Abstract A unified approach is proposed for the prediction of heat transfer coefficients in turbulent falling films undergoing heating, evaporation or condensation for both of the cases with or without interfacial shear. A modified van Driest eddy viscosity model, which incorporated a damping factor f and takes into account the effect of variable shear stress, is used to predict the hydrodynamics of turbulent falling films. The calculated film thicknesses are in good agreement with the Nusselt‐Brauer correlations for the non‐sheared film and the Dukler prediction for highly sheared film. Also, by including a van Driest type turbulent Prandtl number model, the asymptotic heat transfer coefficients are accurately predicted and show better agreement with the extensive literature data and correlations than do most of the existing turbulence models proposed to date.
Abstract Melt mixed metallocene-catalyzed polyethylene elastomer (mPE)/clay nanocomposites, using a functionalized polyolefin elastomer (mPE-g-silane) as a compatibilizer, with the addition of the commercial clay with different intercalant types (Cloisite 20A and 30B) were prepared to investigate the importance of interfacial interaction. Cloisite 30B gave a relatively higher polarity than Cloisite 20A, but smaller original d-spacing. According to X-ray diffraction (XRD) and transmission electron microscopy (TEM) results, Cloisite 20A-filled nanocomposites depicted fairly well-dispersed clay within the mPE matrix, except with higher clay content. By contrast, the clay agglomerates were evident for Cloisite 30B-filled cases. A continuous increase of gel content for Cloisite 20A-filled systems was observed, but only a limited variation for Cloisite 30B-filled systems was found. The roles of the polarity degree of the organically modified clay, original d-spacing, and the compatibilizer, were quite essential. Young’s modulus of Cloisite 20A-filled samples increased with increasing clay content, from 23.8±1.3 MPa [0 parts per hundred resins (phr)] to 34.1±2.0 MPa (9 phr), whereas modulus of Cloisite 30B-filled samples did not show a significant variation. The tear strength of Cloisite 20A-filled nanocomposites increased up to two-fold with increasing clay content, reaching 9 phr. Only a slight increase in tear strength of Cloisite 30B-filled nanocomposites was observed. For the cutting strength, Cloisite 20A-filled cases also conferred higher values in comparison with Cloisite 30B-filled cases.
The preparation of self-healing polymers for use following mechanical failure using commercial, bio-based polymers without complex synthesis and expensive healing reagents has been very rare. In this study two commercial, bio-based polymers, natural rubber (NR) and polycaprolactone (PCL), were melt-blended to form NR/PCL blends. To increase the healing efficiency via supramolecular hydrogen bonding interactions, various amounts of acrylic acid were grafted onto the PCL. The results showed that the healing efficiency of the blends in the self-healing test at 80°Cwas higher than for blends at 60 °C due to higher molecular mobility/diffusion resulting from the molecular motions above the melting temperature of PCL which was near 55 °C in all cases. The highest healing efficiency, 62.8%, was attained for the NR/PCL-g-4AA (40/60) blend containing 4 phr PCL of AA. In addition, with the application of the shape memory-assisted self-healing (SMASH) mechanism, the healing efficiency increased further, up to 79.9%. The high shape recovery ratio (>90%) helped the crack to close faster when the sample was heated to trigger the shape memory process, leading to the increased healing efficiency in comparison with the sample without the shape memory process triggered by heating. To the best of the authors' knowledge, there have been no similar works in the preparation of self-healing, bio-based polymer blends through the current approach so far. We suggest the synergistic effects of both the physical and chemical processes applied to commercial, bio-based polymers provide the chance of expanding the applications of these green polymers with additional functionality.
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