Thermal Conductivity Coefficient Research Articles

Oxysulfide perovskites: reduction of the electronic band gap of RbTaO3 by sulfur substitution

In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of RbTaO3−x S x have been investigated using the WIEN2k code in the framework of density functional theory (DFT). The cubic phase of RbTaO3 transforms to tetragonal for RbTaO2S and RbTaOS2; the latter transforms again to a cubic phase with added sulfur for RbTaS3. The results show that substituting S for O anions in RbTaO3 effectively decreased the band gap [calculated using TB-mBJ functional] from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for the RbTaO3, RbTaO2S, RbTaOS2, and RbTaS3 compounds, respectively. The optical constants such as dielectric constant, refractive index, absorption coefficient, photoconductivity, reflectivity, and loss function have been calculated and analyzed. The elastic constants and moduli and their anisotropic nature were also investigated. Finally, the Debye temperature, thermal conductivity, melting temperature, specific capacities, and thermal expansion coefficients were computed and analyzed using established formalisms. The reduced band gap (1.438 eV) and high absorption coefficient (∼106 cm−1) of RbTaO2S, make it suitable for solar cell applications and for other visible light devices. Both ordered structure and super-cell have been used to cross-check results for RbTaO2S and RbTaOS2 compositions.

Теплопровідність твердих розчинів GeBiTe

The paper calculates the electronic and lattice components of thermal conductivity coefficients for GeBiTe solid solutions. The calculation was carried out using two different models of the band structure of GeTe, which differ in the relative location of the zones of heavy and light holes. The first of the models is generally accepted for A4B6 compounds and assumes the location of the zone of light holes above the zone of heavy ones in the energy spectrum. Another model, obtained on the basis of DFT calculation, predicts the location of the zone of light holes below the zone of heavy ones. A significant difference was established in the numerical values of the electronic and lattice components of the thermal conductivity coefficients, depending on the adopted model. The influence of other calculation parameters on the investigated values was analyzed.

Study of mass and heat transfer for peristaltic transport of cross nanofluid through a curved channel

AbstractNanoparticles have significant applications in drug delivery systems, heat exchanges, treatment of several diseases and chemical reactions. The Cross non‐Newtonian nanofluid model for heat and mass transfer inspection with diethylene glycol‐based fluid is highlighted in this study. The magnesium aluminate nanoparticles are used to evaluate nanofluid characteristics. The current investigation explores the numerical results for magnetohydrodynamics (MHD) peristaltic movement of Cross‐nanofluid via a curved channel under the influences of thermal radiation, heat sink/source and Joule heating. The effects of viscous dissipation, thermophoretic, variable thermal conductivity and Brownian diffusion coefficients in the presence of mass and thermal convection are also taken into consideration. Flow problem is modeled using fundamental conservation laws, and the resulting nonlinear partial differential equations (PDEs) are reduced to a system of nonlinear ordinary differential equations (ODEs) by employing long wavelength and a small Reynolds number approximations. Simplified systems of ODEs are addressed by adopting numerical technique via the NDSolve built‐in command in Mathematica. Furthermore, graphical presentations explain the behavior of relevant flow parameters. Results indicate that better values of the magnetic number and the thermophoresis parameter increase the rate of mass transfer. Results indicate that the nanofluid's temperature increases by improving values of the Brinkman number and falls with the thermal radiation parameter. It is also stated that the nanofluid's velocity reduces near the lower wall for greater values of Hartman number. Moreover, heat transfer rate improves for larger values of the heat generation parameter and curvature parameter.

