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

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

Low-melting-point alloy has the characteristics of high thermal conductivity, low solidus temperature and the wide range of use temperature, which is a potential heat transfer medium. The microstructure and thermal properties of Sn–Bi–Pb–Zn alloys as heat transfer and storage material were investigated in this paper. The phase compositions, microstructure and thermal properties were investigated by X-ray diffusion (XRD), electron probe microanalysis (EPMA) and differential scanning calorimeter (DSC) analysis, respectively. The results show that the phases of Sn–Bi–Zn and Sn–Pb–Zn alloys are mainly eutectic formed by solid solution, while the formation of Pb7Bi3 intermetallic compounds decreases the melting point of Sn–Bi–Pb and Bi–Pb–Zn. The thermal properties of the zinc-containing alloys are better than that of Sn–Bi–Pb, but the weight of the zinc-containing alloys significantly reduces above 900 °C. As the density, specific heat capacity and thermal diffusivity change with temperature and physical state, the thermal conductivity of the alloys first decreases and then increases. These results demonstrate the feasibility of using low-melting alloys as the heat transfer and storage material. [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]

This study aimed at optimizing the injection molding process of an automotive oil filter housing made from PA6.6. Mass accumulations in its design intensely increased the cooling time. In a first successful approach, a copper alloy mold insert (λ = 106 Wm−1 K−1) that contains two externally cooled heat‐conducting copper pins (λ = 310 Wm−1 K−1) was installed. We hypothesized that a biomimetic cooling channel structure in a steel mold insert would even perform superior. Using simulation software Sigmasoft® v5.0, the mold insert materials (steel Bohler X20Cr13, Ampcoloy® 83), the plastics grade PA66‐GF35 (λ = 0.27 Wm−1 K−1 or λ = 0.40 Wm−1 K−1), and three cooling designs were evaluated for their impact on cooling the hot spots in the part: the copper pin‐system, a conformal cooling channel, and blood‐vessel like channels. In the latter, the major artery branches into two sub‐arteries, which further divide into two capillary tubes each. The capillaries merge into two sub‐veins and those fuse in the major vein again. As expected, the plastics heat conductivity dominates the cooling. The biomimetic (blood‐vessel) channels, as hypothesized, cooled the major hot spot more efficient than the conformal channel and the copper pin system do. In detail, compared to the heat‐conductive insert, the cycle time may be reduced by 10 s, in spite of the lower heat conductivity λ (23.5 Wm−1 K−1) of the steel insert. Using the biomimetic (blood‐vessel) structure in a heat‐conductive mold insert would reduce the cycle time by a further second. However, raising the heat conductivity of the plastics would save another 15s. Experimental tests proved the cooling efficiency. Nevertheless, cooling channels only perform well, if they are close enough to the mass accumulation. In conclusion, transferring biologic cooling structures to injection molding seems to be promising. Ongoing advances in Additive Manufacturing will help to efficiently implement these structures into mold inserts for injection molding. POLYM. ENG. SCI., 59:E180–E188, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers. [ABSTRACT FROM AUTHOR]

• The effective measurement temperature of fingertip sensing has been derived. • This may serve as a guideline for iso thermal thermal effusivity measurements. • Doing them yet at room temperature causes <7% bias for airy materials, like textile. • Fingertip mimicking methods deviate <19% from fingertip sensing for airy materials. Thermoreceptors in the fingertips sense the temperature drop upon contact with an object and in that way its thermal effusivity. But, at which effective object temperature? That is the question that this article answers by perturbation analysis for slightly temperature dependent thermal properties. How much deviate thermal effusivity measurements at room temperature from fingertip measurements at said effective object temperature? This question is also answered by perturbation analysis. The bias may be up to 7% using nearly isothermal measurement methods and up to around 19% using fingertip-mimicking measurement methods for airy materials like wool. Rewriting the temperature model reveals a felt delay and its dependency on the thermal contact resistance between fingertip and object. [ABSTRACT FROM AUTHOR]

Highlights • The blade tip and casing heat transfer characteristics were investigated with cavity and winglet cavity tips. • The cooling effects of the blade tip and casing coolant injection are investigated. • The blade tip and casing thermal performance are discussed under three cooling types. Abstract The heat transfer and film cooling effects of cavity tip and winglet-cavity tip have been numerically investigated with blade tip and casing coolant injection with a turbine cascade exit Ma number 0.96. The film-cooling effectiveness, heat transfer coefficient and net heat flux reduction ratio of blade tip and casing at relative tip clearance of 0.8% blade span are compared with blade tip cooling, casing purge cooling and the combination of these two cooling types. The validations and verifications of the numerical methods are performed by contrasting with the experimental results. The results show that the winglet-cavity tip alters the tip leakage flow and affects the heat transfer of blade tip compared to the cavity tip. For these two blade tip types, the blade tip cooling reduces the heat load of blade tip effectively, while it has little cooling effects on the casing. The casing purge cooling obtains high film-cooling effectiveness of the blade tip and the casing at the same time. However, it has no influence on the heat transfer of the pressure side near the tip region and the pressure-side rim. Adopting the blade tip and casing coolant injection simultaneously can further reduce the heat load and improve the film-cooling effectiveness of the blade tip and casing. [ABSTRACT FROM AUTHOR]

Highlights • Single phase flow heat transfer measurement in a vertical channel filled with metal-foams. • Characteristics of fluid flow and heat transfer of R245fa in a hot-water-driven test facility. • Foams made of copper and nickel were compared. • Correlations developed for average heat transfer coefficient and pressure drop. Abstract High-porosity open-cell metal foams made of copper and nickel were inserted into a rectangular channel containing R245fa refrigerant with mass flux ranging from 76 to 391 kg/m2 s. The single-phase heat transfer from the surrounding channels is driven by hot water in a closed cycle and ranges from 0.53 to 1.37 kW. The heat transfer and pressure drop across the embedded metal-foam samples were measured while maintaining constant conditions of the refrigerant inlet pressure and hot water supply. The heat transfer coefficient was calculated based on a modified Wilson-plot method. The results were compared with published correlations, and new correlations are proposed to take into account the characteristics of the foam geometry and material. In addition, three parameters are introduced to compare different types of metal foam samples. The results of the experiment show that the metal-foam-filled channel increases the Colburn j -factor by up to 6.3 times compared to an empty channel. As a result, the metal foams with higher pore density and higher thermal conductivity perform better than other samples in single-phase flow. [ABSTRACT FROM AUTHOR]

Highlights • Filmwise condensation on surfaces with sinusoidal pin fin array was investigated. • Nine surfaces of different fin heights and pitches were fabricated by SLM. • The effects of fin height and pitch on heat transfer coefficient were determined. • New condensate flooding characteristics on sinusoidal pin fin were observed. • The highest thermal enhancement factor of 1.86 was achieved. Abstract An experimental investigation on the use of sinusoidal pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with pin fin arrays were fabricated by Selective Laser Melting (SLM) and tested in a condensation chamber. The pin fin arrays have the same fin base diameter (d b) but are of different fin heights (l) and fin pitches (p). At the same fin pitch (p = 1.25 mm and 1.67 mm), the heat flux ( q ″ ) and condensation heat transfer coefficient (h) increase as l increases from 1.25 mm to 1.66 mm. However, with further increment in l from 1.66 mm to 2.49 mm, reductions in q ″ and h were observed. At the same fin heights of l = 1.25 mm and 1.66 mm, an increase in p from 1.25 mm to 1.67 mm has negligible effects on q ″ and h. However, with further increment in p from 1.67 mm to 2.50 mm, significant reductions in q ″ and h were observed. Visualization studies of the static condensate retention height (H ave) show that two distinct flooding regions can be identified for sinusoidal pin fin surfaces. The static condensate retention height of both regions decreases with increasing p but remains unchanged with varying l. A fin analysis was performed to determine the average heat transfer coefficients (h t) which considers the total heat transfer areas (A t) of the enhanced surfaces. Our results show that the highest thermal enhancement factor (η) of 1.86 is achieved with Specimens S 4 and S 5 whereas Specimens S 3 has the highest average heat transfer coefficient (h t). In comparison with cylindrical pin fin surfaces, the sinusoidal pin fin surfaces show better heat transfer performances at the same p / l ratio. [ABSTRACT FROM AUTHOR]

Highlights • Two tree-like channel networks with different size constraints are studied. • Hydraulic and thermal performances of two tree-like channel networks are compared. • A segmenting model is given to distinguish the network with better performances. Abstract The present work investigates and compares the hydraulic and thermal performances of two tree-like networks with constant surface area constraint and constant volume constraint. The results find that the optimal channel diameter ratio to reach a minimum hydraulic resistance satisfies β m = N −2/5 for the tree-like network with surface area constraint, but β m = N −1/3 for the tree-like network with volume constraint. The convective heat transfer in both of the two tree-like networks with different size constraints is independent on the channel diameter and diameter ratio, but increases with the increasing channel length, channel length ratio, branching level and branching number. For the two tree-like networks with exactly the same channel length, length ratio, branching number and branching level but different channel diameter, the present work provides a segmenting model to choose the network with better hydraulic and thermal performances. [ABSTRACT FROM AUTHOR]

Highlights • Unsteady one-dimensional heat conduction. • Simple solid objects: plate, cylinder and sphere. • Prescribed uniform temperature boundary condition. • Exact, analytical temperature distributions expressed with infinite series for all time. • Plain correlation asymptotes for the center temperature, mean temperature and total heat transfer at small time. Abstract Within the platform of unsteady, one-dimensional heat conduction in simple solid objects (large plate, long cylinder and sphere) cooled/heated with uniform surface temperature, the three important thermal quantities that need to be quantified are: the center temperature, the mean temperature and the total heat transfer. One objective of the study is the accurate determination of new dimensionless critical times for the mean and center temperatures that describe the large time sub-domain using a symbolic algebra software. Another objective of the study is to use regression analysis to construct plain correlation asymptotes for the center temperature, the mean temperature and the total heat transfer in the small time sub-domain using as input data the exact, analytical temperature distributions for the plate, cylinder and sphere expressed by infinite series for all time. Excellent agreement for the center temperature, mean temperature and total heat transfer are achieved in the small time sub-domain using the two different computational procedures. [ABSTRACT FROM AUTHOR]

Highlights • Melting performances for a horizontal LHTES unit with different fins arrangements are evaluated. • The relation between fins arrangement and complete melting time of PCM under different parameters are revealed. • An optimum fins arrangement is recommended to accelerate melting. Abstract Embedded fin in phase change materials (PCMs) is one of the most efficient methods to enhance the heat transfer between the PCM and heat transfer fluid (HTF). An appropriate arrangement of the fins plays significant role to design a highly efficient latent heat thermal energy storage (LHTES) unit. The aim of this study is to find the most efficient arrangement of fins to accelerate the charging rate. A two-dimensional numerical model based on finite volume method (FVM) was developed with considering natural convection and the calculation results were validated with experimental data. The heat transfer characteristics of LHTES unit with different fins arrangements were firstly explored. These include no fins, straight fins, angled fins, lower fins and upper fins. Then, the effects of fins number (N), dimensionless fins length (l), heat transfer fluid temperature (T w) and outer tube material on melting performance for four arrangements were studied. In addition, the best type of arrangements to increase the efficiency of heat exchanger was suggested. The performance enhancement of LHTES through fins configuration were quantitatively described based on complete melting time and heat storage capacity, and the conclusions are arrived as follows: when N ≤ 6, the optimum arrangement is the lower fins, while it is the angled fins when N > 6. For N = 6, only l could change the optimum arrangement of fins. At l equals 0.5 and 0.95, the optimum arrangement is angled case. While at l = 0.75, the optimum arrangement is lower case. It is also found that the heat storage capacity of lower fins configuration is minimal compared to other three configurations. [ABSTRACT FROM AUTHOR]

Highlights • Regularly spaced twin and triple WCs with a TCT were simultaneously employed to give heat transfer enhancement. • Effect of geometric arrangements on thermal-hydraulic-thermodynamic performances were investigated. • Heat transfer rate increases as WC number increases and space ratio decreases. • Nusselt number and friction factor correlations were developed. Abstract Thermal-hydraulic behaviors of air turbulent flow in a traverse corrugated tube (TCT) inserted with twin and triple wire coils (WCs) were investigated experimentally. The effects of two different arrangements (twin WCs and triple WCs) and four space ratios (S / D = 0, 3.88, 8.62 and 18.1) on Nusselt number (Nu), friction factor (f), performance evaluation criterion (PEC), Bejan number (Be) and augmented entropy generation number ( ϕ s ) were investigated at Reynolds number (Re) ranging from 6000 to 18,000. The gained results point out that the compound use of TCT with WCs gives considerably enhanced heat transfer and also increased pressure loss than the plain tube with improved Nu ratios in the range of 1.74–2.61 and augmented f ratios in the range of 4.57–21.34. By analyzing different parameters, it is found that Nu and f in the TCT mounted with WCs increases with WC number increasing and space ratio decreasing. Although the co-use of TCT with WCs exhibits superior Nu than the alone use of the TCT, the former performs higher flow resistance and lower PEC than the latter. The increased heat transfer of about 22.3–84.2% and augmented pressure loss of around 2.91–12.90 times over that of the TCT are obtained for the combined use of TCT with WCs. The largest PEC of about 1.09 is achieved in the TCT with twin WCs at S / D = 18.1 while that is about 1.26 for the TCT alone. In terms of thermodynamic characteristics, both the TCT alone and the co-use of TCT with multiple WCs can reduce the contribution of heat transfer entropy generation to the overall entropy generation, and the Be could be decreased to values of about 0.91 and 0.32 by the former and the latter, respectively. In addition, the obtained results show that the lowest ϕ s of about 0.46 is gained by the TCT with triple WCs at S / D = 0 and Re = 6428 in this study scope. Finally, the Nu and f empirical correlations within respectively ±9.0% and ±11.0% from experimental data are installed. [ABSTRACT FROM AUTHOR]

