701 research outputs found
Fluid Simulation Using GPU
Tato práce se zabývá simulací kapalin, konkrétněji se zaměřuje na propojení částicové a mřížkové simulace modelující vypařování. Přistup k simulaci vypařování čerpá z článku Evaporation and Condensation of SPH-based Fluids autorů Hendrika Hochstettera a Andrease Kolba. Cílem celé práce však není jen tvorba simulace, ale zároveň studium různých metod používaných při simulaci kapalin.This thesis focuses on fluid simulation, particularly on coupling between particle based simulation and grid based simulation and thus modeling evaporation. Mentioned coupling is based on the article Evaporation and Condensation of SPH-based Fluids of authors Hendrik Hochstetter a Andreas Kolb. The goal of this thesis is not purely implementing ideas of the mentioned article, but also study of different methods used for fluid simulation.
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Pore-Scale Study on Two-Phase Flow in Porous Media
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This paper presents currently available pore-scale predictive techniques for two-phase flow in
porous media, which are based on the real description of the pore space. Two pore-scale models are
established with FVM-VOF and LBM-VOF method based on the different complex foam structure,
respectively. The two-phase flow of pore fluid is numerically simulated and the influence of the porous
structure wettability is discussed based on the numerical predictions. These pore-scale models can be
adopted to describe the detailed flow characteristic in porous media and evaluate their average effects
Advances in modeling gas adsorption in porous materials for the characterization applications
The dissertation studies methods for mesoporous materials characterization using adsorption at various levels of scale and complexity. It starts with the topic introduction, necessary notations and definitions, recognized standards, and a literature review.
Synthesis of novel materials requires tailoring of the characterization methods and their thorough testing. The second chapter presents a nitrogen adsorption characterization study for silica colloidal crystals (synthetic opals). These materials have cage-like pores in the range of tens of nanometers. The adsorption model can be described within a macroscopic approach, based on the Derjaguin-Broekhoff-de Boer (DBdB) theory of capillary condensation. A kernel of theoretical isotherms is built and applied to the solution of the adsorption integral equation to derive the pore-size distribution from experimental data. The technique is validated with a surface modification of the samples so that it changes the interaction but not the pore size.
The second chapter deals with the characterization of three-dimensional ordered mesoporous (3DOm) carbons. Similar to opals, these materials have cage-like mesopores, however, these pores are connected with large windows. These windows affect the adsorption process and calculated pore-size distributions. The grand canonical Monte Carlo simulations with derived solid-fluid potentials, which take into account the 3DOm carbons geometry, confirm the critical role of interconnections, their size, and number, for correct interpretation of adsorption data for the PSD calculations.
The fourth chapter discusses a method for the pore size estimation that can serve as an alternative to the adsorption isotherms analysis. It is based on measurements of elastic properties of liquid that can be useful for the pore size estimation. A Vycor glass sample, a disordered mesoporous material with channel-like pores having a characteristic size of ca. 6-8 nm, is considered. The changes in longitudinal and shear moduli from the experimental data and molecular simulations are predicted with a near-quantitative agreement. Then, it follows by their relation of the moduli to the pore size, which is promising for characterization.
The last fifth chapter considers a promising Monte Carlo method, the Kinetic Monte Carlo (kMC) algorithm. This method is efficient for the vapor-liquid equilibrium prediction in dense regions. This chapter shows a benchmark with conventional Metropolis et al algorithms as well as a parallelization scheme of the kMC algorithm
Water and Ethanol Droplet Wetting Transition during Evaporation on Omniphobic Surfaces
Omniphobic surfaces with reentrant microstructures have been investigated for a range of applications, but the evaporation of high- and low-surface-tension liquid droplets placed on such surfaces has not been rigorously studied. In this work, we develop a technique to fabricate omniphobic surfaces on copper substrates to allow for a systematic examination of the effects of surface topography on the evaporation dynamics of water and ethanol droplets. Compared to a water droplet, the ethanol droplet not only evaporates faster, but also inhibits Cassie-to-Wenzel wetting transitions on surfaces with certain geometries. We use an interfacial energy-based description of the system, including the transition energy barrier and triple line energy, to explain the underlying transition mechanism and behaviour observed. Suppression of the wetting transition during evaporation of droplets provides an important metric for evaluating the robustness of omniphobic surfaces requiring such functionality
A high-temperature heat pump for compressed heat energy storage applications: Design, modeling, and performance
