Showing papers on "Countercurrent exchange published in 2005"

CFD Simulations of Coupled, Countercurrent Combustor/Reformer Microdevices for Hydrogen Production

Abstract: Two-dimensional computational fluid dynamics (CFD) simulations are used to study spatially segregated, multifunctional, microchemical devices for hydrogen production. In particular, coupling between homogeneous propane combustion and catalytic ammonia decomposition on a Ru catalyst is studied in a microdevice consisting of alternating combustion and decomposition channels as a function of flow rate and materials conductivity in the countercurrent flow configuration. It is found that the high temperatures generated via homogeneous combustion lead to high conversions in short contact times and thus to compact devices. Different performance measures are evaluated to assess the operability of the device. Sufficiently high ammonia flow rates serve a dual purpose by lowering device temperatures and enabling the production of larger flow rates of hydrogen. Finally, it is shown that device operation is limited only to high-conductivity materials and fast ammonia flows.

Countercurrent flow distribution in structured packing via computed tomography

Abstract: A newly developed γ-ray computed tomography scanner was implemented to study liquid flow distribution in a 30.48-cm-diameter column packed with corrugated structure using countercurrent air–water flow. Validation experiments confirm that spatial resolution of ∼2.5 mm can be achieved by the new CT unit. Within the gas (0–10 cm/s superficial velocity) and liquid (0.6–2.5 cm/s superficial velocity) flow ranges investigated, a good liquid distribution was observed at all conditions, as manifested by uniformity factor in excess of 70%. The liquid saturation increases with increasing superficial liquid velocity as well as down the column height. Within the conditions studied, the effect of gas velocity was, in general, found to be minimal.

On Undercompressive Shocks and Flooding in Countercurrent Two-Layer Flows

Abstract: We consider the countercurrent flow of two incompressible immiscible viscous fluids in an inclined channel. This configuration may lead to the phenomena of ‘flooding’, i.e. the transition from a countercurrent regime to a cocurrent regime. This transition is marked by a variety of transient behaviour, such as the development of large-amplitude waves that impede the flow of one of the fluids to the reversal of the flow of the denser fluid. From a lubrication approximation based on the ratio of the channel height to the downstream disturbance wavelength, we derive a nonlinear system of evolution equations that govern the interfacial shape separating the two fluids and the leading-order pressure. This system, which assumes fluids with disparate density and dynamic viscosity ratios, includes the effects of viscosity stratification, inertia, shear and capillarity. Since the experimental constraints for this effective system are unclear, we consider two ways to drive the flow: either by fixing the volumetric flow rate of the gas phase or by fixing the total pressure drop over a downstream length of the channel. The latter forcing results in a single evolution equation whose dynamics depends non-locally on the interfacial shape. From both of these driven systems, admissible criteria for Lax shocks, undercompressive shocks and rarefaction waves are investigated. These criteria, through a numerical verification, do not depend significantly on the inertial effects within the more dense layer. The choice of the local/non-local constraints appears to play a role in the transient growth of undercompressive shocks, and may relate to the phenomena observed near the onset of flooding.

Controlling turbulence in a rearward-facing step combustor using countercurrent shear

Abstract: The present work describes the application of countercurrent shear flow control to the nonreacting flow in a novel step combustor. The countercurrent shear control employs a suction based approach, which induces counterflow through a gap at the sudden expansion plane. Peak turbulent fluctuation levels, cross-stream averaged turbulent kinetic energy, and cross-stream momentum diffusion increased with applied suction. The control downstream of the step operates via two mechanisms: enhanced global recirculation and near field control of the separated shear layer. The use of counterflow also enhances three dimensionality, a feature that is expected to be beneficial under burning conditions.

An experimental investigation of planar countercurrent turbulent shear layers

Abstract: The spatial development of planar incompressible countercurrent shear layers was investigated experimentally. A facility was constructed to establish countercurrent shear layers without the formation of global stagnation in the flow. Particle image velocimetry was employed to obtain detailed measurements within the region of self-preservation for velocity ratios $U_{2}/U_{1}$ between 0 and −0.3. The spatial growth rate of countercurrent shear layers was found to agree generally with simple analytical theory. At 30% counterflow, the growth rate was approximately twice as large as the case with no counterflow. Peak turbulence quantities, when normalized by the applied shear magnitude, $\Delta U$ , were found to be nominally constant for low levels of counterflow, but at counterflow velocities above 13% of the primary stream velocity, peak turbulence levels increased. The observed transition is accompanied by the development of mean flow three-dimensionality. The deviation occurs at a counterflow level that is in agree- ment with theoretical predictions for transition from convective to absolute instability.

