锥形筛孔塔板流体力学性能的研究

在一个φ500mm的有机玻璃塔中，以空气为物系，测试了普通筛孔塔板和锥形筛孔塔板的干板压降。根据Hughmark-O'Connell关联式计算出流量系数，并对上锥形筛孔塔板干板压降的Hughamrk-O'Connell公式进行修正，得到上锥形筛孔塔板的修正系数β'大于1，其干板压降比普通塔板低20％－30％。在此基础上对普通筛孔塔板和锥形筛孔塔板在气体穿孔时由于流体力不行为不同产生的压降差异进行了分析。     

Computational Approach to Characterize the Mass Transfer between the Counter‐Current Gas‐Liquid Flow

Structured packed columns are widely used in the chemical industry for distillation and absorption. However, the understanding of the transfer mechanism behind the counter‐current gas‐liquid flow in structured packed columns is still limited. In this work, a three‐dimensional CFD model that considers the local absorption and the local momentum transfer mechanism is developed for a film flow on a small plate with a counter‐current gas flow. The model, based on the Volume of Fluid (VOF) method, is built up on the basis of a pressure drop model and the penetration theory to quantitatively investigate the instantaneous hydrodynamics and mass transfer characteristics of the liquid phase. Simulations and experiments are carried out for a system consisting of propane and toluene. A comparison of the simulation results with the experimental data for the outlet concentrations shows good agreement.     

Pressure Drop in Liquid‐liquid Two Phase Horizontal Flow: Experiment and Prediction

The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene‐water mixture through a horizontal pipe of 0.025 m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03–2 m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases.     

Pressure Drop Models for Gas/Non‐Newtonian Power‐Law Fluids Flow in Horizontal Pipes

Models commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry.     

Hydrodynamic Model for Horizontal Two‐phase Flow Through Porous Media

A unidirectional, two‐fluid model based on the volume‐average mass and momentum balance equations was developed for the prediction of two‐phase pressure drop and external liquid hold‐up in horizontally positioned packed beds experiencing stratified, annular and dispersed bubble flow regimes. The so‐called slit model drag force closures were used for the stratified and annular flow regimes. In the case of dispersed bubble flow regime, the liquid‐solid interaction force was formulated on the basis of the Kozeny‐Carman equation by taking into account the presence of bubbles in reducing the available volume for the flowing liquid. The gas‐liquid interaction force was evaluated by using the respective solutions of drag coefficient for an isolated bubble in viscous and turbulent flows. The proposed drag force expressions for the different flow patterns occurring in the bed associated with the two‐fluid model resulted in a predictive method requiring no adjustable parameter to describe the hydrodynamics for horizontal two‐phase flow in packed beds.     

Computational Fluid Dynamics Hydrodynamic Analysis of a Cross‐Orthogonal Fixed‐Valve Tray

A computational fluid dynamics model was developed to investigate the hydrodynamic characteristics of a novel orthogonal fixed‐valve tray, which offers a larger effective contact perimeter under the same orifice area than its previously reported counterparts. The liquid‐gas phases were simulated in the Eulerian framework, with the interphase momentum transfer source term based on the experimentally obtained liquid hold‐up correlation. The simulation results were consistent with the experimental data. In addition, the gas hold‐up profile of this new design was compared with its triangular cousin under the conditions of a typical run, showing that the former has a higher froth height, which indicated better interphase contact on the tray.     

Simulation and Experimental Validation of Two‐Phase Flow in an Aerosol Counter‐Flow Reactor using Computational Fluid Dynamics

A simulation of the hydrodynamic behavior of an aerosol‐counter flow reactor was conducted using an Euler‐Lagrange method. The simulation results were then verified with experiments. The process simulated was a separation process required during the production of biodiesel (fatty acid methyl ester). In this process, the liquid ester/glycerol phases are continuously injected through a hollow cone nozzle with an overpressure of 10⁶ Pa into the reactor, operated at 15000 Pa. The liquid is atomized because of the pressure drop and a liquid particle spray is generated with an inlet velocity of 44.72 m/s. Water vapor of temperature 333 K is injected tangentially through two side, gas inlets with an inlet velocity of 1.2 m/s. Excess methanol is subjected to a mass transfer from the liquid phase into the gas phase, which is withdrawn through the head of the reactor and condensed in an external condenser unit. The stripping of the methanol off the liquid leads to a sharp interface between the glycerol and the ester phase, which can then be easily separated by gravity or pumping. The gas velocity field, pressure field and the liquid particle trajectories were calculated successfully. Simulated dwell time distribution curves were derived and analyzed with the open‐open vessel dispersion model. Experimental dwell time distribution curves were measured, analyzed with the open‐open vessel dispersion model, and compared with the simulated curves. A good consistency between simulated and measured Bodenstein numbers was achieved, but 25 % of the simulated particles exited at the reactor's head, contrary to experimental observations. The difference between simulated and measured dwell times was within one order of magnitude.     

