Longitudinal Heat Research Articles

Use of lithium capillary structures in Ohmic discharges of T-10 Tokamak

The results of experiments at the T-10 tokamak using lithium capillary-porous structures are presented. It is shown that lithium sputtering under conditions of graphite diaphragms can significantly reduce deuterium recycling and the level of impurities in the plasma. At the same time, recycling increases significantly five discharges after the start of the day of the experiment, and the effect of reducing the level of impurities persists for 150—300 discharges. The results of using a capillary-porous structure with lithium filling as a movable rail diaphragm in the T-10 configuration with tungsten main diaphragms are presented. The introduction of a lithium diaphragm into the SOL region makes it possible to reduce recycling and obtain discharges with an effective plasma charge approaching unity. In this case, the effect increases as the lithium sputtered in the chamber is accumulated. It is shown experimentally that a capillary-porous structure with lithium filling can be used as a main diaphragm with longitudinal plasma heat fluxes up to 3.6 MW/m2. However, a necessary condition is the complete impregnation of the porous structure with lithium and the prevention of extrusion of lithium into the discharge as a result of the interaction of the current flowing to the diaphragm with the toroidal magnetic field. Experiments have shown that to obtain discharges with a small lithium admixture, a strong gas injection of deuterium or impurity is required to reduce the temperature of the plasma periphery and effective cooling of the diaphragm below 450 Å°C. Otherwise, the diaphragm transfers into a strong evaporation mode with high lithium flows, which lead to a significant increase in the lithium concentration in the plasma. Strong evaporation reduces the heat inflow and stabilizes the diaphragm temperature.

Effects of external static electrical field on thermal and electrical conductivity in the Al-Cu, Al-Ni, and Al-Si eutectic alloys

This study aims to investigate the effects of external positive and negative static electric fields (E+ and E- respectively) on thermal conductivity (K) and electrical conductivity (σ) in Al-33 wt. % Cu, Al-6.4 wt. % Ni and Al-12 wt. % Si eutectic alloys. For this purpose, the solidifications of Al-Cu, Al-Ni, and Al-Si eutectic alloys were directionally done under E+ and E-. The directions of E were chosen to be parallel (E+) and antiparallel (E-) to the solid-liquid (S-L) growth direction and the magnitudes of E were approximately (+10) and (−10) kV cm−1 and (+16) and (-16) kV cm−1 for the Al-Cu, Al-Ni, and Al-Si eutectic alloys, respectively. The effects of E+ and E− on the K and σ were determined by the longitudinal heat flow and the four-point probe methods, respectively. While the K and σ values decreased with increasing temperature, the K and σ were increased and decreased with E+ and E−, respectively.

Anisotropic ZrO2 porous ceramic constructed using bacterial cellulose nanofiber framework for extreme insulation environment

Zirconium oxide (ZrO2) porous ceramic shows promising application in construction and industry due to its remarkable chemical stability, corrosion resistance, oxidation resistance, and thermal resistance. While the construction of stable anisotropic ZrO2 porous ceramic is still a challenge. In this study, we report an anisotropic ZrO2 porous ceramic using bacterial cellulose nanofiber (BCNF) as a framework and zirconium oxychloride octahydrate as the zirconium source. ZrO2 porous ceramic was achieved through directional freezing, vacuum freeze-drying, and calcination processes. ZrO2 arrangement relies on the BCNF framework and retains the three-dimensional (3D) structure after the calcination of BCNF. Results reveal that the resulting ZrO2 porous ceramic possesses a well-ordered anisotropic network structure, exhibiting excellent stability at 1100 °C in air. Benefiting from the anisotropic structure, ZrO2 porous ceramic exhibits high load-bearing capacity in the longitudinal direction, and thermal insulation with a significant temperature difference of approximately 50 °C between transverse and longitudinal heat transfer. It also keeps stable in extreme conditions including low temperature and acid solution. These unique properties make it an ideal insulation material in extreme environments where the protection of structures with complex shapes and variable dimensions is critical.

