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In the realm of high-tech materials and energy applications, accurately measuring the transient heat flow at media boundaries and the internal thermal conductivity of materials in harsh heat exchange environments poses a significant challenge when using conventional direct measurement methods. Consequently, the study of photothermal parameter reconstruction in translucent media, which relies on indirect measurement techniques, has crucial practical value. Current research on reconstructing photothermal properties within participating media typically focuses on single-objective or time-invariant properties. There is a pressing need to develop effective methods for the simultaneous reconstruction of time-varying thermal flow fields and internal thermal conductivity at the boundaries of participating media. This paper introduces a computational model based on the numerical simulation theory of internal heat transfer systems in participating media, stochastic particle swarm optimization algorithms, and Kalman filter technology. The model aims to enable the simultaneous reconstruction of various thermal parameters within the target medium. Our results demonstrate that under varying levels of measurement noise, the inversion results for different target parameters exhibit slight oscillations around the true values, leading to a reduction in reconstruction accuracy. However, overall, the model demonstrates robustness and accuracy in ideal conditions, validating its effectiveness. [ABSTRACT FROM AUTHOR]

To understand the transient heat transfer characteristics of nanoporous aerogel insulating composites, solving the inverse heat transfer problem would be crucial for identifying the temperature-dependent thermal properties of composites. In this study, with constructed a forward model to numerically investigate the heat transfer in composites, a deep neural network (DNN) model and a particle swarm optimized deep neural network (PSO-DNN) model are conducted to rapidly estimate the effective temperature-dependent thermal conductivity of the desiccated and moist composites from the temperature response measurements. With the DNN model, the retrieved thermal conductivities for desiccated composites possess low deviation to experimental measurements (<3.2%) and constantly low errors (<5.2%) from 280 K to 1080 K. The precision of the DNN solver could be enhanced by adjusting the hyperparameters of the neural networks using PSO. The retrieved thermal conductivities possess low deviation from experiments (<2.5%) and low relative errors within 1.5%. Furthermore, the robustness of the PSO-DNN solver is discussed when commercial thermocouple measurement errors are considered, within retrieving the thermal properties of desiccated and moist aerogel composites. [ABSTRACT FROM AUTHOR]

The vacuum bagging is a common but critical step of various manufacturing process chains for Carbon/Glass Fibre reinforced polymers (C/GFRP). Whilst developing a new generation of vacuum bagging, significant efforts have been made to deeply understand the relevant physics fields, process variables involved and to provide predictive approaches to support dimensioning and scaling exercises prior to implementation into real production process. Main features of the new bagging system are, (1) the reduction of material diversity through merging of various properties within one single layer and, (2) the suppression of critical folding steps by using thermoforming for pre-shaping purposes. This paper will mainly focus on considerations of heat transfer during the pre-shaping of the film, directly on the CFRP part short before the curing step. For the better risk assessment of the short time exposition of an uncured composite part to the heat flow, a problem of transient coupled field analysis involving heat transfer via conduction, convection and radiation is formulated and solved by using Finite Element Analysis in COMSOL under consideration of realistic process conditions. Further a section dedicated to the comparison of the obtained results with measurements performed on a system including an IR-emitter, the bagging material, a ground plate and in some studies as well a CFRP sample is included. During the study the influence of time, power output of the emitter, distance between emitter and surface as well as irradiation angle has been assessed including a comparison of simulated results and performed measurements. [ABSTRACT FROM AUTHOR]

This paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)‐shell and tube heat exchanger (STHE) with the provision of unilateral ladder‐type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP‐STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG‐STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds‐averaged Navier–Stokes‐based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)‐STHE and the CMSP (HB)‐STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG‐STHE, respectively. Furthermore, the overall area‐weighted average pressure drop (ΔP) of CMSP (HB)‐STHE is smaller than that of SG‐STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)‐STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)‐STHE is a suitable replacement for the conventional SG‐STHEs. [ABSTRACT FROM AUTHOR]

Micro/nano electronic devices heat dissipation depends heavily on the thermal interface materials (TIMs). Despite notable progress, it is hard to efficaciously enhance the thermal properties of the hybrid TIMs with high-load additives due to an absence of effective heat transfer routes. Herein, the low content of three-dimensional (3D) graphene with interconnected networks is adopted as the additive to improve the thermal properties of epoxy composite TIMs. The thermal diffusivity and thermal conductivity of the as-prepared hybrids were dramatically improved by constructing thermal conduction networks after adding 3D graphene as fillers. The 3D graphene/epoxy hybrid's optimal thermal characteristics were observed at 1.5 wt% of 3D graphene content, corresponding to a maximum enhancement of 683%. Besides, heat transfer experiments were further performed to determine the superb heat dissipation potential of the 3D graphene/epoxy hybrids. Moreover, the 3D graphene/epoxy composite TIM was also applied to high-power LED to improve heat dissipation. It effectively reduced the maximum temperature from 79.8 °C to 74.3 °C. These results are beneficial for the better cooling performance of electronic devices and provide useful guidelines for advancing the next-generation TIMs. [ABSTRACT FROM AUTHOR]

The temperature distribution in a conductive-radiative rectangular profiled annular fin with internal heat generation is scrutinized in the present investigation. The nonlinear variation of thermal conductivity and heat transfer coefficient governed by the power law is considered. The analytical approximation for the non-dimensional temperature profile is obtained using the differential transform method (DTM)-Pade approximant. The nondimensionalization of the governing energy equation using dimensionless terms yields a nonlinear ordinary differential equation (ODE) with corresponding boundary conditions. The resulting ODE is analytically solved with the assistance of the DTM-Pade approximant procedure. Furthermore, the impact of thermal parameters on the temperature field and thermal stress is elaborated with graphs. The important results of the report divulge that temperature distribution greatly enhances with an augmentation of the heat generation parameter, but it gradually reduces with an increment in the magnitude of the thermogeometric and radiative-conductive parameter. [ABSTRACT FROM AUTHOR]

