Heat transfer deterioration in turbulent mixed convection affects the performance and safety of various pieces of industrial equipment. The reactor cavity cooling system (RCCS), a passive safety system in a very high temperature gas-cooled nuclear reactor (VHTR), incorporates rectangular riser channels to remove residual heat emitted from the reactor vessel, where turbulent mixed convection may occur

Characteristics of flame development and the influence of reverse-flow configuration on these characteristics few seconds after ignition are investigated experimentally. Simultaneous and high-speed OH∗ chemiluminescence and pressure measurements are performed. Methane is used as the fuel, and the fuel–air equivalence ratio is 0.7. Four experimental conditions pertaining to mean bulk flow velocities

It is commonly known that for a sufficiently high Reynolds number, for flow over a rough surface and other previously examined wall topologies, turbulent boundary layer separation generally occurs earlier, and the separation bubble is noticeably larger due to a greater momentum deficit caused by wall irregularities. The recently discovered amplitude modulation effect has provided an improved understanding

This work presents the design and the validation of a non-intrusive capacitance - based densimeter, for the on-line measurement of solid fraction in a slurry pipe flow. An asymmetrical type capacitance sensor was designed by means of numerical electric field analysis. The simulations conducted at different solid volume fractions revealed that the sensor is not sensitive to the distribution and the

In nuclear Pressurized Water Reactors, fuel assemblies are slender structures composed of many rods held together by regularly spaced grids. Intense in-core conditions may sometimes result in permanent deformations impairing the reactor normal operation or even challenging its safety. Fluid-structure interactions are the central plot of this multiphysical storyline, and the water gaps between adjacent

Dependence of boundary layer thickness on layer height in laminar and transient regimes is studied for convection from localised heat source with an open surface. The measurements of Nusselt number and characteristic frequency of thermal plume formation are done for a wide range of Rayleigh number, different Prandtl numbers and different aspect ratios. The obtained results prove that for the developed

This work aims to control the unsteady flow structure of a NACA0012 under full stall by limiting the vortex roll-up from its trailing edge. In this regard, plates with varying lengths at zero incidences were attached at the trailing edge of the airfoil at an angle of attack of α = 16o and low Reynolds number of Rec = 2.0×104. Under these conditions, the flow separates near the leading edge and rolls

The aim of this communication is to analyse the influence of water activity and total pressure on water evaporation. The system is composed of liquid and gas phases, separated by a plane surface, contained in a cylinder whose volume is regulated by a piston. Water activity is regulated by saturated salt solutions and pressure by the piston. The experimental device and procedures were defined to limit

Mars and upper Earth atmosphere missions are booming in recent years increasing the interest in heat transfer in rarefied gases. At these low pressures, the heat transfer problems involving small geometries whose characteristic length is of the order of the mean free path of the gas molecules, raises new difficulties. This being especially severe in the case of free convection, where the velocity of

An experimental study on the compact lean premixed flames stabilized on a bluff-body and swirl burner is performed. The flames are featured with a strengthened Inner Recirculation Zone (IRZ). The objective is to identify the critical causes of blow-off near the lean limit. Meanwhile, the effects of hydrogen addition on the flame stabilization are also examined. Premixed CH4/H2/air mixtures are adopted

Spherically expanding flames are severely affected by flame stretch in the early stage of combustion and therefore stretch models are of great importance in determining the uncertainty of experimental laminar flame speeds (SL) and burned gas Markstein lengths (Lb). In order to prevent the existing large scatter in experimental data of these two fundamental flame parameters, the effect of the lower

Diffusion of colloidal particles in porous media is critical for the development of specially engineered colloids used to aid the recovery of oil from a petroleum reservoir. However, shielded structures, such as dead-end pores, prevent these colloids from reaching the available oil. This article examines the use of ultrasound fields as a mechanism for increasing the mobility of colloidal particles