Activation energy, Rotational and Hall current Effects of Magnetohydrodynamic 3D flow of Non-Newtonian Hybrid Nanofluid over a Stretched Plate

Nanofluids are of great importance to researchers as they have significant uses industrially due to their high heat transfer rates. Recently, a new class of nanofluid, ‘‘hybrid nanofluid” is being used to further enhance the heat transfer rate. This new model in 3D is employed to examine the impact of activation energy, Rotational and hall current on a Non-newtonian hybrid Fe3O4/Al2O3 nanofluid flow over-stretched plate. Using similarity transformations, the controlling partial differential equations are turned into a set of nonlinear ordinary differential equations. For that system of equations, the shooting method is used to generate numerical solutions. The impact of various entry parameters on transversal and longitudinal velocities, temperature, heat flow and surface shear stress are studied numerically and graphically. A good correlation between the earlier studies is obtained in specific cases showing the convergence criteria of the present procedure. Further, the physical significance of the contributive parameters is presented through graphs and tables. The observation shows that the particle concentration for the hybrid nanofluid augments the fluid velocity. Moreover, the inclusion of dissipative heat favors enhancing the fluid temperature for the involvement of the particle concentration.

Large transverse thermoelectric effect induced by the mixed-dimensionality of Fermi surfaces

Transverse thermoelectric effect, the conversion of longitudinal heat current into transverse electric current, or vice versa, offers a promising energy harvesting technology. Materials with axis-dependent conduction polarity, known as p × n-type conductors or goniopolar materials, are potential candidate, because the non-zero transverse elements of thermopower tensor appear under rotational operation, though the availability is highly limited. Here, we report that a ternary metal LaPt2B with unique crystal structure exhibits axis-dependent thermopower polarity, which is driven by mixed-dimensional Fermi surfaces consisting of quasi-one-dimensional hole sheet with out-of-plane velocity and quasi-two-dimensional electron sheets with in-plane velocity. The ideal mixed-dimensional conductor LaPt2B exhibits an extremely large transverse Peltier conductivity up to ∣αyx∣ = 130 A K−1 m−1, and its transverse thermoelectric performance surpasses those of topological magnets utilizing the anomalous Nernst effect. These results thus manifest the mixed-dimensionality as a key property for efficient transverse thermoelectric conversion.

A multidimensional examination of phase separation in single-component fluids

A thermodynamic instability in a homogeneous fluid can lead to spontaneous formation of distinct domains within the fluid. This process involves not only the spatial redistribution of fluid density but also transient exchanges of pressure, temperature, and energy. However, classical theoretical frameworks, such as the Ginzburg–Landau and Cahn–Hilliard models, lack incorporation of these essential thermodynamic aspects. To investigate the dynamics of multiple physical fields during phase separation, we numerically solve a two-dimensional van der Waals fluid model. Thermodynamic consistency is demonstrated by verifying the coexistence curve. While the equilibrium pressure remains similar across the unstable region of the isotherm, we demonstrate that the energy in the system depends on the initial density. Although the majority of energy is stored as heat at typical values of the heat capacity, high-density domains contain less specific energy compared to their low-density counterparts due to interparticle attraction. Consequently, the transition of low-density domains into high-density through the process of coalescence releases excess energy, which redistributes in the form of longitudinal waves and heat. We also highlight the role of parameters, such as heat capacity and thermal conductivity, in less intuitive phenomena, including elevated temperature fluctuations and memory preservation.

