Influence Of Thermal Conductivity Research Articles

Numerical study of radiative non-Darcy nanofluid flow over a stretching sheet with a convective Nield conditions and energy activation

Abstract Numerous industrial processes such as continuous metal casting and polymer extrusion in metal spinning, include flow and heat transfer over a stretching surface. The theoretical investigation of magnetohydro-dynamic thermally radiative non-Darcy Nanofluid flows through a stretching surface is presented considering also the influences of thermal conductivity and Arrhenius activation energy. Buongiorno’s two-phase Nanofluid model is deployed in order to generate Thermophoresis and Brownian motion effects [1]. By similarity transformation technique, the transport equations and the respective boundary conditions are normalized and the relevant variable and concerned similarity solutions are presented to summarize the transpiration parameter. An appropriate Matlab software (Bvp4c) is used to obtain the numerical solutions. The graphical influence of various thermo physical parameters are inspected for momentum, energy and nanoparticle volume fraction distributions. Tables containing the Nusselt number, skin friction and Sherwood number are also presented and well argued. The present results are compared with the previous studies and are found to be well correlated and are in good agreement. The existing modelling approach in the presence of nanoparticles enhances the performance of thermal energy thermo-plastic devices.

Influence of Thermal Conductivity on the Thermal Behavior of Intermediate-Temperature Solid Oxide Fuel Cells

Influence of Thermal Conductivity on the Thermal Behavior of Intermediate-Temperature Solid Oxide Fuel Cells

Investigation on the cooling and temperature uniformity of power battery pack based on gradient phase change materials embedded thin heat sinks

In order to further increase the temperature uniformity of power battery, a thermal management method based on thin heat sink embedded with PCM was investigated in this paper. The thermophysical property and distribution of PCM are the key factors affecting the thermal management performance. A comparative study on the cooling and homogenization performance of the battery thermal management system under different thermal conductivities, melting temperature and distributions of PCM were explored carefully. The main results show that the maximum temperature and temperature standard deviation (STD) of the battery can be decreased with the function of heat sink embedded with PCM. Comparing to air cooling method, the maximum temperature and STD of the battery can be decreased by about 11.2% and 78.3% at 600 s, respectively. The influence of thermal conductivity can be neglected. Lowering the melting temperature and increasing latent heat can reduce the maximum temperature and STD. In additional, it is found that the distribution of PCM with different melting temperature or latent heat can obviously affect the maximum temperature and temperature uniformity of the battery. It could be a useful way to optimize the thermal management performance.

Thermal Mode Optimization of Combustion Chamber Walls for Power-Plants Using Semitransparent Porous Ceramics

The paper examines control and management by thermal mode of the internal surface of heat-insulated combustion chamber walls for green & efficient diesel and gas turbine engines due to the application of opaque or semitransparent thermal barrier materials (coatings). The authors’ model is devoted to combined radiant heat transfer both inside the heat-insulated combustion chamber and its ceramics walls, which could be scattering and absorbing for penetrating radiant component in the subsurface volume of optically heterogeneous porous material. The influence of thermal conduction, scattering (absorption) and external convective effects on the increase of the internal overheating zone in subsurface layers is simulated under intensive radiation. The unique set of optical, thermal-physical and mechanical properties of structural ceramics, depending on their porosity, were first proposed. The radiation fields of the absorbed energy in the near IR region and the corresponding temperature distributions in the modeled opaque and semitransparent ceramics walls were calculated under a stationary radiant-convective heat load during the active combustion phase at time intervals 0.01…0.1 s (diesel engines) and 10...100 s (turbine ones). In order to control the emission of nitrogen oxides, the authors propose a generation model of NOx, its growth or reduction caused by the management of radiant overheating inside semitransparent heat-insulation in which surface temperature is due to volumetric radiant absorption. It is shown that for semitransparent materials (coatings), the optimal thermal mode is determined first of all by thermal radiant characteristics in near IR at heating small times and it begins to correct at long ones due to the effect of thermal conductivity. This process may be modeled and regulated by the selected microstructural porosity of ceramic heat insulation.

