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Microwave heating has been applied to improve cement-based materials (CBMs) structures deicing efficiency, which reduce the effect of icing on their service life. Moreover, the enhanced thermal properties of CBMs can further improve their deicing efficiency. In this study, silicon carbide (SiC) ceramic particles with favorable thermal properties were used to prepare the SiC cement-based materials (SCBMs). The effect of SiC ceramic on the mechanical strength of CBMs was investigated. Next, the heat transfer and storage ability of CBMs were investigated to analyze the changes in their thermal-physical parameters. Then, the surface thermal responses of the CBMs during microwave heating and off were recorded to characterize their temperature evolution in a low-temperature condition. Furthermore, the deicing efficiency of CBMs was determined using the ice layer shedding time (ILST) as the index. The results show that the filling effect of SiC ceramic on CBMs improved their mechanical strength within a certain content range. However, a large content of SiC ceramic caused an increase in the weak area and porosity within the CBMs, further reducing their mechanical properties. The thermal-physical parameters of CBMs were improved after adding SiC ceramic. The thermal conductivity and thermal effusivity of SCBMs-100 were 13.17 W/(m·K) and 1.44 W/(mm2·K), respectively, 7.90 and 2.35 times higher than the control group. Due to the favorable thermal properties of SCBMs, their heating rate and surface temperature field distribution characteristics were further improved. Furthermore, with the increase of SiC ceramic content, the ILST of SCBMs was further reduced during microwave heating. Therefore, the SiC ceramic was a favorable material, improving the thermal properties and deicing efficiency of CBMs to a certain extent. However, considering its effect on the deterioration of the mechanical properties of CBMs, the optimal content of SiC ceramic might be 75%. [ABSTRACT FROM AUTHOR]

• Molecular dynamics method was implemented. • Nano refrigerants include Freon-134a and Freon-407a as base fluids and Cu as nanoparticles. • The density, velocity, and temperature profiles are investigated. • Freon-407a base fluid shows a better thermal performance. • Nano-refrigerant with Freon-407a base fluid has more heat flux (1028 W/m2). Nano-refrigerants, which are the suspensions of nano-sized particles in a base fluid, were applied in many devices and systems to enhance thermal conductivity and improve heat transfer performance. This work studied the thermal and atomic behavior of two kinds of nano-refrigerants located inside an aluminum nanochannel for 5 ns. The molecular dynamics (simulation method simulated Nano-refrigerants, including R-134a and R-407A as base fluids and copper as nanoparticles. The density, velocity, and temperature profiles were studied to investigate the atomic behavior of the simulated sample. The thermal behavior of structures was studied by examining the phase transition rate, phase change time, thermal conductivity, and heat flux. The results show that R-407A base fluid showed better thermal behavior. The results show that in Cu/R-407A, the phase-changed particle reached 31% in 5 ns, and phase change time was estimated to be 3.91 ns. In contrast, in Cu/R-134a, the samples' phase changed particle and phase change time reached 26% and 4.06 ns. Moreover, the study of heat flux shows that nano-refrigerant with R-407A base fluid had more HF (1028 W/m2) than R-134a (654 W/m2). The results show that the thermal conductivity of R-407A and R-134a nano-refrigerant converged to 0.0975 and 0.0098 W/mK, respectively. [ABSTRACT FROM AUTHOR]

• Thermal conductivity of a MOF (HKUST-1) was investigated by EMD. • A new method to truncate heat current autocorrelation function of the Green-Kubo method was devised. • The influence of Ar molecules on decomposed thermal conductivity of the MOF was investigated. • The contribution of the interaction of the atoms was dominant to the thermal conductivity. Metal-organic frameworks (MOFs) are promising porous materials for various applications, which have attracted considerable attention recently. Optimizing their thermal properties, such as their heat accumulation characteristics during the adsorption of fluid molecules, is crucial for enhancing their performance. Molecular dynamics studies are vital for meticulously understanding the thermal transport of MOFs. To determine the thermal conductivity of MOFs using the Green–Kubo formula through equilibrium molecular dynamics (EMD), the heat current autocorrelation function (HCACF) must be truncated at a specific time. However, few studies have been conducted on establishing a method for truncating HCACFs for MOFs, rendering it challenging to assess the reliability of MOF thermal conductivities calculated through EMD. In addition, previous studies focused on the overall thermal conductivity, and the contribution of the components have not been identified. In this study, we devised a method for determining the truncation time of an HCACF to calculate the thermal conductivity of MOFs. After confirming the validity of the method, we decomposed the instantaneous heat flux into individual components and obtained the decomposed thermal conductivities. The results revealed that the contribution of the interaction of atoms was more pronounced than that of the microscopic convection of atoms. In addition, the method introduces an ambiguity while calculating the thermal conductivity of MOFs through EMD. The proposed method is useful for truncating of HCACFs and determining the thermal conductivity of complex materials such as MOFs. [ABSTRACT FROM AUTHOR]

• Analyze the variation of heat transfer as a function of diameter and temperature. • Investigate heat transfer mechanism by crucial direct parameters. • Explore internal mechanism by phonon density of state and phonon overlap energy. Carbyne is a sp1 linear carbon chain (LCC) with characteristics of strong chemical reactivity and extreme instability under environmental conditions, which has become an obstacle to the application of LCC with high thermal and electrical conductivity. Utilizing CNT as a container to store LCC is one of the most feasible ways to realize LCC applications. However, current research of LCC encapsulated in CNT (LCC@CNT) focuses on its preparation and lacks of in-depth exploration of the intrinsic heat transfer mechanism. This paper reports the high axis thermal conductivity of LCC@CNT, explore the thermal transport enhancement degree of LCC@CNT under a wide temperature range and multiple diameters, and analyzed the underling mechanism through crucial thermal parameters and phonon theory. When LCC is loaded in CNT, the axial thermal conductivity of CNT is further increased by 15 %. Moreover, LCC@CNT shows the lower sensitivity diameter than pristine CNT. This work is expected to provide data support for the application of LCC, the lower production standard of CNT, and also attempt the higher efficient one-dimensional thermal energy transfer micro devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Efficiently thermal management in electronic devices calls for creating polymer composites that have superior thermal transport abilities. Compared with single-filler composites, hybrid-filler composites have gained significant attention as they not only utilize the advantages of each filler individually but also allow for the potential cooperation in constructing filler networks between them. Differing from the previous research on hybrid-filler size, geometry, composition, and content and their impact on thermal conductivity (TC) in composites, this study aims to examine the spatial distribution effects of hybrid-fillers. A binary-filler strategy comprising of anisotropic 2D h- BN and 0D isotropic S–Al 2 O 3 has been proposed, with the primary h -BN filler aligned to filly utilize its anisotropy and intrinsic TC properties. Furthermore, positioning a small quantity of S–Al 2 O 3 between adjacent parallel h -BN considerably improves TC in the non-oriented direction of silicon rubber (SiR) composites. A special focus is given to the influence of the interstitial S–Al 2 O 3 filler on the individual through-plane TC (λ ⊥) and in-plane TC (λ ⫽) variation of the binary-filler hybrid SiR composites, which are perpendicular and parallel to the oriented h -BN. When incorporating 40 vol% h -BN and 5 vol% S–Al 2 O 3 , the binary SiR composites exhibit the highest concurrent λ ⫽ and λ ⊥ values of 14.581 and 2.132 W/m·K, respectively. The corresponding effects on the ductility, hardness, and dielectric properties of the SiR composites were explained. Moreover, the use of commercially available TC fillers, along with the effortless preparation method, enables the potential to produce h -BN based TIMs materials on a large scale for thermal management usage. [Display omitted] • A binary filler system consisting in-plane oriented 2D h -BN and 0D isotropic S–Al 2 O 3 is designed. • The addition of S–Al 2 O 3 filler between adjacent parallel h -BN flakes facilitates vertical heat transfer. • The binary structure of h -BN/S–Al 2 O 3 exhibits an anisotropic feature in the filler contact thermal resistances. • The binary filler strategy mitigates the trade-off between in-plane and through-plane thermal conductivity. [ABSTRACT FROM AUTHOR]

