Inhomogeneous Flux Research Articles

Mixed convection in a partially and differentially heated cavity − a finite volume complete flux analysis

Purpose The purpose of this study is to derive a physics based complete-flux approximation scheme by solving suitable nonlinear boundary value problems (BVP) for finite volume method for mixed convection problems, to study the mixed convection phenomenon inside partially and differentially heated cavity for various sets of flow parameters. And, to study the impact of source terms on the cell-face fluxes for various sets of flow parameters for mixed convection problems. Design/methodology/approach The governing equations have been discretized by finite volume method on a staggered grid, and the cell-face fluxes have been approximated by local nonlinear BVP. The cell-face flux is represented as a sum of homogeneous and an inhomogeneous flux term. The proposed flux approximation is fully physics based as it considers the pressure gradient term, thermal buoyancy term and the other source terms in the cell-face flux calculation. The scheme comes out to be second order accurate in space tested with known solution. Also, the scheme has been implemented to study the mixed convection problems in a partially and differentially heated cavity. Findings The numerical order of convergence study shows that the proposed scheme is of second order in space. The scheme is first validated with existing benchmark literature for the mixed convection problem. As the proposed cell-face flux approximation scheme is a homogeneous part and an inhomogeneous part, this study quantifies the influence of the several source terms on the cell-face flux with the help of the inhomogeneous flux term. Then, the mixed convection problems in a partially and differentially heated cavity has been studied. Also, the effect of heat transfer rate at the hot wall is studied for different height of the heat source with different directions of wall movement. The numerical findings show that the local Nusselt number at the left wall is higher when the top and bottom walls move in opposite directions compared to when they move in the same direction, regardless of the Richardson number. In addition, the heat transfer rate at the hot portion of the left wall increases uniformly as the Richardson number decreases when the walls move in opposite directions. However, when the top and bottom walls move in the same direction, the increase in heat transfer rate is not uniform due to the formation of secondary re-circulation of the fluid near the bottom wall. Originality/value In this work, the flux approximation is conducted through local nonlinear BVPs, an approach that, to the authors’ knowledge, has not been previously applied to mixed convection problems. One of the strong advantages of the proposed scheme is that it can quantify the influence of source terms, namely, pressure gradient, cross-flux and the thermal buoyancy force, on the cell face fluxes required in the finite volume methods. Furthermore, the study explores mixed convection in a partially and differentially heated cavity, which is also novel within the current literature. These factors contribute to the originality and scientific value of the research.

Novel Finite‐Volume Complete Flux Approximation Schemes for the Incompressible Navier–Stokes Equations

ABSTRACTWe construct novel flux approximation schemes for the semidiscretized incompressible Navier–Stokes equations by finite‐volume method on a staggered mesh. The calculation of the cell‐face fluxes has been done by solving appropriate local non‐linear boundary value problems (BVP). Consequently, the cell‐face fluxes are represented as the sum of a homogeneous and an inhomogeneous flux; the homogeneous part represents the contribution of convection and viscous‐friction, while the inhomogeneous part represents the contribution of the source terms. We derive three flux approximation schemes to include the impact of the source terms on the numerical fluxes. The first one is based on a homogeneous 1‐D local BVP without source. The second scheme is based on an inhomogeneous 1‐D local BVP considering only the pressure gradient term in the source. Finally, a complete flux scheme is derived which is based on an inhomogeneous 2‐D local BVP. It takes into account both the gradient of the cross‐flux and the pressure gradient in the source term. The numerical validation of the schemes is done for the benchmark lid‐driven cavity flow for considerably high numbers along with a numerical convergence test for the exact solution of the Taylor–Green vortex problem.

