A numerical method for two-phase fluid flows with particular application to planar jets

In modern paper making, the break-up of jets issuing from headboxes is responsible for a degradation in paper quality. Waves present on the jet surface are believed to initiate break-up. Numerical simulation of headbox flows and jets would allow prediction of surface waves and help control paper quality. The thesis objective is to significantly contribute to this task by adding two-phase flow capabilities into an existing finite-volume based fluid-flow solver. The solver is then used to numerically verify experimentally observed surface waves on planar water jets issuing from parallel channels. The Volume of Fluid method is used to reformulate the equations of motion of both the liquid and gas phases into equations for a single composite fluid that describe the behavior of both individual phases simultaneously. The phases are identified within the composite fluid by a indicator field known as the volume fraction. The composite fluid retains the incompressibility and Newtonian behavior of its constituent fluids. The fluid interface is replaced by a discontinuity in the physical properties of the composite fluid, and the reformulation satisfies all boundary conditions associated with standard two-phase flow problems. The reformulated equations are solved by standard finite-volume techniques, while the solution of the volume fraction equation requires special care. Several numerical two-phase techniques are presented and discussed. The CICSAM method is adopted for discretization of the volume fraction equation due to its impressive interface reconstruction abilities and its ease of compatibility with the existing code. The inclusion of surface tension is done through the Continuum Surface Force method, whereby a volumetric force mimicking surface tension effects is added to the momentum equations. These procedures are used in the existing solver and the behavior of the code is verified for a series of standard test cases. The solver exhibits very good quantitative and qualitative agreement with published results. The modified code is used to simulate jets under various conditions. Jet thicknesses are small compared to the breadth to allow two-dimensional simulations to be conducted. Results for jets in the absence of gravity or surface tension are in excellent agreement with available analytical results. The inclusion of gravitational effects poses no additional coni cerns. The addition of surface tension causes dramatic changes in jet interface profiles and increased difficulty in obtaining convergent results. A full two-dimensional simulation of water jets issuing from parallel channels with gravitational and surface tension effects is performed for domains of various downstream lengths. The experimentally observed surface waves cannot be reproduced by the tests performed in this study, due to an insufficient downstream grid length or possible three-dimensional effects. Suggestions for improvements relating to two-phase numerical routines and further simulations of planar jets are given.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

A fast numerical method for the interfacial motion of an electrically conducting bubble in a Stokes flow

There is a great need for efficient numerical methods when solving interfacial motion problems involving coupled physical processes. To this end, a fast numerical method is developed for tracking the motion of an electrically conducting fluid bubble in a Stokes flow subject to an electric field.The motion of a two-dimensional bubble immersed in an infinite expanse of viscous fluid is examined. The Stokes equations governing the fluid dynamics and Laplace\u27s equation governing the electrostatics are recast as integral equations. The electrohydrodynamic free boundary problem is reduced to the solution of integral equations along the bubble interface. The integral equations are discretized and solved with an iterative solver accelerated by the fast multipole method. Results from the numerical method are compared with published results of a simplified, analytical model and are found to be in good agreement

Influence of fibres on temperature and pH responsiveness of microgel in the development of smart textiles