The development of lightweight shape memory materials with exceptional thermal insulation properties is highly important in aerospace applications. Herein, shape memory polyimide (PI) aerogels was fabricated by molecularly designed PI molecular chains through freeze gelation and subsequent thermal imidization. The freezing conditions were controlled to regulate the porous microstructures of the aerogels. The interactions between PI chains formed physically crosslinked netpoints, which could overcome the expansive force and capillary force, thereby creating a stable porous structure. Because shape memory was thermally activated, the shape memory mechanisms associated with the thermal conductivity of the aerogels were comprehensively explored. Upon decreasing the pore size, dense frameworks were formed, contributing to the improved thermo-mechanical and compressive properties. Moreover, the heat transfer efficiency in the aerogel skeleton was enhanced, resulting in a rapid shape recovery response. Benefiting from the physically crosslinked structures, including entangled chains and π-π interactions, the fabricated PI aerogels demonstrated exceptional shape fixation and recovery capabilities. These findings may provide guidelines for designing smart aerogels for aerospace applications. [Display omitted] • Shape memory polyimide aerogels with tunable porous microstructures were fabricated. • The size of the micropores was regulated by controlling the freezing conditions. • The reduction of pore size accelerated the shape recovery process. • The comprehensive exploration of the shape memory mechanisms was conducted. [ABSTRACT FROM AUTHOR]

This study explores the use of copper foam (CF) as a thermally conductive scaffold for phase change materials (PCMs), enhancing shape stability. Employing the ice template method (ITM), we fabricate a CF with a low-density, honeycomb structure and anisotropy from flake copper powders. The resulting phase change composites (PCCs), infused with paraffin wax (PW), showcase high thermal conductivity and shape retention compared to pure PW, with anisotropic heat flow due to directional channels in the CF. With a 34.4 wt% filling ratio, the PCCs achieve axial and lateral thermal conductivities of 2.85 W m−1 K−1 and 1.51 W m−1 K−1, respectively, and a thermal storage enthalpy of 158.18 J g−1. This work presents a novel method for advanced thermal energy storage and management, indicating the promise of ITM-derived CF in high-performance PCCs for diverse applications. • 3D porous copper with lighter weight, honeycomb-like and directional structure was prepared. • The composite has good form-stability and anti-leakage property. • The composite indicates high thermal conductivity of 2.85 W m−1k−1. • The composite indicates heat storage capability of 158.18 J g−1. • The composite has good anisotropic thermal conductivity. [ABSTRACT FROM AUTHOR]

CFRP composite laminates decompose by pyrolysis/oxidation when exposed to high heat fluxes. While gaseous and solid residues created within the composite material are ignored in most models, a multi-species approach is proposed to describe transient decompositions from the virgin to the final charred state of the material. The model is based on a porous medium description that includes gas creation and transport within the laminate, respectively driven by Arrhenius and Darcy's laws. Orthotropic heat transfer and decomposition gas transport within the laminate up to the surface remain often uninvestigated while it can drastically act upon the dynamics of a fire event. An experiment is carried out to analyze multi-dimensional heat and mass transfer during the charring processes of a composite laminate exposed to a high power laser beam. Transient temperature measurements on the unexposed surface of the material are confronted to 3D unsteady numerical results to validate the model formulation. • 3D numerical solver of heat and mass transfer within decomposing composite material. • Microstructure-based homogenization technique of thermal conductivity tensor. • Characterization of physical and chemical properties of virgin and charred laminates. • Experimental and numerical restitution of laser-induced material decomposition. [ABSTRACT FROM AUTHOR]

The ground thermal properties are the basic parameters for the design of borehole heat exchanger (BHE) in ground–coupled heat pump system (GCHPs), and their accuracy directly affects the economy and reliability of the heat pump system. In traditional design, ground is usually regarded as an isotropic homogeneous medium, and its thermal properties are obtained by solving the inverse heat transfer problem in BHE through in-situ thermal response test (TRT). In fact, different geological layers can be observed along the depth of BHE, and thermal physical properties of each layer are different based on the ground geological conditions. In order to investigate the effect of geological stratification on estimated accuracy of ground thermal parameters in TRT, a validated numerical layered BHE model (NLBM) is presented to simulated TRT, and the fluid temperature response is used to estimate effective ground thermal conductivity and borehole thermal resistance based on line source model (LSM). Secondly, the distributions of fluid temperature in U-pipe and heat flux of BHE along the depth are compared and analyzed based on the NLBM and the numerical homogeneous BHE model (NHBM). At last, borehole thermal resistance from the NLBM and estimated borehole thermal resistance from LSM are compared. The results show the maximum heat flux in the 3rd layer of the NLBM is 21.1% higher than that of NHBM, and the minimum heat flux in the 1st layer is reduced by 46.9% in the 100 h duration. The estimated λ LSM using the fluid temperature responses in the NLBM is 1.3% higher than the thickness-weighted thermal conductivity in the NLBM. The minimum relative error between R LSM and R b is still up to 10.45% in the duration of 100 h even though extending the duration is helpful to improve the estimated accuracy of R LSM. • A numerical layered BHE model is proposed and validated by the experiment. • The distributions of fluid temperatures are compared from the two models. • The differences of heat flux are illustrated in the two models. • Effect of geological stratification on estimated accuracy is investigated in TRT. [ABSTRACT FROM AUTHOR]

• Measured through-thickness thermal conductivity of 2 × 2 twill carbon fabric using C-Therm Trident system with MTPS sensor. • Thermal conductivity is reduced by 38% under vacuum, attributed to presence of air in the porous structure of the fabric. • Layup thickness/configuration have negligible impact on thermal conductivity due to limited heat penetration. • Higher fabric compaction increases thermal conductivity owing to improved fibre nesting and contact. For high-fidelity simulation of heat transfer responses during various composite manufacturing processes involving heat, thermal conductivity (TC) of dry carbon weaves is essential. In this paper, the through-thickness TC properties of a 2 × 2 carbon twill weave are presented, employing a state-of-the-art C-Therm Trident module equipped with a Modified Transient Plane Source (MTPS) sensor. The effects of air presence, layup thickness, layup configuration, and fabric compaction on TC are investigated. Results reveal negligible impacts of layer number and configuration on TC. However, TC is significantly influenced by air presence and stack compaction. These findings provide improved comprehension of heat transfer in textile composites for more accurate process modelling and simulation using homogenized models. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) nanosheets, such as graphene and hexagonal boron nitride, are considered as the most promising fillers for enhancing thermal conductivity of polymers and phase-change materials. Nevertheless, the effect of various 2D nanosheets on the effective thermal conductivity of composites is not fully understood, and the corresponding prediction model is still lacking, since numerous influence factors and complex thermal transfer networks are involved. This paper aims to study the macroscopically effective thermal conductivity of the nanosheets-reinforced composites in a systematical way, and develop a robust machine learning based prediction model. To this end, a series of representative volume elements are reconstructed based on the SEM observations of experimental samples, and high-throughput simulations are performed via the updated lattice Boltzmann scheme proposed in our recent work. The effects of shape, size, orientation, intrinsic thermal conductivity, interface thermal resistance, surface coating, and hybrid filling of the 2D nanosheets are clarified. This work could provide a deep insight into the effective thermal conductivity of the nanosheets-reinforced composites, and may offer important guidelines for the custom-design of polymer and phase-change composites with targeted thermal performances. [Display omitted] [ABSTRACT FROM AUTHOR]

The prediction of the prevailing self-heat transfer parameters of a glass/epoxy composite coupon during fatigue testing in general and the distinction between viscoelastic- and frictional crack growth-related energy dissipation in particular, are not trivial problems. This work investigates the feasibility of predicting the convective film coefficient, the total work loss as well as the ratio between viscoelastic and fracture-induced damping from thermal images using Bayesian optimization in conjunction with 3D FE thermal analysis. To this end, glass fiber/epoxy biax coupons are pre-damaged by means of a drop weight impact machine and subsequently tested under uniaxial tension-tension high cycle fatigue conditions. IR images are taken of the self-heating thermal profile at steady-state conditions. Synthetic surface thermal images are generated by numerical thermal analysis of the damage distribution obtained by μ -CT scanning prior to testing. Bayesian optimization of the aforementioned parameters is conducted by minimizing the loss function between the as-measured and the synthetic IR image. The predicted work-loss is consequently validated against the measured hysteretic response, from which a very good agreement is found. [Display omitted] • Thermal heat transfer parameters are predicted via Bayesian optimization (BO). • FEM and BO are combined to find physically meaningful parameters. • The method efficiently handles 3D parameters compared to other approaches. [ABSTRACT FROM AUTHOR]

