International News
NOVEL AIR TECHNOLOGY DELIVERS SUSTAINABLE COOLING
By Saarland University
new type of energy efficient , ecologically sustainable
A cooling technology that does not require the use of climatedamaging refrigerants is currently being developed .
The new technology by Professor Stefan Seelecke and his team at Saarland University makes use of shape-memory materials that are also known as ‘ artificial muscles ’. These materials are able to transport heat by loading and unloading nickel-titanium wires . Seelecke also holds the position as chair of intelligent material systems at the university .
Seelecke ’ s team is currently developing the technology for use in cooling systems for electric vehicles . The researchers presented their technology at the Hannover Messe , showcasing the world ’ s first machine that can cool air by flexing artificial muscles .
From the humble fridge and air conditioner to complex cooling systems for use in industrial processes – keeping cool is a significant part of today ’ s society . Global warming and a growing world population mean that the need for energy-efficient cooling systems will only get larger . But low temperatures typically signify high electricity consumption , which in turn usually means a high carbon footprint and the risk of emissions of refrigerant gases that often have a high global warming potential .
The research team includes academic and industrial partners at Saarland University and the Center for Mechatronics and Automation Technology ( ZeMA ).
“ Our process is energy efficient and doesn ’ t require the use of refrigerants that are harmful to the climate . In fact , our technology is up to 15 times more efficient than systems based on conventional refrigerants ,” explained Seelecke . The EU Commission and the United States Department of Energy have both evaluated the new process and consider it to be the most
" Our technology is up to 15 times more efficient than systems based on conventional refrigerants ." promising alternative to the vapour-compression refrigeration technology in use today .
Seelecke ’ s team has essentially developed the world ’ s first continuously operating prototype using this new process . The technology uses artificial muscle fibres composed of bundles of ultrafine shape-memory wires made from the nickel-titanium alloy ‘ nitinol ’.
These wires have the special property that they return to their earlier shape after being stretched or otherwise deformed . They are thus able to tense and relax like human muscles .
The reason for this behaviour is to be found within the structure of the metal alloy . The atoms in the alloy are arranged in a crystal lattice structure . If the nickel-titanium wire is deformed or pulled in tension , the layers of atoms in the lattice crystal move relative to one another creating strain within the material . This strain is released when the wire returns to its original shape .
These changes in the material ’ s crystal structure are known as phase transitions and they cause the wires to absorb or release heat . It is this effect that Seelecke and his team are exploiting in their novel cooling system . “ The shape-memory material releases heat to its surroundings when it is mechanically loaded in its superelastic state , and absorbs heat from its surroundings when it is unloaded . And this effect is particularly pronounced in the case of nitinol . When pre-stressed nitinol wires are unloaded at room temperature , they cool down by as much as 20 degrees ,” explained Seelecke and confirmed by Susanne-Marie Kirsch , who helped to develop the cooling system as part of her doctoral research project .
However , the Saarbrücken cooling system is significantly more complex . The team has designed and developed a cooling circuit in which a patent-pending cam drive rotates in such a way that bundles of 200 micron-thick nitinol wires are alternately stretched and relaxed so that heat is transferred as efficiently as possible .
Air is blown through the wire bundles in two separate chambers : in one chamber the air is heated , in the other it is cooled . As a result , the machine can cool and can heat . “ When the wires are mechanically loaded they also heat up by about 20
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RACA Journal I October 2022 www . refrigerationandaircon . co . za