Specific Thermal Conductivity Research Articles

Validation of 3D thermal simulations of the Double C Block, a novel composite masonry unit, using in-situ U-value measurements

Energy efficient building envelopes, particularly innovative prefabricated building components, can significantly contribute to lower the building industry energy-related emissions. In this research the composite masonry unit Double C Block (DCB) is quantitatively tested by means of three-dimensional thermal simulation validated by in-situ U-value measurements carried out in both summer and winter conditions.The simulations were enhanced by the experimental measurement of the dry thermo-physical material properties (specific heat capacity, thermal conductivity, and density) in laboratory conditions for both concrete and polyurethane. The samples were extracted from real-scale DCB prototypes. Furthermore, site-specific boundary conditions of Malta — representative a case study of a Mediterranean climate − were utilised in the simulations. Both laboratory and in-situ assessments of thermal transmittance, or U-value, had their uncertainty specified as part of the calculations.The validation exercise was performed by means of hourly recorded surface temperature and the selected indices were the root mean square error and mean absolute error. Results showed that these indices were within the recommended accuracy thresholds during both winter and summer assessments. For the hourly-based heat flux measurements, the mean bias error and coefficient of variation of the root mean square error were found lower than values reported in literature, thus supporting the robustness of the overall simulation outputs. Hence the 3D CVM simulation was experimentally validated by in-situ assessments.The convergence value of the experimental U-value provided respectively 1.51 ± 0.20 W/m2K (winter) and 1.44 ± 0.19 W/m2K (summer). Then, the validated 3D CVM model was adapted to calculate the theoretical U-value of DCB, using monthly values of recorded surface temperatures obtained by the test cells (in both seasons). The predicted thermal transmittance was of 1.47 W/m2K, in both conditions, and this almost matches the above-mentioned experimental assessments and thresholds established in previous works.

An investigation of the physic-mechanical properties of the expanded perlite mortars with thermal-activated concrete waste and microencapsulated paraffin

In the transition to zero waste and sustainable development, it becomes essential to use phase change materials and recycled cement in construction projects to improve energy efficiency and encourage sustainable building practices. The primary goal of this study is to determine how the properties of expanded perlite mortars are affected when Portland cement is partially replaced with recycled cement, produced by thermally treating concrete waste at 550˚C. Recycled cement substituted Portland cement in various percentages (10%, 30%, and 50%). Also, microencapsulated phase change material (m-PCM) was incorporated into the mortar in a proportion of 2 wt.% and 5 wt.%. Cement-based mortars with a 1:3 aggregate volume ratio have been developed for evaluation. The mortars were analyzed in terms of mechanical strength (flexural and compressive), water absorption, thermal properties, differential scanning calorimetry, and microstructure. The experimental results revealed a decrease in mechanical strength values when Portland cement is substituted by recycled cement, regardless of percentage. Recycled cement in proportion of 30% positively influenced the water absorption. The thermal conductivity of reference mortar was higher than that of 30% recycled cement. The reference mortar's specific thermal conductivity values were 0.466 W/(m·K) at 25°C, 0.525 W/(m·K) at 30°C, and 0.589 W/(m·K) at 35°C. On the other hand, the mortar containing 30% recycled cement exhibited much lower heat conductivity throughout these temperatures, suggesting superior insulating qualities. DSC analysis verified that adding m-PCM to the mortars increased their thermal storage capacity, which is essential for raising the energy efficiency of building materials. Nevertheless, the mechanical strength decreased as m-PCM was added. Despite decreases, all mortars satisfied the SR EN 998–1 standard's CS IV classification for interior plaster applications, which is based on compressive strength requirements. Overall, this study shows how using m-PCM and recycled materials can improve the performance of cement-based materials.

