Surface integrity is of great significance in grinding performance since grinding process is often used as a finishing step. For metallic materials, residual stresses play an important role in surface integrity for its strong effect on fatigue life, corrosion resistance, and part distortion. For ceramic materials, the surface damage induced by grinding process could greatly affect the mechanical strength and surface finish of the component. The functional behavior of machined components can be enhanced or impaired by the grinding process. Because of this, understanding the surface integrity imparted by grinding is very important. The use of fluid is common in grinding process, however, the high cost and environmental impact of the conventional flood cooling is very undesirable. The minimum quantity lubrication (MQL) have been introduced in industry for about two decades as a promising alternative to conventional flood cooling for economical and environmental advantages. A comprehensive understanding of the MQL effect on the process performances and surface integrity is of great value to the implementation of MQL technique in industrial situation. Grinding-induced residual stress prediction has been a topic of research since the 1970’s while the studies of MQL grinding is still on the early stage with experimental investigations. A comprehensive study and quantitative description of MQL effect on the residual stress generation in grinding is highly demanded. On the other hand, although there has been significant research in the area of surface damage in ceramic grinding, there are still opportunities for advancing predictive methods. Therefore, the objectives of the current research are set as follows: (1) develop a method of predicting residual stress based on an analytical description of the grinding process under MQL condition, (2) develop a method of predicting surface finish and damage in ceramic grinding, and (3) validate the model with experimental data. The research will first focus on predicting residual stresses in MQL grinding based on first principles. This includes predictive models of grinding forces, and grinding temperature stemmed from grinding kinematics and dynamics principles as part of the overall modeling effort. The effect of MQL on both lubrication and cooling aspects has been integrated into these models. The mechanical and thermal output parameters will serve as the basis for determining the loading history which generate residual stresses. The research will also aim at surface roughness modeling in ceramic grinding. A ductile-brittle mixed surface generation is predicted based on the nature of ceramic materials and grinding kinematics. The crack system developed from indentation fracture mechanics approach will be utilized in evaluating the brittle mode surface generation. The modeling techniques will be applied to a range of grinding conditions and materials. This research would aid in evaluating various surface integrities in grinding of metallic and ceramic materials with little experimental efforts. The output could be used to machine these materials effectively to order to improve the functionality of the component.

Activated carbons are one of the most used adsorbents with lots of applications in many sectors. Activated carbons can be produced from lignocellulosic materials with a large content of carbon. Coffee is the second trade most consumed all over the world; hence their residues can be treated in order to give a value. In order to evaluate the viability of using coffee residues as precursor have been carried out experiments by chemical and physical activation. The chosen chemical was phosphoric acid, a dehydrating chemical widely used in production of activated carbons while steam was selected for a physical activation. In this study have been studied the temperature activation and the concentration of chemical as the main factors. One of the advantages of using a chemical is the lower activation temperature; in this study were selected 500ºC, 600ºC and 700ºC while samples treated by steam were 600ºC, 700ºC and 800ºC. Water is a reactive agent that removes volatile compounds and makes wide pores whereas chemicals create linkages with the carbon and volatile compounds enhancing their porosity. Hence, have been studied the following impregnation concentrations 30%, 40% and 50% in order to evaluate their properties as adsorbents. Isotherms were analysed to determine their surface area and pore size distribution. Also were determined the pore size and pore volume for all samples.

Pavement surface characteristics are important to both the safety of the pavement surface and the comfort of the drivers. As of yet, texture and friction measurements have not been incorporated into the design of pavement surfaces. Seven different wearing surface mixtures, placed at the Virginia Smart Road pavement facility, were studied over a one year time period for both friction and texture properties. A locked wheel skid trailer and a laser profilometer were used to assess the pavement surface characteristics. Laboratory testing of the pavement wearing surface mixtures was performed to determine volumetric and mixture specific characteristics. Testing included gyratory compaction, specific gravity, maximum theoretical specific gravity, ignition testing, and gradation analysis. These material properties were used to study the impact of material properties on pavement surface characteristics. The pavement surface characteristics were analyzed using regression analysis with some measured and calculated parameters relevant to the pavement wearing surface properties. Analysis variables included the skid number at 64 kilometers per hour measured using the ASTM E501 (smooth) and ASTM E524 (ribbed) tires, the mean profile depth, the slope of a linear SN-speed model, the skid number at zero speed from the Pennsylvania State University (1) model, and the International Friction Index parameters. Analysis determined that testing particulars such as the grade of the test did not significantly affect the measured skid number. However, there is a significant difference between the skid numbers measured using the two tires. Additionally, the relationship between speed and skid resistance is assessed differently between the two test tires. Regression analysis concluded that there is a relationship between surface characteristics and HMA design properties such as the VMA, VTM, Percent Passing #200 sieve, and Binder Type. The influence of these variables on each of the analysis parameters varied. / Master of Science

