Thermophysical Behavior Research Articles

Enhancing the heat and load transfer efficiency by optimizing the interface of hexagonal boron nitride/elastomer nanocomposites for thermal management applications

Amine-terminated butadiene-acrylonitrile (ATBN) was covalently grafted on a hexagonal boron nitride (BN) surface to enhance the interface affinity between BN and a carboxylated styrene-butadiene rubber (XSBR) matrix for preparing thermal interface materials with robust thermo-physical properties. The strong attraction between the amino groups on the ATBN-functionalized BN (ABN) and the carboxyl groups on the XSBR chains can further enhance the interfacial adhesion between the fillers and polymer matrix. The mechanical properties, thermal stability, thermal conductivity, thermo-physical properties, and interfacial filler–matrix network of the prepared XSBR/ABN nanocomposites were studied. The XSBR/ABN nanocomposites exhibited better mechanical and thermo-physical behavior compared to the XSBR/BN nanocomposites over the entire range of filler concentration, representing an enhanced interfacial interaction owing to functionalization. Moreover, the XSBR/ABN nanocomposites exhibited superior thermal conductivity as compared to the XSBR/BN nanocomposites, with the former exhibiting approximately 490% higher thermal conductivity than neat XSBR, whereas the latter exhibited 395% higher thermal conductivity than neat XSBR at a filler loading of 90 phr.

Morphological and Thermophysical Behavior of Hidroxyapatite Powders Processed by Mechanical Milling

The current research represents one section of our studies concerning the improvement of the biocompatibility related to the biocomposite materials for bone grafts application. The submicronic/nanometric hydroxyapatite stands for the progress in biocompatibility. This study highlights the wet mechanical milling process and its effects on the morphological and thermophysical properties of the hydroxyapatite powder particles (30-50µm as raw material) obtained by this method (500 nm average). The scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) facility point out the morphological and chemical compositional features of the processed powders during 10 hours in dry argon atmosphere. The thermal analysis (TA) in argon atmosphere, too, reveals the influence of the milling parameters on the thermal effects generated by the processed hydroxyapatite powders. The experimental results of our research validate some milling mechanisms reported by the literature for wet/dry mechanochemical process conditions.

Thermomechanical and thermophysical characteristics of alumina-carbon monolithic refractory containing surface-modified graphites in matrix

The thermophysical and thermomechanical behavior of graphite-containing refractory castable matrix with 20.0 wt% of graphite had been compared with graphite-free high alumina based castable matrix analogous to it. The thermomechanical properties of similar type of castables with and without 5.0% of graphite had also been evaluated. Graphite was incorporated both as coated and as-received forms, the former having a thin sol-gel derived calcium aluminate coating on graphite flakes. The influence of thermal conductivity, thermal diffusivity and pore size distribution had been critically estimated. The changes in flexural strength, porosity and density of the matrices had also been determined to interpret the castable performance, namely refractoriness under load (RUL), spalling resistance and conventional physical properties. The role of coated graphite on improved densification and thermal tolerance of refractories was further explored by microstructure and phase evolution studies of all kinds of fired samples at 1500 °C. It was further supplemented with the scanning electron microscope (SEM) studies of surface-modified graphites at uncalcined and calcined condition.

Electronic structure, magnetic, mechanical and thermo-physical behavior of double perovskite Ba2MgOsO6

The electronic structure, the magnetic, elasto-mechanical and thermodynamic belongings of cubic double oxide perovskites Ba2MgOsO6 have been successfully investigated within the full potential linearized augmented plane wave method (FP-LAPW), based upon the density functional theory (DFT). The structural examination reveals ferromagnetic stability and the spin polarized electronic band structure and density of states display half-metallic nature of the compound. The calculated magnetic moment was found to have an integer value of 2μ_B. From the knowledge of obtained elastic constants mechanical properties like Young’s modulus (E), shear modulus (G), Poisson ratio ( $\nu$ ) and the anisotropic factor have been predicted. The calculated B/G and Cauchy pressure ( $ C_{12}-C_{44}$ ) both portray the ductile nature of the compound. For a complete understanding of the thermo-physical behavior of vital parameters like heat capacity, thermal expansion, Gruneisen parameter and Debye temperature were predicted using quasi harmonic Debye approximation.

