Heat Flux Direction Research Articles

Thermal Rectification in Telescopic Nanowires: Impact of Thermal Boundary Resistance.

A thermal diode, which, by analogy to its electrical counterpart, rectifies heat current, is the building block for thermal circuits. To realize a thermal diode, we demonstrate thermal rectification in a GaAs telescopic nanowire system using the thermal bridge method. We measured a preferred direction of heat flux, achieving rectification values ranging from 2 to 8% as a function of applied thermal bias. We demonstrate that the thermal boundary resistance between the thin part with the wurtzite crystal phase and the thick part with the zinc-blende crystal phase of the telescopic nanowire plays a crucial role in determining the amount and direction of heat flux rectification. This effect is confirmed by numerical solutions of the one-dimensional heat equation based on ab initio data. Additionally, we accounted for the effect of the thermal contact resistance. This work is the first experimental indication of rectification using a telescopic nanowire where we reveal the importance and role of the thermal boundary resistance in determining thermal rectification.

Pore-scale numerical studies on determination of the effective thermal conductivity of the fluid saturated porous media

Accurate prediction of the effective thermal conductivity (ETC) of a fluid saturated rock is crucial for fulfilling efficient geo-energy harvest practices. In this paper, the ETCs of a rock with 23% porosity and 2.7 W/m·K thermal conductivity when saturated with various fluids, including water, oil, hydrogen gas, and air, are numerically investigated. Advanced digital rock technique is employed to reconstruct the complex solid-pore structure in the rock, and CFD simulations are performed to assess the ETCs, focusing on the influence of fluid type and heat flux direction. The results show the maximum ETC values of 2.10 W/m·K for water-saturated rocks, in contrast to the minimum values of 1.3 W/m·K for air-saturated samples. When the internal fluid possesses a higher thermal conductivity than air, the ETCs of the fluid-saturated rock display minimal anisotropy, while significant anisotropy is observed in the air filling rock sample. The methodology is validated based on satisfactory agreements between the numerical ETC results and the Geometric Mean model predictions in the water saturated rock case. Due to the fact that the commonly used empirical correlations produce significant deviations when applying to low thermal conductivity fluids, a new ETC model that achieves less than 8% deviation for all studied fluid types is proposed based on the numerical results. This study provides pore-scale insights into fluid flow and thermal conduction behavior within fluid-saturated porous media.

A new method for temperature field characterization of microsystems based on transient thermal simulation

Microsystems face challenges such as high heat flux density and localized hot spots in the temperature field, significantly impacting their thermal reliability. Accurately and comprehensively characterizing the temperature field is a challenging problem in current research. We present a general high-order finite difference (GHOFD) algorithm for the high-accuracy numerical solution of the two-dimensional transient heat conduction equations (THCEs). The 10th-order GHOFD algorithm is accurate up to 10−7 °C. Secondly, we present a viable approach for characterizing microsystems' steady-state and transient heat conduction mechanisms. We introduce two new characterization parameters: the gradient modulus and the heat flux direction factor (HFDF). The gradient modulus can more clearly characterize the magnitude of the gradient vector and quantitatively analyze the spatial position of the temperature field change in the microsystem. The HFDF can dynamically display the heat conduction process in the temperature field. Finally, using temperature field simulation and microsystem characterization, we have validated the effectiveness of the proposed method and new parameters.

Process optimization and microstructure of Ti3Zr1.5NbVAl0.25 high entropy alloy produced by directed energy deposition

As an emerging materials preparation method, directed energy deposition (DED) has its unique advantages in the preparation of high entropy alloys (HEAs). However, improper process parameters can lead to numerous defects, affecting material properties. In this study, a Ti3Zr1.5NbVAl0.25 HEA was produced by DED. The effects of process parameters on single track cladding layer (STCL) were studied by response surface methodology (RSM), and the parameters were optimized accordingly. It is indicated that the microstructure of the STCL is composed of columnar and equiaxed crystals and the grain growth is parallel to the heat flux direction. 〈001〉//BD (building direction), 〈111〉//SD (scanning direction) and {100}〈001〉 textures were observed in molten pool. The microhardness of the molten pool measures 299.99 HV0.2, while the estimated Young's modulus and yield stress are 87.66 GPa and 945 MPa, respectively. This work provides unique insights into optimizing the DED process parameters of HEAs, further obtaining the solidification microstructure and mechanical properties of STCL.

