Temperature Solid Phase Research Articles

Effects of La2Ce2O7 on the phase composition, microstructure, wetting behaviour and corrosion resistance of magnesia refractory

The addition of rare earth oxides has a significant impact on the improvement of thermal properties of refractory materials. Magnesia refractory with La2Ce2O7 was prepared by high-temperature solid-phase synthetic sintering at 1873 K for 5h using fused magnesia as raw materials, CeO2 and La2O3 as addition, respectively. The effect of La2Ce2O7 on the phase composition, microstructure, apparent porosity, bulk density, wetting behaviour and corrosion resistance with steel of fused magnesia were investigated. When the content of La2Ce2O7 was 20wt%, the results showed that as-prepared samples from fused magnesia with an apparent porosity of 17.63% and a bulk density of 3.11g·cm-3 were obtained by high temperature solid-phase sintering reaction at 1873 K for 5h, respectively. Due to the addition of La2Ce2O7, and raw materials in the impurity phase CaO and SiO2 for the reaction, the generation of a small amount of CaLa4(SiO4)3O and La8.89Si6O25.9 high melting point phase, plugging the air holes, thus improving the bulk density of the fused magnesia and reduce its apparent porosity. The ability of steel corrosion of as-prepared samples from fused magnesia doped with La2Ce2O7 have better resistance than conventional fused magnesia, which the thickness of the corrosion layer was reduced by 42.1% compared to as-prepared samples without La2Ce2O7.

Luminescent color modulation of Zn/BaAl2O4:0.2%Eu phosphors for LED application

Spinel-type aluminate (ZnAl2O4) doped with europium (Eu) ions has garnered considerable attention in the field of luminescence. This study explores a series of Zn/BaAl2O4:0.2%Eu phosphors (x=0∼0.25, x is for the mole fraction of BaAl2O4), fabricated through a high temperature solid-phase reaction method in air or reduction environment. In the case of phosphors synthesized in air, the photoluminescence emission (PL) spectra show a series of sharp emission peaks at 570nm, 589nm, 620nm, 660nm, and 710nm, which are generated by the 5D0-7FJ (J = 0, 1, 2, 3, 4) level transitions in Eu3+. Time-resolved photoluminescence and X-ray photoelectron spectroscopy (XPS) characteristics also validate the presence of Eu3+ in samples synthesized in air. An intriguing observation is the abnormally strong emission peak at 570nm under 346nm excitation, originating from the Eu3+5D0-7F0 level transition. For x=0.15, the corresponding CIE color coordinate is (0.3246, 0.3449), suggesting its potential application as a mono-doped and uni-matrix white phosphor. On the other hand, phosphors synthesized in reduction environment exhibit PL spectra with a wide emission band spanning from 400nm to 550nm, resulting from the electric-dipole-allowed transition of f-d state of Eu2+. The partial substitution of Zn2+ with Ba2+ significantly enhances the Eu2+ luminescence intensity. Moreover, an elevation of the mole fraction of Zn/BaAl2O4:0.2%Eu leads to a notable redshift (450nm→500nm) in the emission peaks of Eu2+ caused by lattice expansion, providing the adjustability of emitting color.

Optimal control of Hydrocarbon Reducer (HC) injection based on Trust-Region-Reflective Algorithm (TRRA) and physical models for Diesel Oxidation Catalyst (DOC)

