A novel sampling technique for monitoring atmospheric methane concentrations: A case study with livestock sources.

The substantial increase in the presence of greenhouse gases (GHGs) in the atmosphere has led to the development of several sampling techniques to quantify and characterize the sources of high global warming potential gas emissions. In this context, we developed a new method to estimate the time-averaged concentration of atmospheric methane that employs a long hose to collect a sample of gas by diffusion through one of its ends. We performed numerical simulations to illustrate the basis of our method and to determine the numerical factors required to estimate the time-averaged concentration of methane.

Analytical solutions for the profile of two-dimensional droplets with finite-length precursor films.

By means of the lubrication approximation we obtain the full family of static bidimensional profiles of a liquid resting on a substrate under partial-wetting conditions imposed by a disjoining-conjoining pressure. We show that for a set of quite general disjoining-conjoining pressure potentials, the free surface can adopt only five nontrivial static patterns; in particular, we find solutions when the height goes to zero which describe satisfactorily the complete free surface for a finite amount of fluid deposited on a substrate. To test the extension of the applicability of our solutions, we compare them with those obtained when the lubrication approximations are not employed and under conditions where the lubrication hypothesis are not strictly valid, and also with axisymmetric solutions.

Final state of a perturbed liquid film inside a container under the effect of solid-liquid molecular forces and gravity.

We investigate theoretically the possible final stationary configurations that can be reached by a laterally confined uniform liquid film inside a container. The liquid is under the action of gravity, surface tension, and the molecular interaction with the solid substrate. We study the case when the container is in an upright position as well as when it is turned upside down.

Closed-form expression for the profile of partially wetting two-dimensional droplets under gravity.

Analytical solutions for the shape of both hanging and sitting droplets under the effects of gravity and surface tension are presented. The modeling also includes the action of molecular forces arising between the liquid and the substrate, which are responsible for the formation of a stable nanometric film in the region close to the droplet contact line. The shape of the droplet is completely described by an analytical solution that also accounts for the pancake-shaped droplets as a limiting case.

Thin-film flows with moving contact lines: An approach to reducing computing time.

A numerical method to reduce the computing times of thin-film flows with moving contact lines is presented. The flows of a film and a droplet are calculated in a frame that moves with a nonconstant velocity U(t). The criterion employed to define this velocity is to reduce the maximum height change in the flow's most critical zone.

Analytical solutions for partially wetting two-dimensional droplets.

We present a new analytical solution for the static shape of a two-dimensional droplet in equilibrium with a surrounding thin film on a solid substrate. The modeling includes the effects of capillarity and disjoining-conjoining pressure accounting for intermolecular forces between the solid and the liquid. We derive new analytical solutions for the shape of the droplet, the cross-sectional area, the half-width, and the maximum curvature and inflection points.

Stability study of a constant-volume thin film flow.

We study the stability of a constant volume of fluid spreading down an incline. In contrast to the commonly considered flow characterized by constant fluid flux, in the present problem the base flow is time dependent. We present a method to carry out consistently linear stability analysis, based on simultaneously solving the time evolution of the base flow and of the perturbations.

Spreading of a micrometric fluid strip down a plane under controlled initial conditions.

We experimentally study the spreading of a small volume of silicon oil down a vertical plane with small Bond number. The initial condition is characterized by a horizontal long fluid strip with cross sectional area A and width w(0). We find that the experiments are characterized by a unique nondimensional parameter, R proportional w4(0)/(a2A), where a is the capillary length.

Spreading of a thin two-dimensional strip of fluid on a vertical plane: experiments and modeling.

We study the thin-film flow of a constant volume of silicon oil (polydymethilsiloxane) spreading down a vertical glass plate. The initial condition is generated from a horizontal fluid filament of typical diameter 0.4 mm.