Flow Channel Blockage Research Articles

Effect of airfoil trailing edge up on the performance of gas-liquid multiphase pumps

Abstract In this study, the impact of blade trailing edge structure on the performance of multiphase pumps was investigated. The modification parameters of the impeller blade airfoil were characterized by defining and adjusting the chord length ratio l/l 0 and deflection k, based on the design methodology employed for wing flap lifting devices. The impeller blade airfoil was modified using the trailing edge up design approach. Comparative analysis was conducted to evaluate the effectiveness of elevating the trailing edge of the airfoil in improving flow channel blockage, reducing turbulent energy at the impeller outlet, minimizing energy dissipation, and ultimately enhancing the efficiency of multiphase pumps. Remarkably, a maximum efficiency improvement of up to 3.04% was observed when the inlet gas content reached 70%.

A lattice Boltzmann analysis of the performance and mass transport of a solid oxide fuel cell with a partially obstructed anode flow channel

A thorough understanding of the solid oxide fuel cell (SOFC) performance and reactants' distribution through modeling and numerical simulation has become essential. In this paper, a comprehensive numerical model based on a lattice-based Boltzmann method was developed to numerically handle gas flow in the partially blocked channel and concentration polarization in porous electrodes while assessing the performance of such a SOFC. After model validation with available experimental data, effects of the blocks height, their number, and the cathode/anode-side flow channel blockage are investigated. Block insertion has been shown to speed up gas progression while enhancing mass transport from the channel to the anode/electrolyte interface and that the performance of the involved SOFC is better compared to a straight channel. The findings demonstrate that the SOFC performance improves by increasing both the blocks number and their height. Specifically, a 90% block with five blocks would improve power density by 14.4%.

New technical concept for alternating tangential flow filtration in biotechnological cell separation processes.

Robust cell retention devices are key to successful cell culture perfusion. Currently, tangential flow filtration (TFF) and alternating tangential flow filtration (ATF) are most commonly used for this purpose. TFF, however, suffers from poor fouling mitigation, which leads to high filtration resistance and product retention, and ATF suffers from long residence times and cell accumulation. In this work, we propose a filtration system for alternating tangential flow filtration, which takes full advantage of the fouling mitigation effects of alternating flow and reduces cell accumulation. We have tested this novel setup in direct comparison with the XCell ATF® as well as TFF with a model feed comprising yeast cells and bovine serum albumin as protein at harsh permeate to feed flow conditions. We found that by avoiding the dead-end design of a diaphragm pump, the proposed filtration system exhibited a reduced filtration resistance by approximately 20% to 30% (depending on feed rate and permeate flow rate). A further improvement of the novel setup was reached by optimization of phase durations and flow control, which resulted in a fourfold extension of process duration until hollow fiber flow channel blockage occurred. Thus, the proposed concept appears to be superior to current cell retention devices in perfusion technology.

Permeability Analysis of Hydrate-Bearing Porous Media Considering the Effect of Phase Transition and Mechanical Strain during the Shear Process

Summary The permeability characteristics of hydrate-bearing reservoirs are critical factors governing gas and water flow during gas hydrate exploitation. Herein, X-ray microcomputed tomography (CT) and the pore network model (PNM) are applied to study the dynamic gas and water relative permeabilities (krg and krw) of hydrate-bearing porous media during the shear process. As such, the dynamic region extraction method of hydrate-bearing porous media under continuous shear is adopted by considering deformation in the vertical direction. The results show that krw and krg of hydrate-bearing porous media are influenced by the effect of disordered sand particle movement under axial strain. Declines in the critical pore structure factors (pore space connectivity, pore size, and throat size) contribute to the reduction in krw and the increase in krg. However, krg decreases during the shear process at a high water saturation (Sw) because of the high threshold pressure and flow channel blockage. In addition, the connate water saturation (Swc) continuously increases during the shear process. Swc is influenced by pore size, throat size, and flow channel blockage. Moreover, the preferential flow direction of krg and krw changes during the continuous shear process. The results of dynamic permeability evolution during the continuous shear process under triaxial stress provide a reference for pore-scale gas and water flow regulation analysis.

