Changes In Thermal Conductivity Research Articles

Characterization of curing status of commercial tire compounds with vein graphite powder and its particle sizes—Experimental and computational study

AbstractThe use of solid tires in demanding industrial applications, subjected to substantial mechanical loads, poses significant challenges due to heat generation from hysteresis and tread friction. Managing this heat is crucial to mitigate the risk of tire blowouts and layer separation. This research investigates the impact of introducing vein graphite powder, varying in particle size, into a commercially used solid tire compound, both experimentally and computationally. The research findings presented in this paper reveal substantial changes in thermal conductivity, specific heat capacity, rate constant, induction time, and the order of reaction in solid tires. Contemporary industry trends involve predictive methods for monitoring the curing process in tire manufacturing. A tire curing simulation model based on finite (FE) element analysis is developed. FE modeling is favored due to its accuracy and adaptability, especially when dealing with the intricate geometry and multi‐layered, multi‐compound structure of tires. The complex interplay between heat transfer and curing processes is effectively addressed using user subroutines (UMATHT) in commercial FE software like ABAQUS. In this analysis, thermal conductivity, heat capacity, order of reaction, rate constant, and induction time of the commercial tire compound are considered as temperature‐dependent variables. The computational model not only demonstrates its potential to significantly enhance the efficiency and quality of tire manufacturing processes but also contributes to a deeper understanding of the curing behavior of graphite powder‐based solid tire compounds. Consequently, it provides a valuable tool for optimizing tire manufacturing procedures and ensuring the safe and reliable performance of solid tires under demanding operational conditions. This research bridges the gap between the traditional commercial tire compound and the use of vein graphite powder in tire manufacturing and advanced computational methods, facilitating improvements in tire quality and safety.

Fabrication of geopolymer composites using egg-shell and fly-ash: Comparison between the strength and stability, physio-chemical and mechanical properties

Nowadays, the demand for developing new structural materials, particulate composites made from industrial waste has been preferred along with conventional fiber-reinforced composites. In this work, two new composites were fabricated by reinforcing flyash and eggshell separately in epoxy with equal volume fractions and were termed geopolymer composites. Further thermo-mechanical characterization of these fabricated geopolymer composites was carried out by conducting various mechanical, physical, chemical, and thermal testing methods. The results were compared with the outcomes of neat epoxy composites. It was demonstrated that eggshell-epoxy composites have 28.48 % and 1.5 % more tensile strength than neat epoxy and flyash-epoxy composites. The flexural strength and hardness in a similar fashion were observed as increased by 31.7 %, 7.37 %, and 29.45 %, 15.6 % over neat epoxy and flyash-epoxy composites. The composites were crystalline confirmed from the XRD analysis. In contrast to the above, the thermal conductivity and thermal stability of flyash-epoxy composites were found superior though eggshell-epoxy composite visualized higher stability at the initial stage of thermal degradation. Further, the change of thermal conductivity of these materials with a temperature change was investigated by finite element modeling in MATLAB using the PDE toolbox. It was examined that thermal conductivity increases non-linearly with the increase in temperature up to 700 °C and then follows a uniform trend on further increase.

Performance of foam concrete developed from construction and demolition waste

Unconscious industrialization, urbanization and consumption of natural resources pose a serious threat to the environment. The threat can be reduced by upcycling construction and demolition waste (CDW) in the production of foam concrete, which is a special type of concrete used especially for thermal insulation purposes. This study aims to use of CDW as a source of fine aggregate (0-4 mm) in the production of foam concrete mixtures. A series of mixtures with target density values between 500 and 900 kg/m3 were designed with various recycled aggregate and foam contents to investigate the physical, mechanical and thermal properties of the mixtures. Findings of the study reveal that mixtures with an elevated foam content possess a greater number of larger pores, which, as observed through microscopy, form interconnected structures that are porous. On the other hand, adding more fine recycled material (FRM) makes the matrix denser, which reduces the overall porosity and increases the packing density. In contrast to increased content of FRM, correlation coefficient of (-0.77) reveal a more powerful inverse relationship between risen level of foam content (-0.67) and the reduction ratio of fresh-to-dry density and the increase in compressive strength from 7 to 28 days. It is also known that mixes with more foam have better thermal insulation because they trap more air, while mixes with more FRM show an increase in thermal conductivity. The sensitivity analysis showed that changes in thermal conductivity are almost three times as sensitive for FRM content, which means they have a bigger effect than changes in foam content. Employing the Taguchi method, (R_0.714) emerges as the most efficient tested combination indicative of superior overall performance. Notably, the Taguchi method predicts the untested combination (0.100-F/C ratio + 0.714-R/C ratio) as potentially more efficient, suggesting avenues for further exploration and optimization. This study furnishes valuable insights into sustainable construction practices by reutilizing CDW in foam concrete production, thereby contributing to both environmental conservation and enhanced structural outcomes.

