ISBN 9783843952057

978-3-8439-5205-7, Reihe Thermodynamik

Christoph Steinhausen
Investigation of macroscopic nearcritical fluid phenomena by applying laser-induced thermal acoustics

177 Seiten, Dissertation Universität Stuttgart (2022), Softcover, A5

Zusammenfassung / Abstract

The political and social aspiration to reduce greenhouse gases while facing increasing energy demands drive the development of new energy solutions. To achieve sustainability both innovative energy sources and improvements in efficiency are essential. Higher process efficiencies have been achieved by raising combustion pressures, reaching values that now exceed the critical pressures of the injected fuels. However, for an efficient and stable combustion a profound understanding of the processes prior to combustion, such as fluid injection, is essential. Besides fluid injection, supercritical fluids themselves have been identified as an opportunity for efficient energy conversion and heat transfer processes.

Laser-induced thermal acoustics (LITA) is a promising diagnostic tool in nearcritical fluid research. By analysing the frequency of recorded signals, speed of sound data can be directly determined. Furthermore, acoustic damping rates and thermal diffusivities can be acquired by an analytical expression for the signal. This leads to important insights into the physics of supercritical fluids. Hence, the purpose of this thesis is to apply LITA in the investigation of macroscopic fluid phenomena in nearcritical fluids. First, the significance of volume viscosities in complex fluids at dense gas conditions as well as the dependency of acoustic damping on mixing states are assessed. Second, the feasibility of time-resolved LITA measurements under complex flow conditions is evaluated. Additionally, a jet mixing process has been studied to characterise the LITA arrangement. At last, to characterise the evaporation process, time-resolved LITA measurements have been performed in the wake of a free falling droplet evaporating in a supercritical atmosphere.