Influence of Thermal Conductivity on Stacking Sequence of Hybrid Composites

Hybrid Composites comprising of two or more reinforcement materials are finding increase in demand in diverse field of applications such as building panels, automotive components and aero parts. There is a need to study the thermal properties to find the suitability of hybrid laminates as insulating materials. In this research article an attempt is made to find the thermal conductivity of laminate materials having varying stacking sequence of its reinforcement fibers. The said laminate is produced using hand layup method. It contain seven layers of reinforcement fibers stacked one over other in three different configurations. First the reinforcements kevlar (K49) and basalt fibers are stacked in alternating layers. Second configuration contain bilayers of kevlar or basalt sandwiching the inner three alternative layers. Third configuration contain tri layer of one of the reinforcement fibers sandwiched between bilayers of another reinforcement fibers. Epoxy resin is used as binding cum matrix element in all the hybrid laminates. The produced hybrid laminates are tested for its thermal conductivity and coefficient of thermal expansion. It is found that increasing the number of layers of basalt fibers increased the thermal conductivity of the hybrid laminate. On the other hand, kevlar fibers contributed in reducing the thermal conductivity of the hybrid laminates. Thermal expansion coefficient depended on the presence of basalt fibers as the outermost layers in the hybrid laminates. The hybrid laminates having kevlar fibers contributed in lowering thermal conductivity and also the coefficient of thermal expansion.

Performance of SrBr2·6H2O based seasonal thermochemical heat storage in a novel multilayered sieve reactor

The salt hydrate-based thermochemical heat storage (TCHS) system, based on a reversible solid-gas chemical reaction, is currently a key technique used to store heat for later discharge. Strontium bromide hexahydrate (SrBr2·6H2O) is one of the most promising candidate materials in seasonal heat storage for residential heating due to its lower desorption temperature. This study develops and numerically investigates a novel multilayered sieve reactor that can promote dehydration and hydration reactions. This paper focuses on the interaction between the porous reactive salt beds and the vapor in an open system. The required time to totally dehydrate and hydrate the salt beds are approximately 1180 min and 940 min, respectively. The effects of various operating conditions such as input temperature, inlet velocity, and relative humidity of fluid on charging and discharging are studied, as well as the influence of thermal conductivity, permeability and kinetic factors. For instance, the reaction kinetic factor Rkin = 1.0 × 10−4 is a threshold in this model. The optimized salt beds reduce dehydration time by 11.4% (130 min). High volumetric thermal powers are obtained for the multilayered sieve reactor, although the values decrease with the degree of conversion. The results indicate that the thermal efficiency η, thermal coefficient of performance (COPth), and exergy coefficient of performance (COPex) of charging are 85.2%, 72.4%, and 21.3%, respectively, and the corresponding values for discharging are 94.5%, 71.5%, and 21.1%, respectively, for the model studied.

Influence of thermal conductivity and of non-constant relaxation time on thermoelectricity in Mg3Sb2

We discuss the effects of different approximations to thermal conductivity and relaxation time on the thermoelectric figure of merit ZT in n-doped Mg3Sb2. We use density-functional electronic structure and Bloch-Boltzmann transport theory with an energy-dependent relaxation time. ZT is monotonically increasing with T in our range (300-700 K) with a maximum value of ∼1.5.

Impact of homogeneous–heterogeneous reactions and non-Fourier heat flux theory in Oldroyd-B fluid with variable conductivity

This article scrutinizes the influence of chemical reactions on flow of an Oldroyd-B fluid due to stretched cylinder. In vision of non-Fourier heat flux model, the heat transfer phenomenon is scrutinized. This enhanced constitutive model anticipates the time space upper-convected derivative which is recycled to depicting heat conduction mechanism. Additionally, heat transfer scrutiny is considered with the influence of thermal conductivity which is temperature dependent. Apposite conversions are engaged to acquire ODEs which are then deciphered analytically via homotopic approach. To highlight their physical consequences, the graphical portrayal of diverse considerations on velocity, temperature and concentration fields is depicted and conferred. It is scrutinized from this study that all the profiles are higher in the instance of the cylinder as equated to a flat plate. This scrutiny also reported that the thermal relaxation parameter decreases the temperature field while the Schmidt number and homogeneous response parameter display the conflicting performance on concentration field. In addition, an assessment in restrictive instance is also presented in this exploration, which ensures us that our outcomes are more precise.