Evaluation of Reflux Condensation Heat Transfer of Steam-Air Mixtures under Gas-Liquid Countercurrent Flow in a Vertical Tube

Abstract: Reflux condensation in steam generator (SG) is one of the major heat removal mechanisms in a loss of residual heat removal (RHR) system event in mid-loop operation during a pressurized water reactor (PWR) plant outage. In order to evaluate the effectiveness of reflux condensation in SG U-tubes, the condensation heat transfer characteristics in the presence of a non-condensable gas must be clarified. Local temperature data were previously measured for steam-air mixtures under gas-liquid countercurrent flow, in a vertical tube of inner diameter 19.3 mm. In this study, local reflux heat transfer coefficients were calculated by evaluating steam flow rate profile along the tube at low heat fluxes assuming saturated steam conditions and empirical correlations were derived. The correlations are valid over a range 2–9,000W/m2-K for 0.1–0.4MPa, 0.014–0.2 air mass fraction. The axial distributions of the steam—air mixture temperatures calculated using the correlation agreed well with the measured results and validi...

Experimental testing of interfacial coupling in two-phase flow in porous media

Abstract: Two-phase flow through natural porous media is affected by the interfacial coupling that takes place across the interfaces located in a porous medium. Such coupling may be of two types: viscous and capillary. In this study, defining equations for the capillary and viscous coupling parameters have been constructed. Moreover, these equations, together with a modified form of Kalaydjian's transport equations, have been used to analyze interfacial coupling in two-phase flow through porous media. On the basis of the analysis carried out, it is argued that interfacial coupling has no effect on steady-state, cocurrent flow, and only a small effect on unsteady-state, cocurrent flow. Moreover, it is suggested that interfacial coupling has a significant effect on steady-state, countercurrent flow. Two methods were used to test the theory. In the first method, data from steady-state, cocurrent, and countercurrent experiments were used to show that experimentally determined values of the capillary coupling p...

Hydrodynamics of PEG-phosphate aqueous two-phase systems in a J-type multilayer countercurrent chromatograph

Abstract: Recently, we have shown that countercurrent chromatography (CCC) is an effective method for the purification of plasmid DNA vaccines and gene therapy vectors.1 As a basis for further work, this paper studies the hydrodynamics of various PEG‐Salt aqueous‐aqueous two‐phase systems in a Brunel J‐type countercurrent chromatograph. The degree of stationary phase retention, S f , once a hydrodynamic equilibrium is achieved has been studied as a function of mobile phase flow rate (0.5–2.0 mL·min−1), coil rotational speed (500–850 rpm), column volume (92.3 and 167.3 mL), choice of mobile phase (PEG or phosphate), and mobile phase pumping direction (Head→Tail or Tail→Head). Three different aqueous two‐phase systems (ATPS) were studied, which consisted of PEG 300‐K2HPO4, PEG 600‐ K2HPO4, and PEG 1000‐K2HPO4, having density and viscosity ratios between 1.15–1.13 and 0.27–0.12, respectively. High S f values in comparison to previous aqueous‐aqueous studies with CCC were obtained of up to 73.7%. These high S ...

Control of a fluid particle under simulated deep-ocean conditions in a high-pressure water tunnel

Abstract: An apparatus that permits the observation of liquid CO2 particles in a simulated deep-ocean environment was designed, modeled, constructed, and tested. Analysis concerning the vertical stability and control of the fluid particle in a countercurrent flow loop is presented. The vertical position of the particle was found to vary due to the gradual dissolution of the CO2 into the water and various other random effects. Using linearized equations for spherical particle motion in the fluid flow, a second-order dynamic equation is derived and analyzed. The servocontrol system consists of a video system that digitizes particle position in a viewing window and a centrifugal pump that can control the speed of the countercurrent flow in order to maintain the particle within the observation window of a charge-coupled device camera. Currently, the system is being used to obtain information on the dissolution behavior of CO2 in seawater at various conditions of pressure and temperature that simulate ocean depths down ...