Proper thermal management is crucial to improving the reliability of aerostatic thrust bearing with high air supply pressures. Due to the obvious temperature diffenence in the flow channel clearance, a remarkable conjugate heat transfer phenomenon exists between the gas film and solid discs. Moreover, the changes in temperature and pressure in the clearance cause apparent variations in thermal properties, which inversely effect the heat transfer characteristics of the gas film. In this study, a 3D aerostatic thrust bearing with high supply air pressure is modelled. To investigate the influence of changes in pressure and temperature in clearance on thermal properties, numerical computations are performed to solve the 3D compressible forced convection conjugate heat transfer. Based on the preceding analysis, an effective correction method of air thermal properties is proposed. The effects of thermal properties correction on 3D conjugate heat transfer of gas film are discussed, and it is demonstrated that thermal properties correction at the temperature plays an important role in the conjugate heat transfer analysis of aerostatic thrust bearing with high air supply pressures. [ABSTRACT FROM AUTHOR]

The paper presents theoretical, experimental and numerical studies on the thermal behavior of mineral wool used in sandwich panels. The aim of this study is to investigate the thermal properties of mineral wool at elevated temperatures and provide a simple model that would allow us to determine the heat propagation in sandwich panels during a fire. The paper proposes a new method to experimentally evaluate thermal diffusivity, derived from theoretical premises. Experiments are conducted in a laboratory furnace where specimens are placed and temperatures inside specimens are measured. Different methods are used to process the test results and calculate the thermal diffusivity of mineral wool. Finally, a numerical analysis of heat transfer using the finite element method (FEM) is performed to validate the obtained thermal properties. [ABSTRACT FROM AUTHOR]

The suspension of different nanoparticles into various conventional thermal fluids to synthesize nanofluids has been proven to possess superior thermal, optical, tribological, and convective properties, and the heat transfer performance over conventional thermal fluids. This task appears trivial but is complicated and significant to nanofluid synthesis and its subsequent utilization in diverse applications. The stability of mono and hybrid nanofluids is significantly related to stirring duration and speed; volume, density, and base fluid type; weight/volume concentration, density, nano-size, and type of mono or hybrid nanoparticles used; type and weight of surfactant used; and sonication time, frequency, mode, and amplitude. The effects of these parameters on stability consequently affect the thermal, optical, tribological, and convective properties, and the heat transfer performance of nanofluids in various applications, leading to divergent, inaccurate, and suspicious results. Disparities in results have inundated the public domain in this regard. Thus, this study utilized published works in the public domain to highlight the trend in mono or hybrid nanofluid formulation presently documented as the norm, with the possibility of changing the status quo. With the huge progress made in this research area in which a large quantum of different nanoparticles, base fluids, and surfactants have been deployed and more are still emerging in the application of these advanced thermal fluids in diverse areas, there is a need for conformity and better accuracy of results. Reproduction of results of stability, thermal, optical, tribological, anti-wear, and fuel properties; photothermal conversion; and supercooling, lubrication, engine, combustion, emission, thermo-hydraulic, and heat transfer performances of formulated mono or hybrid nanofluids are possible through the optimization and detailed documentation of applicable nanofluid preparation parameters (stirring time and speed, sonication duration, amplitude, mode, frequency, and surfactant concentration) employed in formulating mono or hybrid nanofluids. This proposed approach is expected to project a new frontier in nanofluid research and serve as a veritable working guide to the nanofluid research community. [ABSTRACT FROM AUTHOR]

A hybrid nanofluid (HYNF) is an excellent working medium for improved heat transfer performance. To investigate the convective heat transfer performance of an HYNF of various particle mixing ratios (MR), at first samples of MgO-SiO2/water HYNF are prepared by varying the MR of MgO to SiO2 as 0:100, 40:60, 50:50, 60:40, and 100:0 at 0.05 mass % of concentration; then convective heat transfer characteristics are determined experimentally by exposing different mass flows of HYNF from 0.03–0.27 kg/s to a constant heat flux of 5630 W/m2. The results describe that the variation in MR strongly influences the Nusselt number (Nu) of HYNF. The maximum Nu, which is 1.94 times (~ 94.50%) higher than the same with base fluid, is obtained at MR of 60:40 and the mass flow rate of 0.13 kg/s. The variation of MR does not affect the friction factor of HYNF and it is nearly comparable to that of the base fluid. Further, a new concept has been proposed to determine the thermo-economic feasibility of HYNF in heat transfer applications. It was recommended to maintain the MR at 60:40 and 0.13 kg/s mass flow rate for optimum thermo-economic performance. [ABSTRACT FROM AUTHOR]

Long hollow cylinders are commonly utilized in various technological applications, including liquid and gas transmission. As a result, its value is growing, becoming increasingly important to many research efforts. Compared with thermal isotropic homogeneous cylinders, thermo-viscoelastic orthotropic cylinders have less relevant data. In this paper, a thermoelastic fractional heat conduction model was developed based on the Moore-Gibson-Thompson equation to examine the axial symmetry problem of a viscoelastic orthotropic hollow cylinder. Atangana and Baleanu derivative operators with nonsingular and nonlocal kernels were used in constructing the fractional model. The thermal properties of the cylinder materials are assumed to be temperature-dependent. The Laplace transform is applied to solve the system of governing equations. The numerical calculations for temperature, displacement, and stress components are performed by the effect of fractional order, rotation, and changing thermal properties of the cylinder. The results showed that due to the presence of fractional derivatives, some properties of the physical fields of the medium change according to the value of the fractional order. [ABSTRACT FROM AUTHOR]

