Variations of local heat transfer coefficient in piped flow of viscous liquids

Measurements were carried out to determine local coefficients of heat transfer in short lengths of horizontal pipe, and in the region of an discontinuity in pipe diameter. Laminar, transitional and turbulent flow regimes were investigated, and mixtures of propylene glycol and water were used in the experiments to give a range of viscous fluids. Theoretical and empirical analyses were implemented to find how the fundamental mechanism of forced convection was modified by the secondary effects of free convection, temperature dependent viscosity, and viscous dissipation. From experiments with the short tube it was possible to determine simple empirical relationships describing the axial distribution of the local 1usselt number and its dependence on the Reynolds and Prandtl numbers. Small corrections were made to account for the secondary effects mentioned above. Two different entrance configurations were investigated to demonstrate how conditions upstream could influence the heat transfer coefficients measured downstream In experiments with a sudden contraction in pipe diameter the distribution of local 1u3se1t number depended on the Prandtl number of the fluid in a complicated way. Graphical data is presented describing this dependence for a range of fluids indicating how the local Nusselt number varied with the diameter-ratio. Ratios up to 3.34:1 were considered. With a sudden divergence in pipe diameter, it was possible to derive the axial distribution of the local Nusse1t number for a range of Reynolds and Prandtl numbers in a similar way to the convergence experiments. Difficulty was encountered in explaining some of the measurements obtained at low Reynolds numbers, and flow visualization techniques wore used to determine the complex flow patterns which could lead to the anomalous results mentioned. Tests were carried out with divergences up to 1:3.34 to find the way in which the local Nusselt number varied with the diameter ratio, and a few experiments were carried out with very large ratios up .to 14.4. A limited amount of theoretical analysis of the 'divergence' system was carried out to substantiate certain explanations of the heat transfer mechanisms postulated.

Hairpin vortex solution in planar Couette flow: a tapestry of knotted vortices

A numerical continuation method has been carried out seeking solutions for two distinct flow configurations, planar Couette flow (PCF) and laterally heated flow in a vertical slot (LHF). We found that the spanwise vortex solution in LHF identifies a new solution in PCF. The vortical structure of our new solution has the shape of a hairpin observed ubiquitously in high-Reynolds-number turbulent flow, and we believe this discovery may provide the paradigm for a hierarchical organization of coherent structures in turbulent shear layers.

NMR spectroscopy in the presence of ultrasound and other perturbations

The work described in this thesis has been concerned with exploring the potential uses of ultrasound in Nuclear Magnetic Resonance (NMR) spectroscopy, The NMR spectra of liquids provide detailed structural information that may be deduced from the chemical shifts and spin-spin coupling, that are evident in the narrow resonances, arising from some of the nuclear broadening interactions being reduced to zero. In the solid state, all of the nuclear broadening interactions are present and broad lines in the NMR spectrum are observed. Current techniques employed to reduce the line widths in solids are based on coherent averaging techniques such as MAS NMR1,2 which can remove first order interactions. Recently DOR3 and DAS4 have become available to remove higher order interactions. SINNMR (Sonically Induced Narrowing of the NMR spectra of solids) has been reported by Homer et al5 and developed by Homer and Howard6 to reduce the line widths of solids. The basis of their work is the proposal that a colloidal suspension of solid particles can be made to move like large molecules by using ultrasonic agitation. The advantage of the technique is that the particles move incoherently removing all of the nuclear interactions responsible for broad lines. This thesis describes work on the extension of SINNMR by showing that the line width of 27AI and 11B for the glass Na20/B203/AI203 can be reduced by placing solid particles in a colloidal suspension. Further line width reduction is possible by applying ultrasound, at 2 MHz, of sufficient intensity. It is proposed that a cavitation field is responsible for imparting sufficient rotational motion to the solid particles to partially average the nuclear interactions responsible for broad lines. Rapid stirring of the colloidal suspension generates turbulent flow, however, the motion is insufficient to narrow the line widths for 27AI in the glass. Investigations of sonochemical reactions for in situ rate measurements by NMR have been made. 8y using the Weissler reaction7, it has been shown that ultrasonic cavitation is possible up to 10MHz. Preliminary studies have been carried out into the rate of ultrasonic polymerisation of methylmethacrylate by NMR. Long range order in liquid crystals can imposed when they are aligned in the presence a magnetic field. The degree of alignment can be monitored by NMR using, for example a deuterated solute added to the liquid crystal8. Ultrasonic streaming can then be employed to deflect the directors of the liquid crystal from their equilibrium position, resulting in a change In the NMR spectrum. The angle of deflection has been found for the thermotropic liquid crystal (I35) to be ca, 35° and for the lyotropic (ZLI-1167) to be ca, 20°, Mechanical stirring can used to re- orientate the liquid crystal but was found to give a smaller deflection, In a separate study, that did not use ultrasound, it has been found that the signal to noise ratio of 13C NMR signals can be enhanced by rapidly stirring a Iiquid. Accelerating the diffusion of nuclei out of the coil region enables M0 to be re-established more rapidly than the normal relaxation process. This allows the pulse repetition rate to be reduced without saturating the spin system. The influence of varying the relaxation delay, acquisition time and inter-pulse delay have been studied and parameters optimised. By studying cholesterol the technique was found to be most effective for nuclei with long relaxation times, such as quaternary carbon sites. Key Worde: NMR, Ulf.rasciund, 1,.lqi.fi!:l cryllltalt!h SCll1C1otlemlstryl I!r1hano~d algnflllf

