charles a. ward thermodynamics and kinetics laboratory, university of toronto

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 gConfiguration of a Confined Fluid at g0

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

ge>0

Pl >Pu

nSV)l >nSV)u

γSV)l <γSV)u

θl >θu

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!

€

nSV = f (T ,PV )⇒ θ = g(T ,PV )

€

PV − PL = γ LV (1R1

+1

R2)

€

μL = μ V = μ SV = μ SL

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/m2s

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

PIV =593±34Pa

TIL =−0.4±0.05°C

TIV =2.6±0.05°C

j =1.017g/sm2

PIL =617.3Pa

Psat(TIL )=593Pa

Psat(TIV )=766.6Pa

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?

°

PIV =181.0±0.5Pa

TIL =−16.20±0.02°C

TIV =−10.45±0.01°C

j =1.520±0.003g/ sm2

Does Marangoni Convection Alone Explain the Uniform Temperature Layer?

Interfacial Properties During Steady State Evaporation

Assumed Velocity Profile Near the Interface

€

σ (R0 ,θ ) = η (1r

∂vr

∂θ+

∂vr

∂r−

vθ

r) r=R0

€

∇γLV • iθ =1R0

(dγ LV

dTIL

)(dTI

L

dθ)€

∇γLV • iθ = σ (R0 ,θ )

€

vθ (R0 ,θ ) = −1η

(dγ LV

dTIL

)(dTI

L

dθ) ln(1−

2δu

R0

)

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:

€

v(2δu ,θ ) = 0

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

€

j = 0.407g

m2sVapor-phase pressure: 776.1 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 ~10-6g0. The configuration adopted corresponds to the configuration expected under equilibrium conditions if the acceleration were greater than 10-4g0.

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.