A numerical investigation of two-phase steam flow around a 2-D turbine's rotor tip

In flow of steam during the divergence nozzles, expansion and decreasing the enthalpy, brings the flow near the saturation conditions. After supercooling, nucleation forms in the flow and the second phase appears. This phenomenon occurs specially during the last stages of steam turbines as low-pressure case and nuclear reactors as high-pressure. In this research, a numerical scheme for transonic two-phase flow within the passages of 2-D rotor-tip section with various backpressures is applied and an Eulerian–Eulerian reference frame is employed for both phases. A classical homogenous nucleation model applied for the mass transfer in the transonic conditions. Five deferent cases have been tested and through the results, pressure profiles around the blades are compared with the experimental data and good agreement is observed. Results show that the most condensation is on the suction surface of blade and it grows by decreasing the downstream pressure.     

Method for flow measurement in microfluidic channels based on electrical impedance spectroscopy

We have developed and characterized two novel micro flow sensors based on measuring the electrical impedance of the interface between the flowing liquid and metallic electrodes embedded on the channel walls. These flow sensors are very simple to fabricate and use, are extremely compact and can easily be integrated into most microfluidic systems. One of these devices is a micropore with two tantalum/platinum electrodes on its edges; the other is a micro channel with two tantalum/platinum electrodes placed perpendicular to the channel on its walls. In both sensors the flow rate is measured via the electrical impedance between the two metallic electrodes, which is the impedance of two metal–liquid junctions in series. The dependency of the metal–liquid junction impedance on the flow rate of the liquid has been studied. The effects of different parameters on the sensor’s outputs and its noise behavior are investigated. Design guidelines are extracted and applied to achieve highly sensitive micro flow sensors with low noise.     

Lifetime maximized data gathering in wireless sensor networks using limited-order distributed source coding

This paper addresses the problem of efficient data gathering in wireless sensor networks with a complexity constrained data gathering node. Due to the complexity constraint, the data gathering node employs an asymmetric DSC that (de)compresses the data of a given node exploiting its dependency with a limited number of other nodes. This is characterized in a DSC rate allocation structure that is referred to as limited-order DSC. Within this structure, we investigate the problem of rate allocation for the nodes to maximize the network lifetime. To this end, an algorithm is proposed that is proven optimal with polynomial complexity in terms of number of network nodes. Numerical results demonstrate that the algorithm, even with limited complexity, allows for exploiting most of the achievable compression gain.     

The Effects of Differential Diffusion on Nanoparticle Coagulation in Temporal Mixing Layers

The effects of size-independent diffusive transport on nanoparticle growth is studied by performing direct numerical simulation of nanoparticle coagulation in temporal mixing layers. The flow field is obtained by solving the incompressible Navier-Stokes equations, while the evolution of the particle field is obtained by using a nodal approach to approximate the aerosol general dynamic equation. Simulations are performed where particles diffuse according to their size and also where all particles have the same diffusivity. For the latter, the model assumes that all particles of different sizes have the same diffusivity as the smallest particles. The advantage of the second approach is the length scales that need to be resolved are larger, facilitating more affordable computations. Simulations are performed at two volume fractions to assess the effects of the models under different growth rates. The results indicate the use of size-independent diffusion coefficients predicts particle sizes and geometric standard deviations that are larger than those obtained with size-dependent diffusion coefficients.     

A numerical study of two-phase transonic steam flow through convergence-divergence nozzles with different rates of expansion

During transonic flow of steam in divergence nozzles, flow first supercools and then nucleates to become two-phase droplet flow. This phenomenon especially occurs in the last stages of steam turbines and affects performance. In this research, a numerical scheme for two-phase flow in nozzle passages is developed. An Eulerian-Eulerian reference frame is used for both phases. The shear stress transport turbulence model is used to model the Reynolds stresses appearing in the averaged Navier-Stokes equations. The homogeneous nucleation model is applied for the mass transfer in the transonic conditions. In this paper three nozzles with different rate of expansion are employed to be under study. Overall pressure ratio (static to total pressure) and droplet size are compared with the experimental data and good agreements are observed.     

Effects of gender-related geometrical characteristics of aorta–iliac bifurcation on hemodynamics and macromolecule concentration distribution

Aorta–iliac bifurcation has been anatomically shown to be asymmetric. Also, statistical data reveal differences in the structural features of average male and female aorta–iliac bifurcation. In the present work, numerical simulations of the macromolecule transport at the aorta–iliac bifurcation are performed. The transport phenomena within the lumen and the arterial wall are coupled. The arterial wall is modeled as a four-layer porous wall, representing endothelium, intima, internal elastic lamina (IEL), and media layers. The layers are all treated as macroscopically homogeneous porous media with uniform morphological properties. The Staverman filtration coefficient is incorporated to account for selective permeability of each porous layer to macromolecules. Different geometrical attributes of the aorta–iliac bifurcation are studied, i.e. asymmetry and gender-dependence. Profiles of macromolecule concentration distributions are obtained for different cases. The results are discussed with regard to the shear stress distribution, which is believed to be one of the key factors in atherogenesis. The present study appears to be the first one to discuss the effects of gender and geometrical characteristics (e.g. asymmetry) on the transport phenomena at the aorta–iliac bifurcation.     

Characteristics of Iranian almond nuts and oils

Almonds of nine different iranian cultivars were studied. The characteristics of almond nuts and almond oils from these cultivars were determined. They also were studied for possible deterioration of their oils during long storage time. Almond nuts from some cultivars showed significant differences. The variations found in the oil characteristics of different cultivars are not definitely due to varietal differences. The majority of these data does not agree with that found in literature. Acid and peroxide values are very low in both 3 and 12 month old samples, proving the good keeping quality of almonds with regard to their oil content.     

Furfuryl alcohol functionalized graphene nanosheets for synthesis of high carbon yield novolak composites

Graphene oxide and furfuryl alcohol modified graphene nanosheets (G‐FA) were used to prepare graphene/novolak composites. Effect of graphene compatibilization on the properties of the composites especially carbon yield value is evaluated. Both types of graphene nanosheets were dispersed uniquely in the novolak matrix as proved by X‐ray diffraction analysis. However, modification of graphene sheets by furfuryl alcohol results in more improved dispersions. Thermogravimetric analysis confirms the elevated thermal stability of the nanocomposites in comparison with the neat novolak. In addition, G‐FA containing composites have higher carbon yield values. A shift in the wave number of characteristic bonds of graphene after oxidation and modification with furfuryl alcohol, O? H, C?O, and C? O bonds, are seen in the Fourier transform infrared spectroscopy spectra. Raman results and scanning electron microscopy images show that graphene nanosheets reduced in size and wrinkled by oxidation and functionalization. Transmission electron microscopy image of the composite with 0.2 wt % of G‐FA reveals the presence of nanosheets with curvature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40273.