Enhancement Of Thermal Transport Research Articles

Reorientation of Hydrogen Bonds Renders Unusual Enhancement in Thermal Transport of Water in Nanoconfined Environments

Reorientation of Hydrogen Bonds Renders Unusual Enhancement in Thermal Transport of Water in Nanoconfined Environments

Defect scattering can lead to enhanced phonon transport at nanoscale

Defect scattering is well known to suppress thermal transport. In this study, however, we perform both molecular dynamics and Boltzmann transport equation calculations, to demonstrate that introducing defect scattering in nanoscale heating zone could surprisingly enhance thermal conductance of the system by up to 75%. We further reveal that the heating zone without defects yields directional nonequilibrium with overpopulated oblique-propagating phonons which suppress thermal transport, while introducing defects redirect phonons randomly to restore directional equilibrium, thereby enhancing thermal conductance. We demonstrate that defect scattering can enable such thermal transport enhancement in a wide range of temperatures, materials, and sizes, and offer an unconventional strategy for enhancing thermal transport via the manipulation of phonon directional nonequilibrium.

Extraordinary thermal conductivity for carbon nanotube encapsulated linear carbon chain

Carbyne is a sp1 linear carbon chain (LCC) with characteristics of strong chemical reactivity and extreme instability under environmental conditions, which has become an obstacle to the application of LCC with high thermal and electrical conductivity. Utilizing CNT as a container to store LCC is one of the most feasible ways to realize LCC applications. However, current research of LCC encapsulated in CNT (LCC@CNT) focuses on its preparation and lacks of in-depth exploration of the intrinsic heat transfer mechanism. This paper reports the high axis thermal conductivity of LCC@CNT, explore the thermal transport enhancement degree of LCC@CNT under a wide temperature range and multiple diameters, and analyzed the underling mechanism through crucial thermal parameters and phonon theory. When LCC is loaded in CNT, the axial thermal conductivity of CNT is further increased by 15 %. Moreover, LCC@CNT shows the lower sensitivity diameter than pristine CNT. This work is expected to provide data support for the application of LCC, the lower production standard of CNT, and also attempt the higher efficient one-dimensional thermal energy transfer micro devices.

Influence of nanoparticle shapes in nanofluid film boiling on vertical cylinders: A numerical study

This research explores how nanoparticle shapes affect the thermal behavior of nanofluid film boiling along a vertical cylinder, utilizing a Continuous-Species-Transfer method embedded in a Computational Multi-Fluid Dynamics framework. By modeling the behavior of nanoparticles in both liquid and vapor phases, with considerations for Brownian motion and thermophoresis, a comprehensive 2D axisymmetric analysis is conducted. The analysis focuses on the effects of various Al2O3 nanoparticle shapes – spheres, bricks, blades, cylinders, and platelets – on boiling heat transfer performance. Results demonstrate that while nanoparticle shape has a minimal impact on deposition dynamics, it significantly affects kinematic viscosity, particularly for platelet-shaped nanoparticles. Blade-shaped nanoparticles stand out for their substantial enhancement of thermal transport, as demonstrated by pronounced temperature gradients and elevated thermal conductivity. Furthermore, these nanoparticles contribute to a notable improvement in the Nusselt Number, suggesting enhanced efficiency in boiling heat transfer. This improvement is particularly significant at higher nanoparticle concentrations, where the effects are more pronounced, though not strictly linear when compared to the effects at lower concentrations. Future work will explore different nanoparticle materials, boiling scenarios, and experimental validation.

Estimation of heat transfer coefficient and friction factor with showering of aluminum nitride and alumina water based hybrid nanofluid in a tube with twisted tape insert

