In this paper, the heterogeneous combustion of porous metal-containing media is studied taking into account the phase transitions of metal in condensed and gas phases. Such process takes place when applying a novel promising method for the extraction of rare metals from various combustible materials, such as coal and petroleum wastes, by means of filtration combustion. A novel mathematical model, based

Detailed laboratory experiments were performed to study the dynamics and mixing properties of vertically discharged sand-water coaxial jets in stagnant water. The effects of velocity ratio on the fluid dynamics of two-phase coaxial jets were studied. The axial and radial distributions of sand concentration and velocity were measured with an advanced optical fiber probe (PV6), and sand concentration

A literature review on the two-phase flow inside plain tubes, especially for the refrigerant R1234yf, is conducted in this research. The flow boiling, condensation, and visualization of this low GWP refrigerant were examined experimentally to measure the heat transfer coefficients and pressure drop of the refrigerant, and also to present a flow pattern map. The measurements were carried out on smooth

The formation and life-span of clouds as well as the associated unsteady processes concerning the micro-physics of the water phases they may contain are open questions in atmospheric physics. We here use three-dimensional direct numerical simulation to analyse the temporal evolution of a small portion of the top of a cloud. The Eulerian description of the turbulent velocity, temperature and vapor fields

The determination of the liquid film thickness during annular flow condensation in a small diameter channel is complex and very rare in the literature, although important to understand the heat transfer mechanisms involved during the phase change process. In the present paper, the liquid film thickness and heat transfer coefficients have been measured during vertical downflow condensation inside a

The existence of a quiescent core (QC) in the center of turbulent channel flows was demonstrated in recent experimental and numerical studies. The QC-region, which is characterized by relatively uniform velocity magnitude and weak turbulence levels, occupies about 40% of the cross-section at Reynolds numbers Reτ ranging from 1000 to 4000. The influence of the QC region and its boundaries on transport

The purpose of this work is to numerically evaluate the behaviour of microscopic gas-focused liquid sheets in terms of material properties, nozzle structure and operating conditions used for experiments in spectroscopy and scattering where a short optical path is required. The numerical simulations are presented of a gas flow focusing nozzle, capable of producing a stream consisting of a sequence of

The transfer of thermal energy is a core process in industrial processes. Improving the efficiency of heat exchangers could significantly reduce industrial energy consumption and costs. The thermo-hydraulic efficiency is widely used to evaluate heat exchanger efficiency. Dimples increase the thermo-hydraulic efficiency, but the performance of dimples under fouling conditions, and especially for particle-laden

Pressure-driven microdroplet formation was experimentally investigated in glass flow-focusing devices using micro-imaging. The observations illustrated the effects of some important factors affecting the droplet formation, including the channel geometry, two-phase flow rates and non-Newtonian behavior of the continuous phase. Although the droplet formation dynamics showed some different characteristics

A Stefan flow can be generated during a phase change or reactions of a particle immersed in a fluid. This study investigates the effect of Stefan flow on the exchange of momentum (drag coefficient (CD)) and heat transfer (Nusselt number (Nu)) between the particle and bulk-fluid. Fully resolved simulations were carried out for a flow near a spherical particle immersed in a uniform bulk flow. The immersed

Particles-induced turbulence in fluidized beds is vital in dense particulate flow and still lacks detailed investigation. In this study, a multi-direct forcing immersed boundary method coupled with a soft-sphere model is employed in simulations of shallow and deep bubbling beds of movable spheres. Five different particle-resolved direct numerical simulations are performed by varying the inlet gas velocity

In this work, we recall an isothermal version of the broadly accepted macroscopic continuum model of drying, and we impose flux boundary conditions at two interfaces, i.e., at the interface between the (gas-side) boundary layer and the (medium-side) dry region, as well as the interface between the dry and unsaturated regions which evolves freely during drying. Local relative humidity, local saturation

This paper presents a thermo-fluid dynamic analysis in a micro-textured evaporator for loop heat pipes (LHPs) that has a super wetting surface with ethanol on the basis of an experiment and modeling. In the experiment, three kinds of stainless steel plates with various morphologies of heat transfer surfaces were tested: a normal flat plate, a sandblasted plate, and a micro-groove plate. The measured

Adaptive mesh refinement (AMR) provides an attractive means of significantly reducing computational costs while simultaneously maintaining a high degree of fidelity in regions of the domain requiring it. In the present work, an analysis of the performance of AMR supported by simulations is undertaken for liquid injection and spray formation problems. These problems are particularly challenging from

