Showing papers on "Countercurrent exchange published in 1993"

On the use of conventional cocurrent and countercurrent effective permeabilities to estimate the four generalized permeability coefficients which arise in coupled, two-phase flow

Abstract: In the case of coupled, two-phase flow of fluids in porous media, the governing equations show that there are four independent generalized permeability coefficients which have to be measured separately. In order to specify these four coefficients at a specific saturation, it is necessary to conduct two types of flow experiments. The two types of flow experiments used in this study are cocurrent and countercurrent, steady-state permeability experiments. It is shown that, by taking this approach, it is possible to define the four generalized permeability coefficients in terms of the conventional cocurrent and countercurrent effective permeabilities for each phase. It is demonstrated that a given generalized phase permeability falls about midway between the conventional, cocurrent effective permeability for that phase, and that for the countercurrent flow of the same phase. Moreover, it is suggested that the conventional effective permeability for a given phase can be interpreted as arising out of the effects of two types of viscous drag: that due to the flow of a given phase over the solid surfaces in the porous medium and that due to momentum transfer across the phase 1-phase 2 interfaces in the porous medium. The magnitude of the viscous coupling is significant, contributing at least 15% to the total conventional cocurrent effective permeability for both phases. Finally, it is shown that the nontraditional generalized permeabilities which arise out of viscous coupling effects cannot equal one another, even when the viscosity ratio is unity and the surface tension is zero.

A physical model for the prediction of liquid hold-up in two-phase countercurrent columns

Abstract: We present the determination of liquid hold-up in gas/liquid two-phase countercurrent columns filled with random or structured packings. The equations resulting from the established physical relationships are verified against the values for liquid hold-up determined experimentally on 56 different column packings and 16 gas/liquid systems. The experimental and calculated results agree well, with only slight deviations. This also applies to the range between the loading and flooding points for two-phase countercurrent flow

Electroconcentration by using countercurrent due to pressurized flow and electrophoretic mobility

Abstract: A pressurized flow and countermigration, due to electrophoretic mobility of a solute, are used for sample concentration. An apparatus composed of two rooms with electrodes, connecting tubes, and a pump for aspirating the sample solution is proposed. The sample solution is aspirated into small tubes (1.5-mm i.d. and 15 mm long), over which a voltage is applied (300-800 V/cm). A solute of high electrophoretic mobility is found to be drawn back from the small tube. Naphthalene-sulfonic acids, herring DNA, and magnesium ions are concentrated 10-47 times under pressurized flow (0.1-0.4 mL/min). We call this method «countercurrent electroconcentration»

Design and performance of a simulated countercurrent moving‐bed separator

Abstract: The design, construction and isothermal (298 K) operation of a continuous flow simulated countercurrent moving-bed chromatographic separator for the gas-solid separation of binary mixtures is reported. It consists of only four packed columns, with counter currency simulated by advancing the feedpoint from column to column in the direction of gas flow. The separated components have periodic concentration profiles, with a duty cycle that depends on operating parameters, and concentrations greater than in the feed stream. Test mixtures of propylene and dimethyl ether, which have retention times differing by a factor of 2 on the 60/80 mesh Chromosorb 101 packing, were successfully separated. Optimum feed advancement intervals and maximum product purity were experimentally determined as a function of feed rate. At low feed rates, when the adsorption isotherm is nearly linear, dimethyl ether was nearly completely separated from propylene, but propylene was found to contain varying amounts of dimethyl ether due to the effects of a nonlinear isotherm and heterogeneous adsorption.

Method and apparatus for heat treating a fluid product

Abstract: Method and apparatus for heat treating a fluid product, in which the product is preheated in a countercurrent heat exchange process and heated to the desired treatment temperature in a throughflow heat exchange process, wherein in the primary countercurrent heat exchanger section, a higher pressure than the atmospheric pressure prevails, and both in normal operation and during recirculation through the final-temperature heating section, the secondary countercurrent heat exchange section is maintained at a higher pressure than the pressure in the primary countercurrent heat exchanger section, whilst, should the pressure difference between the primary and the secondary countercurrent heat exchanger sections drop out, the supply and discharge of the product are stopped and the product to be treated is recirculated through the final-temperature heating section.