Study of countercurrent flow limitation in a horizontal pipe connected to an inclined one

Abstract: Experiments with air and water in small hot leg reproductions were carried out aiming to acquire a better understanding of the countercurrent flow limitation (CCFL) in this geometry. The effects of various geometrical parameters of the test section and of the inlet water flow rate on the onset of flooding, on the partial delivery of water and on the zero liquid penetration were investigated. It was observed that while the onset of flooding is affected by the inlet water flow rate, the zero liquid penetration is independent of this flow rate. The results with partial delivery showed that, for a fixed air velocity, an increase in the horizontal length, or in the inclined length, of the flow channel leads to an increase of the water carried over by the air. On the other hand, in pipes with larger diameters the drag of the water is smaller. The experimental results showed small differences in the results for tests with inclination of the riser lower than 90 ◦ . For an inclination equal to 90 ◦ , the water carried by the air tends to be lower than in the others angles for a fixed air velocity. The study led also to a new correlation for the flooding.

Discrete countercurrent contacting : An experimental method for developing continuous countercurrent reactors

Abstract: To facilitate experimental studies on countercurrent reactors, a discrete contacting mode was worked out experimentally and theoretically. Enzymatic hydrolysis of penicillin G to phenylacetic acid and 6-aminopenicillanic acid was carried out in biphasic aqueous organic systems without pH control. The two phases were countercurrently contacted in a discrete manner, so that equilibrium was reached in each stage. Sets of three and five shake flasks served to mimic equilibrium stages in the countercurrent setup. It was shown that discrete countercurrent contact leads to the same extent of improvement of the equilibrium conversion as continuous countercurrent contact does, when compared to the batch situation. Therefore, discrete experiments may be used to simplify the development of continuous countercurrent reactors.

Lysine Adsorption on Cation Exchange Resin. III. Multicolumn Adsorption/Desorption Operation

Abstract: A model previously developed to describe ion exchange equilibria, kinetics, and column dynamics of lysine adsorption on a strong acid cation exchanger is extended to simulate the cyclic adsorption/desorption of lysine in a multicolumn, simulated countercurrent system. The system simulated comprises an adsorption zone, a desorption zone, and two zones where unadsorbed feed components and excess desorbent are removed. Multiple columns are distributed among the four zones in different simulated countercurrent schemes, including a scheme that allows recycling of excess desorbent and another where the lysine recovery yield is enhanced at low flow rates by lowering the pH in the last column of the adsorption zone. Model predictions are validated by comparison with experimental results obtained in an eight‐column bench scale apparatus and a parametric study is conducted with the model to determine the effects of critical design variables. This research was supported by Ajinomoto Co., Inc.

A New Route Combining Direct-Contact Evaporation and Vapor Permeation for Obtaining High-Quality Fruit Juice Concentrates. Part II: Modeling and Simulation

Abstract: A mathematical framework is presented for simulating each step of the proposed juice-processing route. Both the gas stripper and the direct-contact evaporator were simulated by combining a transient, well-mixed model for the liquid phase with a detailed model for heat and multicomponent mass transfer in superheated bubbles that was previously developed. For vapor permeation, a multicomponent, one-dimensional, plug-flow model for a hollow-fiber module was developed, considering both countercurrent and cocurrent configurations. These models were tested against experimental data. A sensitivity analysis of the proposed route was also conducted considering two main operation parameters: evaporator and permeate pressures. When the former was reduced, a significant drop in the liquid temperature in tandem with an augmentation of the evaporation rate was observed, whereas an increase in the latter led to a lower recovery degree in the membrane module.

Exchange between the stagnant and flowing zone in gas-flowing solids-fixed bed contactors

Abstract: In countercurrent gas - flowing solids - fixed bed contactors, a fraction of the flowing solids is in motion (dynamic holdup), while the other fraction is resting on the fixed bed elements. In this study it was experimentally proved that the stagnant zone should not be considered as a dead part of the column, but that there is a dynamic exchange between these two portions of flowing solids particles. Combining a mathematical model with tracer experiments, the rate of exchange was determined and it was shown that only a small part (ca. 20 %) of the stagnant region should be considered as a dead one.

