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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]

Thermal energy storage (TES) using phase change materials (PCMs) is one of the potential solutions for stockpiling thermal energy and utilizing it for different applications, which results in effective energy usage. The main drawback of organic PCMs in practical applications is poor heat transfer due to low thermal conductivity (TC). Therefore, investigations into nano-enhanced PCMs are being explored to improve their thermophysical properties. In this work, the various thermophysical characteristics of nano-enhanced lauryl alcohol as a PCM were investigated using carbon-based and metallic nanoparticles. The results indicated that the addition of nanoparticles improved its thermal properties and affected other physical properties, such as viscosity. The latent heat was degraded with the addition of nanoparticles. The results revealed that by adding MWCNTs and CuO nanoparticles, a maximum of 82.6% and 49.6% improvement in TC was achieved, respectively. The maximum drop in latent heat during melting and freezing for the PCM with MWCNTs was about 10.1% and 9.3%, respectively, whereas for the PCM with CuO, they were about 11% and 10.3%, respectively. The lowest supercooling for the PCM with MWCNTs and CuO nanoparticles was 8.6 and 8.3 °C, respectively. The present work confirms that nano-enhanced PCMs can be a potential material for storing thermal energy for various applications. [ABSTRACT FROM AUTHOR]

Thermal energy storage (TES) using phase change materials (PCMs) is one of the potential solutions for stockpiling thermal energy and utilizing it for different applications, which results in effective energy usage. The main drawback of organic PCMs in practical applications is poor heat transfer due to low thermal conductivity (TC). Therefore, investigations into nano-enhanced PCMs are being explored to improve their thermophysical properties. In this work, the various thermophysical characteristics of nano-enhanced lauryl alcohol as a PCM were investigated using carbon-based and metallic nanoparticles. The results indicated that the addition of nanoparticles improved its thermal properties and affected other physical properties, such as viscosity. The latent heat was degraded with the addition of nanoparticles. The results revealed that by adding MWCNTs and CuO nanoparticles, a maximum of 82.6% and 49.6% improvement in TC was achieved, respectively. The maximum drop in latent heat during melting and freezing for the PCM with MWCNTs was about 10.1% and 9.3%, respectively, whereas for the PCM with CuO, they were about 11% and 10.3%, respectively. The lowest supercooling for the PCM with MWCNTs and CuO nanoparticles was 8.6 and 8.3 °C, respectively. The present work confirms that nano-enhanced PCMs can be a potential material for storing thermal energy for various applications.

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]

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]

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]

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]

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]

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]

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 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.

Cloth wearing seems so natural that everyone is self-deemed knowledgeable and has some expert opinions about it. However, to clearly explain the physics involved, and hence to make predictions for clothing design or selection, it turns out to be quite challenging even for experts. Cloth is a multiphased, porous, and anisotropic material system and usually in multilayers. The human body acts as an internal heat source in a clothing situation, thus forming a temperature gradient between body and ambient. But unlike ordinary engineering heat transfer problems, the sign of this gradient often changes as the ambient temperature varies. The human body also perspires and the sweat evaporates, an effective body cooling process via phase change. To bring all the variables into analysis quickly escalates into a formidable task. This work attempts to unravel the problem from a physics perspective, focusing on a few rarely noticed yet critically important mechanisms involved so as to offer a clearer and more accurate depiction of the principles in clothing thermal comfort.

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]

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]

Permafrost regions are experiencing increasing air temperatures, accelerating the thawing process, and thickening the active layer in summer. This can accelerate the release of greenhouse gasses into the atmosphere from the organic carbon stored in the permafrost. The long‐term thawing rates of permafrost below the active layer are governed by the soil thermal properties, the heat capacity, and thermal conductivity, which vary due to differences in grain sizes and distribution and organic matter content. Using nine column experiments comprised of fully saturated synthetic permafrost samples exposed to freeze–thaw cycles, the relative contributions of a range of soil grain sizes and organic matter contents on the soil thermal properties were investigated. The columns were subjected to a freeze and thaw cycle while soil temperatures were recorded in profiles. To infer the thermal properties from these experimental data, a numerical heat transfer model was used. The best fit between the observations and a batch of 5544 numerical models was used to find optimum values for permafrost thermal properties. The optimized heat capacity varied between 500 and 650 (J/m3 K) and thermal conductivity between 2.45 and 3.55 (W/m K). These optimized parameters were subsequently used to model a 100‐year permafrost active layer thaw scenario under warming air temperatures. Variations in the optimized thermal properties resulted in a time difference in thawing depth of 10–15 years and thawing depths varied between 9 and 10 m between the different optimized thermal properties at the end of the 100‐year scenario. Core Ideas: A numerical 1D heat transport model was used to simulate freeze–thaw transitions of permafrost column experiments.The numerical heat transfer model accurately simulated laboratory freeze–thaw dynamics.Numerically obtained thermal conductivity, heat capacity and porosity correspond well with field observations.Variations in organic matter content affect both thaw depth and thaw timescales. [ABSTRACT FROM AUTHOR]

