Search results for "flow [Keywords]"
showing 10 items of 469 documents
Atomic fluorescence spectrometric determination of trace amounts of arsenic and antimony in drinking water by continuous hydride generation
1999
A highly sensitive and simple method has been developed for the determination of As(III), total As, Sb(III) and total Sb in drinking water samples by continuous hydride generation and atomic fluorescence spectrometry (HGAFS). For As determination, water samples aspirated in a carrier of 2 mol l(-1) HCl were merged with a reducing NaBH(4) 3%(m/v) solution, with sample and NaBH(4) flow rates of 12.5 and 1.5 ml min(-1) respectively. The hydride generated in a 170 cm reaction coil was transported to the detector with an Ar flow of 400 ml min(-1), and a limit of detection between 5 and 20 ng l(-1) was obtained. For Sb determination, 2.5 mol l(-1) HCl and 2%(m/v) NaBH(4) were employed, with respe…
Spectrophotometric determination of carbaryl by on-line elution after its preconcentration onto polyurethane foam.
2000
Abstract An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 μg l−1, provided recovery percentages between 94 and 105%. A detec…
Flow resistance law under equilibrium bed-load transport conditions
2018
Abstract The uniform flow resistance equation, in the form due to Manning or Darcy-Weisbach, is often applied to determine the stage-discharge relationship of a river cross-section. The application of this equation, namely the slope-area method, allows to indirectly measure by water level readings the corresponding river discharge. In this paper, a recently deduced flow resistance equation for open channel flow was tested during conditions of equilibrium bed-load transport. First the flow resistance equation was determined by dimensional analysis and applying the condition of incomplete self-similarity for the flow velocity profile. Then the analysis was developed by the following steps: (i…
Testing a theoretical resistance law for overland flow under simulated rainfall with different types of vegetation
2020
Abstract In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using data collected for overland flow under simulated rainfall carried out in plots with vegetation. The available data were obtained exploring a wide range of rainfall intensities (from 60 to 181 mm h−1) and slopes (from 3.6 to 39.6%), and with four different types of vegetation. The database, including measurements of flow velocity, water depth, cross sectional flow area, wetted perimeter and bed slope, was divided in four datasets (one for each vegetation type), which allowed the calibration of the relationship between the velocity profile parameter Γ, the slop…
Assessing an overland flow resistance approach under equilibrium sediment transport conditions
2021
Abstract In this study, for the first time, a theoretically deduced flow resistance equation was tested for an overland flow under equilibrium sediment transport conditions using available experimental data by Liu et al. for five Chinese soils. Initially the relationship among the velocity profile parameter Γ, the channel slope, the flow Reynolds number, the Froude number and the sediment concentration was calibrated using 90 measurements of the available database (Loessial, Cinnamon and Black soil) and tested by other 60 measurements (Red and Purple soil). The results proved that the Darcy–Weisbach friction factor can be accurately estimated by the proposed theoretical approach, with error…
Assessing flow resistance in gravel bed channels by dimensional analysis and self-similarity
2018
Abstract In this paper a new flow resistance equation for open channel flow, based on the integration of a power velocity profile, was tested for gravel bed channels. First this flow resistance equation, theoretically deduced by dimensional analysis and incomplete self-similarity condition, was reported. Then a relationship between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available laboratory measurements of flow velocity, water depth and bed slope carried out in 416 flume experimental runs with a gravel bed. Then the relationship for estimating Γ function and the theoretical resistance equation was tested by 83 independent flume …
Experimental study of boulder concentration effect on flow resistance in gravel bed channels
2021
Abstract Previous studies demonstrated that for open channel flows the power velocity profile can be integrated to obtain the flow resistance law. In this paper the relationship between Γ coefficient of the power velocity distribution, the channel slope and Froude number (Eq. (9) ) is firstly presented. Then the measurements carried out in a laboratory flume covered by hemispheric elements for two different hydraulic conditions (partially inundated and inundated) are used to calibrate this relationship. These elements are placed with a square arrangement and have a concentration range 4–64%. For the two investigated hydraulic conditions, this analysis demonstrates that the relationship to e…
Evaluating the Effects of Sediment Transport on Pipe Flow Resistance
2021
In this paper, the applicability of a theoretical flow resistance law to sediment-laden flow in pipes is tested. At first, the incomplete self-similarity (ISS) theory is applied to deduce the velocity profile and the corresponding flow resistance law. Then the available database of measurements carried out by clear water and sediment-laden flows with sediments having a quasi-uniform sediment size and three different values of the mean particle diameter Dm (0.88 mm, 0.41 mm and 0.30 mm) are used to calibrate the Γ parameter of the power-velocity profile. The fitting of the measured local velocity to the power distribution demonstrates that (i) for clear flow the exponent δ can be estimated b…
Discharge and bed roughness estimation from water level data analysis
2009
Water level data measured at the two ends of a reach are used to compute both the average n Manning roughness coefficient and the discharge hydrograph in the upstream section of the reach. The methodology is first introduced for the simple case of homogenous roughness and large slope, when the kinematic assumption holds for the momentum equation. In the more general case, when subcritical flow can occur along the channel, an approximation of the downstream boundary condition is required to make always identifiable the calibration problem. In this case, the calibration problem is solved by 1) associating to each possible n value the solution of a flow routing problem, with assigned upstream …
The determinants of increasing equity market comovement: economic or financial integration?
2010
This paper investigates to what extent the substantial increase in exposures of local European equity market returns to global shocks is mainly due to a convergence in cash flows (“economic integration”), to a convergence in discount rates (“financial integration”), or to both. We find that this increased exposure is nearly entirely due to increasing discount-rate betas. This finding is robust to alternative ways of calculating discount-rate and cash-flow shocks.