Jorge M. M. Barata

Mixing in gas-liquid contactors agitated by multiple turbines

Abstract Liquid hydrodynamics in multiple-turbine aerated tanks was modelled in the loading regime by the compartments-in-series model with back flow streams. Back flows between compartments were assumed to be the sum of two components, which derive from mechanical and pneumatical mechanisms of flow generation. Liquid flows due to these mechanisms were correlated in terms of the operating variables N and QG. Correct simulation of gassed and ungassed mixing of a pulse input of tracer was achieved in all cases under study. The mixing model is robust to changes in geometrical parameters and operating conditions with tanks of 0.3 and 0.5 m diameter T, double- and triple-turbine agitators and turbine sizes T 3 and T 2 . A dimensionless mixing time correlation was deduced from mixing simulation by the model. The dimensionless gassed mixing time θ is obtained from θ0 in the ungassed situation through θ = θ 0 /∏ − KFl ef (K > 0) where Π is the gassed-to-ungassed power ratio, Fl ef = Fl Π is the effective gas flow number and K is a configurational constant. The correlation is general and it is found to represent the interactive combination of the mechanical and pneumatical mixing mechanisms. It was successfully tested not only in the same situations as the mixing model, but also with single-turbine agitators.

Impingement of single and twin turbulent jets through a crossflow

Laser-Doppler measurements of velocity characteristics of the flowfield resulting from the impingement of single and twin jets against a wall through a low-velocity crossflow are presented and discussed together with visualization of the flow. The experiments have been carried out for a velocity ratio between the jet and the crossflow of 30, for a Reynolds number based on the jet exit between 60,000 and 105,000, and for the jet exit 5 jet diameters above the ground plate. In addition, calculations based on a two-equation turbulence model are presented for the three-dimensional flow characterized by the measurements, and comparison between experimental and numerical results show that the mean flowfield is well predicted. The calculation of the turbulent field requires, however, consideration of the individual stresses. 21 refs.

Alternative compartment models of mixing in tall tanks agitated by multi-Rushton turbines

Liquid mixing in tall tanks agitated by multiple radial turbines can be modelled by a cascade of well-mixed compartments with backflows. Models have been proposed with different numbers of compartments per stage of agitation. In this paper, the five simplest models are compared in their ability to predict mixing times and concentration transients, and in their requirement for adjusted parameters. Examined models have from 1 to 4 compartments per agitation stage. The model which consists of 3 compartments per agitation stage is shown to be the best, since it predicts reasonably accurate turbulent mixing times and concentration transients, regardless of injection point position, without the need for any parameter adjustment. Compartments within an agitation stage are connected by the liquid circulation rate, known from the literature, while interchange of liquid between agitation stages was measured. The other models either require adjustment of one parameter for mixing time prediction or do not have a structure adequate to account for the effect of tracer injection point.

Velocity Characteristics of Multiple Impinging Jets Through a Crossflow

The mean and turbulent velocity characteristics of the flowfield resulting from the impingement of two and three jets against a wall through a low-velocity crossflow are quantified in detail making use of a laser-Doppler velocimeter and are discussed together with the visualixation of the flow. The experiments have been carried out for a velocity ratio between the jets and the crossflow of 30, for a Reynolds number based on the jet exit of 105,000, and for the jet exit five jet-diameters above the groundplate, and provided a basis to improve knowledge of several related complex flow fields in engineering applications

The turbulence characteristics of a single impinging jet through a crossflow

Abstract The flowfield resulting from the impingement of a single asixymmetric jet against a wall after penetrating a confined cross-flowing stream were studied using laser-Doppler anemometry. The experiments were carried out to investigate the effect of the velocity ratio between the jet and the crossflow for a single impingement height of 5 jet diameters. The results are presented for Reynolds numberss based on the jet exit conditions of between 60,000 and 120,000 corresponding to jet-to-crossflow velocity ratios from 30 to 73 and provide a basis for better understanding of several related but more complex practical flowfields. The data are also suitable for evaluation of the accuracy of the turbulence models used in several numerical methods currently under development for the prediction of this type of flow. As an example of this latter use, calculations are also presented of the three-dimensional flow characterized by the measurements using a standard k - ϵ turbulence model. The difficulty of assessing turbulence model performance in these complex flows due to the intrusion of numerical diffusion errors is demonstrated by comparing calculations on two different meshes and by improving the accuracy of the discretizations on two different meshes and by improving the accuracy of the discretization of the convection terms in the transport equations for momentum using the high-order QUICK method. The ability of the model calculations to simulate the mean and the turbulence fields is examined, particularly in the immediate vicinity of the stagnation point.

