Showing papers on "Countercurrent exchange published in 1988"

Buoyancy-driven exchange flow through small openings in horizontal partitions

Abstract: This paper describes an experimental study of the phenomenon of buoyancy-driven exchange (countercurrent) flow through openings in a horizontal partition. A density-driven exchange flow was obtained by using brine above the partition and fresh water below the partition. In the first part of the study, flow measurements were made with a single opening, for opening ratios L/D in the range 0.01 to 10.0, where L and D are the length of the openings (in the direction normal to the partition) and the diameter of the opening, respectively. Four different flow regimes are identified as L/D is increased through this range. As a result of the competition between two of these regimes, the exchange flow rate versus L/D relation exhibits a peak. The exchange flow rate was found for all practical purposes, to be independent of viscosity, enabling a universal correlation between Froude number (dimensionless exchange flow rate) and L/D. The second part of the study was an experimental investigation of the same phenomenon, but with two openings in the horizontal partition. Two openings were observed to give rise to three different flow configurations involving both one-way and countercurrent flows within the openings.

Analysis of equilibrium shift in isothermal reactors with a permselective wall

Abstract: The objective of this study is to obtain a fundamental understanding of the behavior of reactors with a permselective wall (membrane reactors) in terms of: design parameters (reactor length, membrane thickness); operating variables (pressure ratio, feed flow rate); physical properties (rate constant, permeability of fast gas, permselectivity, equilibrium constant); and flow patterns (recycle, cocurrent, countercurrent). Pure feed reacts on the high-pressure side of the membrane, and the product(s) formed are continuously removed to the low-pressure side so that thermodynamic equilibrium is never reached. It is shown by simulation that equilibrium shift can be enhanced by: recycling unconverted reactant; shifting feed location to separate products; and maintaining high permeation rates to reduce backreaction. It is also shown that the choice between cocurrent flow and countercurrent flow depends on the system parameters.

Countercurrent gas‐liquid annular flow, including the flooding state

Abstract: The structure of the wavy interface on a falling liquid film is studied for conditions of countercurrent gas flow in order to investigate mechanisms for flooding. Measurements taken just below the liquid feed and at 1.7 m down the tube show that under all conditions, including flooding, the waves propagate only downward and are never of such amplitude as to bridge the tube. These observations are in contrast to speculations in the literature that upward flow of waves or bridging of liquid due to waves cause flooding. In the mechanism suggested, flooding is due to flow reversal in the film just at the liquid entry.

Dual Countercurrent Chromatography

Abstract: A modern method of performing conventional countercurrent distribution called Dual Countercurrent Chromatography is described. The system consists of a multilayer coiled column integrated with two inlet and two outlet lines for solvent phases and a sample feed line. Subjecting the system to a particular combination of centrifugal and planetary motions produces a unique hydrodynamic effect which allows two immiscible liquids to flow countercurrently through the coiled column. The sample solution is fed at the middle portion of the column and eluted simultaneously through the column in the opposite direction by two liquids. This distinct feature of maintaining a constant fresh two phases within the coiled column permits a rich domain of application, such as continuous sample process and continuous extraction. The present paper describes the application of this dual countercurrent system to the separation of natural products and synthetic intermediates. Preliminary results indicate that this new met...

Studies on a Membrane Reactor

Abstract: Simulation is used to evaluate the performance of a catalytic reactor with permeable wall (membrane reactor) in shifting the equilibrium of three reversible reactions (cyclohexane dehydrogenation, hydrogen iodide decomposition, and propylene disproportionation). It is found that the preferred choice of cocurrent or countercurrent operation is dependent on the physical properties and operating conditions. Methods of enhancing conversion are suggested and temperature effects are discussed.

Ozone-producing plant

Abstract: Each ozonization loop (1) which includes a compressor (2), an ozonizer (3), and a heat exchanger (8) for cooling the oxygen-ozone mixture, is associated with three cylinders (4,5,6) filled with silica gel. Each cylinder operates in succession in a cocurrent adsorption, in countercurrent desorption by a substitution gas, and in scavenging by taking off a part of the flow circulating in the loop. The scavenging flow is recovered and combined with the substitution gas. The substitution gas may be in particular impure nitrogen supplied by an air distillation apparatus producing the necessary oxygen.

An Analytical Solution Countercurrent Heat Transfer Between Parallel Vessels With a Linear Axial Temperature Gradient

Abstract: Presented in this paper is a solution for countercurrent heat exchange between two parallel vessels embedded in an infinite medium with a linear temperature gradient along the axes of the vessels. The velocity profile within the vessel is assumed to be parabolic. This solution describes the temperature field within the vessels, as well as in the tissue, and establishes that the intravessel temperature is not uniform, as is generally assumed to be the case. An explicit expression for the intervessel thermal resistance based on the difference between cup-mixed mean temperatures is derived.