Chemical heterogeneity size effects at nanoscale on interface thermal resistance of solid–liquid polymer interface via molecular dynamics simulations

The shrinking size of integrated chips poses thermal management challenges. Understanding the size effect of chemical heterogeneity on solid–liquid interfacial thermal transfer is essential for heterogeneous chip design, yet the underlying mechanisms remain lacking. The present work used the liquid n-alkanes as the thermal interface material between solid platinum substrates. To characterize chemical heterogeneity, periodic solid surface patterns composed of patches with alternating solid–liquid affinities were constructed. By using non-equilibrium molecular dynamics simulations, we investigated the size effect of chemically heterogeneous patterns on interfacial thermal resistance (ITR) at the nanoscale. At larger heterogeneity sizes, i.e., larger patch sizes, most alkane molecules directly in contact weak interaction patches cannot interact with strong interaction patches due to long atomic distances. In the case of alkanes in contact a cold substrate, alkanes in contact weak interaction patches transferred thermal energy to the substrate at a lower rate than those in contact strong interaction patches. The different rates resulted in the higher temperature of alkanes in contact weak interaction patches than those in contact strong interaction patches and, therefore, a larger disparity between temperature jump at the strong interaction areas and that at the weak interaction areas. The non-uniformity of temperature jump distribution increased ITR when compared to the heterogeneous surface system characterized by a smaller patch size with a more uniform temperature distribution in the plane perpendicular to the heat flux direction. In addition, the classical parallel thermal resistance model predicted ITR accurately for the heterogeneous surface systems with small size patches but overestimated overall thermal resistance.

Investigating combined effects of varying gravity and heat flux direction on the melting dynamics of phase change material in space

The present work investigates the combined effect of varying gravity and heat flux direction with respect to gravity on the melting dynamics of Phase Change Material. Similar conditions are relevant to applications in space, at different space infrastructures, such as orbiting satellites, as well as various extraterrestrial surface assets, landers, and rovers. The numerical simulations are performed to study the melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 and Stefan number Ste ≈ 0.33 inside a differentially heated square enclosure. The mathematical model employs a control volume-based enthalpy porosity approach to simulate the melting process inside enclosure. The direction of the incoming heat flux relative to the gravity vector is defined in terms of an orientation angle, which is varying circularly with a step of 45°, whereas the gravity level is ranging from the terrestrial surface value g to 0.2g to analyze the melting process over a wide range of Rayleigh number 100 ≤ Ra ≤ 107. The study provides a detailed insight into the attributes of heat transfer, flow dynamics, and energy storage, along with a quantitative analysis of the transition between various melting regimes and temporal fluctuations in the performance parameters. The findings demonstrate that the mutual orientation between the directions of incoming heat flux and gravity, as well as the value of the latter, significantly affect features of the convective motion in the liquid phase, as well as the entire thermally driven heat transfer within the domain. In particular, for the oppositely directed gravity and heat flux, the melted fluid closely resembles Rayleigh-Bénard convection with the presence of multicellular flow structures, while at other orientation angles, except for a co-directed gravity and heat flux case, a circular convective motion of the melted fluid takes place. The results of numerical simulations reveal declining melting rates as the mutual orientation of gravity and heat flux changes from opposite to co-directed and vice versa. The low gravity conditions delay the onset of convection-driven melting, reducing the melting rate significantly.

Flow boiling heat transfer performance of R245fa in a vertical enhanced evaporator tube with sintering and electroplating composite coats

The R245fa flow boiling performance was investigated in a vertical evaporator tube of which inner wall surface is coated by a composite sintering and electroplating technology. The effects of vapor quality, heat flux, mass flux, and flow direction were compared and analyzed in the bare tube (BT) and the sintering and electroplating treated tube (SET). The results showed that the heat transfer coefficient increased and then decreased with the rise of vapor quality and heat flux. The heat transfer performance in downward flow was better than that in upward flow, while an opposite trend was observed for frictional pressure drop. With the increased of vapor quality, the frictional pressure drop increased and then decreased, but it monotonically increased with the increasing mass flux. The heat transfer enhancement mechanism was explored through flow pattern visualization. The annular flow pattern conversion line of SET was earlier than that of BT. Due to the strong wettability of SET, the thickness of liquid film was thinner in downward and the mother bubble was bigger in upward, which had a positive effect on flow boiling heat transfer. The maximum the heat transfer enhancement factor (EF) and the performance evaluation parameter (PEC) were 1.83 and 1.75, respectively.

