Showing papers on "Countercurrent exchange published in 2000"

Cocurrent and Countercurrent Imbibition in a Water-Wet Matrix Block

Abstract: er, Summary Imbibition in water-wet matrix blocks of fractured porous med is commonly considered to be countercurrent. The modeling s ies of this paper indicate that when a matrix block is partia covered by water, oil recovery is dominated by cocurrent imb tion, not countercurrent. It is also found that the time for a spe fied recovery by the former can be much smaller than that countercurrent imbibition. Consequently, use of the imbibiti data by immersing a single block in water and its scale-up m provide pessimistic recovery information. Moreover, it is sho that the application of the diffusion equation for modeling of recovery by cocurrent imbibition leads to a large error. Throug detailed study of the governing equations and boundary co tions, significant insight is provided into the mathematical a physical differences between coand countercurrent imbibitio

Low-speed rotary countercurrent chromatography using a convoluted multilayer helical tube for industrial separation

Abstract: An industrial-scale countercurrent chromatographic system was developed using a slowly rotating helical device which can be automated and left unattended during the operation It uses a multilayer coiled column consisting of long convoluted Teflon tubing of 085 cm id, which provides sufficient retention of the stationary phase under a relatively high flow rate The column is mounted on a seal-less continuous-flow rotary device which eliminates various complications such as leakage and clogging as often caused by the use of a conventional rotary seal Using a multilayer coiled column with a 10-L capacity, 150 g of crude tea extract was successfully purified, yielding 40 g of epigallocatechin gallate of over 927% purity at a recovery rate of 826% The present system can be scaled up for a kilogram-scale separation

Mass transport in a novel two-fluid taylor vortex extractor

Abstract: Flow instabilities occurring in rotating flows can be exploited as a new approach to liquid-liquid extraction. Two immiscible liquids are radially stratified by centrifugal force in the annulus between corotating coaxial cylinders. When the inner cylinder is rotated above a critical speed, Taylor vortices form in one or both of the fluids. Although the flow pattern yields a relatively small amount of interfacial surface area, the surface is highly active for interphase mass transfer due to the local vortex motion. By adding countercurrent axial flow, efficient continuous processing is also possible. This flow yields a viable extraction process, particularly for fluid pairs that are easily emulsifiable and therefore have limited processing options with the current equipment commercially available. This article demonstrates that two-fluid Taylor-Couette flow with countercurrent axial flow is achievable in practice and explores, experimentally and computationally, the mass-transfer characteristics of the flow. Experimentally, when the vortices first appear, axial dispersion decreases and the interphase mass transfer starts to increase. Upon further increase in differential rotation rate, the extraction performance continues to improve, with the mass-transfer coefficient proportional to the strength of Taylor vortices. This suggests that very high extraction efficiencies can be obtained with even larger relative rotation rates. Furthermore, mass-transfer boundary-layer theory, in combination with computational fluid dynamics, provides a reliable method for predicting the extraction performance.

Modelling and Simulation of Flow Maldistribution in Random Packed Columns with Gas-Liquid Countercurrent Flow

Abstract: A macroscopic model, based on the volume-averaged equations of momentum and continuity, is presented to predict hydrodynamic characteristics of gas and liquid countercurrent flow in random packed columns. The main advantage of this approach is that the model equations derived from the mass and momentum conversation laws will remain valid on a wider range of length scale, from laboratory to industrial size packed columns. Therefore they can be used as basic tool for more rigorous design and scale up of packed columns. In this study, the large-scale liquid maldistribution was simulated using the proposed model for a 0.6-m diameter column packed with 25mm stainless steel Pall rings. The development of liquid flow patterns along the packed height was obtained for several different initial distributions of liquid phase. Furthermore, the effect of liquid and gas loads on the liquid distribution was examined. The simulation results are in good agreementwith the experimental data obtained in our laboratory for both water/air and isopar/air systems.

Modeling a protein foam fractionation process.

