Temperature Solid Phase Research Articles

Time-varying evolutionary mechanism analysis of the multiphase flow during high-velocity oxygen-fuel (HVOF) thermal spraying WC-12Co particle

HVOF thermal spraying with the fuel of aviation kerosene has unique advantages for spraying WC-12Co ceramic particles. The time-varying evolution mechanism of the multiphase flow formed by the particles wrapping with the combustion flame flow is quantitatively revealed, which is essential for preparing of high-quality coatings. In this study, the breakup and gasification process of kerosene droplet was considered. The fuel droplet, flame flow and spraying particles were directly coupled. Based on the computational fluid dynamics (CFD) method, a transient evolution model of HVOF thermal spraying multiphase flow with JP5000 spray gun was established. The Euler-Lagrange method of bidirectional coupling was used to track the continuous and discrete phases. The spraying combustion flame characteristics were expressed by the realizable k-ε turbulence model and eddy dissipation model (EDM). The results show that the multiphase coupling transient evolution model quantitatively captures the nonlinear changes of the breaking and gasification for the kerosene droplet, combustion reaction, particle flight behavior and others during spraying. The kerosene droplets in the combustion chamber aggregate with each other to form large droplets, which are rapidly broken and gasified in the peripheral areas. Due to the violent combustion, a gas-phase circulation was formed by the heat and cold air. As the combustion progresses, the flame flow becomes stable and orderly. When particles with a size of 20 to 30 μm impact the substrate, the particle temperature is close to the solid phase temperature, and the velocity is fast. The particle temperature and velocity decrease with the increase of the particle size.

Cattaneo–Christov heat flux impacts on MHD radiative natural convection of Al2O3-Cu-H2O hybrid nanofluid in wavy porous containers using LTNE

This paper aims to examine impacts of Cattaneo–Christov heat flux on the magnetohydrodynamic convective transport within irregular containers in the presence of the thermal radiation. Both of the magnetic field and flow domain are slant with the inclination angles Ω and γ, respectively. The worked fluid is consisting of water (H2O) and Al2O3-Cu hybrid nanoparticles. The enclosures are filled with a porous medium, and the local thermal nonequilibrium (LTNE) model between the hybrid nanofluids and the porous elements are considered. Influences of various types of the obstacles are examined, namely, horizontal cold elliptic, vertical elliptic and cross section ellipsis. The solution methodology is depending on the finite volume method with nonorthogonal grids. The major outcomes revealed that the location (0.75, 0.5) is better for the rate of the flow and temperature gradients. The higher values of H* causes that the solid phase temperature has a similar behavior of the fluid phase temperature indicating to the thermal equilibrium state. Also, the fluid-phase average Nusselt number is maximizing by increasing Cattaneo–Christov heat flux factor.

Magnetohydrodynamic mixed convection of TiO2–Cu/water between the double lid-driven cavity and a central heat source surrounding by a wavy tilted domain of porous medium under local thermal non-equilibrium

The magnetohydrodynamic (MHD) mixed convection of heat and mass transfer is carried out using finite difference method applied inside a tilted porous cavity saturated with a hybrid nanofluid due to the presence of the double-moving lid and the heat sources. In contrast to the earlier research, various effects which are recognized by heat generation in the local thermal non-equilibrium case at the extended Brinkman Darcy model subjected to inclined magnetic field are thoroughly examined numerically. For instance, unusual observations of the cold mass surrounding the heat source emphasize that the maximum fluid temperature highly depends on the forced convection. Additionally, solid-phase temperature acts in accordance to the heat source location while fluid temperature is agitated by the moveable sides which points up the disparity at the thermal energy transportation. However, the transfer of heat and mass at the model requires a specific conduct due to the existence of damping factors. The magnetic field, for example, suppresses the fluid flow. Moreover, the thermal non-equilibrium condition deteriorates the global heat generation.

