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

The paper focuses on the use of holographic interferometry in the research of thermal modification and its effect on the heat transfer from the wood surface to the surrounding air. In the experiment, spruce wood samples modified at 160 °C, 180 °C, 200 °C, 220 °C and an unmodified control sample were used. A radiant heat source was placed under the sample. The top of the sample represented the boundary where the observed heat transfer occurred. The temperature fields above the sample were visualized by real-time holographic interferometry and the heat transfer coefficient α was calculated from the obtained interferograms. During the heating of the samples, a decrease of the heat transfer coefficient was observed. The heat transfer coefficient of the control unmodified sample decreased from a maximum of α = 22.66 Wm–2K–1 to a minimum of α = 8.6 Wm–2K–1. In comparison with these values, the heat transfer coefficients of the modified samples treated at 160, 180, 200 and 220 °C, respectively, decreased to 99%, 93%, 68% and 51% of the maximal control value at the beginning of experiment and to 95%, 86%, 80% and 64% of the minimal control value by the end of the experiment. Moreover, an analysis of variance was used to determine the significance of the heat treatment effect on the heat transfer coefficient. A high significance (p < 5%) was observed between the control sample and the modified samples treated at 200 °C and 220 °C. Experiments with the use of holographic interferometry produced results consistent with previous studies conducted by different methods. [ABSTRACT FROM AUTHOR]

Marquetry method is important in the culture of the Italian community as can be witnessed from the large quantity of artworks that have been realized in this way. The monitoring of the integrity of such pieces poses a great challenge given the need for a reliable and nondestructive technique able to detect surface and subsurface defects. In this work, two ancient marquetry samples containing natural defects were inspected thanks to active thermography by using time-tested, safe, and resilient advanced signal processing algorithms (i.e., principal component thermography, correlation contrast, pulsed phase Fourier transform amplitude and phase, cold image subtraction contrast, and polynomial fitting). The latter have been applied to provide a 2D map of the defects. Anyway, in the cultural heritage field, one of the main interests of restorers is the volume of the subsurface defects for structural analyses. The emphasis in this study is placed on the use of dynamic thermal tomography (DTT) as an advanced technique of active thermal nondestructive testing. The main concepts of DTT are illustrated in the manuscript, while a special technique for defect thermal characterization has been used during the second analysis to validate tomographic results. Finally, the position of the main defects retrieved by means of the established techniques applied during the first analysis has been confirmed by DTT. [ABSTRACT FROM AUTHOR]

Transient processes play a major role in geophysical applications. In this paper, we quantify the significant influence arising from transient processes for conductive heat transfer problems for sedimentary basin systems. We demonstrate how the thermal properties are affected when changing the system from a stationary to a non-stationary (transient) state and what impact time-dependent boundary conditions (as derived from paleoclimate information) have on the system's overall response. Furthermore, we emphasize the importance of the time-stepping approach adopted to numerically solve for the transient case and the overall simulation duration since both factors exert a direct influence on the sensitivities of the thermal properties. We employ global sensitivity analyses to quantify not only the impact arising from the thermal properties but also their parameter correlations. Furthermore, we showcase how the results of such sensitivity analysis can be used to gain further insights into the complex Central European Basin System in central and northern Europe. This computationally very demanding workflow becomes feasible through the construction of high-precision surrogate models based on the reduced basis (RB) method. [ABSTRACT FROM AUTHOR]

In this study, a RANS model of turbulent conjugate heat transfer has been developed, which is applicable across a range of different combination of fluid and solid thermal properties. This is achieved by focusing on the transport equations for the temperature variance and its dissipation rate across the solid walls which bound the flow region. In this investigation we make use of a wider range of DNS data reported by other researchers, to advance our understanding of the processes involved and to revise and extend the capabilities of the model of Craft et al [12] including a more physical fluid-solid interface condition on the dissipation of thermal fluctuations and a dependence of model coefficients on Prandtl number. The resulting model is shown to successfully reproduce the penetration of thermal fluctuations into solid regions, and their subsequent decay across the solid, for a wide range of fluid to solid thermal property ratios, and Prandtl numbers, thereby bringing a step change to RANS capabilities in turbulent conjugate heat transfer analysis. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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

