Two-phase Layer Research Articles

Characterization of dual phase boride coatings on Sverker 3 steel and simulation of boron diffusion

AbstractThe Sverker 3 steel was treated by solid boriding in the range 1173–1273 K for holding times ranged from 1 to 7 h. The processes resulted in two-phase (FeB + Fe2B) boride layers except the treatment at 1173 K for 1 h where the Fe2B was formed only. The growth of borides obeys a typical parabolic law, with the maximum thickness of 120 ± 4.5 µm. Considerable redistribution of carbon and alloying elements took place during boronizing; carbon and silicon were pushed out from borides while chromium and tungsten were rather gathered in these compounds. The microhardness of Fe2B ranged between 1600 and 1700 HV 0.1, and that of FeB reached 2100–2200 HV 0.1. The average diffusion coefficient (ADC) approach was applied by assuming the linearity of boron concentration profiles across the iron boride layers. This approach allowed us to obtain the boron diffusivities in both the FeB and Fe2B. Afterwards, the boron activation energies in both layers were obtained by fitting the temperature evolution of calculated boron diffusivities in the two iron boride phases with the Arrhenius relations. The assessed boron activation energies in FeB and Fe2B were, respectively, 215.18 and 203.6 kJ mol−1. Finally, a comparison of these values of energies was made with literature results.

Numerical Solution of Two-Phase Radiated Unsteady Flow Over a Horizontal Stretching Sheet with Simultaneous Effect of Electrification, Radiation and Non-Uniform Internal Heat Source/Sink

A parametric study to investigate the impact of electrification and radiation inside a thermal particulate boundary layer, where the flow is due to an unsteady stretching sheet in presence of non-uniform heat source/sink. Both the fluid as well as the particles are assumed to be gray, emitting and absorbing radiation. Again, neither the fluid is considered in electric medium nor supplied by an external electric force. But, due to the random motion of the particles i.e., the interaction between particle-particle, particle-fluid and particle-wall, a tribo-electrification occurred. As on impact, both the fluid and particles are electrified though the flow has been considered in a neutral medium. Hence, a balanced mathematical model of highly non-linear partial differential equations has been formulated for two-phase unsteady boundary layer considering the above parameters/impacts on both the phases. An appropriate similarity transformation has been employed to transfer the governing equations into ordinary differential equations and solved numerically by built in solver Bvp4c of MATLAB. An excellent agreement between the present and previous literature has been made to validate the result. Moreover, the influence of Electrification parameter, Radiation parameter, Internal heat source/sink parameter on the rate of heat transfer and other flow characteristics has been analyzed.

Experimental study on near wake shedding structure of pyramid roughness element in liquid–solid two-phase turbulent boundary layer

Particle image velocimetry (PIV) on the liquid–solid turbulent boundary layer containing solid particles with an average diameter of 355 μm is used to study the shedding structure near-field of the pyramid with varied yaw angle values (0°, 15°, 30°, and 45°). We find that the recirculation zone grows larger with increasing value by comparing the average velocity field and turbulence intensity at various angles. When closed vortex lines develop behind the pyramid at about (h, 0.8 h), the center of the recirculation zone gradually stabilizes; in the meantime, the turbulence intensity rises relative to the small α values. Power spectral density function (PSD) and proper orthogonal decomposition (POD) are used to analyze the near-field. According to the findings, various values have an impact on wake shedding structures. At the top and base of the pyramid, shearing vortices occur simultaneously on a regular basis, and their incidence is sensitive to variations in α. Similar top shedding structures are observed at various angles in the POD results. Furthermore, with increasing α, the reattachment vortex is observed at the downstream edge of the pyramid. We study the behavior and statistical properties of particles at various positions, and our findings suggest that the upper flow field's particle concentration distribution dispersion is greater than that of the wake. Some particles from the vicinity of the pyramid is attracted into the wake's recirculation zone and is carried downstream by the shedding vortex.

Steam entrainment and heat transfer characteristic of steam submerged jet condensation within steam-water mixture layer

Steam-water interface and mixture layer are the key window for understanding the heat and mass transfer mechanism of steam submerged jet condensation. In this paper, the steam-water two-phase mixture layer is captured and the interfacial vortex is observed with a quasi-two-dimensional submerged steam jet visualization experimental platform. Then, the volume heat transfer capacity of steam-water mixture layer and heat transfer coefficient with steam-water inner interface are obtained. Furthermore, a new turbulent eddy entrainment model is developed to calculate the local entrainment mass rate and local condensation heat transfer coefficient. Both the local entrainment mass rate and local condensation heat transfer coefficient increases along steam jet direction, and reaches the maximum value at the tail of the mixture layer. The calculated condensation heat transfer coefficient ranges from 0.88 to 2.94 MW·m−2·K−1, which is about the half of the value of hypothetical heat transfer coefficient with inner interfacial area.