Laser Doppler Measurements of a Highly Curved Flow

A system for recording and analyzing an activity, such as a golf activity, is provided. The system comprises an impact detection device and one or more video capture unit for recording and displaying recorded activities. Preferred activities are saved, and may be viewed at a separate viewing unit located remote from the video capture unit. The remote viewing unit allows for replay and analysis of the saved activities. In addition, saved activities and data may be uploaded to the Internet for later viewing and analysis.

Fountain Flows Produced by Multijet Impingement on a Ground Plane

A numerical and experimental study is made of the characteristics of three-dimensi onal fountain flows generated by the impingement of two- or three-axisymm etric turbulent jets on a ground plane through the influence of a low-velocity crossflow. This study provides a basis to understanding more complex flowfields in numerous practical situations including jet-powered vertical/short takeoff and landing (V/STOL) aircraft. The simulations are based on the solution of the time-averaged Navier-Stokes equations and the k-e turbulence model. The computed results are compared with laser-Doppler measurements and visualization results for the cases of two and three jets impinging on a flat plate located at five jet diameters from the jet exit, and a velocity ratio between the jet and crossflow of 30. Comparisons between experimental and numerical results show generally good agreement for the mean flowfield quantities.

Experimental Study of a Ground Vortex

Laser-Doppler measurements of the mean and turbulent components of the velocity flowfield resulting from the frontal collision of a wall jet with a boundary layer are presented and discussed, together with the visualization of the flow with direct photography and digital film imaging. The experiments were carried out for boundary-layer-to-walljet velocity ratios of 0.5 and 0.58. The results revealed the existence of a small counter-rotating recirculating zone located upstream (in the sense of the wall-jet flow) of the separation point, not reported before for this type of flow. This secondary vortex has an oscillating behavior observed in other ground-vortex flows, similar to that which can be observed, namely, through the bimodal histogram of the horizontal velocity (parallel to the wall) measurements, although the power spectra measurements do not exhibit any particular peaks.

First Flight From Europe to the South Atlantic - Gago Coutinho and Sacadura Cabral

The History of the transatlantic flights goes back to 1919 and began with a flight performed from Newfoundland to Lisbon; two weeks later another flight was performed between Newfoundland and Ireland. On 1922, the Portuguese airmen Gago Coutinho and Sacadura Cabral crossed the South Atlantic Ocean by air in a flight performed exclusively with internal means of navigation: a new instrument that consisted in a type of sextant improved with two spirit levels to provide an artificial horizon and also with the help of a “path corrector”. Despite this journey had lasted 79 days to cross South Atlantic Ocean, their flight time was only 62:26 minutes, and they’ve flown 8,383 nautical miles, using 3 different hydroplanes christened: Lusitânia, Pátria and Santa Cruz. Despite this journey had lasted 79 days, their flight time was only 62 h 26 m; they’ve flown 8,383 nautical miles using 3 different hydroplanes christened: Lusitânia, Pátria and Santa Cruz. The new artificial horizon sextant had proven itself while flying over the ocean, without external references.

Transitional mixing in multiple-turbine agitated tanks

Abstract Blending of viscous newtonian liquids was studied in dual- and triple-turbine agitated tanks. The dimensionless power, mixing and interstage flow numbers were all found to be dependent on the Reynolds number as long as the full development of turbulence was inhibited by viscosity (Re 4 ) and they were found to be constant above that limit. The complexity of the transitional regime makes it adverse for simple correlation, but, surprisingly, modelling of mixing in the upper transition region (Re > 400) could still be achieved using a compartment model developed elsewhere for turbulent mixing simulation in this geometry. The model corresponds to a simplified physical representation of the hydrodynamics of the tank