Use of Lithium Capillary Structures in Ohmic Discharges of T-10 Tokamak

The results of experiments at the T-10 tokamak using lithium capillary-porous structures are presented. It is shown that lithium sputtering under conditions of graphite diaphragms can significantly reduce deuterium recycling and the level of impurities in the plasma. At the same time, recycling increases significantly five discharges after the start of the day of the experiment, and the effect of reducing the level of impurities persists for 150–300 discharges. The results of using a capillary-porous structure with lithium filling as a movable rail diaphragm in the T-10 configuration with tungsten main diaphragms are presented. The introduction of a lithium diaphragm into the SOL region makes it possible to reduce recycling and obtain discharges with an effective plasma charge approaching unity. In this case, the effect increases as the lithium sputtered in the chamber is accumulated. It is shown experimentally that a capillary-porous structure with lithium filling can be used as a main diaphragm with longitudinal plasma heat fluxes up to 3.6 MW/m2. However, a necessary condition is the complete impregnation of the porous structure with lithium and the prevention of extrusion of lithium into the discharge as a result of the interaction of the current flowing to the diaphragm with the toroidal magnetic field. Experiments have shown that to obtain discharges with a small lithium admixture, a strong gas injection of deuterium or impurity is required to reduce the temperature of the plasma periphery and effective cooling of the diaphragm below 450°C. Otherwise, the diaphragm transfers into a strong evaporation mode with high lithium flows, which lead to a significant increase in the lithium concentration in the plasma. Strong evaporation reduces the heat inflow and stabilizes the diaphragm temperature.

A comprehensive investigation of porous media’s effects on the performance of photovoltaic thermal systems

Porous media in thermal collectors have been found to enhance the performance of photovoltaic thermal systems. However, there is a lack of comprehensive research on the benefits of using porous media in this context. This paper represents the first comprehensive study comparing various types of porous materials and their effects on system performance. The study employs a three-dimensional simulation to analyze the influence of factors such as material type, porosity, permeability, and thermal conductivity on module efficiency in top, middle, and fully filled configurations. In particular, it has been observed that each material has an optimum porosity, and there is little difference among metal foams, ceramic foams, and ordinary materials, such as aluminum and copper screens. Among the different configurations, the middle configuration had the lowest thermal efficiency improvement (∼17 %), the top configuration increased efficiency by ∼7 %, and the full porous configuration had the highest thermal efficiency improvement, 32 %. Materials with very low conductivity, such as wood, perform better in the middle than in the top configuration. Graphite, despite its high thermal conductivity, has low permeability, which leads to lower thermal efficiency compared to that of most other materials in the top configuration. In the full configuration and particularly in the middle configuration, graphite shows the smallest thermal efficiency improvement due to its significant longitudinal conduction heat transfer. Therefore, in these configurations, graphite is not recommended for use as a porous medium. Regarding added mass, metal foam materials add the most mass to the system, followed by ceramic foam materials, which present considerably lower figures. In all cases, the pump power consumption growth is negligible compared to the photovoltaic power output. In all materials and configurations, there was a small improvement in electrical efficiency, reaching 1.25 % in the full porous configuration. From a holistic perspective, this study showed that porous media can improve the overall equivalent power by up to 9.8 %, compared to a smooth channel.

Modeling of Integrated Hollow-Fiber Solar-Powered VMD Modules for Desalination for a Better Understanding and Management of Heat Flows.

The direct integration of membrane distillation and solar energy collection in a single module is a promising technology for autonomous seawater desalination in remote regions; however, the modeling and design of such modules are challenging because of the coupling of the radial and longitudinal heat and mass transfers. In a previous study, we provided as a first modeling approach a hollow fiber solar collector vacuum membrane distillation (VMD) module, considering a constant temperature at the shell side and a pure water feed. Here, a full model is developed to describe the coupled effects of the solar collector and a hollow fiber VMD module operating in an outside/in mode with saline water. The model considers all the main phenomena (membrane distillation, temperature and concentration polarization, absorption of solar radiation and energy balances over the solar collector, radial and longitudinal heat and mass transfer, seawater properties, and more than 30 variables). Applied to simulate the behavior of a semi-industrial-scale module, it allows the influence of solar radiation on the performance/limits of the integrated module to be discussed based on the radial and longitudinal profiles and heat flows. The model can be used to identify key points in the module design to better utilize solar radiation and manage heat flows.

