Showing papers on "Countercurrent exchange published in 1991"

Separation of tocopherols from deodorizer condensates by countercurrent extraction with carbon dioxide

Abstract: The possibility of enriching tocopherols from deodorizer condensates in a countercurrent separation process with supercritical carbon dioxide as solvent has been investigated. In order to obtain separation factors, phase equilibria were measured. Favorable conditions for separation were determined by conducting batch extraction experiments. Separation under steady state conditions was investigated through countercurrent operation of the separation column. Both sets of separation experiments provided information on the distribution of components of low concentration, which is difficult to obtain from equilibrium measurements only. Experiments on phase equilibria and separation behavior were carried out with mixtures of varying fatty acids and tocopherol content to generate information over different concentration ranges.

Modelling of pressure drop in packed columns

Abstract: The correct choice of packing is of decisive importance for optimum process efficiency in the operation of two-phase countercurrent columns. An important criterion for this choice is the pressure drop in the gas flow. Theoretical relationships are derived for calculating the pressure drop in beds with dry and trickle packings. It has been demonstrated by comprehensive experiments that these relationships allow the pressure drop to be determined more accurately than by previous methods. The experiments were performed at the Department of Thermal Separation Processes of Bochum University on 54 different packed beds, using 24 different systems.

Mathematical and experimental analysis of gas separation by hollow fiber membranes

Abstract: A mathematical model was developed and experimentally verified over a wide range of operating conditions for synthetic air and helium-nitrogen mixtures by measuring pressure, flow rate, and concentration profiles on the permeate side of the hollow fiber. Both countercurrent and cocurrent flow patterns are used, and the effect of permeate side radial mixing was examined

Efficiency of the countercurrent transfer of heat and 133Xenon between the pampiniform plexus and testicular artery of the bull under in-vitro conditions.

Abstract: The efficiency of countercurrent transfer of heat and 133Xenon (133Xn) in spermatic cords of the bull was measured under in-vitro conditions. Plasma was pumped through the artery and veins via two separate systems under controlled temperature conditions. Cold plasma or 133Xn-saline was introduced into the afferent veins and the transfer of heat or gas from the venous to the arterial side was measured. The mean efficiency of heat transfer was found to be 91% in five experiments. In four experiments a mean of 12% of the radioactive gas introduced into the venous system was recovered from the arterial side. It is concluded that the countercurrent transfer system in the spermatic cord is very effective with respect to the transfer of heat and probably moderately effective in the transfer of inert gases. The transfer is probably due to diffusion as eventual transfer through arterio-venous shunts was minimal.

Continuous treatment of heavy metal contaminated clay soils by extraction in stirred tanks and in a countercurrent column

Abstract: Extraction of metals from two contaminated waste site clay soils by 0.1–0.3 N HCl solutions was tested in three laboratory scale, continuous processes: two stirred tank reactors (CSTR’ s) in series; a countercurrent sieve‐plate column fed with flocculated. clay soil material; and a combination of tank reactor and column. After extraction clay soil suspension and extractant were separated by means of flocculation and sedimentation. The countercurrent process gave greater efficiencies in removing the metal than the CSTR process but the difference was only small. The following type of cleaning process seemed to be promising: first an extraction in a stirred tank followed by a further second extraction in a countercurrent column. Residence time in the CSTR could be short (15–30 minutes) while it should be as long as possible in the column.

Maximum conversion of dehydrogenation in palladium membrane reactors.

Abstract: The objective of the study is to compare the maximum conversions in two flow models, cocurrent and countercurrent, for the palladium-membrane reactor with that in a conventional catalytic reactor, whose maximum conversion is determined thermodynamically

Apparatus for mixing vapor in a countercurrent column

Abstract: The efficiency of mixing vapor in a countercurrent column (1) is improved by use of one or more vapor 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 center of the distributor tray (5).