The CFD Simulation of Mass-Transfer Process in Falling Film with Countercurrent Two-Phase Flow

Abstract: A CFD model using the volume of fluid (VOF) method was presented for predicting the mass-transfer process of the two-phase countercurrent falling film, in which the momentum source term including surface tension and interface shear stress and a mass-transfer source term were given The model was applied to simulate the stripping process of 2-Propanol dilute solution It is found that the simulated outlet liquid concentrations under different inlet liquid concentrations and various gas flow rates are in good agreement with the experimental data The simulations also confirm that with free surface waving the interface concentration fluctuate violently The enhancement factor R from experiment and CFD simulation are both larger than 1, even under the little mass-transfer impetus Since the Rayleigh-B?nard-Maragoni effect was not considered in the CFD model, the conclusion can be regarded as that in the simulation, the results of the enhancement of the mass-transfer process is caused by fluctuating interfacial waves, which also proves that fluctuating the interfacial waves is an effective means to enhance the separation efficiency

Multilayer film type water-cooled wall flue gas countercurrent flushing water tube oil and gas fired boiler

Abstract: The utility model relates to a multilayer film type water-cooled wall flue gas countercurrent flushing water tube oil and gas fired boiler comprising a burning chamber. The multilayer film type water-cooled wall flue gas countercurrent flushing water tube oil and gas fired boiler is characterized in that it is provided with at least two lines of vertical pipes (17) arranged in circle shape, and a band steel (18) is welded between the vertical pipes to make up an inner membrane wall and an outer membrane wall, and an upper and lower pipe plates and the inner and outer membrane walls make up the burning chamber. The existing vertical oil and gas fired boiler has disadvantages that the burning tail gas is discharged when not completely exothermal, and the temperature of the tail gas is high and the vertical oil and gas fired boiler can make full use of the burning heat, so the vertical oil and gas fired boiler wastes of fuels. The structure of the multilayer film type water-cooled wall flue gas countercurrent flushing water tube oil and gas fired boiler improves the heat exchange area and strength, and has fast heat exchange and low exhaust gas temperature. For the simple, fluent and compact structure, the reasonable heating surface arrangement and the high burning efficiency, the multilayer film type water-cooled wall flue gas countercurrent flushing water tube oil and gas fired boiler is worth to widely popularize to use.

Hybrid heat exchanger

Abstract: A hybrid exchanger utilized to heat a working fluid utilizing counter current heat exchange from a heat source fluid. The plates of the hybrid heat exchanger are configured to be welded to provide a more robust design while also allowing optimum heat exchange of the working fluid. In another embodiment, the hybrid heat exchanger includes a plate assembly and shell combination construction. The plate assembly and shell combination provides both optimized counter current heat exchange, while also controlling leakage of fluid from the hybrid heat exchanger. The plates of hybrid heat exchanger have a plurality of fluid bores which facilitate the exchange of fluids including inlet and outlet ports for both the working fluid and the heat source fluid. The bores of the plates include an open mouth having a greater clearance which allows for optimized flow of fluid while also allowing for simplified cleaning and maintenance of the hybrid heat exchanger.

Method and apparatus for compressing a natural gas stream

Abstract: A method and apparatus for compressing a natural gas stream is disclosed. The natural gas stream to be compressed is liquefied and then compressed by means of at least one cryogenic pump. Liquefaction of the natural gas stream to be compressed preferably takes place using the energy from a low-temperature process, specifically in the exchange of heat countercurrent to at least one medium to be heated, preferably countercurrent to a cryogenic medium.

Cooler of heating element and cooling system using it

Abstract: PROBLEM TO BE SOLVED: To improve the radiation performance of a heat sink for a heating element. SOLUTION: The heat, which is produced from a heating element 3 in a countercurrent vibration stream type heat transfer apparatus 6 of a heat dissipation means, is distributed over the whole heat sink 5. Thereby, as the whole heat sink 5 becomes an almost same temperature, the temperature difference between the atmosphere in a portable phone base station 1 and the heat sink 5 becomes approximately uniform. Moreover, as the whole heat sink 5 can efficiently radiates heat, the radiation performance of the heat sink 5 can be enhanced. COPYRIGHT: (C)2005,JPO&NCIPI

Counter flow typed selective method for adding hydrogen

Abstract: This invention discloses a method for countercurrent selective hydrogenation of C4 hydrocarbons. The method comprises: (1) pumping mixed C4 hydrocarbons into a countercurrent reactor from a top distributor, pumping hydrogen into the countercurrent reactor from a bottom distributor, and countercurrent-contacting on the catalyst surface; (2) reacting at 40-100 deg.C, 0.1-3.0 MPa and a volume space velocity of 1-20 h-1, air-lifting the light-weight impurities in the C4 hydrocarbons by hydrogen, and discharging with unreacted hydrogen from the top of the reactor; (3) discharging refined mixed C4 products from the bottom of the reactor. The method can increase the reaction efficiency and utilization rate.