The reduction of membrane productivity (i.e. membrane fouling) during operation occurs in virtually all membrane applications. Membrane fouling originates from the method by which membranes operate: contaminants are rejected by the membrane and retained on the feed side of the membrane while treated water passes through the membrane. The accumulation of these contaminants on the feed side of the membrane results in increased operating pressures, increased backwashing frequencies, increased chemical cleaning frequencies, and increased membrane replacement frequencies. The most significant practical implication of membrane fouling is increased operating and maintenance costs. As such, membrane fouling must be properly managed to ensure successful and efficient operation of membrane systems. This document presents four independent studies regarding the fouling of size exclusion and diffusion controlled membranes. A brief description of each study is presented below. The first study systematically investigated the fouling characteristics of various thin film composite polyamide reverse osmosis (RO) and nanofiltration (NF) membranes using a high organic surficial groundwater obtained from the City of Plantation, Florida. Prior to bench-scale fouling experiments, surface properties of the selected RO and NF membranes were carefully analysed in order to correlate the rate and extent of fouling to membrane surface characteristics, such as roughness, charge and hydrophobicity. More specifically, the surface roughness was characterized by atomic force microscopy, while the surface charge and hydrophobicity of the membranes were evaluated through zeta potential and contact angle measurements, respectively. The results indicated that membrane fouling became more severe with increasing surface roughness, as measured by the surface area difference, which accounts for both magnitude and frequency of surface peaks. Surface roughness was correlated to flux decline; however, surface charge was not. The limited range of hydrophobicity of the flat sheet studies prohibited conclusions regarding the correlation of flux decline and hydrophobicity. Mass loading and resistance models were developed in the second study to describe changes in solvent mass transfer (membrane productivity) over time of operation. Changes in the observed solvent mass transfer coefficient of four low pressure reverse osmosis membranes were correlated to feed water quality in a 2,000 hour pilot study. Independent variables utilized for model development included: temperature, initial solvent mass transfer coefficient, water loading, ultraviolet absorbance, turbidity, and monochloramine concentration. Models were generated by data collected throughout this study and were subsequently used to predict the solvent mass transfer coefficient. The sensitivity of each model with respect to monochloramine concentration was also analyzed. In the third study, mass loading and resistance models were generated to predict changes in solvent mass transfer (membrane productivity) with operating time for three reverse osmosis and nanofiltration membranes. Variations in the observed solvent mass transfer coefficient of these membranes treating filtered secondary effluent were correlated to the initial solvent mass transfer coefficient, temperature, and water loading in a 2,000 hour pilot study. Independent variables evaluated during model development included: temperature, initial solvent mass transfer coefficient, water loading, total dissolved solids, orthophosphorous, silica, total organic carbon, and turbidity. All models were generated by data collected throughout this study. Autopsies performed on membrane elements indicated membranes that received microfiltered water accumulated significantly more dissolved organic carbon and polysaccharides on their surface than membranes that received ultrafiltered water. Series of filtration experiments were systematically performed to investigate physical and chemical factors affecting the efficiency of backwashing during microfiltration of colloidal suspensions in the fourth study. Throughout this study, all experiments were conducted in dead-end filtration mode utilizing an outside-in, hollow-fiber module with a nominal pore size of 0.1 µm. Silica particles (mean diameter ~ 0.14 µm) were used as model colloids. Using a flux decline model based on the Happel's cell for the hydraulic resistance of the particle layer, the cake structure was determined from experimental fouling data and then correlated to backwash efficiency. Modeling of experimental data revealed no noticeable changes in cake layer structure when feed particle concentration and operating pressure increased. Specifically, the packing density of the cake layer (l-cake porosity) in the cake layer ranged from 0.66 to 0.67, which corresponds well to random packing density. However, the particle packing density increased drastically with ionic strength. The results of backwashing experiments demonstrated that the efficiency of backwashing decreased significantly with increasing solution ionic strength, while backwash efficiency did not vary when particle concentration and operating pressure increased. This finding suggests that backwash efficiency is closely related to the structure of the cake layer formed during particle filtration. More densely packed cake layers were formed under high ionic strength, and consequently less flux was recovered per given backwash volume during backwashing.