CFD investigation of the complex multiphase flow of biomass gasification in industrial-scale dual fluidized bed reactor

In this work, the process of biomass steam-gasification via a dual fluidized bed with a thermal input of 8MWth is numerically modeled by applying the multiphase particle-in-cell method. This model is successfully validated with the experimental data. Based on the simulation, the results can be epitomized as: distinct fluidization regimes in gasifier and combustor reactors give rise to different flow pattern and dispersion coefficients of solid phase in both reactors. Large particle heat transfer coefficients mainly appear in the upper regions of both reactors due to violent reactions. In this industrial-scale apparatus, the time-averaged heat transfer coefficient of sand in the combustor is larger than that of gasifier sand for about 40 W/(m2·K). Relationships between key variables such as volume fraction, heat transfer coefficient, slip velocity, Reynolds number and temperature of solid phase are discussed. Particles with small volume fraction tend to possess large heat transfer coefficient and slip velocity. The results explored at the particle-level might be useful in the industrial operating regarding the biomass steam-gasification processes.

Mg-Doped high voltage LiCoO2 for high performance lithium-ion batteries

Further increasing the voltage is the most efficient means of acquisition to obtain lithium cobalt oxide with high specific capacity, but the irreversible phase transition of LiCoO2 at high voltage leads to poor electrochemical performance. In this paper, a 4.6V high voltage stable lithium cobalt oxide cathode material was achieved by simple high temperature solid-phase synthesis method doped with different contents of Mg elements. Under the condition of Mg content of 0.02, the specific capacity of discharge is 222.7 mAh/g at 0.5C, and the capacity retention rate is 93% after 50 cycles of 1C, showing good electrochemical performance.

Color tunable warm white emitting whitlockite-type phosphor applied in optical thermometry

Whitlockite-type structure phosphors have received extensive attention and research due to their adjustable chemical compositions in isomorphic compounds and providing rich crystal positions for doping activators. Ca2.6K0.2La0.2(PO4)2 whitlockite-type phosphors with Dy3+ singly doping and Dy3+, Eu3+ co-doping were prepared via high temperature solid-phase reaction, and the crystallographic characteristics, luminescence properties and temperature sensing performance were investigated in detail. The prepared phosphors are pure phase and both Dy3+ and Eu3+ enter into the matrix and produce blue, yellow and red emissions. The CCT values of the emitted light from Ca2·6K0·2La0·2(PO4)2: Dy3+, Eu3+ phosphors increase with the Eu3+ concentration rises, changing from cold white light to warm white light. The integrated emission intensity of Dy3+ in the phosphor decreases with the change in the doping ratio of Dy3+ and Eu3+, causing by the energy transfer from Dy3+ to Eu3+. The Ca2·6K0·2La0·13(PO4)2:0.06Dy3+, 0.01Eu3+ phosphor shows temperature sensing performance based on FIR technique, with the maximum relative sensitivity calculated to be 0.181% K−1. All the results reveal that the Ca2·6K0·2La0·2(PO4)2: Dy3+, Eu3+ phosphors can be applied to w-LEDs and display devices, and can be used as a new type of optical thermometer.

Standard enthalpies of formation of 3-hydroxyphthalic anhydride

In this investigation thermochemical properties of 3-hydroxyphthalic anhydride were determined. Fusion enthalpy, fusion temperature and molar heat capacity in solid phase were obtained by differential scanning calorimetry. By the Knudsen effusion method, the molar enthalpy of sublimation at 298.15 K was obtained. By thermogravimetric data, it was possible to determine the molar enthalpy of sublimation and the molar enthalpy of vaporization. On the other hand, the molar enthalpy of formation in solid phase at 298.15 K was determined by combustion calorimetry. The molar enthalpy of formation in gas phase at 298.15 K was calculated from molar enthalpy of sublimation at 298.15 K and molar enthalpy of formation in solid phase at 298.15 K. This experimental value was compared both theoretical enthalpy of formation in gas phase by using Gaussian methods at the G3 and G4 levels and with an estimated value in relation to phthalic anhydride.

