Turbulent Flow In An Active Wind-Driven Ventilation Device

Growing concern on environmental issues has prompted house owners and industries to consider use of roof top ventilators, as a passive form of quality air circulation and comfort using only wind energy. However, many of these ventilators have evolved through trial and error and the flow physics associated with these ventilators is barely understood. This study presents prediction of airflow using Computational Fluid Dynamics (CFD) technique code, FLUENT, so as to visualize the flow behavior around and within turbine ventilator in addition to determining the aerodynamic forces acting on a turbine ventilator during operation and comparing the simulated results to available experimental data. The prototype used for this investigation is a wind driven ventilator from Edmonds Company with a rotor diameter of 330 mm and base diameter of 1 50 mm. The free stream velocities in visualization of flow are set to be 7 and 20 m.s-l when, for determining the aerodynamic forces are considered to be 7, 10, 14, 20 and 25 m.s-l corresponding to experiment. The simulated prototype is placed in a control volume with the same dimensions as open circuit wind tunnel used in experimental investigation. Also the operating pressure and fluid properties are set to be the same as experiment. Standard k-E, Realizable k-E, SST k-w and RSM turbulence models are used by taking advantage of moving mesh method to simulate the rotation of turbine ventilator and the consequent results are obtained through the sequential process which ensures accuracy of the computations. The results demonstrated that, the RSM turbulence model shows the best performance on flow visualization and predicting the aerodynamic forces acting on a turbine ventilator. Results from this study, besides ensuring the reliability of utilizing the CFD method in design process of future turbine ventilators, would lead us to a conspicuous progress on increasing the efficiency at reduced cost of wind driven ventilators and similar devices

Time Limit at vV02max and V02max Slow Component in Swimming: a pilot study of University Students

The aim oftms study was to measure in swimming-pool conditions, the time to exhaustion at the minimum velocity that elicits maximal oxygen consumption (TLim-vV02max) and to verify the existence of an oxygen uptake slow component (02SC) in freestyle swimming. Ten university students performed a continuous incremental protocol for vV02max assessment. Forty-eight hours later, they swam to exhaustion at vV02max to assess TLim-vV02max and 02SC. V02 was directly measured and swimming velocity was controlled by a visual pacer. Blood lactate concentrations ([La-]) and heart rate (HR) values were also measured. Mean V02max for the incremental test was 54.2±8.2 m1.kg'l.min'l, and the correspondent vV02max was 1.19±O.08 m.S,l The mean duration ofthe TLim-vV02max test was 325±76.5 s. 02SC appeared in the allout swim at VV02max (279.0±195.2 ml.min'l) and it was found to significant1y correlate with the TLim-vV02max (r = .74, p< .05). These results demonstrated that 02SC is observed also in swimming-pool conditions and that TLim-vV02max values are in accordance with typical formulations of aerobic power training sets for swimmers.We wish to thank Prof Dr. José Soares, from the Laboratory of Exercise Physiology of our faculty, for his significant contribution.info:eu-repo/semantics/publishedVersio

Physical absorption of CO2 and propene into toluene/water emulsions

The physical absorption of CO2 and propene into toluene/water emulsions is studied in a stirred cell and laminar film absorber. Experimentally observed masstransfer rates are compared to an absorption model, based on Higbie's penetration theory describing physical gas absorption into an emulsion. For all absorption experiments in a stirred cell absorber (toluene fractions and stirring rates), experimentally observed mass-transfer rates are considerably higher than the rates predicted by the absorption model. Moreover, the absorption rate decreases with increasing stirring rate, whereas no influence of the stirring rate is predicted by the absorption model. In contradiction to the absorption experiments in a stirred cell absorber, the observed mass-transfer rates in the laminar film absorber agree with the model simulations. Probable existence of a very thin toluene layer is observed on top of the emulsion for the stirred cell experiments, likely due to minor phase separation. Since in the laminar film absorber gas-liquid interface and the gravity force are parallel, this phenomenon does not probably occur significantly for absorption experiments in this absorber. The observed mass-transfer phenomena can be explained, at least qualitatively, from the occurrence of a thin toluene layer

Multifractal stationary random measures and multifractal random walks with log-infinitely divisible scaling laws

We define a large class of continuous time multifractal random measures and processes with arbitrary log-infinitely divisible exact or asymptotic scaling law. These processes generalize within a unified framework both the recently defined log-normal Multifractal Random Walk (MRW) [Bacry-Delour-Muzy] and the log-Poisson "product of cynlindrical pulses" [Barral-Mandelbrot]. Our construction is based on some ``continuous stochastic multiplication'' from coarse to fine scales that can be seen as a continuous interpolation of discrete multiplicative cascades. We prove the stochastic convergence of the defined processes and study their main statistical properties. The question of genericity (universality) of limit multifractal processes is addressed within this new framework. We finally provide some methods for numerical simulations and discuss some specific examples.Comment: 24 pages, 4 figure

Sampling of stochastic operators

We develop sampling methodology aimed at determining stochastic operators that satisfy a support size restriction on the autocorrelation of the operators stochastic spreading function. The data that we use to reconstruct the operator (or, in some cases only the autocorrelation of the spreading function) is based on the response of the unknown operator to a known, deterministic test signal

Zinc Contents of Mafic Micerals in Granitic Rocks, with Special Reference to Ore Chemistry

In order to know the reason why the Cu/Zn-Pb ratios of skarn-type deposits related with the ilmenite-series granitic rocks are markedly higher than those related with the magnetite-series, comparative mineralogical studies were carried out for the two types of granitic rocks in the Chugoku district. An attention was focused on the be-havior of Zn during the crystallization of granitic magma, because Zn contents of mafic minerals can be obtained by non-destructive electron microprobe analyses. Microscopic observation indicats that no sphalerite occurs in the magnetite-series granitic rocks, which im-plies that the magmas corresponding to the granitic rocks were undersaturated in respect to ZnS. Electron micro-probe analyses revealed that the Fe/(Fe+Mg) ratios of mafic minerals such as biotite and hornblende in the ilmen-ite-series granitic rocks are remarkably higher than those in the magnetite-series, and the Zn contents are posi-tively correlated with the Fe/(Fe+Mg) ratios in the ilmenite-series granitic rocks. Also the Zn/Fe rations seem to be slightly higher in the ilmenite-series granitic rocks. In contrast, the correlation between Zn contents and Fe/(Fe+Mg) ratios is ambiguous in magnetite-series granitic rocks. With a progress of crystallization differentiation, therefore, Zn may be removed more effectively in the il-menite-series granitic magma, and the contents may be growing scarce in the fractionated ilmenite-series granitic magma. On the other hand, magnetite-series granitic magma probably increases the Zn-contents in the advanced stage of the crystallization. The hydrothermal fluids genetically related to the fractionated magnetite-series grani-tic magma are likely to be enriched in Zn, being favorable for the formation of Zn-rich deposits

An evaluation of the accuracy of some radar wind profiling techniques

Major advances in Doppler radar measurement in optically clear air have made it feasible to monitor radial velocities in the troposphere and lower stratosphere. For most applications the three dimensional wind vector is monitored rather than the radial velocity. Measurement of the wind vector with a single radar can be made assuming a spatially linear, time invariant wind field. The components and derivatives of the wind are estimated by the parameters of a linear regression of the radial velocities on functions of their spatial locations. The accuracy of the wind measurement thus depends on the locations of the radial velocities. The suitability is evaluated of some of the common retrieval techniques for simultaneous measurement of both the vertical and horizontal wind components. The techniques considered for study are fixed beam, azimuthal scanning (VAD) and elevation scanning (VED)