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Countercurrent exchange

About: Countercurrent exchange is a(n) research topic. Over the lifetime, 2255 publication(s) have been published within this topic receiving 28687 citation(s). The topic is also known as: Countercurrent exchange.

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Journal ArticleDOI
Abstract: A theory is presented for the fully-developed flow of gas and particles in a vertical pipe. The relation between gas pressure gradient and the flow rates of the two phases is predicted, over the whole range of cocurrent and countercurrent flows, together with velocity profiles for both phases and the radial concentration profile for the particles. The gas and the particles interact through a drag force depending on their relative velocity, and there are mutual interactions between pairs of particles through inelastic collisions. This model is shown to account for marked segregation of gas and particles in the radial direction, and the predicted relation between the pressure gradient and the flow rates of the two phases is surprisingly complex.

590 citations

Journal ArticleDOI
TL;DR: A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer and shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium.
Abstract: A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer. In two recent theoretical and experimental studies [1, 2] the authors have demonstrated that the so-called isotropic blood perfusion term in the existing bioheat equation is negligible because of the microvascular organization, and that the primary mechanism for blood-tissue energy exchange is incomplete countercurrent exchange in the thermally significant microvessels. The new theory to describe this basic mechanism shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium. A remarkably simple expression is derived for the tensor conductivity of the tissue as a function of the local vascular geometry and flow velocity in the thermally significant countercurrent vessels. It is also shown that directed as opposed to isotropic blood perfusion between the countercurrent vessels can have a significant influence on heat transfer in regions where the countercurrent vessels are under 70-micron diameter. The new bioheat equation also describes this mechanism.

410 citations

01 Jan 1960
Abstract: Unit Operations in Chemical Engineering. STAGE OPERATIONS. Mass Transfer Operations. Phase Relations. Equilibrium Stage Calculations. Countercurrent Multistage Operations. Countercurrent Multistage Operations with Reflux. Simplified Calculation Methods. Multicomponent State Operations. MOLECULAR AND TURBULENT TRANSPORT. Molecular Transport Mechanism. Differential Mass, Heat, and Momentum Balances. Equations of Change. Turbulent-Transport Mechanism. Fundamentals of Transfer Mechanisms. Interphase Transfer. APPLICATIONS TO EQUIPMENT DESIGN. Heat Transfer. Mass Transfer. Simultaneous Heat and Mass Transfer--Humidification. Simultaneous Heat and Mass Transfer--Drying. Simultaneous Heat and Mass Transfer--Evaporation and Crystallization. The Energy Balance in Flow Systems. Fluid Motive Devices. Particulate Solids. Flow and Separation through Fluid Mechanics.

373 citations

Journal ArticleDOI
Abstract: This paper reports flow experiments involving cocurrent and countercurrent spontaneous water/oil imbibition performed on the same laterally coated sample of a natural porous medium with local saturation measurements and various boundary conditions. The experiments with countercurrent imbibition showed slower oil recovery, a smoother water/oil front, and slightly lower ultimate oil recovery than those with predominantly cocurrent imbibition. Numerical simulations revealed that the relative permeabilities that enabled good prediction of countercurrent oil recovery rate are about 30% less than the conventional cocurrent relative permeabilities at a given water saturation. Viscous coupling is assumed to be the origin of this difference. A new formulation of Darcy equations that uses a matrix of mobilities was found to be in qualitative agreement with experimental results.

246 citations

Journal ArticleDOI
Abstract: A novel compact adsorption-based process for removal of carbon dioxide and nitrogen from low and medium natural gas flowrates is discussed. The layered pressure swing adsorption (LPSA) process studied is composed of a zeolite 13X to selectively remove carbon dioxide followed by a layer of carbon molecular sieve 3K to make the separation of nitrogen from methane. The advantage of the process is the removal of two different contaminants in the feed step, delivering methane at high pressure without recompression requirements. A four-step cycle was studied comprising countercurrent pressurization, feed, countercurrent blowdown and countercurrent purge with product. The blowdown step was performed in vacuum to remove carbon dioxide from zeolite 13X. Experiments were performed in a single-column LPSA unit at different temperatures and using different ratios of adsorbent layers to study the effects of these parameters in overall performance of the unit. Feeding a mixture of 60% CH4/20%CH4/20%CO2/20%CO2/20%N2N2, methane purity of 86.0% with 52.6% recovery was obtained at ambient temperature while 88.8% purity with 66.2% recovery was obtained at 323 K. At both temperatures there was a ratio of adsorbent layers where purity reaches a maximum, while product recovery always decreases for larger zeolite 13X layers.

231 citations

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