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Thermal & Radiometric Forces

. Hot. Cold. d p. T 1 , c 1. T 2 , c 2. Thermal & Radiometric Forces. Reading: Chap. 8. http://aerosol.ees.ufl.edu/Thermophoresis/section01.html. Thermophoresis: Particle motion in a temperature gradient, from a hotter to a colder region. Molecular impacts on a particle

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Thermal & Radiometric Forces

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  1. Hot Cold dp T1, c1 T2, c2 Thermal & Radiometric Forces Reading: Chap. 8 http://aerosol.ees.ufl.edu/Thermophoresis/section01.html • Thermophoresis: Particle motion in a temperature gradient, from a hotter to a colder region Molecular impacts on a particle (dp < ) in a temperature gradient http://aerosol.ees.ufl.edu/Thermophoresis/section02.html Q: What if the cylinder is colder than the environment?

  2. Continuum Regime • Thermal force on a particle • Velocity Free Molecular Regime • Thermal force on a particle • Velocity http://aerosol.ees.ufl.edu/Thermophoresis/section02_b.html Q: What if Kn << 1? Q: What if kp>>ka? ka ~ kp?

  3. Terminal Settling & Thermophoretic Velocity in a Unit Temperature Gradient @ 20 oC Cumulative Deposition During 100 s by Diffusion & Thermophoresis from Unit Aerosol Concentration in a Unit Temperature Gradient @ 20 oC (kp/ka=10)

  4. Air flow Glass cover slip Brass heat sink @ room temperature Heated Wire Deposition zone Applications • Thermal Precipitator • Problem: Particle deposition in a heat exchanger reduces the heat transfer. Q: Advantages? Can diffusion achieve the same?

  5. Problems with Thermophoresis Carbon sooting fouling in heat exchanger Biological organic growth and corrosion follow http://www.deltathx.com/ContentPg.aspx?itemid=984 http://www.intelligent-sootblowing.com/Seiten/slaggingandfouling.html

  6. Other Radiometric Forces • Photophoresis: Particle motion under the influence of asymmetric light absorption within a particle • Radiation Pressure: Pressure results from a direct momentum transfer by the deflection and absorption of the light (Example?) http://www.ws.chemie.tu-muenchen.de/groups/haisch/techniques0/photophoresis/

  7. Dry air Moist air ? • Diffusiophoresis: Particle motion under the influence of a concentration gradient of surrounding gas molecules http://oldweb.che.ntu.edu.tw/lab/colloidlab/research ChemoTaxi: Acidic Droplet Solves Maze through pH gradient http://pubs.acs.org/cen/news/88/i03/8803notw9.html

  8. Reflection

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