Thermal Conductivity Characteristics Research Articles

Heat Transfer Analysis of Copper Stave in Blast Furnace Based on Slag Crust Characteristics

As a protective layer for the copper stave in the blast furnace, the characteristics of the slag crust have a non‐negligible influence on the heat transfer of the copper stave. Combined with the characteristics of slag crust thermal conductivity, flowing temperature, and thickness, the influence of slag crust on heat transfer from copper stave under different operating conditions is investigated, and the potential of slag crust thickness regulation to reduce carbon consumption in blast furnaces is assessed. It is found that the slag crust thicknesses calculated by the model are consistent with the range of thicknesses of the actual slag crust samples, validating the correctness of the model. To ensure the operational safety of the copper stave, in the actual production process of the blast furnace, the slag crust thickness should be controlled between 30 and 60 mm, and the corresponding thermocouple temperatures, water velocities, and heat flux intervals are calculated. In addition, when the slag crust thickness is increased from 10 to 30 mm, the 2650 m3 blast furnace can reduce the coke ratio by a maximum of about 14 kg t−1.

The Complex Valorization of Black Alder Bark Biomass in Compositions of Rigid Polyurethane Foam.

The use of black alder (BA) bark biomass in rigid polyurethane (PUR) foam compositions was the main task of investigation. Extractive compounds isolated from the bark through hot water extraction were used as precursors for bio-polyol synthesis via acid-free liquefaction with the polyether polyol Lupranol 3300 and through oxypropylation with propylene carbonate. The OH functionality and composition of the polyols were analyzed via wet chemistry and FTIR spectroscopy. The solid remaining after the isolation of extractive compounds was also utilized as a natural filler in PUR foams. The effects of replacing commercial polyols with bio-polyols on the foam rising rate and their mechanical properties, morphology, thermal conductivity, and thermal degradation characteristics were examined. The oxypropylated extractive-based PUR compositions demonstrated the most favorable balance between the biomass content and material properties. At an apparent density of 40 kg/m3, the compressive strength of the produced foams was enhanced by 1.4-1.5 times, while the maximum thermal degradation rate in air decreased by 3.8-6.5 times compared to reference materials without adversely affecting the foam morphology. The composition based on liquefied extractives showed lower performance but still improved properties relative to the reference foams. Introducing 3.7-14% of extracted bark into the foam compositions increased the biomass content to 22-24%, although this led to a decrease in the compressive strength and thermal stability. It was shown that partially substituting fossil-derived components with renewable bark biomass in the composition of PUR foams allows for materials with characteristics similar or better to petrochemical-based materials to be obtained. Therefore, the results presented can be considered a contribution to addressing environmental problems and promoting the development of a sustainable economy.

Spatiotemporal Distribution of Soil Thermal Conductivity in Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is ecologically fragile, and water resources are extremely scarce. Soil thermal conductivity (λ) is a vital parameter for controlling surface heat transfer and is the key to studying the energy exchange and water balance of the soil surface. The objective of this study is to investigate the spatial distribution characteristics of soil thermal conductivity on the Loess Plateau. The research primarily employed soil heat transfer models and the Google Earth Engine (GEE) platform for remote sensing cloud computing, compares and analyzed the suitability of six models (Cambell model, Lu Yili model, Nikoosokhan model, LT model, LP1 model, and LP2 model), and utilized the selected improved model (LT model) to analyze the spatiotemporal characteristics of thermal conductivity on the CLP, examining the impacts of soil particle composition, bulk density, elevation, moisture content, and land use on thermal conductivity. The results show that the LT model is the best in the relevant evaluation indices, with a determination coefficient (R2) of 0.84, root mean square error (RMSE) of 0.18, and relative error (RE) of 0.16. Furthermore, the λ on the CLP shows an overall trend of increasing from northwest to southeast, with a lower λ between May and August and a higher one between September and October. The λ of different land use types is as follows: built-up land > cropland > grassland > forest land > barren. The bulk density (ρb) and altitude mainly influence λ in the CLP. The results of this study can provide a theoretical basis for studying hydrothermal variation in the CLP, model application, energy development, and land resource use.

