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Nanofluids, turbine blade cooling for aircraft engines, environmental effects of aviation, and experimental methods in heat transfer and fluid mechanics
Nanofluids are an exciting new area of scientific investigation and engineering application. These suspensions of nanometer sized particles provide a stable coolant with thermal conductivity up to two orders of magnitude higher than the base fluid alone and temperature dependence of the thermal conductivity that hints at the possibility of ‘smart fluid' applications which will automatically cool more effectively where it is needed most. Yet the physical mechanism behind this behavior is poorly understood. Rebecca Christianson, an Olin Professor of Applied Physics, and I have initiated a joint science and engineering study of these materials with the eventual intent to help elucidate the physics behind the thermal properties of these suspensions and examine their application to high-g engineering problems such as the cooling of ultra-high speed turbines.
Turbine blades in modern aircraft engines must be designed to withstand extreme temperatures. The first stage turbine blades are exposed to gas flows from the combustor at temperatures as high as 2800 ºF and therefore require aggressive cooling. The blades are typically air cooled using a combination of internal and film cooling. Cooler air is drawn from the compressor and routed to the turbine where it is delivered to each blade. My research is focused on Vaporization Cooling, an innovative self-regulating form of turbine blade cooling in which internal evaporation of a liquid metal such as potassium is used to cool the blade. Vaporization cooling can maintain the external blade surface at a nearly uniform temperature, independent of heat flux. The firing temperatures (and therefore the performance) of modern gas turbine engines are limited by the effectiveness of the air cooling technology and by the precision with which the cooling air distribution can be predicted and implemented. It is believed that evaporatively cooled turbine blades can alleviate this problem by reducing the need for accurate prediction of the heat flux to the blade and by enabling heat rejection to sinks other than the compressor discharge air. The overall effect is higher system efficiency due to turbine operation at higher peak cycle temperature, while minimizing the cooling air flow penalty.
I recently completed a project on a study of ways to reduce aviation noise and emissions. Although the negative impact of noise was reduced by 80% between 1992 and 2001, aircraft noise is still the single most significant objection to airport construction or expansion. Aircraft emissions affect both local air quality and contribute to climate change. There is public demand for increasing mobility but a higher importance is also placed on environmental quality. The final result was a Report to Congress with recommendations for how the US can be more active in coordinating policy, research and technology development to reduce or mitigate the environmental effects of aviation.
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