Ionic selective occupation, lattice modulation and photoluminescence properties of garnet typed orange-yellow phosphors for white-light-emitting diodes

Orange-yellow luminescent Y2-xSr1-yAl4SiO12: xCe3+, yMn2+ (x = 0.04–0.06, y = 0.1–0.6, abbreviated as YSAS: xCe3+, yMn2+) phosphors with garnet structure were prepared by the high temperature solid-phase method. The matrix energy band is calculated by DFT, where YAG is 4.535 eV and YSAS is 4.874 eV. The Rietveld refinement of the XRD data indicates that Ce3+ mainly replaces the Y3+ sites, while Mn2+ selectively occupies. The Gaussian peaks of the fluorescence spectrum prove that Mn2+ occupies two luminescent centers, which are further determined by Van Uitert's empirical formula. The doping of Ce3+/Mn2+ units can effectively enhance the structural rigidity of the YAG host and promote the red-shift of the emission peak position of Mn2+. The fluorescence decay kinetics test proves that Ce3+ can transfer energy to Mn2+, and the transfer efficiency reaches 72.08% at y = 0.5. The thermal stability test of the phosphor shows the luminous intensity at 473 K still maintains 86% of the room temperature. The phosphor prepared in this experiment was combined with a blue light chip to make a w-LED device, and the performance showed Ra = 86.1, CCT = 5168 K. The above results show that the emission color of the garnet structure can be tuned by energy transfer, which is attractive for future applications.

Synthesis and photoluminescence performance of single-component Ca3YAl3B4O15:Dy3+, Eu3+ white-emitting phosphor for white light-emitting diodes

A single-component Ca3YAl3B4O15 (CYAB):Dy3+, Eu3+ phosphor was synthesized by the traditional high temperature solid-phase method, Dy3+ and Eu3+ were codoped in the structure to obtain a warm white emission. The results of XRD and EDS revealed that all samples had the standard Ca3YAl3B4O15 structure, and no impurity phase appeared with codoping. The emission of Dy3+ in CYAB consisted of both main peaks at 476 nm and 570 nm, with which a white emission could be observed. Furthermore, a characteristic emission peak of Eu3+ appeared at 617 nm in Dy3+/Eu3+-codoped samples to supplement red component for the white emission of Dy3+, due to the energy transfer effect between Dy3+ and Eu3+. With the amount of Eu3+ raised, the correlated colour temperature of CYAB:Dy3+, Eu3+ phosphor obviously decreased, and a warm white light was successfully realized from the manufactured w-LEDs. Therefore, all results indicated that the single-component Dy3+/Eu3+ codoped CYAB white-emitting phosphor had a potential application in ultraviolet excited w-LEDs.

Influence of Mn2+ doping on the emission spectrum of Sr2La8(SiO4)6O2:Eu(2+,3+) phosphor

A series of novel Sr1.9-xLa8(SiO4)6O2:0.1Eu(2+,3+), xMn2+ (0 ≤ x ≤ 0.10) phosphors were successfully prepared by high temperature solid-phase method. The series of samples belong to hexagonal system, and the space group is P63/m(1 7 6) or P-3. The emission spectrum range of Sr1.9-xLa8(SiO4)6O2:0.1Eu(2+,3+), xMn2+ are 500–750 nm. When x ≥ 0.03 mol, realizing the energy transfer of Eu3+ → Mn2+. The valence states of Eu and Mn in the phosphors were analyzed by XPS spectra. The emission light of Sr1.9-xLa8(SiO4)6O2:0.1Eu(2+,3+), xMn2+ phosphors is shifted from the yellow light region to the orange-red light region by controlling the Mn2+ ion doped.

