Two-phase Flow Performance Research Articles

An intelligent computing methodology for two-phase flow performance assessment of electrical submersible pump using artificial neural network and synthetic minority over-sampling technique

An intelligent computing methodology for two-phase flow performance assessment of electrical submersible pump using artificial neural network and synthetic minority over-sampling technique

CFD analysis in effects of spacer-vane on thermal–hydraulic performance of two-phase flow in annular channel

Spacer performs a key function in the construction of nuclear rod assembly. It is utilized to ensure the appropriate spacing and firmness of the rods in assembly. In rod bundle structures, spacers are typically incorporated with vanes to promote turbulence and improve heat transfer. The aim of this work is to analyze the impacts of spacer-vane on the thermal–hydraulic performance of two-phase flow in an annular channel. CFD model of an upward flow annular channel with spacer-vane has been developed. In addition, an annular channel model with a spacer but without vane has been generated and modeled in order to examine the impact of the spacer-vane in a two-phase flow. Transient simulations were performed with flow considerations of mass flux 714.4 kg/m2s, liquid temperature 330 K, volume fraction 0.35, heat flux 197.2 kW/m2, and atmospheric pressure conditions. CFD results have been validated with experimental data. Results show that the core zone of the annulus gap exhibits the highest level of turbulent intensity, and the outer pipe wall temperature is lower for spacer-vane relative to spacer alone. It is observed that the majority of water vapor is concentrated at the center of the channel in the farthest downstream location.

Visualization of Bubble Behaviors in Flow Fields of PEM Water Electrolyzer

Proton exchange membrane water electrolyzer (PEMWE) has been considered to be a promising technology for green hydrogen production, primarily because of its significant advantages in terms of high efficiency, high purity and fast dynamic response [1]. During its operation, hydrogen/oxygen evolves from the catalyst layer (CL), transports through the diffusion layer (DL) and then releases to the flow channel, forming various two-phase flow regimes, including bubbly, slug, annular, etc [2]. The presence of bubbles not only covers the electrode surface, but also blocks the water delivery, creating a large mass transfer resistance and even terminating the cell operation [3]. Another issue associated with bubble management is that the conventional parallel and serpentine flow-field configurations showed a poor self-pumping effect, exhibiting a mismatch between bubble evolution and removal rates [4]. To address this issue, therefore, some novel flow field designs have also been proposed in recent years, but the underlying mechanism how two-phase flow regime in flow-filed channels affects the electrolyzer performance is still not clear.In this work, we investigate the effect of two-phase behavior on the electrolyzer performance via a visualization approach, as illustrated in Figure 1. Our preliminary results have shown that an increase of water supply flow rate has insignificant effect on the electrolyzer performance even at high current densities. It is observed that with increasing the water supply rate, many bubbles are still covering the electrode surface, meaning that water cannot be effectively supplied to the CL. To address this issue, a degassing layer, with a thinner rib and a wider channel, is introduced to the flow field design, which is able to promote the self-pumping effect of gas bubbles. This novel design can facilitate the rapid detachment of bubbles from the electrode surface, providing more paths for the water penetration into the CL. Acknowledgement This work was fully supported by a grant from the National Natural Science Foundation of China (Project No. 52022003). References Razmjooei, T. Morawietz, E. Taghizadeh, et al, Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer, Joule, 5(7) (2021) 1776-1799.Rakousky, U. Reimer, K. Wippermann, et al, An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis, J. Power Sources, 326 (2016) 120-128.Villagra, P. Millet, An analysis of PEM water electrolysis cells operating at elevated current densities, Int. J. Hydrog. Energy, 44(20) (2019) 9708-9717.O. Majasan, J.I.S. Cho, I. Dedigama, et al, Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterization, Int. J. Hydrog. Energy, 43(33) (2018) 15659-15672. Figure 1