Modified boron nitride reinforced natural rubber composites and molecular dynamics simulation

AbstractFor thermal conductive boron nitride (BN)/polymer composites, an overabundance of BN in the formulation may significantly impair the mechanical integrity, thereby restricting their applicability in practical scenarios. In this work, we introduced a novel modifying agent, which was grafted onto the exterior of BN following high‐temperature calcination. The resultant modified boron nitride demonstrated a marked improvement in the thermal conductivity and mechanical characteristics of natural rubber (NR) composites. Upon incorporating a filler content of 60 phr, the modified boron nitride NR composite achieved tensile strength, elongation at break, and thermal conductivity to 19.34 MPa, 1402%, and 0.735 W/mK, respectively, which represented an increase of 23.97%, 75.69%, and 33.15% over the BN/NR composite. The observed enhancement in mechanical properties and thermal conductivity of the composites is the contribution of the novel modifier grafting on the BN surface, which has notably improved the interfacial interaction with NR. In addition, the binding energy, solubility parameter, free volume fraction, and radial distribution function of BN/NR and modified boron nitride NR composites were analyzed by molecular dynamics simulation, which provided support for the interface reinforcement mechanism. This simple and versatile modification method introduced in this work can broaden prospects in the design of natural rubber composites.Highlights Successful synthesized of a new modifier with long chains. Interfacial compatibility of composites explained by combining molecular dynamics simulations. Effectively improved both the mechanical and thermal conductivity of the composites. Successful use of high‐temperature assisted modification to graft modifiers onto BN surfaces.

Thermal conductivity and shrinkage characteristics of bentonite-fly ash and bentonite-sand backfill material

Thermal conductivity and shrinkage characteristics of bentonite-fly ash and bentonite-sand backfill material

Perspectives of Insulating Biodegradable Composites Derived from Agricultural Lignocellulosic Biomass and Fungal Mycelium: A Comprehensive Study of Thermal Conductivity and Density Characteristics.

The research suggests a production method of insulating composites created from lignocellulosic agricultural biomass with fungal mycelium as a binder agent and offers a deeper investigation of their thermophysical properties. Particularly, the samples were meticulously evaluated for density and thermal conductivity. The function was built on the suggestion by the authors regarding the thermal conductivity-weight ratio indicator. The metric was initially introduced to assess the correlation between these parameters and was also applied to qualitatively evaluate the biocomposite among other commonly used natural insulations. An applied polynomial trend analysis indicated that the most effective densities for the wheat, hemp, and flax, which were 60, 85, and 105 kg·m-3 respectively. It was determined that the optimal density for wheat and hemp composites corresponded to values of 0.28 and 0.20 W-1·kg-1·m4·K of the coefficient, respectively. These values were superior to those revealed in other common natural insulating materials, such as cork, cotton stalks, hempcrete, timber, etc. As a result, the proposed insulating material may offer numerous opportunities for application in industrial settings of civil engineering.

Thermal performance analysis of new bionic “fishbone” fins in a triplex-tube latent heat storage system with single cycle process

Targeting the low thermal conductivity characteristics of energy storage materials in latent heat thermal energy storage (LHTES) systems, a novel bionic fish bone fin design is proposed in this paper, and the numerical simulation is employed to analyze the thermal performance of a system during single charging and discharging cycle. In assessing the system, consideration is given to the time required to complete a cycle, mean temperature change rate, and charging and discharging efficiency over the course of a cycle. The temperature response of each monitoring point within the system was first analyzed for fishbone fins of different curvatures and found that the 30° and 60° fishbone fins have the fastest heat transfer rates and shortest cycle times, respectively. Subsequently, the effect of fishbone fractal position on the thermal performance of the system was investigated. The results showed that the system achieves the best circulating thermal performance when the fishbone fins are positioned in the middle of the straight fins. An increase in the dimensionless position of the fins from 0.2 to 0.5 produced a reduction in the cycle time of 28.03 % and an increase in the energy transfer efficiency of 38.15 %. Finally, the shortest cyclic cycle and the fastest heat transfer rate were taken as the optimization objectives to optimize and predict the thermal performance of the system through the response surface method. The findings demonstrated that the system exhibited optimal thermal performance when the radian angle of the fishbone fin is 44.43° and the dimensionless position is 0.45. Compared to traditional rectangular straight fins, the optimized structure reduces the cycle time by 52.64 % and increases the average heat transfer rate by 101.58 %.

