Experiment based development of a non-isothermal pore network model with secondary capillary invasion

In this thesis, PN simulations of drying are compared with experimentally obtained data fromdrying of a representative 2D microfluidic network in SiO2 under varying thermal conditions withthe aim to identify governing physical pore scale effects. Gravity and viscous effects aredisregarded in this thesis. Instead drying with slight local temperature variation and drying withimposed thermal gradients are studied. Based on this investigation, a powerful non-isothermalPNM is developed. This model incorporates i) the phenomena associated with the temperaturedependency of pore scale invasion, namely thermally affected capillary invasion and vapor flow aswell as ii) the secondary effects induced by wetting liquid films of different morphology. This studyclearly evidences that the macroscopic drying behavior is fundamentally dictated by thetemperature gradient imposed on the PN and moreover by the secondary capillary invasion aswell. In agreement with literature, invasion patterns as in invasion percolation with progressiveevaporation of single clusters are observed in drying with negligible local temperature variation;gradients with temperature decreasing from the surface (negative temperature gradient) canstabilize the drying front, evolving between the invading gas phase and the receding liquid phase,whereas temperature increasing from the surface (positive temperature gradient) leads todestabilization of the liquid phase with early breakthrough of a gas branch and initiation of asecond invasion front migrating in opposite direction to the evaporation front receding from theopen surface of the PN. Special attention is paid on the distinct drying regimes found in thesituation of a positive gradient because they are associated with different pore scale invasionprocesses. More precisely, temperature dependency of surface tension dictates the order ofinvasion as long as the liquid phase is connected in a main liquid cluster (usually found during thefirst period of drying). In contrast to this, detailed study of the vapor transfer mechanismsemphasizes that vapor diffusion through the partially saturated region can control the pore leveldistributions of liquid and gas phase during the period of drying when the liquid phase isdisconnected into small clusters. This is also related to the cluster growth induced by partialcondensation of vapor. It is shown and discussed in detail in this thesis that this effect not onlydepends on direction and height of the temperature gradient for a given pore size distribution butthat moreover the overall evaporation rate influences the cluster growth mechanism. This indicatesthat liquid migration during drying of porous media might be controlled by the interplay of thermalgradients and drying rate. In summary, the study of thermally affected drying of the 2-dimensionalPN reveals complex pore scale mechanisms, usually also expected in drying of real porous media.This leads to the development of a strong mathematical pore scale model based on experimentalfindings. It is demonstrated how this model might be applied to understand and develop moderndrying processes based on the simulation of thermally affected pore scale mass transfe

Selbstwert - eine Frage der Erziehung?

Im Rahmen einer quantitativen online-Studie wurden mehrere Facetten des Selbstwertes und das perzipierte elterliche Erziehungsverhalten hinsichtlich der Dimensionen Ablehnung und Strafe, Emotionale Wärme sowie Kontrolle und Überbehütung in der Erinnerung von Studierenden untersucht und auf Zusammenhänge hin analysiert. Insgesamt nahmen 364 Studierende im Alter zwischen 18 und 29 Jahren an der Erhebung teil, wobei sich die Stichprobe aus 181 weiblichen und 183 männlichen Studierenden zusammensetzte. Die aus drei Teilen bestehende Fragebogenbatterie erfasste soziodemographische und biographische Daten, verschiedene Selbstwertbereiche mittels der Multidimensionalen Selbstwertskala (Schütz & Sellin, 2006) und das zurückliegende elterliche Erziehungsverhalten mittels des Fragebogens zum erinnerten elterlichen Erziehungsverhalten (Schumacher, Eisemann & Brähler, 2000). Im Zuge der Studie zeigten sich hinsichtlich der erinnerten väterlichen und mütterlichen emotionalen Wärme signifikant höhere Werte bei weiblichen Studierenden. Im Gegensatz dazu beschrieben männliche Studierende rückblickend ein höheres Maß an väterlicher Ablehnung und Strafe. Des Weiteren ließen sich einige signifikante Zusammenhänge zwischen dem erinnerten elterlichen Erziehungsverhalten und dem Selbstwert der Studierenden aufzeigen, wobei die Skalen Ablehnung und Strafe sowie Kontrolle und Überbehütung negativ und die Skala Emotionale Wärme positiv mit der Selbstwertschätzung der Studierenden korrelierten. Hinsichtlich des Selbstwertes fanden sich signifikante Geschlechtsunterschiede, und zwar dahingehend, dass sich männliche Studierende über beinahe alle Selbstwertbereiche hinweg höhere Werte zuschrieben. Die Untersuchungsergebnisse wurden auch im Hinblick auf andere Forschungsarbeiten diskutiert und miteinander in Beziehung gesetzt. Aufgrund der geringen Präsenz von Studien hinsichtlich der Langzeitfolgen elterlicher Erziehung im wissenschaftlichen Diskurs hält dieses Thema auch künftig noch viel Forschungspotential bereit

