The influence of relative fluid depth on initial bedform dynamics in closed, horizontal pipe flow

Measurements of time-dependent bedforms produced by the deposition of solid plastic particles in two-phase liquid-solid flows were performed using a novel ultrasonic echo method and via video image analysis in a 100-liter, closed-pipe slurry flow loop. Results are presented for the settled bed thicknesses over a range of nominal flow rates and initial bed depths and are combined into several phase diagrams based on various combinations of parameters, with the bedforms categorized into five types. The novel observation is made that the type of bedform that arises depends on both the flow rate and the initial relative bed or fluid depth, with both ripples and dunes being observed in the same system and in a single experiment. In addition, the critical Shields number at incipient particle motion is measured to be θsc = 0.094 ± 0.043, hysteretic behavior is observed, and the evolution and scaling of each time-dependent type of bedform is analyzed in detail and compared against several expressions for initial and equilibrium dimensions from the literature. A number of universal scalings for bedforms in any type of conduit are proposed with a view ultimately to unifying the observations of bedforms in pipes with those in channels and natural flows

Large-scale trials of a real-time acoustic backscatter system for solids concentration measurement during nuclear waste cleanup

Real time in situ characterisation of solids concentration would aid operational understanding and improve efficiency in many industrial systems. This is especially true in the processing of legacy nuclear wastes where hazardous material is encountered. Acoustic methods have been previously demonstrated for the measurement of concentration in solid-liquid systems at a small scale. This study explores the use of the ultrasound array research platform (UARP) for backscatter measurements of concentration at a large scale in a dynamic settling system. The theory of acoustic measurement of solids concentration is described for both backscatter based attenuation and backscatter power methods. Acoustic based backscatter power and attenuation measurements are compared to laboratory analysed samples. Ultrasonic solids concentration analysis is shown to reveal flow dynamics within the settling tank

Maintaining consistency across design descriptions in engineering product development

The success of engineering product development depends on the effective communication of design descriptions in formats that suit the needs and capabilities of all stakeholders involved in the delivery to market and through-life support of products. Configuration management is a core design process to ensure the consistency of the technical data package, i.e., the collection of design descriptions needed to support the development, manufacture and operation of a given product. Bills of Materials (BoMs) are critical parts of the technical data package because they act as integrators: adapting detailed design descriptions to suit the needs of particular downstream processes. The ability to reconfigure BoMs while maintaining internal consistency of the technical data package (where all BoM configurations are complete and compatible with each other) is a major challenge. In this paper, we introduce research exploring computational tools that could support engineers in manipulating BoMs while also maintaining the internal consistency of the technical data package

Acoustic Method for Determination of the Thermal Properties of Nanofluids

This study determines the thermophysical properties of nanofluids using ultrasonic techniques. Using an acoustic test cell, fitted with 4 MHz high-temperature transducers, measurements of the speed of sound in an aqueous dispersion of alumina nanoparticles (Al2O3, 99.9%, spherical, dp = 50 nm) are made at volume fractions from 1 to 5 vol % over the temperature range of 20−90 °C. The observed relationships between the measured parameters and speed of sound variation are presented. Available theoretical approaches are reviewed and applied to the data of the study. The speed of sound data together with measurements of density and predictions of thermal conductivity, derived from Lagrangian particle tracking (LPT) simulations, is used to determine the ratio of specific heats of nanofluids using a modified version of the Bridgman equation. The results demonstrate the effectiveness of the measurement technique, with outcomes elucidating the dependence of the speed of sound on temperature and particle concentration, and hence the influence of these parameters on the thermophysical properties of nanofluids. Using the speed of sound approach and LPT simulations, the predicted thermal values, which have an estimated accuracy of 5−10%, show good agreement with theoretical and experimental results available in the literature for similar operating conditions. This research forms the basis for the use of novel acoustic techniques for online, in situ measurement of nanofluids, and their potential applications in solar thermal power systems

Measurement and density normalisation of acoustic attenuation and backscattering constants of arbitrary suspensions within the Rayleigh scattering regime

The scattering and attenuation of megahertz frequency acoustic backscatter in liquid suspensions, is examined for a range of fine organic and inorganic particles in the Rayleigh regime, 10−⁴ < ka < 10⁰ (where k is the wavenumber and a the particle radius) which are widely industrially relevant, but with limited existing data. In particular, colloidal latex, mineral titania and barytes sediments, as well as larger glass powders were investigated. A manipulation of the backscatter voltage equation was used to directly measure the sediment attenuation constants, ξ. Decoupling of the combined backscattering-transducer constant, allowing explicit measurement of the backscattering constant, ks, was achieved through calibration of the transducer constant, kt. Additionally, the methodology was streamlined via averaging between a number of intermediate concentrations to reduce data variability. This approach enabled the form function, f, and the corresponding total normalized scattering cross-sections, χ, to be determined for all species. While f and χ are available in the literature for large glass and sand, this methodology allowed extension for the colloidal organic and inorganic particles. Specific gravity normalisation of f collapsed all data onto a single distribution, with the exception of titania, due to scattering complexities associated with agglomeration. There was some additional variation in χ, with measured values of the fine particles up to of magnitude greater than the density-normalised prediction at low ka. Mechanisms accounting for these variations from theory are however analysed, and include viscous attenuation effects, the polydispersity of the particle type and increasing influence of the solvent attenuation. Additionally, thermoacoustic losses appeared to dominate the attenuation behaviour of the organic latex particles. This study demonstrates that particles close to the colloidal regime can be measured successfully with acoustic backscatter, and highlights the great potential of this technique to be applied for in situ or online monitoring purposes in such systems