Research on the design and thermal performance of vacuum insulation panel composite insulation materials

This study introduces a novel design methodology for composite insulation material aimed at reducing the operational energy consumption of buildings. Vacuum Insulation Panels (VIPs) are recognized for their excellent insulating properties due to their vacuum-sealed nature that minimizes thermal transmittance. However, VIPs are susceptible to damage from temperature stress and abrasion, which can compromise vacuum integrity and degrade performance over time. To mitigate this, a protective layer of rock wool board is adhered to the exterior of the VIP to create a composite insulation material. The thermal conductivity characteristics of the composite insulation materials are experimentally measured and then corroborated with simulations using ANSYS software to affirm the precision of finite element analysis methods. A composite Insulation wall model is constructed using ANSYS to analyze the impact of varying the thickness of the composite insulation materials and the pressure within the VIP on thermal performance. The findings demonstrate that the thermal transmittance coefficient of the composite insulated wall diminishes with increased insulation material thickness and rises with increased pressure within the VIP. Additionally, rock wool boards significantly enhance the durability of the composite insulation material.

Pt100 temperature measurement sensors design and transducer simulation

Abstract Temperature measurement (thermometry) is indispensable in industrial operations, aiding engineers in monitoring and evaluating temperatures. This study focuses on the utilization of Platinum Resistance Temperature Detectors (Pt100 RTDs) for precise thermal measurements, operating within an input simulation range of 0-10 V and tailored for measuring temperatures from 10°C to 90°C in chemical processes. Using the Siemens PLC300 simulation system as the power supply, the experiment involved connecting a Pt100 RTD to a DC balance Wheatstone bridge to assess thermal conductivity characteristics. The experiment in this research setup included a simulation of the circuit diagram using Multisim software, comprising a bridge configuration, amplifier circuitry, and voltage display. Results based on the Coefficient of Determination and Mean Squared Error demonstrated the sensor’s high accuracy and reliability. The experiment also underscored the importance of calibration and the impact of ambient conditions on measurement accuracy. The findings affirm the Pt100 RTD’s potential in industrial applications, offering valuable insights into its performance and areas for improvement in circuit design and component selection.

MECHANICAL PROPERTIES OF GLASS FIBER AND CARBON FIBER REINFORCED COMPOSITES

The significant potential of glass fiber-based composite materials in aerospace and aviation industries, automotive manufacturing, and medical equipment production is emphasized. It is concluded that glass fiber is much cheaper and less brittle compared to materials like carbon fiber or other plastic fibers, as glass fiber exhibits high resistance to tensile and compressive loads. The main stages of the technological process of composite manufacturing are described, and the key requirements for evaluating the mechanical parameters of glass fiber products are listed. An analysis of the scientific literature has established that the high strength of fiberglass ensures the stability of its thermal conductivity characteristics, making it resistant to environmental influences and aging. The thermal conductivity of fiberglass composites depends on several factors, the most important of which are the type of fiber and matrix, fiber volume fraction, fiber characteristics, control of heat flow, interaction between the matrix and fiber, and operating temperature. It is summarized that the mechanical properties of fiberglass structures depend on a number of factors, the most important of which are: the type of fiber and resin, fiber orientation (aligned, randomly oriented, woven, etc.), and the percentage content of each component.

Thermal conductivity in modified sodium silicate glasses is governed by modal phase changes.

The thermal conductivity of glasses is well-known to be significantly harder to theoretically describe compared to crystalline materials. Because of this fact, the fundamental understanding of thermal conductivity in glasses remain extremely poor when moving beyond the case of simple glasses, e.g., glassy SiO2, and into so-called "modified" oxide glasses, that is, glasses where other oxides (e.g., alkali oxides) have been added to break up the network and alter, e.g., elastic and thermal properties. This lack of knowledge is apparent despite how modified glasses comprise the far majority of known glasses. In the present work, we study an archetypical series of sodium silicate [xNa2O-(100 - x)SiO2] glasses. Analyses of modal contributions reveal how increasing Na2O content induces increasing vibrational localization with a change of vibrations to be less ordered and a related general decrease in modal contributions to thermal conductivity. We find the vibrational phases (acoustic vs optical) of sodium vibrations to be relatively disordered compared to the network-forming silicon and oxygen species, explaining how increasing Na2O content decreases thermal conductivity. Our work sheds new light on the fundamentals of glassy heat transfer as well as the interplay between thermal conduction and modal characteristics in glasses.

