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.

Distribution of oxygen partial pressure in a two-dimensional tissue supplied by capillary meshes and concurrent and countercurrent systems

Abstract: For the calculations of oxygen partial pressure in a two-dimensional tissue model supplied by a capillary network (inhomogeneously perfused tissue), two differential equations are given that describe the process in the tissue and capillaries. The differential equations are coupled by the boundary conditions. Results obtained by using the method of successive displacements are given for the two-dimensional problem. This method exhibits a satisfactory convergence. The accuracy of the results is about ±5% based on the initial concentration. The results for the network model are compared with those for equivalent concurrent and countercurrent systems. Equivalence means in this connection that the area of tissue, the total length of capillaries, and the constants characterizing blood and tissue are the same. Our results for the two-dimensional models permit us to conclude that the differences between the lowest partial pressure in the tissue and the venous partial pressure are smallest in the countercurrent system and largest in the capillary network.

An Ultrathin Skinned Hollow Fibre Module for Gas Absorption at Elevated Pressures

Abstract: An ultrathin skinned hollow fibre membrane module coupled with a liquid absorbent was investigated experimentally for the removal of CO 2 from a gas mixture. The module consists of a bundle of hollow fibres having a dense skin layer at the outer edge of the fibre. The gas mixture containing 4% CO 2 was introduced into the hollow fibre lumen and was in countercurrent contact with the liquid (either water or NaOH solution) fed into the module shell. The overall mass transfer coefficients of carbon dioxide were obtained in the gas phase. A study ofmass transfer in the membrane module indicates that the overall mass transfer coefficients, K AG, are controlled by both the liquid film and membrane resistances. It was also shown experimentally that the use of the ultrathin skinned hollow fibres module for CO 2 absorption has two advantages. Firstly, the dense skin layer of the hollow fibre membrane eliminates the wetting problem commonly encountered in microporous membranes. As a result, the mass transfer operations are stable with long term exposure of the membrane to the liquid absorbent. Secondly, operations of the feed pressure are flexible. The feed gas pressure of 200 k P a higher than the liquid pressure was maintained without any noticeable bubble formation in the liquid phase. The higher operating pressure in the gas phase suggests that the reduction of the mass transfer rate due to the higher membrane resistance could be compensated by an elevation of the feed gas pressure, i.e. increase of the driving force.