Influence of thermal conductivity of ceramic materials on heating rate/coking time and coke quality in cokemaking

The Iron and Steel Industry has undergone a radical change, and processes have been developed continually for the faster rate of production. The thermal characteristic of reaction depends on the thermal conductivity of coal charge by progressively developing the zone of coke. In general, higher the oven temperature, the more rapid is the initial rate of heating, plastic temperature range, plasticity and volatile evolution characteristics of the coal. The higher thermal conductivity of bricks will increase heat transfer rate and consequently, the output of the oven will increase the throughput. The heating rate is also associated with the pattern of heat supply during carbonization which influences the strength and fissuring of the coke. Results show that replacement of LC-65 castable with higher thermal conductivity castable SiC-30% reduces the coking time by 50% whereas LC-85 reduces the coking time by 20% even at same coke end temperature and coke CSR. The requirement of free space temperature of the laboratories oven is different for using different thermal conductivity of the ceramic castable to maintain same heating rate and coke end temperature during coking. Results confirmed that increasing the thermal conductivity of ceramic castable decrease in the free space temperature to maintaining the constant heating rate (∼4 °C/min) and coke end temperature (∼925 °C). The results also depict that the use of SiC-30 and LC-85 castable, the input temperature should be reduced by ∼200 °C and ∼100 °C to maintain the same heating rate and coke end temperature as compared to LC-65 castable. The study will also beneficial for reducing the Noxs.

Investigation of Thermal Conductivity by Hot Ball Method and its Correlation with Soil Quality Index of Veracruz Sugarcane Soil

Different samples of soil were collected in two sugarcane crops in the Veracruz Region at two different depths. A transient method called hot ball was used to analyze the thermal conductivity of sugarcane soils for analyzing the influence of thermal conductivity on the soil quality index. Thermal conductivity results indicated a low thermal conductivity ranging from 1.81 × 10−1 to 3.15 × 10−1 Wm−1 K−1. Global chemical composition and organic matter content of the studied soils were presented. Physicochemical parameters were used to perform the soil quality index study. pH results were within the 5–5.5 range, whereas the textural analysis tended to the clayed soil. The soil quality index results suggest a very-low-quality soil. The thermal conductivity was also correlated with the soil quality index. The Pearson correlation coefficient of thermal conductivity against the moisture content showed a coefficient of r = − 0.414 which indicated a close and inverse relationship between both parameters. The sampled results pointed out that the Pearson coefficient for thermal conductivity against nitrate and phosphate was higher than the other chemical components, suggesting that the presence of fertilizer increased the thermal conductivity of the studied soil.

The characteristics of pure heterogeneous reaction for H2/Air mixture in the micro-combustors with different thermophysical properties

This paper investigated the characteristics of pure heterogeneous reaction for H2/Air mixture under different wall thermophysical conditions namely; thermal conductivity, convective heat transfer and thermal capacity. The phenomena of pure heterogeneous reaction were observed by OH Planar Laser induced Fluorescence (OH-PLIF) to determine the working conditions. (3D)-models were built to numerically study the effects of different wall thermophysical conditions. The results show that lower thermal conductivity and convective heat transfer coefficient is beneficial to enhancing heterogeneous reaction and improve conversion rate of H2 as less heat is dissipated. The greater thermal capacity has beneficial impact on the reaction stability when the boundary condition changes, but no effect under the steady state. The performance of thermal conduction and convection were comprehensively considered to study the influence and proportion of each on the heterogeneous reaction. Higher thermal resistance can improve the reaction efficiency, reaction stability and reduce application cost. The influence of thermal conduction is greater than that of convective heat transfer.

Thermomechanical and thermophysical characteristics of alumina-carbon monolithic refractory containing surface-modified graphites in matrix

The thermophysical and thermomechanical behavior of graphite-containing refractory castable matrix with 20.0 wt% of graphite had been compared with graphite-free high alumina based castable matrix analogous to it. The thermomechanical properties of similar type of castables with and without 5.0% of graphite had also been evaluated. Graphite was incorporated both as coated and as-received forms, the former having a thin sol-gel derived calcium aluminate coating on graphite flakes. The influence of thermal conductivity, thermal diffusivity and pore size distribution had been critically estimated. The changes in flexural strength, porosity and density of the matrices had also been determined to interpret the castable performance, namely refractoriness under load (RUL), spalling resistance and conventional physical properties. The role of coated graphite on improved densification and thermal tolerance of refractories was further explored by microstructure and phase evolution studies of all kinds of fired samples at 1500 °C. It was further supplemented with the scanning electron microscope (SEM) studies of surface-modified graphites at uncalcined and calcined condition.