Influence of concentration on thermophoresis of spherical aerosol particles within a Brinkman medium

Abstract We are examining the thermophoretic movement of a uniform mixture of spherical aerosol particles, all with the same properties, as they are situated within a porous material. These particles can have various thermal conductivity and surface characteristics. This analysis focuses on situations where the Péclet and Reynolds numbers are small. The influence of particle interactions is carefully considered by using a unit cell model, a well-established method known for its accurate predictions in the context of sedimentation for monodisperse suspensions of spherical particles. The porous medium is represented as a Brinkman fluid characterized by a Darcy permeability, which can be determined directly from experimental observations. This medium is considered to be uniform and isotropic, and the solid matrix is in thermal equilibrium with the fluid flowing through the voids of the medium. The Knudsen number is assumed to be low, enabling the description of fluid flow through the porous medium using a continuum model that includes temperature jump, thermal creep, frictional slip, and thermal stress slip at the aerosol particle’s surface. The conservation equations for energy and momentum are individually tackled within each cell. In this model, each cell represents a spherical particle enclosed by a concentric shell of surrounding fluid. The thermophoretic particle migration velocity is determined across different cases. We derive analytical expressions for this average particle velocity, expressing it in terms of the particle volume fraction. It is observed that different cell models yield somewhat varied results for particle velocity. Generally, with a fixed permeability parameter characterizing the porous medium, an increase in the thermal stress slip coefficient tends to decrease the normalized thermophoretic velocity across the different cell models. The results are in good agreement with the available data as documented in the existing literature. Additionally, a parallel examination of aerosol sphere sedimentation is provided.

Increasing the Thermal Resistance of Water-Based Mud for Drilling Geothermal Wells

Energy demand and growing environmental concerns have fueled increased interest in geothermal drilling in recent decades. The high temperature and pressure in the boreholes present significant challenges to drilling, particularly in terms of the selection of suitable drilling mud, cement slurry, and drilling equipment. Drilling mud is regarded as one of the primary factors that affect the cost and success of geothermal drilling. This paper presents experimental studies aimed at assessing the thermal stability of drilling muds for geothermal drilling. Research on the antidegradation of polymers contained in drilling muds is presented. The thermal stability of drilling fluids was evaluated on the basis of changes in rheological and filtration parameters under the influence of a temperature of 160 °C. Attempts were made to increase the thermal resistance of drilling fluids by using antioxidants and glycol compounds. The effectiveness of increasing the thermal resistance of muds by adding synthetic polymers, nanomaterials, and graphite was tested. A new way of increasing the thermal resistance of drilling muds by using fatty amine compounds in combination with the amine agent ‘TEA’ was proposed. Tests showed that the addition of polyglycol and the antioxidant agent sodium ascorbate to the mud did not protect the polymers from decomposition at 160 °C. There was no effect of increasing the thermal conductivity on improving the thermal resistance of the scrubber. Based on the analysis of results from laboratory tests, a composition of a water-based drilling mud without bentonite was developed for drilling geothermal wells. The developed drilling mud is characterized by thermal resistance up to 160 °C, stable rheological parameters, low filtration, and appropriate thermal conductivity characteristics.

Research on hydrogen distribution of electroless nickel plating on aluminum-based silicon carbide composites

Abstract Aluminum-based silicon carbide composite materials have the characteristics of high thermal conductivity, low thermal expansion, and good dimensional stability. Therefore, the composites are widely used in space microwave component shell products. In order to meet the functional requirements of conductivity, welding, and heat dissipation when applied to antenna microwave components, aluminum-based silicon carbide composite materials need to be chemically plated with nickel, which introduces hydrogen, thus requiring research on hydrogen release and control. Here, SEM, XRD, and other methods are used to characterize the microstructure of aluminum-based silicon carbide substrate and nickel plating layer. There are certain pore structures in both the substrate and plating layer, providing a place for hydrogen storage. The experimental method of hydrogen microprinting has been used to characterize the distribution of hydrogen. The results showed that the hydrogen distribution pattern in aluminum-based silicon carbide nickel plating is as follows: after nickel plating on aluminum-based silicon carbide, hydrogen is distributed in the nickel plating layer and the shallow substrate under the coating; with the extension of time, hydrogen spontaneously diffuses to the deep substrate; hydrogen is mainly distributed in the Al matrix and less on SiC particles.

