Tropospheric transport can be described qualitatively by the slow mean diabatic circulation and rapid isentropic mixing, yet a quantitative understanding of the transport circulation is complicated, as nearly half of the isentropic surfaces in the troposphere frequently intersect the ground. A theoretical framework for the effective isentropic diffusivity of tropospheric transport is presented....

In the previous chapter we dealt with unidirectional flows. Now we turn to the slightly more complicated case of incompressible two-dimensional cellular flows. The velocity field can be obtained from a streamfunction ψ(x, y) according to our usual convention u = (u, v) = (−ψy, ψx). The domain is a periodic array of square cells, each with side , so that the streamfunction has the periodicity ψ(...

The advection of a passive scalar by a quenched (frozen) incompressible velocity field is studied by extensive high precision numerical simulation and various approximation schemes. We show that second-order self-consistent perturbation theory, in the absence of helicity, perfectly predicts the effective diffusivity of a tracer particle in such a field. In the presence of helicity in the flow, ...

The advection-diffusion equation for the concentration of a tracer may be transformed into a pure diffusion equation by using the area inside concentration contours as a coordinate. The corresponding effective diffusivity depends on the geometry of the tracer field, which is determined by the underlying flow. Recent studies have used effective diffusivity, calculated from a suitable tracer, as ...

Thin layer drying of Russian olive (Elaeagnusan gastifolial L.) fruit using a hot air dryer in order to calculate effective moisture diffusivity, activation energy and energy consumption has been evaluated in this article. The selected variables included three levels of air velocity of 0.5, 1 and 1.5 m/s and three air temperature levels of 50, 60 and 70°C. Increased air temperature...

The produced liquid water in cathode catalyst layer (CCL) has significant effect on the operation of proton exchange membrane fuel cell (PEMFC). To investigate this effect, the transport of oxygen in CCL in the presence of immiscible liquid water is studied applying a two-dimensional pore scale model. The CCL was reconstructed as an agglomerated system. To explore the wettability effects, diffe...

This paper is intended to provide a stochastic approach involving the combined use of the Feynman-Kac formula and Monte Carlo method as a solution algorithm for estimating the timedependent effective diffusivity in a one-dimensional parabolic inverse problem. The inverse problem is purposed to design a mathematical model for the gas-diffusion process within the alveolar region of the human's lu...