This research highlights the utilization of two viscosity models to study the involvement of variable properties in heat and momentum transport in a rotating Carreau fluid past over a cone. The rheology of the Carreau material is assessed by the variable dynamic viscosity over the heating cone. The transport of momentum phenomenon is modeled by considering generalized Ohm’s law in Carreau liquid and thermal transport in derived by considering variable thermal conductivity, heat flux model. The considered model is derived in the form of nonlinear PDEs with boundary layer analysis. The nonlinear PDEs are converted into coupled ODEs by using approximate transformation and converted equations are solved numerically by finite element methodology. The impact of numerous parameters is displayed graphically, and their behavior is discussed in detail.

This paper refers to an inaugural lecture prepared by the author for the inauguration of the New Academic Year 2020/2021 at the Faculty of Mechatronics, Armament and Aerospace of Military University of Technology (MUT) in Warsaw (Poland) on 2 October 2020. It presents the origins of research into thermal properties of solids since the mid-1970s by the employees of the thermodynamic research unit at the Department of Aerodynamics and Thermodynamics, followed by the basic modalities of heat transfer, theoretical foundations of thermal expansion, specific heat, thermal conductivity and thermal diffusivity of solids. The measuring apparatus created as a result of proprietary research studies and purchased from market-leading manufacturers is shown with a selection of results from the research into the thermal properties of solids, which are largely the outcome of the application our own research procedures.

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]

Thermal transport plays a pivotal role across diverse disciplines, yet the intricate relationship between amorphous network structures and thermal conductance properties remains elusive due to the absence of a reliable and comprehensive network's dataset to be investigated. In this study, we have created a dataset comprising multiple amorphous network structures of varying sizes, generated through a combination of the node disturbance method and Delaunay triangulation, to fine-tune an initially random network toward both increased and decreased thermal conductance C. The tuning process is guided by the simulated annealing algorithm. Our findings unveil that C is inversely dependent on the normalized average shortest distance L n o r m connecting heat source nodes and sink nodes, which is determined by the network topological structure. Intuitively, the amorphous network with increased C is associated with an increased number of bonds oriented along the thermal transport direction, which shortens the heat transfer distance from the source to sink node. Conversely, thermal transport encounters impedance with an augmented number of bonds oriented perpendicular to the thermal transport direction, which is demonstrated by the increased L n o r m . This relationship can be described by a power law C = L n o r m α , applicable to the diverse-sized amorphous networks we have investigated. [ABSTRACT FROM AUTHOR]

Here, in this work, acid-activated bentonite and its nanocomposite with hematite nanoparticles were synthesized using the simple chemithermal and thermal coupling methods, respectively. The synthesized samples were investigated for morphological, compositional, structural, and thermal properties. Results suggested distortion in clay structure on acid activation and nanocomposite formation with improved thermal stability. Nanocomposite acts as a quencher for thermoluminescence and as an insulator in heat transfer reactions. [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]

The adobe is a widely used traditional material in popular constructions in rural areas of Peru and more generally in Andean countries. In order to increase comfort and energy efficiency of constructions, it is necessary to better know the thermal characteristics of the adobe, seen as a bio-composite material. Different adobes have been studied. Effective thermal conductivity and heat capacity were measured by means of a hot parallel-plate method. Density was estimated using a pycnometer and measuring physical dimensions and mass of each sample, which allowed the calculation of thermal effusivity and diffusivity. Some numerical simulation results displayed good agreement with experimental outcomes. The work presented here has implications for future studies of this traditional building material and might potentially help solving the problem of sustainable housing.