Abstract: A simple staged model for the protein foam fractionation process is proposed in this article. This simplified model does not detail the complex foam structure and gas-liquid hydrodynamics in the foam phase but, rather, is built on the conventional theoretical stage concept considering upward bubbles with entrained liquid and downward liquid (drainage) as countercurrent flows. To simulate the protein concentration distribution in the liquid along the column by the model, the bubble size and liquid hold-up with respect to the position must be known, as well as the adsorption isotherm of the protein being considered. The model is evaluated for one stage by data from the semibatch foam fractionation of egg albumin and data from the continuous foam fractionation of bovine serum albumin. The effect of two significant variables (superficial gas velocity and feed protein concentration) on enrichment is well predicted by the model, especially for continuous operation and semibatch operation when initial concentration is high.

Bubble column and the use thereof

Abstract: A bubble column can be operated using countercurrent flow including perforated trays. The space-time yield of gas-liquid reactions can be considerably increased if the perforated trays have a substantially uniform distribution of holes, if the cross-sectional area of the individual holes is 0.003 to 3 mm 2 , particularly 0.01 to 0.5 mm 2 , and if the open area of the trays is 3 to 20%, particularly 3 to 10%, and if the bubble column comprises passages for liquid between adjacent liquid zones. The bubble column can be used for carrying out gas-liquid reactions, such as oxidation reactions with air, with the gas and liquid preferably being passed in countercurrent flow through the column. Cocurrent flow may also be used.

Improvement in Performance of Double-Flow Laminar Countercurrent Mass Exchangers

Abstract: A laminar counterflow mass exchange device is an open duct divided into two subchannels of uniform wall concentration by inserting a permeable barrier, in which only the composition of the flow stream varies along the channels. Efficiency improvement in mass transfer has been investigated analytically by using an eigenfunction expansion in power series.The results of enhancement in mass-transfer efficiency are represented graphically and compared with those in a single-flow device (without a permeable barrier inserted). Analytical results show that suitable adjustment of the permeable-barrier position can effectively enhance the mass transfer efficiency compared with the efficiency in single-flow operations.

Dynamic and Steady-State Features of a Cooled Countercurrent Flow Reactor

Abstract: A countercurrent flow reactor (CFR) is an autothermal reactor, in which the reactants flow countercurrently at equal velocities and flow rates through two compartments, with negligible heat-transfer resistance between the two sections. Two-reactor configurations can be used: a “regular” one, in which the two components are fed by two separate feeds; a “folded” configuration, in which a single feed flows first through one compartment and then reverses its direction and flows countercurrently in the second. Temperature and concentration profiles in the regular CFR configuration usually have mirror symmetry around its center. Under cooling, however, asymmetric steady-state profiles may form. The interaction between the heat removed by the effluents and by cooling through the wall may generate complex periodic or even chaotic states. The temperature and concentration profiles in a folded CFR are the same as those attained in a regular CFR, which are symmetric around the reactor center. The imposed symmetry causes the steady-state and dynamic features of the folded CFR to be less complicated than those of the regular CFR and is less likely to cause operational problems. Boundaries of parameter regions with qualitatively different features for both CFR configurations were constructed by the method of Khinast et al. (1998a). The analysis of the CFR enhances the understanding of similar dynamics observed in a reverse-flow reactor.

Grain drying in countercurrent and concurrent gas flow - modelling, simulation and experimental tests.

Abstract: Mathematical models and numerical techniques for simulation of parallel flow grain drying has been proposed and tested. Concurrent flow drying has been simulated using a steady state model. In order to overcome numerical difficulties that appears in simulation of countercurrent flow drying under operational conditions that leads to thermodynamics equilibrium in any section of the dryer stage, a robust approach has been developed based on simulation of the operation starting from initial transient conditions. A lab unit for grain drying has been developed, composed of a countercurrent flow stage coupled on a concurrent flow stage. The mathematical models and numerical techniques has been tested through the comparison between calculated results and experimental data measured for com drying.