The aim of this paper is to control the DOC outlet gas temperature between 600 ± 15 °C by optimizing the hydrocarbon (HC) injection into the Diesel Oxidation Catalyst (DOC) for active regeneration of the downstream Diesel Particulate Filter (DPF). First, based on the physical model of the DOC thermal dynamics, the energy conservation equation for the gas phase temperature is simplified by using variable substitution, and the energy conservation equation for the solid phase temperature is simplified by considering only the heat generated by the HC injection. By solving the simplified model using the Trapezoidal Rule-Backward Differentiation Formula 2 (TR-BDF2) method and optimizing the model parameters in combination with the Gauss-Newton method, the computational efficiency and accuracy were significantly improved. Next, the DOC downstream temperature observer is designed by combining the solution characteristics of the DOC model with the unscented Kalman filter (UKF) algorithm to ensure that the catalyst operates within the optimal temperature range. Then, this paper verifies the accuracy of the model and observer through bench tests covering four steady-state operation conditions and World Harmonized Transient Cycle (WHTC) test cycle, and the results show that the model and observer exhibit high accuracy in both steady-state and transient operation conditions. Finally, the DOC temperature was successfully maintained between 600 ± 15 °C by optimizing the control of the HC injection rate, thus achieving the expected temperature control target. These research results provide theoretical and practical support for diesel engine emission control and DPF active regeneration.

The development of environmentally friendly Pr/W Co-doped Bi2MoO6 green pigment with high near-infrared reflectivity

In this article, a green pigment Bi1.95-xPrxW0.05MoO6+δ (x = 0.1–0.5) co-doped with Pr and W was developed using high temperature solid-phase synthesis method. The microstructure, color performance, and optical characteristics of the novel pigment was analyzed using x-ray diffraction instrument (XRD), field-emission scanning electron microscopy (FESEM), L∗ a∗ b∗ color date, and ultraviolet–visible–near infrared light spectrophotometer. The results indicate that all the samples possess a monoclinic structure, characterized by the space group P21/c(14). Compared to Bi2-xPrxMoO6+δ doped solely with Pr6O11, the Pr/W co-doped Bi2MoO6 pigment demonstrates superior green coloration. The solar reflectance in the near-infrared region of all pigment samples exceeds 80 %, highest value reaches 92.82 %. In thermal insulation tests, the temperature difference between the Bi1.95-xPrxW0.05MoO6+δ pigment coating and a blank galvanized sheet reaches up to 10.3 °C after 60 min under infrared lamp irradiation. The color difference ΔE∗ of the pigment powder after immersion in acid and alkali solution and high-temperature calcination are less than 5, indicating good chemical stabilities in acidic, alkaline and high-temperature environments. To our knowledge, Bi1.95-xPrxW0.05MoO6+δ has the highest reflectivity among green pigments without toxic metals.

The study on the coupled influence of water saturation on heat and mass transfer processes within porous media under CW laser irradiation

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology.

Transient thermal management of laser systems using Plate-Fin phase change heat Exchangers: Experimental and computational study

To mitigate transient thermal shocks in lasers and reduce thermal stresses caused by temperature fluctuations, the use of phase change materials (PCMs) in thermal management systems is a viable solution. This study proposes an innovative two-dimensional transient heat transfer model specifically designed for plate-fin phase change heat exchangers (PFPCHEs). The model meticulously simulates the complex heat transfer phenomena within the heat exchanger, including fluid convection, solid thermal conduction, and the phase change processes of PCM. The convective heat transfer coefficient between fluid and plate is calculated using the Wieting correlation. An advanced pulse-mode experimental test platform was constructed to validate the model, dynamically monitoring and recording outlet temperatures and heat exchange performance for stringent experimental comparison. The research explores the impact of key operating parameters such as initial temperature, flow rate, and inlet temperature of the cooling cycle on the performance of the heat exchanger, providing valuable design and control strategies for transient thermal management of laser systems. The experimental results confirm that the model accurately predicts the dynamic response characteristics and temperature distribution of PFPCHEs under multi-cycle pulse loads, with 96% of the predictions within a 10% error margin. A significant finding is that the initial temperature has negligible influence on the heat transfer characteristics when it is below the solid phase temperature of the PCM. Moreover, by meticulously adjusting the flow rate and inlet temperature of cooling cycle, it is possible to effectively maintain the stability of the outlet temperature throughout the entire pulse cycle. This is crucial for minimizing temperature fluctuations within the thermal management system and extending the service life of electronic components.

