New demands and tighter government legislations on greenhouse gases and pollutants, especially for those produced by diesel engines, there has been much focus on developing more efficient diesel engine designs and pollution control devices. There are several pollution control devices currently being implemented in diesel engines such as, diesel particulate filters, selective reduction catalyst, electrostatic filters, exhaust gas recirculation systems, etc. Diesel particulate matter is of particular importance especially when deposited because of its corrosive and thermal insulating nature. There are many complex mechanisms involved in fine particle deposition. This study will focus on the main deposition mechanisms such as convection, diffusion, thermophoresis and electric field effects. The objective of this study was to evaluate experimentally the mechanisms of diesel soot deposition in a rectangular (RWCS) and cylindrical (CWCS) wall cooled sections to evaluate thermophoretic effects. In additional, the coaxial cylindrical wall cooled section with additional with coaxial wire electrode was used to study applied electric field effect (CCWCSE) on soot deposition. A non-destructive Real-Time Neutron Radiography technique was used to evaluate the soot deposition thickness profiles inside the cooled sections. The experiments were conducted using diesel engine exhaust from a single cylinder diesel engine operated at fixed 2.4kW, at a exhaust gas mass flow rate of 20 kg/hr with exposure times ranging 0 to 3hrs, coolant temperatures from 20 to 40°C and exhaust gas temperatures from 250 and 270°C. The resulting Reynolds Number based on the mass flow rate per cross-sectional area times the hydraulic diameter was 6300 for the RWCS and 9000 for the CWCS and CCWCSE. The results show that for the RWCS, the soot deposition pattern qualitatively matched the cooling water channel outer wall surface temperature profile along with thicker deposition at the entrance region due to convection effects. For the ewes, the deposition was more uniformly distributed throughout the device. It was observed for both devices that as the mean soot deposition thickness increases with increasing exhaust gas exposure time and decreasing wall cooling temperature. Finally the experimental results for the CCWCSE shows that the soot deposition was enhanced by a positive or negative applied electric field. / Thesis / Master of Applied Science (MASc)

No description available.

This dissertation presents and explores a technique to confine and manipulate single and multiple nano-objects in solution by exploiting the thermophoretic interactions with local temperature gradients. The method named thermophoretic trap uses an all-optically controlled heating via plasmonic absorption by a gold nano-structure designed for this purpose. The dissipation of absorbed laser light to thermal energy generates a localized temperature field. The spatial localization of the heat source thereby leads to strong temperature gradients that are used to drive a particle or molecule into a desired direction. The behavior of nano-objects confined by thermal inhomogeneities is explored experimentally as well as theoretically. The monograph treats three major experimental stages of development, which essentially differ in the way the heating laser beam is shaped and controlled. In a first generation, a static heating of an appropriate gold structure is used to induce a steady temperature profile that exhibits a local minimum in which particles can be confined. This simple realization illustrates the working principle best. In a second step, the static heating is replaced. A focused laser beam is used to heat a smaller spatial region. In order to confine a particle, the beam is steered in circles along a circular gold structure. The trapping dynamics are studied in detail and reveal similarities to the well-established Paul trap. The largest part of the thesis is dedicated to the third generation of the trap. While the hardware is identical to the second generation, using the real-time information on the position of the trapped object to heat only particular sites of the gold structure strongly increases the efficiency of the trap compared to the earlier versions. Beyond that, the optical feedback control allows for an active shaping of the effective virtual trapping potential by applying modified feedback rules, including e.g. a double-well or a box-like potential. This transforms the formerly pure trapping device to a versatile technique for micro and nano-fluidic manipulation. The physical and technical contributions to the limits of the method are explored. Finally, the feasibility of trapping single macro-molecules is demonstrated by the confinement of lambda-DNA for extended time periods over which the molecules center-of-mass motion as well as its conformational dynamics can be studied.

Nano-scale fluid flow is unlike transport on the macro-scale. Pressure gradients typically dominate effects on a large scale while thermal gradients contribute negligibly to the motion of fluid. The situation entirely reverses on the nano-scale. At a microscopic level, flows induced by thermal gradients are caused by forces that act on atoms or molecules near an interface. These thermo-osmotic forces cannot, at present, be derived analytically or measured experimentally. Clearly, it would be useful to calculate these forces via molecular simulations, but direct approaches fail because in the steady-state, the average force per particle vanishes, as the thermo-osmotic force is balanced by a gradient in shear stress. In our journey to indirectly calculate the osmotic force, we met another unknown in the field of molecular theory at interfaces: the microscopic pressure tensor. The latter is an open problem since the microscopic pressure near an interface is not uniquely defined. Using local thermodynamics theories, we relate the thermo-osmotic force to the gradient of the microscopic pressure tensor. Yet, because the pressure is not uniquely defined, we arrive at multiple answers for the thermo-osmotic force, where at most one can be correct. To resolve the latter puzzle, we develop a direct, non-equilibrium simulation protocol to measure the thermo-osmotic force, whereby a thermal gradient is imposed and the osmotic force is measured by eliminating the shear force. Surprisingly, we find that the osmotic force cannot be derived from the gradient of well-known microscopic pressure expressions. We, therefore, derive a thermodynamic expression that gets close. In this work, we report the first, direct calculation of the thermo-osmotic force while simultaneously showing that standard microscopic pressure expressions fail to predict pressure gradients.

