Search

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]

• 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]

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]

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]

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]

[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]

[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]

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]

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]

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]

Phase change material (PCM) microcapsules are gaining increasing attention because it can overcome the shortage of PCM macrocapsules and increase the heat transfer area, while the pore-scale thermal performance of the PCM microcapsule packed-bed systems, as well as the influence of packing methods and microcapsule sizes on thermal storage, is still poorly understood. This paper introduces various spherical PCM microcapsule pack models, including single-layered, diameter-changed two-layered, and three-layered packing models, to investigate the charging process at pore scale. The indices of thermal storage properties such as charging time, temperature distribution, phase change fraction, pressure drop and thermocline degradation are studied with the finite element method. In the single-layered thermal storage system, the results show that the charging process can be improved by reducing the capsule size and using cross-packing methods. When the capsule size is reduced from 2 to 0.5 mm with cross packing, the charging time can be shortened by 72.97%, but remarkable pressure drop is created. The results indicate that the overall thermal storage performance of multi-layered packed-bed systems is better than that of single-layered packed-bed systems. The charging time of the diameter-changed two-layered and three-layered thermal storage systems can be reduced up to 16.21% and 24.32%, respectively, compared to the single-layered in-line pack with a d = 2 mm. The filling sequence plays a key role in multi-layered thermal systems. A packed-bed system with a diameter decreasing along the heat transfer fluid (HTF) flow direction has a better capacity to reduce thermocline degradation than other packed-bed systems. • The effects of microcapsule sizes and packing methods on thermal behaviour were studied. • Small capsule sizes are favorable for heat transfer, creating high pressure drop. • The method of cross packing has better thermal performances than in-line packing. • Multi-layered thermal storage systems were designed for structural optimization. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel flexible thermal management phase change films (PCPU/mCNTs) was designed. • PCPU/mCNTs exhibit enhanced thermal conductivity and low electrical conductivity. • PCPU/mCNTs films can prevent electronics from being overheated. • PCPU/mCNTs films can be remodeled and recycled. With the continuous miniaturization and integration of electronic devices, electronics needs more advanced thermal management technology and materials to solve thermal failure problem. In this aspect, phase change materials (PCMs) exhibit great prospect in electronic thermal management due to its excellent temperature control properties. However, how to give PCMs high heat transfer performance and flexibility while maintaining low electrical conductivity is still a great challenge. Herein, we designed the alkylated modified carbon nanotubes (mCNTs) into the phase change polyurethane (PCPU) system. Based on the high junction resistance and thermal conductivity properties of mCNTs, PCPU/mCNTs exhibit enhanced thermal conductivities and high electrical resistance. Meanwhile, the phase change segment in polyurethane was used as soft segment, which endows it excellent flexibility, thus achieving effective contact with the applied matrix and conducive to heat transfer. The PCPU/mCNTs films are holding great potential for electronic thermal management. [ABSTRACT FROM AUTHOR]

