2. 2016/1/261 Aerosol & Particulate Research Lab Thermal & Radiometric Forces Thermophoresis: Particle motion in a temperature gradient, from a hotter to a colder region Molecular impacts on a particle (d p < ) in a temperature gradient Reading: Chap. 8 Hot Cold T 1, c 1 T 2, c 2 dpdp Q: What if the cylinder is colder than the environment?

3. 2016/1/262 Aerosol & Particulate Research Lab Thermal force on a particle Velocity Free Molecular Regime Continuum Regime  Thermal force on a particle  Velocity Q: What if Kn << 1? Q: What if k p >>k a ? k a ~ k p ?

4. 2016/1/263 Aerosol & Particulate Research Lab Terminal Settling & Thermophoretic Velocity in a Unit Temperature Gradient @ 20 o C Cumulative Deposition During 100 s by Diffusion & Thermophoresis from Unit Aerosol Concentration in a Unit Temperature Gradient @ 20 o C (k p /k a =10)

5. 2016/1/264 Aerosol & Particulate Research Lab Applications Thermal Precipitator Problem: Particle deposition in a heat exchanger reduces the heat transfer. Heated Wire Air flow Brass heat sink @ room temperature Glass cover slip Deposition zone Q: Advantages? Can diffusion achieve the same?

6. 2016/1/265 Aerosol & Particulate Research Lab 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?) Diffusiophoresis: Particle motion under the influence of a concentration gradient of surrounding gas molecules Dry air Moist air ?

7. 2016/1/266 Aerosol & Particulate Research Lab Reflection