In this research, two alternative approaches to fractional derivatives, namely Caputo–Fabrizio (CF) and Atangana–Baleanu (AB) fractional operators, are used to propose a generalized model of thermoelastic heat transfer of a rigid cylinder with thermal characteristics. The proposed model can be constructed by combining the DPL model with phase delays and the two temperature theories. It will be taken into account that the solid cylinder has variable physical properties. It was also assumed that the surface of the cylinder is penetrated by a continuous magnetic field and is regularly exposed to thermal loading from a continuous heat source. The numerical solutions of the studied physical fields in the AB and CF fractional derivative cases were derived using the Laplace transform method and are compared visually and tabularly and discussed in detail. [ABSTRACT FROM AUTHOR]

Many efforts have recently concentrated on constructing and developing nanoparticles (NPs) as promising thermal agent for optical hyperthermia and photothermal therapy. However, thermal energy transfer in biological tissue is a complex process involving different mechanisms such as conduction, convection, radiation. Therefore, having information about thermal properties of tissue especially when NPs are embedded in is a necessity for predicting the heat transfer during hyperthermia. In this work, the thermal properties of solid phantom based on agar in the presence of three different nanoparticles (BPSi, tNAs, GNRs) and alone were measured and reported as a function of temperature (ranging from 22 to 62 °C). The thermal response of these NPs to an 808 nm laser beam with three different powers were studied in the water comparatively. Agar and tNAs have almost constant thermal properties in the considered range. Among the three NPs, gold has the highest conductivity and diffusivity. At 62 °C BPSi NPs have the similar amount of increase for the diffusivity. The thermal parameters reported in this paper can be useful for the mathematical modeling. Irradiation of the NPs-loaded water phantom displayed the highest radiosensitivity of gold among the three mentioned NPs. However, for the higher power of irradiation, BPSi and tNAs NPs showed the increased absorption of heat during shorter time and the increased temperature gradient slope for the initial 15 s after the irradiation started. The three NPs showed different thermal and irradiation response behavior; however, this comparison study notes the worth of having information about thermal parameters of NPs-loaded tissue for pre-clinical planning. [ABSTRACT FROM AUTHOR]

Expanded polystyrene foams (EPS) are used as packaging materials and are often discarded by consumers after the goods are unpacked (WEPS). Most recycling centers do not accept them because their extremely low weight makes them uneconomic to transport. In the research described here, WEPS was collected from shipping containers and crushed in a blender into 2-4 mm spherical shapes that were used as a replacement for aggregates to make lightweight concretes (LWC) to build lightweight facilities. Eight types of concrete samples were prepared, with the WEPS replacing the natural aggregate at the levels of 0 to 85 percent by volume to study the effects of the WEPS on the properties of the LWC. The densities of the LWCs were less than that of those found from natural aggregate (NAG), as was expected (900–1700 kg/m3). The heat conductivity of the LWC samples was smaller than that of NAG when the composition of WEPS was below 50%. The 28-day compressive strengths of the LWC ranged from 11 MPa to 90 MPa, which satisfies the strength requirement of semi-structural LWC recommended by ASTM to be higher than 17 MPa. [ABSTRACT FROM AUTHOR]

The thermal properties of nanofluids are variable with working temperature and pressure and ignored by the existing empirical formula. In the present work, based on the application of nanofluids in pressurized water reactor (PWR) nuclear power plants, different concentrations of Al2O3/H2O nanofluids are prepared for measuring its thermal properties and then modifying empirical formulas at high temperature and high pressure (HTHP). In addition, the primary heat transfer process of PWR nuclear power plants is simulated by numerical method. The results show that, when volume fraction φ within 2.0%, the heat transfer performance of Al2O3 nanofluid increases with the increase of concentrations; however, it is on the contrary when the volume fraction of nanoparticles is larger than 2%. Comparing with water as the coolant, Al2O3 nanofluids with 2% volume fraction give the largest heat transfer enhancement of 103%. Therefore, Al2O3 nanofluids as the coolant can achieve the goals of heat transfer enhancement and safety limit improvement. [ABSTRACT FROM AUTHOR]

Controlling thermal energy transfer at the nanoscale and thermal properties has become critically important in many applications since it often limits device performance. In this study, the effects on thermal conductivity arising from the nanoscale structure of free‐standing nanocrystalline silicon films and the increasing surface‐to‐volume ratio when fabricated into suspended optomechanical nanobeams are studied. Thermal transport and elucidate the relative impact of different grain size distributions and geometrical dimensions on thermal conductivity are characterized. A micro time‐domain thermoreflectance method to study free‐standing nanocrystalline silicon films and find a drastic reduction in the thermal conductivity, down to values below 10 W m–1 K–1 is used, with a stronger decrease for smaller grains. In optomechanical nanostructures, this effect is smaller than in membranes due to the competition of surface scattering in decreasing thermal conductivity. Finally, a novel versatile contactless characterization technique that can be adapted to any structure supporting a thermally shifted optical resonance is introduced. The thermal conductivity data agrees quantitatively with the thermoreflectance measurements. This study opens the way to a more generalized thermal characterization of optomechanical cavities and to create hot‐spots with engineered shapes at the desired position in the structures as a means to study thermal transport in coupled photon‐phonon structures. [ABSTRACT FROM AUTHOR]

This research focuses on the thermal performance of masonry walls overlayed with textile reinforced concrete (TRC) sandwich panels subjected to different climatic zones. Three types of TRC sandwich panels are explored by integrating expanded polystyrene, gypsum and calcium silicate board as core material. The TRC sandwich panels are integrated as outer layers of clay brick masonry wall panels to reduce the amount of heat transfer. Numerical simulation has been carried out using transient heat transfer analysis to determine the performance of various systems under a realistic daily temperature variation in a hot humid and warm humid climatic zone. Thermal response of TRC sandwich panel integrated masonry is validated against the requirements of a design code accepted thermal performance. From the investigations, the most feasible TRC sandwich panel solution that can be integrated for a specific climatic zone is arrived, which leads to reduced heat transfer and it is also ensured the solution satisfies codal requirements. The acceptance of proposed thermally efficient TRC sandwich panel integration with masonry would lead to environmentally friendly and sustainable alternative to achieve thermal comfort inside buildings. [ABSTRACT FROM AUTHOR]