Modeling the pressure drop of wet gas in horizontal pipe

A model for gas-liquid annular and stratified flow through a horizontal pipe is investigated,using the two-phase hydrokinetics theory.Taking into consideration the flow factors including the void fraction,the friction between the two phases and the entrainment in the gas core,the one-dimensional momentum equation for gas has been solved.The differential pressure of the wet gas between the two tapings in the straight pipe has been modeled in the pressure range of 0.1-0.8 MPa.In addition a more objective iteration approach to determine the local void fraction is proposed.Compared with the experimental data,more than 83％ deviation of the test data distributed evenly within the band of ± 10％.Since the model is less dependent on the specific empirical apparatus and data,it forms the foundation for further establishing a flow measurement model of wet gas which will produce fewer biases in results when it is extrapolated.     

Comparative Investigations of Non‐adiabatic Absorption in Film Flow and Bubble Flow

Comparative non‐adiabatic absorption experiments were carried out using the ammonia–water system under different two‐phase flow regimes. Because of the small thickness of the film, the falling film as a separated two‐phase flow shows an effective dynamic and transport behavior. The hydrodynamics and heat transfer modeling is sufficiently exact and the measurement of the interface temperature allows the discussion of the axial local partial resistance of the heat transfer in the falling film.     

Modeling of Two‐Phase Flashing Flow of Multicomponent Mixtures in Large Diameter Pipes

A two‐phase flashing flow model is developed to predict the distributions of pressure, temperature, velocity and evaporation rate in a transfer line, which is a typical example of a two‐phase flow pipe in the petrochemical industry. The model is proposed based on the pressure drop model and the multi‐stage flash model. The results indicate that pressure drop, temperature drop, and change of evaporation rate mainly occur in the transition section and the junction site of the transfer line. The predictions of the model have been tested with reliable field data and the good agreement obtained may lead to a better understanding of the two‐phase flashing flow phenomenon, as well as demonstrating the feasibility of applying the model into the design and optimization of pipelines.     

Spray Scrubbing of Particulates with a Critical Flow Atomizer

Wet scrubbers are gaining importance over other devices for particulate collection with the increasing stringency of pollution regulations. The scrubbing of particulates (soot and fly‐ash) in a spray tower with a two‐phase critical flow atomizer using water is reported in this article. The atomizer is capable of generating droplets with a high degree of spray uniformity. Preliminary studies reveal that the atomizer deployed in the present investigation is energetically more favorable than existing atomizers. With this atomizer, the scrubbing performances of a model spray tower are determined experimentally in terms of different operating variables. Various physical interactions with the exception of electrostatic effects are found to significantly influence the removal efficiency. The removal efficiency is found to increase with the inlet particle loading, gas flow rate and liquid to gas flow rate ratio. Experiments reveal that the present system collects finer (soot) particles (with a Sauter Mean Diameter (SMD) of 1.43 μm) more efficiently than the relatively coarse (fly‐ash) particles (SMD of 6.38 μm) under similar experimental conditions. Further investigation reveals that almost 100 % removal efficiency (zero penetration) of both soot and fly‐ash particles can be attained at a much lower Q_L/Q_G ratio of 3 m³/1000 actual cubic meters (ACM) than for the existing systems. A unique correlation is developed for predicting the performance of the spray tower in terms of various pertinent variables of the system. The predicted values agree very well with the experimental values (± 10 % deviation). A comparison of the performance of the present system with the existing systems indicates that the spray tower developed is techno‐enviro‐economically more favorable than existing systems.     

Full‐Loop Simulation of Gas‐Solids Flow in a Pilot‐Scale Circulating Fluidized Bed

In order to study the system hydrodynamics in a circulating fluidized bed (CFB), a 3D full‐loop simulation was conducted for a pilot‐scale CFB. The Eulerian‐Eulerian two‐fluid model with the kinetic theory of granular theory helped to simulate the gas‐solids flow in the CFB. The system hydrodynamics including pressure balance, vectors of gas and solids, distribution of solids holdup, and instantaneous circulating rates were obtained to get a comprehensive understanding of the system. It was predicted that the main driving force was the pressure drop of the storage tank. The storage height and valve opening were critical operating factors to control the riser operation. The effects of operating conditions including solids circulating rates and superficial gas velocity on the hydrodynamics were investigated to provide guidance for the stable operation of the CFB system.     