Design and Analysis of a Cooling System for the REBCO Coil Based on GM/JT Cycle

High‐field magnets have been used in a wide range of scientific and industrial areas. REBCO (REBa2Cu3Ox, where RE = Rare Earth) coated superconductors (CCs) have been gaining increasing interest due to the potentialities of using them in high‐field magnets. However, the thermal stability of the REBCO CCs coils is limited by longitudinal heat conduction inside the coils and bubbles generated by evaporating helium. So as to enhance the heat transfer in REBCO coil, a cooling system based on GM/JT cycle was designed. In this paper, the design, thermodynamic calculation, and analysis of the cooling system for the REBCO coil are provided systematically. It is found that when the mass flow rate is 0.75 g/s at a pressure of 10 bar, the cooling capacity of the system is up to 10.16 W. Meanwhile, the inlet pressure and counterflow heat exchangers efficiency are key factors for significantly improving the cooling capacity of the system. An open loop experiment also has been carried out and the cooling capacity of 0.79 W at 4.5 K is obtained finally when He mass flow rate is 0.1 g/s. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Study of the thermal conductivity of natural carbonates

The thermal conductivity of natural monoliths of calcite, dolomite marble, and limestone from various deposits was measured using the absolute stationary method of longitudinal heat flow in the temperature range of 50–300 K and the dynamic method in the range of 323–573 K. A majority of calcite marbles were inferior in thermal conductivity to dolomite marbles. At room temperature, the thermal conductivity coefficients of all studied samples were lower k = 5 W/(m K). The obtained data were compared with the literature data. The diversity of experimental data from different authors on the thermal conductivity of carbonates is associated with qualitative differences in the samples studied

Study on the efficient heat transfer mechanism of microchannel pin-fin arrays under low pumping power

The efficient heat transfer with low pressure loss has long been a critical challenge in the microchannel heat sinks (MCHS) design. Further study is required for the quantitative analysis of the longitudinal vortex heat transfer enhancement mechanism. In this research, a microchannel heat transfer experiment and corresponding simulations are conducted. Based on the common Reynolds number range in engineering applications of MCHS, the underlying causes of heat transfer enhancement and pressure loss increase in MCHS with respect to Reynolds numbers is clarified. The results show that when the Reynolds number is 400, the cylindrical wake reduces the synergistic angle between the velocity and the temperature gradient at the streamwise gap, which greatly enhances the heat transfer performance of MCHS. In addition, when the Reynolds number is 900, the early separation of the cylindrical wake vortex leads to a significant reflux near the center of the spanwise gap, which significantly increases the pressure loss. A Different Reynolds number Efficiency Evaluation Criterion (DEEC) is proposed for evaluating the performance of MCHS. It is found that the flow state of cylindrical wake with Reynolds number of 400 has the best heat transfer efficiency. The concept of introducing longitudinal vortices into the pin–fin array can serve as a key guideline in the heat transfer enhancement optimization design of MCHS.

Horizontal flame spread behavior of densified wood: Effect of structural characteristics

Densified wood (DW) is a recently developed material with excellent mechanical properties, considered as an ideal construction material for high-rise timber buildings. However, its flame spread behavior has not been well understood limiting its applications. This work for the first time experimentally and analytically investigates the horizontal flame spread behavior of DW. The influences of material structural characteristics (e.g. density) on heat transfer characteristics are focused. Thermally thin DW with density ranges of 441–1025 kg/m3 and a constant thickness of 2 mm were tested. The flame spread rate, mass loss rate (MLR) and flame height decreased with the increased wood density. A power-law correlation between the dimensionless MLR and dimensionless density is proposed, which well predicts the experiments with an R2 of 0.922. The increased wood density decreases flame height and reduces flame radiation. The gas-phase heat transfer shifts from radiation-dominant to convection-dominant. The longitudinal and radial thermal conductivities of DW increased with wood density. Empirical equations are optimized to predict the thermal conductivities of DW with R2 of 0.870 (longitudinal) and 0.837 (radial). The preheating zone length and the temperature gradient per unit length don’t vary significantly with wood density. Their values are averaged to 25.62 mm and 9.312 K/mm respectively. The longitudinal heat conduction is increased with the wood density due to the increased conductivity. However, this conduction increase is lower than the radiation decrease as the wood density increases. Thus, the total heat flux is slightly decreased with the wood density. The gas phase heat transfer dominates the flame spread. However, the longitudinal heat conduction can account for more than half of the gaseous heat transfer, and thus cannot be negligible. Results of this work improve the understanding of DW flame spread, which helps to evaluate the fire behaviors of timber construction.

