Heat Flux Direction Research Articles

Graphene/biphenylene heterostructure: Interfacial thermal conduction and thermal rectification

The allotrope of carbon, biphenylene, was prepared experimentally recently [Fan et al., Science 372, 852–856 (2021)]. In this Letter, we perform first-principles simulation to understand the bonding nature and structure stability of the possible in-plane heterostructure built by graphene and biphenylene. We found that the graphene–biphenylene in-plane heterostructure only exhibits along the armchair direction, which is connected together by strong covalent bonds and energetically stable. Then, the non-equilibrium molecular dynamics calculations are used to explore the interfacial thermal properties of the graphene/biphenylene heterostructure. It is found that the graphene/biphenylene in-plane heterostructure possesses an excellent interfacial thermal conductance of 2.84 × 109 W·K−1·m−2 at room temperature. Importantly, the interfacial thermal conductance presents different temperature dependence under opposite heat flux direction. This anomalous temperature dependence results in increased thermal rectification ratio with temperature about 40% at 350 K. This work provides comprehensive insight into the graphene–biphenylene heterostructure and suggests a route for designing a thermal rectifier with high efficiency.

Phonon focusing and anisotropy of drag thermopower in potassium thin films at low temperatures

We have investigated the influence of elastic energy anisotropy on the dependences of drag thermopower in potassium thin films on the orientation of the film planes, directions of heat flux, and their geometric parameters. It is shown that the drag thermopower in square-shaped potassium films with orientations {100} and {111} is isotropic in the film planes. Their anisotropy is determined by the orientation of the film plane. As for square-shaped films with {110} orientation, the drag thermopower dependences appear ellipsoidal, with a long axis that points towards the [100] direction. As the transverse parameters of potassium films with {100} and {111} orientations are increased, the drag thermopower anisotropy of the films in the [110] direction varies in a non-monotonic manner. This effect is due to the competition between the contributions of slow quasi-transverse modes and longitudinal phonons. The relaxation rate of the latter by electrons has proved to be 30 times higher than that for the slow mode. The drag thermopower and phonon mean free paths in potassium films with lengths much larger than their widths in the boundary scattering regime are found to become anisotropic. However, accounting for the electron–phonon relaxation leads to isotropization of these quantities in thin films with {100} and {111} film plane orientations, with the orientation anisotropy being retained. For long films with {110} orientation, the shape of the drag thermopower dependences remains ellipsoidal with a long axis along the [100] direction.

Steady state thermal analysis of debinding process used in metal fused filament fabrication (MF3)

ABSTRACT Metal fused filament fabrication (MF3) is a simple and cost-effective additive manufacturing method for generating three-dimensional (3D) metal-based products. In this study, three models were developed individually using a combination of metal and polymer materials with varying layer thicknesses in the radial direction. The specimen model has been developed with five layers where the consecutive layers were prepared with metal and polymer. Obviously, the thickness of the polymer layer increased in each model. The main objective of this work is to confirm the penetration of temperature from one layer to another when debinding through a metal and polymer interlayer stack. Furthermore, the temperature distribution, total heat flux and directional heat flux were investigated in relation to the polymer layer thickness. As a result, the model created with the polymer layer thickness obtained the largest range of temperature distribution (450.15°C), directional heat flux (6206.4 W/m2) and total heat flux (7845.6 W/m2). Thermal analysis clarified the various materials connecting along with the radial direction of the model in order to confront the debinding procedure for converting the model into a physical object. These findings were anticipated to aid in the fabrication of the actual 3D component utilising the MF3 technique in the future.