Plasmonic gold nanoparticles (AuNPs) can convert laser irradiation into thermal energy for a variety of applications. Although heat transfer through the AuNP–water interface is considered an essential part of the plasmonic heating process, there is a lack of mechanistic understanding of how interface curvature and the heating itself impact interfacial heat transfer. Here, we report atomistic molecular dynamics simulations that investigate heat transfer through nanoscale gold–water interfaces. We simulated four nanoscale gold structures under various applied heat flux values to evaluate how gold–water interface curvature and temperature affect the interfacial heat transfer. We also considered a case in which we artificially reduced wetting at the gold surfaces by tuning the gold–water interactions to determine if such a perturbation alters the curvature and temperature dependence of the gold–water interfacial heat transfer. We first confirmed that interfacial heat transfer is particularly important for small particles (diameter ≤ 10 nm). We found that the thermal interface conductance increases linearly with interface curvature regardless of the gold wettability, while it increases nonlinearly with the applied heat flux under normal wetting and remains constant under reduced wetting. Our analysis suggests the curvature dependence of the interface conductance coincides with changes in interfacial water adsorption, while the temperature dependence may arise from temperature-induced shifts in the distribution of water vibrational states. Our study advances the current understanding of interface thermal conductance for a broad range of applications. [ABSTRACT FROM AUTHOR]

In present work, semiconducting iron (III) oxide (Fe2O3) nanoparticles have been synthesized by sol–gel method. X-ray diffraction (XRD), UV–Visible (UV–Vis) absorption spectroscopy and transmission electron microscopy (TEM) have been used for the characterization of the synthesized nanoparticles. Two-step technique was used to formulate stable ethylene glycol (EG) based Fe2O3 nanofluids at room temperature. Thermal conductivity of nanofluids has been measured using hot disc thermal constants analyzer. Significant enhancement in the thermal conductivity is noted at very low nanoparticle loading (up to 1 wt%). Ultrasonic velocity and ultrasonic attenuation in the prepared nanofluids were investigated using an ultrasonic interferometer and acoustic particle sizer (APS-100), respectively. APS-100 was also used for the analysis of particle size distribution (PSD) of Fe2O3 nanoparticles in the prepared nanofluids. The PSD result of APS-100 has been found in good agreement with that of TEM. The characteristics behaviour of Fe2O3 nanofluid has been illustrated based on its ultrasonic and thermal properties. Our investigations advocate that Fe2O3 nanofluids have potential application for effective heat transfer management in various cooling industries. [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]

Establishing and optimizing a distributed parameter thermal path model for transformer windings is an important means to analyze the hot-spot temperature of the windings; furthermore, in the process of improving the thermal path model of transformers and improving the accuracy of their models, the thermal characteristics of the insulation paper are extremely important. A microscopic thermal contact resistance model was established for the contact interface of insulation paper and copper, according to the microscopic morphology parameters of copper and insulation paper observed by atomic force microscopy, the thermal contact resistance under different temperatures was calculated. A dual heat flow test platform was built to test the heat transfer behavior of four different thickness insulation papers under four temperatures, and the thermal contact resistance and thermal bulk resistance with temperature were analyzed. The results show that as the temperature increases, the thermal resistance of the insulation paper becomes larger and the thermal conductivity decreases. The average error between the experimental and theoretical values of the thermal contact resistance under four temperature points in the study is 6.6%. The results provide a data support for establishing and optimizing transformer heat generation and heat transfer models. [ABSTRACT FROM AUTHOR]

Traditional ice and snow removal methods damage roads. In this paper, the thermal performance and a heat transfer model of conductive ethylene propylene diene monomer rubber composites in pavement were studied. The thermal performance was determined by snow melting tests. An active snow melting model was established and compared with the test results. The temperature field and energy distribution of the conductive rubber composite, upper asphalt layer, and lower asphalt layer were determined. The results show that the conductive rubber composite can be used to melt snow at a low voltage. Active snowmelt pavement can melt 10 mm of snow in 58 min at − 5 °C. For the same mass of snow and ice, snow melts faster than ice. Draining the melted water can shorten the snow melting time. However, capillary action weakens the drainage effect. In addition, the test results verify the accuracy of the numerical simulation. The energy absorbed by the structures was determined by the finite element model. The energy utilization rate for snow was determined to be 24.27%. This study determines the thermal properties of conductive rubber composites in pavement. A new active snow melting method and a finite element model are proposed. Furthermore, the model is convenient for energy analysis and engineering optimization. [ABSTRACT FROM AUTHOR]

The radiative in the UV and visible spectra and the conductivity properties at low temperatures of hematite (α-Fe2O3) samples of different particle size distributions and compositions obtained by the pressure welding procedure within temperatures of 900-1100°C were investigated. In this study, the two samples which have different chemical properties were called as Case 1 and Case 2. Debris iron oxides samples, which are in the morphology of hematite, were separated according to particle sizes by sieve analysis. The absorbancewavelength change and the thermal conductivity-temperature change of the samples of, the smallest, medium and largest of which the particle size were analysed. The coating on particles due to the aging effect was examined using scanning electron microscopy (SEM) images. It has been concluded that the content and size of the particles and the oxidation effect are effective in the variation of the radiation properties of the samples with the wavelength and the temperature of the thermal conductivity coefficient. Radiative and thermal transfer properties of debris hematite particles increase as the particle size increases. However, the radiative property decreases with increasing wavelength and the thermal conductivity property decreases with increasing temperature. [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]