Wet-pavement friction is a public concern because of its direct relation to highway safety. Both short- and long-term seasonal variations have been observed in friction measurements. These variations have been attributed to different factors, such as traffic, rainfall, and temperature. Since both the tire rubber and the HMA pavement surface are viscoelastic materials, which are physically sensitive to temperature changes, temperature should affect the measured frictional properties. Although several researchers have attempted to explain and quantify the effect of temperature on pavement friction, it remains to be fully understood. The objective of this research was to quantify the effect of pavement surface temperature on the frictional properties of the pavement-tire interface. To accomplish this, tests conducted on seven different wearing surfaces at the Virginia Smart Road under different climatic conditions were analyzed. Due to the short duration of this study and the low traffic at the facility, only short-term effects of temperature on pavement friction were investigated. To accomplish the predefined objective, skid test data from both ribbed and smooth tires were collected over two and a half years (from January 2000 to August 2002) and then analyzed. Six sets of tests were conducted under different environmental conditions. The pavement and air temperatures during each test were obtained using thermocouples located directly under the wearing course (38mm below the surface) and close to the pavement surface, respectively. Regression analyses were conducted to determine the effect of pavement temperature on the measured skid number at different speeds, as well as on friction model parameters. The main conclusion of this investigation is that pavement temperature has a significant effect on pavement frictional measurements and on the sensitivity of the measurements to the test speed. Both the skid number at zero speed (SN0) and the percent normalized gradient (PNG) tend to decrease with increased pavement temperature. This results in the pavement temperature on the measured skid number being dependent on the testing speed. For the standard wearing surface mixes studied at low speed (lower than 32 km/hr), pavement friction tends to decrease with increased pavement temperature. At high speed, the effect is reverted and pavement friction tends to increase with increased pavement temperature. Temperature-dependent friction versus speed models were established for one of the mixes studied. These models can be used to define temperature correction factors. / Master of Science

Burning joss paper and incense is a significant Taoist ceremonial practice in Asian countries such as Taiwan and China. The burning of joss paper has been demonstrated to significantly create particulate matters (PM) and to cause air pollution problems. PM in the atmosphere is among the primary air pollutants, and their sources are factories, vehicles, construction fields, combustion, vehicle exhaust dust, and aerosols derived from photochemical reactions. Numerous sources of environmental PM exist. Thus, the ability to rapidly determine the particulate type and source to adjust the controls and develop policies is an important issue for air quality management. This dissertation consists of two parts on the particulate emission control and characteristic identification. In the first part, we study investigates feasible options of air pollution control devices (APCD) for joss paper furnaces in temples, and used a 40 kg/hr joss paper furnace for testing. This paper examined particulate removal efficiencies of two options: a bag house (capacity 30 m3/min at 108 ¢J) and a wet scrubber (capacity 40 m3/min at 150 ¢J). The results indicate that PM in the diluted flue gas at the bag-house inlet were 76.6 ¡Ó 32.7 mg/Nm3 (average ¡Ó standard deviation), and those at the outlet of the bag-house could be reduced to as low as 0.55 ¡Ó 1.28 mg/Nm3. An average PM removal efficiency of 99.3 % could be obtained with a filtration speed of approximately 2.0 m/min evaluated at 108 ¢J. The wet scrubber removed approximately 70 % of PM, with scrubbing intensities higher than 4.0 L/m2.s across the scrubber cross-section. For the duration of the experiment, no visual white smoke (water mist) was observed at the exit of the wet scrubber with a combustion rate of 16 kg/hr of joss paper, and the scrubbing water temperature was automatically sustained at lower than 61 ¢J. The study concluded that both bag filtration and wet scrubbing are suitable techniques to control particulate emission from joss paper furnaces in Taiwanese temples. The bag filtration technique, while achieving higher efficiencies than the wet scrubbing technique, requires more space and cost. Examinations of bottom and fly ashes of combusted joss paper with X-ray diffraction (XRD) revealed the presence of calcium oxide in the fly ash, while certain metals were found in the bottom ash. The second part aimed at the investigates surface characteristics of airborne PM sampled from air pollution control devices of a number of industrial operations. The PM sources selected for this study comprise the following operations or processes: a coke oven, iron ore sintering furnace, blast furnace, and basic oxygen furnace from an integrated steelmaking plant; electric arc furnaces of two secondary steelmaking plants; a municipal solids waste incinerator; two oil-fired boilers; and a coal-fired power plant boiler. The collected PM samples were analyzed using a scanning electronic microscope (SEM) and energy-dispersive X-ray spectroscope (EDS) to determine their chemical composition and surface characteristics. Results for each PM sample regarding size, surface characteristics, and chemical compositions can be used to trace the related emission industrial sources.

Ce travail est une étude préliminaire qui a pour objectif principal d'étudier l'impact des caractéristiques de surface des poudres céréalières sur leurs mécanismes d'agglomération dans le cas particulier de la fabrication de couscous. Cet objectif a été réalisé par une approche multi-échelle : particules, mécanismes, et procèdes. A l'échelle des particules, on a identifié deux caractéristiques relatives à la réactivité physique et chimique des particules (la morphologie et la composition chimique de surface). D'abord, une méthode d'analyse d'images pour décrire la morphologie des particules a été introduite. Ensuite, l'applicabilité de la spectroscopie par photoélectron rayon-X (XPS) pour mesurer la composition chimique de surface des poudres céréalières a été on a examinée. A l'échelle des mécanismes, on a décrit et modalisé une étape importante des mécanismes d'agglomération des poudres céréalières. A l'échelle de procèdes, du couscous a été fabriqué à l'échelle pilote et ses paramètres de qualité ont été estimées. La relation entre les échelles a été évaluée en étudiant l'impact des caractéristiques des particules et de taux d'hydratation sur les mécanismes d'agglomération, le rendement d'agglomération, et la qualité finale de couscous. / Our research work is a preliminary study to investigate the impact that the surface characteristics of wheat powder particles have on their agglomeration mechanisms in the particular case of couscous production process. The objective of this research work was achieved by considering a multi scale approach: particle, mechanism, and process scale. On particle scale, we identified two characterizing factors of particles related to their physical and chemical reactivity (particles shape and surface chemical composition). We first presented a method based on image analyzing system to describe particles shape of wheat powders and then examined the applicability of X-ray photoelectron spectroscopy to measure the surface chemical composition of wheat powders. On mechanism scale, we described and modeled one stage of the wet agglomeration mechanisms of wheat powders. On process scale, we produced couscous in pilot scale and evaluated its quality parameters. The relationship between the scales was evaluated by studying the impact of particles characteristics and hydration rate on agglomeration mechanisms, agglomeration yield, and couscous quality.