We consider the collapse behavior of cavitation bubbles near walls under high ambient pressure conditions. Generic configurations with different stand-off distances are investigated by numerical simulation using a fully compressible two-phase flow solver including phase change. The results show that the stand-off distance has significant effects on collapse dynamics, micro-jet formation, rebound, and

This study considers complex ice particles falling in the atmosphere: predicting the drag of such particles is important for developing of climate models parameterizations. A Delayed-Detached Eddy Simulation model is developed to predict the drag coefficient of snowflakes falling at Reynolds number between 50 and 2200. We first consider the case where the orientation of the particle is known a posteriori

The gas holdup is an important parameter in industrial applications for design and operation of bubble columns as well as for calculation of the pressure gradient in fluid flow through pipelines. This study presents new experimental gas holdup data by using kerosene as the liquid phase, CO2 and N2 as the gas phase, and multiwall carbon nanotubes (one of them without functionalized group and another

Microbubble generators are in wide demand in industry following the discovery of a number of new functions of microbubble mixtures. This paper deals with a Venturi tube microbubble generator in which air bubbles at the inlet are fragmented in the diverging part of the tube. In contrast with past studies, we here regulated the flow subsonic so that fragmentation occurred without the help of pressure

Weakly nonlinear propagation of plane progressive pressure waves in an initially quiescent liquid uniformly containing many spherical microbubbles is theoretically investigated, especially focusing on an initial small polydispersity of both the bubble radius and the number density of bubbles (i.e., void fraction), which appears in a field far from the sound source. Nonlinear waves in polydispersed

The correct calculation of interphase forces exerted on particles is important for particle tracking and interphase interaction. The Basset history force, which accounts for unsteady drag effects, is often neglected in simulations because its calculation is very demanding in CPU time and memory requirements. Thus, it is significant to approximately estimate the relative importance of the Basset force

Stably-stratified flows are characterised by the presence of internal gravity waves (IGWs), which constitute a barrier for mass, heat, momentum and species vertical transport. In this paper, the dynamics of semi- and neutrally-buoyant particles in three-dimensional, stably-stratified turbulent channel flow is investigated, using direct numerical simulations (DNS), one-way coupled with a Lagrangian

Flow topology and unsteady cavitation dynamics in the wake of a backward facing step was investigated using high speed videography and time-resolved X-ray densitometry, along with static and dynamic pressure measurements. The measurements are used to inform the understanding of underlying mechanisms of observed flow dynamics as they are related to shock wave induced instabilities. The differences in

This study investigated the effects of backpressure and operating conditions on the self-pulsation characteristics of a liquid-centred swirl coaxial (LCSC) injector. To this end, a three-dimensional numerical simulation via octree adaptive mesh refinement as well as coupled level-set and volume of fluid method were employed. Self-pulsation is suppressed by backpressure for a constant gas–liquid momentum

In the motion of two gravity-driven bubbles arranged in a line, the trailing bubble is known to accelerate in the wake of the leading bubble. Furthermore, the approaching bubble migrates laterally as a result of bubble–bubble interactions. This paper presents the physical mechanisms for the acceleration and lateral motions of deformable bubbles under stable conditions, i.e., rectilinear motion in a

Liquid fuel atomisation is largely affected by in and near nozzle phenomena. In this paper we establish a link between the initial droplet distribution at the nozzle exit, used as an input parameter in Lagrangian solvers, and the effect that this selection has on the subsequent predicted spray physics. Three initial PDFs with similar mean but different variance are tested in order to represent different

A new formulation for correcting the pressure field in Viscous Potential Theory (VPT) is developed, generalizing previous Viscous Pressure Correction (VPC) methods to simulate multi-phase flows based on VPT. The latter theory is now applicable to a wider range of flow problems. Without limiting the general applicability of the formulation, the present work focuses on the dynamics of two-dimensional

Flow boiling in a network of heated parallel channels is prone to instabilities that can cause uneven flow distribution, thereby degrading the heat transfer performance of the system and limiting predictability. This study experimentally investigates flow maldistribution between two parallel microchannels that arises due to the Ledinegg instability. The channels are heated uniformly and are thermally

