A new flow reactor has been developed that allows the study of heterogeneous kinetics on an aqueous surface coated by an organic monolayer. Computational fluid dynamics simulations have been used to determine the flow characteristics for various experimental conditions. In addition a mathematical framework has been developed to derive the true first-order wall loss rate coefficient, k(1st)(w), from the experimentally observed wall loss rate, k(obs). Validation of the new flow reactor is performed by measuring the uptake of O(3) by canola oil as a function of pressure and flow velocity and the reactive uptake coefficients of N(2)O(5) by aqueous 60 wt % and 80 wt % H(2)SO(4). Using this new flow reactor, we also determined the reactive uptake coefficient of N(2)O(5) on aqueous 80 wt % H(2)SO(4) solution coated with an 1-octadecanol (C(18)H(37)OH) monolayer. The uptake coefficient was determined as (8.1 +/- 3.2) x 10-4, which is about 2 orders of magnitude lower compared to the reactive uptake coefficient on a pure aqueous 80 wt % H(2)SO(4) solution. Our measured reactive uptake coefficient can be considered as a lower limit for the reactive uptake coefficient of aqueous aerosols coated with organic monolayers in the atmosphere, because in the atmosphere organic monolayers will likely also consist of surfactants with shorter lengths and branched structures which will have a smaller overall effect.
The turbulent flow (Re = 1.5 × 10 5 ) near a rough wall with narrow apertures has been numerically analysed to study the effect of the aperture geometry and wall suction on the flow characteristics. The aperture entry geometry is characterized by roughness height and roughness width. The roughness height is varied from 0.3 to 1.2 mm and roughness width is varied from 2.6 to 4.0 mm. The wall suction is characterized by slot velocity which is varied from 0.25 to 5 m/s. The flow characteristics in terms of fluid streamlines, flow resistance, wall pressure, and wall shear have been presented for several cases. The results show that the flow through the apertures is dominated by a separation vortex that covers the aperture. As roughness height increased (or slope of the roughness), the vortex size increased. With increasing wall suction, the vortex size decreased and moved towards the aperture opening. The flow resistance characterized by pressure drop across the aperture is significantly high for very low wall suction and it is increased with increasing roughness slope. At higher wall suction the slot velocity and roughness geometry has less influence on flow resistance. Wall pressure and skin friction coefficients are dependent on the ratio of roughness height to width.Le débit turbulent (Re = 1,5 × 10 5 ) près d'une paroi rugueuse avec orificesétroits a fait l'objet d'une analyse numérique afin d'étudier l'effet de la géométrie de l'orifice et de la succion de la paroi sur les caractéristiques du débit. La géométrieà l'entrée de l'orifice est caractérisée par la hauteur de la rugosité et la largeur de la rugosité. La hauteur de la rugosité variait de 0,3à 1,2 mm et la largeur de la rugosité de 2,6à 4,0 mm. La succion de la paroi est caractérisée par la vélocité de la fente qui variait de 0,25à 5 m/s. Les caractéristiques du débit en termes de lignes de courant du fluide, de résistance au débit, de pression de paroi et de cisaillement de paroi ontété présentées pour plusieurs cas. Les résultats montrent que le débit par les orifices est dominé par un vortex de séparation qui recouvre l'orifice.À mesure que la hauteur de la rugosité augmente (ou pente de la rugosité), le vortex augmente. En augmentant la succion de la paroi, le vortex diminue et se déplace vers l'ouverture de l'orifice. La résistance au débit caractérisée par une chute de pression au travers de l'orifice est significativementélevée en présence d'une succion de paroi très faible et augmente en présence d'une augmentation de la pente de la rugosité. En présence d'une succion de paroiélevée, la vélocité de la fente et la géométrie de la rugosité ont un moindre impact sur la résistance au débit. Les coefficients de pression de la paroi et le frottement du revêtement sont fonction du ratio hauteurà largeur de la rugosité.
in Wiley InterScience (www.interscience.wiley.com).Turbulent flow over a rough wall with suction or blowing is a common fluid mechanics problem that has many practical applications including pulp screening. To better understand, the complex hydrodynamics at the critical region near the surface of the wall, the streamwise mean and velocity fluctuations were determined experimentally using laser Doppler velocietry. The near-wall streamwise velocity fluctuations and local mean streamwise velocity were shown to be a strong function of the surface roughness, and the aperture and cross-flow velocities. A correlation for the mean velocity and the wall shear stress acting near the wall was determined.
In the operation of hydrocarbon liquid pipelines, Computational Pipeline Monitoring (CPM) systems are used for software based leak detection. When installed, CPM systems must meet the regulatory requirements such as API 1130 in the USA and CSA Z662 in Canada. API RP 1130 provides several methods that can be used to test a CPM system: forced parameter testing, simulated leak test (SLT), and fluid withdrawal testing (FWT). Leak tests are performed to establish and verify the leak detection capabilities of the installed CPM system and in some cases test the response of the personnel. One of the primary interests in leak testing is the realism or hydraulic accuracy of the leak signature, in order that the reported leak sensitivity results of the test are reflective of the real performance of the CPM system. Simulated leak tests (SLT’s) use an offline pipeline model to generate hydraulically accurate data which can be fed into the CPM model. SLT’s provide the most flexible and hydraulically accurate solution to simulating leaks, compared to some of the other API RP 1130 compliant test methods. SLT’s do not have leak location restrictions and also correctly models the flow and pressure hydraulic signature of a leak. The paper outlines a novel approach and method to leak simulation, based on its size and shape of the leak hole. This method can be used to represent various sizes of a leak, ranging from a pin hole to a large rupture along the seam. Implementation of the method in a simulator developed with commercial software is discussed. The results of the simulation, namely the hydraulic signatures from the simulated leak and the CPM response, are compared with the widely used leak simulation method using a constant leak rate. Finally, possible applications of this method are considered.
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