Twisted tape is one of the active thermal proficiency boosting technology which has been deeply examined because to consistent efficiency findings and easy implementations. Thermo-hydraulic effectiveness of tubes fitted with twisted tapes is becoming highly significant. Although twisted tapes can cause swirls and disturb boundary layers, this is the most widely used method for improving convection. In the present attempt, to enhance the heat transfer twisted tape is inserted in tube. In the current modern research, the effect of twisted tape, on the enhancement of thermal transport, Nusselt number and friction factor performance of AIN–Al2O3/water hybrid nanofluid is evaluating utilizing CFD and ANSYS-FLUENT software. the consequence of twisted pitch 44 mm, 66 mm, 88 mm, 100 mm and Reynolds numbers 800, 1200, 1600 and 2000 on Nusselt number, heat transfer coefficient and friction coefficient have been computed numerically with 0.01 to 0.04 volume friction of nanopowders. The commercial ANSYS-FLUENT code was used in this analysis utilizing the SIMPLE method for pressure–velocity coupling. The K-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K - \\omega$$\\end{document} model and Navier Stokes equations are integrating utilizing finite volume method in ANSYS-FLUENT. It was observed that inserting the twisted tape in tube significantly improves the thermal conductivity as well as friction factor compared with the simple tube without turbulator.

Synergetic effect of magnetic field location, strength and orientation on heat transfer characteristics of brine-based hybrid nanofluid in rectangular confinement

The hybrid nanofluid emergence is presently receiving untold research attention as an improved cooling medium. This paper presents an investigation into the free convection thermal transport performance of brine (ethylene glycol-deionized water (60:40 vol%)-based hybrid ferrofluid (Fe2O3-Al2O3) (BBHF) in a rectangular cavity under steady-state conditions with and without magnetic inducement. The synergetic effect of different magnetic field orientations and intensities imposed on the various walls of the confinement and their influence on the heat transfer characteristics of BBHF was examined. At volume concentrations of 0.05–0.40 %, the BBHF was formulated and characterised for its viscosity, stability, morphology, and thermal conductivity. Without a magnetic stimulus, the average Nusselt number, heat transfer rate, and coefficient of heat transfer of 0.05–0.2 vol% BBHF samples were improved relative to the brine. At a cavity temperature gradient of 35 °C using 0.05 vol% BBHF, a peak thermal transport enhancement of 10.09 % was observed when compared with the brine. With 0.05 vol% BBHF, the vertical positioning of the magnetic stimulus on the cavity side wall was noticed to yield maximum improvement of heat transfer (4.3 %). An increment in the strength of the magnetic stimulus from 4.89 mT to 13.00 mT enhanced thermal transport by >15 %, which subsequently deteriorated when increased to 21.95 mT for all the studied magnetic stimulus arrangements. In addition, correlations were proposed to predict the Nusselt number, thermal conductivity, and viscosity of the BBHFs. The employment of hybrid nanoparticles, magnetic stimulus, and different arrangements of the magnetic stimulus was observed to amplify the heat transfer of BBHFs in the cavity which is of practical and engineering benefit.

Analysis of thermsolutal performance and entropy generation for ternary hybrid nanofluid in a partially heated wavy porous cabinet

PurposeThis study comprehensively examines entropy generation and thermosolutal performance of a ternary hybrid nanofluid in a partially active porous cabinet. The purpose of this study is to comprehend the intricate phenomena of double diffusion by investigating the dispersion behavior of Al2O3, CuO, and Ag nanoparticles in water.Design/methodology/approachThe cabinet design consists of two horizontal walls and two curved walls with the lower border divided into a heated and concentrated region of length b and the remaining sections are adiabatic. The vertical borders are cold and low concentration, while the upper border is adiabatic. Two cavity configurations such as convex and concave are considered. A uniform porous medium is taken within the ternary hybrid nanofluid. This has been characterized by the Brinkman-extended Darcy model. Thermosolutal phenomena are governed by the Navier-Stokes equations and are solved by adopting a higher-order compact scheme.FindingsThe present study focuses on exploring the influence of several well-defined parameters, including Rayleigh number, Darcy number, Lewis number, Buoyancy ratio number, nanoparticle volume concentration and heater size. The results indicate that the ternary hybrid nanofluid outperforms both the mono and hybrid nanofluids in all considered aspects.Originality/valueThis study brings forth a significant contribution by uncovering novel flow features that have previously remained unexplored. By addressing a well-defined problem, the work provides valuable insights into the enhancement of thermal transport, with direct implications for diverse engineering devices such as solar collectors, heat exchangers and microelectronics.

