Countercurrent exchange

About: Countercurrent exchange is a research topic. Over the lifetime, 2255 publications have been published within this topic receiving 28687 citations. The topic is also known as: Countercurrent exchange.

Mass transfer in a countercurrent, supercritical extraction system for solutes in moist solids

Abstract: Solutions of partial differential equations (PDE) that describe mass transfer in conventional continuous, countercurrent solid-liquid extraction systems also successfully describe mass transfer in nearly continuous, contercurrent extraction systems where supercritical fluid (SF) is used to extract solutes from moist solids. These solutions can also be used to describe mass-transfer behavior in absorbers where solutes are transferred from SF to showers of liquid drops if information about drop diameters and velocities, effects of circulation in drops and, most important, axial dispersion is available. The variables involved include: dimensionless concentrations, Ficks number, F = Dst/a2 , the stripping factor, a the Peclet number, UL/Da and the mass-transfer Biot number, Bi. In extractors, a slightly greater than 1.0 are needed to provided efficient extraction without excessive circulation of solvent; in absorbers, α should be < 1.0. α, Pe and Bi are used in PDE solutions to determine F and extrac...

Step geometry and countercurrent effects in dump combustor, part 1: Cold flow

Abstract: Nonreacting flow in a backward-facing step combustor is studied while employing a novel countercurrent shear (or counterflow) concept. Counterflow is used to manipulate the turbulent shear layer created by the step to increase turbulent burning velocities, and thereby, reduce ignition delay time. Unfortunately, this concept also leads to a smaller residence time because of a shorter recirculation vortex. These competing challenges of achieving higher burning velocities and longer residence time demand modification of the step geometry. Changes in the step geometry will alter the size and characteristics of the recirculation vortex and the shear layer dynamics within the combustor. These issues are addressed in this paper via a numerical study. For the simulations, Reynolds-averaged Navier–Stokes equations are solved in the framework of the realizable k–� turbulence model. A two-layer approach is used for the near-wall modeling. The paper includes a detailed account of the benefits of countercurrent shear technology, a parametric study based on step-geometry modifications, and an aerodynamic performance evaluation.

Liquid Holdup for Two-Phase Countercurrent Flow in the Packed Column with a Novel Internal

Abstract: In the packed column with a novel internal, which is made of several structured porous passages, gas is divided into two branches which meet liquid in countercurrent and cross-current, respectively, so the excessive pressure drop and “flooding” of conventional gas−liquid countercurrent flow can be avoided. A model for predicting dynamic liquid holdup is presented, and it shows a satisfactory agreement with the experimental results. Below the load point, only the superficial liquid velocity and the volume fraction of the internals have evident effects on the liquid holdup. Above the load point, both superficial gas and liquid velocities have great effects on the liquid holdup and so do the parameters of the internal because they can affect gas-flow behavior.