Method and device for capturing fine particles by trapping in a solid mixture of carbon dioxide snow type

Abstract: The invention concerns a method for capturing very fine particles present in a fluid flux in liquid, gaseous or supercritical state and a device therefor. The method is characterised in that it comprises steps which consist in: causing said flux to pass through a filtering element (13); stopping the emission of said flux; countercurrent clearing of the filtering material (31) with a carbon dioxide flow under pressure, so as to drive the particles deposited on the filtering material (31); countercurrent expanding of the flux, so as to trap the particles within a solid carbon dioxide snow-type mixture formed during its expansion.

Experimental study of convective heat transfer instabilities in transient response along a countercurrent heat exchanger

Abstract: This article deals with experimental investigations to reveal the effect of combined natural and forced convection in a horizontal tubular countercurrent heat exchanger in both transient and steady states. In transient response, the temperature profiles of hot fluid in a cross section of the inner tube show the influence of buoyancy forces and radial conduction. These profiles are distorted in time and lead to the appearance of oscillating temperature along the inner tube of the heat exchanger. The transient Richardson dimensionless number is calculated to show these effects. Also, a spectral analysis using the discrete Fourier transform has been performed to characterize these temperature instabilities. Using this technique, the influence of flow rates of hot and cold fluids is investigated.

Flow Control Applications using Countercurrent Shear

Abstract: Experiments conducted in planar unconfined and confined countercurrent shear layers, demonstrated that spatial growth rates increase rapidly with decreasing velocity ratio U2/U1. Particle image velocimetry measurements documented the shear layer development and identified significant increases in turbulence intensity, Reynolds stresses and flow three-dimensionality when comparing countercurrent to coflowing shear layers. Countercurrent shear layers also displayed increased turbulent length scales giving rise to reductions in instantaneous strain rates. Control applications exploiting the characteristics of countercurrent shear will be discussed.

Hydraulic Calculations for Cross‐channeled Packings in Distillation Unit Based on a Physical Model

Abstract: A physically based calculation model has been developed in order to describe the liquid and the gas flow in column packings with any arbitrary cross-channel structure. An equation system is presented which characterizes the film flow on the surface as influenced by the countercurrent flowing gas stream and the respective geometric parameters of the packing. The considered hydraulic operating parameters are the pressure drop, the film thickness, and the radial liquid distribution as a function of the column load up to the flooding point. Care was taken to introduce only constants that can be interpreted physically. Their number was reduced to a minimum of three in order to provide the possibility of easy extrapolation to other packing dimensions. Numerical simulations have been carried out for different liquids assuming a fully wetted packing surface. A distribution width is introduced as the parameter characterizing the radial liquid distribution. Its value together with the respective gas split factors are important variables for the inclusion of maldistribution in the calculation of a distillation column. The numerical simulations up to the flooding point correspond well to the experimental data obtained from a test column.

Heat exchanger assembly having condensed exhaust-heat heat-exchanger

Abstract: The utility model relates to a heat exchanger assembly with a condensed waste heat exchanger, belonging to the field of a fast gas water heater. The utility model carries out the improvement mainly in the aspects of the order of the heat exchange of cold water and fume and the discharge of condensed water in the waste heat exchanger. The purpose is to design a fast gas water heater with a compact structure and high heat exchange efficiency. The conducted method of the utility model is that fins of the waste heat exchanger can form a definite included angle with the horizontal plane, and the condensed water can automatically flow into a condensed water receiving and discharging tank which is arranged aside along the included edge of the fins, and the condensed water can be discharged outside along wit the inclined trend. The improved water way is compact and smooth and is in conformity with the principle of countercurrent flow; the heat exchange efficiency of the water heater can be improved.