Cooperative near- and far-field thermal management via diffusive superimposed dipoles

Active metadevices with external excitations exhibit significant potential for advanced heat regulation. Nonetheless, conventional inputs, like heating/cooling and introducing convection by rotating plate, display inherent limitations. One is the only focus on far-field control to eliminate temperature distortion in the background while neglecting near-field regulation in the functional region. Another is lacking adaptability due to complex devices like thermoelectric modules and stepping motors. To tackle these challenges, the concept of diffusive superimposed dipoles characterized by orthogonal thermal dipole moments is proposed. Cooperative near- and far-field regulation of temperature fields is achieved by designing superimposed dipole moments, enabling transparency, and cloaking functionalities with isotropic and homogeneous materials. Simulation and experiment outcomes affirm the efficacy of this adaptive thermal field control technique, even when interface thermal resistance is taken into account. Adaptivity stems from dipole moment decomposability, allowing metadevices to operate in various heat flux directions (0°–360°) and background thermal conductivity. These findings could pave the way for cooperative and adaptive thermal management and hold potential applications in other Laplace fields, including direct current and hydrodynamics.

Comparative Analysis for Titanium alloy and Silicon Nitride (Si3N4) of Thermal Analysis for Deep Groove Ball Bearing

In this paper, the analysis of the directional heat flux and total heat flux for the bearing balls of Titanium alloy and Silicon Nitride has been demonstrated across a temperature range between 150 to 250 degree celcius. The obtained data allowed comparing the values of total heat flux and various directional heat flux. By comparing directional and total flux of heat in materials it enables the choice of the best-suited material creating bearings with regard to the performance needed. The use of the findings of the current comparison is to ensure efficiency and durability in particular operations. The data presented in the paper helped to analyze the patterns of heat distribution and see the differences between the materials and results a better material for ball bearing. Titanium alloy has excellent mechanical properties like mechanical strength and corrosion resistance. Silicon Nitride is characterized by thermal stability and high thermal resistance and also has excellent wear properties. Thus, using the results of the analysis allows choosing the material for bearing production for high-velocity and high-load operation based on a profound comparison to select the right material. The choice of right material will allow for a more efficient and durable bearing in an industrial setting.

Synergizing ANSYS Simulations and Machine Learning for Transient Thermal Analysis in Aluminium Alloys

Time-dependent thermal analysis plays a pivotal role in the manufacturing industry as it greatly influences the overall performance of the final product. This study delves into transient thermal analysis of an aluminum alloy concerning both temperature and time. Employing ANSYS, a finite element-based software, an axisymmetric model is constructed. This model encompasses a mold made of sand and a pattern filled with aluminum alloy. The analysis focuses on temperatures ranging from 650 to 1050°C, examining the temperature changes in the mold and pattern after 1500 seconds, primarily due to the convection process. Parameters like heat flux and directional heat flux are also determined. Subsequently, machine learning models are utilized to interpret the data acquired from ANSYS, enabling the extension of the results to a broader temperature range of 1150 to 1550°C. This study is instrumental in facilitating the effective design of transient thermal analysis for various alloys at different temperatures.

Experimental Investigation on Thermal Properties of Al2024 Alloy by Friction Stir Welding

Friction stir welding (FSW) connects the parts without melting the metal and produces a plasticized zone of metal. The main objective of this paper is to examine the temperature distribution that results from friction stir-lap welding of Al2024 alloy at varying rotating speeds and feed rates. Temperature distribution, heat flow, directional heat flux, thermal stresses, and strain energy are analyzed at different speeds of 700, 1000rpm, and at feed rate of 20 mm/min and 40 mm/min. Comparing the experimental temperatures with the simulated temperatures an error of 0.6% has been observed which is negligible. By comparing the numerical values of heat flux to the simulated values, the maximum error found to be 5.8% for the similar lap Al 2024-T3 joint. Temperature and heat flux values are gradually decreased from nugget zone to thermo-mechanical zone. But when compared to the nugget zone with the thermo-mechanical zone, the values of thermal stress and strain energy were abnormally altered.