Modelling vortex formation in an unbaffled stirred tank reactors

Agitating liquids in unbaffled stirred tank leads to the formation of a vortex in the region of the impeller shaft when operating in the turbulent flow regime. A numerical model is presented here that captures such a vortex. The volume of fluid model, a multiphase flow model was employed in conjunction with a multiple reference frame model and the shear stress turbulence model. The dimensions of the tank considered here, were 0.585 m for the liquid depth and tank diameter with a 0.2925 m diameter impeller at a height of 0.2925 m. The impeller considered was an eight-bladed paddle type agitator that was rotating with an angular velocity of 7.54 rad s (72 rpm) giving a Reynolds number of 10 and Froude number of 0.043. Preliminary results of a second investigation into the effect of liquid phase properties on the vortex formed are also presented. © 2006 Elsevier B.V. All rights reserved.

Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional flow

A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.

CFD modelling of the fast pyrolysis of an in-flight cellulosic particle subjected to convective heat transfer

The pyrolysis of a freely moving cellulosic particle inside a 41.7mgs -1 source continuously fed fluid bed reactor subjected to convective heat transfer is modelled. The Lagrangian approach is adopted for the particle tracking inside the reactor, while the flow of the inert gas is treated with the standard Eulerian method for gases. The model incorporates the thermal degradation of cellulose to char with simultaneous evolution of gases and vapours from discrete cellulosic particles. The reaction kinetics is represented according to the Broido–Shafizadeh scheme. The convective heat transfer to the surface of the particle is solved by two means, namely the Ranz–Marshall correlation and the limit case of infinitely fast external heat transfer rates. The results from both approaches are compared and discussed. The effect of the different heat transfer rates on the discrete phase trajectory is also considered.

Symmetry of coherent vortices in plane couette flow

A numerical continuation method is carried out in a homotopy space connecting two different flows, the Plane Couette Flow (PCF) and the Laterally Heated Flow in a vertical slot (LHF). This numerical continuation method enables us to obtain an exact steady solution in PCF. The new solution has the shape of hairpin vortices (HVS: hairpin vortex solution), which is observed ubiquitously in turbulent shear flows.

