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• Molecular dynamics method was implemented. • Nano refrigerants include Freon-134a and Freon-407a as base fluids and Cu as nanoparticles. • The density, velocity, and temperature profiles are investigated. • Freon-407a base fluid shows a better thermal performance. • Nano-refrigerant with Freon-407a base fluid has more heat flux (1028 W/m2). Nano-refrigerants, which are the suspensions of nano-sized particles in a base fluid, were applied in many devices and systems to enhance thermal conductivity and improve heat transfer performance. This work studied the thermal and atomic behavior of two kinds of nano-refrigerants located inside an aluminum nanochannel for 5 ns. The molecular dynamics (simulation method simulated Nano-refrigerants, including R-134a and R-407A as base fluids and copper as nanoparticles. The density, velocity, and temperature profiles were studied to investigate the atomic behavior of the simulated sample. The thermal behavior of structures was studied by examining the phase transition rate, phase change time, thermal conductivity, and heat flux. The results show that R-407A base fluid showed better thermal behavior. The results show that in Cu/R-407A, the phase-changed particle reached 31% in 5 ns, and phase change time was estimated to be 3.91 ns. In contrast, in Cu/R-134a, the samples' phase changed particle and phase change time reached 26% and 4.06 ns. Moreover, the study of heat flux shows that nano-refrigerant with R-407A base fluid had more HF (1028 W/m2) than R-134a (654 W/m2). The results show that the thermal conductivity of R-407A and R-134a nano-refrigerant converged to 0.0975 and 0.0098 W/mK, respectively. [ABSTRACT FROM AUTHOR]

Amorphous materials are also distinguished from crystals by their thermal properties. The structural disorder seems to be responsible both for a significant increase in heat capacity compared to crystals of the same composition, but also for a significant decrease in thermal conductivity. The temperature dependence of thermal conductivity, unusual for common interpretations of solid-state physics, gave rise to a lot of debates. We review in this article different interpretations of thermal conductivity in amorphous materials. We show finally that the temperature dependence of thermal conductivity in dielectric materials can be understood by relating it to the disorder-dependent harmonic vibrational eigenmodes. [ABSTRACT FROM AUTHOR]

• Reviewed the experimental studies on nanoparticles-doped refrigeration systems. • Noticed many limitations for using nanoparticles in today's technology. • Observed the enhanced heat transfer mechanism with smaller particle sizes of nanoparticles. • Achieved long-term stability by moving away from the isoelectric point. • Reported a deterioration in the stability with longer sonication time. The popularity of the studies on improving the thermal properties of base fluids in thermal engineering applications is considerably increasing day by day. Recently, many researchers have proved that the use of nanoparticles along with the base fluids exhibits better thermal properties as well as better system performance. In line with this, it is noticed a respectful increase in the number of studies regarding nanoparticle use in refrigeration systems. Accordingly, the present paper aims to summarize the preparation of nanofluids, the variation of thermophysical properties, the stability of nanofluids, impacts on the system performances of nanofluid usage, limitations, and challenges of nanoparticle usage, particularly in the refrigeration systems. Previous studies revealed that the heat transfer mechanism of the lubricants and refrigerants is highly improved with nanoparticle addition. It is observed that the increase in thermal properties becomes more visible as nanoparticle fractions increase, but this case may worsen the viscosity of nanofluids. The enhanced thermal properties contribute to improving refrigeration system performance. Many papers emphasize that nanoparticle-doping triggers an increase in system performance by both reducing the compressor power input and increasing the cooling capacity of the refrigeration systems. However, some critical points such as stability, homogeneous distribution, agglomeration, and sedimentation considerably influence the sustainability of performance improvement. In conclusion, nanoparticle-doping for refrigeration systems can be accepted as a very promising way of improving the performance, nevertheless, some questions such as high cost, toxic effect, poor stabilization, erosion effect, high viscosity, clogging issues should be more addressed in the future. [ABSTRACT FROM AUTHOR]