• The pores act as a "thermal barrier wall" on the heat transfer path in the MPL. • The fractal characteristics of the MPL inhibit heat transfer. • The structural parameters of the MPL is correlated with the thermal properties. Heat transfer in the fuel cells is generally limited by the effective thermal conductivity of the microporous layer (MPL). Due to the complexity of the microstructure and the difficulty of the test conditions, studies on the key parameters that affect the thermal conductivity of MPL is lacking. In this paper, we develop an analytical fractal model for the effective thermal conductivity of the MPL based on a lumped parametric model of the cube and a fractal particle chain model, and provide the contact ratio of the agglomerates using a 3D FIB-SEM reconstruction. The results indicate that the main factors affecting the thermal conductivity of MPL include the structural parameters, fractal dimension, and the thermal conductivity of the carbon particles and pores. The fractal characteristics of the MPL inhibit heat transfer rate and the pores act as a "thermal barrier wall" on the heat transfer path in the MPL. When the volume fraction of the MPL is 40 percent, the contact area ratio and fractal factor of the agglomerates are 0.351 and 0.84, respectively. In addition, this research will help to develop novel MPL structures with high thermal conductivity and improve simulation results for fuel cell temperatures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low concentrations of Au nanoplates involved, up to 0.048 wt%. • Isobaric specific heat was enhanced up to 12.0 % in Au nanofluids. • Thermal conductivity was enhanced up to 24.9 % in Au nanofluids. • No measurable changes in density or dynamic viscosity. • The efficiency of parabolic-trough collectors can increase up to 10.4 % (on an absolute basis) using Au nanofluids. We report about the remarkable changes in the thermophysical properties of the heat transfer fluid used in concentrating solar power plants with parabolic-trough collectors (Dowtherm A, a mixture of diphenyl oxide and biphenyl) by addition of Au nanoplates in mass fractions around 10−2 wt%. The resulting nanofluids are stable for weeks, and their enhanced physical properties make them good candidates for the application. Particularly, with 4.8·10−2 wt% of Au nanoplates, specific heat increases by 12.0 ± 1.2 % at 523 K and thermal conductivity increases by 24.9 ± 6.1 % at 373 K, with no measurable changes in density or dynamic viscosity. This set of physical properties allows to make a realistic estimation of the performance of a prototypical concentrating solar power plant using these nanofluids for solar-to-thermal energy conversion. We determine, using computational cost-free numerical models available in literature, that the performance of a concentrating solar power plant could increase up to 35.1 %, compared to the predicted 24.7 % with the conventional heat transfer fluid, with neither rheological penalties nor economically prohibitive structural changes. The findings here reported may contribute to encourage the application of heat transfer nanofluids in order to improve the efficiency of concentrating solar power plants, and to consolidate a working scheme that positively promotes the transition from laboratory scale to industrial scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • A literature review on the heat and flow properties of lattice structures is performed, and design parameters are identified. • Detailed geometric modeling and clear the knowledge gaps in the flow and heat properties of various lattices. • The results are compared with the findings obtained from existing literature and documented in detailed charts. Lattice structures are known for their capability to be tailored for achieving specific properties such as high porosity and strength, impact energy absorption and lightweight. While the mechanical properties of the strut-based and surface-based lattice structures have already been investigated in the literature, a systematic investigation of their flow and thermal properties has yet to be established. This work investigates the friction factor and convective heat transfer coefficient across strut- and surface-based lattice structures. The modeled structures are simulated in the convective heat transfer environment to gather the heat transfer coefficient and the friction factor outputs. The simulation results are documented in this work and used to generate a flow and thermal property chart to support the design process by providing a guideline for selecting lattice topologies. [ABSTRACT FROM AUTHOR]

• Seepage can promote the temperature field around GHEs to reach the steady faster. • Seepage effects on temperature field around GHEs increases with seepage velocity. • Seepage will reduce the accumulation of heat around the heat exchangers. • Ground stratification effects on temperature field around GHEs depends on the thermal property of adjacent stratum. Heat transfer between the ground heat exchanger and surrounding stratum under the action of groundwater seepage is a potential problem in karst areas, few systematic studies on it have been carried out yet. A model test apparatus was built to experimentally investigate the effects of karst groundwater seepage and ground stratification on the heat transfer characteristics of ground heat exchangers. The heat and seepage transfer coupling model for ground heat exchangers was established, and verified with the measured data from the model test. Base on the model, the influence of seepage velocity and direction on the heat transfer of ground heat exchangers was analyzed and discussed. Test results show that the seepage can promote the temperature field around the heat exchanger to reach the steady state faster, and the influence of seepage on the soil temperature field around the heat exchanger increases with increasing the seepage velocity. The seepage will carry the heat released by the heat exchanger from the upstream side to the downstream, which effectively reduce the accumulation of heat around the heat exchanger. Soil boundary exists the sudden change of temperature when there are great differences in thermal properties between adjacent soil layers, which can be attributed to the influence of ground stratification. The numerical model proposed in this study can well predict the distribution of soil temperature field around heat exchangers in the model test. Simulation results show that the temperature of soil around the heat exchanger will change along the seepage direction. [ABSTRACT FROM AUTHOR]

