Microgravity fridge aims to improve astronauts' menu
Image credit: Purdue University
A refrigerator for astronauts, that could enable residents of the International Space Station (ISS) to enjoy a better diet, has been tested in microgravity.
Currently, astronauts are reliant on canned and dried food that have a shelf life of only about three years, but the new fridge could give astronauts a supply of food that could last five to six years.
A team of engineers from Purdue University, Air Squared, and Whirlpool Corporation has shown that a prototype they developed could potentially overcome the challenges of getting a traditional fridge to work in space just as well as it does on Earth.
The team ran three experiments earlier this month to test various aspects of the fridge design onboard a specially designed plane that flew in microgravity 30 times – for 20-second intervals – during each of four flights.
The plane, Zero Gravity Corporation’s (ZERO-G) unique weightless research lab, is the only testing space of its kind in the USA.
From the data collected so far, it seems the prototype can operate just as well in microgravity as it does on the ground and is no more likely to flood (which can damage a fridge) in microgravity than in normal gravity.
“We want to have a refrigeration cycle that is resistant to zero gravity and works to normal specifications,” said Purdue's Professor Eckhard Groll. “Our preliminary analysis clearly shows that our design allows gravity to have less impact on that cycle.”
While fridge experiments have been tested in space before, they either didn’t work very well or eventually broke down.
The fridge design cools food through a vapour-compression cycle, similar to the process that a typical fridge uses on Earth, but without the need for oil. Having an oil-free vapour-compression cycle removes concerns about oil not flowing where it should in zero gravity.
The team’s prototype is about the size of a microwave, ideal for potentially fitting into the ISS’s rack systems that store research experiment payloads. Air Squared built the prototype and the oil-free compressor inside, which acts as the heart of the fridge.
The team’s experiments aimed to test a common hypothesis that pushing refrigerant liquid through a vapor-compression cycle at a higher velocity would reduce the effects of gravity on the fridge’s performance.
Before the test flights, it was demonstrated that an oil-free vapor-compression cycle can operate in different orientations – even upside down. If a fridge can operate in any position, space crews wouldn’t have to worry about making sure the fridge is right side up at a landing.
“The fact that the refrigeration cycles operated continuously in microgravity during the tests without any apparent problems indicates that our design is a very good start,” said Purdue Ph.D. student Leon Brendel.
“Our first impression is that microgravity does not alter the cycle in ways that we were not aware of when we tested the effects of gravity on the fridge design on the ground by rotating and inclining it.”
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