A new kind of tellurite glass based on TeO2–B2O3–Bi2O3–PbO system is prepared. It is found that B2O3 is the component that contributes most to increase the thermal stability of the glasses, while ...Bi2O3 is the most contributing oxide to decrease the thermal stability. The structural origins for the variations of the thermal stability with the glass composition are discussed based on the Fourier-transform infrared (FTIR) spectrometry measurement. The present glasses show potential to be used for photonic devices and low melting point sealing glasses.
•A new kind of tellurite glass based on TeO2–B2O3–Bi2O3–PbO system is prepared.•B2O3 contributes most to increase the thermal stability of the glasses.•Bi2O3 is the most contributing oxide to decrease the thermal stability.•Increase of PbO content causes a decrease in Tg for the same heat treatment.•The variations of properties with the composition are discussed based on the FTIR.
In this study, free convection heat transfer in a concentric annulus between a cold square and heated elliptic cylinders in presence of magnetic field is investigated. The square and elliptic ...cylinders are maintained at uniform temperatures and it is assumed that the walls are insulating magnetic field. Lattice Boltzmann method is applied to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. The numerical investigation is carried out for different governing parameters namely; the Hartmann number, Rayleigh number and nanoparticle volume fraction. Also a correlation of Nusselt number corresponding to active parameters is presented. The results reveal that average Nusselt number is an increasing function of nanoparticle volume fraction and Rayleigh number, while it is a decreasing function of Hartmann number. Moreover it can be found that the enhancement in heat transfer increases as Hartmann number increases but it decreases with increase of Rayleigh number.
•MHD free convection of nanofluid in a semi annulus enclosure is studied.•LBM is applied to solve this problem.•KKL correlation is used to simulate knf and μnf.•Nuave is an increasing function of ϕ and Ra, while it is a decreasing function of Ha.
Effects of Different Polypropylene Momeni, Vahid; Shahroodi, Zahra; Gonzalez-Gutierrez, Joamin ...
Polymers,
07/2023, Volume:
15, Issue:
14
Journal Article
Peer reviewed
The current study presents the effect of the backbone as an important binder component on the mechanical, rheological, and thermal properties of Aluminium (Al) alloy feedstocks. A thermoplastic ...elastomer (TPE) main binder component was blended with either polypropylene (PP), grafted-maleic anhydride-PP (PPMA), or grafted-maleic anhydride-PPwax (PPMAwax) plus PP, as the backbone. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were performed to investigate the thermal properties of binder systems and feedstocks. Fourier-transform infrared (FTIR) spectroscopy was used to study the chemical interaction between the binder and the Al alloy. After making feedstock filaments, tensile tests, scanning electron microscopy (SEM), and fused filament fabrication (FFF) printing were done. The results showed that although the PP printability was acceptable, the best mechanical properties and printed quality can be achieved by PPMA. TGA test showed that all binder systems in the feedstocks could be removed completely around 500 °C. From FTIR, the possibility of chemical reactions between Al alloy particles and maleic anhydride groups on the grafted PP backbone could explain the better dispersion of the mixture and higher mechanical properties. Tensile strength in PP samples was 3.4 MPa which was improved 1.8 times using PPMA as the backbone.
•For any particular working fluid, there is an optimum mass flow rate which maximizes the collector efficiency.•The highest heat absorption by the collector occurs at different mass flow rates for ...water and CuO nonofluid.•Nanoparticles often enhance the thermal characteristics of the base fluid.•An optimum value of the mass flow rate may be obtained in each individual condition.
Solar water heating is an effective method for heat demands in domestic applications. Solar collector is a main component of any solar water heating system. In this work, the effect of CuO–water nanofluid, as the working fluid, on the performance and the efficiency of a flat-plate solar collector is investigated experimentally. The volume fraction of nanoparticles is set to 0.4% and the mean particle dimension is kept constant at 40nm. The working fluid mass flow rate is varied from 1 to 3kg/min. The experiments are conducted in Mashhad, Iran with the latitude of 36.19°. The experimental results reveal that utilizing the nanofluid increases the collector efficiency in comparison to water as an absorbing medium. The nanofluid with mass flow rate of 1kg/min increases the collector efficiency about 21.8%. For any particular working fluid, there is an optimum mass flow rate which maximizes the collector efficiency. Adding nanoparticles to a base fluid produces a nanofluid which has enhanced thermal characteristics compared with its base fluid.
► Synthesis and characterization of alumina–copper hybrid particles using a thermo-chemical method. ► Preparation of alumina–copper/water hybrid nanofluids by dispersion of synthesized hybrid ...particles in deionised water. ► Heat transfer and pressure drop studies of prepared hybrid nanofluid with volume concentration 0.1%. ► Significant enhancement in convective heat transfer due to the addition of synthesised hybrid particles compared to water. ► Empirical correlations proposed for Nusselt number and friction factor agree well with the experimental results.