Experimental comparison of latent thermal energy storage units with different metal macro-additives

The inherent low thermal conductivity of phase change materials hinders the industry's deployment of practical latent heat storage systems. Adding macro-additives into PCMs is the most economical way to overcome this problem. This study experimentally compares three mid-temperature shell-and-tube LTES units with macro-additives of fins, copper foam, and shavings under the same conditions. The heat transfer mechanism of three macro-additives is investigated by analyzing the temperature evolution curves and comparing their structural characteristics. Experimental results show that the charging time of the fin unit is 68.4% shorter than the copper foam unit and 59.5% shorter than the copper shaving unit. Although the three heat storage units have the same compactness factor, the fin unit has the best thermal conduction performance for two reasons. One is that the local porosity of the fin unit decreases as the radius increases, achieving a higher effective thermal conductivity in the regions with a larger temperature gradient. The other is that the fins have a concentrated thermal energy flow pathway in the radial direction, which aligns the primary effective thermal conductivity direction with the heat flux direction. In addition, the larger pore size in the shaving unit is the main reason for its better performance than the foam unit.

STEADY STATE THERMAL ANALYSIS OF PERFORATED HONEYCOMBPLATE FIN HEAT SINKS USING ANSYS

Heat sink or heat exchanger is a passive cooling device used in electronic components to prolong their longevity, performance and reliability. All electronic components utilize current for the operational purposes and thus become prone to sharp increase in the temperature. The generated heat above the operating level becomes critical in-terms of failure component and hence, appropriate thermal management demands come into act. Finned or extended surface heat sinks are used to cool power electronic devices and components. The comparative results of plate-fin forms on the thermal performance of the heat-sink with inline arrangement is analyzed in this paper. Four forms of fins: Rectangular, One-side tapered, Inverted T section and I section with and without honeycomb perforations are designed on SOLIDWORKS® and analysed using ANSYS® software to identify a cooling solution for a CPU in terms of temperature and directional heat flux along x, y and z directions. The aluminium alloy 6063-T6 and natural graphite are selected as a base plate and fin materials respectively. The main objective of this paper is to contribute to this improving area of research by studying the effect of honeycomb perforations of plate fin heat sinks under natural convection using steady state thermal analysis at a constant heat flow of 20W and 40W in two different cases with air inlet temperature taken as 37.85° C. A total of 16 specimen were analysed. 8 specimen of plate fin heat sinks without perforations were compared with the rest 8 specimen with honeycomb perforations. It was evaluated from both the cases that inverted T sectional fin with perforations provided an improvement in thermal efficiency and better heat flux removal results among other plate fin profiles where as in terms of density and cost trade-offs one side perforated tapered fin outperformed other fins.

Experimental evaluation of thermal rectification in a ballistic nanobeam with asymmetric mass gradient

Practical applications of heat transport control with artificial metamaterials will heavily depend on the realization of thermal diodes/rectifiers, in which thermal conductivity depends on the heat flux direction. Whereas various macroscale implementations have been made experimentally, nanoscales realizations remain challenging and efficient rectification still requires a better fundamental understanding of heat carriers’ transport and nonlinear mechanisms. Here, we propose an experimental realization of a thermal rectifier based on two leads with asymmetric mass gradients separated by a ballistic spacer, as proposed in a recent numerical investigation, and measure its thermal properties electrically with the microbridge technique. We use a Si_{3}N_{4} nanobeam on which an asymmetric mass gradient has been engineered and demonstrate that in its current form, this structure does not allow for thermal rectification. We explain this by a combination of too weak asymmetry and non-linearities. Our experimental observations provide important information towards fabricating rigorous thermal rectifiers in the ballistic phonon transport regime, which are expected to open new possibilities for applications in thermal management and quantum thermal devices.

Effect of asymmetric cooling of sessile droplets on orientation of the freezing tip