Phenolic-based composites are the most promising ablative thermal protection materials for space applications, but optimizing their thermal insulation performance while maintaining high strength remains extremely challenging. Herein, phenolic-based composites with co-optimized thermal insulation and mechanical properties are prepared via 2.5D quartz fabric reinforcing nanoporous phenolic. The pore size of phenolic matrix is efficiently refined to ∼35 nm by adjusting resin concentration, enabling composites to exhibit high density but low thermal conductivity by enhancing Knudsen diffusion. Finite element analysis shows that low braiding angle of 2.5D fabric can further weakening heat transfer of composites due to anisotropic thermal conductivity of fiber yarns. In-situ X-ray micro-CT results indicate that 2.5D fabrics can reinforce composites through interwoven yarns, and straighter weft yarns result in higher strength along weft direction than that along warp direction. Compared with dense quartz/phenolic composite, the resulting composites exhibit 16.5% lower density (1.32 g/cm3), 58.8% lower thermal conductivity (0.21 W/(m·K), ≥372.7% higher tensile strength (≥182.0 ± 9.6 MPa) and comparable ablation resistance. The present results will further advance the application of phenolic-based composites in more extreme re-entry environments. [Display omitted] [ABSTRACT FROM AUTHOR]

With the rapid increase of the thermal power of electronic devices, phase change material(PCM) have shown great application prospects in the field of electronic thermal management. However, due to the irregular surface of the electronic device, PCM can only act on the back of the component or the outside of the package, which leads to the occurrence of heat transfer hysteresis. In order to reduce the heat transfer distance between the heat source and PCM, a new type of ER/SAT/DSP composite functional material with thermal control function was prepared in this paper to solve the key technical problem of fluid seamless packaging thermal control. The composite material is encapsulated in a fluid state and will no longer melt after solidification. Through thermophysical experiments and morphological characterization, the results show that when the mass fraction of PCM is 35%, the composite material has the best physical properties and application performance. And after 200 thermal cycles, the leakage rate is only 3.7%. Through the PTC thermal control experiment, the results show that the maximum temperature at different positions of the device for pouring the new composite was reduced by 7.4 °C and 8.1 °C, respectively, and the operation time corresponding to different temperatures was increased by 5.76 times, 5.80 times and 6.98 times, respectively. Therefore, the composite material shows a good thermal control ability for electronic components of any surface shape. [ABSTRACT FROM AUTHOR]

• Presents an analytical solution for phase change in spherical encapsulated PCM. • Solution accounts for encapsulant thickness, properties and thermal contact resistance. • Results agree with several past papers for special cases. • Understanding of the physics of this problem is developed. • Results help understand the nature of thermal energy storage in encapsulated PCM. Encapsulation of a phase change material (PCM) is a commonly used technique for providing mechanical and chemical stability, and enabling the manufacturing of PCM composites. However, thermal impedance of the encapsulating layer may adversely affect phase change heat transfer in the PCM. Experimental measurement of heat transfer and phase change in an encapsulated PCM is difficult, particularly for the case of micro/nano-encapsulation. As a result, development of robust theoretical phase change heat transfer models in presence of encapsulation is critical. This paper presents theoretical analysis of the problem of phase change heat transfer in a spherical PCM with an encapsulant layer. Temperature distribution in the newly formed phase and the encapsulant layer is determined by solving a spherical two-layer thermal conduction problem in non-dimensional form. The rate of phase change propagation is then determined from the temperature distribution. The effect of thermal contact resistance at the PCM-encapsulant interface is accounted for. Results are shown to be consistent with past work for the special case of no encapsulation. Results are also shown to agree well with numerical simulations. The use of only a few eigenvalues is shown to result in good accuracy. The effect of encapsulant thickness, thermal properties and PCM-encapsulant thermal contact resistance as well as external boundary condition on phase change propagation is analyzed. The non-dimensional model is used to address practical problems in phase change energy storage with typical materials and conditions. This work contributes an important theoretical analysis tool for a problem of much practical importance. Results from this work may help optimize and improve the performance of encapsulated PCMs for energy storage and thermal management. [ABSTRACT FROM AUTHOR]