Studies dedicated to the homogenization approach of microcracked media are largely focused on the determination of effective elastic properties. Some works investigate other properties, but most of them consider only open cracks. This paper intends to provide effective thermal properties related to the conduction problem taking into account the unilateral effect (opening/closure of cracks). Such analysis considers steady-state heat transfer within an initially isotropic media weakened by randomly oriented cracks. According to the boundary conditions, estimates and bounds based on Eshelby-like formalism are developed to derive closed-form expressions for effective thermal conductivity and resistivity in a fixed microcracking state. [ABSTRACT FROM AUTHOR]

The raw earth is a natural material originating from the slow decomposition of rocks and stones. It can be used as a construction material as cob, daub, wattle, adobe, moulded bricks, rammed earth or compressed earth blocks. The use of a specific technique depends on the vernacular habits and also on the climate to which the building will be submitted or on the intrinsic properties of the earth. In this paper, we study the thermal and mechanical properties of compressed earth blocks (CEB) made of raw earth from Benin. In order to improve the mechanical properties of this brittle material, especially the tensile stress, kenaf fibers are incorporated into the mix. To determine the influence of the fibers on the various properties of CEB, the fiber content and the fiber length was varied. The results show a strong influence of these parameters on the porosity and as a consequence on the thermal and mechanical properties (compressive and tensile strengths). The increase in the porosity of the material yields a decrease in the mechanical strengths whatever the fiber content, except for long fibers. This seems to demonstrate combined effects of the porosity decrease and of the resistance to traction efforts due to the fibers. The addition of fibers also induces a decrease in the thermal conductivity of the material mainly due to the increase in the porosity. [ABSTRACT FROM AUTHOR]

Global energy needs continue to rise along with society's desire for carbon-reduced energy sources to limit climate change effects. One viable carbon-reduced energy source is nuclear power, which provides more than half the electricity requirements of the province of Ontario. Within Canada there are more than 2.5 million bundles of spent nuclear fuel, which will be stored in a deep geological repository. Efficiency of the repository system depends on dissipation of thermal energy. A comprehensive experimental study is presented on thermal properties of barrier materials. The influence of bentonite type, variability, moisture, and temperature on thermal properties is examined. Results show strong influence of moisture on thermal properties, some influence of temperature on low-density bentonite, minor influence of bentonite type, as well as low variability in the experimental measurements. The extensive database of physical measurements is compared with values from the literature and then used to statistically evaluate thermal property models selected from the literature. Using the base parameters from the literature, thermal property models performed adequately; however, soil-specific calibration of the model inputs improved the fit significantly. These results are now available to perform the numerical models for the proposed Canadian deep geological repository for used nuclear fuel. [ABSTRACT FROM AUTHOR]

In this work, a Helmholtz free energy equation of state for R290 + R134a based on the multi-fluid approximations model was developed to describe the thermophysical properties of the binary mixture. The present equation shows more competitive than the default equation in REFPROP 9.1 (Lemmon et al., 2013). It covers a temperature range of (252–400) K and pressures up to 6.1 MPa. The estimated standard uncertainties of the present equation are 0.70% and 0.90% for the bubble point and dew point pressures, 0.26 K and 0.29 K for the bubble point and dew point temperatures, 0.13% and 0.60% for the saturated liquid and vapor densities, respectively. The main purpose is to provide a useful model for R290 + R134a, and thus to promote its better applications for the design and optimization of the refrigeration systems. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the thermal insulation properties of the construction materials used in the buildings sector. Initially, the effect of moisture on the thermophysical properties of three types of concrete (classic concrete, concrete with cork aggregate and polystyrene concrete) are investigated experimentally. Then a numerical analysis basing on finite differences method is applied in order to examine simultaneous heat and mass phenomena inside studied materials. Through this study, it was found that the presence of water in building materials, even in small quantities significantly modifies their thermophysical properties, which leads an adverse effect on their thermal insulation power. The results indicate that the addition of cork aggregates and polystyrene beads to concrete improves its thermal performance. This work comes also within an economic framework, given the abundance of cork aggregates and polystyrene beads. [ABSTRACT FROM AUTHOR]