Experimental and numerical investigations on phase change thermal storage foam concrete based on CaCl2∙6H2O/silica aerogel composite phase change material

A new type of phase change thermal storage foam concrete was developed by effectively incorporating a composite phase change material (CPCM) into foam concrete. The CPCM was obtained by using 75 wt% CaCl2∙6H2O as PCM and 25 wt% silica aerogel as carrier, with a phase change temperature of 27.0 °C and an enthalpy value of 110.9 J/g. The mechanical and thermal properties of the obtained phase change thermal storage foam concrete blocks were investigated experimentally, along with a numerical analysis of their heat transfer characteristics. The experimental results demonstrated that after adding CPCM, the thermal performances of foam concrete blocks significantly increased, under the condition of their dry densities and compressive strengths met the specification requirements. Adding 20 wt% CPCM, the enthalpy value, specific heat capacity, thermal conductivity and thermal inertia of foam concrete block respectively reached 37.0 J/g, 1782.0 J/(kg∙K), 0.131 W/(m·K) and 770.9, with appropriate phase change temperature (27.2 °C). Numerical analysis for the heat transfer characteristics of the phase change thermal storage foam concrete wall revealed that optimal thermal insulation and thermal storage performances were achieved when the wall contained 20 wt% CPCM and thickness of 80 mm. In this case, the model exhibited a temperature wave attenuation factor of 6.66, the temperature amplitude of 5.84 K and a decline of 9.87 K for the highest temperature of the wall as well as delay time of 198,000 s, effectively regulating indoor temperature and saving energy. Therefore, the as-prepared phase change thermal storage foam concrete had great potential for application in building energy conservation.

The Influence of Thermophysical Parameters on Thermal Runaway Characteristics for Pouch-Type Lithium-Ion Batteries

Abstract The thermal variation during the temperature rise process of batteries is closely related to multiple physical parameters. Establishing a direct relationship between these parameters and thermal runaway (TR) features under abusive conditions is challenging using theoretical equations due to complex electrochemical and thermal coupling. In this paper, a high-temperature thermal runaway model of pouch-type lithium-ion battery is established through electrical-thermal coupled approach, demonstrating a good agreement between the simulation and experimental results. The results reveal distinct trends in thermal parameters of the early temperature rise, trigger time for TR and peak temperature during TR process, for varying convective heat transfer coefficient, cell specific heat capacity, cell density and cell thermal conductivity. Across various convective heat transfer coefficients, the rates of temperature increase, moments of TR, and peak temperatures within a battery emerge as the cumulative outcomes of competing processes of the intricate exothermic secondary reactions within the battery, and the heat transfer with the surroundings. Batteries with lower heat capacity exhibit reduced thermal inertia and heightened sensitivity to temperature changes. Alterations in the thermal capacity of a battery wield a profoundly significant impact upon the moment of thermal runaway within the battery. Enhancing the thermal conductivity yields limited improvements in heat dissipation during thermal runaway primarily due to the relatively small geometrical scale of the battery. Results of this paper can provide valuable insights for size optimization design, thermal management system optimization design, thermal runaway safety warning and prevention of Lithium-ion batteries.

Experimental analysis of a radiant floor system incorporating phase change materials: Thermal performance and energy efficiency

The incorporation of Phase Change Materials (PCMs) in radiant floors has the potential to improve the thermal and energy performance of the system. PCMs can act as thermal batteries, providing additional thermal energy storage capacity to Radiant Floor Systems (RFS). However, in the case of wet construction, when PCMs are incorporated into the enveloping mortar surrounding the RFS water pipes, the resulting specific heat and thermal conductivity can pose a challenge to system performance. The objective of this paper is to evaluate the impact that the incorporation of microencapsulated PCM (mPCM) in the RFS mortar has on the thermal and energy performance of the system. To tackle this objective, an experimental setup was constructed consisting of two RFS specimens: one reference and the other with mPCM within an innovative mortar. The two specimens were then tested under different heating strategies controlled by: i) timer, and ii) floor surface temperature setpoint. The thermal performance of the PCM-RFS and operating time were compared with the reference RFS. Timer-controlled intermittent heating has proven beneficial when the heating strategy is established to combine renewable solar energy and off-peak electricity tariffs. Thermal fluctuation was reduced and the PCM phase change process was mobilized twice in 24 h, maintaining surface floor temperatures of the PCM-RFS within comfort levels throughout the test period. When the heat source is controlled by floor surface temperature setpoint, the thermophysical properties of the PCM-RFS led to longer operating times, however mitigating high intermittency of the heat source activations, resulting in more regular operation mode, easier control and avoiding peak heating loads.