Pressure swing adsorption/desorption process with multiple countercurrent de-pressurization steps

Abstract: A pressure swing adsorption (PSA) process for purifying or separating gases employs, in addition to a standard PSA cycle comprising an adsorption step (a), one or more cocurrent depressurization steps (b) for equalization or providing purge gas, a countercurrent depressurization step (c), a countercurrent purge step (d), and a repressurization step (f), an additional countercurrent desorption step (e) performed in conjunction with the first countercurrent desorption step at above atmospheric pressure and a countercurrent purge step at about the adsorption temperature which can provide increased capacity and recovery as compared to PSA processes that only have one countercurrent depressurization step or otherwise do not have a countercurrent purge step. Preferably the pressure reduction during the second countercurrent depressurization step is accomplished by passing another stream from the process, such as the effluent from the first countercurrent desorption step, as a motive gas through an ejector which is in operative communication with the adsorber bed undergoing the second countercurrent desorption step.

Membrane separation module

Abstract: An improved shellside feed, countercurrent flow, hollow fiber membrane separation module is provided wherein one or more flow tubes (50,60) are incorporated into the conventional design. The flow tubes increase the efficiency of the membrane separation module by reducing undesirable flow patterns that are present in the conventional module.

Cascades for natural water enrichment in deuterium and oxygen-18 using membrane permeation

Abstract: Heavy isotope enrichment of water using a hydrophobic membrane permeation process is described. Simple and ordinary countercurrent cascades will not be of practical interest because of high energy demand. A better solution is to employ a double countercurrent cascade, reutilizing part of the heat of condensation.

A noniterative solution for periodic steady states in gas purification pressure swing adsorption

Abstract: An analytic solution for periodic steady state concentration profiles in a pressure swing adsorption purification process was obtained from the countercurrent flow analogy. The system is a dilute, isothermal, single component in inert carrier with a general nonlinear adsorption equilibrium isotherm. Diffusion in the solid phase is rate controlling and axial dispersion is neglected. The solution permits the calculation of minimum bed requirements for complete purification without iteration. The effect of isotherm shape, mass transfer, pressure ratio, and purge-feed ratio in the purification of air contaminated with common chlorofluorocarbons is studied theoretically

Dynamic analysis of double-pipe heat exchangers subjected to periodic inlet temperature disturbances

Abstract: A mixed lumped-differential formulation is employed to model the transient energy equations for fully developed laminar-laminar or laminar-turbulent flow situations in concurrent or countercurrent double-pipe heat exchangers. The temperature distribution in the outer annular channel is radially lumped, providing a more general boundary condition for the inner channel differential energy equation, coupled through the interface condition. The case of periodically varying inlet temperatures is more closely considered, and the dynamic response of the exchanger is established in terms of the governing dimensionless parameters, such as heat capacity flow rate ratio, dimensionless inlet temperature oscillation frequency, and relative wall thermal resistence. The ideas in the generalized integral transform technique are extended to yield analytical solutions to the related periodic problem defined in the complex domain, and offer highly accurate numerical results for quantities of practical interest, such as fluids bulk temperatures.

Multi-layered hot water storage tank with countercurrent heat eschanger without external energy source

Abstract: Multi-layered hot-water storage tank with countercurrent heat exchanger without external energy source, for layered charging or discharging. Two techniques fulfil this task: a) A countercurrent heat exchanger built into the storage tank, by means of which the stored water falls due to thermosyphon forces in the case of a domestic-water exchanger, or rises in the case of a charging exchanger. b) The domestic water drives a mini-turbine (10) or a water motor, by means of which a mini-pump (11) is driven, the latter sending hot stored water through a countercurrent heat exchanger (12) in which the domestic water is heated and the stored water is cooled. The cooled stored water is passed into the cooler region of the storage tank again.

Method for concentrating a solute by countercurrent chromatography

Abstract: A method for concentrating a solute from a mixture by countercurrent chromatography, by introducing a stationary phase into a countercurrent chromatographic centrifuge, introducing a sample of a mixture containing a solute into the centrifuge, introducing a sufficient quantity of an elution peak sharpening agent into the centrifuge, introducing a mobile phase into the centrifuge, and performing countercurrent chromatographic centrifugation. The eluting fractions containing the concentrated solute are identified and collected.

Analytical solution for transient response of counter flow heat exchanger with finite wall capacitance

Abstract: The Laplace Transform Method is applied to solve the transient response of the counter flow heat exchanger with finite wall capacitance problem The mathematical model is based on three local energy balance equations which are solved assuming that only the fluid 1 inlet condition is perturbed (step change) As any counter flow problem could be reduced to an adequate integral equation, collocation method is used for solving such equation in the presented case Results are given for the outlet temperatures of both fluids and temperature distributions for both fluids and the wall as an explicit analytical formula

An Analytical Study of Critical Heat Flux of a Two-Phase Thermosyphon.