The modeling of meso-structure of fiber/particle composites and its influence on ETC under different inner pressure: A comprehensive study by RNMG-LBM

Fiber/Particle composites (FPCs) have garnered increasing attention as promising insulation materials in the energy field. Establishing a suitable composite model that can be used to investigate each component is essential. In this paper, the random non-contact multi-phase generation (RNMG) method was proposed for generating the meso-structure of FPCs. Furthermore, a comprehensive investigation was conducted using the Lattice Boltzmann Method (LBM) to quantify the influence mechanisms of various physical parameters, including inner pressure, aspect ratio, and particle diameter, as well as orientation angle, on the effective thermal conductivity (ETC) of FPCs. The validity of the RNMG-LBM was examined by comparing its results with experimental data. The simulation results demonstrated that reducing the particle diameters from 5 nm to 2 nm in FPCs leads to decreased pore sizes. Consequently, this reduces the sensitivity of FPCs to pressure fluctuations in the range of 10−1 Pa–105 Pa. Moreover, a physical parameter, called the orientation angle, was introduced to describe and explore the relationship between heat flux orientation and fiber orientation. The findings revealed that when the fiber was oriented perpendicular to the heat flux direction, it exhibited the lowest ETC among the orientation angles ranging from 0° to 90°. In addition, both the diameter and aspect ratio of fiber impacted its thermal properties. It's suggested controlling the aspect ratio below 20 and reducing fiber diameter as much as possible will significantly decrease the ETC of FPCs. The conclusions are valuable for optimizing the manufacturing process of FPCs and further improving their insulation capacity.

Modeling of the heterogeneous hypergolic ignition with particle packing model

The ignition process of a hypergolic hybrid rocket fuel presents a significant challenge due to its complex and interconnected nature. However, understanding its underlying physics is crucial for accurately estimating the delay time and ignition performance. In this study, we employed an approximate analytical method to directly address the transient conduction problem with nonlinear surface heat generation. By using the Arrhenius equation and considering dual heat flux directions in both the liquid and solid domains, we propose a model for determining the delay time of heterogeneous hypergolic ignition. Our solution is straightforward and computationally efficient. Notably, when subjected to identical initial conditions and property settings, our results exhibit similarity with the solutions derived from other models. Moreover, we advance our approach by developing a particle packing model through the utilization of a well-established algorithm. By simulating the particle arrangement within the pellet, the surface layer properties and the thermal time constant of certain fuel designs can be modeled. This simulation serves the purpose of incorporating the particle size effect of the fuel pellet into our ignition model. The results generated by our heterogeneous hypergolic ignition model, in conjunction with the particle packing model, demonstrated impressive agreement with the experimental data derived from droplet tests. Novelty and significance statementThis study utilized a novel solving method to address a transient conduction problem with non-linear heat generation on the surface during a heterogeneous hypergolic ignition process. The study successfully derived an analytical solution, providing a simpler method for calculating ignition delay times. A scenario involving different initial temperatures was also examined. Additionally, the research integrated particle packing model data and thermal time constants to assess the effect of particle size. The model results were in agreement with the experimental data, confirming its accuracy and offering a reliable method for estimating the heterogeneous hypergolic ignition delay time.

The Thermal Conductivity Coefficient of a Square Thermal Invisibility Cloak Cell and Its Application in Periodic Plate

In this paper, the thermal conductivities of the square thermal invisibility cloak are constructed in two ways. One is the direct method, another is the rotation matrix method. The thermal conductivity coefficients obtained by the two methods are the same. The cloud map of thermal conductivity coefficient of the thermal cloak is drawn, which can help us understand more intuitively how the thermal invisibility cloak works. Besides, to manipulate heat flow in a larger area, the cloaks are arranged periodically by introducing the position parameters into the calculation of the thermal conductivity coefficient of the thermal invisibility cloak. The heat insulation function of both the single thermal cloak and the thermal cloak periodic plate are tested under different heat boundary conditions using COMSOL Multiphysics. For different heat boundary conditions, heat flux direction of the simulation result is given. The results show that both the single thermal cloak and the thermal cloak periodic plate have the function of avoiding heat flow under different heat boundary conditions. The heat fluxes travel around the inner domain with good thermal stealth effect.