Enhancing thermal management systems: a machine learning and metaheuristic approach for predicting thermophysical properties of nanofluids

Abstract In thermal engineering, predicting nanofluid thermophysical properties is essential for efficient cooling systems and improved heat transfer. Traditional methods often fall short in handling complex datasets. This study leverages machine learning (ML) and metaheuristic algorithms to predict key nanofluid properties, such as specific heat capacity (SHC), thermal conductivity (TC), and viscosity. By utilizing Artificial Neural Networks (ANN), Support Vector Regression (SVR), Gradient Boosting (GB), and Linear Regression (LR), alongside metaheuristic models like Differential Evolution (DE) and Particle Swarm Optimization (PSO), we achieve superior prediction accuracy compared to traditional models. The integration of these computational techniques with empirical data demonstrates their effectiveness in capturing the complex dynamics of thermofluids. Our results validate the precision of ML and metaheuristic models in predicting nanofluid properties and underscore their potential as robust tools for researchers and practitioners in thermal engineering. This work paves the way for future exploration of ML algorithms in thermal management, marking a significant advancement in optimizing nanofluid applications in industry and research.

Prediction of wellbore gas hydrate generation based on temperature-pressure coupling model in deepwater testing

With the advancement of oil and gas exploration and development technology, the development of the world's oil and gas resources is gradually advancing from land and shallow waters to deep waters. During the development of gas wells in deepwater regions, the temperature of the wellbore decreases from the bottom of the well to the wellhead, and therefore, common well conditions of high pressure, low temperature, and the presence of free water are encountered, which can lead to gas hydrate plugging of the pipeline and affect the transportation of natural gas. Simulation of temperature and pressure along the wellbore and identification of gas hydrate-generating zones in the wellbore can be used to take timely preventive measures and minimize losses. In this study, a wellbore gas hydrate generation and prediction model is developed by combining the mass, momentum, and energy conservation equations, and the model is solved by the fourth-order Runge-Kutta method, taking into account the temperature-pressure coupling in the wellbore. The effects of gas production, specific heat capacity, thermal conductivity, tubing size, test duration, and ground temperature gradient on the location of gas hydrate generation and the amount of inhibitor used were analyzed in a case study well in the South China Sea. Some suggestions for practical engineering operations, such as increasing the gas production in moderation and choosing smaller tubing sizes within the acceptable range, were given. The study's results can provide a theoretical basis for flow assurance for hydrocarbon production in the wellbore of deepwater gas wells.

Construction of ZrC@SiC shell-core structure in SiBCN aerogel for enhanced thermal stability and thermal insulation

SiBCN aerogels have drawn increased attention as thermal insulation material, but they still suffer from precipitation and phase transition causing the microstructural collapse and performance deterioration under high-temperature environments. Here, ZrC/SiBCN aerogels were prepared using zirconium (IV) butoxide modified polyborosilazane as precursor through solvothermal reaction, frozen casting followed by frozen drying and pyrolysis. Benefiting from its unique hierarchical cellular structure, ZrC/SiBCN aerogel exhibits super-low density (0.042 g/cm3), high specific surface area (287.9 m2/g) as well as low thermal conductivity (24 mW/(m·K)). Shell-core ZrC@SiC nanocrystals are in-situ formed in amorphous SiBCN matrix through step-by-step carbothermal reduction of oxygen-containing phases and free carbon phase during the pyrolysis process, which effectively inhibits the crystallization and growth of SiC crystals, further enhancing the thermal stability under high-temperature environments. It could maintain a high specific surface area (163 m2/g) and low thermal conductivity (29 mW/(m·K)) after thermal treatment at 1800 °C for 2 h. The excellent structural and performance stability of the SiBCN-based aerogels will expand their applications under high-temperature extreme environments.