Heat generation/absorption effects in thermally radiative mixed convective flow of [formula omitted] hybrid nanofluid

Investigation on hybrid nanofluids has increased significantly, and findings indicate that these fluids are effective heat transfer fluids for industrial applications. The thermal conductivity of nanoparticles, particle volume fractions, and mass flow rates play a major role in the enhancement of heat transfer of nanofluids. The enhancement in thermal transport only depends on the thermal conductivity of the nanoparticles when particle volume fractions and flow rates are constant. Therefore, the purpose of this article is to analyze the flow of Zn−TiO2/H2O hybrid nanofluid past an inclined shrinking surface. The PDEs of the flow model are converted into ODEs by using similarity conversions. The mathematical problem is tackled numerically by employing the bvp4c solver in Matlab software. The impacts of controlling parameters on fluid velocity, temperature distribution, skin friction coefficient, and local Nusselt number are studied and graphically depicted. The obtained results reveal that the mixed convection parameter is found to enhance friction drag and heat transport rate for the upper branch while it reduces the lower branch. Moreover, the kinetic energy is inclined as the heat sink/source, Eckert number, and temperature ratio parameters increase, causing the thermal distribution to rise for both branches.

MgO/Molten salt interfacial thermal transport and its consequences on thermophysical property enhancement: A molecular dynamics study

The solid-liquid interface between molten salt and solid oxides is ubiquitous in the molten salt nanocomposite with enhanced heat storage and transfer properties for concentrating solar power (CSP) systems. Understanding the microscopic mechanisms of interfacial thermal transport on this solid-liquid interface have great significance for evaluating the effective thermal properties of nanocomposites. This study combines equilibrium and non-equilibrium molecular dynamics simulations to explore the thermal transport and its connection with interfacial microstructure at the solid MgO-molten Hitec salt interface. Simulation results indicate that the enhancement of thermal transport can be ascribed primarily to the highly ordered adsorption structure of molten salt ions formed at the MgO surface, and the effect medium model incorporated with the simulated interfacial thermal resistance can reproduce the thermal conductivity of nanocomposite accurately. Further investigation indicates that the stronger adsorption at the MgO (110) surface leads to smaller interfacial thermal resistance than the MgO (100) surface, while the heat transfer parallel to the slab does not show much difference in both surfaces. These findings have illustrated the enrichment of molten salt ions at the solid surface does have a strong enhancement effect on their heat transfer properties and it is also necessary to incorporate the contribution from this interfacial thermal transport enhancement when predicting the thermophysical properties of molten salt nanocomposite materials.

Influence of thermal conductivity on transient mixed convection in a vented cavity with a hollow cylinder and filled with CNT-water nanofluid

This study is aimed to perform a numerical time-dependent investigation thermal conductivity effect of the annular cylinder within a vented cavity using CNT based-water nanofluid. For demonstrating the effect of thermal conductivity, four distinct hollow cylinder materials such as Ks = 0.5(Plastic tiles), Ks = 0.84(Clay tiles), Ks = 1.1(Concrete tiles), and Ks = 2(Slate tiles) are introduced together with a suitable variation of dimensionless time (0 ≤ τ ≤ 1). The governing equations of the model with associated boundary conditions is solved using finite element based Galerkin's weighted residual method. Different contour plots for thermal and flow field transformation and mean Nusselt number, mean fluid temperature, bulk convective field temperature, temperature gradient, pressure gradient, vortices, and fluid velocity magnitude are presented for qualitative and quantitative thermal performance analysis. With the decrease of solid thermal conductivity, 27.3% thermal transport enhancement is noted from the heated surface of the cylinder. However, a 16.3% increase in the bulk fluid temperature has been recorded with the increase in cylinder conductivity. The numerical outcomes from this investigation propose a better thermo-fluid efficiency compared to the existing methodology which can be suggestive to engineers and researchers for designing heat exchangers, heat pipes, and other thermal systems.

