Rewetting of Hot Vertical Surfaces by a Falling Liquid Film

In this work, a transient heat conduction model is developed for rewetting a hot wall surface by a falling liquid film. In the model, the heat conduction in the rewetted wall is assumed to be two‐dimensional. Convection heat transfer from the hot surface to rewetting fluid is considered negligible in the dry surface region ahead of the wet front. The numerical solution indicates that the rewetting process is mainly controlled by two‐dimensional heat conduction in the rewetted wall, even for the walls of low Biot number, especially at low initial temperatures. The effects of Biot number and initial wall temperature on the rewetting velocity are investigated. Comparison of the results with previous studies is presented.     

Thermal Interaction between Two Forced‐Convection Boundary Layers across a Conductive Solid Wall

This paper presents an analytical model to the problem of thermal interaction between two forced convection layers of parallel flow on opposite wall sides. The problem is formulated in dimensionless terms to generalize the solution. The two convection layers are analyzed separately by employing the integral technique. The two analyses are then coupled by applying the solid–fluid interfacial conditions. The study indicates that the thermal interaction process is governed mainly by two dimensionless parameters relating the heat transfer effectiveness of two interactive convection modes and wall conduction. The effects of governing parameters on the flow and heat transfer characteristics of two coupled convection layers are documented. Results regarding mean conjugate Nusselt number are obtained for wide ranges of governing parameters.     

Characterization of bio-oils from the fast pyrolysis of white oak and sweetgum

Conversion of lignocellulosic biomass into bio-oil through fast pyrolysis process is considered one of the promising routes to supplement conventional fossil oil. Future bio-refineries require production large amounts of bio-oil from several biomass types. Characterization of the produced bio-oils is important to determine their suitability as bio-refinery feedstock. In this study, bio-oils were produced from white oak and sweetgum woods in an auger reactor at 450°C. The yields of char, liquid, and gas were calculated. The physical characterization of bio-oils was performed based on the investigation of different properties, such as pH, density, viscosity, water content, acid value, and molecular weight distribution of bio-oil components. The chemical compositions of the bio-oils were also investigated by gas chromatography/mass spectrometry and Fourier transform infra-red analyses. The physicochemical properties of the produced bio-oils were comparable to those obtained from similar woody biomass and the oils were suitable for fuel production.     

Effect of Nitrogen and Niobium on the Structure and Secondary Hardening of Super Hard High Speed Tool Steel

High‐speed steels have been used mostly for multi‐point cutting tools and for plastic working tools. High speed steels are ferrous based alloys of the Fe‐C‐X multi‐component system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. The properties of these steels can be improved by modifying their chemical composition or the technology of their production. One of the new trends in modifying the tool steels chemical composition consists in the addition of niobium and nitrogen. In this work, the effects of niobium and nitrogen on morphology of carbides and secondary hardening temperature of investigated high speed tool steels were studied. This experimental work shows that, the conventional ingots have many types of carbides of different shapes and sizes precipitate on the boundary together with thick needle like carbides. On the contrary, for nitrogen steel, the nitrogen alloying leads to form dense, fine and well distributed microstructure. While, on the case of niobium alloying, single carbide (MC), and different types of eutectic carbides were precipitated which have a major effect on the secondary hardening temperature.     

Transdermal Delivery of Tadalafil. I. Effect of Vehicles on Skin Permeation

Transdermal delivery that avoids the presystemic disposition can provide an alternative to oral administration of tadalafil. Accordingly, the aim of this study was to select the best vehicle as the first step in optimization of tadalafil transdermal delivery. The vehicles were used neat or in selected binary combinations and were evaluated for drug solubilization and transdermal delivery. The drug solubility in pure vehicles were ranked as polyethylene glycol (PEG) 400 >?propylene glycol (PG) >?ethanol >?ethyl oleate (EO) >?isopropyl myristate (IPM) >?water. The solubility in binary systems containing ethanol at 2:1 ratios with EO or IPM was greater than that obtained with pure ethanol, EO, or IPM. This effect could be due to the cosolvency effect. The transdermal drug delivery from pure vehicles was ranked as IPM >?EO >?ethanol >?PG >?PEG >?water. The delivery from binary mixtures of ethanol with either IPM or EO was higher than that obtained from pure solvents with the delivery increasing with increasing ethanol concentration in the mixtures. The delivery from binary mixtures was synergistic rather than additive. The study thus demonstrated a potential of tadalafil transdermal delivery. Binary combinations of ethanol with either IPM or EO provided the first step forward toward the development of transdermal delivery system for tadalafil.     

Fabrication and mechanical evaluation of hydroxyapatite/oxide nano-composite materials

In the current study, the semiconducting metal oxides such as nano-ZnO and SiO₂ powders were prepared via sol–gel technique and conducted on nano-hydroxyapatite (nHA) which was synthesized by chemical precipitation. The properties of fabricated nano-structured composites containing different ratios of HA, ZnO and SiO₂ were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The effect of the variation of ratios between the three components on mechanical, microstructure and in-vitro properties was assessed to explore the possibility of enhancing these properties. The results proved that the mechanical properties exhibited an increment with increasing the ZnO content at the extent of HA. In-vitro study proved the formation and nucleation of apatite onto the surface of the fabricated composites after one week of immersion. It is concluded that HA composites containing SiO₂ or SiO₂/ZnO content had a suitable mechanical properties and ability to form apatite particles onto the composite surface. Based on bioactivity behavior, Si-HA is more bioactive than pure hydroxyapatite and nano-arrangements will provide an interface for better bone formation. Therefore, these nano-composites will be promising as bone substitutes especially in load bearing sites.     

Application of artificial neural networks for modeling of biohydrogen production

In this study, an artificial neural network (ANN) model was developed to estimate the hydrogen production profile with time in batch studies. A back propagation artificial neural network ANN configuration of 5–6–4–1 layers was developed. The ANN inputs were the initial pH, initial substrate and biomass concentrations, temperature, and time. The model training was done using 313 data points from 26 published experiments. The correlation coefficient between the experimental and estimated hydrogen production was 0.989 for training, validating, and testing the model. Results showed that the trained ANN successfully predicted the hydrogen production profile with time for new data with a correlation coefficient of 0.976.     

THERMOELASTIC PROPERTIES OF COMPOSITES CONTAINING ELLIPSOIDAL INHOMOGENEITIES

This article studies the thermal stresses and the effective thermoelastic properties of composites containing ellipsoidal inhomogeneities. The cluster scheme developed recently by A. Molinari and M. El Mouden in The Problem of Elastic Inclusions at Finite Concentration, Int. J. Solids Struct, vol. 33, pp. 3131 - 3150, 1996, for the case of elastic inclusions embedded in an isotropic elastic matrix, is generalized to the case of ellipsoidal thermoelastic inclusions embedded in an anisotropic thermoelastic matrix. The shape, spatial distribution, and orientation of the inhomogeneities are taken into account in our scheme. The theoretical results for a composite of S_iO₂ particles in a Kerimid matrix are in good agreement with experimental measurements.