Numerical study on machining of Al/SiC composite materials

Abstract Metal matrix composites (MMCs) comprising aluminum (Al) matrices reinforced with silicon carbide (SiC) particles have garnered significant attention in recent years due to their outstanding specific strength, stiffness, corrosion resistance, and thermal conductivity. However, to achieve the desired geometry and shape of such MMC workpiece, a cutting process is still necessary, which involves a complex phenomenon of mechanical interactions that can result in surface defects and reduced tool life. This study aims to numerically investigate the cutting process of Al/SiC MMC workpieces in a manner that closely resembles reality by developing a finite element model directly from a metallographic image of a composite with a 30% volume fraction of 10 μm SiC grit. The research focuses on the effects of cutting depth, cutter rake, and the interaction between the cutting tool and the SiC particles. The results demonstrate that, depending on the contact point with the SiC particle, there is a variation in the cutting force generated when the cutter tip encounters the SiC particle. This causes the particle to break, rotate, roll over the matrix, and embed deeper into the matrix. Furthermore, based on the analysis of variance applied to the cutting force, the cutting depth exhibits a significant influence, while the cutter rake shows no significant effect on the cutting force.

Thermal calculation and experimental study of a double-disk magnetic coupler

Aiming to tackle the difficulties and inaccuracies in calculating the temperature field of double-disk magnetic coupler, a novel thermal calculation method is proposed, integrating the equivalent thermal network method and CFD method. This approach deviates from traditional methods that substitute empirical formulas with rotational speed. An equivalent thermal network model is established to ascertain the temperature rise at each network node. Additionally, a fluid-solid coupling model is constructed, and the impact of uneven air temperature distribution on air density, specific heat capacity, dynamic viscosity, and thermal conductivity is analyzed using the least squares method. The results reveal that after incorporating variable temperature air physical properties, the high-temperature area of the copper conductor decreases, the calculated temperature rise aligns closer to actual values, and air friction loss on the copper surface is reduced by 6.5 %. Experimental verification, conducted on a 55 kW double-disk magnetic coupler, demonstrates maximum errors of 8.86 % and 6.53 % when comparing experimental values to those calculated by the equivalent thermal network method and CFD method, respectively, thereby validating the proposed method. This research provides a theoretical reference for thermal calculations in double-disk magnetic coupler.

PVA-assisted graphene aerogels composite phase change materials with anisotropic porous structure for thermal management

The rapid development of spacecraft thermal control systems necessitates high-performance phase change materials (PCMs) with low density, high thermal conductivity and high enthalpy. Graphene aerogels (GAs) prepared by unidirectional freezing are ideal candidates as thermal conductive networks for PCMs due to the anisotropic porous structures. However, constructing anisotropic thermal conductive composite PCMs with low graphene aerogel loading while employing environmentally friendly cross-linking agents remains challenging. To fulfill the research gap, this study explores the synthesis of poly(vinyl alcohol) (PVA)/graphene aerogels (PGAs) by hydrothermal reaction and conventional freeze-drying. Anisotropic PGAs with oriented porous structures were fabricated by unidirectional freezing. After annealing and impregnation with paraffin wax, composite PCMs with excellent shape stability were obtained. The prepared composite exhibits low density (0.82 g cm−3) and high enthalpy (165 J g−1). The combination of PVA and graphene enables the composite to achieve an ultralow graphene aerogel loading (0.85 wt%) while maintaining high thermal conductivity (1.37 W m−1 K−1), leading to a high specific thermal conductivity enhancement up to 477. This work sheds light on the potential of combing PVA and graphene to construct thermal conductive aerogels, intending to provide feasible means to develop high-performance PCMs for spacecraft thermal management.