On thermal non-equilibrium (TNE) model for heat transfer in ternary ferro-nanofluid with rectangular porous fin

The heat transmission in a rectangular porous fin affected by a thermal non-equilibrium model with radiation and magnetic field influences is studied in this study. A ferrofluid containing ferroparticles (Fe3O, CoFe2O4, and Cu) and a mixture of 50 % water and 50 % ethylene glycol coats the fin. Dimensionless form is later achieved by formulating the governing equations for both the solid and ferrofluid phases. In order to get the answer, the Runge–Kutta–Fehlberg (RK-45) scheme is used. Visual and tabular representations are used to investigate the effect on heat transmission of the Biot and Rayleigh numbers as well as the porous and convective parameters. The results show that the solid phase temperature profile is inferior for lower Hartmann numbers (H) and Rayleigh numbers (Ra). The disparity in temperature between the solid and ferrofluid phases decreases in proportion to the Ra. Applications for this type of device include heat exchangers, air conditioners, and cooling towers.

Study on heat and mass transfer characteristics of porous media with different pore structures under continuous wave laser irradiation

The pore structure determined by porosity and particle size will directly affect the remediation efficiency of thermal treatment on contaminated soil. To investigate the remediation capability of continuous wave laser soil remediation technology on soils with different pore structures, this paper establishes a heat and mass transfer model within unsaturated porous media under laser irradiation. Four pore structures were simulated, and the model’s reliability was experimentally validated. Under laser irradiation, energy exchange between the solid and gas phases has a minimal effect on the solid phase temperature. The temperature distribution of the solid phase in the four samples is similar, with the differences primarily arising from moisture content. Interface energy exchange dominated the rise in the temperature of the gas. The intrinsic Nusselt numbers for the four samples were 3.5, 4.4, 4.9, and 6.2, respectively. Laser irradiation causes the Nusselt number to decrease over time, but the relative magnitudes of the Nusselt numbers for the four samples remain unchanged. From the perspective of solid phase temperature, the capability of laser remediation for soils with different pore structures is similar. From the standpoint of gas temperature, the Nusselt number is decisive. However, considering the complex coupling relationship between gas temperature rise and Darcy velocity and evaporation rate, the influence of water saturation and intrinsic permeability cannot be ignored. The research findings can provide a theoretical basis and analytical methods for the efficient laser remediation of soils with different pore structures.

Wurster fluidised-bed coating: Coarse-graining technique within CFD-DEM in conjunction with heat and mass transfer

In this study, we use a combined CFD-Discrete Element Method to assess predictive capabilities and numerical implications of a coarse-graining technique in Wurster fluidised-bed coaters. We investigated both hydrodynamics and heat and mass transfer and conducted simulations of a full three-phase system for the original and three coarse-grained systems, analysing velocity distributions, macroscopic solid stresses, moisture content and phase temperatures. We achieved a logarithmic simulation speed-up by aggregating up to 64 original particles into each coarse grain. This was accomplished while maintaining fidelity to the original CFD-DEM system in terms of reproducing with high accuracy macroscopic granular flow properties in different regions of a coater (drying, tube and bed regions). By integrating a liquid spray and humid air, we demonstrated that the phase temperatures were accurately predicted within the coarse-grained system, with a high capability of delivering liquid spray distributions with the same uniformity and drying. We also give arguments for choosing a certain degree of coarse-graining as a compromise between a desired reduction of computational costs and a trustworthy reproduction of granular-flow physics encountered in different regions of a Wurster bed. Our findings pave the way to using CFD-DEM to industrially-scaled Wurster-bed systems, which is currently unfeasible due to prohibitive computational costs.