Highlights • The concept of using customary micro-channel heat-sinks is reviewed. • Thermal performance of the circular perforation heat sinks compared to other shapes. • Flow pulsation and thermal performance are most addressed schemes. • An innovative development is use of phase- change materials (PCMs). • More research is required to focus on influence of by-pass flow regime on heat sink performance. Abstract With the prologue of new components with more and more heat dissipation, urge for novel heat sink philosophy is becoming a real challenge in today's world. The new solutions should be able to cope with massive heat emanation while keeping the space and cost constraints. Finned (plate and pin) heat sinks are contrivance to these challenges with growing applications in present-day engineering arena and drawing the concentration of researchers. Paper deals with the critical review of different heat sink designs, limiting factors, effectiveness, limitations of various techniques and recent advancements in the field of innovative heat sinks. This study initiates with brief and comprehensive discussion regarding importance of heat sinks, its methodology; it's suitability for present day heat dissipation issues, statistical data of various heat sink designs and a rich discussion of the work so far. The sole aspiration for this article is digging out the literature available so far with emphasis on experimental techniques and to propose strategy for future research. The outcome of the research will validate the concept of improved heat transfer approach, provide useful data for innovative design and help better understand the cooling capabilities of the pin fin technology. [ABSTRACT FROM AUTHOR]

Abstract The topological optimization of composite structures is widely used while tailoring materials to achieve the required engineering physical properties. In this paper, the problem of topological optimization of the microstructure of a composite aimed at the construction of a material with most effective values of the bulk modulus of elasticity and thermal conductivity taking into account competing mechanical and thermal properties of the materials included in the composite is defined and solved. A two-phase composite consists of two base materials, one of which has a higher Young modulus but lower thermal conductivity, while the other has a lower Young modulus but higher thermal conductivity. A new class of problems for composites containing material pores or technological inclusions of different shapes is considered. Effective thermoelastic properties are obtained using the asymptotic homogenization method. A modified solid isotropic material with penalization (SIMP) model is used to regularize the problem. The problem of the isoperimetric constraints is solved by the method of moving asymptotes (MMA). The influence on optimal topology of the composite in the presence of two competing materials, and optimality criteria using linear weight functions are investigated. Pareto spaces that provide deep understanding of how these goals compete in achieving optimal topology are constructed. [ABSTRACT FROM AUTHOR]

Abstract Material testing for plasma facing components (PFCs) in future fusion devices reveals important damage mechanisms that impact lifetime and performance. During operation, PFCs in the divertor region will be subjected to high particle fluxes and heat loads. Tungsten (W) is currently the leading candidate material for divertor PFCs, due to its high melting point, high thermal conductivity, and low tritium retention. Laboratory experiments have effectively characterized mechanisms of damage on W due to different forms of radiation. However, understanding how different species of incident plasma particles interact with one another to affect the resultant strength of the material remains in development. In this study, W samples were exposed to simultaneous ELM-like heat loading and high-flux He+ and D+ ion irradiation at different ELM intensities to further elucidate the complex synergistic effects inherent in a fusion environment. ELM-like heat loading was replicated using a 1064 nm Nd:YAG pulsed millisecond laser at different energy densities. Exposures produced a shale-like microstructure with or without concurrent He+ and D+ ion irradiation. However, adding D+ to a simultaneous laser + He+ irradiation reduced pore formation and inhibited early-stage nanostructure formation. Changes in surface morphology with the addition of D+ could be attributed to super-saturation in the near-surface layer. While the addition of He+ and D+ clearly increased W erosion, the laser energy density did not have as clear of an effect. Increasing the ELM intensity reduced the number of pores, but increased the pore size. Future studies need to explore whether near-surface D impacts pore formation and total He desorption. Continued research on the combined effect of high-flux particle irradiation and transient heat loading will help refine predictions of material performance for ITER and beyond. [ABSTRACT FROM AUTHOR]

Highlights • Thermal conductivity of nanofluids is enhanced by mixing two different nanoparticles. • Critical heat flux for hybrid nanofluids in pool boiling is investigated. • Effect of nanoparticle deposition on heat transfer coefficient is explored. Abstract Boiling is a process with maximum heat transfer coefficient (HTC) and heat transfer rate. Researchers are working with techniques such as surface modifications and nanoparticle suspensions in base fluids to enhance the thermal performance. The present work focuses on the enhancement of thermal properties and critical heat flux (CHF) by mixing two different nanoparticles viz., alumina and copper oxide at various concentrations in Deionized (DI) water. Volume concentrations of 0.01 - 0.1% are prepared and the stability of nanofluids is confirmed by Zeta potential. Thermal conductivity of hybrid nanofluids is enhanced by 15.72% for 0.1% concentration at room temperature compared with DI water. CHF of hybrid nanofluids is always higher than single type nanofluid. Maximum enhancement of 49.84% in CHF is obtained for 0.1% concentration. HTC is enhanced by 7.1 and 6.72% for 0.01 and 0.03% volume concentrations than DI water and starts decreasing with increasing volume concentrations. [ABSTRACT FROM AUTHOR]