Ce travail est consacré à l'étude du dépôt des particules de suie transportées par des fumées d'incendie. L'étude de la littérature donne une synthèse des propriétés connues des particules de suie produites par un incendie ainsi qu'une revue de l'état de l'art des outils disponibles pour modéliser leur dépôt. Le code Fire Dynamics Simulator, outil numérique utilisé dans ce travail, permet depuis sa version 6 de simuler le dépôt de suie mais aucune étude expérimentale à échelle réelle ne fournit de données quantitatives de dépôt qui permettraient de valider les performances de l'outil dans ce domaine. Une première campagne expérimentale a donc été réalisée pour pouvoir évaluer FDS et les modèles fournis par la littérature dans le cas du dépôt à échelle réelle de particules de suie produites par la combustion d'heptane. Ces essais ont été suivis d'une seconde campagne expérimentale à échelle réelle avec pour objectif la prise en compte de l'écoulement des fumées le long de la paroi de dépôt et de sa vitesse. Les deux campagnes d'essais à échelle réelle ont enfin été complétées par le montage d'un banc expérimental à petite échelle permettant d'étudier l'influence de la vitesse d'écoulement sur le dépôt de particules produites par un petit foyer, à l'intérieur d'une conduite. / This work is devoted to the study of the deposit of soot particles transported by fire smoke. The literature review provides a summary of the known properties of soot particles produced by fire as well as a review of the state of the art tools to model their deposit. The CFD tool Fire Dynamics Simulator allows since version 6 to predict the deposition of soot. However no full scale experimental study provides quantitative data about thermophoretically driven soot deposition, making validation impossible. A first experimental campaign was conducted to valuate FDS and modelling tools provided by the literature in the case of full-scale deposition of soot particles produced by the combustion of heptane. These tests were followed by a second full-scale experimental campaign with the aim of taking into account the flow of smoke along the wall and its speed. Both full scale campaigns were finally completed by a small-scale experimental bench mounted in order to tudy the influence of the flow rate on particle thermally driven deposition within a duct.

No description available.

The main subject of this thesis is to examine thermo-osmotic flows, which occur on interfaces of non-uniform temperature. Such thermo-osmotic flows are purely non-thermal equilibrium phenomena. Along the non-isothermal interface, specific interaction of a liquid and its solutes with a boundary vary in strength across the interface, according to the local temperature. This boundary can be a solid, a membrane or a phase boundary. The flow is thereby continuously pumping fluid across the interface in direction of the local temperature gradient, resulting in an extended flow pattern in the bulk due to mass conservation. In a system containing particles and heat sources in a liquid under spatial confinement, the thermo-osmotic flow may drive particles in a directed manner, or can lead to collective phenomena. To approach this broad topic of (self-)thermophoresis and collective motion of active particles and quantify the role of the thermo-osmotic flow upon the latter effects, different experiments have been performed: The first experiments aim to quantify the thermo-osmotic flow at a non-isothermal liquid/solid interface for two fundamentally different substrate properties. Further, the bulk flow was investigated for two different systems. The form and spatial extension of this bulk flow pattern depends sensitively on the form of the container and the interface, as well as on the thermo-osmotic flow. The first system is a liquid film confined between two planar glass cover slips. The second case is a Janus particle immobilized on one of the glass slips. In the first case, the non-uniform temperature profile is generated by optical heating of a nanometer sized gold colloid, and in the second case, the heat source is the Janus particle. The bulk flow pattern consists, for the second case, of the flow pattern created by the glass cover slips and the one created by the Janus particle. The following experiments are focusing on the dynamics of mobile self-thermophoretic Janus particles. In particular, their dynamics and the contributions of the thermo-osmotic flow to the interaction of multiple active particles are investigated. To investigate those particles under controlled conditions and examine their interactions at low concentrations for an effectively unlimited amount of time, a real-time feedback algorithm was co-developed to gain control of the motion of multiple active particles simultaneously, called ”photon nudging”. With the help of this method, first experiments have been performed to quantify the dynamics of a Janus particle located close to a heat source.