Energy Storage in Lightweight Aggregate and Pervious Concrete Infused with Phase Change Materials

This study explores the feasibility of utilizing pervious concrete (PC) incorporating diverse lightweight aggregates (LWAs) integrated with phase change materials (PCM) for applications where forced air cooling would be advantageous. The use of such a component provides latent and sensible heat that can cool forced air applications, offsetting ambient temperature increases that occur during the day. Macro- and microencapsulation techniques were used to incorporate inorganic PCM in the PC. The macro-encapsulation technique involved enclosure of PCM within a stable shell prior to addition into the concrete. The microencapsulation technique involved the impregnation of PCM into porous lightweight aggregate. To overcome the PCM reaction with the concrete constituents, an epoxy coating was utilized. The design of the PCM concrete mix and comprehensive laboratory assessment of porosity, water permeability, PCM absorption capacity, compressive strength, and microstructure of the LWAs are detailed. The test results indicate that LWAs have high PCM impregnation rates ranging from 32 % to 57 % by volume. The compressive strengths of PC using LWAs were reduced by 25 % to 65 % when using microencapsulation. The use of microencapsulation was found to reduce the pressure drop under air flow due to the increase in aggregate size as a result of the coating thickness. PCM-PC with a shell thickness of 100 mm, resulted in a pressure drop of less than 100 Pa at a velocity of 0.35 m/s. The use of macro-encapsulated PCM in PC was sensitive to the phase of the PCM, where the liquid phase reduced the compressive strength by 67 %. The failure occurred within the macro-encapsulated PCM at the liquid phase temperatures and at the interface between the encapsulated PCM at solid phase temperatures. The heat transfer provided by the LWA infused PCM when used in a packed aggregate bed or in PC, was shown to match expected latent and sensible heat estimates based on the thermal properties of the materials. This systematic investigation provides valuable insights into LWAs and PCM performance in pervious concrete, offering a comprehensive understanding of their interaction in cooling applications.

Thermal dynamics assessment for multi-phase flow analysis with motile cilia and electric double layer effects: Application of Levenberg–Marquardt backpropagation NNs

Ciliary movement holds substantial importance in the realm of biomedical research. Disorders arising from impaired ciliary motion, such as primary ciliary dyskinesia and specific respiratory ailments, underscore the critical need to investigate both the normal functioning and dysfunction of cilia. Such research is fundamental to the development of effective treatments and therapies. This work explores the application of Levenberg–Marquardt backpropagation neural networks (LMBP-NNs) for simulating the flow of a non-Newtonian Jeffery fluid in peristaltic motion. Inspired by synchronous ciliary movement, microfluidic systems mimicking cilia functionality have been developed. These artificial cilia can generate controlled fluid flow patterns, enabling various applications such as drug delivery, mixing, and particle sorting in lab-on-a-chip devices. The present study focuses on measuring thermal and mass transfer in beating cilia during multiphase peristaltic pumping of Jeffery fluid in two- and three-dimensional channels using transverse magnetohydrodynamics in a porous medium. The governing equations for the non-Newtonian Jeffery fluid in both the fluid and dusty phases are formulated, and exact solutions are calculated for fluid phase velocity, particulate phase velocity, temperature, concentration, and pressure gradient. The physical behavior is investigated by graphing dimensionless parameters for velocity, temperature, and concentration profiles in both solid and liquid phases. The trapping phenomena is depicted by showing streamlines of various dimensionless characteristics such as porosity velocity and volume percentage. The LMBP-NNs approach is then used to train, test, and verify the neural network models using the reference datasets. The accuracy of the LMBP-NN is assessed using statistical data such as mean square error, curve fitting graphs, regression plots, and error histograms. The study also investigates flow model limits for momentum, temperature, and concentration profiles using visual representations. This study illustrates the computational capability of LMBP-NNs in modeling the peristaltic flow of Jeffery fluid and gives useful insights into fluid flow behavior in microfluidic devices containing artificial cilia. The findings help to better understand and optimize these systems for a variety of fluid manipulation and transportation applications.