Flow Pattern and Pressure Drop for Small Long‐Cylinder Cyclones Operating at High Flow Rates

To address the gas flow pattern and pressure drop characteristics for small long‐cylinder cyclones (SLCCs) in the high operating flow rate range, experimental investigation and computational fluid dynamics (CFD)‐based simulation were performed. The pressure drop coefficient depends insignificantly on the Reynolds number at high flow rates. The tangential and axial velocities present the Rankine vortex and the roughly inverted V‐shaped distribution, respectively, similar to those in typical cyclones. The CFD simulation approximated well the experimental data of pressure drop. The pressure drop caused by vortex loss, turbulent energy loss, and resistance loss accounted for 72.5 % of the total pressure drop. The Stairmand model was found to be relatively accurate among the classical pressure drop models for the proposed cyclone. The results may help in the design and applications of cyclone separators and reactors.     

Flow Regime Transitions in an Internal‐Loop Airlift Reactor

The flow regime transitions of the riser and downcomer in an internal‐loop airlift reactor are investigated. Analysis of the effects of mean value, standard deviation and chaotic time series on pressure fluctuation signals is recorded to determine the transition of the hydrodynamics in the riser and downcomer of the internal‐loop airlift reactor. Two major chaotic invariants, the correlation dimension and the largest Lyapunov exponent, are employed to indicate the regime transitions. The regime transitions are determined by the sudden increase and decrease of the chaotic invariants, which are computed by the pressure fluctuation signals obtained by varying the gas flow velocity. The determination of chaotic invariants predicts that there is no heterogeneous phase existing in the downcomer of the internal‐loop airlift reactor. The experimental observations agree well with the predicted results.     

Flow Characteristics in Slot‐Rectangular Spouted Beds with Draft Plates

An experimental investigation was conducted of slot‐rectangular spouted beds with air entry slots spanning the full thickness of the column and vertical draft plates intended to help control the solids circulation rate. With increasing superficial gas velocity, the flow between the draft plates changed from bubbling to slugging and then to spouting with dilute pneumatic between the plates and moving‐bed downward motion on both sides. However, there was difficulty maintaining stability and symmetrical flow on the two sides. Once spouting is established, pressure drops and local voidages vary with gas velocity, particle size and gas entry size in broadly similar manners as for conventional spouted beds     

Modeling of Slug Velocity and Pressure Drop in Gas‐Liquid‐Liquid Slug Flow

Gas‐liquid‐liquid slug flow in a capillary reactor is a promising new concept that allows one to incorporate gas‐liquid reaction, liquid‐liquid extraction, and facile catalyst separation in a single unit. In order to assess the performance of a gas‐liquid‐liquid slug flow reactor, it is necessary to predict the slug velocity and pressure drop to ascertain residence times and reaction rates. New empirical models for velocity and pressure drop were developed based on existing models for two‐phase gas‐liquid and liquid‐liquid slug flows, and these were validated experimentally.     

Influence of Tortuous Geometry on the Hydrodynamic Characteristics of Laminar Flow in Microchannels

Flow visualizations are performed to study the hydrodynamic characteristics of laminar flow in tortuous microchannels for a wide range of Reynolds numbers. The detailed flow patterns in wavy channels are identified and found to be greatly affected by geometrical parameters. In wavy channels, steady flow exists at low Reynolds numbers, but above a critical number unsteady flow develops. The critical Reynolds number is found to depend on the characteristics of the channel path. Recirculation zones form immediately after the inner corners of the sharp bends, with their size and magnitude of the recirculation velocity increasing with higher Reynolds numbers. Large fluctuations in recirculation zone locations highlight the importance of these flow features in the development of transient flow. The flow behaviors play very important roles in determining the pressure drop in wavy channels relative to straight channels.     

Fluidization Characteristics in Micro‐Fluidized Beds of Various Inner Diameters

The fluidization characteristics of quartz sand and fluid catalytic crack (FCC) catalyst particles in six micro‐fluidized beds with inner diameters of 4.3, 5.5, 10.5, 15.5, 20.5, and 25.5 mm were investigated. The effects of bed diameter (D_t), static bed height (H_s), particles and gas properties on the pressure drop and minimum fluidization velocity (u_mf) were examined. The results show that the theoretical pressure drops of micro‐fluidized beds deviated from the experimental values under different particles and gas properties. The possible reason is due to an increase in bed voidage under smaller bed diameters. The equations for conventional fluidized beds did not fit for micro‐fluidized beds. u_mf increased with decreasing D_t. When the ratio of H_s to D_t ranged from 1:1 to 3:1, u_mf was characterized by a linear equation with H_s, while the slope of the equation u_mf versus H_s decreased with increasing D_t. In this paper, D_t/d_p and H_s/d_p were defined as dimensionless variables and a new equation was developed to predict u_mf in micro‐fluidized beds under the present experimental conditions.     

Oil–water two‐phase flow in microchannels: Flow patterns and pressure drop measurements

This paper investigates oil–water two‐phase flows in microchannels of 793 and 667 µm hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two‐phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart–Martinelli models developed for two‐phase flows in pipes. The results show similarity to both liquid–liquid flow in pipes and to gas–liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel.