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Showing papers on "Countercurrent exchange published in 1989"


Journal ArticleDOI
TL;DR: In this article, a theory for the fully-developed flow of gas and particles in a vertical pipe is presented, and 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.
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.

613 citations


Journal ArticleDOI
TL;DR: In this article, a generalized model was developed for the prediction of pressure drop and flooding in packed columns in which gas and liquid flow countercurrently, and validated for a wide variety of packings, both random and structured.

254 citations


Journal ArticleDOI
TL;DR: In this paper, an electrically-driven, high-surface-area solvent extraction system has been conceived and tested, which accomplishes droplet formation, coalescence, and phase separation utilizing a single electric field while operating under countercurrent flow conditions.
Abstract: An electrically-driven, high-surface-area solvent extraction system has been conceived and tested. The system accomplishes droplet formation, coalescence, and phase separation utilizing a single electric field while operating under countercurrent flow conditions. The mass-transport capability of this system has been analyzed by observing the transfer of acetic acid from water (dispersed phase) into methyl isobutyl ketone. Results are reported in terms of the number of theoretical transfer stages per centimeter of column. The emulsion-phase contactor, which has 1.7 stages/cm, outperforms laboratory-scale versions of the York-Scheibel column by a factor of 17 and the Podbielniak centrifugal contactor by a factor of 10. The mass-transfer performance along with the minimal energy requirements of this conceptual device combine to make it an attractive possibility for greatly enhanced solvent extraction operations.

42 citations


Journal ArticleDOI
TL;DR: In this article, the absorption of S02 and NH3 from air and air/CO 2 streams was studied for the first time in a certain novel hollow fiber mass transfer device, for various inlet gas compositions, liquid compositions, gas flow rates, and liquid flow rates.
Abstract: The absorption of S02 and NH3 from air and air/CO 2 streams was studied for the first time in a certain novel hollow fiber mass transfer device, for various inlet gas compositions, liquid compositions, gas flow rates, and liquid flow rates. The gas and liquid flows were countercurrent. Analyses of the amounts of S02and NH3 absorbed demonstrate that the hollow fiber unit has a relatively small membrane resistance and is an effective gas scrubbing device. Additionally, it offers a large interfacial area per unit volume, and avoids flooding problems entirely

35 citations


Journal ArticleDOI
TL;DR: The results of an experimental investigation of the performance of a countercurrent moving-bed chromatographic reactor are presented in this paper, where the reaction and separation of the reactant and product, 1,3,5,trimethylcyclohexane, occur during the continuous contacting, giving good product purity.

31 citations


Journal ArticleDOI
TL;DR: The results indicate that only the single-channel countercurrent unit is efficient enough to meet the established requirements, and the apparent thermal clearance provides a useful and rigorous means for comparing and evaluating blood-warming devices.

21 citations


Patent
30 May 1989
TL;DR: In this article, a multi-stage countercurrent process for the purification of isopropylidenediphenol was proposed, where the crystals are melted by the addition of heat and water prior to each crystallization step and one crystallization is accomplished at a pre-selected low temperature.
Abstract: A process for the purification of an aromatic compound, e.g., isopropylidenediphenol, comprising using a multi-stage countercurrent process wherein the crystals are melted by the addition of heat and water prior to each crystallization step and wherein one crystallization is accomplished at a pre-selected low temperature.

20 citations


Journal ArticleDOI
TL;DR: In this article, a macroscopic model based on the volume-averaged equations of motion is presented for countercurrent gas-liquid flow in a packed bed, which yields a column-limited flooding point as the loss of existence of uniform states.
Abstract: A macroscopic model based on the volume-averaged equations of motion is presented for countercurrent gas-liquid flow in a packed bed The model yields a column-limited flooding point as the loss of existence of uniform states It correctly predicts the existence of two uniform states below the flooding point The lower branch corresponds to the trends commonly observed experimentally It is shown that the upper branch is made unattainable by the gas distributor/support plate at the bottom of the column The occurrence of premature flooding induced by the support plate is also explained It is suggested that the occurrence of spontaneous liquid segregation, necessitating frequent liquid redistribution in columns with large dumped packings and porosities, is a consequence of the loss of stability of the uniform state in the lower branch

19 citations


Journal ArticleDOI
TL;DR: In this article, a microporous hollow-fiber membrane/oil stripping system is used to separate volatile organic contaminants from water using an air-filled gas-permeable membrane.
Abstract: Separation of volatile organic contaminants from water using a microporous hollow-fibermembrane/oil stripping system is evaluated. Countercurrent flow of water and oil on opposite sides of an air-filled gas-permeable membrane is used to concentrate the contaminants in the oil phase. The rate of mass transfer under varying conditions is measured and compared to existing full- and laboratory-scale air-stripping processes, to membrane-extraction processes, and to predictions based on known empirical and theoretical correlations. The correlations can be used as the basis for system design and scale-up. This process incorporates the advantages of other membrane-stripping processes, such as a high surface area to volume ratio for transfer, and independent control of the separate liquid phases. It also overcomes several disadvantages of extraction and stripping processes. There is no contact between the liquid phases and thus no potential for cross-contamination or emulsion formation. The membrane separation of phases prevents flow channeling and flooding present in air-stripping towers. Finally, materials used in this process may be recovered aand recycled, preventing further environmental contamination.

