Influence of flow coefficient on unsteady impeller loading induced by impeller-diffuser interaction

Unsteady Reynolds-averaged Navier-Stokes (URANS) simulation has been conducted to investigate how the flow coefficient affects unsteady impeller loading. Simulations have been carried out at three flow coefficients — near stall, design, and near choke conditions — for a centrifugal compressor with a radial gap of 1.04. For computational efficiency, the unsteady simulation has been conducted for two impeller and diffuser passages via the Fourier transformation method. Unsteady loading is the largest at the near stall condition; second largest at the near choke condition; and smallest at the design condition. Relative to the design condition, the near stall condition shows lower minimum loading, and the near choke condition shows higher maximum loading. Thus, both off-design conditions result in higher unsteady loading than at the design condition. Such increases at off-design conditions stem from the variations in the pitch-wise static pressure at the diffuser vane inlet caused by the diffuser vane incidence.

     

Control of oxygen concentration in water using a hollow fiber membrane contactor

A novel theoretical analysis was performed to regulate the oxygen concentration in water using a membrane contactor composed of nonporous hollow fibers. The governing ordinary differential equations were derived for the countercurrent flow of the feed water and the feed gas in a membrane contactor. The governing equations were regarded as a two point boundary value problem. The nonlinear ordinary differential equations were simultaneously solved using a finite difference method. The computer program was coded in Fortran language using the Compaq Visual Fortran Software. It was found that the concentration of oxygen dissolved in water increases from 28.9 to 64.3 ppm as the area of the membrane increases from 1.24 to 3.73 m² at the given typical operating condition: the flow rate of the feed gas is kept to be 1.0 L/min; its pressure is maintained to be 4 atm; the flow rate of the water is 15 L/min. It is observed that the concentration of oxygen increases from 48.2 to 56.2 ppm as the concentration of the feed gas increases from 0.75 to 0.95 mole fraction. As the flow rate of the water increases from 15 to 25 L/min, the concentration of oxygen decreases from 56.2 to 38.6 ppm with a constant membrane area of 3.11 m².     

Recognizable-image selection for fingerprint recognition with a mobile-device camera.

This paper proposes a recognizable-image selection algorithm for fingerprint-verification systems that use a camera embedded in a mobile device. A recognizable image is defined as the fingerprint image which includes the characteristics that are sufficiently discriminating an individual from other people. While general camera systems obtain focused images by using various gradient measures to estimate high-frequency components, mobile cameras cannot acquire recognizable images in the same way because the obtained images may not be adequate for fingerprint recognition, even if they are properly focused. A recognizable image has to meet the following two conditions: First, valid region in the recognizable image should be large enough compared with other nonrecognizable images. Here, a valid region is a well-focused part, and ridges in the region are clearly distinguishable from valleys. In order to select valid regions, this paper proposes a new focus-measurement algorithm using the secondary partial derivatives and a quality estimation utilizing the coherence and symmetry of gradient distribution. Second, rolling and pitching degrees of a finger measured from the camera plane should be within some limit for a recognizable image. The position of a core point and the contour of a finger are used to estimate the degrees of rolling and pitching. Experimental results show that our proposed method selects valid regions and estimates the degrees of rolling and pitching properly. In addition, fingerprint-verification performance is improved by detecting the recognizable images.     

Effect of frozen-storage period on quality of American sirloin and mackerel (Scomber japonicus)

Food Science and Biotechnology - This study aimed to study the effect of frozen-storage period on the quality of sirloin and mackerel (Scomber japonicus). The samples were evaluated after being...     

Tailoring Luminescent Solar Concentrators for High-Performance Flexible Double-Junction III-V Photovoltaics

Despite the remarkable advantages of luminescent solar concentrators (LSCs), their application has not been of interest in ultrahigh efficient photovoltaic modules such as multi-junctions and related two-terminal tandems due to challenging issues limiting the cell capability and impeding the output current. Here type of multi-junction LSC photovoltaics is presented that consists of transfer-printed arrays of InGaP/GaAs solar cells and strategically tailored luminescent waveguides. A coplanar waveguide with the non-self-aligned quantum dot luminophores enables simultaneous absorptions of the directly illuminated solar flux and the indirectly waveguided LSC flux, where cell deployment and luminophore spectrum are systematically tuned for balanced enhancement of the subcell photocurrents. Through systematic comparisons across various LSC configurations supported by both experimental and theoretical quantifications, the power conversion efficiency of flexible modules with InGaP/GaAs cell arrays is improved from 1.67% to 2.22% by the optimal LSC, where the module area is 14.4 times larger than the total cell area. The details of optical and mechanical studies provide a further comprehensive understanding of the suggested approach toward multi-junction LSC photovoltaics.