Microstructure and thermal properties of ternary chloride eutectic salts for high temperature thermal energy storage

Chloride molten salts are attractive candidate materials used for effective thermal energy transfer and storage in renewable energy system as concentrating solar power, but associated thermal properties at high temperature are still insufficient in research. In this work, eutectic point verification, microstructure and thermal properties of NaCl–KCl–ZnCl2 eutectic salts with four different contents are investigated by molecular dynamics simulation based on Born-Mayer-Huggins potential and experimental measurement. The density, specific heat capacity, viscosity, self-diffusion coefficient and thermal conductivity of four ternary eutectic salts are predicted with experimental validation and their correlations with different temperature and composition are proposed, and the mechanism of desirable thermal performance variation is revealed from the microscopic point of view. As ZnCl2 content increases, the thermal conductivity and specific heat capacity increase significantly, and eutectic salt #4 (18.6 %NaCl: 21.9 %KCl: 59.5 %ZnCl2) has maxima of density, specific heat capacity and thermal conductivity. The above phenomena can be attributed to the increase in potential energy and Columbic energy for more charge of Zn2+, which strengthens the interaction between atoms in the system and intensifies the collision. This work is expected to provide effective guidance on the design and application of molten salts for high temperature thermal energy storage.

Uncertainty analysis of FLiNaK thermophysical properties on convective heat transfer characteristics in circular tube

Molten salts have attracted a spate of quantity of interests in energy and chemistry fields due to their large volumetric capacity, and thermodynamic stability at elevated temperature. However, there are significant uncertainties in the physical properties of molten salts, such as density, specific heat capacity, dynamic viscosity, and thermal conductivity, due to inexperienced measurement techniques and technology. These uncertainties could have certain impact on the evaluation of molten salts heat transfer characteristics. Therefore, an uncertainty analysis is performed regarding FLiNaK thermophysical properties on convective heat transfer characteristics in circular tube. Then, a polynomial chaos expansion (PCE) method is performed to study the uncertainty affecting the heat transfer characteristic. In the process of uncertainty analysis, tensor product quadrature nodes are used to calculate representative sample points and reduce computational costs. Three primary physical properties of molten salt are taken into account as the input parameters. The Sobol composition method is also used to analyze the contributions of each parameter to heat transfer. The results of the uncertainty analysis suggest that the uncertainties in dynamic viscosity, thermal conductivity, and specific heat capacity have a significant impact on the heat transfer of molten salt, contributing to 80 %, 14 %, and 6 % of the total variability, respectively. It also suggests that the polynomial chaos expansion methodology is both novel and reliable when applied to uncertainty analysis of molten salt.

Heat conduction simulation of chondrocyte-embedded agarose gels suggests negligible impact of viscoelastic dissipation on temperature change

Agarose is commonly used for 3D cell culture and to mimic the stiffness of the pericellular matrix of articular chondrocytes. Although it is known that both temperature and mechanical stimulation affect the metabolism of chondrocytes, little is known about the thermal properties of agarose hydrogels. Thermal properties of agarose are needed to analyze potential heat production by chondrocytes induced by various experimental stimuli (carbon source, cyclical compression, etc). Utilizing ASTM C177, a custom-built thermal conductivity measuring device was constructed and used to calculate the thermal conductivity of 4.5 % low gelling temperature agarose hydrogels. Additionally, Differential Scanning Calorimetry was used to calculate the specific heat capacity of the agarose hydrogels. Testing of chondrocyte-embedded agarose hydrogels commonly occurs in Phosphate-Buffered Saline (PBS), and thermal analysis requires the free convection coefficient of PBS. This was calculated using a 2D heat conduction simulation within MATLAB in tandem with experimental data collected for known boundary and initial conditions. The specific heat capacity and thermal conductivity of 4.5 % agarose hydrogels was calculated to be 2.85 J/g°C and 0.121 W/mK, respectively. The free convection coefficient of PBS was calculated to be 1000.1 W/m2K. The values of specific heat capacity and thermal conductivity for agarose are similar to the reported values for articular cartilage, which are 3.20 J/g°C and 0.21 W/mK (Moghadam, et al. 2014). These data show that cyclical loading of hydrogel samples with these thermal properties will result in negligible temperature increases. This suggests that in addition to 4.5 % agarose hydrogels mimicking the physiological stiffness of the cartilage PCM, they can also mimic the thermal properties of articular cartilage for in vitro studies.