A Phase Change Material Emulsion (PCME) is a multifunctional fluid consisting in a Phase Change Material (PCM) as paraffin, dispersed in an aqueous surfactant solution, usually water. PCMEs stand out as potential latent thermal fluid in comfort cooling applications. This article reports experimental results concerning the heat transfer behavior of a 30 wt% paraffin in water emulsion for a temperature range of 0–20 °C. Thermophysical properties of the emulsion were investigated. Then an experimental study of laminar forced convection heat transfer was performed. The convective heat transfer coefficient of the emulsion during cooling was determined in a specific experimental set-up. The setup consists mainly of two heat exchangers, having rectangular sections (80 × 6 mm 2 ) of 1 m lengths. The results show that the emulsion is an attractive candidate for air conditioning applications. It has a heat capacity of 5894 kJ/kg, which is two times higher than water in the same temperature range. Furthermore, convective heat transfer performance for the studied PCME is improved with respect to water due to the use of paraffin. Correlations giving the local and global Nusselt numbers, depending on Reynolds and Prandtl numbers, were established. [ABSTRACT FROM AUTHOR]

The laser filament winding of preimpregnated thermoplastic tapes requires a multiphysical analysis, leading to the control of transformation parameters. Such an analysis is generally carried out by considering the raw material, the tape, as a "standard material". Consequently, conclusions can be biased due to the material variability, which presents at least a natural variability, at worst local or repeated defects. Therefore, in the present work, the subject under study is the thermal behavior of the tape, independently of the manufacturing conditions. The detected thermal irregularities are then put into perspective with the irregularities of the material, such as thickness variations or porosities. [ABSTRACT FROM AUTHOR]

A one-dimensional mathematical model has been developed to solve the heat conduction equation and simulate the freezing process for a slab. The mathematical model was solved using finite differences and the method of lines (MOL). In MOL, spatial derivatives are discretized by finite differences, and the resulting system in time is integrated using an appropriate solver. Several sets of thermal properties were selected to simulate the process. Predicted freezing time values were compared to 142 published experimental data sets. Predictions obtained by published numerical methods were compared to the experimental data. The freezing time predictions of the proposed model give a percentage error in the range of −4.55 <  E (%) < 4.09, which includes the 142 data sets using the best calculation results. In summary, the MOL is a good numerical prediction method since an adequate set of thermophysical properties is especially tested and selected for each data set. [ABSTRACT FROM AUTHOR]

In recent studies, encapsulated phase change materials (PCM) were developed as novel materials for food packaging because of their improved thermal insulation capacity. The PCMs (often liquid in room temperature) are encapsulated in a shell material so as they can be practically handled. In this work, the thermal behaviour of an encapsulated PCM material (Rubitherm RT5 encapsulated in polycaprolactone PCL) with two different PCM mass fractions was studied. The model was validated by experimental cooling and heating processes, under controlled air temperature conditions. The numerical result demonstrated a better thermal buffering capacity of the encapsulated PCM material compared to a standard one (cardboard). [ABSTRACT FROM AUTHOR]

A family of polymer stars has been prepared from early generation dendritic cores with four, six, and eight arms. Four dendritic cores were prepared from the sequential reaction of a multifunctional alcohol with a protected anhydride, followed by deprotection to afford two or three new alcohol functionalities per reactive site. These cores were used as initiators for the tin-catalyzed ring-opening polymerization of l-lactide and rac-lactide to afford isotactic and atactic degradable stars, respectively. Two series of stars were prepared for each monomer, either maintaining total molecular weight or number of monomer units per arm. The polymers were characterized by NMR spectroscopy, light-scattering gel-permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Our results support previous work that suggests that the length of the arms dictates thermal properties rather than the total molecular weight of the star. Little effect was noted between aromatic and aliphatic cores, presumably due to the flexibility of the rest of the core molecule. We have shown that early generation dendrimers can serve as excellent core structures for building core-first polymer stars via the ring-opening of cyclic esters. [ABSTRACT FROM AUTHOR]