The spreading of a n-decane liquid film induced by the impingement of a spray generated by a high-pressure injector is studied experimentally. The experimental setup uses the Refractive Index Matching (RIM) method to observe the development and propagation of the wall film. The influence of injection time, injection pressure, temperature, and injector to wall distance are considered. The film evolution

The breakup characteristics of micro rectangular jets with external disturbances were experimentally investigated. The hydraulic diameter of the orifice changed from 0.1 mm to 0.4 mm, whereas the aspect ratio of the cross section varied from 10 to 30. The external disturbance was generated by the piezoelectric ceramic, which was excited by a function generator with a frequency from 0 kHz to 15 kHz

The interaction of the Wave Phase Conjugation (WPC) process with bubble cloud dynamics is investigated via numerical modeling in application to bubble size measurements. The WPC simulator by Modarreszadeh and Timofeev (Computers and Fluids 197, 104353) is used as a starting point. In the simulator, a modified version of the high-order Nodal Discontinuous Galerkin method is used for modeling of acoustic

In this work, we propose a conductivity-based single-layer wire-mesh sensor (WMS) system to simultaneously measure the planar bubble distribution, equivalent diameter, and rise velocity of micro-to-millimeter sized bubbles in a gas-liquid two-phase flow. Compared with the conventionally available WMS system, the proposed system is capable of simultaneously measuring the bubble size and velocity using

The evolution of concentrated particle suspensions in a two dimensional channel flow between parallel plates is considered. We developed a numerical model based on the finite volume method to solve the full unsteady Navier Stokes equations coupled to a constitutive advection-diffusion equation in order to determine shear-induced migration phenomenon in concentrated suspensions of monodisperse and non-colloidal

We propose a novel polydisperse cavitation model based on population balances, which seeks to provide the bubble size distribution in addition to the void fraction, enabling natural prediction of transitions from large bubbles to small cavities in regions of massive condensation, or from small bubble to large cavities in regions of strong evaporation. The mass transfer rate is modeled from the asymptotic

The present study completes the development of a model for predicting the effect of wall impacts on agglomerates in turbulent flows. Relying on an Euler-Lagrange hard-sphere approach this physical phenomenon is described in an efficient manner allowing practically relevant multiphase flow simulations at high mass loadings. In a recent study (Khalifa and Breuer, 2020) conditions for the onset of breakage

The behavior of the disturbance waves is studied in downward adiabatic air-water annular flow in a vertical pipe with an inner diameter of 11.7 mm. The range of liquid wetting densities is 2.5–4.6 cm2/s and the range of superficial gas velocities is 22–57 m/s. The paper is focused on the downstream evolution of the main properties of individual disturbance waves at the stage of flow development along

A numerical investigation of lateral migration of a neutrally buoyant particle in Couette flow with two different thermal boundary conditions is performed using a lattice Boltzmann method coupled with a discrete element method. The effects of the channel Reynolds number (Re), the Grashof number (Gr) as well as the particle size on the migration behaviour are explored in detail. It was found that when

Understanding the flow dynamics of two-phase systems with partially-miscible components is of great importance to the extraction and purification of chemicals. Based on the generalized bracket approach of nonequilibrium thermodynamics, we propose a phase-field model to describe binary systems with different degrees of miscibility. By formulating the concentration equation associated with one of the

The aim of this study is to identify the flow structure in an airlift pump–bubble generator system by using experimentally obtained differential pressure signals. Differential pressure measurements were applied at both the bottom and top test sections. The normalized time variation of the differential pressure data was analyzed using the probability density function (PDF), power spectral density function

Two-phase data from flashing experiments are presented beyond the traditional time-averaged approach in this work. Probability density functions of parameters such as bubble duration, velocity, chord length, and number frequency are obtained from four-sensor conductivity probes and presented here. The axial evolution of the distributions is discussed in detail along with high-speed videos for a qualitative

The present study aims to reveal gas-liquid flow patterns as gas is injected into co-flowing water. An experimental work was conducted in a loop in which pure water was circulated. The gas-injection nozzle was submerged in the flowing water. Effects of the water flow velocity and gas flow rate were jointly considered. Two-phase flow patterns were visualized using the high-speed photography and then

Experimental instantaneous shadowgraph visualizations on transparent glass nozzle replicas of high-pressure fuel injectors have been used to validate a novel in-house high-fidelity LES-VOF multiphase solver, to study the evolution of vortex flow and fuel cavitation. Both experiments and simulations capture the formation of an unsteady vapor structure inside the nozzle volume, which is referred to as