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

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

This paper considers the artificial freezing of an argillite-like clay layer containing a NaCl salt solution in its pore space. The experimental results of the thermophysical properties of the clay with various salinities and water content in soil samples are presented. We determine the parameters of the soil freezing characteristic curves, the dependences of the specific heat capacity, and thermal conductivity based on temperature and salinity. These parameters are used in the formulation of a simple thermodynamic model for the artificial freezing of a clay layer with a single freezing pipe. The model includes diffusive transfer of heat and salt concentration, as well as salt precipitation when the eutectic point is reached. The motivation for using the simplified model is to understand the general patterns of soil freezing when considering the effect of salinity, as well as to test the proposed numerical finite-difference algorithm for solving the problem of freezing a clay layer based on the method of equivalent heat capacities. Using the algorithm, we analyzed the regularities of the redistribution of dissolved and precipitated salt in frozen soil, and also evaluated the effect of diffusive salt transfer on the numerical solution.

This study reports on combined thermal radiation, chemical reaction, and magnetic field effects on entropy generation in an unsteady nanofluid flow past an inclined cylinder using the Buongiorno model. We consider the impact of viscous dissipation, velocity slip conditions, thermal slip conditions, and the Brownian motion. The transport equations governing the flow are solved using an overlapping grid spectral collocation method. The results indicate that entropy generation is suppressed significantly by thermal radiation and chemical reaction parameters but enhanced with the magnetic field, viscous dissipation, the Brinkman number, and the Reynolds number. Also, fluid flow variables are affected by the thermophoresis parameter, the angle of cylinder inclination, and the Richardson number. We present the findings of the skin friction coefficient, the Nusselt number, and the Sherwood number. The model is applicable in fields such as the petroleum industry, building industries, and medicine. [ABSTRACT FROM AUTHOR]

Pellet heat transfer has always been one of the biggest limiting factors in its direct reduction process in the rotary hearth furnace (RHF). Therefore, strengthening its heat transfer process is very important for productivity in RHF. In this study, a coupling model of the carbon‐containing pellet reduction process considering porosity and chemical heat variation with intermediate media in its center was established. With the pellet radius R0 = 11 mm, the influence of the intermediate spherical medium radius r0, the offset position of the spherical medium ξ, and the materials used on the overall pellet reduction process were analyzed. The results showed that the presence of a spherical medium in the pellet center can increase the temperature inside the pellet, leading to it being more advantageous for reduction of the pellet. With the increase of the medium radius r0, it becomes more favorable for the pellet reduction process, as the spherical medium is more efficient for heat conduction. With the increase of the offset value ξ, the spherical medium acting as heat‐conducting material can allow the heat transferred to the pellet inside faster, which is also more favorable to the reduction process. In addition, when the spherical medium has a smaller effective volume heat capacity ρ∁p and a larger thermal conductivity k, it is more favorable for the pellet reduction process too. These results can serve as a reference for optimum pellet design in RHF. [ABSTRACT FROM AUTHOR]

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

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

The experimental study, thermal performance, and pressure drop of single-walled carbon nanotube (SWCNT) and graphene quantum dot (GQD) nanofluids in shell and tube heat exchanger with fin blade tubes are evaluated. The effects of the working fluid (water) volume flow rates (VÌ= 2.5-10 L/min), volume concentration of nanoparticles (Ï= 0.0%, 1%, 3%, and 5%), Reynolds number of working fluid (Re = 850-3300), and tube building (heat exchanger with fin blade tubes and without fin blade tube) have been analyzed. Results represent that with augmentation of volume concentration of SWCNT nanoparticle up to 1%, heat transfer rate increases by â5% and then up to 5% volume concentration of SWCNT nanoparticle decreased about 17%, also this calculation for GQD nanoparticle conducted and results represented decreasing 6% and approximately unchanged heat transfer rate, respectively. With regard to obtained results, heat transfer rate of heat exchanger can be improved by using the fin blades by 188%, compered without fin blade heat exchanger also most related increase for pressure drop of heat exchanger was recorded about 80% for 5% SWCNT of nanofluid. At the end, the mean enhancement in effectiveness of heat exchanger with various concentrations of SWCNT and GQD nanofluids and using the fin blades is about over 100% and 85%, respectively. In fact, the present study shows that applying the new finned tubes in the heat exchanger has more impact, related to the mentioned nanoparticles on the thermal properties of heat exchanger. [ABSTRACT FROM AUTHOR]