The current paper presents the design and performance of a high-temperature heat pump (HTHP) integrated in an innovative, sensible, and latent heat storage system. The HTHP has been designed to work between a heat source from 40 to 100 °C and a heat sink above 130 °C. An initial refrigerant analysis has revealed that R-1233zd(E) is the best candidate to meet the required performance and environmental considerations. The first part of this paper deals with the sizing and selection of the main components while discussing the challenges and working limits. A numerical model is also presented and validated. The second part of the paper is dedicated to develop parametric studies and performance maps under different operating conditions. The results show that the current HTHP, at a source temperature of 80 °C, consumes from 3.23 to 9.88 kW by varying the compressor’s speed from 500 to 1500 rpm. Heat production is achieved in the form of latent heat (7.40 to 21.59 kW) and sensible heat (from 6.35 to 17.94 kW). The heating coefficient of performance (COPHTHP) is around 4.This work has been partially funded by grant agreement No. 764042 (CHESTER project) of the European Union’s Horizon 2020 research and innovation program. The authors would like to express their deep gratitude to Prof. Dr. Jose Miguel Corberán Salvador for his perseverance, encouragement, and invaluable guidance during this work
Radiative transfer and the energy equation in SPH simulations of star formation
We introduce and test a new and highly efficient method for treating the
thermal and radiative effects influencing the energy equation in SPH
simulations of star formation. The method uses the density, temperature and
gravitational potential of each particle to estimate a mean optical depth,
which then regulates the particle's heating and cooling. The method captures --
at minimal computational cost -- the effects of (i) the rotational and
vibrational degrees of freedom of H2, H2 dissociation, H0 ionisation, (ii)
opacity changes due to ice mantle melting, sublimation of dust, molecular
lines, H-, bound-free and free-free processes and electron scattering; (iv)
external irradiation; and (v) thermal inertia. The new algorithm reproduces the
results of previous authors and/or known analytic solutions. The computational
cost is comparable to a standard SPH simulation with a simple barotropic
equation of state. The method is easy to implement, can be applied to both
particle- and grid-based codes, and handles optical depths 0<tau<10^{11}.Comment: Submitted to A&A, recommended for publicatio
The origin of the Moon within a terrestrial synestia
The giant impact hypothesis remains the leading theory for lunar origin.
However, current models struggle to explain the Moon's composition and isotopic
similarity with Earth. Here we present a new lunar origin model. High-energy,
high-angular momentum giant impacts can create a post-impact structure that
exceeds the corotation limit (CoRoL), which defines the hottest thermal state
and angular momentum possible for a corotating body. In a typical super-CoRoL
body, traditional definitions of mantle, atmosphere and disk are not
appropriate, and the body forms a new type of planetary structure, named a
synestia. Using simulations of cooling synestias combined with dynamic,
thermodynamic and geochemical calculations, we show that satellite formation
from a synestia can produce the main features of our Moon. We find that cooling
drives mixing of the structure, and condensation generates moonlets that orbit
within the synestia, surrounded by tens of bars of bulk silicate Earth (BSE)
vapor. The moonlets and growing moon are heated by the vapor until the first
major element (Si) begins to vaporize and buffer the temperature. Moonlets
equilibrate with BSE vapor at the temperature of silicate vaporization and the
pressure of the structure, establishing the lunar isotopic composition and
pattern of moderately volatile elements. Eventually, the cooling synestia
recedes within the lunar orbit, terminating the main stage of lunar accretion.
Our model shifts the paradigm for lunar origin from specifying a certain impact
scenario to achieving a Moon-forming synestia. Giant impacts that produce
potential Moon-forming synestias were common at the end of terrestrial planet
formation.Comment: Accepted for publication in Journal of Geophysical Research: Planets.
Main text: 44 pages, 24 figures. Supplement: 16 pages, 5 figures, 3 table
Two Phase Flow, Phase Change and Numerical Modeling
The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society
Gap Formation in the Dust Layer of 3D Protoplanetary Disks
We numerically model the evolution of dust in a protoplanetary disk using a
two-phase (gas+dust) Smoothed Particle Hydrodynamics (SPH) code, which is
non-self-gravitating and locally isothermal. The code follows the three
dimensional distribution of dust in a protoplanetary disk as it interacts with
the gas via aerodynamic drag. In this work, we present the evolution of a disk
comprising 1% dust by mass in the presence of an embedded planet for two
different disk configurations: a small, minimum mass solar nebular (MMSN) disk
and a larger, more massive Classical T Tauri star (CTTS) disk. We then vary the
grain size and planetary mass to see how they effect the resulting disk
structure. We find that gap formation is much more rapid and striking in the
dust layer than in the gaseous disk and that a system with a given stellar,
disk and planetary mass will have a different appearance depending on the grain
size and that such differences will be detectable in the millimetre domain with
ALMA. For low mass planets in our MMSN models, a gap can open in the dust disk
while not in the gas disk. We also note that dust accumulates at the external
edge of the planetary gap and speculate that the presence of a planet in the
disk may facilitate the growth of planetesimals in this high density region.Comment: 5 page, 4 figures. Accepted for publication in Astrophysics & Space
Scienc
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