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The scaling theory of the spinodal decomposition of a symmetric binary fluid mixture in the inertial region has been reviewed, and extended by considering energy balance, as well as the momentum balance described by the Navier-Stokes equation (NSE). The prediction for the asymptotic growth rate of the size of the separating fluid domains is ~<I>t<SUP>2/3</SUP></I>, as in simple scaling theory, but the ratio of the nonlinear to viscous terms in the NSE (the Reynolds number) is predicted to remain finite. This is due to the viscous term remaining important to the system dynamics, in contrast to simple scaling theory where the viscous term is assumed to be negligible. Spinodal decomposition in binary fluid mixtures has been successfully simulated using a lattice Boltzmann method. The simulation results were combined using a characteristic length and time obtained from the physical parameters (density, viscosity, interfacial tension) to scale the domain size, the resulting single scaling plot covers five decades of length and eight of time from the viscous hydrodynamic region (linear scaling) through a broad crossover region to the inertial region. This is a larger range than all previous results combined, and the first unambiguous simulation results for the inertial region. Both the order parameter and the fluid velocity in the spinodal system have been analysed in detail. The order parameter shows good scaling behaviour (collapse of the structure factor) while various velocity-related quantities, such as the dissipation rate, were found not to scale. A comparison of the relative magnitude of the terms in the NSE confirmed that the results include simulation of the inertial region where the inertial terms dominate the dynamics. Careful analysis of the growth rate due to diffusion also allowed this to be discounted from making a significant contribution to the hydrodynamic coarsening under observation in this study. The persistence behaviour of the spinodal system has been studied, although the order parameter data are not sufficient for a precise determination to be made of the value of the persistence exponent. It was possible to show that the persistence behaviour follows a power law decay (as opposed to exponential) and to show that there is some dependence on the domain growth exponent (linear/<I>f<SUP>2/3</SUP></I>).

In this study numerical methods for free-surface flows are reviewed and their advantages and disadvantages over each other assessed. This results in the adoption of the Boundary-Integral method (BIM) as the preferred method to model the flows of interest, namely free-surface flows in the vicinity of surface-piercing bodies. A new BIM is then developed which takes features from various existing BIMs and in some cases extends these features. Notable improvements include: the discretisation of the boundary, the treatment of corners in the boundary of the fluid domain and the control of free-surface instabilities. The results of this BIM are then compared with an analytical solution, results from another numerical method and results from an experiment. In all three cases very good agreement is found. The comparison with the analytical solution shows, for the first time, that a properly adapted BIM can accurately predict the fluid motion at the intersection between free-surface flow caused by body/fluid interaction. In addition to this good comparison, hitherto unnoticed features of the analytical solution are also identified and presented. Finally, unlike in many experimental comparisons, in the one performed here the exact geometry of the wavetank and motion of the wavemaker are used as input for the present numerical wavetank.

No description available.

No description available.

The use of mixtures of refrigerants in refrigeration cycles can lead to improvements in cycle efficiency. The majority of refrigerant working fluids have been pure fluids. With pure refrigerants temperature profiles between the working fluid and the heat source and sink fluids may not be well matched. Mixtures of refrigerants boil and condense across a temperature range. This property can be used to reduce the mean temperature differences in the heat exchangers, and to improve the matching of the temperature profiles. This leads to higher coefficients of performance (COP). In this thesis, the improvement in refrigeration COP due to mixtures of refrigerants is investigated. Ratification of the Montreal protocol led to the phasing our of chlorofluorcarbon (CFC) refrigerants. Hydrofluorocarbon (HFC) refrigerants are the leading candidates to replace CFCs. Mixtures of HFC refrigerants are examined. An existing pilot plant refrigeration cycle was adapted and modified for use with HFC refrigerants. A binary mixture of difluoromethane (R32) and 1,1,1,2-tetrafluoroethane (R134a) is examined experimentally. The phasing out of CFC refrigerants means that there exists a need for methods which can predict accurately the thermodynamic properties of a proposed replacement refrigerant, from sparse amounts of data. The Cubic Chain-of-Rotators (CCOR) equation of state requires relatively little knowledge of the fluid it describes. CCOR predictions of pure and mixed HFC thermodynamic properties, were compared with published experimental data. Comparisons were also made with the more complex Carnahan-Starling-DeSantis (CSD) equation. The CCOR equation predicted saturated and superheated vapour pressure with satisfactory accuracy. Liquid density was not predicted with the same precision. Vapour density was described no worse than the CSD equation. CCOR description of binary vapour-liquid equilibrium (VLE) was superior to that of the CSD equation. Prediction of VLE data was improved by using optimal interaction constants. It was shown that if an optimal set of interaction constants was located for each experimental data point for bubble point VLE data, the interaction constants exhibited a regular dependence upon temperature and composition. The CCOR equation can be used to provide approximate preliminary thermodynamic data for a new refrigerant, for which little data exists.