The electronics in logging tools are susceptible to thermal failure due to the extreme thermal environment. Passive thermal management system (PTMS) has been proven to protect the electronics for several hours. In this paper, a numerical model based on the equivalent thermal conductivity method was developed to determine the transient temperature of downhole electronics. Compared with the traditional analytical model or numerical model considering only one single heat transfer process, the complex heat transfer in the logging tool were comprehensively considered through the proposed model. Briefly, the heat transfer processes in the vacuum bottle were theoretically calculated rather than empirically acquired, and the convective and radiative heat transfer inside the vacuum bottle was equated to the temperature-dependent thermal conductivity of air. In addition, the proposed numerical model was compared with experiments and previous numerical models to verify the accuracy of the model, and the temperature deviation of the electronics was within 5 °C. Moreover, the computational time was greatly reduced compared with the traditional three-dimensional numerical simulation process while ensuring the accuracy of calculation. Therefore, the proposed numerical model achieved both computational accuracy and efficiency, which was expected to be widely used in the development of PTMS for logging tools. • A numerical model based on equivalent thermal conductivity method was proposed. • The complex heat transfer processes in PTMS were comprehensively considered. • The proposed model possessed high computational accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Ho 2 O 3 was employed to improve the microstructural densification and performances of pressureless sintered corundum–mullite ceramic composites. This study investigated the influences of Ho 2 O 3 addition on the microstructure, physical properties and thermal shock resistances of the composites. The results indicated that sample AH5 (80 wt% Al 2 O 3 , 20 wt% coal series kaolin, and 5 wt% additional Ho 2 O 3), which was sintered at 1550 °C, showed the best comprehensive properties. In this Al 2 O 3 -rich and SiO 2 -poor system, a reaction between the Ho 2 O 3 and Al 2 O 3 –SiO 2 system produced an Ho 2 O 3 –Al 2 O 3 –SiO 2 liquid phase. This liquid phase increased the microstructural densification and resulted in a lower sintering temperature. The generation of mullite and holmium disilicate during thermal shocks improved the thermal shock resistance. The high bending strength and satisfactory thermal shock resistance of the as-prepared corundum–mullite ceramic composites showed their potential for use in heat transmission pipelines. [ABSTRACT FROM AUTHOR]

Thermal properties are critical parameters to design and implement efficient thermal processes especially for food manufacturing. Current methods to measure temperature-dependent thermal properties are expensive, time consuming and labor intensive with certain methods requiring composition analysis of food. To solve those problems, a novel method and equipment, named TPCell, was developed to estimate temperature-dependent thermal conductivity in a single experiment. For simultaneous estimation of temperature-dependent thermal conductivity and volumetric heat capacity, a new generation of TPCell was designed with complementary experimental profile and parameters were estimated by analyzing the parameter sensitivity coefficients. For different heating profile, the scaled sensitivity coefficients (SSC) of multiple parameters and optimal values were compared to determine the number of parameters that can be estimated. The thermal properties of sweet potato puree were estimated using sequential parameter estimation. The temperature-dependent thermal conductivity was found as 0.516 ± 0.011 W/mK at 26 °C and 0.798 ± 0.030 W/mK at 135 °C. Also, the volumetric heat capacity in the same temperature range was 3.520 × 106 ± 0.124 × 106 J/m3K. Therefore, the complementary experiment was successful in simultaneous estimation of temperature-dependent thermal conductivity and volumetric heat capacity. [ABSTRACT FROM AUTHOR]

Powder bed properties affect the quality of the parts manufactured by powder bed fusion (PBF). On PBF with laser, researchers had thoroughly studied the impact of powder layer on consolidation. In terms of interaction mechanisms with materials, electron beam is different from laser. Thus, an in-depth discussion is required for PBF with electron beam. In this study, numerical simulations were performed to reconstruct the powder bed and analyze the subsequent consolidation. The powder layer's presence altered the emissivity and thermal conductivity to be different from those of a solid. Concerning the powder with different particle size distributions, the differences in thermal properties led to an alteration in the molten pool formation. The emissivity increased, and the thermal conductivity decreased as the fraction of fine powders increased. With the increased fraction of fine powders under a given layer thickness, relatively high energy should be input to ensure exceptional forming quality. Unlabelled Image • Numerical simulations were performed to investigate consolidation of powder beds in PBF-EB. • Powder layer possessed high emissivity and low thermal conductivity compared with a solid base. • Emissivity increased and thermal conductivity decreased as the fraction of fine powder increased. • Relatively high energy of electron beam should be applied as the fraction of fine powder increased. [ABSTRACT FROM AUTHOR]

U-bend deep borehole heat exchanger (DBHE) is a new promising kind of ground heat exchanger, but nowadays there are lack of accurate efficient models to simulate U-bend DBHE. This paper has developed a semi-analytical model of U-bend DBHE, which considers the unsteady heat transfer of borehole, heterogenous soil thermal properties and geothermal gradient. A 2D numerical model and an analytical model based on infinite line-source theory are also developed, and the three models are compared with experimental data for different boundary conditions. Based on the soil thermal properties estimated by logging data and rock identification, the three models have large errors when compared with experimental data. Based on a soil thermal conductivity λ s estimated by matching experimental data, the three models match better with experimental data, and it is inferred that λ s should be measured by thermal response test instead of rock identification. The semi-analytical model and 2D numerical model match very well for all the time, but the analytical model has large differences with 2D numerical model, which is because the analytical model ignores borehole heat capacity and time-varying heat flows at the borehole wall. This paper could provide a cost-effective semi-analytical model and some advices for U-bend DBHE. [ABSTRACT FROM AUTHOR]

We introduce the concept of physics-guided transfer learning to predict the thermal conductivity of an additively manufactured short-fiber reinforced polymer (SFRP) using micro-structural characteristics extracted from tensile tests. Developing composite manufacturing digital twins for SFRP composite processes like extrusion deposition additive manufacturing (EDAM) require extensive experimental material characterization. Even the same material system printed on different EDAM systems can result in significant changes to the printed micro-structure, affecting the mechanical and transport properties. This, in turn, makes characterization efforts expensive and time-consuming. Therefore, the objective of the paper is to address this experimental bottleneck and use prior information about the material manufactured in one extrusion system to predict its properties when manufactured in another system. To enable this framework, we assume that changes in properties of the same material when manufactured in different systems arise solely due to microstructural changes. To that end, we present a Bayesian framework that can transfer thermal conductivity properties across extrusion deposition additive manufacturing systems. While we discuss the transfer of thermal conductivity properties, the development is such that the framework can be used for the transfer of other properties that depend on microstructural characteristics defined in the manufacturing process. These include the coefficient of thermal expansion, viscoelastic properties, etc. The framework begins by using thermal conductivity data of the composite printed in one extrusion system to probabilistically infer the constituent thermal properties of the fiber and the polymer. Next, by conducting limited tensile tests of the same material printed in another extrusion system, we infer its orientation tensor. Finally, the inferred constituent thermal conductivity properties and the inferred orientation tensor are coupled using a micromechanics model to predict the thermal conductivity properties of the composite printed in the second extrusion system. We experimentally verify the predictions and show that our method provides a reliable framework for transferring material properties while accounting for epistemic and aleatory uncertainties. • A probabilistic framework to transfer material information across manufacturing systems. • A framework to account for surrogate uncertainty in parameter inference. • Demonstrate transfer of thermal conductivity across additive manufacturing systems. • Applications to transfer other properties including coefficient of thermal expansion. [ABSTRACT FROM AUTHOR]