V diplomskem delu je bil proučevan vpliv surovinske sestave vlaken na temperaturno- in pH- odzivnost mikrogela na podlagi poli-(N-izopropilakrilamida) in hitozana (PNCS). Mikrogel PNCS je bil po impregnirnem postopku nanesen na tekstilije različnih surovinskih sestav, in sicer 100-odstoten bombaž (CO), viskozo (CV), volno (WO), poliamid (PA) in poliester (PES). Z uporabo vrstične elektronske mikroskopije (SEM) in infrardeče spektroskopije na Fourierevo transformacijo (FTIR) je bil v eksperimentalnem delu določen vpliv nanosa mikrogela PNCS na morfološke in kemijske lastnosti proučevanih vzorcev, odzivnost mikrogela PNCS pa določena z meritvami vsebnosti vlage (MC) in prepustnosti vodne pare (WVTR) pri temperaturah 20 in 40 °C ter z meritvami navzemanja vode (WU) pri temperaturah 20 in 40 °C ter pH medija 3 in 8. Z meritvami togosti ter pretržne sile in raztezka je bil proučen nanos mikrogela PNCS na mehansko-fizikal¬¬ne lastnosti oplemenitenih tekstilij. Rezultati eksperimentalnega dela so pokazali, da je nanos mikrogela PNCS vplival na hrapavost proučevanih tekstilij, medtem ko sama surovinska sestava ni vplivala na razporeditev mikrogela PNCS na površini vlaken. Prisotnost mikrogela PNCS v IR ATR-spektrih proučevanih vzorcev CO, CV in PES so potrdili novi absorpcijski trakovi, ki so značilni za amid I. in amid II. skupine, oz. absorpcijski trakovi, značilni za C-H in CH2 nihanja v primeru vzorcev WO in PA. Nanos mikrogela PNCS je vsem proučevanim vzorcem podelil toplotno odzivnost, kar se je najbolj odrazilo pri tkaninah CO in PES in nekoliko manj pri vzorcih CV, WO in PA. Za doseg dvojne temperaturne in pH-odzivnosti je bil nanos mikrogela PNCS najverjetneje prenizek, saj so proučevana vlakna s svojo naravno temperaturno in pH-odzivnostjo zasenčila delovanje mikrogela PNCS. Prisotnost mikrogela PNCS na vlaknih CO, CV in v PES je vplivala na povečanje togosti in pretržne sile oplemenitenih vzorcev, obenem pa je povzročila nižji pretržni raztezek. V primeru vzorca WO prisotnost mikrogela PNCS ni bistveno vplivala na togost, je pa vplivala na povečanje pretržne sile in raztezka, medtem ko je nanos mikrogela PNCS vplival na znižanje togosti vzorca PA, vpliv na pretržno silo in raztezek pa je bil glede na osnovne oz. votkovne niti različen.In diploma thesis, the influence of fiber type on the temperature and pH-responsiveness of poly-(N-isopropylacrylamide) and chitosan (PNCS)-based microgel was studied. Using the pad dry cure method, the PNCS microgel was applied to textiles with different raw material compositions, namely 100% cotton (CO), viscose (CV), wool (WO), polyamide (PA) and polyester (PES). In the experimental part, the influence of PNCS microgel on the morphological and chemical properties of the studied samples was determined by scanning electron microscopy (SEM) and Fourier infrared spectroscopy (FTIR), while the temperature and pH sensitivity of the PNCS microgel to the studied samples was determined by measuring the moisture content (MC) and water vapor transmission rate (WVTR) at temperatures of 20 and 40 °C, and by measuring the water uptake (WU) at temperatures of 20 and 40 °C and pH of 3 and 8. The results of the experimental work showed that the application of PNCS microgel affected the roughness of the textiles studied, while the fiber type itself did not affect the distribution of PNCS microgel on the fiber surface, as determined by SEM. The presence of PNCS microgel in the IR ATR spectra of the CO, CV and PES samples was confirmed by new absorption bands characteristic of the amide I. and amide II. groups or the C-H and CH2 vibration in the case of the WO and PA samples. The presence of the PNCS microgel led to a thermal response in all the samples studied, which was most pronounced in the case of the CO and PES samples, followed by the CV, WO and PA samples. To achieve a dual temperature and pH-response, the application of the PNCS microgel was most likely too low, as the natural temperature and pH-response of the studied fibers must have blurred the performance of the PNCS microgel. The presence of PNCS microgel on the CO, CV, and PES fibers increased the stiffness and breaking strenght of these samples while resulting in lower elongation at break. For the WO sample, the presence of PNCS microgel did not significantly affect the stiffness, but it did increase the breaking strenght and elongation, while it decreased the stiffness of the PA sample. In this case, the breaking strenght and elongation differed in the warp and weft directions

Viscoelastic properties of Na-carboxymethylcellulose solutions

The rheological characteristics of 5% solutions of Na-carboxymethylcellulose (CMC)I of various origin were investigated. Depending on the molar mass (1.25-1.94 x 10(5) g mol(-1)), i.e., the degree of polymerization (545-851) and degree of substitution (0.748-1.039), as well as the electrolyte (NaCl) content (0.55-36.40%), it was found that microgel particles appear in some cases, while in other cases there are entanglements or isolated particles of CMC macromolecules in solution. Stronger macromolecular interactions were observed when the degree of polymerization was greater than about 600 and the degree of substitution was higher than approximately 0.8. The rheological characteristics of the investigated samples are discussed in relation to the macromolecular structure (defined by X-ray powder diffraction and FT-IR spectroscopy) in the solid state

Optimization of carboxymethylcellulose production

The aim of the study was to obtain water soluble carboxymethylcellulose (CMC) with a high degree of polymerization (DP gt 600) and high degree of substitution (DS gt 800), in industrial conditions, from easily degradable eucalyptus cellulose. The influence of temperature and of the NaOH:MCAA molar ratio cellulose on the structural and degradative changes in cellulose macromolecules during the process was investigated using ethanol as the reaction medium. The structural transformations during alkalization and etherification were investigated by X-ray diffraction. The degradative changes in the macromolecule were followed by determining the degree of polymerization. The degree of substitution and other chemical characteristics were determined by standard analytical methods. The thermal behaviour of the samples was studied by using a Perkin Elmer DSC-2 instrument. The rheological properties of the CMC solutions were also studied

The applicability of DTG to polymerisation studies

The application of derivativ thermogravimetry (DTG) to investigate polymerisation mechanisms is illustrated using the radical polymerisation of di-n-alkyl itaconates as well as the photoinitiated polymerisation of methyl methacrylate by colloidal CdS. The thermal properties of the resulting polymers are described. The advantages and disadvantages of DTG are discussed