In this experimental work, a fully developed laminar convective heat transfer and pressure drop characteristics through a uniformly heated circular tube using Al2O3–Cu/water hybrid nanofluid is presented. For this we synthesized Al2O3–Cu nanocomposite powder in a thermo chemical route that involves a hydrogen reduction technique and then dispersed the prepared hybrid nano powder in deionised water to form a stable hybrid nanofluid of 0.1% volume concentration. The prepared powder was characterized by X-ray diffraction and Scanning Electron Microscope to confirm the chemical composition, to determine the particle size and to study the surface morphology. The convective heat transfer experimental results showed a maximum enhancement of 13.56% in Nusselt number at a Reynolds number of 1730 when compared to Nusselt number of water. The experimental results also show that 0.1% Al2O3–Cu/water hybrid nanofluids have slightly higher friction factor when compared to 0.1% Al2O3/water nanofluid. The empirical correlations proposed for Nusselt number and friction factor are in good agreement with the experimental data.
We have measured the pressure drop and convective heat transfer coefficient of water-based Al2O3 nanofluids flowing through a uniformly heated circular tube in the fully developed laminar flow ...regime. The experimental results show that the data for nanofluid friction factor show a good agreement with analytical predictions from the Darcy's equation for single-phase flow. However, the convective heat transfer coefficient of the nanofluids increases by up to 8% at a concentration of 0.3 vol% compared with that of pure water and this enhancement cannot be predicted by the Shah equation. Furthermore, the experimental results show that the convective heat transfer coefficient enhancement exceeds, by a large margin, the thermal conductivity enhancement. Therefore, we have discussed the various effects of thermal conductivities under static and dynamic conditions, energy transfer by nanoparticle dispersion, nanoparticle migration due to viscosity gradient, non-uniform shear rate, Brownian diffusion and thermophoresis on the remarkable enhancement of the convective heat transfer coefficient of nanofluids. Based on scale analysis and numerical solutions, we have shown, for the first time, the flattening of velocity profile, induced from large gradients in bulk properties such as nanoparticle concentration, thermal conductivity and viscosity. We propose that this flattening of velocity profile is a possible mechanism for the convective heat transfer coefficient enhancement exceeding the thermal conductivity enhancement.
We study the structural phase transition, elastic and thermodynamic properties of HfCr.sub.2 from first-principles calculations. The simulated results are very close to those of previous studies. The ...phase transition from C.sub.15 to C.sub.36 occurs at about 202.7 GPa, while the phase transition pressure from C.sub.36 to C.sub.14 is about 283.9 GPa. It can be seen from the phonon spectra and elastic constants that HfCr.sub.2 is mechanically stable at C.sub.15 phase. It can be concluded that C.sub.15 phase HfCr.sub.2 is ductile from 0 to 200 GPa, and the bigger the pressure, the greater the ductility from G/B value and Poisson's ratio. Then, through the analysis of density of states, the mechanism of metal properties is discussed. Finally, the relation of thermal expansion coefficient, Debye temperature and thermal capacity to pressure and temperature is discussed.
The electronic structure and elastic and thermodynamic properties of the AgMO.sub.3 (M = Nb, Ta) were investigated using first-principles calculations. The lattice parameters and volumes are in ...reasonable agreement with the experimental results. The calculated Cauchy's pressure, Poisson's ratio, and B/G ratio confirm the ductile nature of both the compounds. The variation in entropy (S), thermal expansion coefficient (alpha), constant volume heat capacity (C.sub.v), and the constant pressure heat capacity C.sub.p with temperature have been studied.
The thermal conductivity reduction due to grain boundary scattering is widely interpreted using a scattering length assumed equal to the grain size and independent of the phonon frequency (gray). To ...assess these assumptions and decouple the contributions of porosity and grain size, five samples of undoped nanocrystalline silicon have been measured with average grain sizes ranging from 550 to 64 nm and porosities from 17% to less than 1%, at temperatures from 310 to 16 K. The samples were prepared using current activated, pressure assisted densification (CAPAD). At low temperature the thermal conductivities of all samples show a T(2) dependence which cannot be explained by any traditional gray model. The measurements are explained over the entire temperature range by a new frequency-dependent model in which the mean free path for grain boundary scattering is inversely proportional to the phonon frequency, which is shown to be consistent with asymptotic analysis of atomistic simulations from the literature. In all cases the recommended boundary scattering length is smaller than the average grain size. These results should prove useful for the integration of nanocrystalline materials in devices such as advanced thermoelectrics.