Efficient nanofluids based on Ag nanoparticles and a linear silicone-based fluid for concentrating solar power

Improving the efficiency of renewable energy sources can lead to obtaining electrical energy in an environmentally-friendly way. Therefore, the development of nanofluids for use in parabolic trough collectors in concentrated solar energy (CSP-PTC) is a research line of interest. Thus, in this work, nanofluids based on Ag nanoparticles and a polydimethylsiloxane (PDMS) type fluid used in CSP-PTC technology were prepared. The use of this fluid in this technology and the preparation of nanofluids based on it has not been studied widely, and the evaluation of the use of nanofluids from this type fluid is of great interest. Thus, the physical stability and the properties of interest measured, that are density, surface tension, viscosity, isobaric specific heat and thermal conductivity, were characterized. The nanofluids prepared presented interesting thermal properties. An increase of up to 4.5 % in the isobaric specific heat and up to 24 % in thermal conductivity were observed with respect to the base fluid, without a significant increase in viscosity. Thus, an increase in the heat transfer coefficient of up to 16 % was obtained. These results are really promising for the use of the nanofluids prepared in CSP-PTC technology. Finally, the moderate increase in isobaric specific heat and the significant increase in thermal conductivity is explained by the weak Van der Waals force interaction observed between the Ag surfaces and the PDMS molecules.

Modeling the thermal behavior of multifunctional syntactic foams containing phase change materials for heat management applications

AbstractSyntactic foams are lightweight porous composites obtained by the addition of hollow glass microspheres (HGMs) to a polymer matrix. This work experimentally and numerically investigates the thermal behavior of epoxy‐based syntactic foams with enhanced multifunctionality produced by incorporating microencapsulated phase change materials (PCMs) as functional fillers, providing thermal energy storage and temperature stabilization due to its large latent heat of melting. Foams are fabricated using varying ratios of HGMs (0–40 vol%) and PCM (0–40 vol%) to achieve tuned densities and thermal properties with a total filler content of up to 40 vol%. A one‐dimensional numerical heat transfer model based on the enthalpy method is presented to simulate the thermal behavior of these materials. The model accurately incorporates the specific heat and thermal conductivity of the foam components, as well as the latent heat absorption during PCM melting (up to 68 J/g). The model is experimentally validated by demonstrating good agreement with the measurements of transient temperature profiles during heating tests on the foam samples. The validated tool is then leveraged to model the thermal response of the foams under a sinusoidally varying heat source, similar to the possible real applicative scenarios. These results can help optimize foam compositions balancing energy storage density, heat transfer properties, and structural support for lightweight energy storage systems. Potential applications include high‐efficiency thermal management in battery packs, electronic cooling, solar energy storage, and sustainable temperature‐controlled buildings.Highlights Foams with 0–40 vol% PCM and 0–40 vol% HGM show up to 68 J/g latent heat. 1D numerical model accurately captures thermal conductivity and PCM phase change. Validated model simulates thermal response under sinusoidal heat, optimizing foam composition. Foams act as thermal reservoirs, maintaining up to 5°C lower surface temperatures than epoxy.

Impact of raw material on thermo‐physical properties of carbon foam

AbstractCarbon foam materials are currently used in several industrial and engineering applications due to their outstanding properties. The properties of carbon foam can be altered through the manufacturing processes applied in specific applications. In this paper, we collected and analyzed four samples manufactured by CFOAM and one sample developed by Ohio University (OU) to understand the behaviour of this material and determine its properties. We utilized advanced techniques to experimentally measure and determine the following properties: pore size and volume, porosity, specific surface area, mass, density, and thermal conductivity. Among the samples, the low‐porosity CFOAM (CF35) and the OU sample exhibited higher specific surface areas and densities compared to the others. However, CF35 demonstrated the highest thermal conductivity, while OU displayed the lowest. As a result, CF35 emerges as the optimal choice for applications requiring high‐rate heat transfer, while the remaining CFOAM samples are well‐suited for lightweight applications. Thus, OU foam proves to be a highly suitable candidate for insulation applications such as building sidewalls.