Steady-State Countercurrent Flow in One Dimension

Abstract: Two phase countercurrent steady-state flow through permeable media in one dimension is discussed. For steady-state countercurrent flow in water wet porous media, a saturation profile is predicted with the water saturation decreasing in the direction that the water phase is flowing. The de la Cruz and Spanos equations predict that the Muskat relative permeability curves for countercurrent flow will be less than the Muskat relative permeability curves for steady-state cocurrent flow. This result has immediate implications regarding the use of external drive techniques to determine relative permeabilities based on the Buckley-Leverett theory and Muskat's equations. These equations and current experimental evidence involving countercurrent flow indicate that Muskat's equations do not adequately describe the multiphase flow of immiscible fluids.

Simulation of gas separation in an internally staged permeator

Abstract: Mathematical models have been developed for an internally staged permeator for the cases of cocurrent, countercurrent and perfect mixing conditions. The problem of oxygen enrichment from air in a cellulosic membrane has been considered in the simulation

A PCM/forced convection conjugate transient analysis of energy storage systems with annular and countercurrent flows

Abstract: Latent heat energy storage systems with both annular and countercurrent flows are modeled numerically. The change of phase of the phase-change material (PCM) and the transient forced convective heat transfer for the transfer fluid are solved simultaneously as a conjugate problem. A parametric study and a system optimization are conducted. It is found that the energy storage system with the countercurrent flow is an efficient way to absorb heat energy in a short period for pulsed power load space applications.

Experimental and modeling studies on the transient behavior of a simulated countercurrent adsorber

Abstract: This paper presents a dynamic model which includes axial dispersion and interphase mass transfer for a simulated countercurrent adsorption separation process, together with a numerical technique based on the method of orthogonal collocation for the solution of the governing partial differential equations. It is shown that the experimental transient behavior may be predicted by modeling the system in terms of an equivalent true countercurrent process provided that the inherent limitation of this approach is noted. This approach nonetheless provides a handy tool for predicting the time required for the system to approach quasi-steady state.

Countercurrent flooding in vertical-to-inclined pipes

Abstract: Countercurrent flooding data have been obtained using air and water for vertical-to-downwardly inclined pipes containing elbows of varying angles. Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1-m-tong vertical tube connected to an inclined or horizontal tube The flooding data for 112.5° and 135° elbow angles were almost identical and showed that these geometries required the largest gas flow rates for flooding among all the geometries tested. The flooding gas velocities for the 157.5° elbow were slightly less than those of the 112.5° and 135° elbows but greater than those of the vertical pipe without any elbow and vertical-to-horizontal pipes at low to moderate liquid flow rates In all vertical-to-inclined pipes, flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture was carried up...

Reduced gas holdup in catalytic reactor

Abstract: A reactor for refining resid includes an elongated vertical vessel containing a bed of catalyst which is expanded or ebullated by a liquid/gas mixture. The mixture rises in an updraft through the bed and then is recirculated with an increased velocity by an ebullating pump. To reduce gas holdup of the ebullated bed and to promote a more uniform flow, the gas is entrapped by two cascaded stages of baffles which have an internal conical shape to guide, direct, and entrap the gas. One of these two stages has a shape which creates a countercurrent in the flowing liquid to deflect any catalyst particles which might otherwise be elutriated by the increased velocity.

Countercurrent dual-flow spiral-wound dual-pipe membrane separation device

Abstract: The present invention relates to an improved design for a spiral-wound membrane separation device. The improved module (50) has one feed pipe (51A) separated into compartments (A, B) which are connected axially to a porous spacer (55) surrounded by a membrane envelope (54). A separate permeate pipe (51B) is immediately adjacent and generally in a parallel configuration to the fluid feed pipe (51A) and is in fluid communication with a different porous spacer sheet (58). When the porous feed membrane (54) are combined using appropriate complementary shaped spaced filling means (52A, 52B), a spiral-wound membrane separation device is obtained having two centrally located pipes. In one aspect, the membrane separation module (50) further includes means for the addition of a countercurrent or cocurrent sweep fluid (gas) permeate.