Explicit modeling of pebble temperature in the porous-media model for pebble-bed reactors

In this study, a multiscale model has been developed to include an explicit pebble-temperature model nested in the porous-media model for pebble-bed reactor applications. The multiscale solid-phase energy balance model, including the pebble surface energy balance equation and an explicit modeling of pebble temperature, can predict the macroscopic (pebble bed) and microscopic (pebble) temperature distributions under both steady-state and transient conditions. The proposed multiscale model is solved in a fully coupled manner using the Newton-Krylov method, and therefore iterations between the macroscopic (pebble-bed-scale) and microscopic (pebble-scale) model are avoided. Extensive code verifications, validation, and demonstrations have been performed for this newly developed model. By explicitly modeling pebble temperatures, this new model addresses a major deficiency of the basic porous-media model, which assumes homogeneous solid-phase temperature and is not appropriate for pebble-bed reactor design and safety analyses.

Effect of FeO content on melting characteristics and structure of nickel slag

Nickel smelting produces a large amount of nickel slag which contains a lot of Fe in the form of FeO. The effect of FeO content on the melting properties and structure of nickel slag is investigated by thermodynamic calculations and experiments, using the nickel slag of water quenching furnace as raw material, which is simplified to CaO-SiO2-FeO-MgO slag system. The results are as follows: with increasing FeO content, the precipitated primary phase changes from melilite to olivine. The liquidus temperature, softening temperature, hemispherical temperature, flow temperature, viscosity, and critical viscosity temperature of the slag system tend to decrease gradually, but the solid phase temperature tends to decrease first and then increase. The centre of the symmetric stretching vibration band of the [SiO4]4 tetrahedron -in the slag system shifts to the low wavenumber region. The mole fraction of O0 in the slag continuously decreases, and the mole fraction of O- and O2- increases. The complex silicon-oxygen tetrahedron structure gradually disintegrates and the structural unit tends to be simple.

The effect of low-temperature auto-ignition of W–Cu2O nanopowders with core-shell structure

In this work, the effect of in-vacuum low-temperature auto-ignition of a W–Cu2O nanopowders mixture obtained by natural oxidation of W–Cu composite nanopowders is demonstrated. The powder is obtained via electrical explosion of wire technique and consists of bimetallic particles instead of Cu and W mixture. The evolution of the phase composition has been studied using in situ X-ray diffraction technology during heating. The structural investigation shows that particles have a core-shell structure, increasing a contact surface between reactants. The ongoing reactions are described, and studies of the structure of powders and combustion products are given. Combustion occurs in the solid-phase temperature range, which is confirmed by the thermal imaging data.

Crystal structure, luminescence properties and thermal stability of Lu3+ ion-substituted BaY2Si3O10: Dy3+ phosphors

A series of Dy3+ activated Ba(YLu)2Si3O10 samples were prepared by high temperature solid-phase method. The purity of the phase was determined and the structural changes were analyzed. Under excitation at 350 nm, the BaY2Si3O10: Dy3+ phosphor shows two stronger luminescence peaks at 486 nm and 572 nm and weaker emission peak at 668 nm. In addition, with the continuous replacement of Y3+ in the matrix by Lu3+ ions, the chromaticity coordinates of samples in the system can be adjusted from the cold white region to the warm white region, and the luminescence performance of phosphors can be effectively improved. It was observed that the thermal stability of the phosphor was gradually enhanced with Lu3+ concentration increases, and the emission intensity of the BaLu2Si3O10: 0.04Dy3+ phosphor at 453 K could still maintain 83.78% of that at room temperature, which was discussed in conjunction with the Debye temperature and the rigid structure model to provide a reference for the improvement of the thermal stability performance. In addition, the increase of the concentration of Lu3+ ions doping will shorten the lifetime of phosphors due to the non-radiative energy transfer caused by the shortening of the ion distance in the lattice.