Thermal management for microelectronic chips under non-uniform heat flux with supercritical CO2

With the rapid growth of information technology and the evolution in the use of microelectronic chips, these components are facing major challenges of high heat dissipation and inhomogeneous heat flux. To address the hotspot issues, a combination of microchannel heat sinks (MCHS) with cavity-rib designs and supercritical fluids is a potential solution. This study compares the thermo-hydraulic properties of water and supercritical carbon dioxide (sCO2) under various boundary conditions and hotspot locations during non-uniform heating. The results showed that sCO2 can effectively improve temperature uniformity along the heat sink in the presence of hotspots as compared to water. Considering a mass flow rate of 600 kg/(m2·s), the inhomogeneity index of the basal temperature of sCO2 is found to be 0.24, significantly lower than 4.22 for water. This indicates that sCO2 eliminates hot spots by rapidly increasing specific heat capacity near the pseudo-critical temperature. Furthermore, it is noted that maintaining the operating temperature of sCO2 near the pseudo-critical temperature can increase the specific heat capacity of the fluid in a short time, in addition to reducing the corresponding density and viscosity. Consequently, the entropy generation rate of sCO2 under ideal conditions is 46.6 % of that of water. Therefore, the proposed combination of a microchannel of complex structure and sCO2 in this study is demonstrated to effectively reduce the influence of hot spots and improve the overall thermal performance of heat sinks.

Transition to a weaker Sun: Changes in the solar atmosphere during the decay of the Modern Maximum

Context.The Sun experienced a period of unprecedented activity during the 20th century, now called the Modern Maximum (MM). The decay of the MM after its maximum in cycle 19 has changed the Sun, the heliosphere, and the planetary environments in many ways. However, studies disagree on whether this decay has proceeded synchronously in different solar parameters or not.Aims.One of the related key issues is if the relation between two long parameters of solar activity, the sunspot number and the solar 10.7 cm radio flux, has remained the same during this decay. A recent study argues that there is an inhomogeneity in the 10.7 cm radio flux in 1980, which leads to a step-like jump (“1980 jump”) in this relation. If true, this result would reduce the versatility of possible long-term studies of the Sun during the MM. Here we aim to show that the relation between sunspot number and 10.7 cm radio flux does indeed vary in time, not due to an inhomogeneous radio flux but due to physical changes in the solar atmosphere.Methods.We used radio flux measurements made in Japan at four different wavelengths, and studied their long-term relation with the sunspot number and the 10.7 cm radio flux during the decay of MM. We also used two other solar parameters, the MgII index and the number of solar active regions, in order to study the nature of the observed long-term changes in more detail.Results.We find that the 1980 jump is only the first of a series of 1–2-year “humps” that mainly occur during solar maxima. All five radio fluxes depict an increasing trend with respect to the sunspot number from the 1970s to 2010s. These results exclude the interpretation of the 1980 jump as an inhomogeneity in the 10.7 cm flux, and reestablish the 10.7 cm flux as a homogeneous measure of solar activity. The fluxes of the longer radio waves are found to increase with respect to the shorter waves, which suggests a long-term change in the solar radio spectrum. We also find that the MgII index of solar UV irradiance and the number of active regions also increased with respect to the sunspot number, further verifying the difference in the long-term evolution in chromospheric and photospheric parameters.Conclusions.Our results provide evidence for important structural changes in solar magnetic fields and the solar atmosphere during the decay of the MM, which have not been reliably documented so far. We also emphasize that the changing relation between the different (e.g., photospheric and chromospheric) solar parameters should be taken into account when using the sunspot number or any single parameter in long-term studies of solar activity.

Particle Flow Distribution in a Fluidized-Particles Multitube Solar Receiver

A fluidized-particles two-tube solar receiver was tested at ambient temperature at PROMES Laboratory to investigate the influence of an inhomogeneous solar flux density on the particle mass flow rate between the tubes. The principle of this 3rd generation solar receiver is to fluidize the particles in a container, called dispenser, in which the tubes’ bottom are immersed. The fluidized particles are flowing upward the tubes by applying an overpressure in the dispenser. Air velocities are changed inside the tubes, thanks to air mass flow controllers, to represent temperature heterogeneity between the tubes. Air velocities from 0.05 up to 0.52 m/s were tested, both in homogeneous and heterogeneous conditions. In the heterogeneous ones, the differences in air velocity between the tubes aim to mimic a difference in temperature from 20 to 100 % with homogeneous air flow rates injected. The following conclusions were drawn. First, the particle mass flux in the tubes are the same with homogeneous air velocities, each one following a calibration map previously obtained. Second, different air velocities lead to different particle mass flux. Third, the rise of the total particle mass flux diminishes the pressure in the dispenser. Four, this diminution of pressure leads to a decrease of the particle mass flow rate of the tube with the lower air velocity. This influence can lead in some cases to the stop of the fluidized bed circulation in the affected tube.