Highlights • Thermal conductivity model for nanoparticle packed bed is established with nanoparticle deformation considered. • Our model give good prediction at 0.3 ≤ φ ≤ 0.9, while EMA model predicting well at φ ≥ 0.75. • R cd dominates R at 0.75 ≤ φ ≤ 0.9, while R cb preponderates at 0.3 ≤ φ ≤ 0.75. • The overestimation of k e by EMA model at 0.3 ≤ φ ≤ 0.75 arrives from the ignored R cb. Abstract Theoretically understanding the thermal conductivity of the nanoparticle packed beds (NPBs) is critical for designing high-performance thermal insulation materials. Currently, the classical effective medium assumption (EMA) model, Nan model, just show their good prediction at a high porosity of NPBs (≥0.75). Herein, we propose a generalized model of the thermal conductivity that almost covers the whole porosity range by considering the effect of the nanoparticle deformations on the thermal contact resistance (R). It has been demonstrated that our model matches the experimental results great well. It is also found that at high porosity R is dominated by the phonon diffusive scatterings ( R cd ), while it is determined by the phonon ballistic scatterings ( R cb ) at a low porosity. More interestingly, R can determine the porosity at which the lowest thermal conductivity of NPBs appears. This work opens a new way to design the desired thermal insulation materials. [ABSTRACT FROM AUTHOR]

Socks are prevented against wrinkle formation by preheat setting in greige form prior to wet processing. The current study is proposed to analyze the effect of socks presetting process on thermopysiological and wicking properties of comfort. In this analysis, main yarn linear density, plaiting yarn composition and number of needles are taken as variable on same machine setting. Sock samples were analyzed for comfort parameters (thermal conductivity, thermal resistivity, thermal absorptivity, thermal diffusivity, relative water vapor permeability (RWVP (%)), evaporation resistance (Ret), air permeability, vertical wicking, absorbency and color strength (K/S) value) after various processes (preheat setting, dyeing and postheat setting). The statistical analysis showed that preheat set process significantly affects vertical wicking, K/S value, absorbency, thermal conductivity, thermal resistivity and thermal diffusivity, respectively. While thermal absorptivity, air permeability, porosity, RWVP (%) and Ret couldn't show a significant impact. [ABSTRACT FROM AUTHOR]

Highlights • An inverse heat transfer model linked to Bayesian statistics is presented. • This model is used to identify the conductivity and volumetric heat capacity. • In situ measurements are used by the inverse model. • The proposed model can use shorter time series than the standard ISO 9869. • The proposed model produces more accurate and robust results compared to the standard. Abstract Non-destructive thermal diagnosis is necessary for identification and quantification of structural defects and verification of construction performances. In this paper, we test different inverse heat transfer models to identify the thermal conductivity of a building's wall in its environment. The approaches proposed and used in this paper rely only on non-intrusive measurements: inside and outside wall surface temperatures and heat flow through the wall. First, a Bayesian statistical dynamic inference method, which has the advantage to quantify the unknown parameter and its credible interval, is presented. This method considers the uncertainties of the measured temperature and heat flow data and of the unknown thermal properties. Markov chain Monte Carlo (MCMC) algorithm is used to explore the posterior distribution. Then, the average and the dynamic procedures ISO 9869 (I. 9869-1, 2014) are introduced. Finally, the probabilistic distributions of the unknown parameters are presented and compared to the standard results. The impact of experimental conditions (average indoor-to-outdoor temperature) and the measurements length on the accuracy of the results are discussed. The relationship between the number of iterations of the MCMC , time series length, shape of the prior distribution and accuracy are studied as well as the simulation time to run the inverse models. The Bayesian approach gives the most accurate results and has the advantage of considering several unknowns (conductivity and volumetric heat capacity), which is not the case for the studied standard. The Bayesian method needs much shorter time series than the ISO standard and produces robust results at all times of year, including when the average indoor-to-outdoor temperature difference was low. [ABSTRACT FROM AUTHOR]

The filling and curing stage of resin transfer molding is non-isothermal. The temperature plays an important role in both filling and curing stage and these two stages are strongly interrelated. The unreasonable temperature system will lead to excessive temperature difference and seriously affect the quality of the product. Therefore, it is necessary to analyze the non-isothermal filling and curing stage to find the best temperature system. In this paper, the FLUENT software has been secondarily developed to perform a full three-dimensional simulation of the non-isothermal resin transfer molding process cycle. The results have been compared with the known data to verify the accuracy of the simulation. The influence of temperature on the process cycle has been analyzed and the optimization of temperature system can reduce process cycle time and increase the uniformity of temperature distribution. [ABSTRACT FROM AUTHOR]

Thermal grease is widely used as a method of enhancing thermal conductivity by mixing polymer and high conductivity materials such as alumina and copper powder. In this case, the polymer undergoes deformation due to crystallization, thermosetting, thermoplastic, glass transition depending on the temperature. Therefore, when used in extreme environments, the physical properties and state changes should be investigated. In this paper, the thermal resistance of the thermal grease is measured in-situ from -90°C to end of thermally stable temperature. Materials are prepared by mixing polydimethylsiloxane and aluminum oxide, which is the most representative thermal grease. The silicone grease is prepared with a sandwich structure between two copper for the measurements. The laser flash method is used to determine the thermal conductivity of silicone grease using three layers model. As a whole temperature range, the decrease in thermal conductivity of thermal grease is explained by the breakage of the polymer chain and the increase in distance between the filler materials due to thermal expansion. As a result, the total thermal resistance, which increases with ascending temperature, is influenced by the thermal conductivity of silicone grease. On the other hand, the effect of temperature-dependent changes in thermal contact resistance appears to be insignificant. [ABSTRACT FROM AUTHOR]

The coefficient of linear thermal expansion is a basic physical quantity of interest in many industrial applications. In particular, in order to properly use data in the design phase of a product, accurate thermal expansion of a material should be obtained in a certain temperature range. Correction of the measuring equipment is required to obtain a high accuracy; reference specimens are used for the correction. The reference specimen should have the same properties and length as the test specimen. However, reference materials with a similar structure and length identical to the test specimen are not easily available. Therefore, the effect of the specimen length on the thermal expansion is investigated in this study. Measurement results show that the length of the reference specimen has a different effect on the measured value depending on the specimen type. [ABSTRACT FROM AUTHOR]

Adding solid particles of nanometer scale to fluids is one of the most important passive methods of enhancing heat transfer performance. However, this gives numerous chances to investigate new frontiers, but also raises remarkable difficulties. Nanofluids act as suspension that can be obtained by dispersing nanometer-sized nanoparticles (1-100nm) in host fluids with the aim of enhancing thermal properties. This paper is a review of recent studies on boiling heat transfer of nanofluids for pool and convective flow boiling of nanofluids. The research results, collected since 2012 to present of the recent survey are reviewed and briefly outlined. An emphasis is put on the enhancement and the deterioration of the boiling heat transfer coefficient and critical heat flux of pool and convective flow boiling of nanofluids. Other important parameters affecting the boiling of nanofluids are identified and discussed in this review. While preparing future studies is greatly encouraged in order make this phenomenon well understood. [ABSTRACT FROM AUTHOR]