Numerical investigations on an improved dual-channel porous combustor fueled with lean methane for enhancing thermal performance

In this work, an improved dual-channel porous combustor is designed. Extensive numerical investigations are conducted to compare the thermal performance between the single-channel and the improved dual-channel combustor under various inlet velocity, methane concentration and the pores density of foam ceramics. Moreover, the effective thermal conductivity model of the foam ceramic based on the Kelvin decahedron was introduced. The external and internal heat circulation and the heat circulation efficiency of the burner are calculated and analyzed quantitatively. Results show that, at low methane concentrations conditions, the pores density of foam ceramics have no significant effect on the blow-off limits for both single-channel and dual-channel porous burners. However, under the higher methane concentrations conditions, the blow-off limit would be increase with the pores density of foam ceramics. Compared with the single-channel burner with 20 PPI foam ceramic, the mean nonuniformity of the foam ceramics temperature for the improved dual-channel combustor would be reduced from 2.015% to 26.562% when the inlet velocity increases from 0.1 m/s to 0.16 m/s. However, for the 10PPI to 40PPI burners, the mean nonuniformity of the solid phase temperature of the improved dual-channel combustor would be reduced by 9.78% to 4.36%. Moreover, the preheat zone inside the porous medium would be greatly minimized by the addition of external heat recirculation to the porous media burners.

Mathematical modeling of porous combustion under various working conditions

Porous burner offers attractive advantages including high combustion performance and power ranges, and approximately zero pollutant emission. In this paper, the thermal behavior of premixed flame of a CH4/air mixture in a porous burner was examined using an unsteady In-house CFD code with an appropriate single reaction mechanism. In this regard, to solve the transient term, an implicit scheme was used, and displacement terms were solved using the upwind methodology. Additionally, the discretized central difference was employed to solve diffusion terms. At first, the results were compared with available published data, and then the influences of various working parameters, including solid matrix conductivity and volumetric heat transfer coefficient, were investigated on the flame structure. Thermal performance of the burner is studied by varying relevant parameters within a practical range. The predicted gas temperature profile near the reaction zone is much broader than that in an adiabatic premixed flame. The effect of volumetric heat transfer coefficient on the temperature profile is investigated. The local gas temperature decreases in the reaction zone and the solid temperature increases in the preheat zone with an increase in convective heat transfer. Also, the corresponding local convective heat transfer rates for different values of volumetric heat transfer coefficient are calculated and compared. Simulation results also indicate that increasing the effective thermal conductivity of the solid will decrease the solid phase temperature downstream of the flame location. Due to high temperature gradients in the solid matrix, its effective thermal conductivity has a significant impact on the conductive heat transfer rates.

Facile synthesis of CaO:Eu3+ and comparative study on the luminescence properties of CaO:Eu3+ and CaCO3:Eu3+

CaO:Eu3+ phosphors were prepared by calcination of CaCO3:Eu3+ nanoparticles. The as-obtained samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and photoluminescent (PL) techniques. The results reveal that the CaO:Eu3+ phosphors obtained by this method have significant advantages over those obtained by the traditional high temperature solid-phase method in terms of phase purity, crystallinity, particle size and luminescence properties. In addition, Eu3+ ions are also used as spectroscopic probe to analyse the relationship between the local crystal structure and the luminescence properties of CaCO3:Eu3+ and CaO:Eu3+. The study indicates that the excitation spectrum of CaO:0.02Eu3+ have the stronger Eu-O charge transfer band (CTB) than that of CaCO3:0.02Eu3+, which enhances the luminescence and makes it more suitable for deep ultraviolet excitation. Finally, the luminescent properties and local structure of CaO:xEu3+ phosphors was also investigated.