Biopolymer-Based Protective Layer for Stable and Highly Reversible Zinc Metal Anodes

Zinc (Zn) metal has attracted considerable attention because of its natural abundance and stability in aqueous environments compared with lithium/sodium metal anodes. Moreover, Zn metal as anode showed a high theoretical capacity (820 mAh g−1), high energy per volume (5855 mA cm−3), and low operational potential (–0.78 V vs SHE) in electrochemical systems. However, Zn metal suffers from dendrite growth and poor plating/stripping reversibility, resulting from inhomogeneous Zn ion flux and contamination by generally used glass fiber membranes (GFs) as separators. Although studies to inhibit dendritic Zn growth have been conducted, dendritic Zn remains still a major problem during long-term cycling under practical rate and capacity conditions. In this context, it is essential to investigate Zn deposition behavior from initial nucleation to Zn growth morphologies after long-term cycling.Among the problematic factors pointed out by researchers, the irregular pore distribution of GFs causes uneven Zn ion flux. Moreover, the detached fibers after cycling contaminate the Zn anode surface, resulting in nonuniform Zn deposition and trapping of Zn metal in the separator. To stabilize Zn metal anodes, introducing a protective layer can be an effective strategy to construct ion channels with abundant functional groups for high affinity with Zn metaland protect from direct contact with GFs. Organic polymers are suitable candidates for construction of protective layer which tolerates the volume changes of Zn metal and exhibit good chemical compatibility with Zn metal.Polysaccharides are favorable for use as gel polymers, separators, and binders owing to their cost-effectiveness and good electrochemical properties. Besides, they contain various oxygen-containing groups, resulting in relatively high ionic conductivity. However, it is not sufficient to fabricate membranes for the stabilization of Zn metal using polysaccharide alone because of insufficient ion conductive properties. This problem can be solved by blending polymers with high ionic conductivities such as poly(ethylene oxide) (PEO), poly(vinylidene difluoride), and poly(vinyl chloride). Notably, PEO has mainly been used in gel polymer electrolytes. The hydroxyl groups of PEO can facilitate the transport of metal ions and ether linkages can enhance the affinity with cations, resulting high ionic conductivity.In this study, we designed a functional protective layer by blending polysaccharide and PEO and investigated Zn deposition behavior from the formation of initial nucleation to Zn growth process after long-term cycling. The protective layer, fabricated by a one-pot method, featured highly dispersed blending polymers by phase separation and contained uniformly distributed oxygen-containing functional groups. Moreover, we demonstrated that the protective layer induced the formation of regular Zn nucleation sites and smooth Zn deposition after long-term cycling under the realistic conditions required for high-energy metal battery systems. Using the Zn||Cu and Zn||Zn cells stabilized by the protective layer under low capacity (0.1 mAh cm−2), we confirmed that homogeneous initial Zn deposition patterns were induced by ex situ SEM images of Cu and Zn electrodes. Subsequently, smooth and dense Zn growth was confirmed under fast Zn plating/stripping conditions, indicating that protective layer can induce basal plane (002) dominant deposition to mitigate dendrite formation and protect physically and chemically from GFs.Based on the morphological Zn deposition behavior, we successfully fabricated a functional protective layer and significantly enhanced the electrochemical performance of Zn metal battery systems. The Zn||Cu cells with a functional protective layer showed significantly increased long-term cycling above 3850 cycles (more than 160 days) at high rate and capacity condition (2 mA cm−2 and 1 mAh cm−2). In addition, the durability of protective layer was confirmed by a high-rate test (at 10 mA cm−2). These results are consistent with those of the Zn||Zn symmetric cell tests under harsh conditions of 5 mA cm−2 and 5 mAh cm−2. Furthermore, full cell with the protective layer using vanadium disulfides as the cathode exhibited enhanced cyclability over 1000 cycles with 87 % capacity retention compared to the bare full cell that short-circuited at the 340th cycle.Our work demonstrated that there are two important factors affecting the durability of Zn anodes: (i) Zn metal surface should be protected by a smooth and dense layer with high affinity to Zn metal and ions and (ii) physical and chemical contamination from GFs. Figure 1