The role of incoming flow on crystallization of undercooled liquids with a two-phase layer

Motivated by important applications of crystallization phenomena, we consider a directional solidification process for a binary melt with a two-phase (mushy) layer in the presence of weak melt flow. We consider the steady-state solidification scenario, so that the two-phase layer filled with solid and liquid material keeps its thickness. In addition, we consider that the melt flows onto the two-phase layer slowly in the opposite direction to directional crystallization and solidifies there. A complete analytical solution to non-linear two-phase layer equations is constructed in a parametric form, where the solid phase fraction represents a decision variable. The temperature and solute concentration distributions, mushy layer permeability and average interdendritic spacing as well as solidification velocity and mushy layer thickness are analytically determined. We show that incoming melt flow plays a decisive role on mushy layer parameters and internal structures. The solid phase fraction within the two-phase layer and its thickness essentially grow while the mushy layer permeability and average interdendritic spacing decrease with increasing intensity of incoming melt flow.

Characteristics of boronized Ti6Al4V alloy using boric acid based boronizing mixture

Boronizing processes of Ti alloys are generally performed in atmosphere-controlled furnaces. In this study, it is aimed to carry out boronizing process under atmospheric conditions by using an alternative boronizing mixture containing boric acid and to better the surface characteristics of Ti6Al4V alloy by boronizing. The efficiency of the boronizing mixture was evaluated by performing boronizing at different process temperatures (900-1100 °C) and durations (12 and 20 h). Microstructural (OM, SEM) and chemical (XRD, EDS, XPS) analyzes were performed to characterize the boride layers formed on the surfaces of the boronized samples. As a consequence of these analyzes, it was found out that a two-phase boride layer (TiB2 + TiB) was obtained in the samples. In addition, in vitro tests were done for specifying the bioactivity of boronized samples. In order to determine the effect of boronizing on the corrosion resistance of Ti6Al4V alloy, corrosion tests were performed by the Tafel extrapolation method. The adhesion behavior of the boride layers was determined by the Daimler-Benz Rockwell C indentation test. As a result, boronizing studies have been performed successfully without atmospheric-controlled conditions and it has been defined that surface characteristics of the Ti6Al4V alloy have bettered through the boride layers formed on the alloy surface.

Fatigue crack growth rate of AISI 4140 low alloy steel treated via shot peening and plasma nitriding

In this study, the effects of conventional shot peening (CSP), severe shot peening (SSP), and plasma nitriding (PN) on the fatigue crack growth (FCGR) of AISI 4140 low alloy steel were investigated. FCGR tests were performed on axial fatigue equipment, associated with slow-motion camera and COD gauge. As a result of the experiments, an improvement of 8% in CSP, 15% in SSP, and 5,5% in the PN operations were observed on the number of cycles of all specimens at 30 mm crack length. Particularly for SSP treatments, hardness, compressive stresses, and the creation of nano-crystallization on the surface provide the most effective improvement in FCGR behavior. Additionally, for PN, formation of nitrogen diffusion and effective hardness improvement showed positive results in FCGR behavior. CSP and SSP (particularly SSP) behaved dominant on the improvement of FCGR performance compared to PN treatment. The formation of two-phase brittle structural white layer on the surface prevented the effective FCGR improvement.

A numerical study of the natural transition in a gas–liquid two-phase boundary layer over a flat plate taking account of interphase slip