This work presents experimental investigation on specific heat capacity and thermal conductivity as a function of temperature and vertical density profile over the sample cross section of oriented strand board, particle board, medium density fibreboard, and plywood. A possibility of introducing an universal set of parameters describing various EWPs by averaging the parameters of the four studied materials obtained in this work is investigated. A one-dimensional heat transfer simulation sensitivity study is performed using the experimentally measured values. The study aims to investigate the effect of using spatial- and temperature-dependent properties compared to constant values and to study the importance of these parameters and their combination in predicting one-dimensional heat transfer below the thermal decomposition temperature of engineered wood products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal transport at pillared-graphene (PG)/epoxy polymer (EP) interface is investigated. • We detected some fantastic phenomena at the pillared-graphene (PG)/epoxy polymer (EP) interface. • We detect the number of PG layers was revealed to be one of the most influential elements on ITC. • It predicts the performance of thermal design for PG/epoxy polymer (EP) interface. We investigate the thermal properties of pillared-graphene (PG)/epoxy polymer (EP) interface architectures by using reverse non-equilibrium molecular dynamics. The results show that the interface thermal conductance (ITC) of the PG/EP contact is 147.85 MW/m2 K. The ITC between PG and EP can be substantially enhanced when optimizing the number and length of PG interlayer single-walled carbon nanotubes. In addition, we detected the number of PG layers was revealed to be one of the most influential elements on ITC. The findings of this study offer valuable insights for optimizing thermal transfer interfaces in electronic device thermal design. [ABSTRACT FROM AUTHOR]

Nanofluid has emerged as a promising heat transfer fluid (HTF) due to their significant thermophysical, and optical characteristics enhancement over base fluids. Hybrid nanofluids with multiple nanomaterials have the advantage of synergistic properties in comparison to monocomponent nanofluids. The present study proposes an energy-efficient and cleaner synthesis method for developing carbon quantum dot (C-dot), MXene, and a hybrid MXene/C-dot hybrid nanofluids, for heat transfer application. In-situ microwave pyrolysis technique and two-step method were adopted for nanomaterial and nanofluid synthesis. The morphological, phase structural, chemical, and elemental compositional analysis of the nanomaterials was performed. The material characterization confirms the hybridization of C-dot on MXene nanosheets. The thermal conductivity and volumetric heat capacity of the nanofluids were measured using the transient plane source (TPS) method. Thermal conductivity was observed to increase with nanofluid concentration and temperature. Results indicate that MXene has the highest thermal conductivity enhancement (50 %) over water, followed by hybrid (42.2 %) and C-dot nanofluid (33.2 %). The volumetric heat capacity of nanofluids decreased with concentration and temperature. A semi-empirical correlation, as a function of nanofluid concentration and temperature, was coined for predicting thermal conductivity and volumetric heat capacity. Optical property characterization study shows that C-dot nanofluid exhibited considerable absorption along the UV range, while MXene nanofluid showed absorption in the visible and near-infrared (NIR) region. Hybrid nanofluids demonstrated complementary absorption properties of C-dot and MXene nanofluids. [Display omitted] • Novel MXene/C-dot hybrid nanofluid was synthesized for heat transfer applications. • Study reveals the material and thermal-optical properties of C-dot, MXene and hybrid nanofluids. • Semi-empirical correlation were coined to predict thermal properties of nanofluids. • Highest thermal conductivity enhancement was exhibited by 0.2 wt% MXene nanofluid. • Hybrid nanofluid showed complementary absorption property of component nanofluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • The graphene oxide (GO) was synthesized using the modified Hummer method. • Sonochemically synthesized ZnO was deposited on graphene oxide to get a composite. • Well dispersed and stable composite nanofluids were prepared at varying wt.% concentrations for heat transfer studies. • The thermophysical, hydrodynamic, and thermal characteristics of composite nanofluids were analyzed in detail. • Heat transfer enhancement was analyzed in a closed conduit circular heat exchanger. Nanofluids have expanded a substantial approbation in the renewable and sustainable energy field. A small number of solid nanoparticles with higher thermal conductivity added into conventional fluid could develop a bigger improvement in heat transfer. The current study is focused on the preparation of metal oxide (ZnO) and Graphene oxide (GO) based composite nanofluids to achieve the higher thermal properties of composite as a potential nanofluid. The advanced hummer method and sonochemical techniques were used to synthesize ZnO, GO, and ZnO@GO composites. Further 2-step preparation methods were used to prepare ZnO@GO/DW based stable nanofluids at changing 0.1, 0.075, 0.05, and 0.025 wt% concentrations. All the materials were confirmed by different characterizations like XRD, RAMAN, FESEM, EDX, and UV–Vis analysis. At 0.1 wt% all the nanofluids showed a higher thermal conductivity, viscosity, and density which is 0.821 W/m.K, 2.85 kg.m−1s−1, and 1.0018 g/cm3. All the wt.% were tested for stability analysis using the sedimentation photograph method and found remarkable stability up to 5 weeks after the day of preparation without using any surfactant. Similarly, all the nanofluids were tested for hydrodynamic characteristics like friction coefficient (ff), pressure drop(ΔP), and pumping power (PP) where a notable value of friction was 0.057, a 12000 m. Pa pressure drop and 1.45 MPa pumping power were achieved at 0.1 wt% against the higher value of Reynold numbers (5849 to 24544). Finally, the greater development in average heat transfer/Nusselt numbers was achieved which is 3010/70 W/m2.K, 2490/42 W/m2.K, 2133/32 W/m2.K 2000/29 W/m2.K and 1000/W/m2.K for all wt.% and base fluid (DW) at a higher rate of Reynold Number. This all happened due to the use of ZnO and GO composite together. [ABSTRACT FROM AUTHOR]

Thermal protection and power generation are two of the major technical challenges in developing hypersonic vehicles with long-range/endurance. This research is aimed to provide a system for thermal protection and power generation for hydrocarbon-fueled scramjets. This study proposed a thermal management system based on fuel vapor turbine (FVT) and closed-Brayton-cycle (CBC) to generate power, and a bypass loop is connected with CBC in parallel to ensure thermal protection demand. A performance analysis model considering the combustor and cooling channels is established. The combustion and heat transfer process are described in a quasi-one-dimensional way, while FVT and CBC are described in a zero-dimensional form. Results indicate that large CBC power generation efficiency (η PG,CBC) and FVT expansion ratio (π FVT) can improve power generation with the same thermal protection performance. Because of the integrated variation law of cooling heat exchange and η PG,CBC , there exists an optimal value of fuel outlet temperature (T f 3) while meeting the thermal protection requirement. The high Mach number and low equivalence ratio both require a significant increase in the cooling capability of fuel, and it is feasible to sacrifice the power generation of the CBC subsystem to meet the thermal protection demand. • A thermal management system is proposed for hydrocarbon-fueled scramjets. • A model considering the combustion process and the heat transfer process is established. • There is an optimal value of T f 3 while meeting the thermal protection requirement. • It is feasible to sacrifice the CBC subsystem power generation to meet thermal protection demand. [ABSTRACT FROM AUTHOR]

Nowadays, a bio-inspired heat exchanger incorporating a triply periodic minimal surface (TPMS) structure has demonstrated great potential in the fields of new energy research and aerospace, which necessitates achieving a balance between low volume and high heat transfer efficiency while maintaining low pressure drop. In this paper, the adjustable heat efficiency of the heat exchanger with TPMS in gradient thicknesses is specially designed. A steady-state conjugate heat transfer (CHT) model is coupled with computational fluid dynamics (CFD) analysis. In addition, the temperature profile and velocity streamline are also checked to analyze the fluid flow behavior of the radiator. The results show that the convective heat transfer coefficient of the Gyroid with gradient level set values is 26.02–60.10% higher than that of the uniform Gyroid model, and the pressure drop is decreased by 9.66–18.05%. Both high heat transfer efficiency and low pressure drop can be achieved when the thickness is 0.2–0.3 mm and Re is 100–125. The heat exchangers with a TPMS thickness gradient in the ratio of 2:4:6 demonstrate a remarkable enhancement in overall heat transfer efficiency, achieving a 30.22% improvement compared to those with a TPMS thickness gradient in 6:4:2. [ABSTRACT FROM AUTHOR]