Gas/liquid distribution between two sections in a counter-current column

Abstract: In the gas/liquid distributor (4) of a countercurrent column (1), the outlets (13) of the tubes (8) for the liquid are advanced to close to the column section (2) situated below; to guide and distribute the gas flowing upwards, at least (illegible) chimneys (7) are provided per m of surface of the distributor tray (5). The total flow cross-section of the chimneys (7) is at least 10% of the surface area of the tray (5) occupying the total column cross-section. The flow cross-sections of the chimneys (7) are further narrowed as against their relatively narrow entry cross-sections. By means of this measure, on the one hand a uniform gas distribution is achieved as a consequence of a static gas pressure, and on the other hand gas and liquid are substantially conducted separately on flowing through the intermediate space between the sections (2a and 2b), a relatively high gas velocity being attained. This substantial separation of their flow paths improves, particularly in countercurrent columns having a flow parameter phi > 0.1, the stability of gas flow and liquid flow and thus also the efficiency of the countercurrent column.

Constant pattern behavior for adsorption processes with nonplug flow

Abstract: Adsorption of a dilute solute from fluid in nonplug flow through a porous structure of arbitrary but constant cross section is treated. Mass transfer is determined by diffusion in transverse and axial directions in both fluid and solid phases. A general existence criterion is developed for the constant pattern concentration wave. The criterion is applied to systems with cocurrent and countercurrent flow. The results pertain to fixed-bed adsorbers and adsorptive membrane systems

Heat transfer in countercurrent gas-solid flow inside the vertical pipes

Abstract: Heat transfer characteristics of the countercurrent gas-solid flow inside verical pipes has been investigated with the shell and tube type heat exchanger. Sand particles having the average particle diameter of 1.0 and 1.7mm were used. The effect of gas velocity and sand paticle flow rate on the heat transfer rate and the pressure drop were examined. At room temperatures, the predicted pressure drop agrees well with the experimental results when the larger sand particles are used. The results shows that there exists an optimum sand particle flow rate at which the heat transfer rate become maximum. The increase in the heat transfer coefficient due to sand particles was obtained up to 62%.

Cocurrent vacuum de‐aeration of water for injection into oil reservoirs

Abstract: Conventional vacuum stripping to reduce the oxygen content of injection water for secondary recovery of oil is carried out in packed columns with the released gases and water flowing countercurrently; hence large column diameters (normal liquid load circa 100 m3/(m2h)) and foaming that requires the addition of defoaming agents. Measurements with cocurrent and countercurrent flow at the same flow rate produced practically identical mass transfer coefficients. With flooding excluded in cocurrent flow, columns can be operated with higher liquid loads than in countercurrent flow. In addition, nitrogen released in the top part of the packing is better utilized as stripping gas, and foam is withdrawn as soon as it increases the pressure drop.

Countercurrent flow limitation model for RELAP5/MOD3

Abstract: This paper reports on a countercurrent flow limitation model incorporated into the RELAP5/MOD3 system transient analysis code. The model is implemented in a manner similar to the RELAP5 chocking model. Simulations using air/water flooding test problem demonstrate the ability of the code to significantly improve its comparison to data when a flooding correlation is used.

Function of Thin Segments of Henle’s Loop

Abstract: It is well known that the renal medulla plays an important role in the generation of concentrated urine, which is critical in the maintenance of body fluid osmolality. Since the proposal of the operation of countercurrent systems in the renal medulla by Kuhn and his associates [1–3], it has been widely accepted that the loop structures of the nephron in the renal medulla are essential for the generation and maintenance of a steep osmotic gradient along the axis of the renal medulla. However, the detailed mechanisms by which a steep osmotic gradient is generated by the countercurrent multiplication system remain to be established.