Backing plate type hot water waste heat recoverer

Abstract: The utility model discloses an energy-saving device for a water heater. The utility model is characterized in that a heat exchange pipe is arranged in a channel formed by an upper and a lower separator plates and a bar separator plate in a surrounding mode, and the heat exchange pipe is fixed through a fixing clamp of the heat exchange pipe. Hot water flows into a lower layer tank through a sieve mesh before drained into a sewer, and flows to an outlet along the channel formed by the upper and the lower separator plates and the bar separator plate in a surrounding mode from an inlet of waste hot water; cold water from a tap water pipe enters the heat exchange pipe from the inlet of the heat exchange pipe to form countercurrent heat exchange with the waste hot water, and the water temperature rises after the heat exchange; the cold water enters the inlet of a water heater from the outlet of the heat exchange pipe, that waste heat of the waste hot water is recovered is realized, and the energy-saving purpose is achieved. The utility model can be used for recovering the waste heat of the waste hot water of a shower device in a public bath room, a gas water heater and an electric water heater, and can be matched with the water heater.

Three phase countercurrent extraction

Abstract: Partitioning of bovine serum albumin (BSA) in an aqueous double countercurrent distribution (DCCD) using a three-phase system was studied and compared with countercurrent distribution using a two-phase system. The two-phase system was composed of Dextran and Polyethylene glycol (PEG) solulions, and the three-phase system consisted of Dextran, Ficoll, and PEG solutions. In the double countercurrent distribution experiment, BSA was partitioned from the stationary bottom phase into the moving middle and top phases. Two peaks resulted from these transfers. A mathematical model that predicts peak positions and shapes based on the partitioning behavior of the solute is provided. Based on model predictions, the DCCD method has potential extraction selectivity and recovery advantages over the traditional CCD method.

Method for the purification of a liquid by membrane distillation, in particular for the production of desalinated water from seawater or brackish water or process water

Abstract: A liquid purification method by diaphragm distillation, specifically, a method of producing demineralized water from seawater, brine or treated water, allows a warm vaporized liquid stream (non-permeate stream) 3 to pass over the porous diaphragm 4 to form a diaphragm 4. Flowing vapor (9) through the pores of the diaphragm to the opposite side of the diaphragm, and condensing the vapor (9) on a cold condenser surface (2) to provide a distillate stream (10), the condenser surface (2) separates the distillate stream (10) from the feed Hng stream (1), the feed stream (1) is countercurrent to the non-permeate stream (3), and with the porous diaphragm (4) Between the condenser surface 2 there is a gas gap 5 of width less than 5 mm. In order to improve the distillate flow rate per unit driving force, a pressure lower than atmospheric pressure and higher than the vapor pressure of the feed stream 1 is maintained in the gas gap 5, and the air permeability of the porous diaphragm 4 is higher than 0.7, The surface area of the condenser surface is 1.2 to 6 times the surface area of the porous diaphragm 4, and there is a local effective vapor pressure difference between the non-permeate streams 3 and the detectable heat of the distillate stream 10 is It is discharged by heat exchange with the feed stream 1 and / or the non-permeate stream 3.

Fluidized-bed reactor and method of performing chemical reactions therein

Abstract: chemical engineering. SUBSTANCE: reactor contains vessel and one or more levels of horizontal partitions. Each partition level has separate passages for ascending gas and descending solid particles. Ascending gas comes out of partition level in the first point located above the second point where descending solid particles come out on the same partition level. Chemical reaction is carried out under gas-solids countercurrent conditions. Gas and solid particles move with velocity equal to 70% that of flood. Partitions are regulated such as to increase flow velocity as much as possible to approach it to flood velocity. EFFECT: significantly increased yield of reaction. 17 cl, 5 dwg, 5 ex

Apparatus for countercurrent heat exchange and its application to installations for the distillation of air

Abstract: This apparatus ( 3 A, 3 B) is for heat exchange between at least one first fluid available at a temperature at about ambient and at least one second fluid available at a cryogenic temperature below −20° C. It comprises structure alternately to circulate the first fluid through heat exchange material in an overall centripetal manner relative to a general central axis (X-X) of the apparatus ( 3 ), from a radially external inlet ( 17 ) of the apparatus, and structure to circulate the second fluid through the heat exchange material in an overall centrifugal manner relative to said central axis, from a radially internal inlet ( 18 ) of the apparatus. Use in cooling regenerators and exchangers, and if desired for simultaneous purification, of atmospheric air to be distilled.