Five articles describing the impact of surface characteristics, and development of mass transfer models for diffusion controlled membrane applications are published in this dissertation. Article 1 (Chapter 3) describes the impact of membrane surface characteristics and NOM on membrane performance for varying pretreatment and membranes during a field study. Surface charge, hydrophobicity and roughness varied significantly among the four membranes used in the study. Membrane surface characteristics, NOM and SUVA measurements were used to describe mass transfer in a low pressure RO integrated membrane system. Inorganic and organic solute and water mass transfer coefficients were systematically investigated for dependence on membrane surface properties and NOM mass loading. Inorganic MTCs were accurately described by a Gaussian distribution curve. Water productivity, NOM rejection and inorganic rejection increased as membrane surface charge and NOM loading increased. Inorganic MTCs were also correlated to surface hydrophobicity and surface roughness. The permeability change of identical membranes was related to NOM loading, hydrophobicity and roughness. Organic fouling as measured by water, organic and inorganic mass transfer was less for membranes with higher hydrophilicity and roughness. Article 2 (Chapter 4) describes the development of a diffusion controlled solute mass transfer model to assess membrane performance over time. The changing mass transfer characteristics of four low-pressure reverse osmosis (LPRO) membranes was correlated to feed stream water quality in a 2000 hour pilot study. Solute mass transfer coefficients (MTCs) were correlated to initial solute MTCs, solute charge, feed water temperature, monochloramine loading and organic loading (UV254). The model can be used to predict cleaning frequency, permeate water quality and sensitivity of permeate water quality to variation of temperature, organic and monochloramine mass loading. Article 3 (Chapter 5) describes a comparison of the long standing method of assessing membrane performance (ASTM D 45160 and another approach using mass transfer coefficients (MTCs) from the homogenous solution diffusion model (HSDM) using a common data set, water productivity and standardized salt passage. Both methods were shown to provide identical assessments of water productivity, however different assessments of salt passage. ASTM D 4516 salt passage is normalized for pressure and concentration and does not show the effects of flux, recovery, temperature or specific foulants on salt passage. However the MTC HSDM method is shown to consider all those effects and can be easily used to predict membrane performance at different sites and times of operation, whereas ASTM D 45160 can not. The HSDM MTC method of membrane evaluation is more versatile for assessment of membrane performance at varying sites and changing operational conditions. Article 4 (Chapter 6) describes the development of a fully integrated membrane mass transfer model that considers concentration, recovery and osmotic pressure for prediction of permeate water quality and required feed stream pressures. Osmotic pressure is incorporated into the model using correction coefficients that are calculated from boundary conditions determined from stream osmotic pressures of the feed and concentrate streams. Comparison to homogenous solution diffusion model (HSDM) with and without consideration of osmotic pressure and verification of IOPM using independently developed data from full and pilot scale plants is presented. The numerical simulation and statistical assessment show that osmotic pressure corrected models are superior to none-osmotic pressure corrected models, and that IOPM improves model predictability. Article 5 (Chapter 7) describes the development and comparison of a modified solution diffusion model and two newly developed artificial neural network models to existing mechanistic or empirical models that predict finished water quality for diffusion controlled membranes, which are generally restricted to specific solute MTCs that are site and stage specific. These models compensate for the effects of system flux, recovery and feed water quality on solute MTC and predict permeate water quality more accurately than existing models.

