Modern passenger jets generate and consume huge amounts of electricity, which generates heat and in turn requires extensive cooling systems. As the demand for electricity rises with each new generation of airliners, the more electricity is needed for on-board systems and more efficient cooling systems.
ZAL co-ordinating research group
Researchers at Hamburg’s Centre for Applied Aeronautical Research (ZAL) are trying to come up with this new generation of cooling systems. To this end, ZAL is heading a collaboration of several partners called NAKULEK (Concept, design and verification of a passive closed-circuit cooling system for aeroplane systems). ZAL scientists are working with the Hamburg University of Technology’s Institute of Engineering Thermodynamics, simulation experts at XRG Simulation and researchers at Airbus and Apparatebau Gauting GmbH engineering which is part of the Diehl group. The latter produces air and water management systems for airlines.
ZAL’s experts are devising a new system for an airline while the Institute of Engineering Thermodynamics and XRG Simulation is investigating the thermodynamic characteristics of that system. Over the next three years, passive cooling systems will be designed that can cool on-board electronics and battery systems more efficiently.
Search for lightweight and energy-saving cooling
“Lightweight” and “efficient” are the keywords for this new technology. A passive, closed-circuit cooling system seems ideal as it does not require pumps and simply functions by gravity. A liquid is heated up and then rises in a tube. While rising, it cools down which causes the coolant to drop back down the tube. “The coolant itself has not yet been selected,” says Lutz Bittner, who is in charge of NAKULEK at ZAL. Bittner works as a research engineer for aircraft air-conditioning systems.
Growing demand for electricity
NAKULEK is bringing ZAL closer to realizing the forward-looking “More Electric Aircraft“ concept that aims to reduce the number of mechanical, hydraulic and pneumatic systems aboard an aircraft and gradually replace them with electric systems. During the technological development, demand for electricity on board airliners has grown with each new generation. A modern passenger jet such as the Airbus A320 generates approximately 105 kW. Larger and more modern aircraft such as the A350 even have an output of 1.5 Megawatts – enough to supply a town of 2,000 people with electricity. The electrical systems aboard an airliner include lighting and air-conditioning, vast amounts of electronic equipment, the kitchen, but also key components of the flight control system. While rudders and flaps are still hydraulically operated, the systems themselves contain more and more electronically operated actuators. Hydraulic systems will eventually be replaced to save weight and thus fuel.
Heat sources: passengers, crew and aircraft systems
Electrical generators and countless pieces of machinery generate heat. So every item including the batteries requires cooling. “The demand for cooling grows as more electrical output, more electronic equipment and electric motors are brought aboard an aircraft,” said Bittner. Other sources of heat are the kitchen, and above all, the passengers. “The passengers and the crew are the main sources of heat,” Bittner added. A passenger in his seat emits 70 Watts, a cabin attendant at work even 100 Watts. Sunlight is another source of heat and warms up an airliner. “The value of NAKULEK can best be explained as a result of the growing importance of electrical systems aboard aircraft,” Bittner explained. And the successors to Airbus’s A350 and Boeing’s 787 will feature even more electronic devices.
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