Conjugate heat transfer of a turbulent tube flow of water and GaInSn with azimuthally inhomogeneous heat flux

An experimental study of the conjugate heat transfer in a turbulent tube flow with azimuthally homogeneous and inhomogeneous heat flux distribution, where the tube is heated with a constant heat flux only over the half circumference, is presented. Using two fluids with clearly different Prandtl numbers (water and a liquid metal alloy), thermohydraulic effects that occur when fluids with very low Prandtl number are used in contrast to ordinary fluids (e.g. water with Pr≈1) are discussed. The test section is validated with water (Pr=5−7.4) for a Reynolds number in the range of 5·103<Re<4.2·104. The experimental data agree excellently with literature data. The maximum nondimensional temperature at the inner surface of the tube is expressed using a simple relationship based on the efficiency of a fin with an adiabatic tip. A near eutectic alloy of gallium, indium and tin (GaInSn, Pr=0.03) is used for the liquid metal experiments. The Péclet number is varied within the range of 240<Pe<3·103. Based on the experimental data of this work, an adapted correlation for the Nusselt number in a turbulent liquid metal tube flow with azimuthally homogeneous heat flux is provided:Nu=4.364+0.0276·Pe0.803The experimental data underlines, that the azimuthally averaged Nusselt number for an azimuthally inhomogeneous heat flux distribution can also be calculated with this correlation with an acceptable level of accuracy. Remarkably, the ratio of the local convective heat transfer coefficient to the azimuthally averaged value for GaInSn reaches a value up to 0.6 at the location of the maximum wall temperature. This is in strong contrast to water, where this ratio is close to unity.

Performance analysis of a nanofluid spectral splitting concentrating PV/T system with triangular receiver based on MCRT-FVM coupled method

Optimizing system structure is one promising way to enhance the spectral beam splitting concentrating photovoltaic/thermal (SBS CPV/T) system performance. In this study, a linear Fresnel CPV/T system incorporated with triangular cooling duct and Ag@SiO2/ethylene glycol (EG) nanofluid filter is designed to enhance the overall performance of the system. To quantitatively reflect the heat generation of Ag@SiO2/EG nanofluid filter and silicon PV modules under inhomogeneous solar flux distributions, a coupled method combining Monte Carlo ray tracing (MCRT) method with Finite Volume Method (FVM) is employed. After validating the coupled method, the performance of the system with triangular receiver is discussed under various operating conditions. The results demonstrate that the nanofluid outlet temperature and PV module temperature present 316.3 K and 306.8 K at nanofluid inlet temperature of 298 K, respectively. The high mass flow rate and low inlet temperature allow high thermal and total efficiencies, while they present slight effect on electrical efficiency. To quantify the achievable enhancements with the triangular receiver, a SBS CPV/T system with flat-plate receiver is also discussed. It is found that the total efficiency of the triangular receiver is higher than that of the flat-plate receiver, with a maximum enhancement of 7.9%.

The role of applied potential on particle sizing precision in single-entity blocking electrochemistry

Blocking electrochemistry, a subfield of single-entity electrochemistry, enables in-situ sizing of redox-inactive particles. This method exploits the adsorptive impact of individual insulating particles on a microelectrode, which decreases the electrochemically active surface area of the electrode. Against the background of an electroactive redox reaction in solution, each individual impacting particle results in a discrete current drop, with the magnitude of the drop corresponding to the size of the blocking particle. One significant limitation of this technique is “edge effects”, resulting from the inhomogeneous flux of the redox species’ diffusion due to increased mass transport to the edge of the disk electrode surface. “Edge effects” cause increased errors in size detection, resulting in poor analytical precision. Here, we use computational simulations to demonstrate that inhomogeneous diffusional edge flux of quasi-reversible redox species is mitigated at lowered overpotentials. This phenomenon is further illustrated experimentally by lowering the applied potential such that the system is operating under a kinetically-controlled regime instead of a diffusion-limited regime, which mitigates edge effects and increases particle sizing precision significantly. In addition, we found this method to be generalizable, as the precision enhancement is not limited to geometrically spherical particles but also occurs for cubic particles. This work presents a simple, novel methodology for edge effect mitigation with general applicability across different particle types.