HypothesisThe shape of the “freezing tip” formed by the crystallization of water droplets demonstrated remarkable universality - no dependence on the cooling rate and physico-chemical properties of the substrate has been observed. At the same time, the spatial orientation of the freezing cone may be varied. We hypothesized that the orientation of the freezing tip is determined by the direction of heat flux at the base of the sessile droplet. This direction is expected to be changed when the substrate with a low thermal diffusivity is not cooled uniformly. ExperimentsWe studied the freezing of water droplets placed on the inclined surface of wedges made from a variety of materials (polymers: Polymethylmethacrylate, Polytetrafluoroethylene, Polyurethane and metal: Titanium), which were cooled from below. The shape of the frozen droplets was controlled in situ. ComputationsThe computational model was suggested for the transient temperature field in the polymer wedge to determine a time variation of the local heat flux under the droplets. A comparison of numerical results and the measurements enabled us to confirm the aforementioned hypothesis relating the orientation of the freezing tips to the direction of the heat flux. FindingsIt was established that the orientation of the freezing cone axis depends on the location of the frozen droplet on the inclined surface of the wedge. Calculations of the transient temperature field of the wedge confirmed our hypothesis about the physical reason of the various spatial orientations of the freezing cones.

Development of explicit formulations of G45-based gas kinetic scheme for simulation of continuum and rarefied flows.

In this work, the explicit formulations of the Grad's distribution function for the 45 moments (G45)-based gas kinetic scheme (GKS) are presented. Similar to the G13 function-based gas kinetic scheme (G13-GKS), G45-GKS simulates flows from the continuum regime to the rarefied regime by solving the macroscopic governing equations based on the conservation laws, which are widely used in conventional Navier-Stokes solver. These macroscopic governing equations are discretized by the finite volume method, where the numerical fluxes are evaluated by the local solution to the Boltzmann equation. The initial distribution function is reconstructed by the G45 distribution function, which is a higher order truncation of the Hermite expansion of distribution function compared with the G13 distribution function. Such high order truncation of Hermite expansion helps the present solver to achieve a better accuracy than G13-GKS. Moreover, the reconstruction of distribution function makes the development of explicit formulations of numerical fluxes feasible, and the evolution of the distribution function, which is the main reason why the discrete velocity method is expensive, is avoided. Several numerical experiments are performed to examine the accuracy of G45-GKS. Results show that the accuracy of the present solver for almost all flow problems is much better than G13-GKS. Moreover, some typical rarefied effects, such as the direction of heat flux without temperature gradients and thermal creep flow, can be well captured by the present solver.

Design of an omnidirectional camouflage device with anisotropic confocal elliptic geometry in thermal-electric field

SummaryThe designed confocal elliptical core-shell structure can realize the omnidirectional camouflage effect without disturbing temperature and electric potential profiles as the directions of heat flux and electric current change. Based on the anisotropy of the confocal ellipse, the anisotropic effective parameters of the confocal elliptical core-shell structure are derived under different heat flux and electric current launching. Then, the matrix material should be anisotropic as the effective parameters to satisfy the omnidirectional camouflage effect, which is demonstrated numerically. In addition, we present a composite structure to realize the anisotropic matrix. The experimental results show that the camouflage device embedded in the composite structure can eliminate the scattering caused by the elliptical core under different directions of heat flux and electric current, thus achieving the omnidirectional thermal-electric camouflage effect experimentally. The omnidirectional camouflage effect in thermal and electric fields can greatly widen the application fields of this device with anisotropic geometry.

Path-dependent bifunctional device in thermal-electric field

Janus metamaterial refers to a kind of artificial device that can exhibit different functions along different paths. Compared with the existing metamaterial only possessing the single omnidirectional or unidirectional function, we propose a path-dependent bifunctional device in a thermal-electric field, which can present two distinct thermal and electric behaviors (concentrating and cloaking) under different directions of heat flux and electric current. We theoretically derive the anisotropic material parameters of the ideal Janus device to achieve the path-dependent functionalities based on the successive transformation method. Then, in order to realize the engineering applications of the Janus device, the effective medium theory is employed to eliminate the anisotropy of the material parameters using the multilayered structure, thus avoiding extreme material parameters. We further analyze the path-dependent manipulation effects of the coupled thermal and electric fields. The numerical simulations are carried out to demonstrate the performances of ideal or multilayered Janus devices under different physical conditions. The results show that the performances of the multilayered Janus device coincide with those of the ideal Janus device, and these different Janus devices can perfectly achieve the concentrating function along the x-axis and the cloaking function along the y-axis in different thermal and electric fields simultaneously. It is anticipated that the path-dependent effect of the Janus metamaterial can also be extended to other multi-physical fields with different directional functions.