• New 2-D heat transfer model for coaxial BHE was built to estimate layered λ s. • Novel estimation of layered λ s was presented by using DTRT data and GA. • Effect of layer conditions on estimation was almost eliminated by the method. • 2 h DTRT data was efficient to estimate the layered λ s by the method. Estimation of ground thermal conductivity plays an important role in design of borehole heat exchanger (BHE) for ground source heat pump (GSHP) systems, and the ground is usually heterogeneous with layered thermal properties. Therefore, this study presented a novel estimation method for layered ground thermal conductivity by using distributed thermal response test (DTRT) and genetic algorithm. Firstly, a comprehensive new 2-D heat transfer model for coaxial BHE was built to simulate borehole fluid temperature profiles, it revealed that the distribution of ground thermal conductivity showed a significant influence on outlet temperature and temperature profiles. Then, based on the built model, the vertical distribution of ground thermal conductivity was estimated through DTRT data by using the genetic algorithm. It was found that the DTRT data at 2 h was effective to estimate the layered ground thermal conductivity by using the new 2-D heat transfer model. Furthermore, the estimated distribution of ground thermal conductivity was almost independent of numbers or thickness of sub-layer, and the largest difference in distributions of ground thermal conductivity among different layer thickness was less than 0.3 W/(m·K). Also, the estimation convergence showed independence with layer thickness, converged results could be obtained after 10 iterations for different layer conditions. [ABSTRACT FROM AUTHOR]

• A fabrication method for AP/nanocatalysts core-shell composites (CSC) was proposed. • Nanodispersion technology is employed to avoid aggregation of nanocatalysts in CSC. • The AP/nanocatalysts CSC possesses enhanced thermal decomposition property. To address the aggregation problem of nanocatalysts in ammonium perchlorate (AP), AP/Fe 3 O 4 core-shell composites (CSC) were synthesized by nanodispersion-assisted antisolvent recrystallization induced self-assembly method. DFT and FTIR test results reveal that covalent bonds between citrate and Fe 3 O 4 along with hydrogen bonds between citrate and AP drive the formation of AP/Fe 3 O 4 CSC. With coating 5.4 wt% Fe 3 O 4 , the high-temperature decomposition peak temperature of AP is decreased by 91.3 °C, the heat release is increased by 125% and the apparent activation energy is lowered by 47.9%. AP/Fe 3 O 4 CSC exhibit excellent thermal decomposition performance because the highly dispersed nanocatalysts on AP surface provide more catalytic sites and accelerate the reaction heat transferring from burning surface to condensed AP. Guided by this strategy, AP/Co 3 O 4 and AP/Fe 2 O 3 CSC were also prepared with enhanced thermal decomposition performance, which indicates this strategy has good applicability to improve the catalytic performance of nano metal oxides for AP decomposition. [ABSTRACT FROM AUTHOR]

Optimizing and increasing the efficiency of heat transfer systems was one of the main challenges for engineers and designers in recent years. Therefore, the use of nanoparticles in base fluids is known as a passive method to improve heat transfer and shrink heating and cooling systems. In this research, the heat transfer of copper nanoparticles with ammonia refrigerant in a nanochannel was investigated by molecular dynamics simulation. The results show that, with increasing the electric field frequency from 0.1 1/ps to 0.5 1/ps, the phase change time increases from 2 ns to 3 ns and the thermal conductivity decreases from 0.76 W/m.K to 0.72 W/m.K. Also, the effect of the different cavities (hermetic, spherical, and cube shape) in the nanochannel on the atomic and thermal behavior of the simulated atomic samples is investigated. The results show that the maximum thermal conductivity of the sample with a cubic cavity is 0.80 W/m.K. The particle phase change value and the phase change time of samples with hermitic, spherical, and cube atomic cavities are obtained 65, 66, and 68%, and 2.88, 2.87, and 2.85 ns, respectively. [ABSTRACT FROM AUTHOR]

• Prediction of the effective thermal conductivity of the composite material. • Establishing representative numerical simulation models at multiple scales. • Heat transfer under the condition of conduction & radiation. • Effects of the porosity and fiber volume fraction on the effective thermal conductivity of the composite materials. Composite materials are widely used in the fields of aviation and space, where their thermal properties are of importance since they are often challenged by variations of environmental temperatures. However, thermal properties of composite materials under conditions of conduction & radiation (a key mode of heat transfer in space) remain elusive. In order to address this issue, in this study, numerical simulations of the glass/polyimide composite materials were conducted to determine its effective thermal conductivity under the conduction condition with and without radiation. More specifically, unit cell models of polyimide matrix, glass-fiber yarns, and the composite materials were constructed sequentially to study the effects of the porosity and the fiber volume fraction on the effective thermal conductivities of the composite materials. Simulation results revealed that 1) an increase in porosity can reduce the effective thermal conductivity of the polyimide matrix with the maximal decreasing ratio of 39.5%; 2) an increase in fiber volume fraction can increase the transverse effective thermal conductivity of the glass-fiber yarns with the maximal increasing ratio of 49.0%; 3) differences of 26.0% and 27.6% of the in-plane and out-of-plane effective thermal conductivities of the composite materials were located under the conduction condition with and without radiation. This study provided a simulation approach to investigate thermal properties of composite materials, paving ways for their applications in the fields of aviation and space. [Display omitted] [ABSTRACT FROM AUTHOR]