18 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model of a three-phase, direct-contact, spray-column heat exchanger has been developed, which is used to calculate performance information about this type of device and to compare, where possible, to experiments.
Abstract: A numerical model of a three-phase, direct-contact, spray-column heat exchanger has been developed. This model has been used to calculate performance information about this type of device and to compare, where possible, to experiments. General equations are defined for distance up the column using a physically based model for the local heat transfer. This model has been used to investigate a number of characteristics of these devices, such as temperature and holdup distributions through the column. A new formulation is given for a mixed, time-averaged temperature that may be representative of measurements taken with temperature transducers in direct-contact heat exchangers. Little has been given in the literature about quantitative variations of performance as a function of the key independent variables, and information on these aspects is presented here. Although the results presented are for a specific geometry (0.61 m diameter, 3 m active column height, evaporating pentane in 85/sup 0/ C water), the variations shown can give insights generally into the factors affecting performance in these devices. In virtually all cases examined here, extremely good comparisons are shown between predictions and measurements. Conclusions are drawn about the applicability of the model and the important effects demonstrated.

17 citations


Journal ArticleDOI
TL;DR: In this paper, a modele d'equilibre local on met en place une optimisation du cycle de purge du processus is used to optimize the cycle of purge.
Abstract: En utilisant un modele d'equilibre local on met en place une optimisation du cycle de purge du processus

Journal ArticleDOI
TL;DR: In this article, an equilibrium theory for fixed beds based on coherence of concentration waves to countercurrent processes is presented. But the analysis focuses on the propagation of disturbance waves on nonuniform steady-state backgrounds and takes into account the critical column-end effect observable only under nonequilibrium conditions.

Patent
11 Oct 1989
TL;DR: In this article, a process for producing gaseous crude argon by low-temperature rectification of air is described, where a portion of the compressed air is further compressed.
Abstract: A process is disclosed for producing gaseous crude argon by low-temperature rectification of air wherein a portion of the compressed air is further compressed. The further compressed air is partially liquefied by countercurrent heat exchange with evaporating crude argon obtained in the liquid phase, this crude argon being under elevated pressure.

Journal ArticleDOI
TL;DR: In this paper, the effect of diffusion and reaction parameters on uphill transport and the optimum length of the mass separator were investigated for fully developed, one-dimensional, laminar flow of a Newtonian fluid in either a parallel plate or hollow fiber mass separators, with equilibrium chemical reactions inside the membrane, the countertransport rate in the separator was analyzed.

Journal ArticleDOI
TL;DR: It was found that the limited penetration of flow-related enhancement with cocurrent flow is a consequence of recently saturated upstream protons flowing into the section to be excited, and the flow- related enhancement penetrates farther with countercurrent flow.
Abstract: Patterns of flow-related signal loss and enhancement have been observed in fluid moving perpendicular to the imaging plane on multi-section-acquisition magnetic resonance images. These patterns depend on whether the flow is in the same direction (cocurrent) or opposite (countercurrent) to the direction of sequential section excitation. For a given velocity, flow-related enhancement penetrates deeper into the imaging volume with countercurrent flow than with cocurrent flow. The signal intensity of inner sections is generally greater with countercurrent flow than with cocurrent flow and depends on the velocity. These effects were investigated quantitatively with phantom studies and correlated with theoretical predictions. It was found that the limited penetration of flow-related enhancement with cocurrent flow is a consequence of recently saturated upstream protons flowing into the section to be excited. The flow-related enhancement penetrates farther with countercurrent flow, because inflowing spins have h...

Patent
07 Aug 1989
TL;DR: An axial flow carbon black reactor for producing carbon black particles having a relatively narrow particle size distribution is described in this paper, where feedstock oil is introduced into the reactor by a spray nozzle located coaxial with the longitudinal center line of the reactor.
Abstract: An axial flow carbon black reactor (10) for producing carbon black particles having a relatively narrow particle size distribution. Feedstock oil is introduced into the reactor by a spray nozzle (12) located coaxial with the longitudinal center line of the reactor. The oil spray flows either in the countercurrent or the concurrent direction relative to the flow of hot gas through the reactor and produces an oil spray pattern covering either substantially the entire frontal area of the hot gas flow or substantially less than the frontal area. Countercurrent feedstock flow from (23) increases coverage of the gas flow area by the oil spray and narrows the particle size distribution of carbon black produced by the reactor, and concurrent feedstock flow produces the opposite result.

Patent
22 May 1989
TL;DR: In this paper, the authors describe a heat exchanger which comprises an annular chamber 19 for circulation of a first heat exchange fluid, in which are made, in a circular arrangement, pipes 1 for circulating a second heat exchange fluids, preferably in countercurrent to the first, and in which the said pipes 1 are bounded by radial walls in contact which interact with each other in the manner of those of a plate exchanger, the said walls being obtained by corrugated plates, folded in their longitudinal direction and closed on themselves so as to form pipes 1 of radially elong
Abstract: The invention relates to a heat exchanger which comprises an annular chamber 19 for circulation of a first heat exchange fluid, in which are made, in an annular arrangement, pipes 1 for circulating a second heat exchange fluid, preferably in countercurrent to the first, and in which the said pipes 1 are bounded by radial walls in contact which interact with each other in the manner of those of a plate exchanger, the said walls being obtained by corrugated plates, folded in their longitudinal direction and closed on themselves so as to form pipes 1 of radially elongate cross-section.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model is formulated for diffusive countercurrent exchange of oxygen between paired arterioles and venules, and a closed form solution is obtained by linearizing the nonlinear oxyhemoglobin dissociation curve at the inlet P O 2 in the vessel.

Book ChapterDOI
TL;DR: In this article, the authors show that when the separation factor of the mixture is small and the desired productivities are large, the first process is usually economically preferable with respect to the second one in spite of the additional cost associated with the more complex plant required by the countercurrent operation.
Abstract: As for most two-phase operations, also in adsorption separation processes continuous countercurrent contact is often preferred to the cyclic batch operation mode. When the separation factor of the mixture is small and the desired productivities are large, the first process is usually economically preferable with respect to the second one in spite of the additional cost associated with the more complex plant required by the countercurrent operation [1,2].

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the desorption of a gaseous reactant due to its supersaturation in the liquid phase by using a modified axial dispersion model.

Journal ArticleDOI
TL;DR: In this article, an analytical solution for absorption of a gas with an accompanying first order reaction in a laminar falling film is developed, where the gas flow is countercurrent to that of the liquid film.
Abstract: An analytical solution for absorption of a gas with an accompanying first order reaction in a laminar falling film is developed. The gas flow is countercurrent to that of the liquid film. Change in the gas phase concentration because of the reaction, as it happens in practical situations, has been taken into account. Some computed results are presented to show the effects of the system parameters—namely, the reaction rate parameter, the Biot number, and the absorption factor— on the mass transfer enhancement factor and on the fractional removal of the feed gas over a given non-dimensional film length.

Journal ArticleDOI
TL;DR: In this paper, a continuous chromatographic separation of an equimolar mixture of 1,3,5-trimethylcyclohexane and 1, 3, 5-trimerethylbenzene with a 2.4 m × 1.37 cm ID vertical countercurrent moving bed is reported.
Abstract: An investigation of the continuous chromatographic separation of an equimolar mixture of 1,3,5-trimethylcyclohexane and 1,3,5-trimethylbenzene with a 2.4 m × 1.37 cm ID vertical countercurrent moving bed is reported. The solid adsorbent was 30 mesh Al2O3, and the separation was carried out at 200°C. Steady-state axial concentration profiles of each species were determined by withdrawing vapor samples for analysis by gas chromatography. The binary mixture was continuously fed through a port located at approximately the midpoint of the column. The relative solids and carrier gas flow rates could be adjusted so that the more strongly adsorbed trimethylbenzene was transported downward, and less strongly adsorbed trimethylcyclohexane moved upward. For low feed rates, high-purity product streams of each were obtained at the bottom and top of the separator. For sufficiently high feed rates, trimethylbenzene was transported upward as well as downward, and top product purity deteriorated. This behavior is in qualitative accord with the predictions of a dispersionless, one-dimensional flow, adsorption equilibrium model incorporating a Langmuir isotherm.

Journal ArticleDOI
TL;DR: In this paper, a cascade theory is used to prove that the stages connected in a simple countercurrent mode must produce two effluent streams equal in size, and this theory is extended for the case of multiple-feed and interstage products to provide a general mass balance solution for a multi-stage separation plant.



Journal ArticleDOI
01 May 1989
TL;DR: In this paper, the authors used van Driest eddy diffusivity in the inner wall region and an interface damping eddy diffusion in the outher region of the film modified to include the effect of interfacial shear.
Abstract: Predictions of average film thickness and mass transfer coefficients in the entrance region of gas absorption with high cocurrent and countercurrent gas flow in a turbulent falling film are presented. The model used is a modified van Driest eddy diffusivity in the inner wall region and an interface damping eddy diffusivity in the outher region of the film modified to include the effect of interfacial shear. The calculations show that the entrance length for mass transfer decreases with increasing film Reynolds number and interfacial shear for cocurrent flow. Also the model predicts a decrease in mass transfer coefficient with an increase in Schmidt number in accordance with experimental data. On the other hand, for counterflow and at a fixedRe, an increase in upward gas shear increases the film thickness and eventually leads to rising film flow. The entrance length for mass transfer decreases with increasing Reynolds number but slightly increases with countercurrent interfacial shear. The calculations show that, in practice, the entrance region for mass transfer for gas absorption with shear-thinned film can be neglected for cocurrent shear but often cannot be neglected for countercurrent shear with a shear-thickened film.

Patent
30 Nov 1989
TL;DR: In this paper, a PSA (pressure swing adsorption) process consisting of operation cycles of backfilling by one thick gaseous oxygen, pressurization by supply air, copurge, blowdown, discharge and countercurrent purge using two or more adsorbent beds is presented.
Abstract: PURPOSE: To obtain high-purity gaseous nitrogen from air by a PSA (pressure swing adsorption) process consisting of operation cycles of backfilling by one thick gaseous oxygen, pressurization by supply air, copurge, blowdown, discharge and countercurrent purge using two or more adsorbent beds. CONSTITUTION: The respective beds A, B for air sepn. receive the operation cycles in the following PSA process: (1) The thick gaseous oxygen is introduced to the discharge end of the bed A and is back filled in a countercurrent direction to cause countercurrent repressurization. (2) The supply air is introduced into the inlet end of the bed and is repressurized to have the nitrogen selectively adsorbed. (3) The nitrogen is passed from the supply end of the bed A to the discharge end to make copurge. (4) The high-purity gaseous nitrogen is discharged from the supply end of the bed A to cause blowdown. (5) The discharge is executed by a vacuum pump. (6) The thick gaseous oxygen extracted from another bed B in the system is passed through the discharge end of the bed to make countercurrent purge. Next, the cycle is returned to the bed B and is executed. The bed A turns to a pressure drop sequence.

Journal ArticleDOI
TL;DR: In this paper, mass flow rates and discharge coefficients were calculated in order to characterize and compare the two geometries with a plain hole (square-edged orifice) and the cylindrical insert, which may cause the high-temperature gradients observed under operating conditions.
Abstract: Heavy-duty gas turbine combustion systems have a reverse flow combustion-cooling air network. High-temperature gradients have been observed in some combustion liners around the plain holes, or around the cylindrical inserts welded into the mixing holes. Flow visualization tests were performed in a countercurrent flow facility. Measurements of pressure and velocity distributions in and around the mixing hole jet were taken, and mass flow rates and discharge coefficients were calculated in order to characterize and compare the two geometries. The results with a plain hole (square-edged orifice) and the cylindrical insert show the presence of a sharp separation region at the trailing edge (combustion side) of the liner hole, which may cause the high-temperature gradients observed under operating conditions. The measured discharge coefficients show a dependence on the insert geometry, the flow parameter (K), and the bottom section (combustion side).

Patent
21 Sep 1989
TL;DR: In this paper, the efficiency of mixing vapour in a countercurrent column is improved by use of one or more vapour risers, each incorporating a mixing device, suitable for use in countercurrent columns operating at high pressures or under vacuum.
Abstract: The efficiency of mixing vapour in a countercurrent column (1) is improved by use of one or more vapour risers (6) each incorporating a mixing device (7). The method is suitable for use in countercurrent columns operating at high pressures or under vacuum. For high pressure operation a single riser is preferred positioned in the centre of the distributor tray (5).

Patent
12 Oct 1989
TL;DR: In this paper, a process for the continuous digestion of cellulosic fiber material is described wherein the material is impregnated with liquid in a closed system comprising a concurrent flow zone and a countercurrent flow zone.
Abstract: A process for the continuous digestion of cellulosic fiber material is described wherein the material is impregnated with liquid in a closed system comprising a concurrent flow zone and a countercurrent flow zone, the liquid in the concurrent flow zone including black liquor and possibly white liquor and the liquid in the countercurrent flow zone including white liquor. Liquid is withdrawn from the impregnation system at a point located between the concurrent flow zone and the countercurrent flow zone. Besides white liquor a predetermined amount of black liquor is added to the countercurrent flow zone in order to obtain a high liquid to wood ratio in the inlet of the digester.