Increasing heat transfer in 4-stroke SI engine fins by nanocoating

A large amount of heat is produced in the IC engine during the combustion process, which directly affects the performance, fuel efficiency, and life of the engine. Extended surfaces are extensively uised in many engineering applications as they are simple to design, consume less space, weigh less. Implementation of high emissivity nanoparticles increases the heat transfer by increasing the surface area of the component. In this research, a plasma coating technique was used to provide a coating of silicon carbide (SiC) nanoparticles on 4-stroke IC engine fins. Furthermore, a Finite Element model identical to the test rig was generated and a numerical simulation was carried out using the FEA technique to investigate the heat dissipation, total heat flux and directional heat flux under applied temperature conditions. The emissivity and heat transfer results obtained from the test rig showed improvement in emissivity and enhancement in heat transfer through the fins.

A self-similar solution for shock waves in conducting rotating non-ideal dusty gas medium with monochromatic radiation and magnetic field

Abstract In this paper, the cylindrical shock wave propagation in a perfectly conducting rotating mixture of micro size dust particles and van der Waal gas with magnetic field either axial or azimuthal and monochromatic radiation is investigated. The effect of thermal radiation is included in the energy equation of the governing system. In our study, it is assumed that the flux of radiation moves in the mixture of particles and real gas with invariable intensity and the shock wave is moving appositive to the direction of radiation heat flux and the energy is engrossed behind the cylindrical shock only. In the present model, dusty gas is assumed to be a mixture of micro size dust particles and van der Waal gas in which solid particles are continuously distributed and the equilibrium flow conditions are assumed to hold in the entire flow-field region. The effects of the particles’ density to the initial gas density ratio, the real gas effect, rotational parameter, the concentration of mass of the micro size dust particles in the conducting mixture, Alfven-Mach number and the adiabatic exponent on shock and on the physical variables such as velocity, density etc. are discussed. It is found that due to the rotating medium consideration or by an increase in small particles density to the initial gas density ratio, the shock wave strength increases. Also, it is significant to memorize that the strength of the shock wave decreases by an increase in the strength of initial magnetic field or gas non-ideal parameter or the adiabatic index.

STUDY OF HEAT TRANSFER IN A MONOLAYER BALL PACKING

The features of nonstationary heat transfer of one layer of balls of the same size were studied in a fixed layer of liquid. The experiments were carried out in a cylindrical thermostat with a diameter of 128.9 mm filled with glass balls of 8.9 and 16.0 mm diam and polyoxymethylene balls of 9.0 mm diam with the highest possible packing density. The ball packing was filled with distilled water to a level of 0.1-0.2 mm higher than the ball diameter. The temperature of the ball packing surface was measured using a NEC 7100 thermal imager with a step change in temperature at the outer boundary of the packing. It is shown that, for a monolayer of balls of the same size in a stationary liquid, the temperature field is symmetrical relative to the packing center and the value of the effective thermal conductivity coefficient is constant over the packing cross section, both during heating and cooling. It has been found that the heat transfer coefficient and the time for establishing thermal equilibrium of a ball packing in a layer of stationary liquid at the same temperature difference depend on the heat flux direction at the packing boundary. The numerical values of the characteristic time of thermal equilibrium establishment in the heating and cooling regimes differ from each other by several times; whereas in the water layer without balls, this difference does not exceed 30%.