Structural features of nickel clad carbon fibers and determination of their thermophysical properties using pulsed radiation

It was considered the forming multilayer heat-resistant coatings that work under conditions of elevated temperatures and long-term oxidation. The issue of increasing the service life of the parts by strengthening their bulk and surface is considered. The issue of determining the level of the thermophysical properties is also considered. The thermophysical properties of carbonyl iron reinforced with carbon fibers (CF) pre-clad with nickel are investigated. Unclad and nickel clad carbon fibers were produced. The thermal conductivities of the samples are determined depending on the conditions of their production. The thermal conductivity characteristics of polymer composite materials based on CF with ceramic hollow microspheres and carbonyl iron from CF depending on the conditions of their production were determined. It is shown that heat transfer mechanisms related to the electron-lattice interaction can function in these systems. Heat transfer can occur by various transport mechanisms, such as collisions or diffusion. Nevertheless, the increase in thermal conductivity can be related to the electronic mechanism. The thermal conductivity of materials based on carbonyl iron with nickel-plated CF is 1.2 times higher compared to unclad CF, which is due to better adhesive interaction between the coated carbon fibers and iron was established.

First-principles study on thermal transport properties of GaN under different cross-plane strain

With the development of power devices towards high integration and power, the electrical and thermal stresses per unit area become more concentrated and intensified. The impact of cross-plane strain resulting from inverse piezoelectric effect and thermal expansion on power devices cannot be ignored. Cross-plane strain has a substantial influence on the thermal properties of GaN. However, the research on the influence of cross-plane strain on the thermal conductivity of GaN has not been reported in the literature. Based on the first-principles calculation method and the phonon Boltzmann transport equation, the influence of cross-plane strain on the thermal conductivity and phonon characteristics of the GaN lattice is systematically studied in this study. The thermal conductivity of GaN has anisotropy and increases significantly with the decrease in temperature. The thermal conductivity of GaN at room temperature under the free state is calculated to be 257 and 275 W/(m·K) for in-plane (k⊥) and cross-plane (k∥) directions, respectively. Compared with previous theoretical reports, our calculation results are more consistent with the existing experiment values. Under the state of cross-plane strain, the lattice thermal conductivity changes remarkably. In detail, the average thermal conductivity at room temperature decreased by 35 % under a 5 % cross-plane tensile strain state, while it increased by 11.5 % under a 5 % cross-plane compressive strain state. According to the calculation results, the influence of cross-plane on lattice thermal conductivity is mainly due to the change in phonon lifetime. The analysis of two mechanisms of phonon lifetime suppression indicates that the cross-plane strain will significantly change the frequency of the high-frequency optical acoustic branch. This result leads to a change in the phonon scattering process and thus affects the phonon lifetime. Besides, the anisotropy of thermal conductivity changes under different strain values, which may be due to the weakened piezoelectric polarization effect induced by strain.

A Review of an Investigation of the Ultrafast Laser Processing of Brittle and Hard Materials.

Ultrafast laser technology has moved from ultrafast to ultra-strong due to the development of chirped pulse amplification technology. Ultrafast laser technology, such as femtosecond lasers and picosecond lasers, has quickly become a flexible tool for processing brittle and hard materials and complex micro-components, which are widely used in and developed for medical, aerospace, semiconductor applications and so on. However, the mechanisms of the interaction between an ultrafast laser and brittle and hard materials are still unclear. Meanwhile, the ultrafast laser processing of these materials is still a challenge. Additionally, highly efficient and high-precision manufacturing using ultrafast lasers needs to be developed. This review is focused on the common challenges and current status of the ultrafast laser processing of brittle and hard materials, such as nickel-based superalloys, thermal barrier ceramics, diamond, silicon dioxide, and silicon carbide composites. Firstly, different materials are distinguished according to their bandgap width, thermal conductivity and other characteristics in order to reveal the absorption mechanism of the laser energy during the ultrafast laser processing of brittle and hard materials. Secondly, the mechanism of laser energy transfer and transformation is investigated by analyzing the interaction between the photons and the electrons and ions in laser-induced plasma, as well as the interaction with the continuum of the materials. Thirdly, the relationship between key parameters and ultrafast laser processing quality is discussed. Finally, the methods for achieving highly efficient and high-precision manufacturing of complex three-dimensional micro-components are explored in detail.