Minimal Extractant Flow Rate in Countercurrent Leaching

Abstract: Approaches to determining the minimal extractant flow rate in countercurrent leaching are considered

Optimal plate aspect ratio for the best performance of the enrichment of heavy water in thermal-diffusion columns of a countercurrent-flow frazier scheme

Abstract: The effect of plate aspect ratio on the performance of enrichment of heavy water in thermal-diffusion columns of a countercurrent-flow Frazier scheme was investigated. The equation for the optimal plate aspect ratios and the corresponding best performance were derived. Considerable improvement in performance is obtained when thermal-diffusion columns are operated at the optimal plate aspect ratio. Further improvement can be achieved if the scheme is connected and operated in countercurrent flow, instead of concurrent flow.

Countercurrent Gas-Liquid Flow and Heat Transfer Charicteristics in Narrow Gap with Closed Bottom

Abstract: For severe accident assessment in a light water reactor, heat transfer models in a narrow annular gap between the overheated core debris and the reactor pressure vessel (RPV) are important to evaluate the integrity of the RPV and emergency procedures. This paper discusses countercurrent flow limitation (CCFL) in a narrow gap and heat transfer on heating surfaces based on CCFL calculations and quenching tests. Calculations of the momentum balance between gas and liquid phases showed that CCFLs are greatly affected by flow patterns in a narrow gap. Quenching tests in a verti-cal annulus gave almost the same heat transfer rate and CCFL constant as the quasi-steady state CHF (critical heat flux) tests when the flow patterns were the same in both tests. During the quench-ing of a heated wall with the superheated opposite-side wall, which simulated the cooling of the heated RPV wall facing the superheated debris, the CCFL constant was almost the same as the CCFL constant with the one-side heated wall. The results suggest that the correlation based on quasi-steady state tests with the one-side heated wall could be used to evaluate the total heat transfer rate and the coolant penetration flow rate into a narrow gap during the cooling of core debris.

Characteristics of Bubble Flow Behavior in a Gas-liquid Countercurrent Bubble Column Bioreactor

Abstract: 직경이 0.152 m이고 높이가 3.5 m인 기-액 향류 흐름 기포탑에서 기포의 물성과 흐름의 거동을 고찰하고 진단하였다. 기체와 액체의 유속 그리고 기포의 분산형태(even, wall-side, central or asymmetric distribution)가 반응기 내부에서 기포의 크기, 빈도수, 상승속도와 체류량 등 기포특성에 미치는 영향을 이중 전기 저항 탐침법을 이용하여 측정 검토하였다. 기포의 크기, 빈도수와 체류량은 기체나 액체 유속의 증가에 따라 증가하였다. 기포의 상승속도는 기체 유속의 증가에 따라 증가하였지만, 액체 유속의 증가에 따라서는 감소하였다. 기포 크기 분포의 균일성이나 체류량은 기포 분산판에서 기포의 분산형태가 균일분포에서 벽면, 중앙 그리고 비대칭 분산으로 변화함에 따라 감소하였다. 기포의 체류량과 분포에 대한 균일성을 고려하면, 기포의 중앙 분산 형태가 비대칭 분산 형태보다는 유리하며, 벽면 분산형태분산보다는 좋지 않았다.Abstract

Study on EMCC process of bamboo

Abstract: Laboratory simulated extended modified continuous cooking(EMCC) of bamboo with minor diameter in Fujian was carried out in this study.The results indicated that the optimal conditions of extended delignification at laboratory are: 14%(expressed as Na_2O) of active alkali charge at the impregnating stage and the current stage,30 g·L~-1 of warm white liquor concentration at the countercurrent stage,160 ℃ of maximum temperature,25% of sulfidity.As a result,the Kappa number of the pulp was 12.5,the yield of screened pulp was 44.8% and the viscosity was 1 031 mL·g~-1.Moreover,the pulp cooked by the optimal conditions has better strength property than that cooked by regular conditions.It was also found that the low Kappa number pulp cooked by the higher cooking liquor concentration in the counter-current stage has better strength property than that by the higher maximum temperature.