Effect of phase transition temperature and thermal conductivity on the performance of Latent Heat Storage System

The heat transfer properties of phase change materials (PCMs) are of importance for the efficiency assessment on the heat storage and release in solar thermal systems. Previous research results demonstrate that the increase of thermal conductivity of PCMs can enhance the thermal performance in solar thermal systems; however, the corresponding mechanism is not clear. To this end, this work investigates the influence of PCMs properties on storage performance of solar thermal systems. First, experimental testing was conducted to verify the effectiveness of a thermal simulation model in the heat storage and release process. Then, the proposed simulation model was used to investigate the performance of several commonly used PCMs in the process of melting and solidification. The influence of thermal conductivity and phase transition temperature on the thermal storage properties was analyzed. The analysis results demonstrated that the influence of phase transition temperature on the thermal system performance was greater than that of the thermal conductivity in short time, while the thermal conductivity contributed greater influence on the system performance in long time. The phase transition temperature hardly affected the total system efficiency if given enough heat transfer time. The findings in this work may provide a theoretical reference for the selection of heat storage materials.

Selection of the Optimized Carbon Material for PEFC Separator

Recently, although PEFC begins to commercialize in various fields such as domestic co-generation system and fuel cell vehicle etc., it is necessary to reduce the cost compared with an existing competitive commodity for a further dissemination. One of the costly parts is the carbon separator which demands a high airtightness, a high drainage and a high durability. The current specification of the carbon separator is not optimized by system requirements of each fuel cell commodity though the environment for which the fuel cell is used by each commodity is different. Therefore, we evaluated the influence of each carbon material characteristic on the cell performance by installing each separator made of each carbon material to the PEFC single cell. As a result, although the influence of thermal conductivity on the cell performance was able to be confirmed, and we also consider that the surface-property of the material greatly influences on the cell performance.

Numerical analysis on thermal characteristics of transpiration cooling with coolant phase change

A numerical investigation of phase change transpiration cooling has been conducted in this work using the modified separate flow model, in which the effects of capillarity, non-isothermal characteristics in two-phase region and the local thermal non-equilibrium characteristics between the coolant and the matrix have been considered to describe the liquid coolant phase change and heat exchange process. The influences of thermal conductivity, porosity and sphere diameter of the porous matrix, main flow temperature and heat transfer coefficient at the hot surface on temperature and saturation distributions and temperature difference within the matrix have been investigated numerically. The results indicate that a higher coolant mass flow rate can delay liquid evaporation, increase the temperature gradient in superheated vapor region and decrease the solid temperature at the hot surface, but with an increase in main flow temperature or heat transfer coefficient at hot surface, the coolant temperature increases in liquid region and especially in superheated vapor region, and the solid temperature at the hot surface increases dramatically. The results also indicate that a higher solid conductivity corresponds to a higher temperature in liquid region and in nearly the whole superheated vapor region, but a slightly lower temperature at the hot surface. A special result has been obtained that with an increase in the porosity and sphere diameter the corresponding interface of liquid region moves leftwards with the two-phase region extended, and the coolant temperature decreases in two-phase region and superheated vapor region, while in liquid region firstly it decreases and then increases, as may be determined by both heat transfer and especially pressure drop which varies dramatically with porosity and sphere diameter. The thermal non-equilibrium characteristics have been analyzed, and the results show that it is obvious at the cold surface, at the hot surface and at the beginning and the ending of two-phase region, and it is most obvious near the ending of two-phase region, and the coolant temperature is higher than the solid temperature at the beginning of two-phase region.

Serrated chip formation mechanism analysis for machining of titanium alloy Ti-6Al-4V based on thermal property

Based on the software ABAQUS/Explicit, a finite element (FE) model for orthogonal cutting was established. The FE model was validated by comparing the cutting forces and serrated degree of chips obtained by orthogonal cutting experiments under the cutting speeds 40, 80, 120, and 160 m/min. Based on the developed FE model, the influence of thermal conductivity on the degree of chip segmentation and the adiabatic shear localization were investigated. Furthermore, the plot contours on undeformed shape of cutting simulation was used to investigate the temperature distribution, and the high temperature zone was identified, which can help enhance the understanding of the serrated chip formation. Finally, cracks located in the adjacent segments of chips were observed. The results show that with the increase in thermal conductivity, the degree of adiabatic shear decreases. It can be concluded that the poor thermal conduction performance should be primarily responsible for the formation of serrated chips during machining Ti-6Al-4V alloy. Due to the high temperature at contact surface between cutting tool and workpiece, the increasing of cutting speed facilitates the formation of serrated chips during machining.