Porifera-Inspired Lightweight, Thin, Wrinkle-Resistance, and Multifunctional MXene Foam.

Transition metal carbides/nitrides (MXenes) demonstrate a massive potential in constructing lightweight, multifunctional wearable electromagnetic interference (EMI) shields for application in various fields. Nevertheless, it remains challenging to develop a facile, scalable approach to prepare the MXene-based macrostructures characterized by low density, low thickness, high mechanical flexibility, and high EMI SE at the same time. Herein, the ultrathin MXene/reduced graphene oxide (rGO)/Ag foams with a porifera-inspired hierarchically porous microstructure are prepared by combining Zn2+ diffusion induction and hard template methods. The hierarchical porosity, which includes a mesoporous skeleton and a microporous MXene network within the skeleton, not only exerts a regulatory effect on stress distribution during compression, making the foams rubber-like resistant to wrinkling but also provides more channels for multiple reflections of electromagnetic waves. Due to the interaction between Ag nanosheets, MXene/rGO, and porous structure, it is possible to produce an outstanding EMI shielding performance with the specific surface shielding effectiveness reaching 109152.4dBcm2 g-1 . Furthermore, the foams exhibit multifunctionalities, such as transverse Joule heating, longitudinal heat insulation, self-cleaning, fire resistance, and motion detection. These discoveries open up a novel pathway for the development of lightweight MXene-based materials with considerable application potential in wearable electromagnetic anti-interference devices.

Effects of Hall Current and Activation Energy on a Three-Dimensional Rotating Casson Hybrid Nanofluid Flow over a Stretched Plate in the Presence of Joule Heating and Nonlinear Thermal Radiation

Nanofluids are of great importance to researchers as they have significant uses industrially due to their high heat transfer rates. Recently, a new class of nanofluid, ‘‘hybrid nanofluid” is being used to further enhance the heat transfer rate. This new model in 3D is employed to examine the impact of magnetic field, joule heating, rotation parameter, Hall current, with nonlinear thermal radiation, on a rotating hybrid Fe3O4/Al2O3 nanofluid over-stretched plate in the presence of chemical reaction is the focus of this research. Using similarity transformations, the controlling partial differential equations are turned into a set of nonlinear ordinary differential equations. For that system of equations, the shooting method is used to generate numerical solutions. The impact of various entry parameters on transversal and longitudinal velocities, temperature, heat flow and surface shear stress are studied numerically and graphically. A good correlation between the earlier studies is obtained in specific cases showing the convergence criteria of the present procedure. Further, the physical significance of the contributive parameters is presented through graphs and tables. The observation shows that the particle concentration for the hybrid nanofluid augments the fluid velocity. Moreover, the inclusion of dissipative heat favors enhancing the fluid temperature for the involvement of the particle concentration.

Modeling-based investigation on the contribution of radial heating into integrated VMD hollow-fiber modules at different scales for autonomous desalination

Integrating solar energy with vacuum membrane distillation (VMD) is a promising means to provide fresh water in remote areas. Our previous work on integrated solar VMD modules focused on optimizing flat-sheet integrated modules; this study examines the feasibility of up-scaling VMD modules containing outside/in hollow fibers with an external module surface collecting solar heat (HF-SC-VMD). Such modules have been experimented with at the lab scale; however, additional information is required concerning the parameters governing the productivity in such modules at the industrial scale, notably concerning the impacts and limits induced by radial heating. We contribute to this goal by estimating the temperature profiles and the maximal permeate production achievable for an HF-SC-VMD module at a semi-industrial scale in the case of the more favorable heating conditions provided via solar radiation, where the maximum temperature acceptable for the constituent materials of the module is assumed to be the temperature reached by the feed close to the shell wall (Twall). A two-dimensional shell-side model is developed to describe the coupled radial and longitudinal heat and mass transfers accounting for temperature polarization while considering module design parameters and operating conditions for future optimization. The model properly describes the experimental VMD performances (without radial heating) with and without temperature polarization. The influence of Twall on the permeate flux and temperature profiles is examined to discuss the effect of radial heating. The specified semi-industrial-scale HF-SC-VMD module (2.1 m2) could produce 37.8 L/h of drinkable water (covering the daily needs of ~150 people) if the full module design (including the solar collector) allows Twall to reach 70 °C, confirming the interest of continuing research toward optimizing a full HF-SC-VMD module.