The present inspection elaborates the thermal distribution through a convective-radiative longitudinal trapezoidal moving fin with an internal heat source by considering the linear and nonlinear temperature-dependent thermal conductivities and heat transfer coefficient. The non-dimensionalization of the energy equation is carried out using dimensionless terms, and the resulting nonlinear ordinary differential equation (ODE) is solved analytically using the differential transform method (DTM) with Pade approximant approach. Furthermore, the consequence of several non-dimensional parameters, namely thermal conductivity parameter, convection-conduction parameter, Peclet number, radiation-conduction parameter, fin taper ratio, temperature ratio parameter, and internal heat generation parameter on temperature gradient and fin efficiency is explained with the help of graphs. The significant primary results of the investigation illustrate that the thermal distribution through the fin gradually decreases as the magnitude of the convection-conduction parameter, temperature ratio parameter, and radiation-conduction parameter rise. In contrast, it upsurges for heat generation and thermal conductivity parameters.

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]

In this article, a time dependent partial differential equation is used to model the nonlinear boundary value problem describing heat transfer through a radial porous moving fin with rectangular profile. The study is performed by applying a numerical solver in MATLAB (pdepe), which is a centered finite difference scheme. The thermal conductivity and fin surface emissivity are linearly dependent on temperature while the heat transfer coefficient is given by power law function of temperature. The effects of thermo-physical parameters, such as the Peclet number, surface emissivity coefficient, power index of heat transfer coefficient, convective-conductive parameter, radiative-conductive parameter and non-dimensional ambient temperature on temperature are studied.

This study presents a one-dimensional mathematical model developed to simulate multi-zone thermal storage systems using phase change materials (PCMs). The model enables precise analysis of temperature distribution in the layered storage based on several PCM configurations and properties. It is distinguished by its adaptability to various tank geometries and the number of PCM capsules, enabling its application under diverse operating conditions. By simplifying the implementation of heat transfer processes that depend on the shape of the capsule and the thermal properties of the PCM, the computation time can be reduced to a level that makes simulations over longer periods feasible. Experimental validation confirmed the accuracy of the model, with deviations below 6%, underscoring its practical applicability. The study demonstrates that individual layering in the storage tank can be achieved by filling it with PCMs of different melting points without compromising the maximum storage capacity. It is shown that including a PCM layer can maintain the outlet temperature 20% longer while storing 14% more energy. The results point out the model's potential to improve the performance of thermal storage systems through targeted PCM layer configurations. The model serves as the basis for the planning and optimization of these systems. [ABSTRACT FROM AUTHOR]

The DIGIT experiment was launched at the Tournemire Underground Research Laboratory URL with the aim of determining the effects of temperature on the transfer of analogues of most mobile radionuclides (i.e., 36Cl, 129I and 79Se) in the Toarcian clay rock, the properties of which are close to host rocks being considered for future deep geological disposal of high-level (HL) radioactive wastes. The experimental principle involves the monitoring of an exchange between a test water traced with stable halides and deuterium at constant concentration and the porewater of the Toarcian clay rock submitted to various temperatures. This experiment seeks to partially address questions regarding the potential spread of contaminants during the thermal phase of High Level Waste (HLW) waste packages. Specifically, the in situ experiment aims to evaluate the role of scale effects and thermodiffusion, a process that combines Fick's law and the Soret effect, in the transfer of radionuclides. This paper presents the first steps of the study, including the scoping calculations, the experimental set-up and the first results obtained during the unheated phase. The study started with the acquisition of the initial parameters, including the rock thermal properties, the concentrations of the four tracers (chloride, bromide, iodide and deuterium) naturally present in the clay porewater and their diffusive transport parameters by using four diffusion exchange techniques (phase 0). A model coupling heat and mass transfers was then developed using Comsol Multiphysics®, integrating data acquired so far with existing literature data. A test water with a tracer concentration around 1000 times higher than those in the pore water was proposed with a temperature imposed at the test section wall of 70 °C. A large test zone of 50 cm height and 1 m in diameter and installed in a 3 m deep vertical well located in a sound zone at the URL was then proposed. The installation of the experiments required the realization of one shaft and of nine peripheral boreholes for the monitoring of temperature, water pressure and deformation. The experiment started with phase 1, involving a traced, unheated water start-up for a period of 5 months. Then, a core sampling was conducted in the emptied well, and the same diffusion exchange techniques were applied. The results of anionic tracers were compared to simulations based on initial parameters (phase 0), revealing that tracer penetration at the end of phase 1 exceeded simulated values by approximately 2 cm. This result is interpreted as an increase in the accessible porosity to tracers, possibly due to the excavation damaged zone. Future simulations should incorporate these adjusted diffusive transport parameters. Following phase 1, the heating system was activated, applying a temperature of 70 °C to the test zone. New data will enable the comparison of tracer penetration and assess the actual impact of temperature on tracer transfer. [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]

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]

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]