Experimental investigation of flow orientation effects on cryogenic flow boiling

Cryogenic flow boiling physics is of paramount importance for future cryogenic space applications employing Cryogenic Fluid Management (CFM) technologies. This experimental study investigates the two-phase flow and heat transfer performance of LN2 flow boiling across five distinct flow orientations: vertical upflow, vertical downflow, horizontal flow, 45° inclined upflow, and 45° inclined downflow. The study employed the steady-state heating method within a circular heated tube featuring an 8.5-mm inner diameter and a 680-mm heated length. High-speed video recordings were utilized to capture two-phase flow patterns and interfacial behaviors across various flow orientations. The experiments covered a wide range of operating conditions, including mass velocities ranging from 351.80 to 1572.77 kg/m²s and inlet pressures from 297.14 to 1032.97 kPa, primarily with near-saturated inlet subcooling. Distinct two-phase flow patterns and regime transitions were identified for each flow orientation. Symmetrical flow patterns were evident in vertical orientations, whereas non-vertical orientations exhibited asymmetric flow stratifications, primarily influenced by the buoyancy force in a terrestrial gravity environment. Bubble dynamic parameters were quantified, and bubble collision and dispersion phenomena were visualized. Analyzing heat transfer performance based on local flow boiling curves and variations in heat transfer coefficients (HTCs), it was observed that vertical upflow demonstrated the most enhanced heat transfer performance, while vertical downflow exhibited the lowest. As mass velocity exceeded 830 kg/m²s, the differences in heat transfer among orientations became less distinct, emphasizing the role of flow inertia in mitigating the influence of flow orientation. A direct comparison of microgravity HTC data from a recent study by the authors against the 1-ge HTC data indicated enhanced heat transfer performance in microgravity for flow orientation configurations in terrestrial gravity. However, this enhancement progressively diminished as the heat flux increased. Distinct HTC trends were observed as mass velocity increased for different flow orientations and gravity levels.

Blade Number Effects in Radial Disc Pump Impellers: Overall Performances with Cavitation Sensitivity Analysis

Straight radial impeller disc pumps are widely used in several industrial applications for hard-to-pump working flow media, such as two-phase inlet conditions, either including non-miscible bubbles or solid particles with a high concentration within the main working flow. Compared with conventional pump designs, these pumps have not been widely studied, because of their particular simple design and low efficiency values that can however reach a maximum value of 0.5 with a good pressure increase in single-phase conditions. Regarding this, no basic analysis has been performed to build one-dimensional design rules considering the relative effects of design parameters proper to these unusual designs like the blade number, blade height and disc spacing. This step is an important one for two-phase flow performance evaluations which are usually derived from single-phase ones as for conventional pumps. Two different disc pump designs with, respectively, 8 and 10 radial blades, are numerically and experimentally investigated. Experimental investigations are performed in an open loop tap water test facility, under various working conditions, combining flow rate and rotational speed variations. The overall pump performances are compared and analyzed, including cavitation onset phenomena that have been found to influence the experimental performances of both pumps. The overall performance modification between both impeller designs is analyzed. Comparisons between CFD and experimental results give reliable results and can be considered to cover a sufficiently wide range of design parameters allowing us to build future adapted design rules for such specific designs.

Numerical study on the effect of the vane channel parameters on the performance of gas-water separators for a PEMFC system

In this study, the effects of vane channel parameters on the flow field and separator performance are investigated based on a vane type gas-water separator for a PEMFC (proton exchange membrane fuel cell) system. The Eulerian-Eulerian model combines with the Multi-Fluid VOF (volume of fluid) modeling approach is used to comprehensively investigate the gas-liquid two-phase flow field and performance indexes in the separator, and the sensitivity analysis of the structural parameters is carried out. The results show that the pressure drop of the separator gradually increases with the increase of the vane contraction ratio, while the separation efficiency has a tendency to increase and then decrease with the increase of the vane incidence angle. For the separation efficiency, the most beneficial structural variant results in an increase of 11.63%, while for the pressure drop, almost all structural variants result in a reduction of the pressure drop from the standard structure with a maximum reduction of 36.58%. By analyzing the phase distribution, pressure field and velocity distribution of different structures, it can be obtained that the main factors affecting the performance of the separator are the extreme values of tangential velocity inside the separator and the symmetry of velocity distribution in the internal flow field. The results presented in this study can provide a reference for the PEMFC gas-water separator.

Experimental study of the effect of mechanical vibration and water velocity on bubble management in PEM electrolysis cell

The anode of a proton exchange membrane electrolysis cell (PEMEC) has a complex two-phase flow. Excessive gas concentrations tend to build up on the catalyst layer (CL) surface and inside the porous transport layers (PTLs), inhibiting electrolytic reactions from occurring. Therefore, efficient bubble management methods are required. In this paper, the principle of actions and the effect of mechanical vibration and water velocity as methods of bubble management are investigated. PEMEC bubble kinetic and two-phase flow performance were investigated using high-speed optical imaging at different amplitudes, frequencies and water velocities, and the results were correlated with electrochemical performance. The results show that the vertical sinusoidal vibration can cause cyclic compression of the PTL by the ribs, which promote the discharge of the blocked gas into the flow channel. This effect can be enhanced by increasing the amplitude of the vibration. During vibration, the inertia of the water causes the large bubbles to break up into smaller bubbles and can generate longitudinal shear forces that can promote the bubbles to detach and move. Increasing the frequency can enhance this effect by shortening the period of the action. However, the vertical sinusoidal vibration does not promote the discharge of air bubbles from the flow channel out of the cell, in which the thrust and lateral shear provided by water flow is necessary. Increasing the water velocity can also generate more bubble flow. The combination of vibration and high water velocity can significantly reduce the gas concentration in the cell. Polarization data shows a 7.2% reduction in cell polarization under the experimental conditions (80 mL/min, 1.5 mm, 150 Hz) compared to the normal state. The results of this study can provide theoretical basis and experimental data for the study of bubble management methods, optimization of working conditions and improvement of operating efficiency of PEMEC.