Analytical and numerical investigation of heat transfer of porous fin in a local thermal non-equilibrium state

This research employs a local thermal non-equilibrium (LTNE) model to analyze the heat transfer phenomenon through a porous fin, considering natural convection and radiation effects. The infiltration velocity within the porous medium is evaluated using the Darcy model, and buoyancy effects are accounted for using the Boussinesq approximation. The Akbari-Ganji method (AGM) is applied to address the governing energy equations. The accuracy of the proposed solution is verified by comparing it with numerical results obtained from the finite difference method (FDM), the finite element method (FEM), and earlier investigations. The results are presented regarding the total average Nusselt number and temperature profiles. These results shed light on the influence of several important parameters, such as the thermal conductivity ratio, dimensionless thickness, convectional heat transfer, and external and internal radiation. The analysis reveals that decreasing Rayleigh and Biot numbers reduces the temperature profiles of the solid phase. Additionally, when the Rayleigh number is low but the assigned Biot number is high, the temperature difference between the solid and fluid phases diminishes. Furthermore, increased thermal conductivity ratio and dimensionless thickness for assigned Biot and Rayleigh numbers lead to higher solid phase temperatures. The Nusselt number exhibits a decreasing trend with a decreasing thermal conductivity ratio but increases with higher Rayleigh and Biot numbers and increased external radiation.

Thermally-stable and color-tunable novel single phase phosphor Ca2GaTaO6:Dy3+, Sm3+ for indoor lighting applications

This study successfully synthesized novel phosphors Ca2GaTaO6:xDy3+ (CGTO:xDy3+) and Ca2GaTaO6:0.06Dy3+, ySm3+ (CGTO:0.06Dy3+, ySm3+) using the high temperature solid-phase reaction preparation. The microstructure, optical properties, and energy transfer mechanism of the phosphors were studied through X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and fluorescence lifetimes. XRD and corresponding refinement results indicate that Dy3+ and Sm3+ ions were effectively doped into the Ca2GaTaO6 (CGTO) lattice. The SEM graphs show that the elements in CGTO:0.06Dy3+, 0.5Sm3+ phosphors are uniformly distributed. PL spectra analysis show the CGTO:xDy3+ phosphors display two strong emission peaks located at 482 nm for blue emission and 575 nm for yellow emission when excited with 350 nm light. Under uniform conditions, when excited with 365 nm of light, the CGTO:0.06Dy3+, ySm3+ phosphors emit light that can be tuned with adjustable color coordinates and correlated color temperature (CCT) by incorporating varying proportions of Sm3+ ions. This tunability is achieved through the effective energy migration from Dy3+ to Sm3+ ions within the phosphor material. Furthermore, the emission spectra and weaken lifetimes of the CGTO:0.06Dy3+, ySm3+ confirm the energy transport between Dy3+ and Sm3+, and the energy transfer efficiency reached to 76 %. At 423 K, the luminescence intensity of CGTO:0.06Dy3+, 0.05Sm3+ phosphor retains 87 % of the intensity observed at 298 K, signifying its excellent thermal durability. Finally, the electroluminescent performance of the CGTO:0.06Dy3+ and CGTO:0.06Dy3+, 0.05Sm3+ phosphors packaged on 365 nm light-emitting diode (LED) chips respectively were studied to investigate the capability applications of the phosphors in white light-emitting diodes (WLEDs) field. The CCT of the packaged LEDs decline from 3396 to 2825 K, indicating CGTO:0.06Dy3+, 0.05Sm3+ phosphor shifts to warmer white light. At a voltage input of 3.4 V and a current of 600 mA, the thermal sensing shows that the WLEDs maintain aptitude for 90 min, showing that the packaged WLEDs can function consistently under elevated temperatures. These studies indicated the phosphors have potential applications in indoor lighting.

Effect of the Cross-Section of a Porous Burner on the Combustion Stability Limit of Premixed Oxy-Methane Flames.