THE COMBINED EFFECTS OF UNSTEADY ELECTRO-OSMOTIC AND MAGNETO HYDRODYNAMIC WITH VISCOSITY AND THERMAL CONDUCTIVITY IN REACTIVE FLUID FLOW

This work examined the combined effects of unsteady electro-osmotic and magneto hydrodynamic when viscosity and thermal conductivity of the reactive fluid flow is assumed to vary exponentially with temperature. The dimensionless variables was use to dimensionalized the governing equations of the flow using suitable variables. The Galerkin weighted residue method was used to solve both the momentum and energy equations in the unsteady state for a constant viscosity and thermal conductivity. The graphical results were used to study the Thermo physical behavior of the unsteady flow of the model.

Liquid metal gallium laden organic phase change material for energy storage: An experimental study

This paper presents the experimental study on the thermophysical behavior, thermal cyclic characteristics and energy storage performance of liquid metal (LM) laden in organic solid-liquid phase change material (PCM) for energy storage. In this view, Gallium (Ga) is added into D-Mannitol (DM) with a weight fraction of 0.1% and 0.5% by dispersion technique using a ball mill. Repeated melting/freezing cycle was carried out for 350 cycles and the samples were characterized using Differential Scanning Calorimetry (DSC), Thermogravimetry Analysis (TGA) and Fourier Transform Infrared (FTIR). The DM/Ga composite PCM showed enhanced thermal conductivity of ∼8.4%, ∼27.8% for 0.1 and 0.5 wt % Ga as compared to pure DM. XRD studies reveal that the pure DM exhibited β polymorphic phase while TGA and FTIR analysis confirm the thermal reliability and chemical stability of composites in the temperature range of 50–200 °C. Non isothermal crystal kinetic study proved that the addition of Ga increased the crystallization rate due to heterogeneous nucleation effect and leads to the reduction in subcooling temperature of the PCM. The experimental setup results to test the charging and discharging performance of the composite PCM revealed that the total time for one complete cycle reduced from 97.48 min for pure DM to 84.73 min and 63.92 min for DM-Ga composite with 0.1 wt % and 0.5 wt % respectively. Based on the results obtained, D-Mannitol based composites could be recommended as potential PCM candidates for solar heat and industrial waste heat recovery application due to its high energy density capacity, thermal/chemical stability and good heat transfer performance.

Analytical modelling of Breathing Walls: experimental verification by means of the Dual Air Vented Thermal Box lab facility

Breathing Walls are air permeable envelope components based on porous materials. In contra-flux operation air flows opposite to conductive flux, while in pro-flux they have the same direction. The Breathing Wall behaves either as a ventilation heat exchanger or as an active insulation.In literature an analytical model describing steady state heat transfer across a Breathing Wall can be found. Since it lacks an exhaustive experimental validation, a facility developed at the Energy Department of Politecnico of Milano was used to investigate the thermo-physical behavior of a no-fines concrete based Breathing Wall in steady state Dirichlet conditions and contra-flux operation.

Local Order-Disorder Transition Driving by Structural Heterogeneity in a Benzyl Functionalized Ionic Liquid.

A local order-disorder transition has been disclosed in the thermophysical behavior of the ionic liquid 1-benzyl-3-methylimidazolium dicyanamide, [Bzmim][N(CN)2], and its microscopic nature revealed by spectroscopic techniques. Differential scanning calorimetry and specific heat measurements show a thermal event of small enthalpy variation taking place in the range 250-260 K, which is not due to crystallization or melting. Molecular dynamic simulations and X-ray diffraction measurements have been used to discuss the segregation of domains in the liquid structure of [Bzmim][N(CN)2]. Raman and NMR spectroscopy measurements as a function of temperature indicate that the microscopic origin of the event observed in the calorimetric measurements comes from structural rearrangement involving the benzyl group. The results indicate that the characteristic structural heterogeneity allow for rearrangements within local domains implying the good glass-forming ability for the low viscosity ionic liquid [Bzmim][N(CN)2]. This work sheds light on our understanding of the microscopic origin behind complex thermal behavior of ionic liquids.

