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

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

Apparatus Used on the Space Shuttle

Position of the Apparatus and Observations on the Space Shuttle

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

Summary of the Proposed Mechanism

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

New Theory  Gibbs adsorption equation, Young Eq.  Statistical mechanics

Comparison of Isotherms with Measurements

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.

Way it looks and the Way It Should Look!

Experimental Apparatus Used to Study Liquid-Vapour Phase Change Processes

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/m 2 s 2. Without opening the system, rotate the 3- dimensional positioner 90° and measure in the second horizontal direction.

Near the Interface During Steady State Water Evaporation

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? °

Does Marangoni Convection Alone Explain the Uniform Temperature Layer?

Interfacial Properties During Steady State Evaporation

Assumed Velocity Profile Near the Interface

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:

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

Image of Interface and Probe During Steady State Evaporation

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

Effect of Marangoni Convection on Evaporation

Comparison of Speed Determined by Two methods

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

Power Spectra of Probe Oscillations

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

Conclusions 1.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 -6 g0. The configuration adopted corresponds to the configuration expected under equilibrium conditions if the acceleration were greater than g0. 2.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.