Andreas Preusche's research while affiliated with Technische Universität Darmstadt and other places

Publications (14)

Chapter
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Physics of supercritical fluids is extremely complex and not yet fully understood. The importance of the presented investigations into the physics of supercritical fluids is twofold. First, the presented approach links the microscopic dynamics and macroscopic thermodynamics of supercritical fluids. Second, free falling droplets in a near to supercr...
Article
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Mixing and evaporation processes play an important role in fluid injection and disintegration. Laser-induced thermal acoustics (LITA) also known as laser-induced grating spectroscopy (LIGS) is a promising four-wave mixing technique capable to acquire speed of sound and transport properties of fluids. Since the signal intensity scales with pressure,...
Article
Mean temperatures of acetone, millimeter-sized, freely falling droplets in a nitrogen atmosphere are studied at two different locations downstream a capillary-type injector. Injection and ambient temperatures have been varied independently between 433 and 513 K and pressures from 2 to 6 MPa. The ratio of simultaneously measured laser-induced phosph...
Conference Paper
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Droplet evaporation within combustion chambers is of high importance for stable and efficient combustion. For ambient pressures exceeding the critical pressure of the injected fuel, evaporation processes are not fully understood yet. Especially the temperature evolution of the injected fuel is a key parameter to understand the transition of near cr...
Conference Paper
In modern gas turbines and internal combustion engines, fluids are injected at high pressures, at fuel states either close to or exceeding the critical point. Accurate prediction of these processes require increasingly precise modelling of evaporating drops. Especially the transition of classical two phase evaporation to single phase dense fluid mixi...
Article
The present work summarises the main findings of a systematic study on the behaviour of liquid droplets embedded in a high pressure and temperature environment. Thanks to the availability of quantitative temperature data, it was possible for the first time to assess the conceptual soundness of different theoretical approaches. In all cases, the pre...
Conference Paper
Several diffusion models are compared for their applicability in droplet evaporation modeling over a wide range of temperatures and pressures. Major differences in the physical derivation of the methods are being discussed. Most models being evaluated are only valid for the infinite dilution limit. Additionally they use various numbers of empiricall...
Conference Paper
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The disintegration process of liquid fuel within combustion chambers is one of the most important parameters forefficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been introduced...
Conference Paper
Full-text available
An electrohydrodynamic model for the simulation of droplet formation, motion and detachment in an electrically driven droplet generator is introduced. The numerical approch is based on the coupled solution of the multiphase flow problem with the charge continuity equation. A conduction-convection model, taking into account conductive , capacitive a...
Article
An electrohydrodynamic model for the simulation of droplet formation, detachment and motion in an electrically driven droplet generator is introduced. The numerical approach is based on the coupled solution of the multiphase flow problem with the charge continuity equation. For the latter, a modified convection-conduction model is applied, taking i...
Article
Rising pressures in modern combustion systems lead to conditions that can be supercritical for the injected liquid fuels. Quantitative measurement data is required for a better understanding of this complex process and for validation of corresponding simulations. The present study focusses on the evaporation of single free-falling droplets to reduc...