Design and analysis of piston using aluminum alloy and composites in Solidworks and Ansys

The present paper reports the modelling and analysis of piston fabricated from Steel, Aluminum alloy and Composites for 4-stroke petrol engine of a specific version followed by comparison between the both. Solidworks software is used for 3D modelling of the piston. Ansys software is used for static structural and steady state thermal analysis of the piston. A static-structural analysis is being performed to find out the deformation, stresses, strains, and forces in structures or factors caused by the loads. A static analysis calculates the impact of steady loading conditions on a structure, while ignoring inertia and damping as those carried by time varying loads. Steady state thermal analysis is used for evaluating the thermal equilibrium of a system in which the temperature remains constant over time. Steady-state thermal analysis can be used to determine the temperature distributions in an object with thermal loads that do not vary with time. The heat transfer includes conduction, convection and radiation. Most thermal analyses are steady state thermal analyses. Total Deformation, Factor of Safety (F.O.S.), Equivalent (Von-mises) stress and Equivalent (Von-mises) strain were obtained under static structural analysis for piston using different materials. Total heat flux, Directional heat flux and temperature distribution were obtained using steady state thermal analysis. Performance of standard material used for piston and aluminum alloys was compared and the best material was recommended for manufacturing of piston.

Tensile strength, wear characteristics and numerical simulation of automotive brake pad from waste-based hybrid composite

Environmental impact of asbestos brake pad and negative impact on human health has been a real concern for years because the first generation of composites materials had relied heavily on asbestors reinforced composites. The aim of this work is to develop banana peel composite, test its mechanical and wear properties. On this study, a composite material made up of banana peel powder with carbon. Composition 1 increased in both stress and elongation to the maximum output stress of 2.1 MPa and elongation of approximately 13.0. Despite decrease in the weight percent of the carbon powder, the stress output decreased by 14.3% with composition 2 and likewise for composition 3 to approximately 1.40 MPa. Composition 1 experienced minimal loss of weight. This was concluded to be due to influence of the strength on the weight differentials. Composition 1 with minimal loss of weight would be applicable for the brake pad application. It is equivalent to 60% loss of weight in composition 2 and 67.7% loss of weight was experienced in composition 3 compared to composition 1. The results gotten were in correlation with the natural composite materials investigated for brake pad application by previous researchers. With directional heat flux (maximum) value of 604. 24 W/m2 recorded for the specified areas of the produced composites. As the boudary conditions were applied, the equivalent strain from the numerical simulation was 0.003174 m/m. Around the regions with bolt fixing, the numerical simulation gave 1.429 × 10−7 Pa equivalent stress (Maximum). Though there was less stress around the remaining parts.

Enhanced Thermal Conductivity of Composite Materials by Filling Sheet and Fiber Under Effect of Filler Contact

Abstract The most common nongranular fillers are sheet and fiber. When they are distributed along the heat flux direction, the thermal conductivity of the composite increases greatly. Meanwhile, the filler contact also has a large effect on the thermal conductivity. However, the effect of filler contacts on the thermal conductivity of the composite with directional fillers has not been investigated. In this paper, combined effects of the filler contact, content, and orientation are investigated. The results show that the effect of filler orientations on the thermal conductivity is greater than filler contacts in the low filler content, and the exact opposite in the high filler content. The effect of filler contacts on fibrous and sheet fillers is far greater than cube and sphere fillers. This rule is affected by the filler contact. The filler content of 8% is the ideal percolation threshold of composites with fibrous and sheet fillers. It is lower than cube filler and previous reports. The space for the thermal conductivity growth of composites with directional fillers is still very large. The effect of the interfacial thermal resistance should be considered in predicting the thermal conductivity of the composite under high interfacial thermal resistances (>10−4).

Finite Element Analysis of The Thermal Behaviour of Different Types of Connecting Rod for Various Materials

Thermal analysis of different types of the connecting rods are under stead state condition using finite element method. The energy equation and heat transfer equation in the solids are completely addressed and solved using the Newton-Raphson technique and finite element method. SOLID WORKS is used for modelling different types of connecting rods and ANSYS© software is used to perform this numerical investigation. Three different materials like structural steel, aluminium alloy and titanium are selected as the material of connecting rod to do the comparative studies. In a steady thermal analysis, properties like temperature distribution, total heat flux and directional heat flux are calculated. The knowledge of the above properties is required to identify the viscosity of oil used for lubrication and also temperature distribution is helpful to find the thermal deformation in the connecting rod. Temperature and convection co-efficient are the boundary conditions. 22°C is the initial temperature value and the value of convection co-efficient is 350W/m2°C. As a result of thermal analysis, titanium alloy is the best material among the three materials as it with stand higher temperatures, high lifecycle and high performance.