A numerical approach based on preconditioning and dual-time stepping (DTS) is proposed to simulate cavitating flows at low Mach numbers. The methodology is based on a fully-compressible homogeneous mixture model and finite rate mass transfer as discussed in Gnanaskandan and Mahesh (2015). The method has shown promising results for capturing the large-scale cavitation in developed cavitation regimes

Water and air are usually employed as a heat exchange medium in cold channels of a plate heat exchanger (PHE), while air, in the state of bubbles in water, has an apparent impact on PHE performance, such as heat exchanging efficiency, flow resistance, etc. However, individual bubble behavior, such as bubble rupturing, merging, colliding, etc., are difficult to detect due to the flow complexity in PHE

A droplet subjected to external aerodynamic perturbations and fragmenting into smaller droplets is defined as secondary atomization. In the past decades, droplet breakup at low Ohnesorge numbers (Oh < 0.1) had been characterized with unanimity in the community regarding its physics. However, droplet breakup at high Oh number, i.e. atomization where the influence of viscosity is significant, has not

The self-pulsation characteristics of a liquid-centered swirl coaxial (LCSC) injector are investigated numerically based on the coupled level set and volume of fluid (CLSVOF) model. Effects of recess length on self-pulsation characteristics are evaluated and discussed. The results demonstrate the crucial role of recess length in exciting self-pulsation. As the recess length increases, spray patterns

The effect of inclination on instability of two-phase stratified flow in inclined rectangular ducts is studied for the first time via a rigorous linear stability analysis that accounts for all possible infinitesimal three-dimensional disturbances. The results of stability analysis of concurrent downward, concurrent upward, and countercurrent air-water flows are presented in the form of stability diagrams

The settling process and wall impact of large spherical particles in a stagnant, highly viscous fluid has been observed by means of high-speed shadow imaging. The particles included in this study vary in size and material properties: steel, polytetrafluorethylen (PTFE), polyoxymethylen (POM), or rubber. The corresponding terminal Reynolds numbers range from 333 to 4012, covering in principle the transitional

In order to deploy CO2 capture and storage (CCS) systems to mitigate climate change, it is crucial to develop reliable models for design and operational considerations. A key element of the system is the interface between transportation and storage, namely the injection well, where various transient scenarios involving multiphase flow will occur. In the literature there are very few data relevant for

For the simulation of bubbly flows, knowledge of the lift force as an interaction between gas bubbles and a surrounding shear field is of great importance. The sign of the lift coefficient CL changes with increasing bubble size, i.e. with more pronounced bubble deformation. Beside this, impurities in terms of surface-active components are well-known to change the complete hydrodynamic behavior of a

A liquid sheet breaks up into drops by fast air streams at airblast type atomizers, which are widely utilized for jet engines. Fuel spray flux in space directly determines the local mass ratio of fuel to air inside a combustion chamber. However, it has been difficult to measure the quantitative spatial distribution of spray flux using laser techniques and mechanical patternators. Therefore, in the

This experimental study analyzes submerged hydraulic jumps generated in a 1.05-m wide stilling basin that receives overflow rectangular impinging jets, with the vertical distance between the sharp-crested weir and the bottom of the plunge pool being 2.20 m. Five submerged hydraulic jumps downstream of non-developed nappe jets were analyzed, with vertical falling distances to break-up length ratios

Focusing on the spray simulation in engines using the Lagrangian-Drop Eulerian-Fluid (LDEF) approach, a new hybrid stochastic/trajectory (HST) droplet collision model with the improved collision frequency, the redivided collision cell, and an updated method for selection of the candidate collision pairs was developed in this study. The stochastic method used in the HST model was based on the theoretical

The interfacial structure of annular flow in upward inclined pipes is examined experimentally by a non-intrusive multilayer conductance liquid film sensor (LFS). In horizontal and inclined pipes, cross-sectional distribution of gas and liquid phases is asymmetric even on average. Thus, the ratio between the characteristic film thickness and the mean dominant wave parameters may vary significantly as

Models for prediction of drag forces within a particle cloud following shock-acceleration are evaluated with the aid of results from particle-resolved simulations in order to quantify how much the disturbances introduced by the proximity of nearby particles affect the drag forces. The drag models evaluated here consist of quasi-steady forces, undisturbed flow forces, inviscid unsteady forces, and viscous