A physics-driven and machine learning-based digital twinning approach to transient thermal systems

Purpose In this study, the authors propose a novel digital twinning approach specifically designed for controlling transient thermal systems. The purpose of this study is to harness the combined power of deep learning (DL) and physics-based methods (PBM) to create an active virtual replica of the physical system. Design/methodology/approach To achieve this goal, we introduce a deep neural network (DNN) as the digital twin and a Finite Element (FE) model as the physical system. This integrated approach is used to address the challenges of controlling an unsteady heat transfer problem with an integrated feedback loop. Findings The results of our study demonstrate the effectiveness of the proposed digital twinning approach in regulating the maximum temperature within the system under varying and unsteady heat flux conditions. The DNN, trained on stationary data, plays a crucial role in determining the heat transfer coefficients necessary to maintain temperatures below a defined threshold value, such as the material’s melting point. The system is successfully controlled in 1D, 2D and 3D case studies. However, careful evaluations should be conducted if such a training approach, based on steady-state data, is applied to completely different transient heat transfer problems. Originality/value The present work represents one of the first examples of a comprehensive digital twinning approach to transient thermal systems, driven by data. One of the noteworthy features of this approach is its robustness. Adopting a training based on dimensionless data, the approach can seamlessly accommodate changes in thermal capacity and thermal conductivity without the need for retraining.

Improving freeze resistance of cement-based materials with modified graphite-paraffin composite low-temperature microencapsulated phase change materials

This study examines the influence of microencapsulated phase change materials (MPCM) on enhancing the freeze-thaw resistance of cementitious structures, overcoming the limitations commonly associated with traditional phase change materials (PCM), such as insufficient thermal conductivity and non-optimal phase change temperatures. The research focused on developing MPCM with improved thermal conductivity and lower phase transition points, utilizing a binary mixture of tetradecane and hexadecane as the core material, supplemented by modified graphite. The phase change performance and physicochemical stability of the prepared MPCM were thoroughly assessed. Cement specimens, incorporating different contents of MPCM, were then subjected to a series of tests under both room temperature and simulated freeze-thaw conditions. These tests included mechanical testing, temperature response experiments, and monitoring of internal damage. The findings identified the optimal MPCM formulation as a 9:1 mixture of tetradecane and hexadecane, with an addition of 2 % hydrophobically modified graphite, which exhibited a phase change temperature near 0 °C and a range exceeding 6.7 °C, along with stable physicochemical properties. When 3 % MPCM was included in cement specimens cured for 28 days under freeze-thaw conditions, a significant reduction in internal damage caused by freeze-thaw cycles was observed, leading to an increase in compressive strength by 0.12 % and in flexural strength by 11.77 %. Additionally, temperature tests confirmed the efficacy of MPCM in stabilizing internal temperature fluctuations within the cement specimens. The results of this study present a viable approach to enhance the durability of cement-based infrastructure in cold climates.

Experimental study on preparation and performance of the Corn Straw Fiber (CSF) reinforced EPS concrete