The efficiency of thermal protection of ICE pistons with the micro-arc oxidation

BACKGROUND: In order to protect pistons of internal combustion engines (ICE) from burnout and increase their durability, it is reasonable to use ceramic coatings formed on the piston head with micro-arc oxidation (MAO). Many scientific papers have been devoted to the study of the efficiency of these coatings. However, most of these studies were carried out at laboratory facilities simulating the engine operation, generally, not taking into account the real thermophysical parameters of the MAO coating. Therefore, the thermal protection efficiency of these coatings is difficult to assess. AIM: Study of efficiency of the thermal protection of pistons using a ceramic coating formed by micro-arc oxidation on the piston head with numerical simulation. METHODS: The study was conducted in the SolidWorks Simulation software. Two piston aluminum alloys were used as the piston material: AK12d (with a silicon content of 12%) and AK4-1 (with a silicon content of 0.35%). Temperature loads corresponding to the operation of a real engine were applied to the surfaces of the model piston. At the first stage of the study, the thermal state of pistons made of different uncoated alloys was simulated. At the second and third stages of the study, the effect of the coating thickness on the piston thermal state was simulated. The piston material of the second study stage was the AK4-1 alloy. The piston material of the third study stage was the AK12d alloy. Ceramics, which properties correspond to the coatings properties formed with the micro-arc oxidation method on these alloys, were used as the coating material. The coating thickness varied in the range from 50 to 350 µm in increments of 100 µm. The probing method was used to determine the temperature in various areas of the piston, such as at the piston head surface at the MAO coating and under it, in the area of piston grooves, at a piston skirt and the piston head from the side of a crankcase. RESULTS: With the simulation, it was found that: The micro-arc coating of the piston head reduces the thermal tension of the piston regardless of the aluminum alloy chemical composition. The efficiency of the piston’s thermal protection increases with an increase in the ceramic coating thickness and a decrease in its thermal conductivity coefficient. The greatest heat-protecting effect is achieved by the piston made of the AK12d eutectic alloy. CONCLUSIONS: It is found that the MAO coating at the piston head is an effective way to reduce the thermal tension of the ICE pistons. Increasing the ceramic coating thickness and a decrease in its thermal conductivity coefficient increases the efficiency of the pistons thermal protection. Reducing the thermal conductivity of the MAO coating and increasing the MAO coating thickness increases the temperature on the coating surface.

Mechanical and thermal properties of in situ AlN/Al-12Si composite fabricated by laser powder bed fusion

This work reports on the synthesis, mechanical, and thermal properties of in situ AlN/Al-12Si composite through laser powder bed fusion (LPBF) by blending Al-12Si powder with 5 vol% nano-sized BN particles. Incorporating nano-BN particles results in (i) formation of thermally stable AlN phase, preventing Si diffusion and breakdown of cellular structure, (ii) improvement of compressive yield strength (CYS), and (iii) reduction in coefficients of thermal expansion (CTE) and thermal conductivity. In addition, compared to Al-12Si alloy, the composite exhibits grain refinement from 38.8 to 1.2 μm in size, and the alteration of columnar grains (Al-12Si) to equiaxed grains (AlN/Al-12Si). At annealing temperatures above 573 K, the CYS of the unadulterated Al-12Si alloy had a ∼ 2.1 times greater reduction (from 285 to 200 MPa) compared to that of the composites (from 301 to 260 MPa). The formation of the AlN phase mitigates the significant reduction in CYS. The CTE of Al-12Si and AlN/Al-12Si are 27.3 × 10−6 K−1 and 24.3 × 10−6 K−1 respectively. There is good agreement between the measured CYS results and the calculated strengthening mechanisms. This work offers both theoretical insights and experimental data to support the use of LPBF AlN/Al-12Si composite in low- and moderate-temperature applications.

Fire Protection of Steel Structures of Oil and Gas Facilities: Multilayer, Removable, Non-Combustible Covers

Fire protection is required to protect metal structures of oil and gas facilities from fires. Such fire protection should provide high fire resistance limits: 60, 90, 120 and more minutes. Specialists of LLC “RPC PROMIZOL ” developed a multilayer, removable type of fire protection made of superfine basalt fibre and ceramic materials for operation in Arctic conditions. Five experimental studies were carried out in standard and hydrocarbon fire regimes. The fire protection effectiveness of the products for I20 beams without load was obtained: a 50 mm thick coating provided 130 min of a standard fire regime; a 15 mm thick coating provided 60 min. The 15 mm thick coating provided 30 min of a hydrocarbon fire regime and the 50 mm thick coating provided 93 min of a hydrocarbon fire regime. The I40 beam under a load of 19.9 tf showed an R243 for the standard fire regime. The coefficients of effective thermal conductivity and specific heat capacity of fire-retardant compositions were determined by solving the inverse heat conduction problem. The problem was solved by modelling using the QuickField 7.0 software package, which implements FEM. Modelling showed that for obtaining the fire resistance limit R120 under the standard fire regime for the sample steel structure from an I40 beam, it is enough to apply fire protection with a thickness of 25 mm instead of 50 mm, which agrees with the experimental data. For the hydrocarbon regime, it is predicted that R120 can be obtained at a thickness of 45 mm instead of 50 mm.