Unsteady buoyant convection of nanofluid in a porous annulus: impacts of size and location of thermal source–sink pairs

The current numerical investigation deals with natural convection in a nanofluid-saturated porous cylindrical annulus subjected to partial heating and cooling of side walls by adopting Brinkman-extended Darcy Model to govern the fluid flow in porous media. By choosing five different locations and four lengths of thermal source–sink pairs, the impact of discrete heating–cooling on fluid flow, thermal transport rates and thermal mixing in a porous annular enclosure has been addressed. From the vast range of numerical simulations, the results provide information on the proper size and location of source–sink combinations to dissipate maximum thermal transport along with better thermal mixing in the enclosure. The importance of porosity, nanoparticle concentration, Darcy and Rayleigh numbers on overall thermal dissipation rate has also been discussed. The results showed that identifying an optimum source–sink location along with an appropriate choice of other control parameters can lead to higher thermal transport enhancement and thermal mixing.

Ultra-High Interfacial Thermal Conductance via Double hBN Encapsulation for Efficient Thermal Management of 2D Electronics.

Heat dissipation is a major limitation of high-performance electronics. This is especially important in emerging nanoelectronic devices consisting of ultra-thin layers, heterostructures, and interfaces, where enhancement in thermal transport is highly desired. Here, ultra-high interfacial thermal conductance in encapsulated van der Waals (vdW) heterostructures with single-layer transition metal dichalcogenides MX2 (MoS2 , WSe2 , WS2 ) sandwiched between two hexagonal boron nitride (hBN) layers is reported. Through Raman spectroscopic measurements of suspended and substrate-supported hBN/MX2 /hBN heterostructures with varying laser power and temperature, the out-of-plane interfacial thermal conductance in the vertical stack is calibrated. The measured interfacial thermal conductance between MX2 and hBN reaches 74 ± 25 MW m-2 K-1 , which is at least ten times higher than the interfacial thermal conductance of MX2 in non-encapsulation structures. Molecular dynamics (MD) calculations verify and explain the experimental results, suggesting a full encapsulation by hBN layers is accounting for the high interfacial conductance. This ultra-high interfacial thermal conductance is attributed to the double heat transfer pathways and the clean and tight vdW interface between two crystalline 2D materials. The findings in this study reveal new thermal transport mechanisms in hBN/MX2 /hBN structures and shed light on building novel hBN-encapsulated nanoelectronic devices with enhanced thermal management.

Numerical appraisal of time-dependent peristaltic duct flow using Casson fluid

Interruption of continuous process and decreasing flow rate over time are very common challenges in peristaltic flow. This research takes an initiative to restrain the thermal and fluid flow rate over time by unsteady finite element analysis of Casson fluid flow through a two-dimensional peristaltic duct. The time-dependent flow equation exists in conjugate forced convection and the energy equation consists of radiative heat flux and entropy reduction. The top and bottom walls of the peristaltic duct are considered as contact with air. A circular bolus is set up in the middle of the duct. Four types of Casson fluids like slurry, silicone oil, apple juice, and blood are used as working fluids. The finite element method of Galerkin's residual technique is applied to solve the leading second ordered non-linear partial differential equations with proper border conditions. The effects of pertinent parameters on entropy reduction and thermal transport are analyzed. Results are displayed qualitatively in terms of streamlines, vortex field, and heatline contours as well as quantitatively in the form of average temperature, mean thermal, viscous, and total entropy. The obtained numerical results show that thermal performance and entropy reduction are significantly influenced by forced convection, atmospheric characteristics, internal thermal radiation, and Casson fluids. Approximately 6.99% and 72.13% increment of temperature and flow irreversibility are found for shear stress variation of Casson fluid from thickening to thinning. Decreasing thermal performance of 18.71% and increasing energy loss of 38.07% are noticed within the variation of Casson fluids (slurry, silicone oil, apple juice, and blood). About 14.05% enhancement of thermal transport and 64.91% reduction of total entropy are observed due to increasing internal thermal radiation from 0.5 to 2. The numerical results from this research represent a better thermal and fluid flow rate over time compared to the experimental/existing methodology/numerical research. The obtained flow and thermal transport phenomena expose many attention-grabbing performances which deserve additional investigation on Casson fluid characteristics particularly the continuation of flow rate. A fine approach to the biological peristaltic system is offered by the results.