With the full factor experimental design method carried out, 20 sets of EPS concrete specimens with different mass fractions of Corn Straw Fiber (CSF) and Expanded-Polystyrene (EPS) particles were designed to study their density, water absorption, compressive strength, flexural strength, splitting tensile strength, mass loss and strength loss after freeze-thaw cycles, and changes in thermal conductivity, to evaluate the effect of CSF content and EPS content on the properties of EPS cement-based composites. The experimental results show that adding CSF can improve the mechanical properties of EPS concrete while reducing its density, the maximum increase rate of compressive strength is 69.7 %, with a maximum value of 1.12 MPa; The maximum improvement rate of flexural strength is 127.38 %, with a maximum value of 0.885 MPa; The maximum improvement rate of splitting tensile strength is 68.07 %, and the maximum value is 0.256 MPa. After 50 standard freeze-thaw cycles, straw fibers can delay the quality loss of EPS concrete, but show adverse effects on its strength loss, the maximum quality loss rate is 4.23 %, and the maximum loss rates for the three strengths are 24.46 %, 24.22 %, and 24.61 %, respectively. In addition, in terms of improving the thermal insulation performance of EPS concrete, the role of the two aggregates is manifested as EPS > CSF, and the thermal conductivity coefficient values under different aggregate dosages were obtained, when the content of EPS is 1.4 % and the content of CSF is 4 %, the minimum thermal conductivity value is 0.0402 W/(m·°C), and the thermal conductivity coefficient of calcium silicate board is 0.0378 W/(m °C) by the thermal conductivity coefficient formula of composite materials. which can serve as a reference for selecting building insulation materials in areas with high temperature differences.

Enhancement of Flexural Strength by Slip Casting Cordierite Ceramics with h-BN Nanoparticles

In this study, we enhanced the flexural strength of cordierite ceramics by incorporating h-BN (hexagonal boron nitride) nanoparticles, facilitated by the slip casting process. Initially, commercial cordierite powder with an average particle size of 10 mm underwent a ball-milling process to reduce the size to 2.5 mm and simultaneously achieve a narrower particle size distribution. The resulting slurry, composed of 67% solid content, exhibited improved stability during the slip casting process for both pristine cordierite and the mixture containing 1 – 2 wt% h-BN nanoparticles. After sintering, the bulk material containing 2wt% h-BN nanoparticles demonstrated a remarkable flexural strength of 174.8 MPa, a significant improvement compared to the initial 119.5 MPa obtained without the addition of h-BN. It is worth noting that the introduction of h-BN nanoparticles did not induce substantial changes in dielectric constant and thermal conductivity, indicating that the desired mechanical enhancement did not compromise other crucial material properties. This research demonstrates a successful approach to concurrently optimize the flexural strength, dielectric constants, and thermal conductivity of cordierite ceramics. This breakthrough opens up new avenues for advanced applications in a wide range of fields, from electronics to aerospace, where high-strength, thermally stable materials are in demand.

Thermal bridging effect enhancing heat transport across graphene interfaces with pinhole defects

Interfacial thermal conductance (G) is of critical significance to the efficient thermal management of two-dimensional (2D) material devices. Despite the importance of defects engineering in tuning G, the mechanisms of heat transport across defective graphene interfaces remain unclear. In this study, we have identified and demonstrated the origins of the enhanced heat transport across pinhole defective graphene through our ultrafast pump-probe measurements and molecular dynamics (MD) simulations. In prior work, the enhanced G across defective graphene interfaces was commonly attributed to the improved overlap of phonon density of states (DOS) or interfacial coupling strength. We, however, observe a remarkable 2.5-fold increase in heat conduction and a distinctly different temperature dependence of G for defective graphene with the same superstrate and substrate material, compared to pristine graphene. In contrast, interfaces with different superstrate and substrate materials show only minor changes (<15%) in thermal conductance after introducing defects in the graphene layer. Through careful analysis of our MD simulations for various defective graphene interfaces, we conclude that, contradictory to common beliefs, it is the formation of direct contact thermal bridge, instead of the improvement in the phonon DOS overlap or interfacial coupling strength, that has a decisive effect and promotes heat transport across defective graphene interfaces. The differing impacts of the thermal bridge on G of defective graphene sandwiched by layers of the same and different materials are primarily attributed to the varying coupling strength between the substrate and superstrate. Our work provides important insights and physical understandings of the mechanisms of heat conduction across defective graphene interfaces.