Enhanced partitioning of tryptophan in aqueous biphasic systems formed by benzyltrialkylammonium based ionic liquids: Evaluation of thermophysical and phase behavior

Ionic liquids (ILs) based aqueous biphasic systems (ABS) are envisioned to be promising separation and environmentally benign extraction media. In this context, novel ternary phase diagrams were determined for two ILs namely, Benzyltrimethylammonium chloride and Benzyltributylammonium chloride in presence of various potassium salts, K3PO4, K2HPO4, K2CO3 and KOH at 298.15K. The influence of benzyl group substitution on the cation of IL and nature of various potassium salts on the phase behavior were analyzed. Experimental binodal data were fitted to Merchuk's equation and tie line compositions and tie line length were also determined. Further, these IL based ABS in presence of various potassium salts have been systematically scrutinized for their efficiency to extract Tryptophan. For the better understanding of the role of thermophysical properties on phase behavior and extraction capability, density and viscosity of coexisting phases were measured at various compositions in the temperature range from 293.15 to 328.15K. Enhanced extraction coefficients achieved for the studied combinations of ILs and inorganic salts indicate the possible use of these ABS as efficient extraction systems. Further, the study of thermophysical properties suggested that selected ternary systems present more desirable features in terms of density and viscosity as compared to traditional polymer based ABS.

Experimental validation of the exact analytical solution to the steady periodic heat transfer problem in a PCM layer

Phase change materials (PCM) are used in many industrial and residential applications for their advantageous characteristic of high capacity of latent thermal storage by means of an isothermal process. In this context, it is very useful to have predictive mathematical models for the analysis of the thermal performance and for the thermal design of these layers. In this work, an experimental validation of an analytical model that resolves the steady periodic heat transfer problem in a finite layer of PCM is presented. The experimental investigation was conducted employing a PCM with thermophysical and thermochemical behavior very close to those hypothesized in the formulation of the analytical model. For the evaluation of the thermophysical properties of the PCM sample used, an experimental procedure created by the authors was employed. In all tests realized in a sinusoidal and non-sinusoidal periodic regime, the comparison between the measured and calculated trends of the temperature at different sample heights and of the surface heat fluxes show an excellent agreement. Moreover, also having verified the analytical total stored energy, the analytical model constitutes a valid instrument for the evaluation of the latent and sensible contribution and the trend in time of the position of the bi-phase interface.

Reformulation of Gasoline To Replace Aromatics by Biomass-Derived Alkyl Levulinates

In the search for a “green gasoline”, a new reformulation strategy, having no or reduced amount of aromatics, is proposed. Biomass-derived alkyl levulinates (ALs) are prospected as oxygenated additives as well as blending components to circumvent the use of aromatics and methyl tertiary butyl ether (MTBE) in gasoline. By utilizing molecular dynamics (MD) simulations, the thermophysical and dynamical behavior of gasoline blends with four alkyl levulinates, viz. methyl levulinate (ML), ethyl levulinate (EL), propyl levulinate (PL), and butyl levulinate (BL), was scrutinized and compared with those of MTBE–gasoline mixtures. It is shown that, at 300 K and 1 atm, ALs in conventional gasoline can be used for reformulation with amounts up to 18 mol % while maintaining the density, viscosity, and compressibility within the recommended limits. However, this amount can be further increased to 35 mol % by modification of aromatic content. Among the studied oxygenates, BL was observed to have the lowest miscibility in water as compared to other ALs studied. The methodology may be applied to study similar biomass-derived oxygenates for their applicability as a fuel additive or blend.

Thermo-physical behavior of atmospheric plasma sprayed high porosity lanthanum zirconate coatings

Lanthanum zirconate (La2Zr2O7) is one of the potential thermal barrier top coat material due to its high melting point, phase stability and low thermal conductivity in comparison to the conventional yttria stabilized zirconia (YSZ) coatings. In this work, an attempt was made to further reduce the thermal conductivity of lanthanum zirconate from its bulk value by fabricating a highly porous microstructure. For this purpose, lanthanum zirconate top coating with different porosities (16, 21 and 28%) was prepared by atmospheric plasma spraying under selective operating conditions and their microstructure, permeability and thermo-physical properties were investigated. SEM micrographs of the porous lanthanum zirconate show the features of the coating microstructures and porosity percentage. The bond strength of the as-sprayed coatings linearly decreases while increasing the porosity in the coating microstructure. The gas permeability of the porous coating microstructure significantly increased with increase in the porosity. An increase in coating porosity, results in significant reduction of both thermal diffusivity and conductivity of the coating microstructure.