A numerical analysis for a damage propagation in a plate-type fuel assembly of a research reactor

If several flow channels are completely blocked in a plate-type fuel assembly of research reactors with high power density, a flow instability (FI) can occur in an unblocked channel and can be propagated to the other adjacent flow channels. Such FI propagation can cause a propagation of fuel plate damages during the flow blockage accident. Hence, the thermal hydraulic behaviors of flow channels have been analyzed in order to investigate the FI propagation process by the simulation of CFD code for a multiple flow channel blockage in KiJang Research Reactor (KJRR) which is the model reactor assumed for this paper. Simulation results show that a FI occurs at the first unblocked channel if 8 flow channels are completely blocked and most of fuel plates are significantly damaged in 29 s after a complete blockage of 8 flow channels occurs in a plate type fuel assembly of the model reactor.

Computational flow and heat transfer design and analysis for 1/12 gas-cooled space nuclear reactor

The computational simulations of 1/12 full core gas-cooled space nuclear reactor have been conducted using the STAR-CCM+ code. The reactor is cooled by the He-Xe mixture and coupled with direct Brayton turbo-machines. To analyze the flow and heat transfer characteristics of the reactor, a series of calculations with complex core structures under zero gravity condition are conducted. The influences of the bypass vessel cooling, surface radiation, flow channel blockage and the fuel rods are studied. Results show that, although the bypass vessel cooling can decrease the temperature of the reactor vessels and the heat loss through surface radiation, it also increases the highest coolant temperature. Besides, the flow channel blockage will increase the uniformity of the radial temperature and velocity distribution. Finally, it is presented that the peak temperature is higher than the case without fuel rods and the fuel structure has little effects on the flow and heat transfer characteristics of the coolant region.

Visualization of phase distribution in lead–bismuth eutectic during one-dimensional solidification process

Solidification process of lead–bismuth eutectic (LBE) is one of the key phenomena to prevent flow channel blockage accident in an LBE-cooled accelerator-driven system. However, the solidification of liquid metal cannot be observed optically and it is difficult to detect noninvasively. In this study, the one-dimensional solidification process of the LBE was visualized by pulsed neutron transmission imaging. Neutrons have higher transmittivity to the LBE than X-ray and neutron transmission spectrum of the LBE sample can be obtained by pulsed neutron imaging technique. The solid and liquid phases of the LBE were identified during the solidification process by the presence or absence of Bragg edge in the measured neutron transmission spectrum, and the transient behavior of the solid–liquid interface could be visualized. In addition, the characteristic spatial distribution of the crystalline structure was found in Bragg-edge transmission image after the solidification.

Fouling behavior and scaling mitigation strategy of CaSO4 in submerged vacuum membrane distillation

Fouling and scaling in membrane distillation (MD) is one of the major obstacles to its long term stability. Submerging the membrane directly into the feed is an alternative method to prevent flow channel blockage. The fouling behavior of CaSO4 in submerged vacuum membrane distillation at varying experimental conditions was investigated. It presented a two-stage trend when the initial concentration of CaSO4 was <2700mg/L. Dramatic flux decline occurred once the feed was concentrated to a critical level of saturation. A on-line periodically air backwash was applied to reduce CaSO4 crystals deposition on the membrane surface or penetration in the membrane pores. While the role of air bubbles in affecting the fouling behavior of CaSO4 largely depended on the crystal formation mechanism. The fouling rate was reduced by 54% with the help of air backwash when surface crystallization controlled the process while negligible effect was made when bulk crystallization played a more important role. The result could be explained by combining the experimental data with a first-order kinetic model proposed by Tansel. The off-line water cleaning suggested that the fouling layer could be removed effectively without additional chemical agent.