Experiment and numerical analyses were conducted to study the thermal performance and circulation characteristic of the working fluid of a T-shaped vapor chamber special designed for the motorcycle LED light. The influences of heat loads and cooling magnitude were experimentally investigated. Results show that both the heat loads and cooling conditions have strong influences on the thermal performance of the vapor chamber, and the thermal resistance in the extended section occupies over 75.8% of the overall thermal resistance of the vapor chamber. Simulation results indicate that large pressure drop occurs along the extended section of the vapor chamber, and causes large temperature difference along the extended section. [ABSTRACT FROM AUTHOR]

Abstract The anomalous glasslike behavior of heat transfer in Er:Yb: YCa 4 O(BO 3) 3 crystal was explored by means of temperature dependence Raman scattering spectra and synchrotron radiation X-ray topography. Crystal samples were prepared by the Czochralski technique, and the corresponding thermal properties, including thermal expansion, specific heat and thermal conductivity were investigated. The temperature-dependent Raman scattering results indicate the frequencies of Raman peaks as a function of crystal temperature followed a linear dependency on crystal temperature with different slopes. Nevertheless, the temperature-dependent linewidths of different Raman peaks were inconsistent and complicated. The X-ray topography firstly revealed a core situated in the center of crystal. Surrounding the core, a number of other defects like striations and dislocations were observed. The existence of such defects can lead to phonon scattering, which will introduce complicated influence into heat transfer process. As a result, the anomalous behavior of heat transfer can be influenced by disordered structure and crystal defects. Graphical abstract From a new perspective, we investigated the anomalous glasslike behavior of heat transfer in Er:Yb:YCOB crystal by means of temperature dependence Raman scattering spectra and the synchrotron radiation X-ray topography. The inconsistent and complicated temperature dependences of the linewidths of different Raman peaks, indicates the complicated influences of the disordered structure and crystal defects on the phonon scattering processes. Image 1 Highlights • The glasslike behavior of heat transfer in Er:Yb:YCOB crystal was firstly studied. • A core structure in Er:Yb:YCOB crystal was clearly revealed by X-ray topography. • The temperature dependent Raman scattering of Er:Yb:YCOB was firstly analyzed. • Temperature dependences of the linewidths of different Raman peaks were analyzed. • Disorder structure and defects bring a glasslike behavior of heat transfer. [ABSTRACT FROM AUTHOR]

Abstract The three-dimensional (3D) numerical modelling of laminated glass (LG) plate subjected to coupled thermomechanical loading is in the scope of this paper. The method called FEM23 is applied, in which a 2D in-plane mesh is used, however full 3D results are obtained. In any LG plate glass panes are bonded by very thin polymer films. This layered structure consists of subsequent thick and thin layers of glass and polymer, respectively. Additionally, the thermal and mechanical properties of the glass and the bonding polymer are significantly different. FEM23 is suitable for analyses of such kind of structure. The full 3D results of the coupled problem are obtained following special FEM23 postprocessing. FEM23 is a relatively simple, robust and effective method and 3D thermo-mechanical results obtained are correct for both stationary and non-stationary heat transport. The accuracy of the method has been examined with the use of solutions obtained from the ABAQUS system. The examples presented in the article include two-, three- and four-paned LG plates. [ABSTRACT FROM AUTHOR]

A wide range of speculation regarding lithospheric thermal thickness in a region calls for quantifying the uncertainties associated with model parameters. In this paper, we present an attempt to decipher it by solving the differential equations governing the heat transfer through the lithosphere. Adequately quantifying the temperature field is very important, since it is highly dependent on the controlling thermal parameters. Thermal conductivity is modeled as a random parameter with a known mean value and correlation structure. We compute the temperatures in the crust and lithospheric mantle, along with their error bounds, using an analytical solution to the steady-state heat equation and the Adomian method of decomposition. We apply these solutions in the Archean Dharwar craton, which is divided into western Dharwar craton (WDC) and eastern Dharwar craton (EDC). We obtain a Moho temperature estimate of 304 ± 58 °C in WDC, whilst in EDC it is 375 ± 74 °C for a 20% coefficient of variability in thermal conductivity. The range of lithospheric thickness obtained for WDC is 150-280 km, and 110-160 km for the EDC. These values are in agreement with other geophysical and geological findings in the region. The thermal lithosphere obtained from this study is based on the mantle solidus and the surface wave seismological studies considering radial anisotropy reveal that the lithosphere is characterized by higher shear wave velocities, and decrease at the lithosphere-asthenosphere boundary. Average shear velocity model for two different cratonic blocks (EDC and WDC) is used to show the LAB thickness for the eastern and western Dharwar craton. The two independent studies show a correlation in the lithospheric thickness. [ABSTRACT FROM AUTHOR]

A procedure for the metrological evaluation of the self‐heating effect in resistance thermometers is reported. This procedure is applied to different designs of resistance thermometers, used for meteorological and climate applications. The study of the self‐heating effect variation with the applied electrical current, temperature and different surrounding environments is described, as well as the influence of wind speed on the self‐heating effect. Variation of the standard deviation of the thermometer resistance mean with the applied electrical current, at different temperatures and with different external environments. [ABSTRACT FROM AUTHOR]

Surimi-based products from lisa blanca (Mugil curema) were produced using different heating processes of steaming, boiling, frying, and baking. The cooking time, thermophysical properties, and overall acceptability of each product were determined. The specific heat (Cp) and density (ρ) of raw samples was determined by differential scanning calorimetry and by volume displacement with water, respectively. The temperature variation inside the surimi was measured by several thermocouples strategically placed. Experimental data of temperature and time were recorded and used to estimate thermal conductivity (k) and heat transfer coefficient (h) by nonlinear regression. A simulation of heat transfer was carried out by COMSOL Multiphysics 4.3 software. A sensory evaluation was performed with 100°C judges using a 9-point hedonic scale. The values of Cp and of raw surimi were 3768.56 ± 15.35 J/kg℃ and 1030 ± 15 kg/m3, respectively. The experimental cooking time of surimi was 120 and 65 min for the baking and boiling processes, respectively, and 50 min for steaming and frying processes. k and h were dependent on the thermal process used and could be used to calculate the process time of new products with different shapes and other operation conditions. The sensory evaluation of products indicated a good acceptance by consumers. [ABSTRACT FROM AUTHOR]