Comparative analysis of material for flat & dome top piston for SI engine using ansys

Compared to other areas of the IC engine, the working condition of piston attracts the most attention rather than any part in IC engine due to its complexity. Pistons have undergone many significant material and topographic changes since their first industrial introduction to overcome these working conditions. It is being said that electric vehicles will take over the world, but until the Lithium-ion battery remains, there will always be a shortage for batteries. Taking this as an assumption and the fact that carbon neutral fuel is currently in development, our goal is to make the piston lighter and more durable to make it future ready. In this research article, our objective is to substantiate and analyze the stress distribution of the piston with various [1] piston crown designs, namely, [1] flat top and dome top; integrated with various synthetic and alloy materials, namely, Titanium alloy, [2] Aluminum alloy, [3] Super magnesium, and [4] 3D Graphene. [5] Static Structural and Steady state thermal analysis is performed on these pistons using ANSYS R2 2022 software, while designing is performed on AutoCAD 2020 software. This article presents and analyses [5] thermal stress analysis and damages due to pressure application. Results are displayed comparing based on [5,6,7] total deformation, Von-mises strain, Von-mises stress, strain energy, normal elastic strain, normal stress, total heat flux and directional heat flux. Result is concluded by comparing to find the most preferable material for the piston in an engine. The preference is given based upon weight reduction, strength, and future scope of the material.

Identifying some regularities of the heat transfer in the welded joint of SUS304 pipe using a numerical approach

In this study, an investigation into the impact of heat transmission in the welded junction of SUS304 pipe has been carried out with the use of a numerical method. An investigation was carried out by employing ANSYS’s static structural tools in conjunction with the software package’s thermal transient analysis. Based on the heat flow on the welding point, where the temperature reaches 507 °C within 200 mm of the end of the welded pipe, an examination into the efficiency of heat transfer has been carried out. This analysis was based on the heat flow on the welding point. As the total heat flux approaches 7.02e6 W∙m–2, studies have been conducted on the topic. There have been three types of directional heat flux measurements made (X, Y, and Z), with the numerical findings indicating that the X direction produces the most variable heat flow readings. These checks were performed in a variety of settings. These were chosen as the correct paths to go since they led directly to the source of the warmth. whereas the Z-axis permits the minimum amount of heat flow throughout the board. The damaged area identified on the trees that were still standing was factored into the calculation. To calculate the amount of residual stress, the Von Mises stress was applied repeatedly during the whole procedure. This tactic ended up being employed. Due to the tension caused by the pipe’s increased bending radius, the piece of pipe located 200 mm from the pipe’s distal end is the most vulnerable. The value was calculated to be 2.49e6 Pa when the temperature was increased to 500 °C.

Study on the competition effects between thermal conductivity and viscosity of graphene reinforced octadecane phase change material

In this study, a combination of microscale molecular dynamics (MD)-based and macroscale computational fluid dynamics (CFD)-based simulations are employed to investigate the effects of graphene with varying mass ratios on the thermal conductivity and viscosity of octadecane, revealing the nature of the competition effects of thermal conductivity and viscosity in the heat transfer process. The results show that graphene can significantly increase the average thermal conductivity of octadecane. But when its synergy angle in the direction of heat flux is close to 90°, the thermal conductivity of nanocomposite phase change materials (NCPCMs) is only 0.125 W·(m·K)−1, which is lower than that of pure octadecane by 18.83 %. The viscosity of NCPCMs decreased significantly with the decrease of graphene weight ratio and the increase of temperature, and the viscosity of NCPCMs with 9.15 wt% and 28.71 wt% at different temperatures was 812.65 % (max) and 313.75 % (min), respectively. Finally, the equilibrium point between the thermal conductivity and viscosity competition effects favors the viscosity side as the graphene mass ratio increases. Accordingly, natural convection became more crucial in the heat transfer process as the graphene mass ratio increased. Consequently, NCPCMs with the best heat transfer performance should possess a low graphene mass ratio, which results in a high Rayleigh number, providing them with high synergistic efficiency.