Performance of Gas Separator with High-Flux Polyimide Hollow Fiber Membrane

Abstract: The permeation properties of H2-CO mixtures through a high-flux asymmetric polyimide membrane are studied experimentally and theoretically. Experimental results measured with miniature module-equipped hollow fibers indicate the advantage of countercurrent flow pattern. The calculation model used for the analysis of the conventional symmetric membrane can predict the gas separation performance. However, the model is necessary to take the longitudinal mixing into account for analyzing the experimental results measured with a pilot scale module.

Relationship between residence time, fluid dynamics and efficiency in countercurrent flow equipment†

Abstract: The suitability of any item of equipment for a given thermal separation process cannot always be judged solely in the light of efficient and loading range data. In vacuum rectification, involving a large number of theoretical stages, the vapour pressure drop per transfer unit exerts a considerable effect on the energy consumption and thus largely governs the choice of column fittings. Furthermore, the pressure drop per transfer unit determines the temperature at the bottom of a rectification column and, hence, the suitability of the equipment for the separation of heat-sensitive products. It is also an important criterion for compressor requirements in absorption processes. Another factor of considerable importance in separating heat-sensitive mixtures by distillation is the time during which the product, particularly the liquid phase, is exposed to a given temperature in the column. Therefore, a standardized liquid residence time has been adopted to evaluate the systems in their entirely. This residence time depends on the hydrodynamic conditions in the column and is thus closely related to pressure drop and efficiency. Further important factors, which may decide the selection of column internals, are the specific volume and mass of the column. Based on theoretical considerations, a flow model is derived for describing the main loading range of countercurrent packed columns; the relationships between the above mentioned parameters are presented.

Pressure swing adsorption process and system for gas separation

Abstract: An improved pressure swing adsorption process and system enable a high purity product comprising the more readily adsorbable component of a feed gas mixture to be economically recovered, e.g. nitrogen from air. A processing cycle is employed in which the more readily adsorbable component is used as a copurge gas at upper adsorption pressure, and the less readily adsorbable component is used for countercurrent purge at a subatmospheric desorption pressure and for initial repressurization in a countercurrent backfilling step following said countercurrent purge step.

Two stage vapor recovery system

Abstract: Disclosed is a system for recovering vapor from an air/vapor process stream. The system is operated in two stages, a high temperature stage and a low temperature stage. The high temperature stage may be referred to as a condenser column. The low temperature stage is referred to as the stripper column. The air/solvent vapor stream is conducted first through the condenser column and then through the stripper column. A countercurrent flow of liquid solvent is provided to both the condenser column and the stripper column. In the low temperature stage (condenser column), the countercurrent flow of liquid solvent is at a temperature near but above the freezing point of water. This results in the removal of most of the solvent vapor and water vapor from the air/solvent vapor mixture. The process stream next flows through the stripper column which has a countercurrent flow of liquid solvent below the freezing point of water which serves to remove the remaining solvent vapor and water vapor contained in the process stream. The system may be operated on a once through basis although better overall recovery will be accomplished if the system is operated in a recirculation mode. Because it is operated in two stages, there is accomplished a significant reduction in the power requirements of the refrigeration system. Further, the removal of the majority of the water vapor from the process stream prior to the low temperature stage significantly reduces the problems created by fouling of the stripper column by water ice.

Heat Transfer in a Countercurrent, Gas–Solid, Packed Column

Abstract: A theoretical model has been used, in conjunction with pressure drop and solid holdup data, to predict correctly the thermal efficiency of a countercurrent, gas-solid, packed heat exchanger. In the model, the ideal efficiency is multiplied by a ratio of particles in contact with the gas to the total amount of particles in the packed section. The Erugun equation is used to obtain both the effective packing porosity and the number of particles in contact with the gas. The results show that the model correctly gives the efficiency versus gas velocity curve for different packing heights and solids mass fluxes. The calculated and experimental velocities for which exchanger efficiency is a maximum are also in agreement.

非共沸2成分混合蒸気の水平管内凝縮熱伝達 : r113+r11の場合

Abstract: Complete condensation of nonazeotropic binary mixtures of R11-R113 refrigerants is experimentally studied. The test apparatus consists of two concentric horizontal tubes, with the vapor mixture flowing in the inner tube and the cooling water in the annular space in the countercurrent direction. The composition and the mass flow rate of the binary-component mixture are systematically varied. Through the measurement of the local temperature of the wall, the cooling water and the vapor along the tube axis, the axial distribution of the local heat transfer coefficients are obtained. An empirical equation is derived to correlate condensation heat transfer performance.