This study presents the idea of using a porous media burner to improve the oxy-methane combustion reaction rate and broaden the stability limit. Numerical studies on the premixed combustion of CH4/O2/CO2 in a two-layer porous medium burner using a two-dimensional symmetrical volume-average model with the skeleton mechanism based on OpenFOAM. The combustion characteristics of burners with variable cross-sectional (VC) and straight cylindrical (SC) structures were compared, including stable range, temperature field, thermal cycle efficiency, and CO emissions. It is confirmed that the cross-sectional structure is effective for broadening the stable range, and the broadening rate is more than 4 times. As more heat is lost from the outlet due to the increased cross-section, the solid-phase temperature of VC is lower than that of SC. As a result, the flame temperature of VC will be about 200 K lower than that of SC under the condition of insulated walls. It also leads to a reduction of about 2% in thermal cycle efficiency compared with SC. Meanwhile, it is shown that the VC structure slightly increases CO emissions at low thermal power but is smaller than that of SC at high power. When the wall heat loss of the burner is considered, the VC structure is still effective for improving the stable range. In addition, the VC structure slightly affects flame tilt and temperature uniformity at the burner outlet when the thermal power is large. It is confirmed that the VC structure is effective for increasing the power adjustment range and reducing pollutant emissions at high power.

Direct and non-contact measurement of liquid fraction in unconstrained encapsulated PCM melting

Almost all of the experiments on PCM melting rely on temperature measurement. However, based on the experimental evidence, the presence of a thermometer in the solid PCM affects the results. Because the solid phase covers the probe and in fact, the solid phase temperature is measured instead of the liquid phase. On the other hand, since the PCM sticks to the probe, the regime of melting can change from unconstrained to constrained melting. In this study, a new method is proposed to measure directly the liquid mass fraction of PCM during melting. This method can be categorized as a non-contact measurement method and is based on the image processing technique.In this method, images of the melting process are prepared under controlled conditions at successive times. By performing image processing techniques, the solid core boundary is determined and the enclosed area is calculated and divided by the solid phase initial surface area. The method was applied to PCM melting inside a cylinder. Meanwhile, the problem was also simulated numerically by the multi-phase method (VOF). The multi-phase method allows considering the change in the total volume of PCM (summation of volumes of both solid and liquid phases) due to the difference between solid and liquid densities. Good agreement was observed between numerical and experimental results. The RMSE was 1.8 %. Moreover, it was observed that the shapes and sizes of the solid core in experimental images and numerical results at different times match well. But for lower solid volume fractions, the solid core sinks deeper in experimental images in comparison with numerical results.

Modeling of a Rotary Adsorber for Continuous Capture of Indoor Carbon Dioxide

Removing indoor CO2 as a pollutant via solid sorbents is a promising solution to maintaining acceptable indoor air quality while minimizing the energy consumption of ventilation. Compared to fixed-bed and fluidized-bed configurations, which require at least two beds to allow for continuous operation, a rotary adsorber is more compact and suitable to be integrated into the ventilation systems of buildings. In the present study, a regenerative rotary adsorber based on temperature swing adsorption was modeled to investigate continuous CO2 capture in an indoor environment. The governing equations of heat and mass transfer processes associated with the capture were established and coded in ANSYS Fluent software. The spatiotemporal variations of CO2 concentration and temperature in gas and solid phases within the rotary adsorber were obtained. The key findings are: (1) adjusting the speed mainly affects circumferential concentration and temperature distribution, but has little impact on axial concentration and temperature; (2) Increasing desorption inlet flow rate has little impact on adsorption outlet concentration, but significantly decreases desorption outlet concentration; (3) Raising desorption inlet temperature can increase both adsorption and desorption outlet average concentrations; (4) Reducing the volume proportion of the desorption sector will slightly increase adsorption outlet concentration and slightly decrease desorption outlet concentration, but barely affects average adsorption and desorption outlet temperatures.

Analysis of Phase Diagram of CaO-CoOx-ErOy and Crystal Structure of Perovskite (Ca3−xErx)Co2O6−z Solid Solution

In this work, a series of compounds in the CaO-CoOx-ErOy ternary oxide system were synthesized in air at 885 °C, using a high temperature solid-phase synthesis method. The phase boundary of each solid solution region in the CaO-CoOx-ErOy system was determined by X-ray powder diffraction techniques. The phase diagram of the CaO-CoOx-ErOy system at 885 °C includes three series of ternary oxide solid solutions: (Ca3−xErx)Co4O9−z (0 ≤ x ≤ 0.9), (Ca3−xErx)Co2O6−z (0 ≤ x ≤ 1.25), and (Er1−xCax)CoO3−z (0 ≤ x ≤ 0.33). Four three-phase regions and five solid solution tie-line regions were obtained. The structure of the perovskite solid solution (Ca3−xErx)Co2O6−z has been analyzed by Rietveld refinements. With the increase of Er content, the cell parameters of (Ca3−xErx)Co2O6−z exhibit a decreasing trend in a and b directions and an increasing trend in c direction. A brief comparison of the phase diagrams of the CaO-CoOx-ROy (R = La, Dy, and Er) systems in air at 885 °C is provided.