Insights Into Viscosity/Thermal Conductivity of a Micropolar Nanofluid Flow Near a Horizontal Cylinder

The purpose of this study is examining the changes in viscosity and thermal conductivity of a micropolar nanofluid on a horizontal cylinder, specifically on the axisymmetric stagnation inflow. Nanofluid viscosity is known to exhibit an exponential change with temperature, while thermal conductivity was found as a linear with temperature to enhance the heat transfer rates of nanofluid flow by numerical calculations. A horizontal circular cylinder with an axisymmetric stationary point was the subject of the mathematical model, which described an incompressible, constant micropolar nanofluid flow over it. The importance of predicting heat and mass transfer for a horizontal cylinder are common in many applications, including refrigerator condensers and flat-plate solar collectors. For this reason, it is imperative to study heat and mass transfer in horizontal cylinder geometries. Furthermore, taken into account were fluid temperature factors like nanofluid viscosity and micro-rotation viscosity. It introduced aluminum oxide nanoparticles to two common fluids: pure water and ethylene glycol. It was capable of to estimate the pressure gradient profiles, temperature gradient profiles, shear stress, Nusselt number, angular and azimuthal velocities, and curvature parameters for various numerical values of micropolar, variable viscosity/thermal conductivity, and curvature. An exact match is found in a table that contrasts the current numerical computation with the published data. Based on our simulation results, it seems that the temperature profile variation for both pure water with alumina nanoparticles and ethylene glycol is significantly influenced by the Reynolds number and the viscosity/thermal conductivity characteristics of the nanofluid. Nevertheless, the micropolar parameter barely makes a difference. Furthermore, the concavity of the pressure profiles is pushed upwards, and it appears that the pressure biographies for ethylene glycol are more pressure-intensive than those for pure water. By increasing the value of the variable viscosity parameter of the nanofluids, it can be achieved to discern clearly between the angular velocity profiles in the two scenarios. Engineers and researchers working on propulsion technology for missiles, airplanes, and spacecraft can especially benefit from these perceptions.

A numerical study of catalytic combustion of methane-air in excess oxygen and deficient oxygen environments with increasing initial pressure: A molecular dynamic approach

In the low-temperature range, catalytic combustion results in few emissions of nitrogen oxide and happens without a visible flame. This work investigates the effect of initial pressure (IP) on catalytic methane-air combustion (CMAC) in a microchannel using the molecular dynamics (MD) method. Palladium particles with an atomic ratio of 4 % were used as a catalyst. The study also investigates the CMAC in two environments: excess oxygen (EO) and deficient oxygen (DO). The research investigates the changes in density (Den), velocity (Velo), temperature (Temp) profiles, heat flux (HF), thermal conductivity (TC), and combustion efficiency (CE). The results of the MD simulation indicate that the maximum values of Den and velocity decrease as the IP increases to 10 bar. This reduction was more pronounced in the EO medium than in the DO medium. The maximum values of density and velocity decrease to 0.105 atom/Å and 0.17 Å/ps, respectively, in the EO medium. These values decrease to 0.080 atom/Å and 0.20 Å/ps, respectively, in the DO medium. Additionally, the HF and TC values decrease in both mediums, with the EO medium showing values of 1839 W/m2 and 1.01 W/m.K, and the DO medium showing values of 1869 W/m2 and 1.04 W/m.K. If there was a DO medium, the atoms and particles of the system had a greater ability to heat transfer to different parts. Therefore, TC and HF are more in this case.

Analysis of the effect of surface coating and texturization on the estimation of effective thermophysical properties

This article aims to investigate the influence of surface modifications on the effective thermophysical properties of textured carbon steel and coated hard metal. The novelty of this work lies in the simultaneous estimation of thermal diffusivity and thermal conductivity via measurements using one active heating surface and Bayesian inference to solve the inverse heat conduction problem. To achieve this, an experimental setup was developed where samples were partially heated on an active surface, and the temperature was measured at two different points on the surface to estimate the thermal properties. The method was applied to two different thermal models using the same set of experimental data. Thus, the thermophysical properties were determined with and without the Markov Chain Monte Carlo technique using the Metropolis-Hastings sampling algorithm. Both techniques proved suitable for estimating the thermophysical properties. It is noteworthy that texturization and coating did not significantly modify the effective thermal diffusivity of the analyzed samples. However, there were considerable changes in the effective thermal conductivity, with an increase of approximately 13 % in the textured carbon steel sample and a reduction of approximately 11 % in the coated hard metal sample. The expanded uncertainty of the estimated effective thermophysical properties was less than 14 %. These results reflect low dispersion and good accuracy of the experimental technique used.