Impact of Thermal Source-Sink Arrangements on Buoyant Convection in a Nanofluid-Filled Annular Enclosure

AbstractThis investigation is devoted to analyze the buoyancy-driven flow behavior and associated thermal dissipation rate in a nanofluid-filled annular region with five different single source-sink and three different dual source-sink arrangements along the vertical surfaces. The remaining region on the vertical boundaries and horizontal surfaces are kept adiabatic. Numerical simulations have been performed by employing the finite difference method. To analyze the impacts of different nanofluids, nanoparticle volume fraction, Rayleigh number, size, and arrangement of sources and sinks, the results are graphically represented through streamline and isotherm contours, thermal profiles, average Nusselt number, and cup-mixing temperature. The results showed that identifying an optimum location and length of source-sink with a proper selection of other control parameters can lead to enhanced thermal transport and thermal mixing in the enclosure. In particular, middle-middle thermally active location and placing source-sink separately on the vertical walls lead to the production of maximum heat transport compared to other single and dual source-sink arrangements, respectively. Also, among the two nanofluids considered in the current investigation, larger enhancement in thermal transport has been achieved for Cu-water nanofluid. The calculated enhancement ratio of the heat dissipation rate enhances with an increment in nanoparticle concentration.

On the enhancement of thermal transport of Kerosene oil mixed TiO2 and SiO2 across Riga wedge

Efficient thermal transportation in compact heat density gadgets is a prevailing issue to be addressed. The flow of a mono nanofluid (SiO2/Kerosene oil) and hybrid nanofluid (TiO2 + SiO2/Kerosene oil) is studied in context of Riga wedge. The basic purpose of this work pertains to improve thermal conductivity of base liquid with inclusions of nano-entities. The hybrid nanofluid flow over Riga wedge is new aspect of this work. The concentration of new species is assumed to constitute the base liquid to be non-Newtonian. The fundamental formulation of the concentration laws of mass, momentum and energy involve partial derivatives. The associated boundary conditions are taken in to account. Similarity variables are utilized to transform the leading set of equations into ordinary differential form. Shooting procedure combined with Runge-Kutta method is harnessed to attain numerical outcomes. The computational process is run in matlab script. It is seen that the velocity component f′(η) goes upward with exceeding inputs of modified Hartmann number Mh and it slows down when non-dimensional material parameter αh takes large values. Also, Nusselt number − θ′(0) is enhanced with developing values of Eckert number Ec and Biot number Bi.

Hydrodynamically enhanced thermal transport due to strong interlayer interactions: A case study of strained bilayer graphene

Manipulating interlayer interactions in two-dimensional (2D) materials is a widely used and effective method for regulating heat transport, which is important for thermal management of electronics. In this paper, we find that thermal transport can be enhanced by strong interlayer interactions. For instance, 2D bilayer materials with interlayer bonding have larger thermal conductivity than their monolayer counterparts. To further verify the conjecture, we take bilayer graphene (BLG) as a study case to gradually strengthen the interlayer interactions in BLG by applying a series of compressive strains along the out-of-plane direction. It is found that the thermal conductivity of BLG first decreases and then anomalously increases when the strain is larger than the threshold of 12%. For the decreasing trend, it is mainly due to the strain-induced reduction of phonon group velocity and lifetime. While at larger strain (>12%), the anomalous increase of thermal conductivity is found to be caused by hydrodynamic phonon transport and weak phonon anharmonicity. Thus, enhanced interlayer interactions can enhance the hydrodynamic phonon transport and thus improve the heat transfer performance. In this paper, we not only report the hydrodynamic enhancement of thermal transport through enhanced interlayer interactions but also provide solid evidence. These findings will deepen the understanding of thermal transport in layered materials and heterostructures, which will benefit the applications in thermal management.