Effective electronic properties and coupling for two-temperature model-molecular dynamics simulation of ultrafast laser ablation of nickel

ABSTRACT The accuracy of hybrid two temperature model-molecular dynamics (TTM-MD) simulations in predicting the ultrafast laser ablation phenomena in metals is influenced by the functional definition of subsystem properties and electronic-lattice coupling. In this work, laser ablation of nickel is simulated using hybrid TTM-MD with empirical and density function theory (DFT) derived electronic and coupling parameter sets. The investigation revealed that the empirically derived temperature-dependent parameterisation of electronic specific heat, thermal conductivity, and coupling factor enhanced the fidelity of electron–phonon nonequilibrium dynamics when used in conjunction with simple optical absorption models, aligning closely with prior experimental observations for nickel specimens. The TTM-MD setup is then coupled utilising two widely used coupling techniques – the temperature difference scaled and Langevin thermostat. It is found that the former exhibits increased tensile stress due to artificial enhancement of the collision cascade owing to deterministic nature of the coupling force. While the probabilistic nature of the Langevin thermostat offers more accurate predictions of the ablation threshold/yield. Under these conditions, the TTM-MD scheme is tested for a range of absorbed laser fluence, with ablation threshold, and the onset of phase explosion is determined as 115 and 270 mJ/cm2, respectively for a 1 picosecond (ps-) laser pulse.

Thermophysical Characterization of Materials for Energy-Efficient Double Diaphragm Preforming

The Double Diaphragm Preforming (DDPF) process uses vacuum pressure and heat to pre-shape dry carbon fabric reinforcements between flexible diaphragms in liquid composite molding (LCM). Accurate modeling of heat transfer within DDPF requires knowledge of the thermophysical properties of the constituent materials under processing conditions. This study investigates the thermal conductivity of silicone diaphragms and carbon fabrics with embedded thermoplastic binder webs, utilizing transient plane source (TPS) and modified transient plane source (MTPS) methods, respectively. Additionally, the specific heat of silicone, carbon fibers (both chopped and powdered), and binder were measured using differential scanning calorimetry (DSC). Mixed samples comprising chopped fibers with 1.8 wt% binder and powdered fibers with 3.6 wt% binder was also analyzed with DSC. This study also examined the influence of reheating cycles on the specific heat of carbon fiber—3.6 wt% binder samples—and the effect of compaction and vacuum on the thermal conductivity of carbon fabrics with an embedded binder. While silicone exhibited linear-specific heat behavior, the thermoplastic binder showed non-linearity due to phase change. The combined carbon fiber-binder samples demonstrated slight non-linear specific heat variations depending on reheating cycles. The thermal conductivity of the fabric preforms decreased with the addition of thermoplastic binder and under vacuum-compaction conditions. The established temperature-dependent specific heat relationships and thermal conductivity provide valuable data for optimizing DDPF preforming parameters and enhancing energy efficiency in composite manufacturing.

Molecular dynamics simulation on thermal and transport properties of LiF-KF

Molten fluoride is considered as an attractive heat transfer and storage medium in advanced energy utilization facilities, but it is short of the necessary thermal and transport properties at high temperature. In this paper, the thermal and transport properties of the binary LiF-KF mixtures at 1073–1473 K are obtained by classical molecular dynamics. The deviation of simulated thermal conductivity of binary LiF-KF at 1073 K from experimental value is less than 19 %. Moreover, the deviation of simulated viscosity of pure LiF at different temperatures from experimental value is around 10 %. It is indicated that reverse non-equilibrium molecular dynamics (RNEMD) is acceptable for describing fluoride salts. An exponential correlation is established between molar fraction of LiF and thermal conductivity at different temperatures. Furthermore, the macroscopic thermal and transport properties correlated with local structure are analyzed, especially the dependence of local structure on temperature and composition of LiF is discussed deeply. With temperature increasing, ion clusters are considered to be formed and overall structure become loose, which leads to reductions in density, thermal conductivity and viscosity. An increase in composition of LiF results in higher specific heat capacity, thermal conductivity and viscosity, which is related to the reduction of Li-Li bond length and the enhancement of interactions between F−. The comparison of properties enhancement of different compositions is completed through the analysis of the synergy coefficient of macroscopic properties. This work provides the basic data for the accurate design of high-temperature heat transfer system.