Influences of bipolar plate channel blockages on PEM fuel cell performances

In this paper, the effect of partial- or full-block placement along the flow channels of PEM fuel cells is numerically studied. Blockage in the channel of flow-field diverts the flow into the gas diffusion layer (GDL) and enhances the mass transport from the channel core part to the catalyst layer, which in turn improves the cell performance. By partial blockage, only a part of the channel flow is shut off. While in full blockage, in which the flow channel cross sections are fully blocked, the only avenue left for the continuation of the gas is to travel over the blocks via the porous zone (GDL). In this study, a 3D numerical model consisting of a 9-layer PEM fuel cell is performed. A wide spectrum of numerical studies is performed to study the influences of the number of blocks, blocks height, and anode/cathode-side flow channel blockage. The results show that the case of full blockage enhances the net electrical power more than that of the partial blockage, in spite of higher pressure drop. Performed studies show that full blockage of the cathode-side flow channels with five blocks along the 5cm channel enhances the net power by 30%. The present work provides helpful guidelines to bipolar plate manufacturers.

Permeation and Blockage of Fine Particles Transported by Updraft through a Packed Bed

The fines generated in iron making blast furnace bring about the unsteady or unstable gas/liquid permeability and solid motion. Fundamental experiment was carried out to investigate the inhomogeneous phenomena such as flow channel blockage by fine particles transferred by updraft through a fixed packed bed. The alumina sphere and coke were used for packed bed and fine particles transferred, respectively. Conclusion of this study is as follows. The principal factor controlling a criterion for the blockage is a particle diameter ratio of coke to alumina particle, and fines concentration is not a primary factor. Consideration on a hydraulic equivalent diameter of a regular packing model of spheres is effective to predict the critical diameter ratio and it resulted in good agreement with the experimentally determined. Locally blocked mass, that is, a cluster consisting of coarse alumina particles and fines through which gas is incapable of flowing is dispersed in the bed. The void fraction of packed bed being equivalent to the pressure drop, calculated from Ergun's equation, is considerably small compared with the initial value when the local blockage is in existence. Fraction of the local blockage calculated from the void fraction and static holdup of fines is 15–20% as far as the present experimental condition.

10506 改良界面追跡法による燃料集合体内流路閉塞効果実験解析(産学における混相研究(2),OS.13 産学における混相研究)

10506 改良界面追跡法による燃料集合体内流路閉塞効果実験解析(産学における混相研究(2),OS.13 産学における混相研究)

Study of water distribution and transport in a polymer electrolyte fuel cell using neutron imaging

A procedure to utilize neutron imaging for the visualization of two-phase flow within an operating polymer electrolyte fuel cell has been developed at the Penn State Breazeale Nuclear Reactor. Neutron images allow us to visualize the liquid water inside the flow channel (∼0.5 mm deep) and gas diffusion media (∼200 μm thick) in real operating conditions. The current temporal and spatial resolution for radioscopy is approximately 30 frames/s and 129 μm/pixel in a 50 cm 2 image area. Continuous digital radioscopy can be recorded for 45 min. The determination of water volume within the cell has been enabled by referencing a calibration look-up table that correlates neutron attenuation to an equivalent liquid water thickness. It was found that liquid water tends to accumulate at specific locations within the fuel cell, depending on operating conditions. Anode flow channel blockage was observed to occur at low power, while higher power conditions resulted in more dispersed distribution of liquid droplets. Under high-power conditions, liquid water tended to accumulate along or under the channel walls at 180° turns, and radioscopy revealed that individual liquid droplet velocities were several orders of magnitude less than that of the reactant flow, indicating a slug-flow regime up to at least 1 A/cm 2.

Effective kinetic inhibitors for natural gas hydrates

Kinetic inhibition is a new means of preventing flow channel blockage by natural gas hydrates. In kinetic inhibition the system is allowed to exist within the hydrate thermodynamic stability zone, so that small crystals are stabilized without agglomerating to larger hydrate masses which plug pipelines. A hydrate formation mechanism is reviewed to suggest the new inhibition method. Macroscopic experiments on two apparatuses are presented for the best kinetic inhibitors among approximately 1500 chemicals. Pressure, concentration, and salinity limitations were measured for the three best kinetic inhibitors: poly(N-vinylcaprolactam) (PVCAP), N-vinylpyrrolidone/N-vinylcaprolactam/N,N-dimethylaminoethyl-methacrylate (VC-713), and N-vinylpyrrolidone-co-N-vinylcaprolactam (VP/VC). Field tests have verified the laboratory research.