The effect of flow regimes in the distillation of systems containing two liquid phases

Single phase solutions containing three components have been observed to exhibit foaminess near a single to two liquid phase boundary. It was seen, in a sintered plate column under mass transfer conditions, that distillation systems where the liquid appeared as one phase in one part of a column and two phases in another part, exhibited foaminess when the liquid concentration was near the one phase to two phase boundary. Various ternary systems have been studied in a 50 plate. 30mm i.d. Oldershaw column and it was observed that severe foaming occurred in the middle section of the column near the one liquid phase to two liquid phase boundary and no foaming occurred at the end of the column where liquid was either one phase or two phase. This is known as Ross type foam. Mass transfer experiments with Ross type ternary systems have been carried out in a perspex simulator with small and large hole diameter trays. It was observed that by removal of the more volatile component, Ross type foam did not build up on the tray. Severe entrainment of liquid was observed in all cases leading to a 'dry' tray, even with a low free area small diameter hole tray which was expected to produce a bubbly mixture. Entrainment was more severe for high gas superficial velocities and large hole diameters. This behaviour is quite different from the build up of foam observed when one liquid phase/two liquid phase Ross systems were contacted with air above a small sintered disc or with vapour in an Oldershaw distillation column. This observation explains why distillation columns processing mixtures which change from one liquid phase to two liquid phases (or vice versa) must be severely derated to avoid flooding. Single liquid phase holdups at the spray to bubbly transition were measured using a perspex simulator similar to that of Porter & Wong (17). i.e. with no liquid cross flow. A light transmission technique was used to measure the transition from spray regime to bubbly regime. The effect of tray thickness and the ratio of hole diameter to tray thickness on the transition was evaluated using trays of the same hole diameter and free area but having thickness of 2.38 mm, 4 mm, and 6.35 mm. The liquid holdup at the transition was less with the thin metal trays. This result may be interpreted by the theory of Lockett (101), which predicts the transition liquid holdup in terms of the angle of the gas iet leaving the holes in the sieve plate. All the existing correlations have been compared and none were found to be satisfactory and these correlations have been modified in view of the experimental results obtained. A new correlation has been proposed which takes into account the effect of the hole diameter to tray thickness ratio on the transition and good agreement was obtained between the experimental results and the correlated values of the liquid holdup at the transition. Results have been obtained for two immiscible liquids [kerosene and water] on trays to determine whether foaming can be eliminated by operating in the spray regime. Kerosene was added to a fixed volume of water or water was added to a fixed volume of kerosene. In both cases, there was a transition from spray to bubbly. In the water fixed system. the liquid holdup at the transition was slightly less than the pure kerosene system. Whilst for the kerosene fixed system, the transition occurred at much lower liquid holdups. Trends In the results were similar to those for single liquid phase. New correlations have been proposed for the two cases. It has been found that Ross type foams, observed in a sintered plate column and in the Oldershaw column can be eliminated by either carrying out the separation in a packed column or by the addition of defoaming additives.

The morphology of spray-dried particles

Samples of Various industrial or pilot plant spray-dried materials were obtained from manufacturers together with details of drying conditions and feed concentrations. The samples were subjected to qualitative and semi-quantitative examination to identify structural and morphological features. The results were related to measured bulk physical properties and to drying conditions. Single particles were produced in a convective drying process Analogous to spray drying, in which different solids or mixtures of solids were dried from solutions, slurries or pastes as single suspended droplets. The localized chemical and physical structures were analysed and in some cases the retention of volatiles monitored. The results were related to experimental conditions, viz.; air temperature, initial solids concentration and the degree of feed aeration. Three distinct categories of particle morphology were identified, i.e.; crystalline, skin-forming and agglomerate. Each category is evidence of a characteristic drying behaviour which is dependent on initial solids concentration. the degree of feed aeration, and drying temperature. Powder flow ability, particle and bulk density, particle-size, particle friability, and the retention of volatiles bear a direct relationship to morphological structure. Morphologies of multicomponent mixtures were complex, but the respective migration rates of the solutes were dependent on drying temperature. Gas-film heat and SDSS transfer coefficients of single pure liquid droplets were also measured over a temperature range of 50•C to 200•C under forced convection. Balanced transfer rates were obtained attributed to droplet instability or oscillation within the airflow, demonstrated in associated work with single free-flight droplets. The results are of relevance to drier optimisation and to the optimisation of product characteristics, e.g.; particle strength and essential volatiles-retention, in convective drying.

