Reducing aircraft noise and improving air conditioning

A new "nozzle", a device used in aeroplanes, can reduce noise levels around airports and boost the performance of aeroplane engines.
Developed by a team of scientists at the Indian Institute of Science, Bangalore, these nozzles also have potential applications in next generation eco-friendly refrigerators and fuel cells, says a release by Gubbi Labs.
"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," according to Srisha Rao, lead member of the team.

Nozzles are simple tubes designed for some specific applications. Used routinely in many of the engineering applications that involve flow of liquids or gases, nozzles kept inside specially designed ducts 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 research team 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 fast 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, Gubbi Labs said quoting the IISc.

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.