Application of a two-dimensional ballooning model to out-pile and in-pile simulation experiments

The FRETA-B code which has thermal and mechanical models for the fuel behavior during a postulated Loss of Coolant Accident was applied to out-pile tube ballooning experiments and an in-pile integral simulation experiment MT-1 in the NRU reactor. From the analysis of the out-pile experiments, the ballooning model based on the thin-shell model together with an empirical rupture criterion was found effective in predicting the cladding deformation kinetics and the average strain left after rod rupture. The mechanical analysis of the MT-1 experiment was based on the calculation of the temperature history and its transverse distribution under reflooding which were consistent with the limited experimental data. The analysis indicated that the restriction of flow channel blockage to 70% in MT-1 was a result of an azimuthal cladding temperature difference of up to 60 K due mainly to eccentric relocation of pellet fragments.

On certain aspects of alternative core disruption accidents in LMFBRs

This paper examines the initial course of a postulated accident scenario in an LMFBR, involving the rupture of all piping connected to the reactor vessel, in the event of an earthquake (or an equivalent scenario involving both loss of heat removal and system rupture). The core is successfully shut down, but decay heat imposes a threat to core integrity. At the onset of pipe rupture, the fuel elements are cooled by natural circulation, followed by subcooling and nucleate boiling. Continuation of sodium evaporation leads to core dryout, clad melting, and subassembly wall failure. Clad melting is found to occur at a location close to the top of the core at a rate of 0.08 ft 3/s. The sodium vapor velocity is not high enough to carry the molten steel to the upper blanket region; therefore, flow-channel blockage in the lower axial blanket region is expected. At the time of clad melting, the fuel temperature rises by approximately 2°F/s, while the temperature-rise rate at the can wall, due to heat radiation from the fuel pin, is 10°F/s. Failure of the can wall initiates gross fuel motion. Continuation of the heat generation in the fuel pellet leads to the melting of the control rod support. Both the fuel motion and the control rod failure mark the start of reactivity insertion.

Experiments on Temperature and Flow Velocity Fluctuation of Coolant and the Possibility of Determination of Noise Source

Experiments on temperature and velocity fluctuations were conducted with an out-of-pile heat transfer loop. A number of experimental results are presented, such as the dependence of coolant temperature fluctuations on flow rate and heat flux, as also the power spectral density of temperature and flow velocity fluctuations. The dependence relations thus established will make it possible to detect flow channel blockage and coolant boiling by measuring coolant temperature fluctuations. To measure directly the velocity fluctuations in water flow, a newly developed device named “cell flowmeter” was used. A formulation of power reactor noise is presented to examine the noise spectrum distortion in the low frequency region by Langevin's method. One of the conclusions derived from the study is that it will be possible to determine the dominant noise source in a power reactor by observing the reactor power and coolant flow rate dependence of the “magnitude” of neutron noise spectrum, or the dependence of the ampli...

Experiments on Temperature and Flow Velocity Fluctuation of Coolant and the Possibility of Determination of Noise Source

Experiments on temperature and velocity fluctuations were conducted with an out-of-pile heat transfer loop. A number of experimental results are presented, such as the dependence of coolant temperature fluctuations on flow rate and heat flux, as also the power spectral density of temperature and flow velocity fluctuations. The dependence relations thus established will make it possible to detect flow channel blockage and coolant boiling by measuring coolant temperature fluctuations. To measure directly the velocity fluctuations in water flow, a newly developed device named “cell flowmeter” was used. A formulation of power reactor noise is presented to examine the noise spectrum distortion in the low frequency region by Langevin's method. One of the conclusions derived from the study is that it will be possible to determine the dominant noise source in a power reactor by observing the reactor power and coolant flow rate dependence of the “magnitude” of neutron noise spectrum, or the dependence of the amplitude of neutron fluctuations on the reactor power and coolant flow rate.