Intensification of hydrodynamics and heat transfer characteristics of coal-char-gas flow in a high solids-flux downer with swirling blade nozzle

Achieving high-density particle operation and obtaining uniform inlet particle distribution in the downer is the key to improving pyrolysis yield. In this work, a multifluid framework was developed to systematically study the hydrodynamics and heat transfer characteristics of a downer with swirling blade nozzle (DSBN). A heat transfer model that considers gas-solid convective, solid-solid collision, and thermal radiation was established. And a swirling blade enhancement factor (β) was defined to quantify the flow mechanism and heat transfer characteristics of coal-char particles. Results indicate that SBN can shorten the time for flow to reach stability by 33.3%. The βCV on coal and char can reach a maximum of 87.6%, enhancing the uniformity of particles velocity flow field. Regarding heat transfer characteristics, the stable temperature of coal in DSBN is higher than conventional downer (CD), βU on coal and char can reach 6.64% and 1.69%, respectively. The optimal strengthening effect of SBN on the char-coal mixing is concentrated at the inlet, with a maximum βIM of 70.17%. Also, compared to the CD, coal-gas and char-gas heat transfer coefficients in the DSBN have increased by 147.3% and 31.5%, respectively, and the coal-char thermal conductivity coefficient has increased by 77.8%.

Kaolin Clay-Based Geopolymer for Ionic Thermoelectric Energy Harvesting.

Geopolymers, a class of sustainable inorganic materials derived from natural and recycled resources, hold promise for various applications, including thermoelectric power generation. This study delves into the thermoelectric properties of Ikere white (IKW)-geopolymer, derived from kaolin clay, by employing rigorous measurements of thermal conductivity, electrical conductivity, and Seebeck coefficient. The investigation elucidates the pivotal role of temperature and ions in shaping the thermoelectric performance of IKW-geopolymer. Electrical conductivity analysis pinpoints ions within the geopolymer's channels as primary contributors. Beyond a critical temperature, the evaporation of bulk water triggers a transition of charge carriers from one- to three-dimensional motion, resulting in reduced conductivity. The Seebeck coefficient exhibits a range from -182 to 42 μV/K, with its time-dependent profile suggesting that ions potentially drive thermoelectricity in cementitious materials. Notably, a unique transition from n-type to p-type behavior was observed in the geopolymer, opening new avenues for ionic thermoelectric capacitors. These insights advance our understanding of thermoelectric behavior in geopolymers and have the potential to propel the development of novel building materials for energy conversion applications.

Thermal Sintering Matchability between Low‐Temperature Cofired Ceramic Substrate and Silver Pastes and the Effect of CuO on Silver Diffusion Inhibition

Low‐temperature cofired ceramic (LTCC) materials are a promising material for heat dissipation substrates due to their excellent thermal conductivity and thermal expansion coefficient similar to that of silicon. However, the difficulties in surface metallization techniques limit its application. This work uses Bi–B–Si–Zn–Al glass/ceramic composite as the substrate and Bi–B–Si–Zn–Al glass powder as the inorganic binder for silver pastes. The silver thick film with a glass content of 3 wt% is sintered at 800 °C for 30 min, and the samples have excellent electrical conductivity (surface square resistance of 0.29 mΩ £−1) and mechanical properties (interface bonding force of 17.56 MPa). In addition, the introduction of CuO into the glass phase can inhibit the silver diffusion phenomenon during the sintering process and improve the conductive performance of the material. The results are beneficial for the preparation and application stability of LTCC devices.