Measuring particle concentration in multiphase pipe flow using acoustic backscatter: Generalization of the dual-frequency inversion method.

A technique that is an extension of an earlier approach for marine sediments is presented for determining the acoustic attenuation and backscattering coefficients of suspensions of particles of arbitrary materials of general engineering interest. It is necessary to know these coefficients (published values of which exist for quartz sand only) in order to implement an ultrasonic dual-frequency inversion method, in which the backscattered signals received by transducers operating at two frequencies in the megahertz range are used to determine the concentration profile in suspensions of solid particles in a carrier fluid. To demonstrate the application of this dual-frequency method to engineering flows, particle concentration profiles are calculated in turbulent, horizontal pipe flow. The observed trends in the measured attenuation and backscatter coefficients, which are compared to estimates based on the available quartz sand data, and the resulting concentration profiles, demonstrate that this method has potential for measuring the settling and segregation behavior of real suspensions and slurries in a range of applications, such as the nuclear and minerals processing industries, and is able to distinguish between homogeneous, heterogeneous, and bed-forming flow regimes

Turbulent Heat Transfer In Nanoparticulate Multiphase Channel Flows With A High Prandtl Number Molten Salt Fluid

The growing interest in energy efficient and sustainable technologies has created significant demand for novel heat transfer and thermal energy storage materials, such as nanofluids. The importance of nanoparticle science cannot be underestimated, since the motivation for the manipulation, through nanoparticle addition, of the properties of existing thermofluids (e.g. molten salt) arises from their poor thermal properties which represent a major limitation to the development of more energy-efficient processes. In this work, consideration is given to investigating the role of heat transfer in nanofluids in three-dimensional flows using an advanced computational modelling approach to simulate such flows. In the present work, we use direct numerical simulation coupled with a Lagrangian particle tracking technique. The heat transfer behaviour of a nanofluid within a turbulent wall-bounded flow is investigated, with the fluid phase properties chosen to represent a solar molten salt (NaNO3-KNO3, 60:40 weight ratio) thermofluid typical of those present in solar thermal power plants. The configuration is a fully developed channel flow with uniform heating/cooling from both walls. The continuous phase is modelled using the open source spectral element-based solver, Nek5000. Predictions of a statistically steady turbulent channel flow at shear Reynolds number Reτ = 180 and high turbulent Prandtl number Prt = 5.0 are first obtained and validated. A particle tracking routine is implemented to simulate the dispersed phase which can accommodate one-, two- and four-way coupling between the fluid and discrete phases. To investigate the effect of particles on the turbulent heat flux and temperature field, the nanoparticle concentration response to temperature variations and turbulence is obtained across the channel, with the associated first and second-order flow and temperature field statistics presented. The advantage of the model developed is its ability to study in detail phenomena such as interparticle collisions, agglomeration, turbophoresis and thermophoresis, with the approach also being of value in investigations of the heat transfer performance and long-term thermal stability of nanoparticle dispersions which as yet have not been considered in detail. The outcome of this study allows conclusions to be reached regarding the implications of nanoparticle-seeded molten salts for solar thermal energy storage systems

Cirsium species show disparity in patterns of genetic variation at their range-edge, despite similar patterns of reproduction and isolation

Genetic variation was assessed across the UK geographical range of Cirsium acaule and Cirsium heterophyllum. A decline in genetic diversity and increase in population divergence approaching the range edge of these species was predicted based on parallel declines in population density and seed production reported seperately. Patterns were compared with UK populations of the widespread Cirsium arvense.Populations were sampled along a latitudinal transect in the UK and genetic variation assessed using microsatellite markers. Cirsium acaule shows strong isolation by distance, a significant decline in diversity and an increase in divergence among range-edge populations. Geographical structure is also evident in C. arvense, whereas no such patterns are seen in C.heterophyllum. There is a major disparity between patterns of genetic variation in C. acaule and C. heterophyllum despite very similar patterns in seed production and population isolation in these species. This suggests it may be misleading to make assumptions about the geographical structure of genetic variation within species based solely on the present-day reproduction and distribution of populations