Countercurrent Electrolysis in a Cell Where Porous Membranes Have Been Connected in Series with Ion-Exchange Membranes. Part 2. Experimental Verification

Abstract: Countercurrent electrolysis in a cell wehre porous membranes have been connected in series with ion-exchange membranes has been studied experimentally for the ternary system NaCl-KC1-H2O. The number of porous membranes was varied from one to four, and the effect of cationic fluxes on separation was also studied. A comparison between three different kinds of cell arrangements was made, and the present method was found to be the most attractive for practical purposes.

An investigation into stratified co- and countercurrent two-phase flows

Abstract: This paper investigates theoretically and experimentally certain stratified co- and countercurrent two-phase flows in circular pipes that have not been studied adequately. The theoretical analysis produced semiempirical relationships based on the momentum-balance concept. These relationships were then experimentally evaluated with two fluid systems of significantly different density ratios. It is suggested that the equations that correlated these results can be accepted for general use. An example is presented for a certain natural-gas/condensate application.

Solar enhanced separation of volatile components from a liquid

Abstract: A process and apparatus for separating volatile components from a volatile-containing liquid by a stripping gas flowing countercurrent to the liquid. Separation of the volatile components is enhanced by heating the liquid with radiant solar energy and agitating the liquid as it flows.

Countercurrent heat-exchanger

Abstract: A counterflow plate-type heat exchanger has heat exchange areas which are arranged at an oblique angle relative to the stack direction. This arrangement enables channels to be formed having a smaller width for the passage of fluid than the distance between the plates in the stack direction. As a result, a high rate of heat exchange can be obtained. Corresponding inflow and outflow channels are arranged on opposite lateral sides of the stack. This provides for fluid flow through the stack from one side to the other in a manner such that the entire heat exchange area is contacted by fluid. The channels narrow in the inflow direction and widen in the outflow direction in order to provide optimum flow conditions in the exchanger.

Countercurrent Electrolysis in a Cell Where Porous Membranes Have Been Connected in Series with Ion-Exchange Membranes. Part 1. Method

Abstract: A new cell arrangement for countercurrent electrolysis in a porous membrane is presented. In this cell, where porous membranes are connected in series with ion-exchange membranes, much better separations are obtained compared to the procedure where the membrane is made thicker. However, separation is less than if convection is increased, but power consumption is also less. An iterative method is presented for solving convection as well as the concentrations in different compartments, when electric current, outflow rate, and concentrations of the product stream are specified.

Process and plant for the physical refining of edible oils, fats and esters

Abstract: In a process for the physical refining of edible oils, fats and other high-boiling esters having a preliminary stage for degassing and dewatering and having a single-or multi-stage countercurrent falling- film steam distillation stage for deacidification and/or deodorization, in the preliminary stage a multi-stage treatment of the liquid is carried out at a pressure decreasing from stage to stage until the operating pressure of 1 to 10 mbar is reached. In this case the residual water content of the liquid is decreased to less than 0.005% by weight and the liquid thus treated can be flashed without any mist formation into the falling film column of the countercurrent falling-film steam distillation stage. Preferably, between preliminary stage and countercurrent falling-film steam distillation stage, a flashing stage can be additionally provided in which the previously degassed and dewatered liquid at a temperature of 230 to 270@C is flashed to the operating pressure of 1 to 10 mbar.

Crude oil desalting by counterflow electrostatic mixing

Abstract: Chlorides in crude oil which are normally contained in finely dispersed connate brine are detrimental to refinery processes from both corrosion enhancement and catalyst degradation considerations. These have been removed historically by mechanically mixing the crude oil with fresh water and separating the phases with the aid of heat, chemicals, and electric fields. A new process has been developed which produces both mixing and coalescence by an electrostatic field allowing multiple contact stages to be realized with countercurrent flow in a single vessel. The improvement in separation is similar to that of a multi-tray distillation column as compared to a single stage flash drum. Because the energy of the electrostatic field is expended primarily on the transport of the polar phase (water), mixing efficiency is much greater that can be obtained with conventional means using differential pressure across an adjustable orifice. A controlled and varying DC field is employed in the process and is adjusted to achieve both effective mixing and maximum coalescence. This results in a much drier oil than is obtained by conventional means. A refinery installation of the system is now under evaluation. Although only limited information can be made public at this time regarding this system,more » some of the concerns which have surfaced and their resolution will be discussed.« less

On Gas Separation by Permeation with One-Side Mixing

Abstract: A calculation method for gas separation by permeation with one-side mixing is proposed. Five types of stage flow patterns (one-side mixing, countercurrent flow, cross flow, cocurrent flow, and perf...

Gas/liquid heat exchanger

Abstract: A gas/liquid heat exchanger. Process gases leaving the heat-transfer elements of a heat-transfer-surface unit are guided through the displacement body that is associated with that unit. Feed water is introduced into the displacement body at the lower end thereof. After countercurrent heat-exchange flow relative to the process gas, the feed water is withdrawn from the upper end of the displacement body, and is introduced into a zone of downwardly flowing water.