Experiment Launches With Shuttle Discovery To International
Space Station
Here on Earth, the process of boiling is used for tasks ranging
from cooking and heating to power generation. In space exploration,
boiling may also be used for power generation and other
applications, but because boiling works differently in a
zero-gravity environment, it is difficult to design hardware that
will not overheat or cause other problems.
Professor Jungho Kim of the A. James Clark School's Department
of Mechanical Engineering at the University of Maryland, College
Park, is working with John McQuillen, project scientist at NASA's
Glenn Research Center in Ohio, to study how boiling is altered in
zero-gravity. Their experiment, the Microheater Array Boiling
Experiment (MABE), launched Thursday aboard Discovery, and be
placed aboard the International Space Station for operation in the
following few months. The experiment, which has already been tested
on NASA's "Vomit Comet" and the ESA's Parabolic Flight Campaign in
France, will be installed in the Microgravity Science Glovebox once
aboard the ISS.
The results of the experiment could help engineers design space
hardware that utilizes boiling for multiple applications. "In
space, boiling may be required to generate vapor to power turbines
in some advanced concepts for power generation, for temperature
control aboard spacecraft, and for water purification," says
Kim.
When a liquid is boiled on Earth, vapor, which is less dense
than liquid, is removed from heated surfaces through the action of
buoyancy. In zero-gravity, the buoyancy force becomes negligible
and vapor can blanket the heated surfaces rather than moving away,
potentially leading the surfaces to a state known as critical heat
flux.
Critical heat flux occurs when a heater or plate becomes too
hot, restricting the flow of liquid to the surface and causing the
plate to overheat and potentially burn out. Since liquids boil
differently in space, an understanding of how these fluids behave
can improve the reliability and expand the applications of space
exploration hardware.
The experiment that will take place on the ISS will use two
arrays of platinum microheaters bonded to a quartz plate. The
arrays measure 7 mm and 2.7 mm across. The heaters are warmed when
electricity is applied, and spaces between the heaters lines will
allow the boiling process to be visualized through the transparent
quartz. Boiling of a refrigerant-like fluid (FC-72) will be filmed
at high speed and the video sent back to Earth along with the
heater data in real-time for analysis.
"We have calibrated these heaters as a function of a
temperature, and we measure the power level required to keep each
of the heaters in the array at a constant temperature," Kim states.
"Using a camera that looks through these microheaters, we can
examine the relationship between the power level and the state of
the fluid above that microheater."