Nucleating boiling is a repeating cycle of bubble initiation, growth and departure at many nucleation sites at the heated wall. Thereby, the bubble growth process significantly affects the dynamics of bubble departure. Experiments were performed to study the influence of heater surface characteristics, such as wettability and roughness, on single bubble growth and departure dynamics for natural circulation and upward flow boiling conditions. Self-assembled monolayer (SAM) coating, wet-etching and femtosecond pulsed laser treatment were used to alter the surface wettability and produce nano- and microstructures on stainless steel surfaces with a roughness in the range of micrometers. These surface preparation techniques allowed to separately quantify the effect of surface wettability and roughness on the bubble dynamics. The surface wettability and roughness are represented by the liquid contact angle hysteresis (θhys) and root mean square roughness of the surface (Sq). Boiling experiments were conducted at atmospheric pressure with degassed deionized water at low-subcooling. Stainless steel heater surfaces were vertically oriented during natural circulation boiling. In the experiments, bubbles were generated from an artificial nucleation cavity on the treated stainless steel heater surfaces. High-resolution optical shadowgraphy has been used to record the bubble generation, departure, sliding, detachment and inception of the next bubble. Higher bulk liquid velocity yielded smaller bubble departure diameters and slower bubble growth rates for all heater surface types. The effect of surface wettability on single bubble dynamics was studied for smooth surfaces with different liquid contact angle hysteresis. Low wetting surfaces yielded a greater bubble growth rate and departure diameter. The bubble growth rate and departure diameter were found maximum for an intermediate surface roughness Sq between 0.108 and 0.218 m. The corresponding roughness height is referred to as the ‘optimal roughness height’ in this work. Surface roughness was found very influential to the bubble growth and departure, which can be explained by considering its interaction with the microlayer underneath a bubble. The role of the heater surface parameters for the bubble growth was qualitatively assessed by evaluating the microlayer thickness constant C2. Hence, an improved bubble growth model was derived in this work. The bubble growth model was formulated on the basis of the evaporation of the microlayer beneath a bubble with the dryout area, inertia and heat diffusion controlled bubble growth and condensation at the bubble cap. The model can also predict the superheated liquid layer around a bubble which helps to determine the portion of a bubble that is in contact with the subcooled liquid. As bubble growth Abstract is highly dependent on the effective interactions of heater surface roughness and microlayer, a term Ceff was introduced in the bubble growth model. The effective microlayer thickness constant Ceff incorporates the impact of heater surface characteristics on the bubble growth process until the departure of a bubble. The bubble growth model was utilized in the analysis of high-resolution experimental data of steam bubble growth and the values of Ceff were calculated for different heater surface characteristics. The value of Ceff was found to decrease with the increase of bubble growth rate. A simplified model for the bubble departure criterion was derived from the expressions of forces which act on a nucleating bubble throughout its growth cycle. It was found that 90% of the departing bubbles satisfy the bubble departure criterion model with ±25% deviation. The knowledge gained from this work shall be particularly useful to improve nucleate boiling models for numerical simulations. The findings are also useful for designing heater surfaces in the future.:Abstract v Kurzfassung vii Acknowledgements xiii Abbreviations and Symbols xv Chapter 1: Introduction and Motivation 1 1.1 General overview 1 1.2 Theoretical background 3 1.3 Objectives and outline of the thesis 7 Chapter 2: Fundamentals of Bubble Dynamics in Nucleate Boiling 9 2.1 Bubble growth in nucleate boiling 9 2.2 Bubble growth models 12 2.3 The physical process of bubble departure 16 2.4 Experimental investigations of bubble dynamics 20 2.4.1 Effects of heater surface characteristics 21 2.4.2 Effects of bulk liquid velocity 24 2.5 Chapter conclusion 26 Chapter 3: Heater Surface Preparation and Characterization 27 3.1 Surface properties 27 3.2 Surface preparation 29 3.2.1 Self-assembled monolayer coating 30 3.2.2 High-power pulsed laser irradiation 31 3.2.3 Wet-etching 32 3.3 Surface cleaning 32 3.4 Surface characterization 32 3.4.1 Wettability measurement 32 3.4.2 Roughness measurement 33 3.4.3 Analysis of surface characteristics 