Abstract: An analytical study has been made of critical heat flux of a two-phase thermosyphon, in which a liquid film and a vapor flow in a manner of countercurrent annular flow. An equation governing the flow of the liquid film and other equations for mass and energy balance in the thermosyphon are solved together under two conditions ; first, the critical heat flux takes place when liquid supply to the thermosyphon is just equal to the evaporation of the liquid due to the heat input into it, and second, thickness of the liquid flow is determined such that interface of the annular flow is kept stable. Thereby, two correlations are derived for both limiting conditions of 2/(C2ik2Nk) and then one of them for 2/(C2ik2Nk)»1 is in good agreement with the existing CHF data in a closed two-phase thermosyphon as well as a generalized correlation derived from dimensional analysis.

A new apparatus for continuous countercurrent flow of solids and liquids

Abstract: A contactor was developed to provide true countercurrent, continuous flow of gel spheres and liquid in a moving bed. To provide smooth and controlled movement of solids, the key features consisted of a common cross section for the moving bed and a small fluidized bed, a jet to form a slurry at the bottom of the moving bed, and a controlled flow of part of this slurry to the fluidized bed. A completely continuous pilot plant for preparation of nuclear fuel by a gel-sphere process was operated with three of these moving-bed fluidized-bed contactors. Different control procedures and good countercurrent washing results were demonstrated.

Direct-contact condensation of low-density steam on seawater at high inlet noncondensable concentrations

Abstract: Computer models and experimental data are summarized to characterize the condensation of low-density steam in direct contact with a process fluid that is distributed over structured packings of various geometries. The one-dimensional models integrate the heat, mass, and momentum processes in the two streams, over the height of the contactor. Both cocurrent and countercurrent flows of the two streams were analyzed. The models were validated extensively with experimental data obtained with fresh water and with seawater, at high inlet noncondensable concentrations. The data obtained in these experiments provide a broad engineering data base to design and evaluate the performance of advanced heat exchangers for a number of applications, such as production of electrical power and/or potable water using low-density steam, as could be used in Ocean Thermal Energy Conversion systems and in the low-pressure stages of conventional power cycles. 13 refs., 14 figs., 3 tabs.

Parametric study on the bulk hydraircooling of spherical food products

Abstract: A numerical study of the bulk hydraircooling of spherical food products is performed using the technique of spraying chilled water to form a thin film over the food products while blowing cold unsaturated air in the countercurrent or cocurrent direction. This precooling process is found to combine the advantages of hydro-and air cooling.Governing equations describing the simultaneous heat and mass transfer occurring in the hydraircooling process for both counterflow and parallel-flow arrangements are solved using finite-difference numerical methods. A parametric study is performed to determine the effect of important processing parameters on the process time. It is generally observed that higher quantities of spray water, air-mass flow rate and product thermal conductivity, as well as lower values of water temperature will result in faster rates of cooling. For the same operating conditions, parallel-flow arrangement leads to higher plant capacities.

Converting air-liquid pressure contacting oxidizing column

Abstract: The utility model relates to an air-liquid countercurrent pressurization contact oxidation tower, belonging to the technical field of waste water treatment. The utility model provides a specific structure of an air-liquid countercurrent water distribution and air distribution pressurization contact oxidation tower, comprising a water distribution device with perforated pipes, an air-water re-distributor, an air chamber, etc. Air-water distribution in a tower can be efficiently controlled, filling materials on an air-liquid inlet are not easy to be damaged, the contact of the air and the liquid in the tower is good, the physiochemical efficiency is high, the control of liquid face is stable, and no air bubble is carried by water yielding. The utility model can be used for the waste water treatment of chemical fibers, chemical engineering, pharmacy, printing and food industry.

Optimization of the countercurrent moving-bed chromatographic separator

Abstract: A dispersionless, adsorption equilibrium, plug-flow model of a countercurrent moving-bed chromatographic separator operating at steady state is investigated. The flux of the constituents of a binary mixture is examined via concentration-phase plane plots, which reveal a complex behavior depending on a parameter [sigma], the ratio of solid- and fluid-phase flow of the mobile phase. When the model is modified by incorporating finite mass-transfer rates, axial concentration profiles exhibit behavior that is characteristic of experimental observations, rather than the predictions of the ideal model. Numerical simulations with the finite mass-transfer model reveal an optimum operating condition.