Topic
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.
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TL;DR: In this paper, a laminar parabolic velocity has been employed to describe the convective diffusive mass transport equation, and the relation of the dimensionless Sherwood number to the Graetz number is in a good agreement with the Leveque semianalytical solution.
Abstract: Hollow fiber membrane modules are extensively used as gas–liquid contactors for acid gas removal from waste gas streams. Hydrogen sulfide is an important indoor and outdoor contaminant, but, given its toxicity, a limited number of experimental results have been reported for this compound. Moreover, chemical absorption has been exclusively investigated. In this study, hydrogen sulfide odor control by absorption in water thanks to a hollow fiber contactor has been studied both experimentally and theoretically. The scrubbing of hydrogen sulfide from air gas mixture is investigated in two porous polypropylene (PP) hollow fiber modules of different contact area and fiber packing fraction. The gas phase is circulated in the lumen of the fiber bore and the liquid phase in the shell in a nonwetted mode, i.e. the membrane pores being filled with gas. The gas phase was run in countercurrent contact with the liquid phase at constant pressure. A laminar parabolic velocity has been employed to describe the convective diffusive mass transport equation which has been solved analytically and numerically. The calculated extents of hydrogen sulfide depletion reasonably compare with the generated experimental results for both membrane modules. Up to 85% of acid gas could be removed at gaseous flowrates of 200 cm3/min for the large module and removals as high as 89% at 10 cm3/min have been observed for the smaller one. The overall mass transfer coefficients calculated from the experimental data, agree satisfactorily with those generated by the mathematical model. The relation of the dimensionless Sherwood number to the Graetz number is in a good agreement with the Leveque semianalytical solution. © 2007 American Institute of Chemical Engineers AIChE J, 54: 122–131, 2008
22 citations
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TL;DR: In this paper, an analytical model that includes steam condensation effect has been derived and a parametric study has been performed to predict the onset of countercurrent flow limiting (CCFL) in nearly horizontal countercurrent two-phase flow for various flow rates of water.
22 citations
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TL;DR: In this article, the process of high purification of gas from easily penetrating impurities in a countercurrent radial membrane element is investigated theoretically and experimentally, and a mathematical model of the process is developed in view of longitudinal mixing impurities.
22 citations
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TL;DR: It is concluded that countercurrent exchange does not influence passive absorption of highly diffusible substances from the small intestine of the rabbit.
Abstract: The purpose of the present study was to quantitate the influence of countercurrent exchange on passive absorption of highly diffusible substances from the small intestine of the rabbit. The absorption of carbon monoxide, which is tightly bound to hemoglobin and therefore cannot exchange, was compared to the absorption of four unbound gases (H2, He, CH4, and 133Xe), which should exchange freely. The degree to which the observed absorption of the unbound gases falls below that predicted from CO absorption should provide a quantitative measure of countercurrent exchange.
CO uptake at high luminal Pco is flow-limited and, assuming that villus and central hemoglobin concentrations are equal, the flow that equilibrates with CO (Fco) was calculated to equal 7.24 ml/min/100 g. The observed absorption rate of the unbound gases was from two to four times greater than would have been predicted had their entire uptake been accounted for by equilibration with Fco. This is the opposite of what would occur if countercurrent exchange retarded absorption of the unbound gases.
The unbound gases have both flow- and diffusion-limited components, and Fco should account for only the fraction of absorption that is flow limited. A simple model of perfusion and diffusion made it possible to calculate the fraction of the total uptake of unbound gases that was flow limited. This fraction of the total observed absorption rate was still about 1.8 times greater than predicted by CO absorption. A possible explanation for this discrepancy is that plasma skimming reduces the hemoglobin of villus blood to about 60% of that of central blood. Thus, Fco is actually about 1.7 times greater than initially calculated, and with this correction, there is close agreement between the predicted and observed rates of absorption of each of the unbound gases. We conclude that countercurrent exchange does not influence passive absorption under the conditions of this study.
22 citations
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13 Jul 1982TL;DR: In this article, the regular packing element is formed by layers of inclined deflecting elements, arranged in crisscrossing relation to each other and providing continuous flow channels which are open at both ends.
Abstract: The regular packing element is formed by layers of inclined deflecting elements. The deflecting elements are arranged in criss-crossing relation to each other and provide continuous flow channels which are open at both ends. In addition, the flow channels are open laterally to the flow channels of the adjacent layers of the deflecting elements. The packing provides for an improved and accelerated mass transfer between two media flowing through the packing in countercurrent.
22 citations