Drift current-induced tunable near-field energy transfer between twist magnetic Weyl semimetals and graphene.

Both the nonreciprocal surface modes in Weyl semimetal (WSM) with a large anomalous Hall effect and the nonreciprocal photon occupation number on a graphene surface induced by the drift current provide a promising way to manipulate the nonreciprocal near-field energy transfer. Interestingly, the interactions between nonreciprocities are highly important for research in (thermal) photonics but remain challenging. In this study, we theoretically investigated the near-field radiative heat flux transfer between a graphene heterostructure supported by a magnetic WSM and a twist-Weyl semimetal (T-WSM). The nonreciprocal surface mode could be changed by the separation space between two Weyl nodes and the twist angle. Notably, we found that in the absence of a temperature difference between two parallel plates, nonequilibrium fluctuations caused by drift currents led to the transfer of near-field radiative heat flux. Furthermore, these nonreciprocal surface modes interacted with the nonreciprocal photon occupation number in graphene to achieve flexible manipulation of the near-field heat flux size and direction. Additionally, graphene adjustable flux in the case of a temperature difference between the two plates was also discussed. Our scheme can provide a reference for near-field heat flux regulation in nonequilibrium systems.

Near-Field Thermal Splitter Based on Magneto-Optical Nanoparticles

Based on the many-body radiative heat transfer theory, we investigate a thermal splitter based on three magneto-optical InSb nanoparticles. The system comprises a source with adjustable parameters and two drains with fixed parameters. By leveraging the temperature and magnetic field dependence of the permittivity of InSb, the direction of heat flux in the system can be controlled by adjusting the magnetic field or temperature at the source. Under magnetic field control, the coupling between the separated modes, and the suppression of the zero-field mode induced by the magnetic field, are utilized to achieve a thermal splitting ratio within the modulation range of 0.15–0.58. Furthermore, temperature control results in a thermal splitting ratio ranging from 0.15 to 0.99, as a result of the suppression of the zero-field mode by the magnetic field and the blue shift effect of the zero-field mode frequency increasing with temperature. Notably, the gap distance between nanoparticles does not significantly affect the splitting ratio. These findings provide valuable theoretical guidance for utilizing magneto-optical nanoparticles as thermal splitters and lay the groundwork for implementing complex heat flux networks using InSb for energy collection and heat transfer control.

Experimental study on the combustion properties of four common engineered bamboo and wood composites

AbstractEngineered bamboo and wood composites are increasingly utilized in construction due to their eco‐friendly, low‐carbon footprint, and superior mechanical properties. To investigate the effect of heat flux and grain direction on the combustion properties of parallel strand bamboo (PSB), laminated veneer bamboo (LVB), cross‐laminated timber (CLT), and laminated veneer lumber (LVL), a total of 54 specimens in 3 groups were tested through a cone calorimeter. Parameters including the ignition time, heat release rate, mass loss rate, and smoke production rate were investigated. The analytic hierarchy process method was adopted for a multi‐level, qualitative, and quantitative comprehensive fire risk assessment of the corresponding structural materials. The test results reveal that PSB and LVB demonstrated superior performance to the CLT and LVL through the comparison of four combustion characteristics parameters, despite their drawbacks and virtues. The heat flux increases in inverse proportion to the ignition time. As for the heat release rate, the larger peak value is accompanied by an earlier appearance, along with the greater average mass loss rate and the lower smoke rate of engineered bamboo. The peak heat release rate of engineered bamboo composites parallel to the grain is larger than that perpendicular to the grain, whereas other parameters are not significantly influenced by the grain direction. Compared with engineered wood, engineered bamboo composites have the potential to be a safer and more reliable building material in terms of fire risk assessment.Highlights Cone calorimeter was used to analyze the combustion properties of materials. PSB, LVB, CLT, and LVL were studied considering different grain directions. Analytic hierarchy process method was adopted for a fire risk assessment. Engineered bamboo has the potential to be a reliable building material.