Thermal and Conjugate Heat Transfer Analysis of Exhaust Manifold of Multi-cylinder IC Engine

The exhaust manifold of multi cylinder IC engine is kept in between the engine block and the catalytic converter. So the exhaust manifold is exposed to very high temperature and care should be taken at the critical zone during the design stage. At several critical zones of the exhaust manifold, large compressive deformations are generated at elevated temperatures and tensile stresses remain at cold conditions. The thermal analysis will help in estimating the deformations and stress concentrations due to thermal loads. Therefore, the main aim of this study is to perform thermal analysis and conjugate heat flow analysis of an exhaust manifold of a multi-cylinder engine. The 3D model is generated using SolidWorks and analysis is carried out using Ansys workbench. Materials like grey C.I., aluminium nitride, silicon nitride, and stainless steel are used in this analysis. The results of total heat flux, directional heat flux and temperature distribution were compared. Silicon nitride material is suggested to be the suitable material for engine exhaust manifolds based on the material mechanical properties and thermal distribution-related thermal stress developed on the exhaust manifold.

Engine Performance Analysis by Studying Heat Transfer in the Valve Seat through Steady-State Thermal Simulation

As the engine reached high speed, the exhaust valve temperature increased exponentially due to the exhaust gas produced by the combustion process between the mixture of air and fuel within the combustion chamber of the internal combustion engine. The valve is subjected to thermal loading due to high temperature and pressure within the cylinder, which must withstand a material temperature for sustainable and optimal operation. To avoid this loss, a perfect medium must be prepared to ensure that the heat is extracted smoothly. This can be done when the valve is in contact with the seat and there is a periodic heat transfer contact. Therefore, it is imperative to research the correlation between valve and valve seat to understand the two sections’ heat transfer mechanism. In this study, thermal contact analysis was used to identify heat transfer between the valve and the valve seat as both parts are interconnected. This research also has an interest in studying the two surface conduction mechanisms as the exhaust valve closed in steady-state conditions. Thus, this study portrays a significant method, particularly for the determining the distribution of temperature, heat flux, and heat flux direction between the valve and its seat using ANSYS Workbench.

On the effect of rapid annealing on the microstructure and mechanical behavior of additively manufactured stainless steel by Laser Powder Bed Fusion

This work presents an investigation on the effect of rapid annealing on the microstructure evolution and mechanical performance of stainless steel 316L (SS316L) fabricated by Laser Powder Bed Fusion. In this process, it is well documented that the intensive thermal gradient in the heat flux direction leaves remarkable residual stress and promotes strong texture along the building direction (BD). In the current research, to swiftly reduce residual stresses, a short-term heat treatment at 1300 °C for different holding times of 10–120 s was designed and studied. Microstructural observation through the optical microscopy and scanning electron microscopy, as well as the X-ray diffraction analysis, revealed that rapid annealing longer than 30 s resulted in the gradual annihilation of the cell walls which are indeed the sub-grain boundaries (SGBs). In addition, electron backscatter diffraction outputs demonstrated that rapid annealing significantly reduced the low angle grain boundaries and attenuated the texture developed along the BD. Moreover, the analysis of grains size and shape illustrated that annealing up to 30 s recovered the structure. In contrast, longer annealing resulted in increasing the aspect ratio of grains along the direction with maximum residual strain (i.e. BD) due to activation of the strain induced grain boundary migration (SIGBM) mechanism. After the rapid annealing, the mechanical performance of the samples also indicated that annealing up to 30 s would not reduce the compressive and tensile strength more than 6%. In comparison, longer annealing resulted in 24% reduction in mechanical properties along with coarsening of dimples in the fracture surface of the samples.