Interpretation of the North‐South Asymmetric Oxygen Aurora Morphology on Europa Using Test Particle Simulation

AbstractSeveral observations using the Hubble Space Telescope reported that the brightness morphology of the oxygen OI] 135.6 nm emissions on Europa's atmosphere has a north‐south asymmetry which changes with the position of Europa with respect to the Jovian magnetospheric plasma sheet. Similar north‐south asymmetry of Io's auroral limb glow has been explained by higher electron flux into the atmosphere on the hemisphere that faces the plasma sheet center. This explanation, however, has not yet been evaluated for the case of Europa quantitatively. In this study, we used a test particle simulation for the Jovian magnetospheric electrons to estimate the brightness of the 135.6 nm aurora in Europa's atmosphere and evaluate the cause of the north‐south asymmetry with the previously suggested idea, in which the strong deceleration of the magnetospheric flux tube results in the inhomogeneous electron flux into Europa's atmosphere (the “slow‐down effect”). Our simulation successfully recreates the systematically changing north‐south asymmetry of Europa's oxygen aurora brightness using the “slow‐down effect.” With deceleration into 10% of the background plasma flow, the maximum north‐to‐south brightness ratio is estimated at 2.17 and 2.56 on the trailing (plasma‐upstream) and leading (downstream) side, respectively. However, the previously observed brightness ratio is larger on the trailing side (up to ∼5). The results indicate that additional model scenarios are required to fully explain the north‐south asymmetry of Europa's oxygen aurora morphology.

Numerical investigation on the thermal load heterogeneity of multi-assembly helical coil steam generator in high temperature gas-cooled reactor

The thermal load heterogeneity will lead to inhomogeneous local heat flux and thermal stress, extremely detrimental to the operational stability of heat exchangers with multi-assembly structure. In this paper, a full-scale analysis method for the helical coil steam generator in industry was developed and implemented. The validation was performed against flow boiling heat transfer experiment of helical tube. The simulation of single assembly and full-scale helical coil steam generator in high temperature gas-cooled reactor was performed, and the distributions of thermal-hydraulic parameters in heat exchange region were obtained. The results show that the nonuniform helium flow distribution with the inhomogeneous factor Dm value of 34.83% has a significant influence on the heat transfer characteristics. The peak heat transfer power of central assembly increases by 33.76% against design condition, introducing large thermal load heterogeneity with the inhomogeneous factor Dp value of 30.45%, even threating the structural integrity of helical tube in long-term operation circumstances. The structural elements design in the superior compartment should be optimized to increase the helium mass flow rate of the assemblies below the nozzle and behind the helium baffle, improving flow distribution uniformity and reducing the peak value of local heat flux and thermal stress.

Edge effects on the electromagnetic response of inhomogeneous type-II superconductors

From a macroscopic point of view, the edges of a type II superconductor are degraded non-homogeneous regions compared with the bulk of the sample. This paper presents numerical simulations of a long superconducting bar with square cross section subjected to an axial external magnetic field, the edges effect on its electromagnetic properties is studied. The edges of the sample are modeled as finite width regions with lower critical current density than the rest of the material. The simulations are based on a continuum electrodynamics model which describes the magnetic induction dynamics of partially penetrated states. Unlike a simpler homogeneous superconductor, in an inhomogeneous material rough flux fronts are formed. It was established that the stochastic profile of the current density produces jets of magnetic flux near a macrodefect.