The paper considers the application of metal - fibrous microstructures in the development of highly efficient heat exchangers. Such structures can be successfully used in air conditioning systems of modern planes or in heat pipes located in planes and spacecraft. Copper fibers of 50 mm diameter have been used to produce coatings of different volumetric porosity. The sintering process was used to produce the samples. Pool boiling heat transfer tests have been performed on the non - isothermal surfaces of the fin with distilled water and ethyl alcohol (99.8% purity) as boiling agents. A significant enhancement of heat transfer has been recorded with the use of the metal - fibrous microstructures in comparison to the smooth surface without any coating. The enhancement proved to vary considerably depending on the superheat value. [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]

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 article, thermal analysis of radial moving fins of hyperbolic and rectangular profiles is performed. A time-dependent nonlinear differential equation modeling heat transfer in a radial moving fin is considered. The thermal conductivity and heat transfer coefficient are modeled as linear and power-law functions of temperature, respectively. The analytical solutions are generated using the differential transform method which is an analytical solution technique that can be applied to various types of differential equations. The accuracy of the analytical solutions is validated by benchmarking against the numerical solutions obtained by applying the inbuilt numerical solver in Maple (pdsolve). A good agreement is observed between the analytical and numerical solutions. The effects of embedding parameters on the dimensionless temperature and heat transfer rate are analyzed. The results show that the fin rapidly dissipates heat to the surrounding fluid with an increase in the speed of the moving fin, that is, an increase in the values of the Peclet number. The results also show that the heat transfer through a rectangular fin is more efficient when compared to a fin of hyperbolic profile. [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]

Powder bed metal additive manufacturing (AM) utilizes a high-energy heat source scanning at the surface of a powder layer in a predefined area to be melted and solidified to fabricate parts layer by layer. It is known that powder bed metal AM is primarily a thermal process, and further, heat conduction is the dominant heat transfer mode in the process. Hence, understanding the powder bed thermal conductivity is crucial to process temperature predictions, because powder thermal conductivity could be substantially different from its solid counterpart. On the other hand, measuring the powder thermal conductivity is a challenging task. The objective of this study is to investigate the powder thermal conductivity using a method that combines a thermal diffusivity measurement technique and a numerical heat transfer model. In the experimental aspect, disk-shaped samples, with powder inside, made by a laser powder bed fusion (LPBF) system, are measured using a laser flash system to obtain the thermal diffusivity and the normalized temperature history during testing. In parallel, a finite element (FE) model is developed to simulate the transient heat transfer of the laser flash process. The numerical model was first validated using reference material testing. Then, the model is extended to incorporate powder enclosed in an LPBF sample with thermal properties to be determined using an inverse method to approximate the simulation results to the thermal data from the experiments. In order to include the powder particles' contribution in the measurement, an improved model geometry, which improves the contact condition between powder particles and the sample solid shell, has been tested. A multipoint optimization inverse heat transfer method is used to calculate the powder thermal conductivity. From this study, the thermal conductivity of a nickel alloy 625 powder in powder bed conditions is estimated to be 1.01 W/m K at 500 °C. [ABSTRACT FROM AUTHOR]

An attractive feature of nanomaterials is the possibility of tuning their properties through controlling their size and surface morphology, and understanding the effects of various parameters on thermal transport properties of nanostructures has been an active research topic in the past two decades. Through systematic studies of kinked silicon nanoribbons, we show how the kink morphology, a newly recognized degree of freedom for tuning thermal transport in nanostructures, modulates the thermal conductivity of these nanoribbons. For kinked Si nanoribbons that are 34 nm thick and 141 nm wide, the measured thermal conductivity first decreases as the period length reduces from 2 μm to 0.5 μm, reaching a 21% thermal conductivity reduction as compared to that of a straight counterpart at 300 K. However, as the period length drops to a level at which a straight heat transfer channel opens between the heat source and the sink, the thermal conductivity exhibits a steep increasing trend. Moreover, the comparison of thermal conductivity reduction for kinked ribbons along different crystalline directions indicates that phonon focusing could be exploited to further suppress thermal transport in kinked silicon nanoribbons. These results provide important guidelines on modulating heat transfer in nanostructures using kinks, which could be adopted to tune the thermal properties of nanostructures for different applications, such as thermoelectrics, microelectronic device thermal management, and functional thermal regulators. [ABSTRACT FROM AUTHOR]

Rare-earth barium copper oxide (REBCO) tape is used for resistive type superconducting fault current limiters (RSFCLs) owing to its quick response and simple structure. To shorten the recovery time, film boiling on the REBCO tape should be suppressed as it exhibits poor heat transfer performance. To address the aforementioned issue, this study utilized low thermal conductivity materials as the thermal/electrical interface material for porous-stabilized REBCO tape. The experimental results showed that the cooling and recovery performances were dramatically improved by utilizing an insulating epoxy, which has a thermal conductivity of 0.6 W/mK. Based on the visualization of the boiling behavior, the liquid-solid contact between liquid nitrogen and the REBCO tape was promoted by the insulating epoxy, in which the film boiling was easily broken. [ABSTRACT FROM AUTHOR]

Underground nuclear explosions generate non-isothermal two-phase flow, heat and mass transfer, and tracer transport through fractured porous media. The governing equations of these coupled phenomena on the Darcy scale are presented and the corresponding numerical code is briefly described. Two configurations are considered. In the first one, the damaged zone generated by the explosion is replaced by equivalent macroscopic boundary conditions at the bottom of the medium. Vapor condensation at distance from this zone plays a crucial role and slows down the tracer transport to the ground surface, while the presence of hot liquid water and of hot rubble particles in it accelerates it. In the second configuration, the damaged zone itself is treated as a porous medium with specific properties and is integrated in the simulation domain. Several regions can be distinguished with different properties, such as the chimney, the cavity, the solidified magma, the fractured porous medium, and the intact porous medium. Phase change, heat transfer and tracer transport can be detailed in these regions and at the boundaries between them. Among the most important conclusions, the role of phase change, of the thermal properties and therefore of the temperature, is pointed out. [ABSTRACT FROM AUTHOR]