Physical characteristics of variable thermal conductivity and MHD flow across a continually stretched sheet

The primary purpose of this paper is to investigate the flow and thermal properties of a continuously stretching sheet. To determine temperature, variable thermal conductivity is also encountered. Furthermore, the flow problem considers the convective circumstances of heat and mass transfer. By lowering the number of independent components, the governing equations are reduced into non-dimensional types, which are then numerically solved using the RKF-4 method and shooting methodology. A visualization evaluation of the entangled flow properties is done for velocity concentration and temperature distributions. It is found that the fluid concentration is discovered to be more significant in the [Formula: see text] case, followed by the [Formula: see text] and [Formula: see text] cases. Furthermore, the efficiency of the [Formula: see text] the [Formula: see text] parameter’s shifting values control field.

Generation of cutting heat and simulation of core tube wall temperature during coring in primary structure coal seam

When the drilling core method is used to determine the coalbed gas content, the cutting heat generated by the core bit cutting coal will increase the core tube temperature, and the excessively high core tube temperature will have an heating effect on the coal core, which will accelerate the coal core gas desorption rate and increase the gas loss amount. The generation of cutting heat of core bit and the measurement of core tube temperature are the basis for grasping the gas desorption law of coal core and projecting the amount of gas loss. Firstly, the self-developed core tube temperature measurement device was used to conduct on-site core temperature measurement experiments at different cutting speeds. Then, the cutting temperature of core bit was solved by establishing thermodynamic model for cutting coal and heat transfer model of cutting edge. Finally, based on the thermal conductivity characteristics of the core tube, the core tube temperature at different cutting speeds was simulated, and the simulated temperature was compared with the on-site measured temperature to verify the reliability of the model. The results show that when coring in primary structural coal, the temperature change trend of core tube wall temperature measurement point at different cutting speeds is basically consistent, the temperature measurement point at the front end of the core tube mainly goes through a relatively stable period in the drilling process, a sharp rising period in the cutting process, a slow rise and cooling period in the withdrawal process. However, the temperature measurement point at the back end of the core tube wall mainly goes through a relatively stable phase and a slowly increasing phase. The temperature rise of the core bit and the core tube wall are significantly positively correlated with the cutting speed. When coring in hard coal seam and the core depth is not large, the cutting heat generated by the core bit and the coal body is the dominant factor for the temperature rise of the core tube. The core tube wall temperature calculated using the model matches well with the field measured temperature, and the error is small, which fully shows that the coring thermodynamic model is feasible. This study provides a basis for further research on the dynamic distribution characteristic of coal core temperature during coring, which is of profound significance to calculate the gas loss and coalbed gas content.

Investigation on ignition characteristics of charring conductive polymers stimulated by electric energy

The arc ignition based on charring conductive polymers has advantages of simple structure, low ignition power consumption and restart capacity, which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite. In order to optimize the performance of arc ignition system, it is essential to have a deeper understanding of the ignition processes and ignition characteristics of charring conductive polymers. In this paper, the thermal decomposition, electrical conductivity and thermal conductivity characteristics of charring conductive polymers with different conductive additives and matrix materials were comprehensively evaluated. An experimental investigation was conducted to determine the ignition behaviors and characteristics of different charring conductive polymers in a visual ignition combustor. The experiment result showed that the ignition delay and external energy required for ignition are negatively correlated with voltage and initial temperature of the ignition grain, but positively correlated with oxidizer flow velocity. Compared with charring conductive polymers containing multi-walled carbon nanotube, the ignition delay of charring conductive polymers with carbon black is significantly higher and the pyrolysis time is relatively longer. However, the ignition and initial flame propagation of charring conductive polymers with carbon black is more violent and more inclined to carbon particle ignition. Finally, the restart characteristic of different charring conductive polymers was studied. The ignition delay and external energy required for ignition of different charring conductive polymers all reduced with the increasing of the number of ignitions. However, the ignition characteristics would not change a lot after repeated ignition.