Project

Cryogenic fluids are involved in the propulsion and thermal management of space missions, such as systems for Earth-to-Orbit Transportation, Planetary exploration, and In-Site Resource Utilization (ISRU) [5] as well as in medical and industrial applications. Furthermore, the future of space exploration is highly dependent upon the ability to supply cryogenic fluids to spacecraft in a safe and reliable manner to ensure the functionality of propulsion devices, life support equipment and power generation systems. One of the most challenging aspects of working with cryogenics is that transporting such fluids requires the system to be initially chilled down and to maintain the cryogenic in its liquid state. During the transportation process, gravity plays a key role in the flow pattern development as well as the heat transfer mechanism. On Earth, cryogens are forced to contact the bottom wall of the duct due to gravity. However, in a microgravity environment, the cryogens tend to flow through the center of the duct, while vapor contacts the duct's wall forming an inverted annular flow. This results in an increased chill down time due to the vapor film between the liquid and the duct that decreases the heat transfer rate . The objective for this experiment is to expand upon last year‟s research by studying liquid helium, rather than liquid nitrogen. This cryogen was chosen because its properties closely resemble those of liquid hydrogen, which is commonly used as a rocket propellant. Additionally, this research is relevant to superconducting magnets, MRI‟s and other research applications where liquid helium is utilized. A more complete characterization than the one performed during last year‟s study is expected by recording the flow visually from multiple angles, and by studying the effects of complex pipe geometries that are commonly used in industry on chilldown rate and flow patterns.

Illustration


Stratified Flow on Earth vs. Inverted Annular Flow in Microgravity

In microgravity conditions the more desirable stratified flow separates from the wall to form a convection-dominated inverted annular flow. While the above image describes liquid nitrogen, the same effect occurs with the liquid helium being used this year.

Aircraft

Our experiment was conducted aboard NASA's chartered "Weightless Wonder" microgravity-producing aircraft. By following a parabolic path, the upward momentum of those in the plane continues to exist once the crest of the parabola is reached, and as the plane begins its descent. It's this upward acceleration which cancels Earth's gravity for about 20 seconds as the passengers continue to move upward, or stay stationary, with respect to the earth.

For detailed information about this aircraft, consult NASA's ICB.

Apparatus

The apparatus pictured below was used last year to study liquid nitrogen chilldown rates. A redesigned apparatus will be constructed this year, including a revamped cryogenic liquid delivery system (CLDS), a faster computer and new high speed camera, a freshly built vacuum chamber, a new vacuum pump and a new layout. Stay tuned for a picture of the new apparatus, it will be posted as soon as it's done!

Objectives

We will answer...

I. When compared to flow in a straight pipe, how and why does cryogenic flow in a complex geometry pipe behave differently during chilldown?

II. What is the effect of turbulent flow on the chilldown rate in microgravity when compared to laminar flow in the same environment?

III. How significant is the difference between laminar and turbulent flow in both terrestrial and microgravity condition?