An experimental investigation of drop deformation and breakup in steady, two-dimensional linear flows

We consider the deformation and burst of small fluid droplets in steady linear, two-dimensional motions of a second immiscible fluid. Experiments using a computer-controlled, four-roll mill to investigate the effect of flow type are described, and the results compared with predictions of several available asymptotic deformation and burst theories, as well as numerical calculations. The comparison clarifies the range of validity of the theories, and demonstrates that they provide quite adequate predictions over a wide range of viscosity ratio, capillary number, and flow type

The creeping motion of liquid drops through a circular tube of comparable diameter

The creeping motion through a circular tube of neutrally buoyant Newtonian drops which have an undeformed radius comparable to that of the tube was studied experimentally. Both a Newtonian and a viscoelastic suspending fluid were used in order to determine the influence of viscoelasticity. The extra pressure drop owing to the presence of the suspended drops, the shape and velocity of the drops, and the streamlines of the flow are reported for various viscosity ratios, total flow rates and drop sizes

A computer-controlled four-roll mill for investigations of particle and drop dynamics in two-dimensional linear shear flows

In this paper we describe the design and operating characteristics of a computer-controlled four-roll mill for investigations of particle and drop dynamics in two-dimensional linear flows. The control system is based upon the use of: a video camera to visualize the instantaneous position of the drop or particle; a PDP 11/23 computer, with a pipeline processor acting as an interface between the camera and computer, to calculate the position and implement a control strategy, and d.c. stepping motors to convert an electronic signal to angular velocities of the four rollers. The control objective is to keep the centre of mass of the drop/particle at the centre of the region between the rollers where there is a stagnation point in the undisturbed flow, while maintaining the shear-rate and the ratio of vorticity to strain rate in the flow at fixed values. The resulting system is suitable for studies of: the rotational motions of single solid particles; the deformation and burst of single droplets; or the hydrodynamic interactions of two particles or drops, one of which is held with its centre-of-mass fixed at the stagnation point of the undisturbed flow. In all cases, the flow can be varied from pure rotation to pure strain, and the shear rate can be either steady or changing as a prescribed function of time

Migration of rigid spheres in a two-dimensional unidirectional shear flow of a second-order fluid

The lateral migration of a neutrally buoyant rigid sphere suspended in a second-order fluid is studied theoretically for unidirectional two-dimensional flows. The results demonstrate the existence of migration induced by normal stresses whenever there is a lateral variation of the shear rate in the undisturbed flow. The migration occurs in the direction of decreasing absolute shear rate, which is towards the centre-line for a plane Poiseuille flow and towards the outer cylinder wall for Couette flow. The direction of migration agrees with existing experimental data for a viscoelastic suspending fluid, and qualitative agreement is found between the theoretically predicted and experimentally measured sphere trajectories

Lattice-Boltzmann Method for Non-Newtonian Fluid Flows

We study an ad hoc extension of the Lattice-Boltzmann method that allows the simulation of non-Newtonian fluids described by generalized Newtonian models. We extensively test the accuracy of the method for the case of shear-thinning and shear-thickening truncated power-law fluids in the parallel plate geometry, and show that the relative error compared to analytical solutions decays approximately linear with the lattice resolution. Finally, we also tested the method in the reentrant-flow geometry, in which the shear-rate is no-longer a scalar and the presence of two singular points requires high accuracy in order to obtain satisfactory resolution in the local stress near these points. In this geometry, we also found excellent agreement with the solutions obtained by standard finite-element methods, and the agreement improves with higher lattice resolution

Community and Ecosystem Effects of Buffelgrass (\u3cem\u3ePennisetum ciliare\u3c/em\u3e) and Nitrogen Deposition in the Sonoran Desert

Buffelgrass is a non-indigenous, invasive, C4 grass that was introduced throughout much of southern Texas, the Southwestern United States, and northern and central Mexico to improve degraded rangelands. The successful introduction and spread of buffelgrass follows a trajectory similar to that of other invasive C4 grasses in arid and semiarid ecosystems. In the Plains of Sonora of the Sonoran Desert (Mexico) buffelgrass is favored by widespread removal of native vegetation and seeding, but, why, following initial introduction, the species persists remains unclear. In this study, we addressed two concerns associated with buffelgrass invasion in the Plains of Sonora. We hypothesized that under arid rangeland conditions, buffelgrass outcompetes native herbaceous species (1) through rapid acquisition of limiting nutrients (here assumed to be nitrogen) and (2) under conditions with high nitrogen input. In summer 2002, a 2 by 2 factorial experiment was established with buffelgrass removal and nitrogen addition in both intact desert and converted buffelgrass grassland habitats. In winter 2003, we found that, regardless of habitat type, buffelgrass removal had a positive effect on abundance, biomass, and richness of native herbaceous species while addition of nitrogen, as urea (at 50 kg N ha−1yr−1 or 9.18 lbs N ac−1yr−1), and disturbance resulted in reduction in abundance and biomass. Nitrogen addition did not negatively alter buffelgrass cover. Nitrogen addition had the expected result of increasing initial, peak and total NO3 and NH4 mineralization with the exception of NO3 measures in intact desert. Removal of buffelgrass did not result in significant increases in soil NO3 or NH4 with the exception of peak NH4 in intact desert. Results of this study support observations that native herbaceous species are displaced by buffelgrass invasion and that nitrogen pollution will likely favor buffelgrass over the native herbaceous species in this ecosystem

