An Attempt to Realize Experimental Isotropic Turbulence at Low Reynolds Number

This paper presents an attempt to realize experimental isotropicturbulence at low Reynolds number. For this aim an experimentalapparatus, a turbulence chamber “Box”, was designed and built togenerate a turbulent flow field in the center of the chamber. Theturbulent airflow field was generated by eight electrical fans placedsymmetrically at the eight internal corners of the externally cubicchamber. The turbulence intensity was controlled by the fans speed.Laser Doppler velocimeter (LDV) in single and two-point velocitymeasurements was used to fully characterize the turbulent field insidethe chamber. The main results indicate that the turbulence ishomogeneous and isotropic with a quasi-zero mean velocity within aspherical region of 20 mm radius from the center of the chamber. Themeasured turbulent integral length scale was found to be constant andindependent of the turbulence intensity (or fans speed). Furthermore, anoticeable spectral inertial subrange as prescribed by the Kolmogorovtheory has not been observed at the range of Reynolds number exploredhere, where Re_λ < 100. But rather a scaling region characterized by anexponent that is lower than the Kolmogorov value, ?5/3, has beenidentified. Moreover, the value of this exponent showed no definedtrend, while the width of the inertial scaling region expands as themicroscale Reynolds number increases.     

Dissipation Rate Estimation in a Highly Turbulent Isotropic Flow Using 2D-PIV

Flow, Turbulence and Combustion - In experimental turbulent flows, the estimation of the dissipation rate of turbulent kinetic energy, $$\varepsilon$$ , is a challenge. The dimensional analysis...     

Data-driven fuzzy models for nonlinear identification of a complex heat exchanger

This paper presents and discusses experimental results on nonlinear model identification method applied to a real pilot thermal plant. The aim of this work is to develop a moderately complex model with interpretable structure for a complex parallel flow heat exchanger which is the main component of the thermal plant using a fuzzy clustering technique. The proposed Takagi–Sugeno-type (TS) fuzzy rule-based model is derived through an iterative fuzzy clustering algorithm using a set of input–output measurements. It is shown that the identified multivariable fuzzy rule-based model captures well the key dynamical properties of the physical plant over a wide operating range and under varying operating conditions. For validation, the model is run in parallel and series-parallel configurations to the real process. The experimental results show clearly the high performance of the proposed fuzzy model in achieving good prediction of the main process variables.     

Déplacements Chimiques Induits par Complexation à l'Europium en Série Δ1-Pyrazoline

The complex Eu (FOD)₃ is shown to be a convenient shift reagent for Δ¹-pyrazolines. The five examples described here were chosen to illustrate the usefulness of this method in the attribution of the stereochemistry of polycyclic Δ¹-pyrazolines.     

Theoretical modeling of water vapor transport in cellulose-based materials

The theory of mass transport in porous media is of fundamental importance for different applications such as food, paper packaging, textiles, and wood for building materials. In this study, a theoretical water vapor transport model has been developed for cellulose-based materials, such as paper and regenerated cellulose film. Pore diffusivities were determined from the dynamic moisture breakthrough experiments comprising a stack of paper sheets and regenerated cellulose films in a configuration similar to a packed adsorption column. Other mass transfer parameters were determined from transient moisture uptake rate measurements. The model incorporates pore and surface diffusion as a lump parameter into a variable effective diffusion coefficient. The mass transport, involving both pore and surface diffusions, is evaluated independently. The theoretical water vapor transmission rates (WVTRs) obtained from the model were compared with experimentally determined WVTRs measured under steady-state conditions. The theoretical model, based on intrinsic diffusion, stipulates higher WVTR values compared to the experimental results. However, the theoretical water vapor transfer rates agree well with the experimental results when external mass transfer resistance is incorporated in the model.     

Experimental investigation of spray characteristics of a liquid jet in a turbulent subsonic gaseous crossflow

Two perforated plates with different solidity ratios, S=50% and 67%, were used to investigate the effect of the velocity fluctuations of a subsonic gaseous crossflow on the spray characteristics of a liquid jet including droplet size and velocity distributions. The experiments were conducted over a range of jet-to-crossflow momentum flux ratio of q=16.5-172, and two gas Weber numbers of ?We_g=2.7 and 5.9, corresponding to the enhanced capillary breakup and bag breakup regimes, respectively. The experimental results of this study revealed that the distribution of droplets size associated with a turbulent and a uniform crossflow for each specific breakup regime were approximately identical. The bimodal and single peak distributions of droplets size, respectively, associated with enhanced capillary and bag breakup regimes were generally consistent with the literature reports. However, the transition of the liquid primary breakup regime from enhanced capillary to bag breakup mode was delayed in a turbulent crossflow compared to its uniform counterpart. The general behavior of droplets size-velocity profiles were also consistent with the literature reports. Nonetheless, complex variations in the distribution of droplets velocity when changing the crossflow turbulence intensity were observed and linked with the presence of instabilities on the liquid jet's surface. Finally, the present experiments allowed shedding more light on the reason why the breakup mechanisms of a liquid jet in a conventional uniform crossflow should not be generalized to predict the distinct breakup process of a liquid jet in a turbulent crossflow.     

Bio-guided isolation of Centaurea bruguierana subsp. belangerana cytotoxic components

Centaurea bruguierana subsp. belangerana was extracted by 80% ethanol. The total extract was then partitioned into four fractions including chloroform, ethyl acetate and methanol. Cytotoxic effect of fractions was examined by MTT assay in K562 (chronic myelogenous leukemia), AGS (gastric adenocarcinoma), MCF-7 (breast adenocarcinoma) and SW742 (colon adenocarcinoma) cell lines. The Chloroform fraction, with the lowest LC₅₀ against K-562 cell lines, was partitioned into 14 subfractions and subjected to further purification by reversed-phase (C18) silica gel and sephadex LH-20 column chromatography. Three flavonoids including cirsimaritin, cirsilinelol and eupatilin were isolated for the first time from the species and the structures were confirmed by spectroscopic data. The high selectivity index of the purified flavonoids indicates valuable components with potential few side effects for normal cell lines. However, solubility tests for isolated components indicates the need for novel pharmaceutical dosage forms, in the case for using natural flavonoids as chemotherapeutic agents.     

Adsorption of an organic zwitterion on a Si(1 1 1)-7 × 7 surface at room temperature

The couple sulfonato/Si(1 1 1)-7 × 7 leads to remarkable 2D chiral molecular assembly with a stability improved at room temperature. The voltage-dependency of the STM images has been experimentally investigated and the correlation between STM images and PDOS has been studied. The proposed empirical model of the adsorption of molecules on Si(1 1 1)-7 × 7 has been justified by the experimental and theoretical data.