Highlights • Examine data describing heat transfer in heterogeneous living skin. • Skin is two-layer heterogeneous material & measurements made at one location. • Explore the extent to which we can parameterise a two-layer model with data from one location. • Ability to parameterise heterogeneous model is very sensitive to data collection. • Explore optimal design. Abstract In this work we consider a recent experimental data set describing heat conduction in living porcine tissues. Understanding this novel data set is important because porcine skin is similar to human skin. Improving our understanding of heat conduction in living skin is relevant to understanding burn injuries, which are common, painful and can require prolonged and expensive treatment. A key feature of skin is that it is layered, with different thermal properties in different layers. Since the experimental data set involves heat conduction in thin living tissues of anesthetised animals, an important experimental constraint is that the temperature within the living tissue is measured at one spatial location within the layered structure. Our aim is to determine whether this data is sufficient to reliably infer the heat conduction parameters in layered skin, and we use a simplified two-layer mathematical model of heat conduction to mimic the generation of experimental data. Using synthetic data generated at one location in the two-layer mathematical model, we explore whether it is possible to infer values of the thermal diffusivity in both layers. After this initial exploration, we then examine how our ability to infer the thermal diffusivities changes when we vary the location at which the experimental data is recorded, as well as considering the situation where we are able to monitor the temperature at two locations within the layered structure. Overall, we find that our ability to parameterise a model of heterogeneous heat conduction with limited experimental data is very sensitive to the location where data is collected. Our modelling results provide guidance about optimal experimental design that could be used to guide future experimental studies. [ABSTRACT FROM AUTHOR]

Highlights • An effective thermal conductivity model is derived based on fractal theory. • Predictions of proposed model show good consistent with experimental data. • The proposed theoretical model reveals the physical basis of heat transfer in porous media. Abstract Thermal conduction in porous media has received wide attention in science and engineering in the past decades. Previous models of the effective thermal conductivity of porous media contain empirical parameters typically with ambiguous or even no physical rationales. This study proposes a theoretical model of effective thermal conductivity in porous media with various liquid saturation based on the fractal geometry theory. This theoretical model considers geometrical parameters of porous media, including porosity, liquid saturation, fractal dimensions for both the granular matrix and liquid phases, and tortuosity fractal dimension of the liquid phase. Effects of these geometrical parameters on the effective thermal conductivity of porous media are also evaluated. This proposed fractal model has been validated using published experimental data, compared with previous models, and thus provides a physics-based theoretical model that can provide insight to geoscience and thermophysics studies on thermal conduction in porous media. [ABSTRACT FROM AUTHOR]

The thermal boundary resistances (TBRs) of twin boundaries occurring at three different atomic layers (Te1, Bi, and Te2) of bismuth telluride (Bi2Te3) are investigated in use of the non-equilibrium molecular dynamics (NEMD) simulation method. The simulation results show that among all, the Te1-twin boundaries bring about a lowest interfacial energy corresponding to a most stable system, which explains why this type of twin boundaries is mostly often observed in the laboratory; the Te2-twin boundaries on the other hand possess a largest interfacial energy, resulting in a least stable system. The order in magnitude of the TBRs associated with these three types of twin boundaries is Te2-twin > Bi-twin > Te1-twin. Moreover, the TBR associated with a pair of twin boundaries separated by a distance of 4 unit cell (UC) is found to be about twice as large as that of a single twin boundary of the same type. It implies that the mutual coupling, which causes an increase in TBRs, may be ignored and the effect of twin boundaries may be counted individually as long as the separation distance is larger than 4 UC. [ABSTRACT FROM AUTHOR]

Abstract Vertical thermal stratification is typical for partially conditioned large space building. Heat accumulation in the upper part of unoccupied zone will have significant effect on the cooling load of occupied zone. In order to accurately estimate this cooling load, calculation of the heat migration occurs in the thermally stratified environment is critical. Heat migration in this study refers to the amount of heat transferred from unoccupied zone to occupied zone (or between other adjacent zones). This paper discusses the method to calculate heat migration through convection and conduction in a large space building served by side wall nozzle air-supply system. In a scaled laboratory, three experiment cases with different exhaust air flow ratio are investigated. CFD simulations of the same cases are performed. Vertical temperature distribution and detailed cooling load results of the whole system as well as those of occupied zone are validated against experiment result. A detailed analysis on the total heat migration and its components between different zones is conducted. Inter-zonal heat transfer coefficient C b used in a zonal BLOCK model and heat conductivity across the intersection of zones is obtained by dividing the whole space into two and four zones vertically. It is found that both C b and thermal conductivity value across the intersection is greater than expected and affected by the local turbulent intensity. Highlights • Inter-zonal heat migration in large space building is investigated in a scaled laboratory. • CFD simulation result is validated by air temperature distribution and cooling load components. • Turbulent characteristics are key determinant for inter-zonal heat migration in stratified air distribution system. [ABSTRACT FROM AUTHOR]

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The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as convenient as the analytic solutions in engineering applications. In this paper, a new heat transfer mathematical model of HWHE-based on analytic solutions was developed, which could be much faster to obtain the heat transfer properties of HWHE. The proposed model was validated under four conditions with literature values, which showed that the deviations of heat flux are 2.53%, 0.99%, 2.12%, and 1.96%, indicating its accuracy is satisfied. The model was then used to analyze the thermal property of HWHE. The results show the thermal resistance caused by panel with heat convection and conduction accounts for 96.54% of HWHE thermal resistance, and the thermal resistance caused by heat convection on the surface of panel is 74.43%. The analyzation results also show that adding aluminum foil around pipes could decrease HWHE thermal resistance by 5.11%. Besides, the influence of pipe diameters, pipe distance, pipe heat conductivity, side wall heat conductivity, and convective heat transfer coefficient on the heat transfer performance of HWHE was analyzed. The research in this paper can be used for fast prediction and optimization of heat transfer in HWHE. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to assess the thermal protective performance of firefighter's clothing by a sweating manikin in low-level radiation.Design/methodology/approach A new method and a novel objective index based on measurements of the sweating thermal manikin are proposed to measure the thermal protection performance of firefighter's clothing under low-level radiation exposure of 3.0 kW/m2. Finally, the effect of thermal insulation on thermal protective performance of firefighter's clothing was analyzed.Findings The results reveal that the new index which used the changing rate of core temperature of the clothed manikin is a vital indicator of the thermal protection performance. Furthermore, the results demonstrated that there is a linear correlation between thermal protection performance of firefighter's clothing and the thermal insulation.Originality/value A new method and a novel objective index are proposed to quantify the thermal protective performance of firefighter's clothing in low-level radiation. [ABSTRACT FROM AUTHOR]