Efficient preparation of polydimethylsiloxane‐based phase change composites with sandwich structure

AbstractWith the rapid development of portable electronic devices, there is an urgent need for the multifunctional composites like excellent electromagnetic interference (EMI) shielding performance, mechanical property, and thermal management capabilities. Here, due to the low thermal conductivity of phase change materials (PCMs), a sandwich structure carbon nanotube/phase change microcapsule/carbon nanotube (CNT/PMC/CNT (CPC)) film was prepared by vacuum‐assisted filtration (VAF) method. CNT, PMC, and cellulose nanocrystal (CNC) were used as functional fillers. The addition of CNCs was used to improve the mechanical performance of CPC film. Compared with PMC‐CNC (PC) film, CPC film with sandwich structure prevented leakage phenomenon efficiently. Subsequently, the use of ultrasonic‐assisted forced infiltration (UAFI) successfully infiltrated polydimethylsiloxane (PDMS) matrix in the filler skeleton to obtain CNT/PMC/CNT/PDMS (CPCP) composites. When filler mass ratio (CNT: CNC and PMC: CNC) reached 10:1, the thermal conductivity of CPCP composites was 2.32 W/(m·K) and total EMI shielding effectiveness (EMI SET) of it with 0.38 mm thickness reached 37.46 dB at 12.4 GHz. Besides, these sandwich composites exhibited the good mechanical properties and heat storage capacity. And we systematically observed the impact of different addition amounts of PC homogeneous dispersing solution on phase change ability of CPCP10:1 composites. In summary, CPCP phase change composites with sandwich structure shows potential application prospect in thermal management materials with EMI shielding of electronic devices.Highlight The sandwich structure CPCP composites prepared by the combination of VAF and UAFI method, showing superior thermal conductivity and phase change ability. CPCP has excellent EMI shielding performance, which can meet the need of TMMs with EMI shielding performance. Compared with same thickness PC film, sandwich CPC film can prevent leakage phenomenon efficiently.

Development of test methods for fire-retardant coatings of steel engineering structures during operation

Introduction. Prediction of the durability of flame-retardant coatings of steel engineering structures and preservation of their performance during operation remain important research directions. There is a lack of normative documents in the field of fire protection, regulating the process of testing of flame-retardant coatings during operation, as well as determination of their durability (service life).Aim. To develop test methods for determining the resistance of flame-retardant coatings of steel engineering structures exposed to climatic factors, preservation of their fireproof and anti-corrosion properties during operation.Materials and methods. Test specimens included 600 x 600 x 5 mm plates made of 08kp and 08ps sheet steel according to State Standard 16523-97 and State Standard 9045-93 with a flame-retardant agent applied on the front side.Results. Methods for testing thin-layer intumescent and structural flame-retardant coatings during operation are proposed. The methodology of accelerated climatic testing of specimens coated with thin-layer intumescent flame-retardant coatings (flame-retardant paints) corresponds to State Standard 9.401-2018. These coatings are inherently high-solid paint materials. A new methodology, sequence, and modes of testing are developed for structural flame-retardant coatings. The subsequent assessment of fireproof properties of coatings and their preservation is carried out by the methods of fire protection efficiency according to State Standard R 53295-99 and the methods of thermal analysis. These methods imply comparison of the characteristics of the initial flame-retardant coating and those obtained after sample aging. The preservation of fireproof properties by thin-layer intumescent and structural coatings is additionally evaluated by the intumescence coefficient and the change in thermal conductivity, respectively.Conclusions. Test methods for flame-retardant coatings of steel engineering structures during operation are developed. Threshold levels of changes in their properties are established. After accelerated climatic tests, fire protection efficiency should not decrease by no more than 20 %. For structural fire protection, an increase in thermal conductivity by no more than 5 % is permitted. For thin-layer coatings, the arithmetic mean value of the intumescence coefficient should not decrease by no more than 30 % of the initial value.Implications. The developed methods were used in the preparation of a draft national standard of the Russian Federation “Steel engineering structures with fireproof coatings. Test methods for anticorrosion properties and resistance to climatic factors during operation” to ensure regulatory fire safety requirements for these structures.