The natural transition in a gas–liquid two-phase boundary layer over an underwater flat plate is studied, taking into account the interphase slip between gas and liquid. An interphase slip model is proposed to determine the dynamic viscosity of the two-phase flow based on the physical origins of fluid viscosity. The model is then applied to laminar flow calculation, instability analysis, transition prediction, and prediction of the spectrum of wall fluctuating pressure in the laminar region. Numerical calculations are conducted for boundary layers for different void fractions, including liquid single-phase flow at a zero void fraction. The results reveal the differences between two-phase and single-phase flows and show that these differences become more obvious as the void fraction increases: (i) the thickness of the two-phase laminar boundary layer becomes less; (ii) the unstable zone becomes larger; (iii) the transition location moves upstream, and the transition advance distance caused by the microbubbles becomes longer and is proportional to the void fraction; (iv) the dangerous frequency becomes higher, and the frequency bandwidth becomes wider; and (v) the wall fluctuating pressure in the laminar region becomes stronger, and its peak frequency becomes slightly higher. As the oncoming flow velocity increases, the transition advance coefficient becomes smaller, and the dangerous frequency becomes higher. The comparison of the results of the interphase slip model and those of the conventional homogeneous flow model implies that the above differences between two-phase and single-phase flows are caused by the interphase slip between gas and liquid.

Dynamical law of the phase interface motion in the presence of crystals nucleation

In this paper, we develop a theory of solid/liquid phase interface motion into an undercooled melt in the presence of nucleation and growth of crystals. A set of integrodifferential kinetic, heat and mass transfer equations is analytically solved in the two-phase and liquid layers divided by the moving phase transition interface. To do this, we have used the saddle-point method to evaluate a Laplace-type integral and the small parameter method to find the law of phase interface motion. The main result is that the phase interface Z propagates into an undercooled melt with time t as Z(t)=sigma sqrt{t}+varepsilon chi t^{7/2} with allowance for crystal nucleation. The effect of nucleation is in the second contribution, which is proportional to t^{7/2} whereas the first term sim sqrt{t} represents the well-known self-similar solution. The nucleation and crystal growth processes are responsible for the emission of latent crystallization heat, which reduces the melt undercooling and constricts the two-phase layer thickness (parameter chi <0).

Applying the FMR Technique to Analyzing the Influence of Nitriding on the Magnetic Properties of Steel.

This paper presents the relationship between the chemical composition and size of steel balls, the parameters of the nitriding process, and their magnetic properties, defined in this study by ferromagnetic resonance (FMR) and SQUID. Balls made from AISI 1010 and AISI 52100 steels, with diameters of 2.5 and 3 mm, respectively, were investigated. On samples made of AISI 1010 and AISI 52100 steel, single-phase layers of iron nitrides γ’ with a thickness of gmp = 50 and 37 μm, respectively, were produced. Then, the samples were annealed at a temperature of 520 °C for 4 h in an inert atmosphere (N2/Ar) at a pressure of 200 Pa. After the nitriding processes, steel balls were subjected to standard physical metallurgy and X-ray examinations. During annealing of nitrided layers with a two-phase layer of iron nitrides, at first, the transformation of the ε phase into the γ’ phase with the release of nitrogen into the atmosphere takes place. The FMR signals did not originate from isolated ions, but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters, while the observed FMR line position is normally even lower and occurs for a magnetic induction below 200 mT. The fact that the magnetic centers did not contain mainly isolated Fe ions, additionally confirmed the abnormal increase in resonance signal intensity as a function of temperature, which is a behavior inconsistent with the Curie–Weiss law. The results obtained from measurements by the SQUID method, recording variations in magnetization as a function of temperature, confirm the untypical reinforcement of the magnetic conditions of the samples with the increase in temperature. For the samples tested, the magnetization was relatively weaker when the tests were conducted in a stronger magnetic field.

Compressible gas-droplet flow and heat transfer behind a condensation shock in an expanding channel

A two-fluid mathematical model of a supersonic gas-droplet mixture flow with account of droplet growth due to vapor condensation behind a condensation shock in a plane expanding channel is constructed. The flow structure in both the inviscid core and the two-phase boundary layer assumed to be laminar is studied numerically. The range of flow parameters is considered in which the spontaneous condensation zone (“condensation shock”) is fairly narrow, and just behind this shock thermal parameters of the phases almost reach thermodynamic equilibrium. Downstream, the droplet radius continues to grow due to the flow expansion and further vapor condensation. Of primary concern is the flow region where the droplets become sufficiently inertial to travel with a velocity slip, and hence to model adequately the velocity and temperature fields in both phases a two-fluid model is required. In addition to the Stokes drag, the Saffman lifting force exerted on the droplets in the boundary layer is taken into account. The Saffman force results in droplet deposition and the formation of a thin liquid film on the channel walls. A parametric numerical analysis of the two-phase flow structure in the inviscid flow region and in the near-wall boundary layer is performed, and the effects of phase transitions (droplet condensation and evaporation, as well as the film formation) on the reduction of the adiabatic channel wall temperature are analyzed.