Effect of liquid flow patterns on distillation trays

The thesis describes experimental work on sieve trays in an air-water simulator, 2.44 m in diameter. The liquid flow pattern, for flowrates similar to those used in commercial scale distillation, was observed experimentally by water cooling experiments, in which the temperature of the water is measured at over 100 positions over the tray area. The water is cooled by the rising air which is forced through the tray. A heat and mass transfer analogy is drawn whereby the water temperature is mapped to liquid concentration in mass transfer, and the water temperature profiles reveal how liquid channelling may reduce the tray efficiency. The first experiment was to observe the flow of water only over an unperforated tray. With the exception of very low weir loads, the flow separated at the ends of the inlet downcomer. This caused liquid to flow straight across the tray between the downcomers and large circulating regions to be formed in the side regions of the tray. The effect of the air crossflow on the flow pattern was then observed on a sieve tray of 10% free area with 1 mm diameter holes (such as is used in cryogenic distillation). The flow patterns developed on the tray were similar to those produced with water only on the unperforated tray, but at low weir loads the air crossflow prevented separation of the water flow and the associated circulating regions. At higher weir loads, liquid channelling down the centre of the tray and circulation in the side regions occurred. The percentage of the tray occupied by circulating liquid depended upon the velocity of the liquid entering the tray, which was set by the weir load and size of the gap under the inlet downcomer. The water cooling experiments showed that the temperature of the water in a circulating region is much lower than in other parts of the tray, indicating that the driving force for heat transfer is reduced. In a column section where trays (and circulating areas) are mounted on top of each other, the circulating regions will cause air (or vapour) passing through them to have a reduced change in temperature or concentration leading a loss in tray efficiency.

Octane requirement increase arising from the use of lead free fuel

Lead in petrol has been identified as a health hazard and attempts are being made to create a lead-free atmosphere. Through an intensive study a review is made of the various options available to the automobile and petroleum industry. The economic and atmospheric penalties coupled with automobile fuel consumption trends are calculated and presented in both graphical and tabulated form. Experimental measurements of carbon monoxide and hydrocarbon emissions are also presented for certain selected fuels. Reduction in CO and HC's with the employment of a three-way catalyst is also discussed. All tests were carried out on a Fiat 127A engine at wide open throttle and standard timing setting. A Froude dynamometer was used to vary engine speed. With the introduction of lead-free petrol, interest in combustion chamber deposits in spark ignition engines has ben renewed. These deposits cause octane requirement increase or rise in engine knock and decreased volumetric efficiency. The detrimental effect of the deposits has been attributed to the physical volume of the deposit and to changes in heat transfer. This study attempts to assess why leaded deposits, though often greater in mass and volume, yield relatively lower ORI when compared to lead-free deposits under identical operating conditions. This has been carried out by identifying the differences in the physical nature of the deposit and then through measurement of the thermal conductivity and permeability of the deposits. The measured thermal conductivity results are later used in a mathematical model to determine heat transfer rates and temperature variation across the engine wall and deposit. For the model, the walls of the combustion cylinder and top are assumed to be free of engine deposit, the major deposit being on the piston head. Seven different heat transfer equations are formulated describing heat flow at each part of the four stroke cycle, and the variation of cylinder wall area exposed to gas mixture is accounted for. The heat transfer equations are solved using numerical methods and temperature variations across the wall identified. Though the calculations have been carried out for one particular moment in the cycle, similar calculations are possible for every degree of the crank angle, and thus further information regarding location of maximum temperatures at every degree of the crank angle may also be determined. In conclusion, thermal conductivity values of leaded and lead-free deposits have been found. The fundamental concepts of a mathematical model with great potential have been formulated and it is hoped that with future work it may be used in a simulation for different engine construction materials and motor fuels, leading to better design of future prototype engines.

Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional channel flow

A consequence of a loss of coolant accident is the damage of adjacent insulation materials (IM). IM may then be transported to the containment sump strainers where water is drawn into the ECCS (emergency core cooling system). Blockage of the strainers by IM lead to an increased pressure drop acting on the operating ECCS pumps. IM can also penetrate the strainers, enter the reactor coolant system and then accumulate in the reactor pressure vessel. An experimental and theoretical study that concentrates on mineral wool fiber transport in the containment sump and the ECCS is being performed. The study entails fiber generation and the assessment of fiber transport in single and multi-effect experiments. The experiments include measurement of the terminal settling velocity, the strainer pressure drop, fiber sedimentation and resuspension in a channel flow and jet flow in a rectangular tank. An integrated test facility is also operated to assess the compounded effects. Each experimental facility is used to provide data for the validation of equivalent computational fluid dynamic models. The channel flow facility allows the determination of the steady state distribution of the fibers at different flow velocities. The fibers are modeled in the Eulerian-Eulerian reference frame as spherical wetted agglomerates. The fiber agglomerate size, density, the relative viscosity of the fluid-fiber mixture and the turbulent dispersion of the fibers all affect the steady state accumulation of fibers at the channel base. In the current simulations, two fiber phases are separately considered. The particle size is kept constant while the density is modified, which affects both the terminal velocity and volume fraction. The relative viscosity is only significant at higher concentrations. The numerical model finds that the fibers accumulate at the channel base even at high velocities; therefore, modifications to the drag and turbulent dispersion forces can be made to reduce fiber accumulation.

The development of a market orientation in a turbulent, transitional environment:the case of Ukraine

This research is concerned with the case of Ukraine where there has been a fundamental change in the economic environment engendered by the transition from a centrally planned to a market economy and the resulting conditions of economic crisis. The way that Ukrainian marketers and consumers are reacting to this environmental change is the principal concern of the research together with the basic linkages between critical environmental elements and strategic marketing decisions. This research analyses the way in which marketing evolves in a turbulent, transitional environment. The study is based on eight case analyses within the retail sector of the Ukrainian market. The process of transition to a free market economy leads a researcher to question the validity of existing theories that have been based on empirical data that has been collected in the stable marketing environment of the West. For this reason an in-depth, theory building methodology is preferred. A number of broad research objectives were set. Firstly, to establish whether the sales - production - marketing stages model of marketing evolution, derived from empirical data collected in stable Western environments, is relevant in the context of the turbulent, transitional environment of Ukraine. Secondly, to establish if, in this turbulent, transitional environment, idiosyncratic approaches to marketing are emerging and thirdly to assess the development of attitudes to marketing, organisation for marketing and the development of marketing strategy in Ukraine. The main conclusions of this thesis are firstly, that the stages model of marketing orientation is not relevant in the context of Ukraine, secondly that there are idiosyncratic approaches to marketing emerging in the turbulent, transitional environment of Ukraine and finally that the above developments have a profound impact on the development of attitudes to marketing, organisation for marketing and the development of marketing strategy in Ukraine.

Transition in convective flows heated internally

The stability of internally heated convective flows in a vertical channel under the influence of a pressure gradient and in the limit of small Prandtl number is examined numerically. In each of the cases studied the basic flow, which can have two inflection points, loses stability at the critical point identified by the corresponding linear analysis to two-dimensional states in a Hopf bifurcation. These marginal points determine the linear stability curve that identifies the minimum Grashof number (based on the strength of the homogeneous heat source), at which the two-dimensional periodic flow can bifurcate. The range of stability of the finite amplitude secondary flow is determined by its (linear) stability against three-dimensional infinitesimal disturbances. By first examining the behavior of the eigenvalues as functions of the Floquet parameters in the streamwise and spanwise directions we show that the secondary flow loses stability also in a Hopf bifurcation as the Grashof number increases, indicating that the tertiary flow is quasi-periodic. Secondly the Eckhaus marginal stability curve, that bounds the domain of stable transverse vortices towards smaller and larger wavenumbers, but does not cause a transition as the Grashof number increases, is also given for the cases studied in this work.