Thermal analysis of rectangular moving fins with temperature‐variant properties by employing the Galerkin scheme

AbstractIn the present study, the thermal behavior of a longitudinal fin considering three types of heat transfer mechanisms (conduction, convection, and radiation) is investigated. For this research, thermal conductivity, heat source, and heat transfer coefficient are assumed nonindependent. A semianalytical scheme called the Galerkin Method is utilized for solving the dimensionless governing equation. The impacts of important physical variables like Peclet number, gradient of thermal conductivity, thermo‐geometric parameter, and radiation–conduction parameter on temperature profiles are analyzed comprehensively. The obtained results indicate that raising the thermo‐geometric parameter from 0 to 2 leads to a 32% reduction in the temperature profile. Also from the results, it can be found that a 28% increment in the temperature is observed by changing the gradient of thermal conductivity from 0 to 2.

The Potential of 3D Printing in Thermal Insulating Composite Materials-Experimental Determination of the Impact of the Geometry on Thermal Resistance.

This paper focuses on the analysis of the thermal properties of prototype insulation structures produced using SLS and SLA additive technologies. There is a noticeable lack of analysis in the scientific literature regarding the geometry of 3D-printed structures in terms of their thermal properties. The aim of this paper was to analyze printed samples of prototype thermal insulation composite structures and their potential for use in building applications. The research material consisted of closed and open cell foams of varying structural complexity. Increasing the complexity of the composite core structure resulted in a statistically significant decrease in the value of the thermal conductivity coefficient λ and the heat transfer coefficient U, and an increase in the thermal resistance Rc. The experimental results showed that the geometric structure of the air voids in the material is a key factor in regulating heat transfer. The control of porosity in materials produced by additive technology can be an effective tool for designing structures with high insulation efficiency. The best performance of the prototype materials produced by the SLS method was a three-layer cellular composite with a gyroid core structure. It was also shown that the four-layer gyroid structure panels with an outer layer of metallized polyethylene film produced using 3D SLA printing had the best thermal insulation. As a result, the analysis confirmed the possibility of producing energy-efficient insulation materials using 3D printing. These materials can be used successfully in construction and other industries. Further research will significantly improve the quality, accuracy, and speed of printing insulation materials, reduce the negative impact on the natural environment, and develop intelligent adaptive solutions.

First principles insights into Cs2XAgCl6 (X= Sc, Y) compounds for energy harvesting applications

Herein, the investigation is presented to analyze the structural, electronic, optical, and thermoelectric features of Cs2XAgCl6 (X= Sc, Y) by applying the first principles approach. The confirmation of the stable structure of both compounds is reinforced by the negative values of formation enthalpies. The electronic band gaps (Eg) of 3.78/4.86 eV are computed for Cs2ScAgCl6 /Cs2YAgCl6 through Tran-Blaha modified Becke-Johnson (TBmBJ) potential, correspondingly. The tolerance factor(τ) is found as 0.9 for Cs2ScAgCl6 and 1.0 for Cs2YAgCl6 which confirmed the stable cubic nature of both compounds. Optical factors like dielectric-function ε(ω), absorption coefficient α(ω), and others related parameters are analyzed within 0 to 10 eV of energy span. Both compounds demonstrated high absorption in the ultraviolet region, rendering them as well-suited materials for photovoltaic applications. The calculated values of refractive index for Cs2ScAgCl6 and Cs2YAgCl6 indicated super-luminescent characteristics in the ultraviolet region. For thermoelectric (TE) features, electrical conductivity (σ/τ), figure of merit (ZT), power factor (PF), thermal conductivity (k/τ), and Seebeck coefficient (S) are calculated using the BoltzTraP code. According to the findings, both materials are advocated as promising candidates for thermoelectric and optoelectronic applications.