• The role of the particle–fluid interface on nanofluid thermal conductivity. • The heat transfer at the interface mainly depends on surface-solvent compatibility. • The thermophysical properties of materials are not always the deciding factor. • Conductance at the interface decides the thermal conductivity in nanofluids. Thermal properties of nanofluids are very well investigated by the global research community for their various applications. The dispersion and stability of the nanoparticles in the base fluid are the essential requirements for the efficient utilization of nanofluids in many applications. The interfacial layer plays a crucial role in the dispersion, stability, and heat transfer properties of the nanofluid. The heat transfer property of the nanofluids is mainly influenced by the heat transfer properties at the particle–fluid interface. The thickness and thermal conductivity of the interfacial layer are the crucial factors that decide the heat transfer at the interface, and the difficulties in the determination of these factors limits the progress of the research. In this review article, the experimental studies on the thickness and thermal conductivity of the interfacial layer are reviewed briefly. The effect of interfacial the layer on the nanoscale mechanisms and thermophysical properties of nanofluids are reviewed. The effect of various tunable parameters on the heat transfer properties of the interfacial layer is also reviewed. This review will be beneficial for fine-tuning nanofluid's thermal properties and their commercial applications. [ABSTRACT FROM AUTHOR]

A critical need to accurately model thermal behaviors of materials that exhibit strong elastocaloric effects, including predicting the effects themselves at varying stresses and temperatures, has been addressed using a simple and versatile physics-based approach. The key factor leading to the high precision is approximating the underlying elastic phase transition as a smooth modification of lattice entropy between coexisting phases. Once the phase transformation entropy is modeled to match experimentally measured strain as a function of temperature and applied stress, estimating the heat capacity, entropy, and isothermal entropy and adiabatic temperature changes in temperature-stress coordinates becomes straightforward. This approach provides insight into how thermal properties of elastocaloric materials vary through the transition based on strain measurements that are simple to perform and interpret. In addition to aiding in the rapid evaluation of new and existing elastocaloric materials, this advance is expected to prove invaluable for accurate heat transfer modeling aimed at designing efficient regenerative elastocaloric cooling devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• Highly porous Cu foams were used to improve the thermal conductivity of paraffin PCM. • Cu foams were fabricated by a simple solution combustion synthesis method. • The SCS condition was optimized for the ratio of copper nitrate oxidizer and starch fuel. • Paraffin was embedded in Cu foams to form PCM composites with improved heat transfer properties. Regardless of the high latent heat of organic phase change materials (PCMs) for thermal energy storage, their intrinsically low thermal conductivity has constrained their wide application. In order to improve the thermal conductivity of paraffin PCM, porous copper foams as supporting frameworks are fabricated by a simple solution combustion synthesis (SCS), using copper nitrate as oxidizer and starch as fuel. The SCS is conducted under inert atmosphere and the efficient exothermic reaction occurs at around 100 °C. At an optimal oxidant-fuel condition of 4.43 g copper nitrate to 2 g starch, a good porous copper scaffold is prepared, which is further shaped and sintered to form robust copper foams. Paraffin is infiltrated into the copper foams to form PCM composites and the thermophysical properties are analyzed. Due to the continuous copper skeleton as heat transfer path, the thermal conductivity of the composite is improved to 3.29 W m−1 K−1 from 0.25 W m−1 K−1 of pure paraffin. The enhanced heat transfer properties of PCM composites as-supported by the facilely SCS-derived copper foams can reinforce the application in solar thermal harvesting and thermal management. [ABSTRACT FROM AUTHOR]