The modelling of ocean waves is an integral part of coastal and offshore engineering. Both theoretical and experimental modelling methods are available and are commonly used in support of each other. In particular, due to the difficulty in measuring the velocity throughout the water column, the wave kinematics are often derived, by means of wave theory, from a measurement of the free surface elevation

In this work, we compared the microscopic characteristics of the free and impinging spray tip using double-pulse laser particle image analysis technique. Droplet population density, diameters, and velocities were experimentally resolved for both the free and impinging spray at three spray tip penetration positions (STP = 32, 37 and 42 mm) under three injection pressures (10, 20 and 30 MPa). Results

An experimental study of a simple NACA 0012 airfoil fitted with two different flap profiles was carried out to characterize their aerodynamic and aeroacoustic performance. The airfoil with a flap deflection angle of β=10° was tested for a wide range of angles of attack at a chord-based Reynolds number of Rec=2.6×105. The aerodynamic lift and drag measurements show improved lift-to-drag performance

Heat transfer characteristics of water flow boiling in a minichannel were investigated through the direct measurement of local heat flux using a fabricated MEMS heat flux sensor with a multi-layered structure. Local temperatures and heat fluxes in the water flow boiling were measured at a sampling frequency of 10 kHz in synchronism with the high-speed visualization of the boiling behavior. The measurement

Experimental testing on the unsteady aero-breakup of ethyl alcohol droplets was carried out at the rotating arm facility of INTA. The selection of the working fluid was driven by the need to explore wider ranges of the dimensionless parameters that govern the problem. A model airfoil was attached at the end of a 2.3 m long rotating arm driven by an electric motor. Droplets, whose diameter ranged from

The understanding of diesel sprays is very important to enable a better and cleaner marine engine design, but unfortunately little knowledge is openly available on marine engine fuel sprays. In this paper, evaporating sprays for medium speed marine engines were studied in a constant volume combustion chamber by performing optical measurements through Schlieren and Mie diagnostic techniques. The effects

Hydraulic fracturing is an important approach for stimulating the production of ultra-low-permeability oil reservoirs; however, the low flowback efficiency of the fracturing fluid (FF) may cause contamination of the groundwater and reduce oil recovery. This study experimentally investigates the possibility of improving the flowback efficiency of water-based FF and oil production through the achievement

The process of normal impingement of a single drop onto a quiescent liquid film was investigated experimentally to determine the thresholds of the early and late splashes. Seven liquids of different hydraulic properties were used and the liquid film thickness was varied within about 0.2–3 times the impacting drop diameter. It was found that the critical Weber number for the early splash to occur is

Time-resolved infrared thermography through infrared-transparent windows provides a novel measurement approach for non-invasive quantitative analysis of near-wall fluid flows. Here, we apply this approach to study a water flow induced by an axisymmetric submerged impinging jet in the immediate vicinity of the impingement plate. The variations in thermal radiation emitted from a thin near-wall layer

In this study, droplet impact dynamics on superheated cylindrical surfaces are investigated experimentally, through high-speed imaging. The outcome regimes of impacting droplets observed in the experiments are mapped and described. Four distinguishable regimes are identified, namely rebound-transition boiling, rebound-film boiling, breakup-transition boiling, and breakup-film boiling. In addition,

Stagnation-point heat flux was measured on 7° half-angle circular cones with spherical nose diameters of 5, 10, and 25 mm using infrared thermography in hypersonic flow. All models were machined from polyether ether ketone (PEEK). A nominal freestream Mach number of 6 with varying initial stagnation conditions allowed for testing at length Reynolds numbers based on nose diameter ranging from 5×104–5×105

In this paper, an experimental study was performed to examine the flow characteristics of fabricated micro corrugated wings by fully mimicking the real 3D Odonata wing. For this purpose, a true scale hind wing from the Orthetrum caledonicum species with a semi span length of 60 mm was reconstructed by non-destructive close-range photogrammetry and fabricated with an advanced 3D printer. The accuracy