Phonon thermal transport in graphene has attracted significant interest in recent years. Phonon thermal properties of graphene are investigated by molecular dynamics simulations using the Tersoff, Tersoff-2010, REBO, and AIREBO potentials. By calculating the phonon properties and thermal conductivity of graphene, the performance of the potentials is evaluated based on comparisons with experimental data. It shows that the Tersoff-2010 and REBO display better dispersion curves for graphene than the original Tersoff and AIREBO. The Tersoff-2010 correctly provides the G point phonon velocities of the LA and TA branches as well as the G peak frequency with a value of 46 THz. In addition, the acoustic phonon relaxation time derived from the Tersoff-2010 satisfies the ideal relation "τ-1 ∝ ν²." It is also found that the Tersoff-2010 provides the highest graphene thermal conductivity among the used potentials, and estimates about 30.0% contribution for flexural phonons to the total thermal conductivity. By comparison, the Tersoff-2010 potential is demonstrated to be the most suitable one to describe the phonon thermal properties of graphene. [ABSTRACT FROM AUTHOR]

The procedure of numerical identification of thermophysical properties of concrete during its hardening is presented. Heat of cement hydration, thermal conductivity and specific heat are determined for purpose of modelling temperature evolution in massive concrete elements. The developed method is based on point temperature measurements in a cylindrical mould and the numerical solution of the inverse heat transfer problem by means of direct search optimization algorithm. The determined thermal characteristics of concrete are not constant and depend on the maturity of concrete. The procedure was verified on set of concrete mixes designed with Portland cement CEM I 42.5R and Portland-slag cement CEM II/B-S 32.5 N. Calcareous fly ash was also used for partial replacement of cement in the mixtures. The obtained results have been compared with experimentally measured temperature in concrete and a fair agreement has been found. [ABSTRACT FROM AUTHOR]

In engineering, agricultural and meteorological project design, sediment thermal properties are highly important parameters, and thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially in very shallow geothermal systems. Herein, the first 2 m of depth from surface is of critical importance. However, the heat transfer determination in unconsolidated material is difficult to estimate, as it depends on several factors, including particle size, bulk density, water content, mineralogy composition and ground temperature. The performance of a very shallow geothermal system, as a horizontal collector or heat basket, is strongly correlated to the type of sediment at disposal and rapidly decreases in the case of dry-unsaturated conditions. The available experimental data are often scattered, incomplete and do not fully support thermo-active ground structure modeling. The ITER project, funded by the European Union, contributes to a better knowledge of the relationship between thermal conductivity and water content, required for understanding the very shallow geothermal systems behaviour in saturated and unsaturated conditions. So as to enhance the performance of horizontal geothermal heat exchangers, thermally enhanced backfilling material were tested in the laboratory, and an overview of physical-thermal properties variations under several moisture and load conditions for different mixtures of natural material was here presented. [ABSTRACT FROM AUTHOR]

Temperature controlled food transport is essential for human safety and to minimise food waste. The thermal properties of food are important for determining the heat transfer during the transient stages of transportation (door opening during loading and unloading processes). For example, the temperature of most dairy products must be confined to a very narrow range (3-7 °C). If a predefined critical temperature is exceeded, the food is defined as spoiled and unfit for human consumption. An improved empirical model for the thermal conductivity and specific heat capacity of a wide range of food products was derived based on the food composition (moisture, fat, protein, carbohydrate and ash). The models that developed using linear regression analysis were compared with the published measured parameters in addition to previously published theoretical and empirical models. It was found that the maximum variation in the predicated thermal properties leads to less than 0.3 °C temperature change. The correlation coefficient for these models was 0.96. The t-Stat test (P-value >0.99) demonstrated that the model results are an improvement on previous works. The transient heat transfer based on the food composition and the temperature boundary conditions was found for a Camembert cheese (short cylindrical shape) using a multiple dimension finite difference method code. The result was verified using the heat transfer today (HTT) educational software which is based on finite volume method. The core temperature rises from the initial temperature (2.7 °C) to the maximum safe temperature in ambient air (20.24 °C) was predicted to within about 35.4 ± 0.5 min. The simulation results agree very well (+0.2 °C) with the measured temperature data. This improved model impacts on temperature estimation during loading and unloading the trucks and provides a clear direction for temperature control in all refrigerated transport applications. [ABSTRACT FROM AUTHOR]

InAs-On-Insulator (InAs-OI) structures fabricated by the Smart Cut process are promising for three-dimensional (3D) integration of complementary metal–oxide–semiconductor devices owing to the low thermal budget, high mobility, and low contact resistance. InAs-OI structures are also expected to reduce the leakage current and parallel conduction channels in InAs n-channel MOSFETs, which are serious problems. Smart Cut is a promising way to integrate III–V semiconductors on Si substrates for 3D integration. However, the electrical characterization of InAs-OI films realized by Smart Cut has not been reported yet. In addition, since InAs-OI's crystallinity is severely degraded by passage of a large amount of H+ ions in the Smart Cut process, we need to study the effects of thermal annealing on the electrical properties of the InAs-OI layers. It is found from the annealing temperature dependence of the electron concentration and the mobility that annealing at 500 °C significantly recovers InAs-OI crystallinity. Here, bulk and interface electrical properties are separately evaluated from the InAs-OI thickness dependence on the electron concentration and the sheet conductance. As a result, fabricated InAs-OI has the electron density of (6.3 ± 1.4) × 1017 cm−3 in the bulk region for an intrinsic donor InAs wafer and the high bulk mobility of 5800 ± 900 cm2/V s, indicating the high crystallinity of InAs-OI after 500 °C annealing. Also, the reusability of donor InAs wafers without degradation of InAs-OI film quality, which is one of the most important points for Smart Cut, is demonstrated by using (111) InAs donor wafers, attributed to much smoother (111) InAs-OI surfaces after splitting than (100) InAs-OI ones. [ABSTRACT FROM AUTHOR]