34 3.4.4 Uncertainty of surface parameters 38 3.5 Artificial cavity preparation 38 Chapter 4: Experimental Setup and Procedure 41 4.1 Natural circulation boiling (NCB 41 4.1.1 Experimental procedure and measurement techniques 41 4.1.2 Uncertainty analysis 44 4.2 Upward flow boiling (UFB) 45 4.2.1 Experimental procedure and measurement techniques 45 4.2.2 Uncertainty analysis 48 4.3 Image processing 50 Chapter 5: Experimental Results 53 5.1 Introduction to the analysis of the bubble dynamics 53 5.1.1 The bubble life cycle 53 5.1.2 Calculation of the bubble equivalent diameter 55 5.1.3 Bubble dynamics with the increase of heat flux 57 5.1.4 Qualitative assessment of the bubble dynamics for different parameters 60 5.2 Bubble dynamics 61 5.2.1 Effect of heater surface wettability 61 5.2.2 Effect of heater surface roughness 65 5.2.3 Effect of bulk liquid velocity 70 5.3 Bubble departure 76 5.3.1 Effect of heater surface wettablity 76 5.3.2 Effect of heater surface roughness 76 5.3.3 Effect of bulk liquid velocity 78 5.4 Chapter conclusion 79 Chapter 6: Analysis and Model Development 81 6.1 Numerical evaluation of the role of heater surface characteristics 81 6.1.1 Derivation of an improved bubble growth model 86 6.1.2 Calculation of Ceff 82 6.2 Effect of liquid velocity on the bubble growth 93 6.3 Improved modeling of bubble departure 95 6.3.1 Analysis of important parameters 95 6.3.2 Formulation of a bubble departure criterion 100 6.4 Chapter conclusion 102 Chapter 7: Summary and Outlook 105 Bibliography 109 List of Figures 121 List of Tables 127 Appendix: Surface Parameters and Profile 129 / Der Blasenabriss von einer Keimstellenkavität ist ein komplexer Ablösemechanismus und spielt eine wichtige Rolle beim Wärmetransport. Zur Beschreibung der Blasendynamik sind Kenntnisse über den Blasenwachstumsprozess sowie die Vorhersage eines Kriteriums für die Blasenablösung erforderlich. In den existierenden Blasenwachstums- und Blasenablösungsmodellen wird die Oberflächencharakteristik des Heizers bisher nicht berücksichtigt. Im Rahmen dieser Promotion wurden Experimente durchgeführt, um den Einfluss der Heizeroberfläche und der Hauptströmungsgeschwindigkeit auf diese Parameter für eine vertikale Heizfläche zu untersuchen. Hierbei wurden das Naturkonvektionssieden und das aufwärtsgerichtete Strömungssieden betrachtet. Die Experimente wurden mit vollentsalztem Wasser bei einer Unterkühlung zwischen 1,68 und 4,00 K bei Atmosphärendruck und einem aus Edelstahl gefertigten Heizer durchgeführt, dessen Oberfläche anhand der Parameter Oberflächenrauigkeit und Benetzbarkeit charakterisiert ist. Unterschiedliche Oberflächenbearbeitungstechniken, wie Beschichtung durch Self-Assembled Monolayer (SAM), Nass-Ätzen und Hochleistungspuls-Laserbestrahlung wurden genutzt, um die Oberflächenbenetzung und –rauigkeit zu modifizieren. Der Unterschied zwischen dem gemessenen Fortschritts- (θadv) und Rückzugskontaktwinkel (θrec) der Flüssigkeit wird als Flüssigkeitskontaktwinkelhysterese (θhys) bezeichnet und beschreibt die Oberflächenbenetzbarkeit. Die Oberflächenrauigkeit wurde durch ein Konfokal-Mikroskop bestimmt und durch das gemittelte Quadrat der Rauigkeit (Sq) und den Maximalwert der Rauigkeit (St) definiert. Insgesamt wurden 18 unterschiedliche Heizoberflächen mit einer Größe von 130 x 20 mm² untersucht. Davon kamen jeweils die Hälfte für das Naturkonvektionssieden bzw. aufwärtsgerichtetes Strömungssieden zur Anwendung. Der Einfluss der Oberflächenbenetzbarkeit auf die Blasendynamik wurde für polierte Oberflächen (Sq  0,01 μm) analysiert. Die Wirkung der Oberflächenrauigkeit auf die Blasendynamik wurde für konstante Flüssigkeitskontaktwinkelhysteresen von 40,05°±1,5° und 59,97°±1,5° für Naturzirkulation und Strömungssieden untersucht. Eine künstliche zylindrische Kavität mit einer Fläche von 1963,5 m² und einer Tiefe von 50 m wurde mittels Mikrolaser in die Heizoberflächen eingebracht, um die Blasen in einer spezifischen Position zu erzeugen. Während des Naturkonvektionssiedens betrug die Wärmestromdichte 19,22 bis 30,29 kW/m². Bei den Experimenten mit aufwärtsgerichtetem Strömungssieden wurde die Hauptströmungsgeschwindigkeit im Bereich von 0,052 bis 0,183 m/s variiert und eine Appendix: Surface Parameters and Profile Wärmestromdichte zwischen 39,41 und 45,47 kW/m² aufgeprägt. Daraus resultierten insgesamt 87 Experimentalserien. Um den Blasenlebenszyklus zu erfassen, wurde hochauflösende Bildgebungstechnik verwendet. Mit der Bildverarbeitungssoftware ImageJ wurden die erfassten Videos weiterverarbeitet. Die Temperatur der Hauptströmung wurde mit Typ-K Thermoelementen gemessen. Die zeit- und ortsgemittelten Heizerwandtemperaturen wurden für die Naturzirkulation durch Infrarotthermografie und für das aufwärtsgerichtete Strömungssieden durch Typ-K Thermoelemente erfasst. Die mittlere Flüssigkeitsgeschwindigkeit