No description available.

No description available.

Homogeneous, isotropic turbulence in fluids is a highly complicated phenomenon, involving the interaction of many degrees of freedom. A brief statement of the problem is made, with an outline of historical solutions. The renormalization group is introduced and the technical problems of its application to turbulence detailed. A real-space formulation is presented of the theory of iterative averaging (<I>W.D. McComb and A.G. Watt, Phys. Rev. A </I>46, <I>4797 (1992)</I>). The turbulent velocity field is iteratively filtered using a sharp filter. At each stage, the subgrid field is averaged and its mean effect incorporated into an eddy-viscosity term, in which the viscosity is convolved with the velocity field. A two-field decomposition of the subgrid field is used to perform the averaging. After a brief summary of the <I>k</I>-space derivation of the iterative-averaging method, results of numerically calculating the theory are present. A value for the Kolmogorov spectral constant of α = 1.6 is found. This value is independent of input parameters over a significant range. Two analytical results are derived, which provide useful checks on the computation. A new renormalization-group formulation, loosely based on the prescription of Forster, Nelson and Stephen (<I>Phys. Rev. A </I>16, <I>732 (1977)</I>) for stirred hydrodynamics, is presented. A fictional force is introduced to model the stirring of the small scales by the large eddies. The definition of the force is based on the two-field decomposition of the subgrid velocity field. Higher-order nonlinearities in the velocity field are produced by the elimination procedure, and are treated as part of a modified equation of motion. When the theory is numerically iterated, a value for the Kolmogorov constant of α = 1.71 is found, but only after a large error term, due to the absence of a spectral gap between subgrid- and explicit-scale modes, is neglected. A comparison is made of this theory with iterative averaging, with particular reference to the role of the higher-order nonlinearities, and the use of conditional averaging as opposed to filtered ensemble averaging. The behaviour of the two theories in the continuum limit of the renormalization group process is analysed. Both theories are found to break down in some way in this region. The behaviour of other formulations in the limit is also briefly examined, and it is argued that the non-existence of the continuum limit is a property of the Navier-Stokes equations. Some of the above ideas are extended to the case of passive scalar convection. Results of calculating iterative averaging for this case are shown, with a value for the Obukhov-Corrsin spectral constant of β = 1.0. The perturbative formulation is adapted for the passive scalar equation. The results for the Obukhov-Corrsin constant do not display any independence of input parameters in this case. It is found that 0.69 ≤ β ≤ 0.76.

The use of a photon count correlator for the analysis of different flow situations is described. The problem of flow parameter estimation from the correlogram is discussed in some detail. After describing some, approximate methods, the least square fitting and Fourier transformation methods are considered. The effect of frequency shifting on parameter estimation is described. The use of high resolution estimators such as the Maximum Entropy and Maximum Likelihood spectra have been considered. An experiment on a sinusoidally fluctuating flow is described. The error involved in uniform random clipping of photon counts in order to make the correlogram independent of the field statistics is derived. The errors in the determination of the mean and variance of the velocity using a burst counter are derived. This is accomplished by assuming Poisson sampling of a continuous velocity record with a known correlation function. The method of obtaining the turbulence spectra from the burst counter data is described.