When astronauts head for Mars, keeping them cool will be a major concern, so a team of mechanical engineers at the Worcester Polytechnic Institute (WPI) led by Jamal Yagoobi is working on a new electrical cooling system that has no moving parts. Already being tested aboard the International Space Station (ISS), the electrohydrodynamic (EHD) cooler uses electrically charged fluids running through tiny tubes to carry away heat without noise or vibrations.
Heat is one of the biggest and most persistent threats to space travel. Though a spacecraft set in shadow is theoretically subjected to temperatures hundreds of degrees below zero, the real problem is high temperatures. When subjected to sunlight, the craft will quickly heat up to above the boiling point of water unless its surface is made reflective.
But the bigger problem is that space is a vacuum and a spacecraft is essentially a giant thermos flask. Spacecraft produce a lot of heat from their power systems, electronics, mechanical parts, and even the bodies of the astronauts. And because these are all surrounded by a vacuum, the fact there's no air to conduct or convect the heat away makes getting rid of this heat is difficult.
Instead, the heat needs to be transferred to panels that allow it to be radiated out into space. One drawback with this is that current systems aren't as efficient as they could be, and their pumps and motors generate noise and vibrations that create their own problems. So a simpler, quieter system that uses less energy has more than one advantage.
"When you're in space, you can't open the window and let the cold air come in and cool you off," says Yagoobi. "As we move forward, a lot of electronics will be jammed into a very small area in a spacecraft or in a satellite. We're going to use a lot more advanced electronics and produce a lot more heat. That's why we need to develop this technology. Whether it's for travel to Mars or any other mission outside Earth, you have to have cooling devices that are very effective, durable, and non-mechanical, and which require minimal power to function."
Called "Electrohydrodynamically Driven Liquid Flow in Parallel Micro-Tubes," the WPI experiment has already flown on zero-gravity airplane flights in 2012 and 2013, and a version was sent to the ISS aboard a SpaceX Dragon cargo ship in February 2017, where it will operate until this August. It will be replaced in 2021 by a more complex version that is anticipated to cost around US$10 million all up and is expected to run for about a year during testing.
Like the present experiment, the more complex "Electohydrodynamically Driven Liquid Film Flow Boiling," system uses electrically charged liquids for cooling, but instead of using electric fields to just circulate the fluid, the new version uses a two-phase, non-mechanical EHD pumping system with a condenser section and a boiling section. According to WPI, this allows the circulating fluid to boil, so it absorbs more heat like in a domestic refrigerator, then it returns to a liquid form as it passes through a radiator, which dumps the heat into a radiator panel and then out into space.
Outside of being used on space stations and future manned Mars missions, the team also sees the technology as having applications on satellites and deep space probes, as well as in industrial cooling and heating, ventilation, air conditioning, and refrigeration systems back on Earth.
"We're greatly encouraged that our work has been deemed a success" says Yagoobi. "This is the first time ever for this type of cooling pump technology in space, and the outcome has been very positive. This positions us well for the next phase of the work."
The video below shows the electrodynamic cooling system in action.
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