wurde bei der Naturzirkulation mittels Particle Image Velocimetry (PIV) und beim Strömungssieden mittels Coriolis-Durchflusszähler bestimmt. Eine hochauflösende optische Schattenbildtechnik diente zur Aufzeichnung der Hauptphasen des Blasenlebenszyklus: Blasenerzeugung, Blasenwachstum, Blasenablösung, Blasengleiten und Blasenabriss. In dieser Arbeit wurden die der Blasenablösung vorrausgehenden Phasen untersucht. Blasenhöhe, Blasenbreite, Blasenbasisdurchmesser und Schwerpunkt der Blase wurden mit Hilfe der Bildverarbeitung ermittelt. Der blasenäquivalente Durchmesser wurde mittels des geometrischen Mittelwertes, der Blasenbreite und der Blasenhöhe berechnet. Basierend auf den Messdaten können folgende Erkenntnisse für das Blasenwachstum und den Blasenablösemechanismus postuliert werden: (i) Eine höhere Wärmeströmedichte führen zu größen Blasen und kürzeren Wachstumsperioden. Der Einfluss der Oberflächenbenetzbarkeit und der Oberflächenrauigkeit auf die Blasendynamik zeigt ähnliche Tendenzen für Naturkonvektion und aufwärtsgerichtetes Strömungssieden. (ii) Eine höhere Flüssigkeitskontaktwinkelhysterese führt zu einer schnelleren Expansion der Blasenbasis und zu einem schnellern Blasenwachstum. Für gut benetzbare Oberflächen bewegt sich der Blasenschwerpunkt schneller entlang der Strömungsrichtung. Für Oberflächen mit geringer Benetzbarkeit ist die Blasengröße vor der Blasenablösung größer und die Ablöseperiode länger. Der mittlere Blasenablösedurchmesser für unterschiedliche Hauptströmungsgeschwindigkeiten der Flüssigkeit erhöht sich von 0,75 auf 1,75 mm bei zunehmender Flüssigkeitskontaktwinkelhysterese von 42,32° auf 62,30°. (iii) Eine, bezogen auf die Mikrogrenzschichtdicke, optimale Oberflächenrauigkeit erhöht die Blasenwachstumsrate und die Blasengröße. Dieses Ergebnis ist bisher einzigartig bei der Untersuchung der Einzelblasendynamik beim Blasensieden. Die Expansion der Blasenbasis und der Blasenwachstumsrate erreicht ein Maximum für das gemittelte Quadrat der Rauigkeit (Sq) im Bereich zwischen 0,156 und 0,202 m für Naturzirkulation. Für aufwärtsgerichtetes Strömungssieden war die Expansion der Blasenbasis und die Blasenwachstumsrate für Sq-Werte zwischen 0,108 und 0,218 m maximal. Der Blasenablösedurchmesser wurde für einen großen Bereich der Hauptströmungsgeschwindigkeiten und Wärmestromedichte gemittelt. Das Maximum des mittleren Ablösedurchmessers wurde für die Oberfläche mit einem Wert von Sq = 0,218 m erreicht. Die Oberflächenrauigkeit erweitert die Wärmeübertragungsoberfläche neben der Blasenbasis. Der Einfluss der Oberflächenrauigkeitshöhe auf die Blasen hängt von der Mikrogrenzschichtdicke sowie vom Blasenbasisradius ab. Das Modell der Mikrogrenzschichtdicke von Cooper und Lloyd [1] und die konzeptionelle Idee zur Störung der Mikrogrenzschicht durch die Rautiefe von Sriraman [2] wurden analysiert. Es wurde nachgewiesen, dass die Oberflächenrauigkeit die effektive Mikrogrenzschichtdicke und die dazugehörige Wärmeübertragung beeinflusst. (iv) Es wurden geringere Blasenwachstumsraten für höhere Hauptströmungs-geschwindigkeiten gemessen. Weiterhin reduzieren sich der Blasenablösedurchmesser sowie Ablöseperioden mit zunehmender Hauptströmungsgeschwindigkeit bei unterschiedlichen Wärmeoberflächencharakteristiken. Bei niedrigen Hauptströmungs-geschwindigkeiten im Bereich zwischen ungefähr 0,052 und 0,16 m/s reduziert sich der durchschnittliche Blasenablösedurchmesser deutlich. Die experimentellen Ergebnisse zeigen einen wesentlichen Einfluss der Oberflächenbeschaffenheit auf das Blasenwachstum und den Ablöseprozess beim Blasensieden. Um diesen Einfluss numerisch zu charakterisieren, wurde ein neues Blasenwachstumsmodel entwickelt. Existierende Blasenwachstumsmodelle berücksichtigen den umfangreichen Einfluss der Oberfläche des Heizers bisher nicht. Das vorgeschlagene Model bezieht die plausibelsten Mechanismen des Blasensiedens mit ein. Dazu zählen: Mikrogrenzschichtverdampfung im Bereich der Austrocknung, trägheits- und wärmediffusionskontrolliertes Blasenwachstum und Kondensation an der Blasenoberseite. Das Modell berücksichtigt, dass die überhitzte Flüssigkeitsschicht an der Heizerwand durch die wachsende Blase nach außen verdrängt wird und die so gestreckte Flüssigkeitsschicht einen Teil der Blase einhüllt. Kondensation erfolgt an der Blasengrenze, die in Kontakt mit der unterkühlten Flüssigkeit steht, und demzufolge mit der überhitzen Flüssigkeitsschicht nicht in Kontakt kommt. Das vorgeschlagene Blasenwachstumsmodel arbeitet mit drei Konstanten für die beschriebenen Wärmeübertragungsmechanismen beim Blasenwachstum. Dabei handelt es sich um eine Konstante für die effektive Mikrogrenzschichtdicke (Ceff ), eine weitere Konstante 𝑏 ́ für die Wärmediffusion hin zur Blase und der Trägheit sowie letztendlich einer Konstante S zur Abbildung des