Natural killer (NK) cells are a subpopulation of effector lymphocytes with cytotoxic activity and cytokine-producing functions considered as an integral part of the innate immune response. Functions of NK cells include tumour elimination, engagement and regulation of antiviral immune responses and regulation of immune cells by production and secretion of chemokines and cytokines. CD69 is a C-type lectin-like transmembrane receptor expressed in NK cells. CD69 is an activating receptor and acts also as a very early marker of lymphocyte activation. Putative protein ligands have been described for CD69 in the last years: Galectin-1, S1P1, S100A8/S100A9 and Myl9/12. Galectin-1 is a prototypical lectin characterized by the presence of a common lectin structural fold and a carbohydrate recognition domain involved in carbohydrate binding. Galectin-1 was identified as a binding partner for CD69 based on biological and functional studies, but structural details about the complex are still missing. This thesis describes the successful establishment of an expression protocol for a tag-less cysteine-less mutant of galectin-1 and the study of the interaction between galectin-1 and NK cell receptors. The interaction was studied using microscale thermophoresis and confirmed as dependent on the presence of a...

This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing applications and basic concepts of thermophoresis and outlines some of the experimental and theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general theoretical description for thermophoresis is formulated using the theory of non-equilibrium thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution and a bulk contribution, followed by a determination of transport coefficients based on Onsager’s reciprocal relations. It is further shown how the phenomenological expression of the thermophoretic flux can be recovered when the fluid is at steady-state. The results issuing from this description are then discussed and compared to other existing approaches, some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis. Chapter 3 is dedicated to the validation of the introduced theoretical framework by means of computer simulations, using a simulation technique known as multi-particle collision dynamics. More specifically, the dependence of the thermophoretic force on different system parameters is examined and deviations from the theoretical prediction are explained by an advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents steady-state measurements of functionalised colloids in a temperature gradient, showing how the addition of molecular surface groups increases the experimental complexity of thermophoretic motion. The relaxation process behind this steady-state is also studied, to determine how the relaxation speed depends on the applied temperature gradient. In chapter 5, a general conclusion is drawn from the presented work and its implications are briefly discussed in relation to the current state of knowledge. Finally, the discussion is closed with an outlook on remaining challenges in understanding colloidal motion that could be the subject of future research.

Theoretical and experimental studies of particle deposition in turbulent pipe flow have been carried out for over forty years, but some of the most important transport mechanisms are still not well understood. The first part of this thesis is concerned with the calculation of particle density when using Lagrangian methods to predict inertial particle transport in two-dimensional laminar fluid flows. Traditionally, Lagrangian calculations involve integrating the particle equations of motion along particle pathlines, and the particle density is obtained by applying a statistical averaging procedure to those pathlines which intersect a particular computational grid cell. Unfortunately, extremely large numbers of particles are required to reduce the statistical errors to acceptable levels, and this makes the method computationally expensive. Recently, the Full Lagrangian approach has been developed, which allows the direct calculation of the particle density along particle pathlines. This method had previously been applied only to simple analytical flow fields. The application of the method to CFD generated fluid velocity fields was shown to be possible, and the results obtained using the Full Lagrangian approach were compared to those from a traditional Lagrangian approach. It was found that better quality solutions could be obtained with the use of far fewer particle pathlines. An analysis of the manner in which the Full Lagrangian approach deals with particles whose paths cross each other (and the resulting discontinuity in particle density) was also undertaken, and this illustrates the sophistication of the method. The second part of the thesis comprises an experimental and theoretical study of the deposition of small particles in turbulent flows by thermophoresis. Thermophoresis is the phenomenon whereby small particles suspended in a gas in which there exists a temperature gradient experience a force in the direction opposite from that of the temperature gradient. Previous researchers have attempted to impose a radial temperature difference in pipe flow experiments, but have not yet succeeded in attaining a constant thermophoretic force along the length of the pipe. This limits the accuracy and usefulness of the data for the validation of theoretical expressions for the thermophoretic fluxes. An experimental rig has been designed to achieve a constant thermophoretic force. This was done by using an annular geometry with a cold inner wall and hot outer wall. The particle size was varied and the deposition flux was measured for turbulent flow with three temperature differences. The deposition fluxes for small particles were found to be independent of dimensionless particle size, with each increase in temperature difference resulting in an increase in magnitude of the flux. Evidence of a thermophoresis-turbulence coupling was found for intermediate-sized particles, and large particles were not influenced by thermophoresis. A theory of particle deposition, developed for the case of turbulent pipe flow, was modified to study flow in a turbulent annulus, so that theoretical expressions for the thermophoretic fluxes could be included and compared with the experimental results. Agreement with experimental data was quite good, but some deficiencies in a widely used theoretical expression for the thermophoretic flux were exposed. An alternative expression was used, which gave much better agreement with the experimental data, and the mechanisms behind the thermophoresis-turbulence coupling were also investigated. The validation of this expression for the thermophoretic force will allow its inclusion in numerical studies of particle deposition in more complex geometries.