Microgravity will provide a clear window to liquid/vapor interaction in a heat pipe.
A near absence of gravity, as afforded by the low Earth orbit of the International Space Station (ISS), may be the key to a full explanation of how heat pipes actually work their magic. Although thermal engineers understand that the liquid-to-vapor phase change that occurs inside heat pipes makes them many times more effective than solid copper, the exact behavior of the fluid and vapor at the molecular level goes on unobserved and is little understood. The ISS lab will have no buoyancy-driven convection and the liquid’s surface tension will be reduced. Without the interference of the Earth’s gravity, the underlying principles of how heat pipes actually work could be revealed. Only at the high altitude of the ISS can the effects of Earth’s gravity be filtered out and expose the microscopic mechanisms of the liquid/vapor interaction inside a heat pipe.
“As electronic devices continue to shrink in size while simultaneously generating more power, and technologies for long-term space missions require the utmost reliability and minimal maintenance, efficient cooling becomes paramount to prevent overheating and ensure optimal performance,” said project leader Joel Plawsky, who teaches chemical engineering at Rensselaer Polytechnic Institute (RPI). “Conducting this experiment on the space station allows us to eliminate the influence of gravity and study vapor-liquid interfaces of organic mixtures used in heat pipes in an entirely new light.”
RPI, along with Tec-Masters, has been exploring the effects of microgravity to better understand what happens in the vapor-liquid interface of the fluid used in heat pipes to increase their efficiency.
How microgravity works and how infinitesimally small things are attracted to each other—things as small as the molecules of fluid inside a heat pipe, the actual moving parts of a heat pipe’s work—may finally be understood.
Heat pipes are used in electronics. You might have noticed them when you opened up your notebook computer. The copper, rectangular pipes contain a liquid-vapor mixture. As with all heat pipes, the variety of heat pipes used in notebooks work by absorbing heat from a hot surface (the microprocessor) and dumping it on the other end (assisted by a fan, in the case of a notebook).
NASA uses heat pipes in spacecraft avionics, on the Hubble Telescope and on Mars rovers. They are also in wide use on satellites operated by space agencies, the military and commercial enterprises. The heat pipes’ ability to whisk away heat without moving parts or a power supply makes them ideal cooling devices in space.
Heat pipes are able to take away from four to one hundred times as much heat as a solid copper heat exchanger of the same shape (according to one manufacturer of heat pipes). Thermal engineers know that if they want to get heat out in a hurry with the least amount of design change, they can throw in a heat pipe.
About the International Space Station National Laboratory
The heat pipe investigation is one of several on Northrop Grumman’s 19th Commercial Resupply Services mission (NG-19) to be performed by the ISS crew. The experiments are being funded by the U.S. National Science Foundation (NSF).
The ISS National Laboratory is available to government agencies and can be “rented” for commercial interests. Previous experiments have included 3D printing, starting with a Print the Future contest open to students in 2016. The lab is managed by the Center for the Advancement of Science in Space (CASIS) under a cooperative agreement with NASA.