The volumetric effect indicator – A new dimensionless characteristic number for the optimum design and operation of volumetric solar receivers

This work introduces a new dimensionless number Z that should aid in the design phase of volumetric receivers. The number Z is able to indicate whether the volumetric effect is achievable for a specific combination of absorber geometry and thermal boundary conditions. It can be seen as an indicator of the slope of the solid-phase temperature profile in direction of gas flow. The volumetric effect is expected to occur at values of Z smaller than 1, when the convective plus radiative cooling (Pc) outweighs the absorbed solar power (Pa). An experimentally validated numerical model is used for a parametric simulation study, which sheds light on the absorber’s operating conditions (incident solar flux density and operating temperature) that favor the ideal temperature profile.

An analytical solution for a phase change nano-capsule cooled by forced convection

Great efforts have been made on the solidification of phase change nano-capsules (PCNCs). However, the analytical solutions received less attention when its initial temperature is not at the fusion temperature. Therefore, this work aims to analytically study the thermal behavior of PCNC with the same solid-liquid phase density during forced convective cooling when its initial temperature is greater than the fusion temperature. Asymptotic solutions are developed for long- and small-time scale. Asymptic solutions in the limit of large Stefan number to the solid phase temperature and the position of the free boundary were derived using the perturbation method with boundary-fixing transformations. The results predicted by the derived solutions are in good agreement with the data reported in the reference. It is shown that the surface temperature decreases negatively and exponentially under the Robin boundary conditions during the pre-cooling process. Increasing the values of the interfacial tension or the large Stefan number has the effect of slowing down the movement of the free boundary. The rate of change of the solidification time with respect to the Stefan number is maintained constant for a stationary free boundary. The analytical solutions can also be used to solve the classical Stefan problem (large Stefan number) by ignoring the surface tension. The analytic estimate provides a more convenient option for engineering applications than the complex numerical solution.

Numerical study on the effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant fuel

The effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant is investigated in the present study. Detailed combustion mechanism with 42 species and 136 reactions and segmented regression rate model are established and validated for the propellant fuel. The results show that temporal evolution of regression rate is not synchronous with temperature due to the heterogeneous properties of the burning surface. With combustion time increasing from t = 0.6 ms to t = 6.0 ms, the standard deviation of temperature of the burning surface increases by 65.08% while the standard deviation of regression rate decreases by 18.80%. Although raising pressure increases both the temperature and regression rate of the burning surface, the distribution uniformity of temperature and regression rate exhibits distinct response characteristics to pressure. With pressure increasing from 2 MPa to 10 MPa, the standard deviation of temperature of burning surface decreases by as much as 36.50% due to enhanced heat transfer to the burning surface. However, the standard deviation of regression rate increases by as much as 66.68% with pressure. Both the gas-phase temperature and solid-phase temperature increase and become more uniform with pressure. With progress of combustion, total heat transfer coefficient decreases slightly due to the reduced combustion heat release rate. Although the contribution of heat radiation increases significantly during the combustion process, heat convection is dominant heat transfer. With the increase of pressure, the combustion heat release rate increases significantly due to the enhanced oxidation reactions in diffusion flame. With consumption of the propellant, the combustion heat release rate decreases and squeezes to a smaller region. The experimental results of extinguished burnt surface show that AP particles become higher than the surface of HTPB binder as pressure increases. The non-uniformity of morphology of the burning surface of the AP/HTPB/Al composite propellant increases with pressure.