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Piske & Wassom Summer Presentation
- 1. Studying the Mass Transport Phenomena Associated with Evaporation Greg Wassom & Taylor Piske Advised by Dr. Peter Kelly-Zion, Dr. Chris Pursell, and Dr. Hoa Nguyen
- 2. Details of Evaporation Applications: • Coating • Spray cooling • Printing • Surface Patterning • DNA stretching and depositing Vapor Transport Mechanisms: • Diffusion and Convection Image take from: Lin, Zhiqun. Evaporative Self-Assembly of Ordered Complex Structures. World Scientific, 2012.
- 3. • Molecular Transport • Driven by Concentration gradients
- 4. Buoyancy Induced Convection Video taken from Sharma, Vidit. “VOF in Ansys Fluent 14”. https://www.youtube.com/watch?v=wys3qiBQzYY • Bulk Transport Phenomena • Driven by a Density Gradient • Gravity
- 5. Experimental Techniques • Gravimetric Analysis • Shadowgraph • Pressure Chamber • Schlieren Imaging • IR Spectral Analysis y = -0.1085x + 53.43 R² = 0.999 -10 0 10 20 30 40 50 60 0 100 200 300 400 500 600 700 800 Mass(mg) Time (s) Mass vs. Time Measured Data Fitted Slope (evaporation rate) Linear (Fitted Slope (evaporation rate))
- 7. IR Spectroscopic Measurements 0.0 0.2 0.4 0.6 0.8 1.0 -40 -30 -20 -10 0 10 20 30 40 Concentration/Sat.Conc. Radial Position (mm) Hexane Methanol Z = 1mm Z = 2 mm Z = 3 mm Z = 4 mm Z = 5 mm Z = 6 mm Z = 8 mm Z = 10 mm Z = 15 mm
- 8. Using the Experimental Conc. Data with Gridfit • MATLAB function Gridfit models the data with a surface • Concentration gradients ( 𝜕𝐶 𝜕𝑟 and 𝜕𝐶 𝜕𝑧 ) are computed along a cylindrical control volume • Flux through the control volume is calculated • Flux → Diffusion rate 0 5 10 15 20 -5 5 15 25 35 z-position(mm) r-position (mm)
- 9. Analytical Methanol Data from the Weber’s Disc Model Modeled by Gridfit
- 10. Methodology Check - Comparing Methanol Diffusion Rates of Different Control Volumes 5.5E-08 6.0E-08 6.5E-08 7.0E-08 7.5E-08 8.0E-08 8.5E-08 9.0E-08 0.75 0.95 1.15 1.35 1.55 1.75 1.95 2.15 2.35 2.55 2.75 DiffusionRate(kg/s) Height of Control Volume (mm) Diffusion Rates of Methanol Using Analytical Data Methanol Theory CV Radius = 8.5 mm CV Radius = 8 mm CV Radius = 7.5 mm CV Radius = 7 mm CV Radius = 6.5 mm Theory
- 11. Experimental Methanol Data Modeled by Gridfit
- 12. Comparing Diffusion Rates of Different Control Volumes (Experimental Data) 0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07 2.5E-07 0 0.5 1 1.5 2 2.5 3 DiffusionRate(kg/s) Control Volume Height (mm) Control Volume Radius = 7 mm 3MP 3MP Theory Hexane Hexane Theory Methanol Methanol Theory 0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07 2.5E-07 3.0E-07 5.5 6 6.5 7 7.5 8 8.5 9 DiffusionRate(kg/s) Control Volume Radius (mm) Control Volume Height = 1.5 mm 3MP 3MP Theory Hexane Hexane Theory Methanol Methanol Theory
- 13. Traditional Theory vs. Real Hexane Data -25 -20 -15 -10 -5 0 5 10 15 20 25 Radial Position, r [mm] Elevation,z[mm] 0 5 10 15 20 25 MeasuredComputed: Diffusion-Only
- 14. Summary • Vapor concentration data measured for methanol, hexane, and 3-methylpentane • Data modeled by Gridfit • Gridfit model used to compute gradients, calculate diffusion rates • Diffusion rates and theory compared • Evidence of convection found
- 15. Acknowledgments • Petroleum Research Fund • Dr. Peter Kelly-Zion • Dr. Chris Pursell • Dr. Hoa Nguyen • Chemistry Department, Trinity University • Engineering Department, Trinity University • Mathematics Department, Trinity University
Hinweis der Redaktion
- Say: Evaporation is an important process involved in many applications. For instance, Surface patterning…(talk about surface patterns and why they are important) Talk about how evaporation happens to different species in different ways, and has practical applications many people don’t think of.
- Molecular Trqansport Driven by concentration gradient
- Bulk transport phenomena Driven by density gradient Bulk flow of vapors above a droplet moving away from their natural position due to a difference in density between the ambient gas and the evaporating droplet. Because of this, there is room for more vapor to diffuse outward from the droplet. Now imagine that just outside of the station, there is a tornado. Once people get outside, the gust takes them far away from the station. Because of this, more room is present for people to escape out of the door in order to try to maintain equilibrium vapor pressure, so they do (escape), and the cycle continues until no one is left in the station. This is an example of a density difference in the evaporating species, and the gases that it evaporates into, causing evaporation rates to be expedited. This could happen the other way too. Imagine a lighter compound evaporating into a heavier one. This could be represented by a snowstorm which causes the exits in the train station to be blocked. Depending on how high the snow is outside, the evaporation rate changes up to the point where it can no longer escape.
- Not worry about details involved in Studying Evaporation (not rates) In our lab, weve developed techniques to meaure and analyze evaporation rates. Gravimetric Scale: Allows for comparison of evaporation rates in room temperature conditions across devices. IR Spectrometer: Allows us to find concentrations of vapor clouds above droplets. Pressure Chamber: Allows us to change ambient conditions around sessile droplets in order to see how they affect evaporation rates. Shadowgraph: Imaging technique used in the pressure chamber which observes the droplet evaporate, and computes its rate of evaporation. Schlieren Imaging: Allows observation of vapor clouds above droplets to see how distribution correlates with evaporation rates.
- Use slides Talk about how wavenumbers are chosen to integrate under. Integration from 3200 to 2500 wavenumbers w/ baseline of the same
- Try to change colors Explain that this is infrared spectroscopy. This technique relates the absorbance of infrared light to the concentration of vapor. Absorbance is proportional to the concentration. To measure vapor concentration, the IR beam of an FTIR is passed horizontally through the cloud at various locations above the drop. From these IR beam measurements, we will have a projection of the average concentration in the x-z plane. Each pass measures average absorption of vapor-air mixture in the path of the beam. (bottom image) this is the front profile of the vapor cloud and (point at the top left image) here is a top view of the vapor cloud. The measurements are done at multiple x-positions throughout the cloud. This is all for one elevation, this gives a 2 dimensional distribution. By repeating this process for multiple elevations, we can obtain a 3 dimensional distribution.