10,826 research outputs found

    Mineralisation of 2,4-dichlorophenoxyacetic acid by acoustic or hydrodynamic cavitation in conjunction with the advanced Fenton process

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    The mineralisation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the presence of zero-valent iron and hydrogen peroxide (the Advanced Fenton process – AFP) whilst being subjected to acoustic or hydrodynamic cavitation is reported. If the reaction is merely stirred then there is 57% removal of TOC whilst on irradiation the figure is 64% although the latter reaction is more rapid. Use of ultrasound alone results in only 11% TOC removal in 60 min of treatment time. Addition of iron powder marginally enhances the extent of degradation but an appreciable increase is observed in the presence of hydrogen peroxide which acts as a source for hydroxyl radicals by Fenton chemistry as well as by dissociation in the presence of ultrasound. The use of hydrodynamic cavitation in conjunction with the advanced Fenton process has also been found to be a useful tool for continuous remediation of water contaminated with 2,4-D. After 20 minutes of treatment the residual TOC is reduced to 30% and this probably represents the remaining highly recalcitrant small organic molecules

    Investigation of boundary layer and turbulence characteristics inside the passages of an axial flow inducer

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    A study of the boundary layer and turbulence characteristics inside the passages of an axial flow inducer is reported. The first part deals with the analytical and experimental investigation of the boundary layer characteristics in a four bladed flat plate inducer passage operated with no throttle. An approximate analysis for the prediction of radial and chordwise velocity profiles across the passage is carried out. The momentum integral technique is used to predict the gross properties of the boundary layer. Equations are given for the exact analysis of the turbulent boundary layer characteristics using the turbulent field method. Detailed measurement of boundary layer profiles, limiting streamline angle and skin friction stress on the rotating blade is also reported. Part two of this report deals with the prediction of the flow as well as blade static pressure measurements in a three bladed inducer with cambered blades operated at a flow coefficient of 0.065. In addition, the mean velocity and turbulence measurements carried out inside the passage using a rotating triaxial probe is reported

    Equivelar and d-Covered Triangulations of Surfaces. I

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    We survey basic properties and bounds for qq-equivelar and dd-covered triangulations of closed surfaces. Included in the survey is a list of the known sources for qq-equivelar and dd-covered triangulations. We identify all orientable and non-orientable surfaces MM of Euler characteristic 0>χ(M)≥−2300>\chi(M)\geq -230 which admit non-neighborly qq-equivelar triangulations with equality in the upper bound q≤⌊12(5+49−24χ(M))⌋q\leq\Bigl\lfloor\tfrac{1}{2}(5+\sqrt{49-24\chi (M)})\Bigl\rfloor. These examples give rise to dd-covered triangulations with equality in the upper bound d≤2⌊12(5+49−24χ(M))⌋d\leq2\Bigl\lfloor\tfrac{1}{2}(5+\sqrt{49-24\chi (M)})\Bigl\rfloor. A generalization of Ringel's cyclic 7mod127{\rm mod}12 series of neighborly orientable triangulations to a two-parameter family of cyclic orientable triangulations Rk,nR_{k,n}, k≥0k\geq 0, n≥7+12kn\geq 7+12k, is the main result of this paper. In particular, the two infinite subseries Rk,7+12k+1R_{k,7+12k+1} and Rk,7+12k+2R_{k,7+12k+2}, k≥1k\geq 1, provide non-neighborly examples with equality for the upper bound for qq as well as derived examples with equality for the upper bound for dd.Comment: 21 pages, 4 figure

    Pressure algorithm for elliptic flow calculations with the PDF method

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    An algorithm to determine the mean pressure field for elliptic flow calculations with the probability density function (PDF) method is developed and applied. The PDF method is a most promising approach for the computation of turbulent reacting flows. Previous computations of elliptic flows with the method were in conjunction with conventional finite volume based calculations that provided the mean pressure field. The algorithm developed and described here permits the mean pressure field to be determined within the PDF calculations. The PDF method incorporating the pressure algorithm is applied to the flow past a backward-facing step. The results are in good agreement with data for the reattachment length, mean velocities, and turbulence quantities including triple correlations
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