We present atomistic valence force field calculations of thermal transport in Si nanowires of diameters from 12 nm down to 1 nm. We show that as the diameter is reduced, the phonon density-of-states and transmission function acquire a finite value at low frequency, in contrast to approaching zero as in the bulk material. It turns out that this effect results in what Ziman described as the "problem of long longitudinal waves" [J. M. Ziman, Electrons and Phonons: The Theory of Transport Phenomena in Solids (Clarendon, Oxford, 1962)], which states that the thermal conductivity of a material increases as its length is increased due to the vanishing scattering for long-wavelength phonons. We show that this thermal transport improvement also appears in nanowires as their diameter is decreased below D = nm (not only as the length increases), originating from the increase in the density of the long wavevector modes. The observation is present under ballistic transport conditions, and further enhanced with the introduction of phonon-phonon scattering. Because of this, in such ultra-narrow nanowires, as the diameter is reduced, phonon transport is dominated more and more by lower energy phonons with longer mean-free paths. We show that ~80% of the heat is carried by phonons with energies less than 5 me V, most with mean-free paths of several hundreds of nanometers. [ABSTRACT FROM AUTHOR]

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

This paper is concerned with the measurement of thermal properties and in-cavity pressures in cold chamber high-pressure die casting. The influence of in-cavity pressure on the casting porosity, heat flux, and heat transfer coefficient has been investigated during die casting of an A380 alloy. The die was instrumented with heat transfer and pressure sensors to measure these values directly. Direct measurement of the in-cavity pressure was found to be more reliable than the metal pressure calculated from pressure measurements in the hydraulic system. Variations on the intensification pressure directly affect the in-cavity pressure. Changing the intensification pressure between 17 MPa and 90 MPa had little effect on the heat flux and heat transfer which likely reach saturation at a lower pressure during the rapid filling stages. Increases in intensification pressure reduced the level of porosity within the castings, being most effective up to a value of 67.4 MPa. [ABSTRACT FROM AUTHOR]

Cool-touch polyester knitted fabrics with excellent thermal-wet and cooling comfort ability are desired for summer and sports clothing. Jade nanoparticle content and twist of filaments have significant effects on comfort-related properties. In this work, the effects of jade content and twist level of two types of cross-section polyester filament on fabric comfort-related properties were investigated in detail. Filaments were prepared and further knitted to fabric samples. The physical performance of polyester filaments, the thermal-wet transfer properties and dynamic cooling property of their fabrics were measured and analyzed. It was found that the jade nanoparticles mainly affected thermal transfer property of fabrics, and the best thermal transfer was exhibited by fabric with 7% cool-touch PET chip. With the increase of twist level, air permeability, water spreading and drying performance improved but thermal transfer ability decreased, and lower twist level of yarns was beneficial for achieving real moisture cooling properties. These results showed a major advance in developing thermal-wet comfort knitted fabrics using cool-touch filaments with appropriate twist level. [ABSTRACT FROM AUTHOR]

In this work, we propose an experimental setup to measure the thermal conductivity and specific heat of a single suspended glass fiber, as well as the thermal contact resistance between two glass fibers. By using optical lithography, wet and dry etching and thin film deposition, we prepared suspended glass fibers that are coated by niobium nitride (NbN) thin film used as room temperature thermal transducer. By using the 3ω technique, the thermal conductivity of glass fiber was measured to be 1.1 W m-1 K-1 and specific heat 0.79 J g-1 K-1 around 300 K under vacuum conditions. By introducing exchange gas into the measurement chamber, influence of the gas on the heat transfer was studied, and the convection coefficient h for all the measurement ranges from a pressure of 0.01 hPa to 1000 hPa, over more than five orders of magnitude, has been obtained. By adding a bridging glass fiber on top of two other suspended glass fibers, it was possible to estimate the thermal contact resistance between two glass fibers Rc in the range of 107-108 K W-1. [ABSTRACT FROM AUTHOR]