A new concept of vapour condenser is proposed to solve the drainage problem and to provide an effective condensate flow under weightlessness conditions. The concept combines the capability of a curvilinear surface to drive liquid, and a combination of a porous media and a pump, as an active condensate retraction system. The porous media collects and stores the condensed fluid and acts as a barrier

Small scale experiments examining the propagation of a hemispherical flame in a hydrogen–air mixture were performed under conditions of constant pressure. The shape of the propagating flame front in a 15% hydrogen–air mixture was reconstructed with the use of near-infrared imaging. The wrinkled flame surface was restored from experimentally obtained two-dimensional IR photographs using data on the

In this study, the liquid and vapor phase distributions on a boiling surface are visualized using a simple visible ray optic setup with high-speed and high-resolution. We find that the thermal and fluidic nature of the boiling process originates from the behaviors of the dry spot, microlayer, and liquid wetting, and their intertwined dynamics. At a high surface heat flux condition, large coalesced

Cavitation phenomena, produced when a flow is accelerated through a restriction, are of fundamental importance because of the large pressure oscillation they induce on pipelines. This paper presents an experimental investigation of various cavitation regimes produced at the exit of an orifice and its downstream propagation and attenuation. A cylindrical and a conical orifice are investigated over a

The void fraction is a key parameter of the two-phase flow in vertical downward pipes, particularly for calculating the mixture density, mixture velocity, mixture viscosity, heat transfer coefficient, and pressure gradient of the flow. Studies on two-phase flows have focused primarily on vertical upward and horizontal pipe flows, while vertical downward pipe flows have been largely neglected. Compared

The dynamics of droplets and oscillation of electrified meniscus at low flow rates in an external electric field were investigated. An electric field is created by nozzle-plated electrode. The evolution of droplet formation is recorded by a high-speed digital camera. Meanwhile, the time evolution of meniscus is also focused. The critical sizes of the droplet and liquid thread were used to characterize

The concept of in-vessel retention (IVR) by passive external reactor vessel cooling (ERVC) in a flooded cavity during a severe accident has now been recognized as a viable approach to retain the radioactive core melt (i.e., corium) within the reactor vessel. During the process of long-term in-vessel cooling of core melt, the heat flux must remain below the critical heat flux (CHF) level to maintain

This paper describes an experiment conducted to investigate thermal distribution during liquid atomization. An infrared camera was used to measure liquid temperature changes over time during atomization. Effects of device frequency, input power, and liquid viscosity on thermal distribution during surface acoustic wave (SAW) atomization were investigated, both experimentally and through simulation.

This research study investigated the three-dimensional nature and characteristics of buoyant thermals in the mixed convection turbulent boundary layer. Thermals were visualized using a multi-plane flow visualization technique. Experiments were performed in a variety of conditions where the bulk Richardson number was varied to cover a range describing both inertia dominant flow (RiL=0.05) and buoyancy

Droplets impacting on superhydrophobic surfaces with submillimetric or millimetric macrotextures can rebound completely after a short contact time, which is of practical importance in applications like self-cleaning and anti-icing. Many researches have been done on the centered impact, but the off-centered impact is rarely studied, even though it occurs more often. In the present work, we investigate

Sloshing refers to the motion of the free liquid/gas interface inside a partially filled container subjected to an external excitation with a consequent motion of the system center of gravity. Several parameters related to the fluid container, the fluid properties, the excitation levels, and the gravitational environment govern this phenomenon. Moreover, it is a significant cause of disturbance in

The effect of drag reducing riblets on the flow structure was examined experimentally for a turbulent boundary layer at Reθ = 9890 and riblet spacing s+ = 13.4. Trapezoidal riblets were used, which were attached to the water tunnel wall as a coating. Force measurements were performed to quantify the amount of drag reduction. Then, the mechanism underlying this reduction was investigated by stereo-PIV

Two phase flow is of great interest in chemical and petroleum industries, and multiphase pipe flow models with closure relationships require experimental data for their development and validation. However, only little experimental information is available for slightly upward inclined pipes. Experimental investigations of single elongated bubble in marginally upwardly inclined pipes less than 10° have