Designing Anti‐Swelling Nanocellulose Separators with Stable and Fast Ion Transport Channels for Efficient Aqueous Zinc‐Ion Batteries

AbstractSeparators swelling in aqueous electrolytes can cause inhomogeneous ion flux and unregulated dendrite propagation, yet the corresponding phenomenon and mitigation strategy are rarely studied. This article deals with the issue of pore structure variation caused by separator swelling in aqueous zinc‐ion batteries (AZBs) by employing nanocellulose separator as a representative example. A multifunctional separator composed of Zr4+‐hydrolysate‐coated nanocellulose (Zr‐CNF) is developed by in situ hydrolysis of Zr4+, which demonstrates excellent swelling resistance, pore‐structure stability, and percolating porosity due to cross‐linking and hydrogen bond shielding effect. Consequently, the homogeneous Zn‐ion flux, high ionic conductivity, and Zn2+ transfer number are maintained upon cycling. Moreover, the amorphous ZrO containing coating induces a homogeneous directional electric field around the interface, accelerating the Zn2+ influx, reducing the nucleation overpotential, and promoting homogeneous nucleation for Zn deposition. The Zr‐CNF separator enable dendrite‐free Zn anode with high Coulombic efficiency (99.7%) and exceptional cyclability for 680 h under 5 mA cm−2/5 mAh cm−2. The feasibility of the Zr‐CNF separator is verified in PANI/V2O5‐based AZBs and activated carbon‐based Zn‐ion capacitors. This study provides a facile approach to address separator swelling issue, enlightening novel insights into the efficient and sustainable aqueous battery technologies in the future.

Hybrid thermal and optical modeling of a solar air heater with a non-flat plate absorber

In this study, we developed a model based on a SAH. We can enhance air turbulence by creating a non-flat plate on a SAH absorber using a ratio of (e/H = 6), thereby increasing the solar collector’s convective heat transfer coefficient, Nusselt number, and thermal performance. A validation experiment was conducted to determine the accuracy of the developed model. Ray tracing and FEM simulation techniques were used to analyze the optical and thermal properties of the system simultaneously. Various operational and structural conditions were applied to analyze the system’s thermal performance under inhomogeneous heat flux on the absorber’s surface. The data demonstrate that non-flat plate surfaces contribute to wall-induced turbulence, which affects air temperatures. Outcomes demonstrate that mass flow rate excessively affects thermal efficiency, useful energy, and outlet temperatures. Thus, when the inlet air flow rate increases from 0.02 to 0.06 kg/s, the average hot air temperature at the SAC outlet during the daytime reduces from 55.6 to 47.82 °C, applicable heat energy increase from 646.5 to 970 W, and the average thermal efficiency increased from 28.8 to 54.7 %. Instantaneous non-flat absorber plates increased average thermal efficiency and heat transfer coefficient (h) to 9.10 and 27.24 % compared with flat plate absorbers (e/H = 1) at the same mass flow rate (0.05 kg/s). The highest Nusselt number increase observed during the day is 141.5% for non-flat plate compared to flat plates.

Topology Optimization Method of a Cavity Receiver and Built-In Net-Based Flow Channels for a Solar Parabolic Dish Collector.

The design of a thermal cavity receiver and the arrangement of the fluid flow layout within it are critical in the construction of solar parabolic dish collectors, involving the prediction of the thermal-fluid physical field of the receiver and optimization design. However, the thermal-fluid analysis coupled with a heat loss model of the receiver is a non-linear and computationally intensive solving process that incurs high computational costs in the optimization procedure. To address this, we implement a net-based thermal-fluid model that incorporates heat loss analysis to describe the receiver's flow and heat transfer processes, reducing computational costs. The physical field results of the net-based thermal-fluid model are compared with those of the numerical simulation, enabling us to verify the accuracy of the established thermal-fluid model. Additionally, based on the developed thermal-fluid model, a topology optimization method that employs a genetic algorithm (GA) is developed to design the cavity receiver and its built-in net-based flow channels. Using the established optimization method, single-objective and multi-objective optimization experiments are conducted under inhomogeneous heat flux conditions, with objectives including maximizing temperature uniformity and thermal efficiency, as well as minimizing the pressure drop. The results reveal varying topological characteristics for different optimization objectives. In comparison with the reference design (spiral channel) under the same conditions, the multi-objective optimization results exhibit superior comprehensive performance.

