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Reducing aircraft noise and improving airconditioning

An article based on this release appeared on the PTI website, from which it was picked up by The Economic Times, Business Standard, Financial Express, and The Hindu. Bangalore Mirror also carried a story.
 
A new “nozzle”, a device used in aeroplanes, can reduce the noise levels in our airports and boost the performace of aeroplane engines. Developed at the Indian Institute of Sceince, these nozzles also have potential applications in next generation eco-friendly refrigerators and fuel cells.
 
Nozzles are simple tubes designed for some specific applications. They are used routinely in many of the engineering applications that involve flow of liquids or gases. Nozzles kept inside some specially designed ducts make what are called 'ejectors'. In aeroplane engines, ejectors are used to control the velocity of hot gases produced, which ultimately control the thrust developed by the engine. 
 
The two member research team from the IISc has developed a couple of novel nozzles, which basically promote mixing of different gases. In the case of a jet engine, the nozzles enhance mixing of hot exhaust coming out of the engine, and the cold air surrounding it. Technically, these are 'supersonic ejectors', the term supersonic denoting the fact that the exhaust gases are moving faster than sound. Sound, under normal conditions, travels 1 km in about 3 seconds.
 
When the exhaust of a jet plane moves fastm it produces more noise. One obvious way to reduce noise is to slow down the hot exhaust by mixing it with the cold air outside.  This not only makes engines quieter, but also improves their ability to push the aeroplane.
 
“One of the key concerns of the aircraft industry is noise from jet exhaust. There is a tremendous push towards design of quieter engines. Busy airports experience very high noise levels that can be harmful to human hearing over long run and affects residents close to such airports”, said Dr Srisha Rao, the lead author of the paper.
 
Air conditioners in buildings are energy guzzlers, and account for most of the carbon dioxide emissions. One of the alternatives for such traditional air conditioners is a system that runs on green energy. In large scale industrial buildings, a lot of energy comes out as heat, and is not utilised. Researchers have been working on cooling systems that utilise this heat. 
 
“In the eco-friendly alternative, the supersonic ejector replaces the compressor thus doing away with a large part of electrical energy consumption. The ejector is a passive device requiring no energy input. However, there must be some means to produce the vapors that drive this refrigeration cycle -- solar energy or waste heat from industrial sources. The high pressure high energy vapors are then passed through a supersonic ejector which is just a pumping device -- like a compressor”, explained Dr Srisha Rao.
 
“Our nozzles improve the performance of supersonic ejectors and hence the performance of refrigeration”, he said. 
 
According to him, these ejectors can also be used in gas supply circuits for fuel cells in fuel cell vehicles. 
 
About the authors:
Gopalan Jagdeesh is a Professor at the Department of Aerospace Engineering, Indian Institute of Science, Bangalore. He is associated with the Laboratory for Hypersonic and Shock Wave Research. 
Contact: 080-22933030/22932424;  jaggie@aero.iisc.ernet.in
 
Dr Srisha Rao is a Post Doctoral Fellow at Muroran Institute of Technology, Muroran, Hokkaido, Japan. The present work was done when Srisha was a PhD student under the supervision of Prof G Jagdeesh. 
 
The paper will be published on 5th October 2014. There is an early edition available online here: http://www.sciencedirect.com/science/article/pii/S1359431114005055