Liquid desiccant dehumidification, a clean energy technique for creating comfortable environments has received a lot of interest. Several dynamic models have been proposed to predict the outlet air humidity ratio and temperature, however, a study on presenting variations of heat and mass transfer coefficients and thermal mass of desiccant during the dynamic dehumidification process was not encountered according to authors' best knowledge. This gap is primarily due to the complex nature of the coupled heat and mass transfer processes, which make it challenging to capture the evolution of heat and mass transfer coefficients over time. In this study, variations of these parameters are analyzed at first. A theoretical study is conducted to show the thermal mass of the desiccant can be considered constant when changing the inlet air humidity ratio or desiccant temperature, simplifying the dynamic modeling process. While the variation of heat and mass transfer coefficients show significant impact in such conditions. Subsequently, a new method based on mass conservation is provided to determine the thermal mass of desiccant. By examining the cause-and-effect relationships between heat and mass transfer coefficients and outlet air humidity ratio, the evolution of heat and mass transfer coefficients following exponential laws is deduced by inversion. Then a dynamic model of packed dehumidifiers can be completed easily based on above derivations, and its viability is confirmed by experimental results. Compared to the existing method, the prediction accuracy can improve by 50% based on the proposed methods. This study characterizes evolution rules of heat and mass transfer coefficients over time, and with this, evolutions of outlet air parameters during the dynamic dehumidification process can be acquired conveniently based on the existing steady dehumidification model. • Variations of heat and mass transfer coefficients and thermal mass of desiccant are analyzed. • Simple methods are proposed to figure out the evolutions of thermal masses, and heat and mass transfer coefficients. • The prediction accuracy of air outlet humidity ratio could improve by 50% based on the proposed methods. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated photovoltaic vacuum glazing unit with an intermediate air cavity and a calibrated modelling approach to quantify its thermal properties and evaluate the heat transfer performance. Theoretical analyses of the heat transfer process are conducted with reasonable hypotheses and traceable boundary conditions. Three-dimensional heat transfer models are then established and cross-validated against previous publications. The detailed validation demonstrates the reliability of the developed complex models under different circumstances. Furthermore, four photovoltaic vacuum glazing configurations are compared in terms of the temperature distribution and overall heat transfer coefficient (i.e. U-value). Simulation results show that the photovoltaic vacuum double glazing can achieve the optimum performance among the four configurations based on simultaneous consideration of the PV module temperature and U-value. Sensitivity analyses of glazing design factors are also conducted for the U-value, which is found to be greatly reduced by decreasing the density and diameter of vacuum pillars as well as the glass thermal conductivity. A lowest U-value of 0.23 W/(m2·K) is achieved for the photovoltaic-vacuum double glazing and can be further improved with future design optimizations. This research can provide guidance to design improvement of PV vacuum glazing systems and promote their integration with building modelling tools. • A 3D heat transfer model of PV vacuum glazing is established and cross-validated. • Four compositive PV vacuum glazing configurations are proposed and compared. • The intermediate air cavity can reduce the U-value of PV vacuum glazing by 25%. • The PV vacuum glazing can achieve a U-value of 0.23 W/(m2·K). • Sensitivity analysis can provide a design guideline for PV vacuum glazing. [ABSTRACT FROM AUTHOR]

NaCl–CaCl 2 molten salt is considered as a promising high-temperature heat transfer and storage fluid for advanced nuclear power plants and concentrating solar power plants in the field of renewable energy utilization. However, the comprehensive physical properties and their microscopic mechanisms for the molten NaCl–CaCl 2 are failed to be measured accurately due to the extremely measuring condition. In this work, the ab-initio molecular dynamics simulation is used to investigate its microstructures and thermophysical properties for entire operating temperatures. It reveals that ion clusters are formed in terms of three for face-sharing, two for edge-sharing, and one for corner-sharing Cl− ions between the coordination shells of two neighboring cations. The coordination numbers of Na+-Cl- and Ca2+-Cl- ion pairs decrease from 5.88 to 6.46 at 783 K to 5.33 and 6.02 at 1173 K respectively. Meanwhile, the reliable and meaningful values of densities, ion self-diffusion coefficients, viscosities, and thermal conductivities were evaluated from 783 to 1173 K. It suggests that the distances and interactions between ions pairs determine thermodynamic properties directly. The ab-initio molecular dynamics simulation is proved to be an effective way to obtain the essential data for the designs of heat transfer and thermal energy storage systems in practical applications. • Ab-initio molecular dynamics simulations are applied for NaCl–CaCl 2. • Approach-to-equilibrium molecular dynamics method is used for thermal conductivity. • The correlation between microstructures and thermophysical properties are studied. • The distances and interactions between ion pairs determine its properties. [ABSTRACT FROM AUTHOR]

The anisotropic mechanical and thermal conduction properties of unidirectional aligned alumina aerogels (AAs) were investigated in our part II. The anisotropic structure characteristics are the main factors to decide the physical properties of AAs. The results show that the brittle failure behavior reflects the fracture of the long pore walls along ice-crystal growth direction, but the excellent strain and low compressive strength are ascribed to the weak second structures. The structural difference in the direction of heat transfer results anisotropic thermal conduction. The heat transfers layer-by-layer at intervals of solid walls and air pores is more effective for the heat insulation. [ABSTRACT FROM AUTHOR]

Effective utilization of solar energy resource enables to improve the thermal performance of solar evacuated tube. In present work, the back side of solar vacuum tube was coupled with mini-compound parabolic concentrator (mini-CPC). The thermal characteristics of the presented mini-CPC solar vacuum tube were analyzed theoretically and experimentally. A mathematical model of heat transfer for the mini-CPC vacuum tube was established according to the energy conservation, and solved by iterative calculation based on home-built C programming language. The obtained numerical solutions fit in well with the experimental results. Furthermore, analysis indicates the vacuum interlayer plays a crucial role in hindering heat transfer. The thermal-convection resistance (R co-air,conv) dominates the heat loss from cover tube to ambient rather than thermal-radiation resistance (R co-sky,rad). The measured final temperature increment of working water for the mini-CPC and ordinary evacuated tube can reach 63.4 K and 49.8 K, respectively. An experimental result also reveals that the thermal efficiency of the mini-CPC vacuum tube is increased by 24.3%–29.2% compared with that of vacuum tube without mini-CPC, considering various weather conditions. Consequently, the designed mini-CPC evacuated tube shows a preferable performance, which may provide a certain reference in technology for engineering applications. • A mini-CPC evacuated tube to utilize effectively solar energy was designed. • Construction and solution of heat transfer model for mini-CPC evacuated tube. • Theoretical solution fits in well with the experimental result. • The temperature increment of working water can reach 63.4 K for the mini-CPC. • The improved ratio of thermal efficiency is 24.3%–29.2%. [ABSTRACT FROM AUTHOR]

In this study, a steady state analytical investigation of conjugate heat transfer in a planar micro-combustor is presented by considering the detailed reaction mechanisms for a methane/air mixture with 10% and 20% hydrogen addition. The primary objective is studying the effects of hydrogen addition on the wall and gas temperature distribution in order to propose a practical solution to manage the significant heat transfer in micro-combustors. The reactive mixture is divided into the pre-flame, reaction, and post-flame zones. Then, the conservation equations are analytically solved in each zone using the matching conditions. Moreover, to present a general analysis, appropriate non-dimensional thermal parameters are recommended considering the thermal interaction between the reactive mixture, solid structure and ambient. As a result, appropriate correlations for the normalized wall temperature profile are presented for different situations that can be used as a prescribed wall temperature distribution in numerical simulations. Moreover, it is found that for the cases with solid-fluid thermal diffusion ratio greater than 50, the thermal properties can negate the effect of hydrogen addition on the wall temperature distribution. • Effect of hydrogen addition on conjugate heat transfer is analytically investigated. • Appropriate correlations for wall temperature profile are proposed under different conditions. • The outlet gas temperature becomes more sensitive to SFTDR by hydrogen addition. • Hydrogen addition is highly effective in changing the length of pre-flame and post-flame zones. • The maximum gas temperature is raised around 8% by adding 10% hydrogen. [ABSTRACT FROM AUTHOR]