Experimental study on heat transfer performance of high temperature heat pipe with large length-diameter ratio for heat utilization of concentrated solar energy

• A conceptual model of dish concentrated solar receiver based on finned high temperature heat pipe (HTHP) is designed. • A batch of HTHPs with large length to diameter ratio and excellent performance were prepared. • The frozen start-up, steady heat transfer and consecutive operation performance of the HTHP with large length to diameter ratio are studied theoretically and experimentally. • A finned HTHP with excellent performance is prepared, and its enhanced heat transfer capacity was verified by experiment. Solar receiver, as the core device of the dish concentrated solar thermal power generation system, is becoming a research focus and has attracted much attention. High temperature heat pipe, which works by following the principle of vapor–liquid circulation, has the ability to flatten the temperature of the hot spot, and maintain excellent heat transfer performance with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density; Through the structural design, the compressed air flows outside of the high temperature heat pipe, and thus, compared with flowing in the pipe, the heat transfer coefficient is increased and the flow resistance is reduced. In view of the above advantages, we designed a dish concentrated solar receiver with finned high temperature heat pipe as the core heat transfer device, prepared a high temperature heat pipe with a large length-diameter ratio, and conducted a quantitative performance study comprehensively and systematically. The present study verified the safety and stability of the high temperature heat pipe with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density, theoretically analyzed the process of frozen start-up and heat transfer limits of high temperature heat pipe, explored the reasonable frozen start-up mode, carried out the parameter optimization and consecutive long-time operation stability test, and quantitatively verified the enhanced heat transfer capacity of finned high temperature heat pipe through the experiment. The results show that the HTHP prepared by the same process can operate safely and stably with the illumination of concentrated facula at the average energy flux density of 2.3 × 10 6 W/m 2 , and maintain a high temperature above 700 ℃ as well as excellent temperature uniformity, which fully verifies the feasibility and superiority of HTHP as the core heat transfer device of the dish concentrated solar receiver. In addition, these results can provide quantitative experimental data and theoretical reference for the design and development of the dish concentrated solar receiver.

Complexity analysis of charged dynamical dissipative cylindrical structure in modified gravity

This article focuses on the formulation of some scalar factors which are uniquely expressed in terms of matter variables for dynamical charged dissipative cylindrical geometry in a standard gravity model \(\mathcal {R}+\Phi \mathcal {Q}\) (\(\Phi \) is the coupling parameter, \(\mathcal {Q}=\mathcal {R}_{\varphi \vartheta }\mathcal {T}^{\varphi \vartheta }\)) and calculates four scalars by orthogonally decomposing the Riemann tensor. We find that only \(\mathcal {Y}_{TF}\) involves inhomogeneous energy density, heat flux, charge and pressure anisotropy coupled with modified corrections, and thus call it as complexity factor for the considered distribution. Two evolutionary modes are discussed to study the dynamics of cylinder. We then take the homologous condition with \(\mathcal {Y}_{TF}=0\) to calculate unknown metric potentials in the absence as well as presence of heat dissipation. The stability criterion of the later condition is also checked throughout the evolution by applying some constraints. We conclude that the effects of charge and modified theory yield more complex system.

Ultra-Low Concentration Electrolyte Enabling LiF-Rich SEI and Dense Plating/Stripping Processes for Lithium Metal Batteries.

The interface structure of the electrode is closely related to the electrochemical performance of lithium‐metal batteries (LMBs). In particular, a high‐quality solid electrode interface (SEI) and uniform, dense lithium plating/stripping processes play a key role in achieving stable LMBs. Herein, a LiF‐rich SEI and a uniform and dense plating/stripping process of the electrolyte by reducing the electrolyte concentration without changing the solvation structure, thereby avoiding the high cost and poor wetting properties of high‐concentration electrolytes are achieved. The ultra‐low concentration electrolyte with an unchanged Li+ solvation structure can restrain the inhomogeneous diffusion flux of Li+, thereby achieving more uniform lithium deposition and stripping processes while maintaining a LiF‐rich SEI. The LiIICu battery with this electrolyte exhibits enhanced cycling stability for 1000 cycles with a coulombic efficiency of 99% at 1 mA cm–2 and 1 mAh cm–2. For the LiIILiFePO4 pouch cell, the capacity retention values at 0.5 and 1 C are 98.6% and 91.4%, respectively. This study offers a new perspective for the commercial application of low‐cost electrolytes with ultra‐low concentrations and high concentration effects.