Highlights • Minimization of thermal resistances for point to area kind of heat flow corresponds to a snowflake shaped fin design. • The results uncover snowflake designs corresponds to minimum peak temperature. • The shape of snowflake should be altered as the conditions change. • The snowflake shape was uncovered with the minimization of thermal resistance and the guidance of Constructal Theory. • The snowflake design was not dictated, i.e. it is free to vary, but uncovered. Abstract Here, we show numerically how thermal resistance in a two-dimensional domain with a point heat source can be reduced with embedded high-conductivity snowflake shaped pathways. The external shape of the domain is square, and its boundaries are heat sink. The geometry of the inserted pathways which corresponds to the minimum T max was uncovered with the consideration of Constructal Theory, i.e. the constructal design. In the first assembly, number of mother (big) fins was uncovered as the area fraction increases. The results of the first assembly indicate that the increase in number of mother fins does not increase heat transfer after a limit number for the fins. After uncovering the mother pathway geometry corresponding to the minimum T max , the daughter (small) fins inserted at the tip of them, i.e. second assembly. In the second assembly, the fin ratios, small fin location and angle were discovered when the area fraction is fixed. In addition, in the third assembly, larger daughter fins were attached to mother fins. The results of the second and third assemblies document what should be the geometric length scales and the number of daughter fins in order to minimize T max . The constructal design uncovered is similar to the shape of snowflakes. Therefore, the results also uncover snowflakes correspond to the designs with minimum thermal conductivity, i.e., not mimicking the nature but understanding it with physics. [ABSTRACT FROM AUTHOR]

Highlights • Liquid temperature and vapor concentration of sprays were studied using LIEF. • Effects of injection parameters on spray evaporation and heat transfer were studied. • The superheated region of flash-boiling spray was a quasi-steady state. • Evaporation of flash-boiling spray was enhanced significantly by decreasing P a /P s. • Heat transfer scheme was studied based on experimental observations. Abstract In order to improve engine thermal efficiency with reduced emissions, substantial studies have been carried out to improve the atomization and evaporation of fuel sprays, as well as fuel-air mixing in the engine cylinder. It has been found that flash-boiling spray is an effective way to achieve these goals. To further understand the evaporation characteristics and hear transfer phenomena between flash-boiling sprays and ambient gas, liquid temperature and vapor concentration of flash-boiling spray were measured quantitatively using laser induced exciplex fluorescence (LIEF) technique. The effects of fuel temperature, ambient pressure and superheated index (P a /P s) on the evaporation characteristics and heat transfer of fuel spray were investigated. The experimental results demonstrate that compared with non-flash-boiling spray, the rapid evaporation of flash-boiling spray leads to a higher vapor concentration along the center line. Meanwhile, the remarkable amount of energy absorbed from liquid phase of flash-boiling spray results in a faster liquid temperature decrease along the center line. When hot fuel is injected into cold environment, increasing fuel temperature leads to an increase of heat transfer from fuel spray to ambient gas because of the higher temperature difference between them. On the other hand, increasing ambient pressure decreases the evaporation rate of fuel spray due to the higher P a /P s. As such, the energy absorbed for fuel evaporation from liquid phase of spray is decreased, the heat transfer from fuel spray to ambient gas is increased. [ABSTRACT FROM AUTHOR]

Highlights • A new lab test is proposed to study dynamic energy systems and composites with PCM. • Transient plane source technique and controlled dynamic environment sensing are coupled. • Concrete with PCM for thermal energy storage in buildings are dynamically tested. • The test method allows to identify PCM dispersion and activation and TES contribution. Abstract In recent years the combination of latent and sensible thermal energy storage processes within passive and active building components has gathered increasing attention among researchers all over the world. All this considered, an ever-increasing hunger for bridging the gap between chemistry-based characterization methods and engineering-scale monitoring solutions is spreading worldwide, with the aim of developing new experimental procedures allowing to test these advanced systems under realistic operative environmental conditions. In this view, the present paper aims at proposing an innovative characterization procedure for real-scale engineered applications with reference to dynamically variable composites, such as PCM-doped cement-based mixes for building envelope applications. Therefore, in this work, thermally enhanced concretes were produced using micro-encapsulated paraffin and their activation was investigated by means of an innovative experimental technique coupling transient plane source method and controlled environmental dynamic forcing. The dynamic-TPS analysis allowed to produce temperature dependent profiles for three basic material thermal properties, i.e. thermal conductivity, thermal diffusivity and volumetric specific heat. Results show that the proposed methodology is capable of detecting PCM activation within the engineered composites during the imposed hygrothermal cycle, where, for example, the effective thermal conductivity of the composites varied between 40 and 90% amid the melting/freezing process. Furthermore, the transient plane source method also showed to be suitable to investigate PCM dispersion within the composites. [ABSTRACT FROM AUTHOR]

The polar bear hairs have special hierarchical structure with fractal dimensions of golden ratio, which endows the creature with remarkable cool prevention. Fractal calculus is adopted in this paper to reveal its thermal properties, and a fractal derivative model of one-dimensional heat conduction along the hair is established and solved, the results reveal that there is an optimal hair length for the cool prevention. This paper sheds a new light on bio-inspired fabrics for fire-protection clothing and clothing for extreme environment. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of doping of electro-insulating liquids with nanoparticle materials on the thermal properties of the obtained nanoliquids and heat transport in the transformer. Mineral oil, synthetic ester, and natural ester were used as base liquids. The effectiveness of doping base liquids with nanoparticles was supported by ultraviolet-visible (UV/VIS) measurements. In turn, Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) confirmed the absence of intermolecular interactions (i.e., hydrogen bonding). The influence of modification of electro-insulating liquids with fullerene C60 and titanium dioxide TiO2 nanoparticles on such thermal properties as thermal conductivity, specific heat, kinematic viscosity, density, and thermal expansion was investigated. Based on these properties and the theory of similarity, the cooling efficiency of the transformer filled with the analyzed nanofluids was determined. Nanofluids' cooling effectiveness was compared with the cooling effectiveness of the base liquids. This comparison was supported by an analysis of Grashof, Prandtl, and Nusselt numbers. It has been shown that the modification of electro-insulating liquids with nanoparticles widely used in order to improve their dielectric properties, such as C60 and TiO2, does not have a significant influence on their thermal properties. The addition of fullerene C60 caused an increase in kinematic viscosity, which was compensated by the increase in specific heat. In the case of TiO2, the addition of this nanoparticle resulted in an increase in kinematic viscosity and a decrease in specific heat, which were balanced out by the increase in thermal conductivity. In summary, the heat exchange-capacity of liquids did not change due to doping with nanoparticles. [ABSTRACT FROM AUTHOR]