Numerical study of the formation of liquid layer at the liquid–solid interface near the graphene in nanofluid

The interfacial liquid layer formed by liquid atoms around the nanoparticle which is dispersed in a base fluid is considered among the mechanisms responsible for the thermal transport enhancement in nanofluid. The present work shows the effect of vibration of graphene nanosheets inside the argon liquid on the formation of a liquid layer at the liquid -solid interface near the graphene. This feature has been examined by using the (MDS) molecular dynamics simulation. The vibration of graphene nanosheet is surveyed by studying the behaviors of positions and velocities of carbon atoms that are recorded at each time step during molecular dynamics simulation. Similarly, the formation of the interfacial liquid layer near the graphene is examined by calculating the number density of liquid atoms in specified space near the graphene in the simulation domain. The numerical results show that the carbon atoms of graphene nanosheets vibrate around their local positions inside the liquid argon. Also, they show that no significant layering of liquid argon near the graphene nanosheet is observed, this last indicates that the interfacial liquid layer near the graphene nanosheet is not formed inside the liquid argon. Therefore, these results lead to the conclusion that the vibration of graphene is mechanism responsible for the lack of the layer liquid around the graphene nanosheet that is dispersed within liquid argon. Furthermore, the liquid layer at the liquid argon- graphene nanosheet interface in nanofluid (argon-graphene) is not a mechanism possible producing the enhanced thermal transport in nanofluid containing graphene nanosheets.

Thermal transport enhancement resolution for graphene/Si and graphene/SiC interfaces

Interfacial thermal transport property between graphene and semiconductor is an important factor affecting heat dissipation of graphene based semiconductor devices. Here, we investigate thermal transport across graphene/Si and graphene/SiC interfaces using reverse non-equilibrium molecular dynamics simulations, and phonon vibrational density of states are calculated to reveal the mechanism of enhancement of interfacial thermal conductance. Results show that for van der Waals bonded interfaces, the interfacial thermal conductance between graphene and Si is obviously higher, while for covalently bonded interfaces, the interfacial thermal conductance between graphene and SiC is higher. Different to the graphene/SiC interface, interfacial thermal conductances of graphene/Si interfaces can benefit from the increasing temperature, which is because the phonon matching between graphene and Si as well as the interfacial phonon inelastic scattering are improved under higher temperatures. The results are excepted to help promote the understanding of interfacial thermal transport between graphene and semiconductors and provide theoretical basis for the design and modification of related interfaces in graphene based semiconductor devices.

Buoyant Convective Flow and Heat Dissipation of Cu–H2O Nanoliquids in an Annulus Through a Thin Baffle

This article numerically investigates the buoyant convective flow and thermal transport enhancement of Cu–H2O nanoliquid in a differentially heated upright annulus having a thin baffle. For the analysis, the outer and inner cylinders are cooled and heated respectively through insulated top and lower boundaries. Also, the baffle temperature is assumed to be that of the hot cylinder. The finite difference based numerical technique is used to solve the system of equations governing the physical processes. The findings are accessible in terms isotherms, streamlines and Nu number for wider ranges of baffle positions and lengths, Rayleigh numbers, and by considering different nanofluid (NF) volume fractions. The average Nu number is enhanced in addition of the Cu nanoparticle to the base liquid and it is also found the liquid flow and heat transport can be successfully controlled via the appropriate selection of baffle location and length. Principally, the baffle length having 20% of annular width placed at 80% of the annular height has been found to produce higher thermal transport rates as compared to other choices of baffle lengths and positions.

Unusual thermal performance in Cu-60Ag by WC nanoparticles

Nanoparticles have been widely used to tune the mechanical, thermophysical, and chemical properties of materials for widespread applications 1-3. Despite achieving other unprecedented functionalities, metals containing ceramic nanoparticles often suffer a significant loss in thermal conductivity with theoretical upper limits set by the Hashin-Shtrikman (with interfacial interactions) and Weiner (without interfacial interactions) models. Here, we discover that the Cu-60Ag alloy with 10 vol% WC nanoparticles delivers a surprisingly high thermal conductivity, breaking the theoretical upper limits. To understand the underlying mechanisms, thermal transport contributions from phonons and electrons, as well as microstructure, are studied. The study suggests that there exists an unusual enhancement of thermal transport in Cu-60Ag by the less conductive WC nanoparticles. Though thermal analysis including 3ω-method may be needed to decouple influencing factors, this new finding is of significance for development and application of nanoparticles reinforced metals with both superior mechanical strength and high thermal conductivity.