The University of Wisconsin ZeroGravity Team develops, conducts, and analyzes microgravity experiments as participants in NASA's Reduced Gravity Student Flight Opportunities Program. I flew with the experiment my freshman and sophomore years and co-lead the Linear Spray Cooling experiment with Lisa McGill. My involvement has been very rewarding and I have enjoyed considering and hopefully minimizing the effect of gravity on our experiments.
Participating in NASA's Reduced Gravity Student Flight Opportunities Program, I joined students from across the nation in designing experiments to be performed in a microgravity environment. Over three years, we submitted three research proposals, and NASA selected two of these experiments for investigation aboard the DC-9B Weightless Wonder. This plane achieves microgravity (zero-g) by flying a parabolic path, during which the plane, occupants, and experiments experience zero gravity for 30 seconds. My flights capped 11 consecutive years of UW experiments in this program; see below for descriptions.
2006-7: Measuring Capillary Forces in Microgravity
Our team designed an experiment to research capillary action in microgravity. Capillary action is the phenomena that allows plants to transport liquid from their roots up to the highest branches. In contrast to terrestrial applications, microgravity fluid systems cannot rely on gravity to collect fluids; instead the absence of gravity often 'allows' fluids to get trapped in the corners of tanks far from the tank exit. In these cases, the fluid cannot be drawn out of the tank, and though unspent, is useless. To better understand this situation, this experiment measured the flow velocities of two liquids as they flowed up five differently-angled surfaces (see video, below). These velocities are a function of the fluid properties and the surface geometry; interpreting our results will guide fluid system design to avoid trapped-fluid scenarios. This research can also be applied to transporting fluids in space without pumping.
2007-8: Spray Cooling in Microgravity
As computer processors, power amplifiers, laser diodes, and similar devices increase in performance they are also becoming smaller. Since these devices are not 100% efficient some of the input energy is lost as heat which is increasingly concentrated due to shrinking size. Removing this thermal energy is essential to the continued operation of these devices but current methods are fundamentally limited in their heat transfer capability. Specifically, forced air convection cooling quickly requires absurd velocities to cool high heat flux devices and liquid cooling breaks down when vaporized liquid prevents cool liquid from contacting the hot surface. Linear spray cooling is a two-phase technique that shoots coolant droplets at the heated surface and uses their inertia to prevent the formation of a vapor bubble. Working with Professor Tim Shedd we showed that coolant flow rate is the primary determinant of a linear spray cooling system's performance and that the influence of gravity is minor (2.6% at the largest). While further work is needed, there does not appear to be any fundamental reason that would prevent linear spray cooling from being used in satellites, on the International Space Station, and in variable-gravity environments (fly-by-wire aircraft for instance).
This research was presented at the 2009 Space, Propulsion, and Energy Sciences International Forum in Huntsville, AL.
2008-9: Continued Investigation of Linear Spray Cooling
Our previous spray cooling experiment answered some questions but motivate a number of others. In my Junior year we proposed a new array design and a more thorough characterization of spray cooling in microgravity. The new array design was precisely machined from a single piece of aluminum, as opposed to the array of tubes used in previous linear spray arrays. Unfortunately, NASA's support was reduced by 2/3rds and we were not selected to fly this experiment.
The new array concept:
As mentioned, UW has been active in this program for a number of years; here are some of the materials I've collected which document our research.
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