The applied thermo-mechanical loading during cutting process leads to an important tool failure especially when machining is effected on refractory super-alloys such as titanium and/or nickel based-alloys. Heat removal generated by tool/workpiece friction plays an important role in preserving the structural integrity of the cutting tool. Efficient heat removal in machining depends solely on the thermal properties of the tool and on their evolution with temperature and mechanical parameters (strain, strain rate, etc.). In the present work, the effect of these thermal properties on the produced wear during the machining of refractory alloys is particularly investigated. Finite-Element Analysis (FEA) and SEM-imagery were used to map the thermal conductivity within the affected tool zone. The results indicate that depending on the temperature rise, the tool-tip might undergo a severe drop in thermal conduction. This drop may locally restrict the ability of the tool material to dissipate the applied thermal load. This may nucleate thermally congested clusters within the tool-tip where the material completely loses the ability to transport heat. Thermal congestion renders an energetically active zone where the thermal energy available may be used to activate wear through different mechanisms. It is also found that the immediate layer under the surface of the tool tip is important to enhance the ability of the tool material to dissipate the thermal loads. The results also highlight the importance of matching the temperature dependant properties of the different coating layers in order to enhance delamination resistance. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of mix design factors on the thermal properties of Superpave asphalt concrete. The thermal properties were measured using a guarded testing device (k-alpha device) developed recently at the University of New Brunswick. Two aggregate types, three gradations (determined by the material retained on a 4.75 mm sieve), and four compaction levels (at 35, 70, 100, and 160 gyrations) were investigated. The aggregate was 12.5 mm maximum nominal size with PG58-34 asphalt binder used for all mixes. The findings show that the thermal conductivity of the asphalt concrete ranged from 1.7 to 2.1 W/m·K. The specific heat capacity varied with the aggregate source and ranged from 940 to 2000 J/kg·K. The thermal diffusivity was found to vary with aggregate source. The aggregate type was found to have the most significant effect on the thermal properties. The compaction level had an effect but not a statistically significant one. The range of thermal properties determined in this paper is comparable to that found in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Calculations of refrigerant thermal properties are desired to be very fast and stable in cases of simulation of refrigeration system, etc. The traditional method based on equation of state cannot meet such requirement because of unavoidable iterations in calculation. In this paper, a new calculation method for refrigerant thermal properties is presented. Low order implicit polynomial equations are got by using curve-fitting method at first, and then explicit formulae for calculating refrigerant thermal properties quickly are obtained by getting the analytical solution of these implicit equations. Explicit fast calculation formulae for thermal properties of R22 and R407C, covering the saturated temperature of −60∼80°C and superheat of 0–65°C, are presented as examples. The calculation speeds of the formulae of R22 are about 140 times faster than those of REFPROP 6.01 while the formulae of R407C are about 1000 times faster. The total mean relative deviations of the fast calculation formulae for R22 and R407C are less than 0.02%. [Copyright &y& Elsevier]

Microwave-induced esterification of cellulose in homogeneous phase has been investigated. Cellulose was first solubilized in the solvent system LiCl/N,N-dimethylacetamide and then esterified by lauroyl chloride in the presence of N,N-dimethyl-4-aminopyridine. Microwave activation resulted in a drastic reduction of reaction time (1 min) compared to conventional heating. The mechanical and thermal properties of the plastic films obtained were established and a preliminary study of their biodegradability has been performed. To cite this article: C. Satge´ et al., C. R. Chimie 7 (2004). [Copyright &y& Elsevier]

The amplitude and phase of the PPE signal for a strongly scattering sample were calculated using a four-flux model. The sensitivity of both PPE amplitude and phase with respect to the thermal properties and water content of the sample were calculated together with the correlations between the parameters. We show that the water content of a sample can be estimated from the signal amplitude, provided the availability of an a priori knowledge of the optical parameters'' dependence on the water content. Once the optical characterization is completed, the phase signal can be used for the thermal properties evaluation. The experimental values of the thermal parameters depend on composition, structure and water content. The difference between the results obtained by the photothermal method and those obtained by DSC and Alambeta methods is discussed. [Copyright &y& Elsevier]

Glasses in the system Li2O–SnO–B2O3 system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B2O3 glasses exhibited relatively low glass-transition temperatures (Tg) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of Tg indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B2O3 binary system. [Copyright &y& Elsevier]