A visual mass transfer study in the ejector considering phase change for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

The multi-effect distillation with thermal vapour compression (TVC) seawater desalination system provides an excellent energy-saving scheme by escalating the low-level energy. The internal mass and heat transfer in ejectors is an important element to improve efficiency. In this study, a visual mass transfer simulation model considering real thermodynamic properties is used to observe the inner-mixing process. The assessment is from the perspective of visible mixing layer growth and the effect on entrainment ratio. As shown in the mass percentage distribution graph, there is an inescapable phase change on mixing layer boundary, where the wetness of wet steam can reach to 16.0%. Meanwhile, the mixing layer length predicted by dry model is 25.1% higher than wet model. The condensation weakens the mixing process and leads to shorter length. Under subcritical mode, the cross-sectional area of the entrained flow is deducted and the mixing layer cannot develop completely. The critical pressure range predicted without condensation is 18.5% lower, which causes a misjudgment in entrainment ratio because overvaluing the influence of outlet pressure on entrained flow. Thus, mass transfer during development of the two-phase mixing layer has great impact for MED-TVC system.

A phenomenological investigation on near-wall bubble behavior close to CHF in flow boiling

The insight information of subcooled flow boiling is very important for the development of boiling crisis mechanistic model. In this paper, visual experiment is carried out in a vertical square channel with a heating rod with diameter of 9.5 mm. Based on the near-wall bubble behavior captured by a high-speed camera, combined with advanced image post-processing technique developed in-house, the qualitative and quantitative analysis of flow boiling behavior near the heating wall are presented when approaching the CHF (Critical Heat Flux). According to the visual experimental study, a detailed discussion on the phenomena before CHF and during the CHF is presented. With high heat flux, periodic large vapor clot passes with relatively constant frequency. Then periodic wavy vapor layer and liquid film clearly appear in the near-wall region when the working condition is extremely close to the CHF. It is found that high thermal-hydraulic parameters, including system pressure, mass flux and inlet subcooling, prevent the formation of thick vapor layer, and this is a significant precursor to trigger boiling crisis. This implies that the possibility of triggering boiling crisis is reduced due to the difficulty in forming thicker vapor layer, and lead to higher CHF value. Additionally, a prediction of wavelength between two-phase layers is proposed by combining visual observations and instability theory. The predicted results show good agreement compared with experimental data. Those results can provide predictions of key interfacial feature parameters for developing CHF mechanistic model.

Theoretical Profiles of Two-Phase Transcritical Laminar Boundary Layer Near the Widom Line

Theoretical Profiles of Two-Phase Transcritical Laminar Boundary Layer Near the Widom Line

Study of wear characteristics under conditions of dry sliding friction of 08Kh18N10T steel after electrolysis-free boriding

Effect of liquid electrolysis-free boriding on tribotechnical characteristics of 08Kh18N10Т steel is studied. It is established that after boriding at temperature 900 °С and 5 h soaking it is formed a boride two-phase layer with thickness of 30...35 microns and transition zone with thickness of 10 microns. The microhardness in FeB and Fe2B phases is 2000...2100 and 1800...1900 HV 0.1 respectively. The wear tests under dry friction conditions showed that coefficient of friction for specimens made of 08Kh18N10Т steel without treatment and with boriding in pair with counterbody made of ShKh15 steel is 0.83 and 0.85 respectively. At the same time, the wear intensity of samples with boration is an order of magnitude less than that of samples without treatment, and on average is 7.7 · 10–6 mm3 /(H · m) instead of 8.5 · 10–5 mm3 /(H · m). The average depth of the wear track of the sample with boriding is 5 times less than that of the sample without treatment.

Dynamics of thermal Marangoni stagnation point flow in dusty Casson nanofluid

ABSTRACT The current perusal presents a stagnation point (SP) flow and heat transfer analysis of Casson dusty nanofluid over a surface with Marangoni convection. Here, non-Newtonian nanoliquid suspended with as nanoparticle and dust particles in base fluid sodium alginate is utilized to scrutinize the present two-phase boundary layer model. Further, suitable transformations are used to reduce the modelled governing equations to a set of ordinary differential equations. Later, numerical solutions are secured using an efficient and well-known Runge-Kutta-Fehlberg fourth fifth-order (RKF-45) method using the shooting technique. The impacts of the governing parameters on various profiles are illustrated with the help of graphs. The significant findings of the current model are that the escalating values of the Marangoni number deteriorations the velocity gradient of both dusty nanoliquids. The augmentation of dust particle mass concentration declines the thermal gradient of both liquid and particle phases. The boost up values of dust particle mass concentration and thermal dust parameter advances the rate of heat transfer.