An LBM-FDM coupled numerical model for ignition and transient downward flame spread over solid fuel

The ignition and subsequent transition to steady-state flame spread behaviors over a vertical solid fuel in normal gravity and static environment were numerically studied in this work. Unlike the general approach based on the NS equation for buoyancy flow, the lattice Boltzmann method (LBM) was employed to solve the velocity field in the gas phase. Elliptic equations of temperature and concentration in gas and solid phases were solved by the finite difference method (FDM). An LBM-FDM coupling model for investigating the downward flame spread over solid fuel was developed. The ignition and the flame propagation behavior can be predicted quantitatively. The results show that a point flame with the shape of a disk appears first at the sheet surface when the vertical solid fuel is ignited. The instantaneous temperature response of ignition lags behind the chemical reaction. The point flame gradually develops into an asymmetric arch-shaped flame with two flame fronts near the sample surface. And then, the flame in the downstream zone is separated from the upstream flame source under the effect of the induced buoyant flow, and eventually disappears at the downstream boundary. Finally, the flame on the upstream gradually develops into a steady downward flame spread. The developed model in this work is validated by comparing the gas-phase temperature and flame spread rate between the predicted results and previous experimental data. This paper provides another method to predict the development of solid flame spread.

Оксидный поверхностный слой и твердофазная свариваемость титановых сплавов

It is known that the ultrafine-grained (UFG) structure in alloys is thermally unstable. An important task for the modern aviation engineering is to preserve the UFG structure in parts for responsible purposes after their production in order to maintain the high level of their mechanical properties. In particular, the solution to this task necessitates the reduction of the temperature of solid-phase bonding while ensuring the necessary quality of the permanent joint. It is known that along with the average grain size, the oxide surface layer can also significantly affect the solid-phase weldability of titanium alloys at low temperatures, but the latter has been extremely poorly studied. In this regard, the influence of an oxide film is considered for domestic two-phase titanium alloys VT6 (Ti-Al-V system) and VT8 (Ti-Al-Mo system), which differ in the main alloying element for the stabilization of the β-phase. As a result of the experiments, the absence of an oxide layer in the zone of solid-phase connection of the ultrafine-grained (UFG) VT6 alloy after welding in vacuum at a reduced temperature of 600°C was metallographically revealed. This has a positive effect on the quality of welded samples according to the conducted mechanical tests. A continuous oxide layer was found in the solid-phase joint zone after welding at a temperature of 600°C for the UFG alloy VT8. The experimental results indicate that the UFG titanium alloy VT6, doped with relatively “mobile” vanadium, has the potential to reduce the lower temperature of solid-phase welding in vacuum by 50°C in comparison with the titanium alloy VT8.

Heat transfer analysis of rectangular porous fins in local thermal non-equilibrium model

• Analytical solutions on convective-radiative porous fin in LTNE is accomplished. • Darcy model and Boussinesq approximation are used to simulate the porous medium. • The two energy equations are solved using the Adomian Decomposition Method. • Results are given as temperature profiles and total Nusselt numbers. • Criteria to compare LTNE and LTE hypothesis are given for both scale analysis and ADM. In this study, an analytical solution of a porous fin with natural convection and radiation heat transfer is carried out. For the first time, the analysis is accomplished in Local Thermal Non-Equilibrium (LTNE) model. The investigation is carried out on a porous fin with finite length and adiabatic tip. The Darcy model and Boussinesq approximation for buoyancy effects are used to evaluate the infiltration velocity in the porous medium. Two energy equations are solved using the Adomian Decomposition Method (ADM). The solution is validated with the numerical solution of the finite difference method, and with the asymptotic solution for the Local Thermal Equilibrium (LTE) model. The results are presented in terms of temperature profiles and total average Nusselt numbers. They pointed out the effects of internal and external radiation and convection heat transfer, as well as thermal conductivity ratio and dimensionless thickness. It was found that solid phase temperature profiles decrease as the Biot, Bi , and Rayleigh, Ra *, numbers decrease, whereas the difference between the solid phase and fluid phase temperatures, for assigned Bi , decreases for lower Ra . Thermal conductivity ratio and dimensionless thickness increase engender higher solid phase temperature for assigned Bi and Ra *. The total Nusselt number increases as Ra *, Bi and external radiation increase, whereas it decreases with the thermal conductivity ratio. Criteria to compare LTNE and LTE assumptions are proposed, and they highlight the fact that the minimum Biot number to accept the LTE assumption becomes lower as the Rayleigh number decreases.