Fluid Behavior In Absence
Of Gravity: Confined Fluids and Phase Change
Charles A. Ward
Thermodynamics and Kinetics Laboratory,
University of Toronto
Second g-jitter Meeting
Victoria, British Columbia
Configuration of a Confined Fluid at g
Prediction from thermodynamics
g
Liquid
0
Apparatus Used on the Space Shuttle
Position of the Apparatus and Observations on
the Space Shuttle
Measure the contact angle at the upper and
lower interface...
Thermodynamic
predictions
Average OARE reading
Average values from a confined fluid
Average SAMS reading
Summary of the Proposed Mechanism
ge  0
Pl  Pu
n SV )l  n SV )u
 SV )l   SV )u
l   u
Examine the Effect of Adsorption on the
Contact Angle of the Water-Glass System
New Theory

Statistical mechanics

Gibbs adsorption equation, Young Eq.
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!
 L   V   SV   SL
PV  P L   LV (

1 1
 )
R1 R2
nSV  f (T,PV )    g(T,PV )
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 3dimensional
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
V
thePI  181.0  0.5Pa
uniform
temperature
TIL  16.20
 0.02C
layer?
V
TI  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
Determine Tangential Speed from Measured Temperature Profile
Equate tangential surface tension gradient with viscous shear stress
 LV i   (R0 , )
Surface Tension is only a function of temperature

LV
L
1
d

dT
 LV i  ( L )( I )
R0 dTI
d
Viscous Shear Stress

 (R0 , )  (
1 vr vr v

 ) rR0
r  r r
Expression for the fluid speed:

v(2 u , )  0
1 d LV dTIL
2
v (R0 , )   ( L )(
)ln(1 u )
 dTI
d
R0

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: 776.1 Pa

j  0.407
g
m2 s
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.