Experimental investigation of drying by pore networks: influence of pore size distribution and temperature

Isothermal and non-isothermal drying of pore structures has been experimentally investigated using 2D square network models of interconnected etched channels with different (Gaussian) distributions of the channel width. In experiments with imposed temperature gradients, the temperatures either increase from the open side of the network with increasing network depth (referred to as the positive temperature gradient) or the temperatures decrease with increasing distance from the network opening (i.e. a negative temperature gradient). Experiments reveal that the observed phase patterns, or the distributions of liquid and gas, during drying are significantly depending on the direction of the temperature gradient; but also the presence of macro channels can have a strong effect on the phase patterns as well as on drying time

REGULATION OF THE INNATE IMMUNE RESPONSES AUTOPHAGY AND INFLAMMASOME ACTIVATION DURING BACTERIAL INFECTION

Autophagy is an innate anti-microbial host defense that maintains tissue homeostasis. Autophagy is negatively regulated by the nutrient-sensing mTORC1 complex. In this study, we examined the regulatory mechanisms of autophagy and inflammasome activation during Ehrlichia infection. Monocytic Ehrlichia is a Gram negative intracellular bacterial pathogen that causes fatal human monocytic ehrlichiosis. Ehrlichia lacks LPS, but induces inflammasome activation leading to acute liver damage. In humans, the potentially fatal human monocytic ehrlichiosis (HME) mimics sepsis and toxic shock-like syndrome [1, 2], making Ehrlichia a viable model system for these conditions in the absence of LPS. During virulent Ehrlichia infection confocal data shows that autophagy increased with infection, despite clear activation of the autophagy inhibitor mTORC1. This is likely due to a balance of mTORC1 dependent and independent autophagy. Employing bone marrow derived macrophages (BMM) from mice deficient in MyD88 and TLR9 we reveal a novel signaling pathway for IOE mediated autophagy regulation and inflammasome activation centered around IFNβ production. We have previously shown that the virulent Ehrlichia strain Ixodes ovatus Ehrlichia (IOE) expresses higher levels of IFNβ than the avirulent strain Ehrlichia muris (EM) [3]. When IFNβ is added to BMM mTORC1 activation increases, a phenomenon further increased when IFNβ is added to IOE infected BMM. Both IOE and IFNβ mediated mTORC1 activation are abrogated by knockout of the TLR9 receptor. This placed IFNβ upstream of TLR9 in the IOE mediated mTORC1 signaling pathway. As both TLR9 is activated by dsDNA, we have hypothesized that these receptors are activated by mitochondrial DNA released in response to IFNβ mediated DAMP production. These data suggest that LPS-negative Ehrlichia regulates autophagy with mTORC1, and that this mTORC1 activation is achieved via IFNβ mediated TLR9. Our findings reveal a novel regulation of autophagy and the inflammasome in macrophages via MyD88 and mTORC1 during infection with intracellular pathogens

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Pore network models are powerful tools to simulate invasion and transport processes in porous media. They are widely applied in the field of geology and the drying of porous media, and have recently also received attention in fuel cell applications. Here we want to describe and discuss how pore network models can be used as a prescriptive tool for future water electrolysis technologies. In detail, we suggest in a first approach a pore network model of drainage for the prediction of the oxygen and water invasion process inside the anodic porous transport layer at high current densities. We neglect wetting liquid films and show that, in this situation, numerous isolated liquid clusters develop when oxygen invades the pore network. In the simulation with narrow pore size distribution, the volumetric ratio of the liquid transporting clusters connected between the catalyst layer and the water supply channel is only around 3% of the total liquid volume contained inside the pore network at the moment when the water supply route through the pore network is interrupted; whereas around 40% of the volume is occupied by the continuous gas phase. The majority of liquid clusters are disconnected from the water supply routes through the pore network if liquid films along the walls of the porous transport layer are disregarded. Moreover, these clusters hinder the countercurrent oxygen transport. A higher ratio of liquid transporting clusters was obtained for greater pore size distribution. Based on the results of pore network drainage simulations, we sketch a new route for the extraction of transport parameters from Monte Carlo simulations, incorporating pore scale flow computations and Darcy flow

Fractal Phase Distribution and Drying: Impact on Two-Phase Zone Scaling and Drying Time Scale Dependence.