Computational modeling and analysis of a fluid test rig

Nanofluids, which are suspensions of metallic or ceramic nanoparticle fillers in a variety of liquids, are a new category of heat-transfer fluids. Owing to the changes in thermal conductivity caused by nanofillers, they have thermal properties that are superior to those of conventional fluids; this leads to a more efficient heat transfer, making them attractive for various industrial applications. Using numerical models to support in situ experiments is necessary to analyze nanofluids’ thermal properties and flow; creating a test ring has been suggested to describe the characteristics and behavior of fluids under controlled conditions. Modeling and computational analysis support such advances, which are essential for understanding and optimizing phenomena occurring during experimental tests; the modeling and computational analysis of a test rig designed to characterize a diphenyl oxide/biphenyl blend base fluid are presented in this research work. The test rig design included an integrated stainless-steel piping system with a flow-controlled pump and heat exchanger; the computational model considers the conjugate effects of fluid dynamics to facilitate the construction of test rigs.

Hydrogenation driven ultra-low lattice thermal conductivity in β 12 borophene

Borophene gathered large interest owing to its polymorphism and intriguing properties such as Dirac point, inherent metallicity, etc but oxidation limits its capabilities. Hydrogenated borophene was recently synthesised experimentally to harness its applications. Motivated by experimental work, in this paper, using first-principles calculations and Boltzmann transport theory, we study the freestanding β 12 borophene nanosheet doped and functionalised with hydrogen (H), lithium (Li), beryllium (Be), and carbon (C) atoms at different β 12 lattice sites. Among all possible configurations, we screen two stable candidates, pristine and hydrogenated β 12 borophene nanosheets. Both nanosheets possess dynamic and mechanical stability while the hydrogenated sheet has different anisotropic metallicity compared to pristine sheet leading to enhancement in brittle behaviour. Electronic structure calculations reveal that both nanosheets host Dirac cones (DCs), while hydrogenation leads to shift and enhancement in tilt of the DCs. Further hydrogenation leads to the appearance of additional Fermi pockets in the Fermi surface. Transport calculations reveals that the lattice thermal conductivity changes from 12.51 to 0.22 W m−1 K−1 (along armchair direction) and from 4.42 to 0.07 W m−1 K−1 (along zigzag direction) upon hydrogenation at room temperature (300 K), demonstrating a large reduction by two orders of magnitude. Such reduction is mainly attributed to decreased phonon mean free path and relaxation time along with the enhanced phonon scattering rates stemming from high frequency phonon flat modes in hydrogenated nanosheet. Comparatively larger weighted phase space leads to increased anharmonic scattering in hydrogenated nanosheet contributing to ultra-low lattice thermal conductivity. Consequently, hydrogenated β 12 nanosheet exhibits a comparatively higher thermoelectric figure of merit (∼0.75) at room temperature along armchair direction. Our study demonstrates the effects of functionalisation on transport properties of freestanding β 12 borophene nanosheets which can be utilised to enhance the thermoelectric performance in two-dimensional (2D) systems and expand the applications of boron-based 2D materials.

Optoelectronic–thermomagnetic effect of a microelongated non-local rotating semiconductor heated by pulsed laser with varying thermal conductivity

Abstract In this study, we investigated the effect of a rotation field and magnetic field on a homogeneous photo-thermoelastic nonlocal material and how its thermal conductivity changes as a result of a linearly distributed thermal load. The thermal conductivity of an interior particle is supposed to increase linearly with temperature under the impact of laser pulses. Microelastic (microelements distribution), non-local semiconductors are used to model the problem under optoelectronic procedures, as proposed by the thermoelasticity theory. According to the microelement transport processes, the micropolar-photo-thermoelasticity theory accounts for the medium’s microelongation properties. This mathematical model is solved in two dimensions using the harmonic wave analysis. Non-local semiconductor surfaces can generate completely dimensionless displacement, temperature, microelongation, carrier density, and stress components with the appropriate boundary conditions. The effects of thermal conductivity, thermal relaxation times, magnetic pressure effect, laser pulses, and rotation parameters on wave propagation in silicon (Si) material are investigated and graphically displayed for a range of values.

Thermal effect on the modal characteristics of the rotor of a typical cryogenic turbine for helium refrigerator

The helium turbine is a critical component of the cryogenic system for nuclear fusion devices. To ensure the turbine's steady functioning and avoid resonance, it is essential to understand and clarify the influence of key factors on its modal characteristics. This paper investigates the influence of thermal effect, fluid-structure interaction and rotational effects on the intrinsic frequency of a helium turbine used in the Comprehensive Research Facility for Fusion Technology (CRAFT) cryogenic system. The effects of coefficient of thermal expansion, thermal conductivity and Young's modulus on the intrinsic frequency of the rotor are explored, considering these thermal factors that vary with temperature. The results indicate that thermal effect has the greatest influence on the intrinsic frequency of the rotor over rotational effectand fluid-structure interaction. Lower-order modes are more sensitive to changes in thermal conductivity, while higher-order modes are more sensitive to changes in Young's modulus at low temperatures. The intrinsic frequency of the rotor is more sensitive to changes in the thermal factors of the shaft rather than the thermal factors of the impellers.