Citations

... A less complex nonlinear technique that does not require fitting to a spectrally resolved signal is laser-induced grating scattering (LIGS), also known as laser-induced thermal acoustics (LITA) [16][17][18]. LIGS/LITA experiments measure the speed of sound in a gas directly, and models of the LIGS signal evolution can be used to determine transport properties such as the acoustic damping rate and thermal diffusivity, of key interest for studies of fundamental fluid physics [19]. Previous studies have demonstrated the capabilities of the LIGS technique for temperature measurements, which can readily achieve sub-1% precision and accuracies of order of 1% [20][21][22][23][24]. ...
... In this paper, we provide new insight into the turbulence development and diffusive transport characteristics of supercritical cryogenic jets. We will focus our analysis to single specie cryogenic fluids, as phase transition in mixtures is governed by more complex mechanisms 23,24 and the research is still in preliminary stages with respect to the thermophysical properties of mixtures of supercritical fluids 17,25 . Our aim is to provide answers to three fundamental questions that are still open regarding the nature of these jets: ...
... The latter have received increased attention in the past decade, as the recently published literature shows (Falgout et al. 2016;Müller et al. 2016;Baab et al. 2016Baab et al. , 2018Crua et al. 2017). Since the main objectives are evaporation and disintegration processes of liquid fluids at pressures and temperatures either close to or exceeding their critical points, quantitative data for validation of numerical simulations have recently become a research concern with increasing interest (Bork et al. 2017;Lamanna et al. 2018;Steinhausen et al. 2019;Stierle et al. 2020;Nomura et al. 2020;Lamanna et al. 2020;Qiao et al. 2020). Microscopic investigations by Santoro and Gorelli (2008), Simeoni et al. (2010) as well as Bencivenga et al. (2009) made it possible to distinguish various regions above the critical pressure, as is depicted in Fig. 1. ...
... The latter have received increased attention in the past decade, as the recently published literature shows (Falgout et al. 2016;Müller et al. 2016;Baab et al. 2016Baab et al. , 2018Crua et al. 2017). Since the main objectives are evaporation and disintegration processes of liquid fluids at pressures and temperatures either close to or exceeding their critical points, quantitative data for validation of numerical simulations have recently become a research concern with increasing interest (Bork et al. 2017;Lamanna et al. 2018;Steinhausen et al. 2019;Stierle et al. 2020;Nomura et al. 2020;Lamanna et al. 2020;Qiao et al. 2020). Microscopic investigations by Santoro and Gorelli (2008), Simeoni et al. (2010) as well as Bencivenga et al. (2009) made it possible to distinguish various regions above the critical pressure, as is depicted in Fig. 1. ...
... 1 In order to obtain more reliable bulk and local properties, perturbed-chain statistical associating fluid theory (PC-SAFT) 24 was used in their studies to provide the bulk and local properties for vapor−liquid systems as an alternative to the cubic EoS. 1 Based on the developed DFT-PC-SAFT model, temperature jumps among the vapor−liquid interface for the evaporation of droplets have been predicted. 16,17 However, the predicted temperature jumps were 1 or 2 orders of magnitude smaller than the temperature jumps in the Knudsen layer computed with the model of Young, suggesting that the reliability of the calculated interfacial resistivities in their work needs further discussion. 16,17,25 In addition to DFT, the density gradient theory (DGT) model has also been widely accepted as a promising model to describe the interfacial properties of fluids due to its accuracy and simplicity in calculation. ...
... Some studies investigated the phase change behavior of free falling single droplet at high ambient temperature and pressure [59][60][61]. Bork et al. used Raman scattering technique for free falling heptane droplets in nitrogen to determine the fuel concentration in the wake of the droplet at different thermodynamic ambient conditions near to its critical temperature and concluded that a Heptane droplet is cooled due to local mixing and evaporative effects instead of being heated up towards its critical temperature [19]. A droplet which falling free from droplet generator at evaporative conditions might generally indicate the local evaporation behavior and transport phenomena around the droplet, but is still very different from complicated phase change behavior of Diesel spray. ...
... 13,14 It is difficult to quantitatively investigate the evolution characteristics of various forces at the interface by traditional experimental methods, but numerical simulation provides a powerful means to solve this problem. Ouedraogo et al. 15 numerically simulated the droplet formation process in electrically controlled capillaries based on the volume of fluid (VOF) method. They found that for droplets with high electrical conductivity, the electric force is in the same direction as gravity, while for droplets with low electrical conductivity, the direction of the electric force is opposite to that of gravity. ...
... The study results showed that droplet combustion condition was more than one kind even if the droplet Reynolds number and environmental temperature were the same. Bork et al. [14] measured the species concentration field in the wake of n-heptane droplets with 2D Raman imaging. The temperature results suggested that the droplet was cooled due to evaporation rather than heated up towards its critical temperature. ...