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Thermal storage and transfer fluids have important applications in industrial, transportation, and domestic settings. Current thermal fluids have relatively low specific heats, often significantly below that of water. However, by introducing a thermochemical reaction to a base fluid, it is possible to enhance the fluid's thermal properties. In this work, density functional theory (DFT) is used to screen Diels–Alder reactions for use in aqueous thermal fluids. From an initial set of 52 reactions, four are identified with moderate aqueous solubility and predicted turning temperature near the liquid region of water. These reactions are selectively modified through 60 total functional group substitutions to produce novel reactions with improved solubility and thermal properties. Among the reactions generated by functional group substitution, seven have promising predicted thermal properties, significantly improving specific heat (by as much as 30.5%) and energy storage density (by as much as 4.9%) compared to pure water. [ABSTRACT FROM AUTHOR]

Material behaviour is often affected by the heterogeneities existing at the microscopic level. Especially the presence of cracks, voids, etc collectively known as defects, can play a major role in their overall response. Homogenization can be used to study the influence of these heterogeneities and also to estimate the effective properties of a given material. Several research works have been dedicated to determining the elastic behaviour of microcracked media. Yet, thermal properties are not investigated as much. Moreover, the question of unilateral effect (opening/closing of cracks) still remains an important issue. So, this paper aims to provide the effective thermal conductivity of 2D microcracked media with arbitrarily orientated cracks, either open or closed. With the help of Eshelby-like approach, homogenization schemes (dilute and Mori-Tanaka) and bounds (Ponte Castañeda-Willis) are developed to provide the closed-form expressions. In addition, these results are compared to numerical simulations performed based on finite element modelling. [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]

Applying lumped thermal model networks to interconnected electrical systems and fluids, in analogy with the electrical circuit methods, the system temperatures can be advantageously calculated in every node of the thermal networks with a complete system of equations, which considers the geometry, heating sources, fluid properties and material characteristics. In this paper, the lumped model parametrization for steady-state calculation is explained, and comparisons of the calculated results with the lumped model and with the computational fluid dynamic tools are presented. For example, the heat transfer is calculated here in the case of a) - heating of cooled hollow conductors and b) - heat exchangers of a water heating system. [ABSTRACT FROM AUTHOR]

Cardiac surgeries that involve cardiopulmonary bypass technique require a stable temperature maintenance for oxygenated blood or the cardioplegia solution. For this purpose, the heat exchangers are used. Nowadays, these exchangers consist of stainless steel tubes or bellows in a plastic shell. The blood is then warmed or cooled by water flowing in the shell around these structures. In the paper, the thermal specifications of two commercially used cardioplegia heat exchangers Capiox Cardioplegia and MYOtherm XP were evaluated and compared. For this purpose, a water was used as a substitution for blood. Both components were tested for varying flow rates in the pipes in the range 20-150 l/h and fixed flow rate 700 l/h in the shell. The thermal performances of both devices resulted similarly (up to 2.4 kW) at maximal flow rate. The performance factors for low flow rates approached values close to 0.98 and with increasing flow rate decreased down to 0.50. MYOtherm XP shows lower pressure drop than Capiox Cardioplegia due to more optimal construction. The major difference between the heat exchangers was observed in overall heat transfer coefficients at maximal flow rate and resulted in 2191.3 W/m²K or 1760.2 W/m²K for MYOtherm XP or Capiox Cardioplegia, respectively. [ABSTRACT FROM AUTHOR]

In order to predict the thermal insulation performance of coated carbon fiber fabric, a numerical heat transfer model under high temperature was established. The simulation results were validated by quartz lamp ablation experiment. The experimental values were in agreement with the numerical values, and the average relative error between them was 9.47%. Furthermore, the impact of structural parameters on the thermal insulation of coated carbon fiber fabrics, by using the numerical heat transfer model, was investigated. The results show that thermal insulation for the samples is in the order of plain < 2/1 twill < 3/3 twill < 5/3 stain, when using constant structure density and yarn fineness. Thermal insulation performance of the samples dramatically increases as yarn fineness goes from 3 to 12 K. Furthermore, when the structure density increases to more than 70 ends/10 cm, the thermal insulation property shows an increasing trend. [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]