Complexity of a dynamical dissipative cylindrical system in non-minimally coupled theory

This paper aims to formulate certain scalar factors associated with the matter variables for a self-gravitating non-static cylindrical geometry by considering a standard model R+ζQ of f(R,T,Q) gravity, where Q=RφϑTφϑ and ζ is the arbitrary coupling parameter. We split the Riemann tensor orthogonally to calculate four scalars and deduce YTF as a complexity factor for the fluid configuration. This scalar incorporates the influence of the inhomogeneous energy density, heat flux and pressure anisotropy along with correction terms for the modified gravity. We discuss the dynamics of the cylinder by considering the two simplest modes of structural evolution. We then take YTF=0 with a homologous condition to determine the solution for the dissipative as well as non-dissipative scenarios. Finally, we discuss the criterion under which the complexity-free condition shows stable behavior throughout the evolution. It is concluded that the complex functional of this theory results in a more complex structure.

Comparison of quasi-geostrophic, hybrid and 3-D models of planetary core convection

SUMMARY We present investigations of rapidly rotating convection in a thick spherical shell geometry relevant to planetary cores, comparing results from quasi-geostrophic (QG), 3-D and hybrid QG-3D models. The 170 reported calculations span Ekman numbers, Ek, between 10−4 and 10−10, Rayleigh numbers, Ra, between 2 and 150 times supercritical and Prandtl numbers, Pr, between 10 and 10−2. The default boundary conditions are no-slip at both the ICB and the CMB for the velocity field, with fixed temperatures at the ICB and the CMB. Cases driven by both homogeneous and inhomogeneous CMB heat flux patterns are also explored, the latter including lateral variations, as measured by Q*, the peak-to-peak amplitude of the pattern divided by its mean, taking values up to 5. The QG model is based on the open-source pizza code. We extend this in a hybrid approach to include the temperature field on a 3-D grid. In general, we find convection is dominated by zonal jets at mid-depths in the shell, with thermal Rossby waves prominent close to the outer boundary when the driving is weaker. For the thick spherical shell geometry studied here the hybrid method is best suited for studying convection at modest forcing, $Ra \le 10 \, Ra_c$ when Pr = 1, and departs from the 3-D model results at higher Ra, displaying systematically lower heat transport characterized by lower Nusselt and Reynolds numbers. We find that the lack of equatorially-antisymmetric motions and z-correlations between temperature and velocity in the buoyancy force contributes to the weaker flows in the hybrid formulation. On the other hand, the QG models yield broadly similar results to the 3-D models, for the specific aspect ratio and range of Rayleigh numbers explored here. We cannot point to major disagreements between these two data sets at Pr ≥ 0.1, with the QG model effectively more strongly driven than the hybrid case due to its cylindrically averaged thermal boundary conditions. When Pr is decreased, the range of agreement between the hybrid and 3-D models expands, for example up to $Ra \le 15 \, Ra_c$ at Pr = 0.1, indicating the hybrid method may be better suited to study convection in the low Pr regime. We thus observe a transition between two regimes: (i) at Pr ≥ 0.1 the QG and 3-D models agree in the studied range of Ra/Rac while the hybrid model fails when $Ra\gt 15\, Ra_c$ and (ii) at Pr = 0.01 the QG and 3-D models disagree for $Ra\gt 10\, Ra_c$ while the hybrid and 3-D models agree fairly well up to $Ra \sim 20\, Ra_c$. Models that include laterally varying heat flux at the outer boundary reproduce regional convection patterns that compare well with those found in similarly forced 3-D models. Previously proposed scaling laws for rapidly rotating convection are tested; our simulations are overall well described by a triple balance between Coriolis, inertia and Archimedean forces with the length-scale of the convection following the diffusion-free Rhines-scaling. The magnitude of Pr affects the number and the size of the jets with larger structures obtained at lower Pr. Higher velocities and lower heat transport are seen on decreasing Pr with the scaling behaviour of the convective velocity displaying a strong dependence on Pr. This study is an intermediate step towards a hybrid model of core convection also including 3-D magnetic effects.