A novel nano phase change material emulsion (NPCE) with low supercooling and high thermal conductivity was prepared by sonication method. N -octadecane was employed as phase change material, multi-walled carbon nanotubes (MWCNTs) were utilised as high thermal conductivity material, and octadecanol was utilised as nucleating agent. The characterization and thermal properties of the nanoemulsions prepared with various concentrations of MWCNTs and octadecanol were measured and analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analyser, differential scanning calorimeter (DSC) and thermal conductivity meter. The results indicated that the nanoemulsions prepared had great stability, low supercooling and enhanced thermal conductivity. The thermal conductivity was enhanced by 4.32% for 10 wt% nanoemulsion with addition of 1 wt% MWCNTs. The supercooling degree of 20 wt% nanoemulsion was decreased by 36.4% from 17.3 °C to 11.0 °C with addition of 1 wt% octadecanol. It can be concluded that the nanoemulsions prepared were able to be utilised as heat transfer and energy storage fluids, with great potential in thermal system applications. • The enhancement ratio of thermal conductivity was 4.32% for 10 wt% nanoemulsion. • The supercooling of 20 wt% nanoemulsion was decreased by 36.4% with addition of 1 wt% octadecanol. • Fabricated nanoemulsions presented good stability and thermo-physical properties. • Fabricated nanoemulsions have great potential application in the thermal systems. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (BN) hold great promise as emerging building blocks for thermal interface materials owing to their outstanding heat transfer performance. Herein, we report a carboxylated polystyrene-coated hydroxylated BN (BN–OH@PS-COOH) nanocomposite with highly thermal conductivity (TC) and extraordinary mechanical properties for thermal management. The exfoliated BN-OH nanosheets were obtained via molten alkali hydroxide pretreatment and sonication. Subsequently, PS-COOH nanospheres were grew on the surface of BN-OH nanosheets by in situ polymerization. Noncovalent interactions between PS-COOH and BN-OH are favor to reduce interfacial thermal resistance, which contributes to accelerate heat transport. As a result, the TC of the resultant BN-OH@PS-COOH nanocomposite with 12 wt% BN-OH addition is 1.131 W/mK, which is much higher than that of neat PS (0.186 W/mK) and BN/PS blend nanocomposite (0.312 W/mK). Moreover, the BN-OH@PS-COOH nanocomposite exhibits outstanding mechanical properties. Our study may stimulate novel perspectives on the design of high-performance polymer-based thermal interface materials. [ABSTRACT FROM AUTHOR]

• Less studied thermal properties of ILs are explored. • A series of parameters are essential for mitigating the degree of thermal hazard. • The kinetic of reactions which often difficult to evaluate is determined. • A kinetic parameter application with thermal safety was identified in this work. • Experimental specification data can be applied to actual process. Using batteries to convert chemical energy into electrical energy is one of the significant technologies that must be enhanced in the 21 st century. In the fuel battery development area, ionic liquids (ILs) are outstanding electrolytes for batteries. According to their thermophysical and phase equilibrium properties, ILs are widely used in different energy fields due to their diversity in the synthesis field. However, there are few detailed thermokinetic studies on ILs. To ensure the thermal safety of ILs in the process of creation, a commonly used IL, 1-butyl-3-methylimidazolium nitrate ([Bmim]NO 3), was chosen for exploration. In this study, thermal decomposition characteristics were obtained by differential scanning calorimetry. The obtained data were input into the thermokinetic equation to determine the basic thermal hazards of [Bmim]NO 3. In addition, based on thermal equilibrium theoretical models, the reaction kinetics and critical safety parameters were extrapolated for consideration. The influences of the sample mass and the overall heat transfer coefficient were simulated and discussed in 25.0 g and 50.0 g packages. The results showed that [Bmim]NO 3 had a shorter TMR ad and TCL (<1 day) when the temperature was greater than 200 °C. Moreover, SADT< 150 °C can be used for evaluating the cooling system efficiency of [Bmim]NO 3. [ABSTRACT FROM AUTHOR]

• Lightweight, thermostable and strong SiC aerogels are fabricated from biomass. • The SiC aerogels have highly interconnected porous structure decorated with in situ grown SiC nanowires. • The SiC aerogels exhibit superior EM wave absorption, thermal insulation properties and mechanical stability. • The effects of structure on the enhanced performance are thoroughly revealed. Lightweight and strong silicon carbide (SiC) aerogels with a three-dimensional architecture and in situ grown SiC nanowires are obtained from natural eggplants by direct graphitization and subsequent carbothermal reduction. Effective synergism is achieved by decorating the SiC frameworks with one-dimensional SiC nanowires, which impart the aerogels with excellent electromagnetic (EM) wave absorption, thermal insulation, and mechanical properties. Highly porous, interconnected SiC networks facilitate the multiple reflection–absorption effects of infiltrated EM waves and extend the routes of heat transmission in the samples. SiC nanowires, which consist of numerous stacking faults and heterojunctions, play key roles in dissipating EM energy, obstructing heat transfer, and reinforcing the SiC skeleton. Given their 97.6% porosity, the SiC aerogels show a minimum reflection of −43 dB and effective bandwidth of 4 GHz at 2 mm thickness. The in situ grown SiC nanowires substantially increase the compressive stress of the SiC aerogels to 2.12 MPa, which is nearly 50-fold than that of carbon aerogels derived from eggplants. Moreover, the SiC aerogels show a very low thermal conductivity of 0.035 W/m·K. These results indicate that the developed SiC aerogels are outstanding materials with potential applications in high-performance EM absorption and thermal insulation in the aviation and aerospace fields. [ABSTRACT FROM AUTHOR]

Series of NaBa 0.97 Ce 0.03 B 9 O 15 : x Tb3+, y Sm3+, z Dy3+ are synthesized by the traditional high temperature solid-state method. Ce3+ is used as a sensitizer to improve the spectral properties of Tb3+, Sm3+ and Dy3+ by the way of energy transfer which is proved by the fluorescence decay curves. And the mechanisms of energy transfer from Ce3+ to Tb3+, Sm3+ and Dy3+ are all determined as dipole-dipole interaction. The color of NBB:3%Ce3+, x Tb3+, 0.5%Sm3+ can shift from light violet thought white to yellow. And NBB:3%Ce3+, z Dy3+ can give out white light and move to green field. Moreover, the thermal stability makes NBB:3%Ce3+, 0.2%Dy3+ be a potential candidate for the self-referencing luminescent thermometry. Image 1 [ABSTRACT FROM AUTHOR]

The traditional bottom liquid-cooling thermal management system (TMS) has poor cooling performance and is prone to causing significant temperature difference in the lithium-ion battery (LIB) module. In order to solve the above problems, this study takes the Z-shaped micro heat pipe array (MHPA) as the core heat transfer element and establishes a top liquid-cooling (TLC) TMS based on Z-shaped MHPA. The thermal management performance of the TLC TMS based on Z-shaped MHPA is analyzed by comparing it with the traditional bottom liquid-cooling TMS. Results show that under the conditions of 40 °C ambient temperature and 25 °C cold water inlet temperature, the bottom liquid-cooling TMS can no longer meet the thermal management requirements of the module at a 2C charge–discharge rate. In comparison, the TLC TMS based on Z-shaped MHPA can ensure the module's maximum temperature below 55 °C, and the battery and module level's temperature difference can be controlled below 4 °C under 3C charge–discharge rate. The TLC TMS based on Z-shaped MHPA can not only effectively delay the battery's temperature rise under high charge–discharge rate, but also significantly reduce the temperature difference; its thermal management performance is significantly better than the bottom liquid-cooling TMS. • A top liquid-cooling TMS based on Z-shaped MHPA is presented. • This design provides excellent thermal management performance. • This design is safety and easy to combine with the battery swap mode. [ABSTRACT FROM AUTHOR]

An inverse heat transfer approach for predicting the moving freezing front and the temperature distribution inside tumors during cryosurgery is presented. By recording the time-varying temperature at the surface of the diseased tissues, the inverse method is able to estimate simultaneously the blood perfusion rate and the metabolic heat generation of the tumor. Once these thermal properties are determined, the temperature field and the moving freezing front are predicted with a direct method. The direct problem is solved with the one-dimension Pennes bioheat equation and the enthalpy method. The inverse model rests on the Levenberg-Marquardt Method (LMM) combined to the Broyden Method (BM). The following effects on the predictions of the inverse method are investigated: (i) the initialization of the unknown thermal properties; (ii) the thermal properties of the diseased tissues; (iii) the duration of cryosurgery; (iv) the temperature of the cryoprobe; (v) the noise level on the recorded temperatures; and (vi) the total number of recorded data. It is shown that the proposed inverse method remains accurate and stable for all cases investigated. Recommendations are made for the initialization of the parameters of the inverse method and for the total number of measurements. [Display omitted] • A promising alternative to MRI and ultrasound for controlling the motion of the freezing front during cryosurgery is proposed. • A non-isothermal phase change process of freezing tissues is developed. • The inverse approach is able to predict the blood perfusion rate and the metabolic heat generation during cryosurgery. • The effect of the most influential parameters on the inverse predictions is examined. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thermally conductive HDPE/BN/CNT composite was fabricated by an in-house Rotational Shear System. • The interlocking crystal structure improves thermomechanical properties. • Constructing the ternary synergistic network of aligned BN, shish-kebab and elongated CNT. • The thermal conductivity of RB20C5 reach as 2.37 W/mK with higher Heat transfer efficiency in hoop direction. Fabricating polymer composites with excellent thermomechanical properties remains a challenge due to the tradeoff between high filler loading and loss of strength. Conventional composites made of randomly oriented lamellae and aggregated fillers fail to construct thermally conductive pathways for filler-filler or filler-crystal contacts. To address this issue, a synergistically ternary network composed of aligned BN and elongated CNT in a shish-kebab structure has been prepared by an in-house Rotation Shear System (RSS). The composite with 20 wt% BN and 5 wt% CNT achieved a high thermal conductivity of 2.37 W/(mK) under shear modification. The tensile strength and Vicat softening temperature of the composite are 2.29 times higher and 21.9 °C greater than those of unsheared samples. Such superior thermal and mechanical properties are mainly attributed to the interlocking shish-kebab structure, which serves as a support skeleton in composites, where aligned BN and CNT construct a heat-resistant barrier. This work provides an effective strategy to fabricate high thermally conductive composites with excellent mechanical properties, providing new insights into reducing material replacement frequency under extreme operating conditions. [ABSTRACT FROM AUTHOR]

