Charles A. Ward Thermodynamics and Kinetics Laboratory, University of Toronto

1. Charles A. Ward Thermodynamics and Kinetics Laboratory, University of Toronto Fluid Behavior In Absence Of Gravity: Confined Fluids and Phase Change Second g-jitter Meeting Victoria, British Columbia

2. Configuration of a Confined Fluid at g 0 Prediction from thermodynamics g Liquid

3. Apparatus Used on the Space Shuttle

4. Position of the Apparatus and Observations on the Space Shuttle

5. Measure the contact angle at the upper and lower interface... Thermodynamic predictions Average OARE reading Average values from a confined fluid Average SAMS reading

6. Summary of the Proposed Mechanism

7. Examine the Effect of Adsorption on the Contact Angle of the Water-Glass System

8. New Theory • Statistical mechanics • Gibbs adsorption equation, Young Eq.

9. Comparison of Isotherms with Measurements

10. Mechanism by Which Large Contact Angles on the Space Shuttle are Produced 5°C • Space shuttle observations compared to those in a ground-based laboratory.

11. Way it looks and the Way It Should Look!

12. Experimental Apparatus Used to Study Liquid-Vapour Phase Change Processes

13. 1. Measure in one •     horizontal direction. • A. No evaporation when • pressure was 820 Pa. •     B. Pressure in the vapor •   775Pa, • j = 0.407±0.006 g/m2s 2. Without opening the      system, rotate the 3-     dimensional positioner      90° and measure in the      second horizontal      direction.

14. Near the Interface During Steady State Water Evaporation

15. ° Temperature During Steady State Evaporation of Water 1. Uniform temperature     layer in the liquid near the interface. 2. Thermal conduction      below the uniform      temperature layer. 3. How does the energy     cross the uniform     temperature layer?

16. Does Marangoni Convection Alone Explain the Uniform Temperature Layer?

17. Interfacial Properties During Steady State Evaporation

18. Assumed Velocity Profile Near the Interface

19. Determine Tangential Speed from Measured Temperature Profile Equate tangential surface tension gradient with viscous shear stress Surface Tension is only a function of temperature Viscous Shear Stress Expression for the fluid speed:

20. Tangential Speed Determined from Thickness of the Uniform-Temperature Layer and Measured Interfacial Temperature Gradient

21. Image of Interface and Probe During Steady State Evaporation

22. Vapor-phase pressure: 776.1 Pa Results Suggest Marangoni Flow is Unstable

23. Effect of Marangoni Convection on Evaporation

24. Comparison of Speed Determined by Two methods

25. Probe Position as a Function of Time When Evaporation is Occurring at Different (Steady) Rates

26. Power Spectra of Probe Oscillations

28. If there is no Marangoni convection, energy conservation is not satisfied!

29. Conclusions A fluid confined in a cylindrical container and exposed to the acceleration field of the Shuttle adopts the two-interface configuration, but not the configuration it would be expected to adopt if the system were in equilibrium and the acceleration were ~10-6g0. The configuration adopted corresponds to the configuration expected under equilibrium conditions if the acceleration were greater than 10-4g0. During water evaporation, thermocapillary (or Marangoni) convection exists at the interface. Even in a ground-based laboratory the flow parallel to the interface is oscillatory. At higher evaporation rates, the thermocapillary convection can become turbulent.