Two Phase Flow in a Microgravity Environment

Team Members:

Dustin Schlitt Shem Heiple

Jason Mooney Brian Oneel

Jim CloerAcademic Advisor

Mark Weislogel

Mission

While Two-Phase flow cycles are more efficient in the transfer of heat energy, they have been avoided in low gravity applications due to the lack of experimental data describing the behavior of the flow regimes. It was the goal of the Portland State Team to develop a reliable, inexpensive testing apparatus that would reproduce a steady slug flow regime that could be easily employed in ground based micro-gravity test facilities, such as NASA’s KC-135.

Two Phase Flow Over View

Micro-Gravity vs. Normal GravityFluid flows in which the effect of surface tension is significant are called capillary flows. Generally in normal gravity such flows are limited to small channels less than a few millimeters in diameter.

The Bond number, Bo = ρgr2/σ is the ratio of the gravitational force and the surface tension of the liquid, where ρ = density of fluid, g = the gravitational acceleration, r = the radius, σ = surface tension. When Bo >> 1, the gravitational force dominates fluid behavior. For Bo<< 1, surface tension plays a significant role in the behavior of the fluid. In the absence of gravity Bond numbers for large radius tubes can remain extremely small allowing flow patterns that are totally unique and unable to attain in normal gravity.

Bubbly Flow: Normal Gravity vs. Micro-Gravity

Slug Flow: Normal Gravity vs. Zero Gravity

Annular Flow: Normal Gravity vs. Zero Gravity

Design Requirements• Because the apparatus was to be used in NASA’s unique KC-135

test environment certain design criteria were imposed by NASA’s Reduced Gravity Flight Office. These deign criteria along with a weighing factor enabled the evaluation of various designs to a common metric.

• The design criteria provided by NASA were broken down into the following categories: Performance, Ergonomics, Installation, and Safety. The following table highlights the design specifications.

PerformanceCustomer Requirement Metric Importanc

e

1 NASA The device is required to withstand hard landing loads.

Forward 9*9.8 m/s2Aft 3*9.8 m/s2Down 6*9.8 m/s2Lateral 2*9.8 m/s2Up 2*9.8 m/s2

10

2 NASA The device is to withstand inadvertent contact loads that could exceed “hard landing loads” locally.

81.64 kg impacting the structure at a velocity of .6096 m/s.

556 N over a 5.08 cm

radius

10

3 NASA The device must attain steady state operation within a short

period of time.

Because of the limited time available to take data the device must reach steady state within 25 seconds.

10

ErgonomicsCustomer

Requirement Metric Importance

1 NASA The device must be easily transported on and off the air craft.

For manual transport no one person shall carry more than 222.4 N.

10

InstallationCustomer

Requirement

Metric Importance

1 NASA The apparatus must be secured to the floor of the aircraft

The apparatus must not exceed the maximum floor loading of 9576 N/m2. The straps that will be used to secure the device to the floor of the air craft yield when 22241 N is applied, the device should not exceed this limit for any gravitational loading with less than a safety factor of 2

10

SafetyCustomer Requirement Metric Importance

1 NASA The device should not contain any sharp edges or points

10

2 NASA The device must have a “kill switch” for emergency shut down procedures

The “kill switch” must de-energize all components in the system to a safe state.

10

3 NASA All electronic wiring and cabling must be installed to both the Johnson Space Center Safety and Health Handbook and the National Electronic Code Standards.

10

4 NASA Liquids approved for use in the air craft must be contained

Non-hazardous liquids in volume greater than 177 ml must be doubly contained, and the containment method should be structurally sound and able to with stand the inadvertent contact loads described in the performance section of this document.

10

Theory

The testing apparatus employs the use of four transparent flexible tubes partially filled with a fluid of known properties ( viscosity (μ), surface tension (σ), density (ρ) ). These tubes are made to rotate around two drums. The drums in turn are mounted on a large rotating disk. As the large disk rotates the liquid slugs in the tubes experience a centripetal acceleration. This centripetal acceleration is sufficient enough to drive the fluid motion while maintaining a capillary dominated flow. As the large disk is rotated the drums are made to rotate dragging the fluid from the outer edge of the drum to the linear portion of the tube path shown.

A force balance in the linear path can be obtained between the acceleration force ( Fa ), the viscous dissipation force( Fμ ), and the surface tension force ( Fσ ). When these forces balance a steady slug velocity develops.

Theory

V

Rrec Radv

Balancing forces yields,

FFFma g

1

8281222222

2

22l

rR

Vl

rRl

Caf

dt

drl

Rtdt

dr

dt

dl

dt

rdl

t r

From this force balance the governing differential equation describing this flow is,

At steady state the governing differential equation reduces to,

1

82222l

rR

Vl

rRl

Cafr

Our Design

1. Aluminum Frame 2. Mounting Plate3. Motor/Gear Box ( Large Disk )4. Motor/Gear Box ( Drums )5. Drum Pack Assembly6. Counter Weight7. Digital Video Camera

8. Large Disk Rotational Velocity Display9. Back Light Switch10.DV Monitor11.Speed Controls ( Large Disk, Drum )12.Power Supply13.Outreach Experiment Controls14.Outreach Experiment Housing

Our Design

Our Design

The Zero G Experience

KC135 Reduced Gravity Aircraft

Number of Parabolas: 32 Top of Parabola : 32,000 ftFree Fall Time : 21 seconds Bottom of Parabola : 24,000 ft

Not Zero Gravity…but free fall

Fluids in Reduced Gravity

Reduced Gravity Fun

Data Analysis

Data Analysis

• Steady state slug velocity.

• Steady slug length.

• At least one revolution of the tube loop during steady state.

Measuring Film Thickness

Average Velocity

True slug distance vs. time

y = 11.168x - 10.469

R2 = 0.9992

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

time (s)

dis

tan

ce (

cm)

Change In Slug Length

Slug Length vs. time

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

time (s)

len

gth

(cm

)

Length of slug is nearly steady.

Comparison of Data Against Previous Correlations

Dimenssionles Film Thickness vs. Capillary Number

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Ca

h/R

Jing-Den Chen

Bretherton

Albert 2

R =3/16"

Beyond Bretherton'sprediction

Results

• Steady state flow ± 1%

• Prediction match

• Errors– Aircraft– Apparatus– Film thickness sensitivity