• The sensitivity of thermal response tests using resistively heated methods under various setups is demonstrated. • The effect of test setups on estimation results is examined using numerically generated data. • A distance-based generalized sensitivity analysis method is employed. • The in-situ design strategy of the novel tests is illustrated combining sensitivity analysis and field tests. Thermal response tests employing resistively heated methods (TRT-RH) have shown advanced performance in evaluating ground properties, while the effect of various TRT-RH setups is still vague in practice. This study examines the effect of different TRT-RH setups based on numerically generated data and field data. As a result, the various setups alter the heat transfer and change the test time required to meet the ideal linear heat source (ILHS) assumption. Time thresholds that indicate TRT-RH are positively related to eccentric distance, negatively related to borehole radius, and positively related to grout thermal conductivity difference. The distance-based general sensitivity analysis result shows that the radius of the borehole or trench, which separates the heat source and the ground, has intensive sensitivity to the test effectivity. This study presents the standard setup strategy for TRT-RH to measure the thermal and hydraulic properties based on the ILHS assumption. [ABSTRACT FROM AUTHOR]

Silver (Ag) paste sintering is used as a die-bonding technology for the next generation of power electronic modules as Ag offers a high melting temperature as well as excellent thermal and electrical conductivities. Ag paste sintering is performed using specific conditions depending on the type of paste and the users' specifications (temperature, time, pressure), ending up in a porous joint. As a result, the properties of those joints are heavily influenced by their densities (i.e. porosity). Despite the numerous studies reported in the literature, the relationship between the density of the joint and its thermal conductivity remains an issue since access to the density of an embedded thin joint is very challenging. Furthermore, little is known on the evolution of the thermal conductivity in operating conditions. In this study, these issues were investigated by developing self-standing specimens with microstructures representative of those of real joints. In order to study a wide range of porosity, sintering was performed using a single time/temperature under various pressures. The thermal conductivity was measured using 3D flash method, consisting in applying a short non-uniform laser excitation on the surface of the sample, leading to three-dimensional heat transfer. The relationship between porosity and thermal conductivity is established for the as-sintered state and after aging up to 500 h at temperatures ranging from 150 °C to 350 °C and is compared to existing models. The evolution of the thermal properties during thermal aging is discussed considering both the elaboration conditions and the microstructure evolution. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights • Presents theoretical solution for a phase change heat transfer problem. • Utilizes perturbation method and an iterative approach. • Results may be helpful in analyzing phase change heat transfer in energy storage. • Results expand our theoretical understanding of phase change heat transfer. Abstract Heat transfer problems involving phase change occur in a wide variety of engineering applications. Except a few simple cases, most phase change problems do not have an exact solution, and a number of approximate analytical methods have been developed. This paper presents a theoretical solution for a one-dimensional phase change problem that includes a pre-melted or pre-solidified length between the region of interest and a time-dependent temperature boundary condition. Such a scenario can occur in multiple engineering applications when the heating or cooling process is intermittent in time. The theoretical approach involves iteratively solving the coupled problem involving thermal conduction and phase change, utilizing a perturbation-based method for the phase change problem with a time-dependent boundary condition. The resulting theoretical solution compares well with numerical simulations. Results are used for analyzing the effect of geometry, thermal properties and other parameters on the nature of heat transfer and phase change in this problem of much technological importance. These insights may be helpful in analyzing and optimizing heat transfer in several applications such as phase change based cooling of Li-ion cells during intermittent operation. [ABSTRACT FROM AUTHOR]

Abstract How to effectively enhance the flame retardancy of polyamide 46/polyphenylene oxide (PA46/PPO) alloy is one of the key issues needed to be addressed. In this work, organic-modified zirconium phosphate (OZrP) nanosheet was incorporated with PU-coated carbon fiber (CF) to flame-retard PA46/PPO alloy. The combination of OZrP and CF showed an outstanding combination effect in improving the flame retardancy and thermal stability of PA46/PPO. With the incorporation of 2 wt% OZrP and 20 wt% CF, the peak heat release rate and peak smoke production rate of PA46/PPO were reduced by 65.6% and 86.2%, respectively. Besides, the T i (temperature at 5% weight loss) and the residue of PA46/PPO/OZrP/CF were increased by 13.2 °C and 20.9 wt%, respectively, compared with PA46/PPO. The flame-retardant mechanism was further studied and revealed: when being burned, CF acted as the skeleton to improve the strength of char; simultaneously, OZrP catalyzed the carbonization of the polymer chains on the CF surface to form a strong and compact protective char layer, which blocked the transmission of heat and combustible gases, thus effectively improved the flame retardancy of the composite. Highlights • An efficient strategy simultaneously improving the flame retardancy and mechanical properties of PA46/PPO alloy was proposed. • The synergistic mechanism of OZrP nanosheet and PU-coated carbon fiber (CF) on the flame retardancy of PA46/PPO was revealed. • OZrP catalyzed the carbonization of the polymer chains on the CF surface to form a strong and compact protective char layer. [ABSTRACT FROM AUTHOR]

Abstract In the present work, an experimental investigation was conducted to quantify the heat transfer coefficient, thermal resistance and the thermal performance of a thermosyphon heat pipe charged with zirconia-acetone nanofluid. The thermosyphon was designed to operate at high heat fluxes such as 200 kW/m2 (∼200 sun) similar or larger than the evacuated solar tube heat pipes. The zirconia-acetone nanofluid was prepared and stabilized by adding a surfactant, homogenizing with sonication and setting the pH of the nanofluid with a buffer solution. The thermosyphon was fabricated with an oxygen-free copper with the internal and outer diameters of 10.7 mm and 12 mm, respectively and the axial length of 280 mm. The thermal performance of the heat pipe was assessed for various heat fluxes (1 kW/m2-200 kW/m2), filling ratio (20%–75%), tilt angle (5°–70°) and the mass fraction of the nanofluid (0.025%–0.1%). Results showed that the presence of the nanofluid decreases the total thermal resistance of the heat pipe reaching the minimum value at the largest heat flux applied to the evaporator. Also, the heat transfer coefficient of the evaporator was increased. Likewise, the zirconia-acetone nanofluid enhanced the boiling heat transfer mechanism and the geyser boiling, which resulted in the enhancement in the thermal performance of the heat pipe due to the increase in the heat transfer coefficient of the heat pipe by 36.3% at wt. % = 0.1 in comparison with the pure acetone. The optimum tilt angle and filling ratio values were 65° and 60%, respectively, in which the highest heat transfer coefficient was achieved. A correlation was also developed using a dimensionless analysis to predict the Kutateladze number as an index for the thermal performance of the heat pipe. Highlights • Zirconia-acetone nanofluid was assessed in a thermosyphon. • Nucleate boiling and geyser boiling were the dominant heat transfer mechanisms. • A tradeoff between filling ratio, tilt angle and performance was identified. • A new correlation was developed for estimating Kutateladze number. • The boiling HTC was in a good agreement with Stephan-Abdelsalam equation. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the quasi-stationary Wilson-Rosenthal solution for isothermal contours in a semi-infinite medium due to a moving heat source. There is a single dimensionless governing parameter which could correspond, for example, to a conduction-limited heat flow in a point-source driven, fusion process, such as that witnessed in modern metal additive processes. Variables involved in this heat transfer problem are the power and speed of the heat source as well as the thermal properties of the domain being heated. On one hand, the forwardmost location for a generic isothermal contour profile, for example the melting isotherm, is calculated by (i) a fixed-point numerical method, (ii) second-, third- and fourth-order Taylor series expansions, and (iii) a direct calculation of the location using the Laplace-Carson transform and an approximate anti-transform. On the other hand, the rearmost point of the isothermal contour is found to be invariant with the source speed parameter while the horizontal coordinate corresponding to the maximum depth of the contour is predicted by the semi-sum of the forwardmost and rearmost coordinates. Experimental results suggest that this analytical solution provides accurate physical understanding of the process, for example, when the melt pool contour geometry of a conduction-limited fusion process requires to be controlled during an specific heat driven process. In this latter situation, a single dimensionless governing parameter can be of benefit. [ABSTRACT FROM AUTHOR]