In an article published in 2008, Professor A.R. Mujumdar and his colleagues reviewed some applications of fractal concept on drying. As a modest continuation to this article, we give an overview on three drying-related issues where fractal aspects are present. First, we discuss within the framework of the theory of invasion percolation in a gradient the characteristic lengths that determine the extent of the hydraulically connected region during drying. It is pointed out that the scaling of this region is fundamentally different in 2D and in 3D, owing to the different percolation properties in 2D and 3D. In particular, it is shown that the fractal region only represents a small region of a drying front in 3D systems. Then a situation is described where fractal porous structures form as a result of an evaporation process. Finally, we consider drying in systems characterized by an initial fractal distribution of the liquid phase (invasion percolation cluster), a situation expected to happen in PEM fuel cells, and explore the size-dependent property of the overall drying time from pore network simulations

A pore network model of drying with capillary liquid rings

Modelling of drying processes without adjustable parameters is still a challenge. As emphasized in several previous works,e.g. [1-3], this might be due to the impact of liquid films trapped in the corners of the pore space. In this study, we present and analyse a drying experiment with a micromodel which clearly shows the presence of corner films. In contrast with previous works, however, the corner films do not form a system of interconnected films extending over large regions. They rather form isolated capillary rings surrounding the solid blocks of the device. These capillay rings can be regarded as a quasi-two dimensional version of liquid bridges often observed in the contact regions between grains in soils and packings of particles, [4]. These capillary rings essentially remain confined in the two-phase region. As a result, their impact on drying rate is much smaller than in the systems favouring films hydraulically connected over long distances. The capillary liquid ring formation is taken into account in a pore network model of drying [5]. This model leads to a satisfactory agreement with the experiment provided that the lateral pinning of liquid phase observed in the experiment is included in the model. This model enriches the family of pore network models of drying and can be considered as a step toward the modelling of secondary capillary effects in drying in more complex geometry, such as a random packing of particles. The consideration of capillary rings in drying is important not only for a better prediction of evaporation rates but also for situations where the liquid phase contains particles or dissolved salt for example. For example, in the presence of salt, capillary rings are special locations where crystallization will take place as a result of ring evaporation. Since the capillary rings are likely to form in the contact regions between grains, they might play a role in the damages induced by the crystallization process

Drying of thin porous disks from pore network simulations

Thin porous media (TPM) are porous layers that are characterized by a small thickness, usually orders of magnitude smaller than the lateral dimensions. We present pore network simulation revealing that drying of TPM is substantially different from drying of thicker porous media because of the impact of the small thickness of only a few pore layers on the liquid phase structure during drying. The small thickness limits the long-distance connectivity within the liquid clusters and thus causes the formation of smaller clusters characterized by shorter residence times. As a result of this stronger and earlier liquid phase fragmentation the drying of TPM is shown to be significantly more sensitive to the distribution of the evaporation flux at the surface. It is also shown that the drying behavior transition from thin to thick porous media is progressive. Moreover, it is discussed how an imposed temperature distribution can be used to control the evolution of the liquid cluster distribution in a TPM and thereby the evolution of the evaporation rate

Temperature gradient induced double stabilization of the evaporation front within a drying porous medium.

Drying of porous media very often occurs in the presence of significant temperature gradients because heat fluxes are imposed in many situations in order to decrease the drying time or to facilitate the moisture removal at a higher humidity of the surrounding gas phase. Here we consider the situation where the temperature increases with depth. We show from experiments with a micromodel that the temperature gradient induces the stabilization of the evaporation front within the model porous medium according to two different mechanisms occurring consecutively. The first mechanism occurs in the liquid phase and is explained by the dependence of surface tension upon temperature. This results in the preferential invasion of the warmer zones. The second mechanism occurs gas-sided due to the dependence of saturation vapor pressure upon temperature. We show that the time scales of both mechanisms are different leading to the temporary formation of distinctive phase patterns from which different periods of drying can be discriminated

Microwave drying of wet clay with intermittent heating

In this article, we study an alternative process for the conservative drying of wet clay based on combined microwave heating and convective drying. The study is founded on an experimental analysis of the processes that control drying of porous matter in presence of temperature gradients. We show and discuss that process control cannot be reliably based on temperature alone because mass transfer phenomena associated with microwave heating dictate drying kinetics. Essentially, the occurrence of pressure build up and liquid expulsion, dominating mass transfer if microwave heating is uncontrolled or with high power, vitally depend on the moisture content of the clay. As a consequence, the deterioration of clay is problematic if internal evaporation rates are high, thus at the start of drying when also the moisture content is high. Following this, we propose intermittent microwave heating in combination with convective drying periods with the aim to reduce overall drying time (compared to conventional convective drying) and to improve product quality by reduced material shrinkage. Drying experiments indicate that the overall drying time reduction and product quality depend on the frequency and duration of the two subsequent periods of intermittent heating and convective drying. The observations can be explained with the evolution of the pore-scale distribution of liquid and vapor during drying