Köpük Beton Üretiminde İnşaat Yıkıntı Atığı İnce Agregası Kullanımı ve Optimum Su/Çimento Oranının Belirlenmesi

İnşaat sektöründe hammadde temini doğal kaynaklarımız hızlı azalmasına veya tahrip edilmesine neden olmaktadır. Doğal kaynakların azalmasını veya tahrip edilmesini azaltmak için inşaat yıkıntı atıklarının geri kazanılması, hammaddeye ihtiyacını ve aynı zamanda çevresel kirliliğini de azaltılacaktır. Bu çalışmada inşaat yıkıntı atığı ince (kum) agrega ile köpük beton üretile bilirliği araştırılmıştır. Karışımlarda agrega olarak 4 mm elekten geçen inşaat yıkıntı atığı kullanılarak 5 farklı su/çimento oranı ile köpük beton üretilmiştir. Üretilen köpük beton numunelerinin birim hacim ağırlıkları, basınç dayanımları, su emme oranı, ultra ses geçiş hızı ve ısıl iletkenlik katsayıları gibi özellikleri incelenmiştir. Bu özeliklerden en uygun olanlar S/Ç oranı 0,45 olan karışım tasarımı vermiştir.

Revisiting thermo-physical property models of Al2O3-Water nanofluid for natural convective flow

One of the comprehensive ways of heat transport performance augmentation of thermo-fluid systems is to use nanofluid over base fluid. This study mainly scrutinizes several existing models of thermal conduction coefficient and absolute viscosity of Al2O3-water nanofluid with the experimental data. A benchmark problem of natural convective flow is selected to test the performance of the available nanofluid models. The Rayleigh number varies between 103 and 109, while the solid-volume proportion (φ) changes from 0 to 4%. The governing mathematical model is numerically discretized via the Galerkin finite element procedure under appropriate auxiliary conditions. The results produced by the models are verified with the existing experimental findings based on the evaluation of the Prandtl number and average Nusselt number. It has been confirmed that the AH model (Azmi's viscosity and Ho's conductivity models) is suitable for lower nanoparticle concentration (φ = 0.01), the AM model (Azmi's viscosity and Maxwell's conductivity models) for moderate concentration (0.01 < φ < 0.04), and the NH model (Ngueyn's viscosity and Ho's conductivity models) for higher value of the solid-volume proportion (φ = 0.04).

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption

AbstractThe development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero‐structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)‐(AgNWs@BNNS)‐(BNNS/ANF) (denoted as BAB) composite films by “filtration self‐assembly, air spraying, and hot‐pressing” method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in‐plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption.

The development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero-structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)-(AgNWs@BNNS)-(BNNS/ANF) (denoted as BAB) composite films by "filtration self-assembly, air spraying, and hot-pressing" method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in-plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015 Ω ⋅ cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Heat-insulating foam-silicate materials

Purpose: The aim of this work is to study the density, thermal conductivity and strength of insulating materials and fine-grained concrete based on cement binder with the use of foamed silicates. Vermiculite from Tatarsky deposit (Krasnoyarsk region), perlite from Khasynsky (Magadan region) and Mukhor-Talinsky (Republic of Buryatia) deposits, and tripoli from Potaninsky deposit (Chelyabinsk region) are used to obtain porous fillers.Research findings: It was found that the strength of materials based on cement binder and foamed silicates is determined by the strength of hydrated cement, aggregate, and contact zone of hydrated cement and filler. The coefficient of thermal conductivity of insulating materials based on foamed granules of natural dispersed raw materials (vermiculite, perlite, tripoli) with cement (23.5 vol. %) ranges from 0.112 to 0.181 W/(m·deg), which is 1.5–1.6 times higher than thermal conductivity of the granular layer.Compressive strength of the obtained materials ranges between 2.0 and 4.0 MPa. Compressive strength of lightweight concrete with the silica sand content of 32 vol.% and plasticizer, increases up to 8.5 MPa in compositions with vermiculite and up to 9.4 MPa in compositions with perlite from Mukhor-Talinskoe deposit.Depending on the quartz sand content, the density of concrete with foamed vermiculite and foamed perlite varies from 1100 to 1400 kg/m3 and from 1300 to 1600 kg/m3, respectively. Thermal conductivity of concretes with minimum density is 0.193 W/(m·deg) in the composition with vermiculite and 0.286 W/(m·deg) in the composition with perlite. At the maximum density of fine-grained concrete, the thermal conductivity increases to 0.277 and 0.411 W/(m·deg), respectively.