Kondensationswärmeübergangs, anhand der Beschreibung des Anteils der Blase, welcher in Kontakt mit der unterkühlten Flüssigkeit steht. Die effektive Mikrogrenzschichtdickenkonstante (Ceff) definiert den Einfluss der Heizoberflächencharakteristik auf die Verdampfung der Mikrogrenzschicht und somit die Blasenwachstumsrate beim Blasensieden. Die numerisch berechnete und experimentell gemessene Blasengröße wurde verglichen, um die Mikrogrenzschichtdickenkonstante Ceff zu definieren. Der Einfluss der Kondensation auf Ceff wurde geprüft.:Abstract v Kurzfassung vii Acknowledgements xiii Abbreviations and Symbols xv Chapter 1: Introduction and Motivation 1 1.1 General overview 1 1.2 Theoretical background 3 1.3 Objectives and outline of the thesis 7 Chapter 2: Fundamentals of Bubble Dynamics in Nucleate Boiling 9 2.1 Bubble growth in nucleate boiling 9 2.2 Bubble growth models 12 2.3 The physical process of bubble departure 16 2.4 Experimental investigations of bubble dynamics 20 2.4.1 Effects of heater surface characteristics 21 2.4.2 Effects of bulk liquid velocity 24 2.5 Chapter conclusion 26 Chapter 3: Heater Surface Preparation and Characterization 27 3.1 Surface properties 27 3.2 Surface preparation 29 3.2.1 Self-assembled monolayer coating 30 3.2.2 High-power pulsed laser irradiation 31 3.2.3 Wet-etching 32 3.3 Surface cleaning 32 3.4 Surface characterization 32 3.4.1 Wettability measurement 32 3.4.2 Roughness measurement 33 3.4.3 Analysis of surface characteristics 34 3.4.4 Uncertainty of surface parameters 38 3.5 Artificial cavity preparation 38 Chapter 4: Experimental Setup and Procedure 41 4.1 Natural circulation boiling (NCB 41 4.1.1 Experimental procedure and measurement techniques 41 4.1.2 Uncertainty analysis 44 4.2 Upward flow boiling (UFB) 45 4.2.1 Experimental procedure and measurement techniques 45 4.2.2 Uncertainty analysis 48 4.3 Image processing 50 Chapter 5: Experimental Results 53 5.1 Introduction to the analysis of the bubble dynamics 53 5.1.1 The bubble life cycle 53 5.1.2 Calculation of the bubble equivalent diameter 55 5.1.3 Bubble dynamics with the increase of heat flux 57 5.1.4 Qualitative assessment of the bubble dynamics for different parameters 60 5.2 Bubble dynamics 61 5.2.1 Effect of heater surface wettability 61 5.2.2 Effect of heater surface roughness 65 5.2.3 Effect of bulk liquid velocity 70 5.3 Bubble departure 76 5.3.1 Effect of heater surface wettablity 76 5.3.2 Effect of heater surface roughness 76 5.3.3 Effect of bulk liquid velocity 78 5.4 Chapter conclusion 79 Chapter 6: Analysis and Model Development 81 6.1 Numerical evaluation of the role of heater surface characteristics 81 6.1.1 Derivation of an improved bubble growth model 86 6.1.2 Calculation of Ceff 82 6.2 Effect of liquid velocity on the bubble growth 93 6.3 Improved modeling of bubble departure 95 6.3.1 Analysis of important parameters 95 6.3.2 Formulation of a bubble departure criterion 100 6.4 Chapter conclusion 102 Chapter 7: Summary and Outlook 105 Bibliography 109 List of Figures 121 List of Tables 127 Appendix: Surface Parameters and Profile 129

Skidding contributes to up to 35% of wet pavement accidents. Pavement surface friction therefore is an important component of highway safety. The skid resistance also varies seasonally and reduces over time due to surface polishing. These leave the pavement in a state of increased risk of skidding accidents. An adequate surface friction that accommodates the seasonal and long term variations is essential for safety over the pavement surface service life. The resistance to skidding, however, depends on surface microtexture and macrotexture. Alternatively, increased texture aimed at increased and durable surface friction may affect the noise generated on the road. In fact, traffic noise is a growing problem throughout the world. Noise barriers, traditionally used for noise reduction, are expensive and inefficient in some cases. As the pavement surface characteristics play a key role in noise generation and propagation, it provides a window for noise reduction by altering the pavement surface. The challenge, however, is to provide a smooth, quiet, long-lasting, and economic pavement with adequate and durable surface friction. This research has been directed to address this challenge and to provide a realistic guideline. The tire-pavement noise, sound absorption, and skid resistance performances of various flexible and rigid pavement surfaces have been examined using the field and laboratory test data. Models for the prediction of pavement skid resistance including the seasonal and long term variations have also been developed correlating the influencing factors. A value engineering approach has been proposed to accommodate the construction and maintenance costs, longevity, smoothness, safety and noise in the selection of pavement surfaces.