Thermal Performance Characteristics of Porous Media Receiver Exposed to Concentrated Solar Radiation

Solar thermal power plants with central receiver systems are promising candidates for the harvest of solar energy. However, the development and application of volumetric receivers are restricted owing to the nonuniformity of incident heat flux distribution, which may reduce thermal efficiency and even lead to structural damage. In the present work, the influence of thermal conductivity and radiation distribution on the thermal response of porous receivers is studied. On this basis, a transient thermal model was developed. It was found that porous media receivers with larger thickness will ensure that the thermal energy of the receivers will be fully taken advantage of by flowing air and improve the efficiency of the whole system. For porous receivers exposed to concentrated solar radiation with a Gaussian distribution, the temperature distribution along the radial direction also distributes in a Gaussian shape, with a mean temperature the same as that of uniform distribution heat flux. In working conditions where the intensity of concentrated solar radiation changes rapidly, the rate of temperature increase/decrease may be too high, which may cause damage to receivers.

Numerical analysis of the NiTi solidification process influence of thermal conductivity

The present study deals with the numerical analysis of the solidification process of a NiTi binary alloy. The physical medium is taken as an incompressible fluid where the heat is transferred by conduction and convection, including the thermal phase change phenomenon. The energy equation, which includes both convection-diffusion heat transfer and a mushy region for the phase-change (solidification), is modelled by using an enthalpy-based formulation. The numerical approach is based on the finite volume method in body fitted coordinates with a PISO scheme to couple the pressure and velocity fields. The results are presented for the temperature field, as well as for the NiTi mass fraction during the solidification process.

Concurrent design of composite materials and structures considering thermal conductivity constraints

ABSTRACTThis article introduces thermal conductivity constraints into concurrent design. The influence of thermal conductivity on macrostructure and orthotropic composite material is extensively investigated using the minimum mean compliance as the objective function. To simultaneously control the amounts of different phase materials, a given mass fraction is applied in the optimization algorithm. Two phase materials are assumed to compete with each other to be distributed during the process of maximizing stiffness and thermal conductivity when the mass fraction constraint is small, where phase 1 has superior stiffness and thermal conductivity whereas phase 2 has a superior ratio of stiffness to density. The effective properties of the material microstructure are computed by a numerical homogenization technique, in which the effective elasticity matrix is applied to macrostructural analyses and the effective thermal conductivity matrix is applied to the thermal conductivity constraint. To validate the effectiveness of the proposed optimization algorithm, several three-dimensional illustrative examples are provided and the features under different boundary conditions are analysed.

Thermal conductivity and arcing resistance of micro or hybrid BN filled polyethylene under pulse strength

In this work, in order to investigate the effects of thermal conductivity on arcing resistance from the view of thermal accumulation under pulse strength, a range of polyethylene (PE) based composites filled with micro or hybrid boron nitride (BN) particles at different loadings (0, 3, 6 and 9 wt%) were prepared. Thermal conductivity and relative permittivity were measured to characterize the basic properties of various samples. Influences of thermal conductivity on thermal accumulation and arcing resistance were discussed through surface dielectric breakdown test. Obtained results show that the thermal conductivity of BN filled PE composite is obviously improved and the relative permittivity could maintain a relatively low value. At the same pulse frequency, with increasing filler concentration from 0 to 40 wt%, thermal conductivity and the time to surface dielectric breakdown all present increase trend, whereas sample surface maximum temperature and damage degree reflect the opposite tendency. It implies that the increased thermal conductivity contributes to reduce thermal accumulation during arcing discharge, which can help to promote the resistance to arcing discharge. Moreover, PE/hybrid-BN composite presents a higher thermal conductivity, a longer time to surface dielectric breakdown and a lower surface damage degree at the same filler content. It is concluded that adding hybrid-BN filler into PE resin can suppress thermal accumulation and improve arcing resistance more effectively.