Highlights • This study measured the thermal properties of peat soils by DPHP method. • Compared with sand soil, peat soil decreased thermal conductivity. • The de Vries model described the measurements well except that from 0 °C to −4 °C. • The measured thermal properties can be used for designing peat soil cover reclamation. Abstract In situ measurements of soil thermal properties are frequently required when studying coupled heat and water transfer in soils. While these values are widely available for mineral soils, but not for organic-rich peat soils. This study aimed at measuring the thermal properties of six peat:mineral mixtures collected from an oil sands mine reclamation study site using a dual-probe heat-pulse (DPHP) method. The soil mixes were tested across a range of water contents (θ) and bulk densities (ρ). Generally, compared with the thermal conductivity (λ) of sand soil, λ of peat soil subsequently decreased with increasing peat:mineral ratios and increased slightly with the increase of θ, indicating the significant impact of organic matter. Similar to λ, the heat capacity (C) decreased with the increase in soil organic matter content, and the decrease in θ and ρ, but differences were relatively small between the different soil mixtures. With increasing θ, λ increased exponentially, but C increased linearly. At all temperatures but between −2 °C and 0 °C for sandy soils and −4 °C and 0 °C for peat soils due to ice melting, the de Vries thermal conductivity model described the measurements very well and the DPHP method is suitable to measure the real soil thermal properties. The measured thermal properties for the peat soil can be used in modeling heat conduction in a high latitude cold area, and is a prerequisite for designing peat soil cover in reclamation soil. [ABSTRACT FROM AUTHOR]

Summary: Solid‐solid phase change materials (SSPCMs) used in thermal energy storage (TES) system attract much attention in recent days. Here, graphene nanoplatelets (GnPs) were introduced into pentaglycerine (PG) with mass ratios of 1 wt%, 2 wt%, and 4 wt% to obtain PG/GnPs PCMs. The structure and thermal property of PG/GnPs PCMs were characterized by SEM, XPS, FT‐IR, POM, DSC, thermal conductivity tester, and heat transfer performance test system. The effect of GnPs on the crystallization kinetic of PG was investigated by isoconversional method. The results indicated that PG and GnPs were uniformly mixed together by physical reaction. GnPs reduced the subcooling and enhanced the thermal conductivity of the PG/GnPs. The heat transfer rate of PG/GnPs was improved during to the high thermal conductivity. Crystallization kinetic results presented that the activation energy increases with the GnP content. In summary, GnPs improved the thermal behaviors of PG. [ABSTRACT FROM AUTHOR]

Nanofluids of LiCO-NaCO-KCO improved by three nano-AlO samples are firstly prepared by means of two-step aqueous method to enhance thermal properties for high-temperature heat transfer, when used as heat transfer fluids and thermal energy systems for concentrating solar power systems. Specific heat of ternary carbonates containing AlO of 0.2, 0.4, 0.8, 1.0, 1.4 and 2.0 mass% is measured, and nanofluids with 1.0 mass% of 20-nm AlO, 1.0 mass% of 50-nm AlO and 0.8 mass% of 80-nm AlO are selected as superior candidates. The maximum enhancement of specific heat is 18.5% in solid and 33.0% in liquid, 17.9% in solid and 22.7% in liquid, 13.2% in solid and 17.5% in liquid for nanofluids containing 20-, 50- and 80-nm AlO. Thermal conductivity is, respectively, improved by 23.3, 28.5 and 30.9% under the addition of AlO. New chemical bonds and crystals are scarcely formed in composites through FT-IR and XRD determination. SEM images certify that nano-AlO are homogeneously mixed into nanofluids and this structure may be a critical incentive for enhancing thermal properties. There are no significant changes with respect to the heat flow, melting/freezing point and latent heat after the 30 circles of determination. Briefly, it can be speculated that these nanofluids will exhibit tremendous potential in the coming applications of heat transfer and thermal storage for concentrating solar power systems. [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]

Rigid polyurethane foam (PUF) is one of the outstanding insulation materials and has been widely used in freezers and cryogenic facilities. Among the various blowing agents used in the manufacturing PUF, water-blown PUF is attracting much attention as environmentally friendly PUF as prominent replacements for the environmentally hazardous CFCs and HCFCs due to their significant ozone depletion potential. We investigated the effective thermal conductivity of PUF blown with different amounts of water, on the basis of the heat transfer mechanisms in terms of thermal conduction of solids and gases and the thermal conductivity of radiation in the cells. A predictive model for the effective thermal conductivity of PUFs with different densities is presented. The predictive model was validated by comparing the predicted values with the experimentally measured ones. The result showed that the effective thermal conductivity increased from 0.023 to 0.027 W m−1 K−1 as the PUF density increased from 48 to 120 kg m−3: increased by 158% from 0.0034 to 0.0089 W m−1 K−1 for the thermal conductivity of solid PUF and decreased by 50% from 0.0037 to 0.0018 for the thermal conductivity of radiation. [ABSTRACT FROM AUTHOR]