We analyze the operation of melting probes as a Stefan problem for the liquid/solid interface surrounding the probe. We assume that the liquid layer is thin and, therefore, amenable to analysis by the lubrication theory. The resulting Stefan problem is solvable in the closed form. The solution determines the dependence of the penetration speed on the temperature differential between the probe and the surrounding ice, the size, shape and weight of the probe, the viscosity of liquid water and the thermal properties of solid ice. [ABSTRACT FROM AUTHOR]

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

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

As the size of materials, particles, and devices shrinks to nanometer, atomic, or even quantum scale, it is more challenging to characterize their thermal properties reliably. Scanning thermal microscopy (SThM) is an emerging method to obtain local thermal information by controlling and monitoring probe–sample thermal exchange processes. In this review, key experimental and theoretical components of the SThM system are discussed, including thermal probes and experimental methods, heat transfer mechanisms, calibration strategies, thermal exchange resistance, and effective heat transfer coefficients. Additionally, recent applications of SThM to novel materials and devices are reviewed, with emphasis on thermoelectric, biological, phase change, and 2D materials. [ABSTRACT FROM AUTHOR]

Experimental investigations on heat transfer of RP-3 kerosene at supercritical pressures are conducted in this paper. It is found that there are three regimes, namely common heat transfer, enhanced heat transfer and deteriorated heat transfer. Variations of thermal properties are responsible for common heat transfer. Turbulence is the main reason for enhanced heat transfer. Cracking reactions are attributed to deteriorated heat transfer. Parametric studies show that heat flux has little effects on heat transfer of RP-3 at supercritical pressures while mass flow rate plays a positive role. Influence of pressure is complicated, related to thermal property variations. A new correlation for heat transfer of RP-3 flowing in miniature tube at supercritical pressure is proposed. [ABSTRACT FROM AUTHOR]

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

Agitated drying of pharmaceuticals remains a challenging manufacturing step due to the simultaneous heat transfer, mass transfer, and physicochemical changes occurring during the process. This work focuses on the heat transfer component by implementing the discrete element method to model dry particles in a heated bladed mixer. Simulations varying material conductivities and impeller agitation rates were conducted to evaluate the influence on the mean bed temperature and distribution.The results indicated that increasing the agitation rate generally improved heat trans-fer up until a critical agitation rate where the rate of heat transfer plateaued. The magnitude of this improvement in heat transfer depended on the material's thermal properties. We observed three regimes: a conduction-dominated regime where particles heated quickly but with an annular temperature gradient, a granular convection-dominated regime where particles heated slowly but uniformly, and an intermediate regime. The results were nondimensionalized to enable predictions and help inform drying protocols. [ABSTRACT FROM AUTHOR]

In this work, graphene/nature rubber (GE/NR) composites with filler content from 0 wt% to 1 wt% were prepared by an in situ reduction process. Thermal properties of the nanocomposites were studied by thermogravimetric (TG) analysis and thermogravimetric difference (ΔTG). Composites with higher GE content evidenced stronger thermal stability-enhancing effect. Kinetic analysis showed that the activation energies ( E a ) during degradation of composites were always higher than pure NR. However, E a reached its maximum at 0.1 wt% GE content and started to decrease with further increase in GE loading. The changes in the thermal properties were attributed to the chemical structure and heat transfer properties of graphene sheets. [ABSTRACT FROM AUTHOR]

In this article, pressure drop and thermal characteristic of the staggered strip fin (SSF) microchannel were investigated by using the simulation method. In recent decades, the pressure drop and thermal properties of many fins with different geometries were studied. However, the SSF has a high heat transfer coefficient (HTC) and the highest heat conductance at uniform pumping power. We believe that SSF can be widely used in IC cooling, so it was studied systematically in this article. First, the feasibility of simulation method was verified with the experimental results in a reference. Then, the design of experiment (DOE) was performed to investigate the effect of fin configuration on the pressure drop between the inlet and the outlet of microchannel and the thermal resistance between the base and inlet of microchannel. The results show that the pressure drop is decreased by about 200%, and the thermal resistance is increased by about 100% with channel pitch increased by two times. The ratio of fin width to channel width increased from 0.5 to 1.5, resulting in an increase in pressure drop of about 200% and no significant change in thermal resistance. There is no obvious change in pressure drop and thermal resistance when the fin length and end angle are increased. Finally, the formulas for predicting pressure drop and convective HTC (CHTC) were fit by 220 sets of simulation results, and the formula for predicting thermal resistance was deduced by theory. In addition, the validity of prediction formulas was verified, and the application range of the formula was studied preliminarily. [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]

