculture Systems Short Course

  4. Gas Solubility Equations The solubility of a gas (mg/L) is determined using Henry’s Law i = Bunsen Coefficient for gas species “i”, L/L-atm Xi = Mole fraction of gas (dimensionless) PBP = Barometric pressure, mm Hg PWV = Water vapor pressure, mm Hg Solubility (gas) Coefficient = ml’s gas per ml’s liquid (water) Recirculating Aquaculture Systems Short Course

  5. Gas Transfer Gas Transfer Occurs Due to Pressure Differences Qx (mass/time) = ( 1/ R) (Pi,high – Pi,low) where • Q = rate of gas flow of species x • P = pressure • X = gas species • R = Resistance to flow (design related) Design and Operation will influence RESISTANCE to gas transfer Recirculating Aquaculture Systems Short Course

  6. Values for Pressure • Atmospheric Pressure • Sea Level • 760 mm Hg (mercury) • 34 feet of water column • 14.96 psi • Correcting for Elevation h is feet (not meters) of elevation above sea level Recirculating Aquaculture Systems Short Course

  7. Terms Used to Describe Pressure Total Gas Pressure = SUM of all Partial Pressures where: Partial Pressure = pressure contribution of an “individual gas” Gauge Pressure = Total Pressure – Atmospheric Pressure Recirculating Aquaculture Systems Short Course

  8. Fundamentals of Gas Transfer Two factors that directly impact the rate of gas transfer: • the area of gas-liquid interface • the difference between the concentration (partial pressure) at saturation and the existing concentration of the gas in the water. Recirculating Aquaculture Systems Short Course

  9. Gas Transfer Options Aeration Systems – Air Stones, Packed Towers Sources of Air Recirculating Aquaculture Systems Short Course

  10. Gas Transfer Options Air stones: very inefficient O2 transfer devices (3 – 7%) Recirculating Aquaculture Systems Short Course

  11. Gas Transfer Options Sources of Oxygen Oxygen Transfer Systems Recirculating Aquaculture Systems Short Course

  12. Gas Transfer Options U-tubes • "Rule of Thumb" • U-Tube Aerator • Design U-Tubes for a down flow velocity between 2 m/s to 3 m/s • Limit G/L ratio to <25% Recirculating Aquaculture Systems Short Course

  13. Gas Transfer Options Packed Columns Recirculating Aquaculture Systems Short Course

  14. Gas Transfer Options LHO’s Recirculating Aquaculture Systems Short Course

  15. Gas Transfer Options Aeration Cone Or Down-Flow Bubble Contactors Recirculating Aquaculture Systems Short Course

  16. Gas Transfer Options • Diffused Aeration (Air Stones) Recirculating Aquaculture Systems Short Course

  17. Gas Transfer Options Oxygen Injection Recirculating Aquaculture Systems Short Course

  18. Gas Transfer CO2 Degassing: Carbon Dioxide (Nitrogen) Recirculating Aquaculture Systems Short Course

  19. Gas Transfer CO2 Carbon Dioxide Stripping: counter-current air-stripping columns Recirculating Aquaculture Systems Short Course

  20. Gas Transfer CO2 Carbon Dioxide Stripping: counter-current air-stripping columns Recirculating Aquaculture Systems Short Course

  21. Gas Transfer HLR Recirculating Aquaculture Systems Short Course

  22. Gas Transfer Installation and Safety Concerns Recirculating Aquaculture Systems Short Course

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