High value utilization of waste peanut shell: Prepared novel shape stable composite phase change materials with high thermal conductivity

To address the leakage and low thermal conductivity issues of phase change materials (PCMs), this study aims to prepare high thermal conductivity shape stable composite phase change materials (sscPCMs) using waste peanut shell. Employing pyrolysis technology, waste peanut shell has been successfully converted into high-performance framework materials. In addition, it also compared the thermal energy storage performance of shape stable composite stearic acid/peanut shell biochar (ss-cSA/PSC) with that of shape stable composite stearic acid/peanut shell (ss-cSA/PS). Excitingly, the thermal energy storage performance of ss-cSA/PSC has been significantly improved. Specifically, the thermal conductivity of ss-cSA/PSC reached 0.527 W/(m·K), which is 3.2 times higher than that of pure SA and 2.4 times higher than that of ss-cSA/PS. In addition, the phase change latent heat of ss-cSA/PSC can reach 70.59 J/g, which is 27.2% higher than that of ss-cSA/PS. The high thermal conductivity and phase change latent heat highlighted its significant superiority in the field of thermal energy storage. Furthermore, ss-cSA/PS and ss-cSA/PSC have been characterized by SEM, FTIR, XRD, and TGA. The results indicated that both two kinds of sscPCMs have excellent chemical compatibility, thermal reliability, and thermal stability. In summary, PSC is an economical, environmentally friendly, and sustainable framework material which used to prevent the leakage of PCMs and improve the thermal performance.

Heat dissipation performance research of battery modules based on composite phase change materials cooling and electrochemical thermal coupling model

In order to improve electric vehicle lithium-ion batteries (LIBs) performance and increase cycle life, it is crucial to design a reliable and efficient battery thermal management system (BTMS). Compared with other active battery cooling methods, passive phase change material (PCM) cooling has the advantages of simple structure, good temperature control uniformity, strong reliability, and no additional energy consumption. This article uses a series of experimental procedures to add expanded graphite to traditional paraffin wax PCM and obtain composite phase change materials (CPCM) with different mixing ratios. A control experiment is created to compare the cooling performance of the CPCM cooling with natural convection cooling, research shows that the cooling performance of CPCM can well meet the cooling demand which maximum temperature and maximum temperature difference of battery modules. In addition, to study the performance of thermal properties parameters related to CPCM, a COMSOL numerical calculation model of battery module based on CPCM cooling and electrochemical thermal coupling model is established. The effectiveness and accuracy of the model are verified through heat generation experiments at different rates (0.5 C, 1 C, 1.5 C), with a maximum temperature error of 1.6 K and an error accuracy of less than 0.6%. Subsequently, the performance of phase change temperature, thermal conductivity and phase change latent heat is studied and reasonable value ranges are obtained, which are 312 K∼318 K, 2.5 W /(m·K), and 175 J/g∼200 J/g, respectively.

Controllable thermal rectification design for buildings based on phase change composites

Phase-change material (PCM) is widely used in thermal management due to their unique thermal behavior. However, related research in thermal rectifier is mainly focused on exploring the principles at the fundamental device level, which results in a gap to real applications. Here, we propose a controllable thermal rectification design towards building applications through the direct adhesion of composite thermal rectification material (TRM) based on PCM and reduced graphene oxide (rGO) aerogel to ordinary concrete walls (CWs). The design is evaluated in detail by combining experiments and finite element analysis. It is found that, TRM can regulate the temperature difference on both sides of the TRM/CWs system by thermal rectification. The difference in two directions reaches to 13.8 K at the heat flow of 80 W/m2. In addition, the larger the change of thermal conductivity before and after phase change of TRM is, the more effective it is for regulating temperature difference in two directions. The stated technology has a wide range of applications for the thermal energy control in buildings with specific temperature requirements.