Lattice materials provide unusual thermal and vibrational properties but not within the same structure. Thermal and vibrational multifunctionality is, however, crucial for thermomechanical applications such as automotive, aerospace, building, transportation, and energy infrastructure. In applications involving mobility, both high heat transfer and low mass are desired. Although there have been various efforts to design multifunctional lattice materials, the focus has largely remained on quasi‐static mechanical and thermal properties or mechanical and vibrational properties. Herein, designs of realizable lattice materials are reported, which are inherently thermally resistive, with vastly improved thermal conductance and omnidirectional phononic band gaps. By redesigning the truss structures to serve as interconnected heat pipes, a three‐order‐of‐magnitude improvement in the specific thermal conductance is found. Nodal masses at truss junctions are further used to obtain full vibrational band gaps. It is shown that it is possible to independently tune vibrational and thermal properties within the same structure. This work provides background for the design and fabrication of multifunctional lattice materials that simultaneously prevent structural vibrations and enhance heat conduction. [ABSTRACT FROM AUTHOR]

In this experimental study mainly focused the thermal property such as thermal resistance and heat transfer analysis for the air gap variations provided in between two glasses on window for the domestic purposes. Easily available surrounding air considered as the experimental mater because of its arrangements. Thermal resistance of inside, outside and glasses (both glasses have same thermal conductivity such as 0.78 W/mK) all are maintained as constant throughout the investigation. But only air gap distance increased from 2 mm to 14 mm with gradual increase focused. The thermal conductivity of air considered as 0.026 W/mK. Thermal resistance and heat transfer impact with respect to the air gap between glasses were identify with the help of graphical representations. [ABSTRACT FROM AUTHOR]

In this work, the convection heat transfer and pressure drop of the turbulent flow for a non-Newtonian fluid containing nanoporous graphene were investigated in baffled heated annulus tube by considering the inner tube under constant heat flux. The solution of 0.2 mass% carboxymethyl cellulose (CMC) in DI water was used as the base non-Newtonian fluid. The rheological properties of the nanofluid (0.2 mass% nanoporous graphene, 0.2 mass% CMC and DI water) were measured through an experimental setup. By measuring the thermophysical and rheological properties at several temperatures, the temperature-dependent equations were calculated by a least square approximation method. By using the extracted equations and adding the nanoporous graphene to the base fluid in the annulus, the thermal performance was numerically investigated. Furthermore, the effects of the geometry and perforated baffles number at the various Reynolds numbers were studied. According to the results, the nanoporous graphene had a significant effect on the average Nusselt number and pressure drop which were increased by up to 32 and 75%, respectively, compared to the base fluid. It was also predicted that in the annular tubes possessing three and seven baffles with four holes (Re = 4000 and H = 4 mm), applying nanoporous graphene can improve the efficiency of the system up to 11.9%. [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]

The graphene-based additives containing polyethyleneimine (PEI) or hydroxyapatite (HAP) were synthesized and their effects on the flame retardancy, thermal, mechanical properties of polyvinyl alcohol (PVA) matrix were evaluated. Thermogravimetric analysis studies (TGA) and Scanning electron microscope (SEM) images were indicated that PEI and HAP have a strong influence on the fire behavior of the composites which might be explained by the forming of a uniform and compact char during combustion. The presence of nitrogen in PEI and phosphorus in HAP which are generated nonflammable gases and phosphoric radicals, respectively at combustion conditions could represent a significant role in the catalytic char residue formation, heat transfer limitation and then diminish or even stop the combustion reactions. The char yields of the 5 wt% PVA/GO-PEI nanocomposites were increased up to 22 folds without any significant change in mechanical properties; Moreover, the char yield of PVA/GO-HAP nanocomposites was more than pure PVA (24 folds) because of its thermal stability at high temperature. All these data demonstrated that not only did PVA/GO-PEI keep the mechanical properties nearly the same as in pure PVA but also improved flame retardancy. But, the PVA/GO-HAP has great potential as flame retardants between all obtained composites. [ABSTRACT FROM AUTHOR]