Experimental studies on metallic fuel relocation in a single-pin core structure of a sodium-cooled fast reactor

Experiments dropping molten uranium into test sections of single fuel pin geometry filled with sodium were conducted to investigate relocation behavior of metallic fuel in the core structures of sodium-cooled fast reactors during a hypothetical core disruptive accident. Metallic uranium was used as a fuel material and HT-9M was used as a fuel cladding material in the experiment in order to accurately mock-up the thermo-physical behavior of the relocation. The fuel cladding failed due to eutectic formation between the uranium and HT-9M for all experiments. The extent of the eutectic formation increased with increasing molten uranium temperature. Voids in the relocated fuel were observed for all experiments and were likely formed by sodium boiling in contact with the fuel. In one experiment, numerous fragments of the relocated fuel were found. It could be concluded that the injected metallic uranium fuel was fragmented and dispersed in the narrow coolant channel by sodium boiling.

Thermophysical behavior of thermal sprayed yttria stabilized zirconia based composite coatings

The effective thermal conductivity of a composite coating depends on intrinsic thermal conductivity of the constituent phases, its characteristics (size, shape) and volume fraction of porosities. The present study concerns studying the effect of CoNiCrAlY and Al2O3 content on the coefficient of thermal expansion and thermal conductivity of the YSZ (YSZ-CoNiCrAlY and YSZ-Al2O3) based composite coatings developed by thermal spray deposition technique. The coefficient of thermal expansion and thermal conductivity of the composite coatings were measured by push rod dilatometer and laser flash techniques, respectively, from room temperature to 1000 °C. Variation in density, porosity, coefficient of thermal expansion, and thermal conductivity was observed in the composite coatings with the addition of different volume fraction of CoNiCrAlY and Al2O3 powders in YSZ-CoNiCrAlY and YSZ-Al2O3 composites, respectively. Comparison between the theoretical and experimental thermal conductivities showed a mismatch varying from 4% to 58% for YSZ-CoNiCrAlY composite coatings and from 58% to 80% for YSZ-Al2O3 composite coatings. Model based analyses were used to understand the mechanism of thermal conductivity reduction in the composite coatings. It was concluded that the morphology of porosities varied with composition.

Thermophysical Characterization of Furfuryl Esters: Experimental and Modeling

The use of compounds with high oxygen content in the fuels field is very promising because they can increase combustion engine efficiency and minimize pollution emissions. The study of the thermophysical properties of these compounds is essential in order to evaluate their possible applications. In this study, different thermodynamic and transport properties of three furfuryl esters—furfuryl acetate, furfuryl propionate, and furfuryl butyrate—have been determined and compared with those of fluids that are commonly used as fuels or additives. Finally, the thermophysical behavior of these compounds has been analyzed using different models such as PC-SAFT equation of state and density gradient theory. The results indicate that these compounds exhibit similar characteristics to those of the normafluid ISO4113 (standard fluid in diesel injectors) except the density, bulk modulus, and surface tension, which are higher in the esters studied. It can be concluded that, given their thermophysical properties, these ...

Thermal transmittance of historical brick masonries: A comparison among standard data, analytical calculation procedures, and in situ heat flow meter measurements

The paper presents the results of an on-site survey on several historic brick masonries with different heritage values, historical ages, and internal functions. The experimental data have been compared with the results of the standard procedures normally used in Italy for assessing the thermo-physical behavior of traditional walls, in order to provide a guidance for energy audit, simulation, and labelling of historic buildings. The research methodology is based on the following steps: (i) selection of traditional building masonries; (ii) interdisciplinary assessment for materials characterization; (iii) thermal performance evaluation using different standard procedures suggested by the Italian legislation framework; (iv) comparison between the results; and (v) final performances assessment. Compared with the experimental measurements, standard and analytical procedures tend to overestimate the thermal performance of historic brick masonries. There is a correspondence between the historical ages and the λ-value of bricks. The bricks manufactured by pre-industrial techniques have lower densities than the industrial ones. This is due to the artisanship of clay, which caused the presence of sand, raw materials, and air, improving their thermal performance.