A multi-channel gliding arc (MCGA) plasma was used to enhance ignition and combustion of ethylene fuel in a cavity-based scramjet combustor with an inflow speed of Ma = 2.92. Simultaneously electro-optical diagnostics were conducted to show characteristics of the MCGA-enhanced ignition and combustion, as well as simultaneous schlieren and CH* emission images. The voltage and current measurements demonstrate

Experiments were preformed to measure the mass and size of secondary droplets splashed during liquid jet impingement onto a horizontal solid surface. To explore the effects of liquid hydraulic properties such as viscosity and surface tension, pure water, two aqueous solutions of glycerin, and two aqueous solutions of ethanol were used as the test solutions. Using the experimental data accumulated in

This work presents a data-driven approach for the identification of relevant flow features and the breakdown of their contributions to unsteady forces in flapping airfoils. The method exploits the correlation between simultaneous flow-field and force measurements. The Extended Proper Orthogonal Decomposition of flow fields and force is employed to identify relevant flow features and to ascertain their

This paper presents the experimental results obtained in a directly irradiated fluidized bed. A bed with a diameter of 314.76 mm was filled with SiC particles and directly irradiated from the top with a beam-down reflector with a 2 kW Xe-lamp. The study examines the influence of the bed height and airflow rate on the temperature distribution over the top surface of the bed (where the concentrated irradiation

To control the wake flow around a wall-mounted cube, passive control is performed by drilling a front inclined hole (FIH) from the front surface to the free end of the cube. To study the control features and mechanism, controlled and uncontrolled cubes are experimentally investigated. A circulation water tunnel is used to perform PIV measurements, where the Reynolds number is ReD = 11550 based on the

There is a significant decrease in flow boiling CHF when the inertial force of the fluid is not large enough in microgravity, but this tendency decreases with the increase of the inertial force. In the present study, the critical heat flux (CHF) of subcooled flow boiling at different gravity levels on smooth silicon surfaces was investigated. The working fluid is FC-72, with the subcooling of 15 K

The effect of surface hydrophobicity on the air-water two-phase flow pattern transition was experimentally investigated. Experiments and the two-phase flow visualization were carried out in a hydrophobic polymer tube (4.76 mm ID). The tube material is fluorinated ethylene propylene (FEP) with a hydrophobic surface, and the static contact angle of a water droplet on a smooth surface is 97.28°. The channel

Because wire-meshes have a great potential application for designing high-efficient heat and mass transfer systems, a deformable bubble of Re ~ 800 rising in still tap-water near a vertical mesh of different porosity is studied using a high-speed shadowgraphy apparatus including two mutually perpendicular projections. We focus on the effect of the boundary conditions with three types of meshes (Mesh-L

The impingement dynamics of a promising ionic liquid absorbent, namely, 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) in droplet falling film flow modes on heated porous surfaces in absorption refrigeration were investigated experimentally. The influences of impact velocity and surface temperature on the ionic liquid droplet spreading diameter, dynamic contact angle, spreading height, and residual

In this paper, we have performed an experimental study of the effect of changing the surface tension of the water in vertical annular concurrent two-phase flow (air + liquid) by adding small amounts of 1-butanol to the liquid phase. Adding small amounts of this chemical compound diminishes the surface tension of the water, while the dynamic viscosity remains practically unchanged. A set of experiments

The flow fields around different pile groups (multiple circular cylinders) mounted vertically on a flat bed were experimentally studied by using Particle Image Velocimetry (PIV). The characteristics of the horseshoe vortex (HV) in front of the pile groups were systematically investigated, including its time-averaged flow topology and instantaneous evolution, and the associated bed shear stress. The

Two-phase flow characteristics of gas injection through a slot nozzle into a liquid bath were studied experimentally. A dual-sensor electrical probe measurement system was used to obtain the distributions of multiple two-phase flow parameters. Measurements were conducted under various gas flow rates, nozzle widths and at different planes vertical to the slot nozzle. It is found that the void fraction