Multilayered mullite ceramics with anisotropic properties

Anisotropic layered porous ceramics are crucial to satisfy the demand for devices with directional functions. However, challenges, such as complicated preparation processes and difficulties in regulating the oriented structure, severely limit their application. Here, multilayered mullite ceramics (MLMCs) with specific porosities and strongly anisotropy properties, were prepared by designing porous thin-layered units and an interlayer layout, in combination with a simple gel-casting. Benefiting from the suitable slurry properties, the samples did not show obvious defects, and a perfect bonding was observed between the layers. The optimized MLMCs exhibited a porosity of 65.12%, the differences in compressive and flexural strengths of 14 (±0.7) and 5 (±0.2) MPa in different pressure directions respectively, and the anisotropy factor of thermal conductivity up to 0.98, as well as exhibited good high temperature thermal insulation properties. Ultimately, the MLMCs formed transverse heat conductor and longitudinal heat insulation heat-transfer patterns, with promising applications in thermal insulation.

Experimental evaluation and real-time forecast of smoke propagation in tunnels under intervention of sub-critical longitudinal ventilation

Sub-critical longitudinal ventilation can restrict the back-layering length in the upstream region and maintain suitable smoke stratification in the downstream region of a tunnel fire. In this study, experiments using a 1/15 scale, 80-m long, 1.2-m wide, and 0.5-m high model tunnel were conducted to investigate the effects of sub-critical longitudinal ventilation velocity and heat release rate (HRR) on the key parameters describing smoke propagation. The smoke front temperature near the fire source decreased significantly as the longitudinal ventilation velocity increased. The longitudinal ventilation velocity and HRR were incorporated into a regression model describing the smoke front velocity, which was applied to the evaluated fire scenarios using an ensemble Kalman filter to account for intervention of sub-critical longitudinal ventilation. The smoke front temperatures at discrete locations were assimilated to estimate the heat exchange correction coefficient and air entrainment ratio of smoke front in real-time and dynamically correct the forecasted smoke front temperature and velocity accordingly. When sub-critical longitudinal ventilation intervened, the smoke front parameters could be forecasted with a maximum lead time of 60 s and an average error within 5%. Therefore, the proposed forecasting method can inform the selection of disposal measures in early tunnel fire emergencies.

Hall current and thermal radiation effects of 3D rotating hybrid nanofluid reactive flow via stretched plate with internal heat absorption

The present analysis deals with the impact of a magnetic field, joule heating, rotation parameter, and Hall current, as well as nonlinear thermal radiation, on a rotating hybrid Fe3O4/Al2O3 nanofluid over-stretched plate in the presence of a chemical reaction with thermophoresis and a Brownian motion parameter. The primary focus of this research is on the Brownian motion parameter. Similar transformations are used to translate the governing partial differential equations into a set of nonlinear ordinary differential equations. The shooting technique obtains numerical solutions for that system of equations. The impact of various entry parameters on transversal and longitudinal velocities, temperature, heat flow and surface shear stress are studied numerically and graphically. It was shown that there is a strong connection between the primary research when looking at particular situations that indicate how the current technique meets the convergence requirements. In addition, the physical relevance of the contributed parameters is shown via graphs and tables. The discovery demonstrates that an increase in the particle concentration of the hybrid nanofluid accelerates the flow of the fluid. In addition, factoring in dissipative heat makes it more likely that the fluid temperature will be increased to accommodate the participation of the particle concentration.

Retracted: Development of Intelligent CAD Technology for New Longitudinal Shell-Side Heat Exchange Equipment

Retracted: Development of Intelligent CAD Technology for New Longitudinal Shell-Side Heat Exchange Equipment