In the past decade, research on nanofluids has been increased rapidly and reports reveal that nanofluids are beneficial heat transfer fluids for engineering applications. The heat transfer enhancement of nanofluids is primarily dependent on thermal conductivity of nanoparticles, particle volume concentrations and mass flow rates. Under constant particle volume concentrations and flow rates, the heat transfer enhancement only depends on the thermal conductivity of the nanoparticles. The thermal conductivity of nanoparticles may be altered or changed by preparing hybrid (composite) nanoparticles. Hybrid nanoparticles are defined as nanoparticles composed by two or more different materials of nanometer size. The fluids prepared with hybrid nanoparticles are known as hybrid nanofluids. The motivation for the preparation of hybrid nanofluids is to obtain further heat transfer enhancement with augmented thermal conductivity of these nanofluids. This review covers the synthesis of hybrid nanoparticles, preparation of hybrid nanofluids, thermal properties, heat transfer, friction factor and the available Nusselt number and friction factor correlations. The review also demonstrates that hybrid nanofluids are more effective heat transfer fluids than single nanoparticles based nanofluids or conventional fluids. Notwithstanding, full understanding of the mechanisms associated with heat transfer enhancement of hybrid nanofluids is still lacking and, consequently it is required a considerable research effort in this area. [ABSTRACT FROM AUTHOR]

Micro-aeration is a method to modify the sensorial attributes of chocolate but also affects the material properties of chocolate, which in turn, determine its material response during manufacturing and oral processes. This study aims to define the effect of micro-aeration on the thermal properties of chocolate by considering the changes of chocolate microstructure due to micro-aeration. Micro-aeration was found to alter the chocolate microstructure creating a layer of a third phase at the porous interfaces, which is argued to consist of cocoa butter of higher melting properties. A multiscale Finite Element Model is developed, which was confirmed by macroscale heat transfer measurements, to parametrically simulate the structural changes of micro-porous chocolates at the microscale level and estimate their effective properties, such as thermal conductivity and specific heat capacity. The developed multiscale computational model simulates the porous chocolate as a two-phase (chocolate- pores) or three-phase material (chocolate-cocoa butter layer- pores). The investigation identified a new, complex transient thermal mechanism that controls the behaviour of micro-aerated chocolate during melting and solidification. The results showed a maximum 13% reduction of k eff and 15% increase of C peff with 15% micro-aeration resulting to a slower transient heat transfer through the micro-aerated chocolate. The reason is that the micro-aerated chocolate can store a larger amount of thermal energy than its solid counterpart. This effect slows down the transient heat transfer rate in the chocolate and modifies melting/solidification rate and impacts sensorial attributes during oral processing and cooling during manufacturing. • New numerical model simulates the thermal mechanisms in porous chocolate. • A three-phase model is adopted to capture the complex thermal mechanisms in chocolate. • Cocoa butter, present at the pores' interfaces, impacts chocolate's thermal response. • Increased thermal storage, i.e. slower heat transfer rate, occurs with micro-aeration. • Chocolate's thermal response impacts sensory and manufacturing processes. [ABSTRACT FROM AUTHOR]

Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Several methods, including the classical divided bar technique, are available for laboratory measurements of thermal conductivity, but much fewer for thermal diffusivity. We have generalized the divided bar technique to the transient case in which thermal conductivity, volumetric heat capacity and thereby also thermal diffusivity are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity can also be determined. The finite element formulation provides a flexible forward solution for heat transfer across the bar, and thermal properties are estimated by inverse Monte Carlo modelling. This methodology enables a proper quantification of experimental uncertainties on measured thermal properties and information on their origin. The developed methodology was applied to various materials, including a standard ceramic material and different rock samples, and measuring results were compared with results applying traditional steady-state divided bar and an independent line-source method. All measurements show highly consistent results and with excellent reproducibility and high accuracy. For conductivity the obtained uncertainty is typically 1-3 per cent, and for diffusivity uncertainty may be reduced to about 3-5 per cent. The main uncertainty originates from the presence of thermal contact resistance associated with the internal interfaces in the bar. These are not resolved during inversion and it is imperative that they are minimized. The proposed procedure is simple and may quite easily be implemented to the many steady-state divided bar systems in operation. A thermally controlled bath, as applied here, may not be needed. Simpler systems, such as applying temperature-controlled water directly from a tap, may also be applied. [ABSTRACT FROM AUTHOR]

• We used models of heat transfer by conduction and convection to estimate soil thermal properties. • We used 1.5 years of experimental data on a natural pasture area in the Pampa biome in southern Brazil. • We consider the effects of soil heterogeneity and thermal convection due to the vertical movement of water in the soil, W. • Soil thermal diffusivity (k) showed an inverse seasonal variation with soil temperature. • Increasing values of W led to an increase in the variability of k with depth. Soil temperature, composition, and structure directly affect the heat transfer mechanisms in soil. Understanding the thermal behavior of soil is fundamental for describing the processes of mass and energy exchange in the soil-plant-atmosphere system. In addition, estimating thermal property values is necessary to determine the amount of heat transferred, stored, or transmitted by conduction and convection between the soil surface and deeper layers. This study used two soil heat transfer models (the conduction and conduction-convection methods) to estimate soil thermal properties. Soil data were collected in a natural pasture area in the Pampa biome in southern Brazil over 1.5 years. The results showed that soil thermal diffusivity (k) has an inverse seasonal variation with soil temperature (T s). The k and soil thermal conductivity (λ) values are higher as the soil depth and soil moisture (θ) increase, confirming the vertical variation of thermal properties. The liquid water flux density (W) represents the vertical movement of water in the soil and decreases in periods of higher T s. Increasing values of W led to an increase in the variability of k with depth. The conduction–convection method provides the best estimates for T s with R2 = 0.99 for deeper layers compared to the conduction method. However, we found that both models gave similar results for near-surface layers since, in this case, the conduction process was responsible for most of the heat transfer from the surface to the ground. The results obtained here allowed us to evaluate heat transfer at different depths and estimate thermal properties as a function of soil moisture in a natural pasture area in the Brazilian Pampa biome. Furthermore, the results can be integrated into global land surface models intended to represent the behavior of the energy exchange between soil, surface, and atmosphere. [ABSTRACT FROM AUTHOR]