Effect of hydrostatic pressure on opto-electronic, elastic and thermoelectric properties of the double perovskites Rb&lt;sub&gt;2&lt;/sub&gt;SeX&lt;sub&gt;6&lt;/sub&gt;(X=Cl,Br): a DFT study

Double perovskites find applications across a diverse range of situations and varying pressure conditions. In this work, Quantum ESPRESSO code with a plane wave basis set was used to study the opto-electronic, elastic, and thermoelectric properties of Rb2SeX6 (X=Cl, Br) double perovskites under hydrostatic pressure (0 - 8 GPa). Perdew-Burke-Ernzerhof for Solids (PBESol) with generalized gradient approximation (GGA) was used as exchange-correlation functional. The band gap values of the materials decrease under hydrostatic pressure. Rb2SeCl6 has a band gap value of 2.44 eV at 0 GPa, 2.21 eV at 2 GPa. Above 2 GPa, the material has a metallic nature. Rb2SeBr6 has a band gap value of 1.56 eV at 0 GPa, but has a metallic nature under hydrostatic pressure (2 GPa to 8 GPa). The optical properties results indicate that the materials exhibit maximum absorption, high reflectivity, low optical loss in the visible and ultraviolet regions, good optical conductivity, and a refractive index suitable for use in opto-electronic applications. The materials are confirmed to be mechanically stable under all the hydrostatic pressure values studied. Electrical conductivity, thermal conductivity, and Seebeck coefficient (S ) values of the studied materials increase with an increase in hydrostatic pressure and temperature. The maximum value of S for Rb2SeBr6 is 0.248 x 103 (m V/k), while for Rb2SeCl6, maximum S = 0.175 x 103 (m V/k). The positive values of S suggest that the predominant charge carriers of Rb2SeCl6/Br6 are holes. Also, Rb2SeBr6 has a figure of merit (ZT) value of 3.44, while for Rb2SeCl6, ZT = 1.07. Since the values of ZT are greater than unity, the two double perovskite materials have good ZT values for thermoelectric device engineering. The results also suggest that Rb2SeBr6 is a better thermoelectric material than Rb2SeCl6.

Utilization of variable thermal conductivity and diffusion coefficient on non-Newtonian Prandtl model with modified heat and mass fluxes

PurposeThis study aims to analyze the Prandtl fluid flow in the presence of better mass diffusion and heat conduction models. By taking into account a linearly bidirectional stretchable sheet, flow is produced. Heat generation effect, thermal radiation, variable thermal conductivity, variable diffusion coefficient and Cattaneo–Christov double diffusion models are used to evaluate thermal and concentration diffusions.Design/methodology/approachThe governing partial differential equations (PDEs) have been made simpler using a boundary layer method. Strong nonlinear ordinary differential equations (ODEs) relate to appropriate non-dimensional similarity variables. The optimal homotopy analysis technique is used to develop solution.FindingsGraphs analyze the impact of many relevant factors on temperature and concentration. The physical parameters, such as mass and heat transfer rates at the wall and surface drag coefficients, are also displayed and explained.Originality/valueThe reported work discusses the contribution of generalized flux models to note their impact on heat and mass transport.

Numerical prediction of thermal conductivity and thermal expansion coefficient of glass fiber-reinforced polymer hybrid composites filled with hollow spheres

The optimal performance of composites enriched with hollow spheres has been reported in contemporary literature, whereas their thermal properties have received less attention. In this regard, a finite element method (FEM)-based micromechanical model has been developed systematically to investigate the role of intra-matrix embedding of hollow spheres on the thermal conductivity and coefficient of thermal expansion (CTE) of unidirectional fiber-reinforced hybrid composites. In so doing, the concept of representative volume element (RVE) considers microstructures comprising an epoxy matrix, E-glass fiber, and E-glass hollow spheres, assuming perfect bonding (ideal interface) between the components and modified approximate periodic boundary conditions. By computing the longitudinal and transverse temperature gradients generated due to the application of uniform heat flux as well as the geometrical variation in RVE owing to temperature enhancement, thermal conductivity and CTE have been respectively determined. Comprehensive evaluations have been conducted to examine the effects of microstructural-level features, including fiber volume content and orientation, plus volume content and thickness of hollow spheres, on the effective thermal conductivity and CTE of pseudo-porous ternary E-glass/epoxy composites.