Thermal design of helium cooled divertor for reliable operation

Nuclear fusion is the promising energy sources because the fuels for power generation are abundant and by-products are eco-friendly rather than other power generations. However, there are several conundrums that must be solved for developing the nuclear fusion plants, including DEMO (DEMOnstration nuclear fusion reactors), such as superconducting system, blanket, cryostats and others. In particular, a divertor is one of essential components because of withstanding the excessive heat flux (∼10MW/m2) from the high-temperature plasma. Therefore, it is necessary for thermal design of divertor module under tremendous heat flux to develop the nuclear fusion plants. We investigate thermophysical behavior by convective heat transfer and suggest principle operating variables to decide for appropriate thermal design for divertor module. Based on the simplified thermal circuit, we demonstrate that the observed correlation can predict thermophysical characteristics of the divertor module and present the prerequisites for reliable thermal design based on the thermal design maps in terms of principle operating variables of divertor module. Finally, we reveal that the safety factor of thimble is primary concern to establish thermal design of divertor module. The present study will contribute to the development of divertor in nuclear fusion plants and the applications for high heat flux and temperature devices.

Myo-inositol based nano-PCM for solar thermal energy storage

The thermo-physical behavior of Myo-Inositol (MI), (a sugar alcohol), was investigated as a potential material for developing more compact solar thermal energy storage systems than those currently available. This latent heat storage medium could be utilized for commercial and industrial applications using solar thermal energy storage in the temperature range of 160–260°C, if its thermal performance was modified. The objective of this investigation was to determine via experimentation, if Al2O3 and CuO nanoparticles dispersed in pure MI for mixtures of 1, 2 and 3% (by weight) improved the thermal performance of MI for solar thermal energy systems. Nanoparticles only physically interacted with MI, and not chemically, even after 50 thermal cycles. The distribution of CuO nanoparticles in the nano-PCM was found to be more uniform than alumina nanoparticles. After cycling, nano-MIs studied here suffered a lower decrease in heat of fusion than pure MI, which makes nano-MIs more suitable for solar thermal storage applications at 160–260°C. Between CuO and Al2O3 nanoparticles, latter was found to be more suitable for compact solar thermal energy storage owing to an increase in melting point observed.

A New Volume-Based Approach for Predicting Thermophysical Behavior of Ionic Liquids and Ionic Liquid Crystals.

Volume-based prediction of melting points and other properties of ionic liquids (ILs) relies on empirical relations with volumes of ions in these low-melting organic salts. Here we report an accurate way to ionic volumes by Bader's partitioning of electron densities from X-ray diffraction obtained via a simple database approach. For a series of 1-tetradecyl-3-methylimidazolium salts, the volumes of different anions are found to correlate linearly with melting points; larger anions giving lower-melting ILs. The volume-based concept is transferred to ionic liquid crystals (ILs that adopt liquid crystalline mesophases, ILCs) for predicting the domain of their existence from the knowledge of their constituents. For 1-alkyl-3-methylimidazolium ILCs, linear correlations of ionic volumes with the occurrence of LC mesophase and its stability are revealed, thus paving the way to rational design of ILCs by combining suitably sized ions.

Effect of Oxygenation on Carbon Dioxide Absorption and Thermophysical Properties of Ionic Liquids: Experiments and Modeling Using Electrolyte PC-SAFT

The thermophysical properties (decomposition temperature, glass transition temperature, density, and viscosity) of imidazolium-based ionic liquids (ILs) paired with the tricyanomethanide ([TCM]−) anion and the bis(trifluoromethylsulfonyl)imide ([Tf2N]−) anion were studied within a wide temperature range. The effect of the ether functional group (in [Tf2N]− and [TCM]− ILs) and hydroxyl functional group (in [Tf2N]− IL) incorporated in the cation’s alkyl chain on the thermophysical behavior and carbon dioxide (CO2) solubility was evaluated by comparing their behavior to the corresponding nonfunctionalized ILs. The thermal stability was enhanced by the inclusion of hydroxyl functionalization in the cation’s alkyl chain while ether functionalization had no major effect on the thermal stability. The ether groups (one or two) resulted in an increase in the density and a decrease in the viscosity of all ILs. The hydroxyl group resulted in an increase in both properties. The CO2 solubilities were not affected by the presence of the ether groups, while the hydroxyl group led to a significant decrease in the solubility. Additionally, the electrolyte perturbed-chain statistical associated fluid theory (ePC-SAFT) equation of state was used to calculate the CO2 solubility in the ILs and the Henry’s law constant. The model showed great predictive ability. The Henry’s constants were applied to calculate the partial molar thermodynamic properties of solvation.