• A PVT collector with a roll-bond absorber is designed for rural home application. • Thermo-laminating is a novel and convenient method for PV-absorber connection. • The validated PVT model can simulate the roll-bond PVT performance accurately. • The model is available for predicting the dynamic performance of PVT systems. This paper mainly investigated the performance of a low-cost roll-bond water-type photovoltaic thermal (PVT) collector from both experimental and modelling approaches under the climatic conditions of Sichuan Basin of China. The design and manufacturing process of the PVT prototype adopted the available commercial PV panels for convenience and for reducing the manufacturing cost. The experiment measured all the main properties of the developed PVT module. The excellent heat transfer performance of its roll-bond absorber plate was also validated by outdoor steady-state tests. Then, the steady-state numerical models were used to simulate the performance of the PVT prototype in TRNSYS. By comparing the simulation and experimental results, two robust models were selected which have their own advantages in charactering the thermal and electrical properties of the PVT collector. Through validating the numerical models with experimental data, the deviation between the simulated and the measured values was further reduced. In addition, a complete photovoltaic thermal–domestic hot water (PVT-DHW) system with such PVT collectors was developed in TRNSYS, by which the annual system output and efficiency were predicted and analysed. [ABSTRACT FROM AUTHOR]

Abstract The aim of the current paper is modeling the thermal performance factor of water under influence of functionalized multi-walled carbon nanotubes. For this purpose, artificial neural networks (ANNs) have been employed. The thermal performance factor of the nanofluid is related to the drop in pressure and heat transfer. Therefore, usually the data associated with it does not follow a specific trend. In such cases, the neural network can be used well. Here, an optimal neural network was designed with 65 neurons, the inputs of which were Reynolds number and volume fractions. Moreover, 78 data were used for modeling, which included 62 data for training and 16 data for testing the model. With the aim of evaluation of the precision of the modeling by ANN, the experimental results were compared with neural network outputs in all cases. The results revealed that optimal ANN model has adequate accurateness to predict the complex trend of thermal performance factor. Highlights • Modeling thermal performance factor of water under influence of functionalized MWCNTs. • Data associated with thermal performance factor does not follow a specific trend. • The experimental results were compared with neural network outputs in all cases. • Optimal ANN has adequate accurateness to predict the trend of thermal performance factor. • The maximum margin of deviation is about 1.8%. [ABSTRACT FROM AUTHOR]

Abstract This study proposes a novel ultra-thin aluminum flat heat pipe with thickness of 1.5 mm for the first time in order to satisfy the ever increasing requirements for cost-effective, physically compact and highly efficient thermal management solutions. The extruded aluminum tube contains multiple separate micro cavities that work as independent micro heat pipes and a two-level compressing process is applied to flatten the tube to the ideal thickness. Sintered aluminum fibers and aluminum fiber meshes with surface treatment are inserted into each cavity of the ultra-thin heat pipe as the extra wicks for comparison. The thermal response characteristics of the fabricated aluminum heat pipes, including the temperature uniformity, thermal resistance, and effects of wick structure and inclination angles, are fully investigated. Under large inclination angle (90°), the smooth heat pipe without any extra wick performs lower temperature difference, lower thermal resistance, and higher heat transport capacity compared to that with aluminum fiber wick whereas the heat pipes with wicks present superiority under smaller inclination angles (60° and 30°) due to the liquid backflow enhancement. Besides, comparative study also shows that wick structure optimization holds the potential to improve the thermal performance of this ultra-thin two-phase device. Highlights • Ultra-thin aluminum heat pipe with only 1.5 mm thickness is developed. • It contains multiple separate micro cavities working as independent heat pipes. • The thermal response characteristics are fully investigated. • Wick structure optimization holds potential to improve the thermal performance. [ABSTRACT FROM AUTHOR]

Highlights • Nanoscale hypercrosslinked polyurethanes were studied at the first time. • Effect of crosslinkers on heat and mass transfer properties was discussed. • Thermal properties of hypercrosslinked polyurethanes with water were considered. Abstract Four different trihydroxy crosslinkers were respectively used to construct molecular models of hypercrosslinked polyurethanes as shell materials of phase change nanocapsules for thermal energy storage so as to investigate the heat and mass transfer properties. The impacts of microscopic characteristics of crosslinkers on glass transition temperature, thermal expansion and diffusion, interaction energy, thermal conductivity, mechanical properties under tensile and shear stress as well as some of thermal properties after packing water molecules into the hypercrosslinked polyurethanes were simulated and analyzed based on equilibrium or non-equilibrium molecular dynamics methods. The results showed that the detailed molecular structure of crosslinkers, namely the positions of hydroxyl groups, the geometric features of skeleton and even involved element type, will determine the structural characteristics of the hypercrosslinked polyurethanes, such as the formed micro cavities, the dangling functional groups as well as stiffness of short chain, and then affect the heat and mass transfer as well as mechanical properties. Furthermore, the hypercrosslinked polyurethanes possess relatively high glass transition temperature, better heat transfer performance and excellent mechanical properties compared to the polyurethanes with low crosslink density. [ABSTRACT FROM AUTHOR]

Abstract An improved integral equation method based on radiation distribution factors (RDFIEM) is developed to solve the radiative intensity with high directional resolution in semitransparent media with graded refractive index (GRI). The radiation distribution factors (RDFs) are solved by using the reverse Monte Carlo curved ray tracing technique (RMCCRT). Based on the RDFs, the source terms along the curved ray path decided by the Fermat principle are predicted accurately. Then, the integral equation method (IEM) is employed to solve the radiative intensity through integral along the curved ray path. One-dimensional and two-dimensional test cases are done, and all the results show that the RDFIEM is not only flexible in treating directional radiation problems but also very accurate and efficient. Highlights • RDFIEM is developed to solve radiative intensity with high directional resolution. • RDFIEM simplifies the integral process while retains the high accuracy of IEM. • Effects of radiative properties on radiative intensity are investigated. [ABSTRACT FROM AUTHOR]

Highlights • UNI 13786 describe a mathematical method to dynamic heat transfer. • Sinusoidal steady-state analysis is the "dynamic" model used. • Direct method: from mathematical model to physical propriety. • Proposal for inverse method: from physical propriety to mathematical model. • Test by the wall in climatic chamber and results. Abstract This study investigates energy efficiency in buildings. The accurate evaluation of energy consumption in existing buildings is a difficult task, particularly due to the Mediterranean climate, which is in the temperate zone. Among the various analytical models, the most effective measurement of the energy consumption of buildings is the dynamic type. In evaluating the energy consumption of buildings, the greatest contribution is provided by opaque components and particularly by the external walls of that building. In the model, which is reported in the EN ISO 13786, the thermal properties (the specific heat (J/kgK) and thermal conductivity (W/mK) of the layers of the wall were tested, and the technical standard reported that the physical properties (from which they derive the phase shift and decrement factor) transferred through the wall when a sinusoidal wave temperature variation was applied in a periodic steady state. We propose an inverse approach to measure the sinusoidal periodic steady state (temperature and thermal flux) on the two faces of the wall. With this approach, it is possible to obtain the thermal properties of the wall through an inverse analytical model. The model was applied in a real experiment on a full-size wall in a climatic chamber to verify the dynamic thermal and physical properties of the layers. [ABSTRACT FROM AUTHOR]