Double-Layer Energy Efficient Synchronous-Asynchronous Circuit-Switched NoC

A network-on-chip (NoC) offers high performance, flexibility and scalability in communication infrastructure within multi-core platforms. However, NoCs contribute significantly to the overall system’s power consumption. The double-layer energy efficient synchronous-asynchronous circuit-switched NoC (CS-NoC) is proposed to enhance the power utilization. To reduce the dynamic power consumption, single-rail asynchronous protocols are utilized. The two-phase and four-phase encoding algorithms are analyzed to determine the most efficient technique. For the data layer, the two asynchronous protocols reduced the power consumption by 80%, with an increase in latency when compared with the fully synchronous protocol. However, the two-phase single-rail protocol had better performance compared with the four-phase protocol by 38%, with the same power consumption and a slight increase in area of 5%. Based on this conducted analysis, the asynchronous two-phase layer had significant power reduction yet operated at a moderate frequency. Therefore, the proposed NoC is divided into two data transfer layers with a single control layer. The data transfer layers are designed using synchronous and asynchronous protocols. The synchronous layer is designated to high-frequency loads, and the asynchronous layer is confined to low-frequency loads. The switching between the layers creates a trade-off between the maximum allowed frequency and the power consumption. The proposed NoC reduces the overall power consumption by 23% when compared with recent previous work. The NoC maintains the same system performance with an 8% area increase over the fully synchronous double-layer in the literature.

Impact of inlet gas turbulence on the formation, development and breakup of interfacial waves in a two-phase mixing layer

Abstract

Electrochemical micromachining of ZrCu-based amorphous alloy in ethylene glycol solution

Their excellent physical, chemical, and mechanical properties give ZrCu-based amorphous alloys a wide range of application prospects as advanced functional and structural materials for military and aerospace uses and in precision devices. Micro-electrochemical technology has been used to process amorphous alloys, and this paper reports the wire electrochemical micro-machining (WECMM) of the Zr67Cu15Ni11Al4Ti3 amorphous alloy. The dissolution characteristics and processing of the alloy in aqueous solutions are analyzed to understand the WECMM of this ZrCu-based amorphous alloy. Unlike with Cu-free Zr-based amorphous alloys, the Cu in the present case is electrolyzed quickly and generates a large amount of product deposition on the surface of the cathode after it is ionized, thereby seriously hindering the processing. Unlike the pure charge-transfer control process in an aqueous solution, the polarization process of the alloy in a glycol solution is controlled by both charge transfer and diffusion. In a glycol solution, the two-phase electric double layer comprises a compact layer and a diffusion layer, ions move relatively slowly between the cathode and anode, and products form relatively slowly. This is effective in (i) strengthening the reverse electric field effect of the bipolar pulse, (ii) hindering the migration of cations to the cathode, and (iii) directly avoiding the formation of products, thereby allowing the formation of high-quality micro-structures of ZrCu-based amorphous alloy with a relatively large thickness of 550 μm.

Metallic skeleton promoted two-phase durable icephobic layers

HypothesisThe accretion of ice on component surfaces often causes severe impacts or accidents in modern industries. Applying icephobic surface is considered as an effective solution to minimise the hazards. However, the durability of the current icephobic surface and coatings for long-term service remains a great challenge. Therefore, it is indeed to develop new durable material structures with great icephobic performance. ExperimentsA new design concept of combining robust porous metallic skeletons and icephobic filling was proposed. Nickel/polydimethylsiloxane (PDMS) two-phase layer was prepared using porous Ni foam skeletons impregnated with PDMS as filling material by a two-step method. FindingsGood icephobicity and mechanical durability have been verified. Under external force, micro-cracks could easily initiate at the ice/solid interface due to the small surface cavities and the difference of local elastic modulus between the ice and PDMS, which would promote the ice fracture and thus lead to low ice adhesion strength. The surface morphology and icephobicity almost remain unchanged after water-sand erosion, showing greatly improved mechanical durability. By combining the advantages of the mechanical durability of porous Ni skeleton and the icephobicity of PDMS matrix, the Ni foam/PDMS two-phase layer demonstrates great potentials for ice protection with long-term service time.