Feno de pastagem nativa da "Zona de mimoso", como opcao para suplementacao do rebanho, na epoca seca.

Entre os diversos tipos de vegetacao do Piaui, a pastagem nativa da "zona de mimoso" e considerada uma das mais importantes do Estado. O maior problema enfrentado pelo pecuarista da regiao e a falta de forragempara o rebanho, na seca, ja que a pastagem cultivada e insignificante.Neste periodo a pastagem nativa seca totalmente e parte dela e carregada pelos ventos, tornando-se escassa a disponibilidade de forragem. Noperiodo chuvoso, a pastagem nativa chega a ser abundante e, as vezes excedendo o consumo animal. A producao de feno do excedente da pastagemnativa e uma opcao para suplementacao do gado na epoca critica. A UEPAE de Teresina produziu na "zona de mimoso" cerca de 9,0 t de feno parasuplementacao de seu rebanho. O trabalho foi realizado em marco de 1982, quando havia excedentes de forragem. Foram usados dois sistemas: 1)Todas as operacoes (roco, enleiramento e enfaradmento) forma executados manualmente. 2)Foi realizado roco mecanico, e enleiramento manual. Em ambos o enfardamento foi manual em prensa de feno. A maior producao de feno no sistema totalmente manual foi devido a altura de corte das plantas ter sido mais baixa. O feno produzido em Campo Maior tinha 7,85% de proteina bruta e 0,08% de fosforo, com base na materia seca. Este dados mostram que o teor de proteina e superior as necessidades de mantenca dos bovinos, que e de 7,0%. Quanto ao fosforo, esta abaixo de suas necessidades, precisando portanto, de suplementacao mineral.bitstream/item/95804/1/CT190001.pd

Soft lubrication: the elastohydrodynamics of non-conforming and conforming contacts

We study the lubrication of fluid-immersed soft interfaces and show that elastic deformation couples tangential and normal forces and thus generates lift. We consider materials that deform easily, due to either geometry (e.g. a shell) or constitutive properties (e.g. a gel or a rubber), so that the effects of pressure and temperature on the fluid properties may be neglected. Four different system geometries are considered: a rigid cylinder moving parallel to a soft layer coating a rigid substrate; a soft cylinder moving parallel to a rigid substrate; a cylindrical shell moving parallel to a rigid substrate; and finally a cylindrical conforming journal bearing coated with a thin soft layer. In addition, for the particular case of a soft layer coating a rigid substrate we consider both elastic and poroelastic material responses. For all these cases we find the same generic behavior: there is an optimal combination of geometric and material parameters that maximizes the dimensionless normal force as a function of the softness parameter = hydrodynamic pressure/elastic stiffness = surface deflection/gap thickness which characterizes the fluid-induced deformation of the interface. The corresponding cases for a spherical slider are treated using scaling concepts.Comment: 61 pages, 20 figures, 2 tables, submitted to Physics of Fluid

Emissão de amônia em arroz irrigado em várzea tropical, usando clorofilômetro na racionalização de nitrogênio.

O trabalho teve como objetivo estimar as perdas de N, na forma de NH3, derivada da fertilização nitrogenada com uréia em cultivo de arroz irrigado em várzea tropical

Effect of the Target Size in the Calculation of the Energy Deposited Using PENELOPE Code

The specific and linear energy was calculated in target sizes of 10 μm, 5 μm, 1 μm, 60 nm, 40nm and 20 nm by taking into account the contribution of the primary photon beams and the electrons generated by them in LiF: Mg, Ti (TLD-100). The simulations were carried out by the code PENELOPE 2011. Using different histories of primary particles, for each energy beams the mean deposited energy is the same, but to achieve a statistical deviation lower than 1% the value of 108was fixed. We find that setting the values C1 = 0.1 C2 = 0.1 and Wcc = Wcr = 50 eV the time of simulation decreases around the 25%. The uncertainties (1 SD) in the specific energy increases with energy for all target sizes and decreases with target size, with values from 1.7 to 94% for 20 nm and between 0.1 and 0.8% for 10 μm. As expected, the specific and linear energies decrease with target size but not in a geometrical behavior