It is interesting to compare the residual strength of laminated carbon fiber reinforced polymer under thermal environments with finite heating rate, and laser irradiation with rapid heating rate. In these two conditions, heating rates are varied in two orders of magnitude, and thermally‐induced damage mechanisms are quite different, which may influence the performance of residual strength. Systematic experiments are performed to obtain the tensile failure behavior of laminated carbon fiber reinforced epoxy composites at different temperatures with a heating rate of about 102°C/min. In comparison, composite samples are subjected to laser irradiations of different power densities and then tested for residual strengths, the laser induced heating rate is above 104°C/min. Experimental results indicate that the residual strength decreases with the increase of heating temperatures and laser power densities, however the damage mechanisms for conventional heating are thermal pyrolysis, oxidation and delamination, whereas the main damage mechanisms for laser irradiation are thermal pyrolysis and fiber ablation. The experimentally obtained residual strength and modulus are also compared with those predicted by theoretical model. POLYM. ENG. SCI., 58:2311–2319, 2018. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

This paper evaluates the behavior of cutting temperature under the influence of specific cutting parameters by applying both Factorial Design and the Surface Response Methodology. Cutting speed, the feed rate and type of material were selected as input parameters to perform this study. As type of material is a non quantitative factor, it is necessary to establish a particular index to define it. Although different properties were analyzed, the average stress between the yield and strength stresses was demonstrated as the most representative property to describe material. The experimental values of temperatures during the turning process were obtained with an infrared thermography camera and experiments were designed to run the statistical analysis with commercial software. Both the Factorial Design and Surface Response methodologies showed the influence that specific values of the input parameters had on cutting temperatures. Factorial Design allowed more accurate results, but more experiments had to be carried out, while the Surface Response Methodology provided suitable information with fewer tests. A comparison was made between the experimental and some analytical results, for example those obtained by Cook, and showed a good agreement. [ABSTRACT FROM AUTHOR]

Hybrid nanofluid can be considered as a new generation of nanofluids. Despite the success of the researchers in the field of hybrid nanofluids, no acceptable model has been proposed yet that can accurately predict the thermal conductivity of these nanofluids. The nanofluids, containing carbon nanotubes, are not excluded. This research to provide a model based on previous models to predict the thermal conductivity of hybrid nanofluids containing carbon nanotubes. For this reason, the thermal conductivity of MWCNT-MgO/water-EG nanofluids was experimentally measured. The experimental data were in seven solid volume fractions from 0.015 to 0.96%, in which the tests have been done at the temperature range 30-50 °C. A modified conventional model (as a proposed correlation in present study) can produce better results in forecasting the experimental data. The predicted data error by modified Jang-Choi model as proposed correlation was less than 3%. In addition, the price-performance analysis of the thermal conductivity data shows that hybrid nanofluids are better than single particle nanofluids. [ABSTRACT FROM AUTHOR]

In this paper a one-phase Stefan problem with size-dependent thermal conductivity is analysed. Approximate solutions to the problem are found via perturbation and numerical methods, and compared to the Neumann solution for the equivalent Stefan problem with constant conductivity. We find that the size-dependant thermal conductivity, relevant in the context of solidification at the nanoscale, slows down the solidification process. A small time asymptotic analysis reveals that the position of the solidification front in this regime behaves linearly with time, in contrast to the Neumann solution characterized by a square root of time proportionality. This has an important physical consequence, namely the speed of the front predicted by size-dependant conductivity model is finite while the Neumann solution predicts an infinite and, thus, unrealistic speed as t  → 0. [ABSTRACT FROM AUTHOR]

The tendency of the polymers to melt and drip when they are exposed to external heat source play a very important role in the ignition and the spread of fire. Numerical simulation is a promising methodology for predicting this behaviour. In this paper, a computational procedure that aims at analyzing the combustion, melting and flame spread of polymer is presented. The method models the polymer using a Lagrangian framework adopting the particle finite element method framework while the surrounding air is solved on a fixed Eulerian mesh. This approach allows to treat naturally the polymer shape deformations and to solve the thermo-mechanical problem in a staggered fashion. The problems are coupled using an embedded Dirichlet-Neumann scheme. A simple combustion model and a radiation modeling strategy are included in the air domain. With this strategy the burning of a polypropylene specimen under UL-94 vertical test conditions is simulated. Input parameters for the modelling (density, specific heat, conductivity and viscosity) and results for the validation of the numerical model has been obtained from different literature sources and by IMDEA burning a specimen of dimensions of 148×13×3.2mm3. Temperature measurements in the polymer have been recorder by means of three thermocouples exceeding the 1000 K. Simultaneously a digital camera was used to record the burning process. In addition, thermal decomposition of the material (Arrhenius coefficient A=7.14×1016min-1 and activation energy E=240.67kJ/mol) as and changes in viscosity (μ) as a function of temperature were obtained. Finally, a good agreement between the experimental and the numerical can be seen in terms of shape of the polymer as well as in the temperature evolution inside the polymer. [ABSTRACT FROM AUTHOR]

In this paper, an enriched FEM technique is employed for thermo-mechanical contact problem based on the extended finite element method. A fully coupled thermo-mechanical contact formulation is presented in the framework of X-FEM technique that takes into account the deformable continuum mechanics and the transient heat transfer analysis. The Coulomb frictional law is applied for the mechanical contact problem and a pressure dependent thermal contact model is employed through an explicit formulation in the weak form of X-FEM method. The equilibrium equations are discretized by the Newmark time splitting method and the final set of non-linear equations are solved based on the Newton-Raphson method using a staggered algorithm. Finally, in order to illustrate the capability of the proposed computational model several numerical examples are solved and the results are compared with those reported in literature. [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]

This research was conducted for an in-depth analysis of changes in thermal properties and in comfortability as well as physical properties before and after sputtering on fabrics. It was found that the sputtering treatment could give significant effects on the heat transfer of nylon without much loss in its shear property, water vapor transmission, and bending property, which suggested that sputtering treatment with metals on the surface of fabric helped reduce the surface temperature by releasing body heat. When the metal coating layers of the sputtered fabrics were pointed toward the cold air (15℃), the surface temperature was lowered drastically from 35℃ to 22.07℃ by depending on metals. Also, the computed surface temperatures based on the heat transfer theory displayed a high level of consistency with the measured values. The conductive fabric, which was used for comparison, showed an increased bending rigidity after sputtering, making the fabric stiffer. In the future, a metal-sputtered fabric is expected to be used as a special material by utilizing its surface temperature-controlling function in the high-functional clothing material field. [ABSTRACT FROM AUTHOR]