Flow distribution and heat transfer performance of two-phase flow in parallel flow heat exchange system

Flow distribution and heat transfer performance of two-phase flow in parallel flow heat exchange system

Flow Performance Analysis of Double-Chamber Gas–Liquid Transferring Device

Gas–liquid transportation is an efficient and economical transportation technology developed in recent years. It mainly uses some transportation equipment to simultaneously transport crude oil, associated natural gas, produced water, and so on for the purpose of reducing costs and energy consumption. In this paper, a double-chamber gas–liquid transferring device was selected as the research object. The VOF multiphase flow model of FLUENT software was used to simulate the gas–liquid two-phase flow performance under the design condition. The relationships between the two-phase flows, pressure, temperature, liquid level in the tank, outlet flow rate of the device, and time were calculated and analyzed. The results show that the operating cycle of the device can be divided into three processes, namely ‘suction-compression-discharge’, in which the cycle period formula is proposed as well. The pressures of gas and liquid in the device are basically the same, but the temperatures of the two phases are quite different in the compression process. In the compression process, the outlet valve is closed so that the outlet flow rate of the device is zero, and the gas compression process can be approximately treated as isothermal compression in engineering design. The comparison between the measured performance data in the oil field and the calculation results indicates that the calculation method in this paper is feasible for the performance prediction and optimization of the double-chamber gas–liquid transferring device.

Electrochemical performance study of proton exchange membrane electrolyzer considering the effect of bubble coverage

Bubble dynamics are closely related to the electrochemical performance of a proton exchange membrane electrolyzer (PEMEC). However, tiny bubbles need to be clustered together to affect the electrochemical performance of PEMEC significantly. In this paper, the effect of microscopic bubbles on macroscopic electrochemical properties were assessed by bubble coverage. The bubble dynamics, two-phase flow, and electrochemical performance were captured under different conditions using a high-speed, microscopic visualization experimental system. The results show that various factors influence the two-phase flow pattern. At 60 °C, 1.5 A/cm2 and 5 mL/min, the annular flow occupied 76.8% of the gas phase area, and when the water flow increased to 80 mL/min, the annular flow ratio decreased substantially to 2.7%. The two-phase flow of bubbles in the flow channel showed different flow patterns over time. Under the experimental conditions (60 °C, 20 mL/min, 0.8 A/cm2), the bubble flow pattern experienced the emergence of bubbles, bubble flow, segmental plug flow, annular flow, and final steady state with the occurrence times of 0.15 s, 1.5 s, 5.0 s, 10.5 s, and 21.2 s, respectively. The bubble coverage increased with current density and temperature, while it decreased with the increase of water velocity. In addition, the effects of temperature and water velocity on bubble coverage and PEMEC performance vary in principle. Specifically, higher temperature mainly improves the bubble coverage by increasing the electrochemical performance of PEMEC. In contrast, higher water velocity mainly improves the electrochemical performance of PEMEC by decreasing the bubble coverage. This study elucidates the relationship between microscopic bubbles and macroscopic electrochemical performance, contributing to a better understanding of the processes and principles of bubble effects on the electrochemical performance of PEMEC. The results may provide a theoretical basis and experimental data for operating condition optimization, operating efficiency improvement, multiphase flow study, gas diffusion layer structure, and flow field design of PEMEC.

Hydrodynamics behavior and mass transfer performance of gas–liquid two-phase flow in the honeycomb fractal microreactor

The gas–liquid two-phase flow and mass transfer performance in the honeycomb fractal reactor with equal diameter were visually investigated. The effects of operating conditions on flow pattern, fluid distribution and mass transfer coefficient were studied. The intrinsic dependence of mass transfer coefficient on fluid uniformity was revealed. Four flow patterns were observed in this work: non-breakup flow, symmetrical flow, unobvious asymmetrical flow, and obvious asymmetrical flow. It was found that the fluid distribution was mainly influenced by the downstream feedback of the channel. The bubble uniformity relies dramatically on the bubble breakup, pressure fluctuations, and downstream feedback. A relatively uniform bubble distribution could be obtained at partial symmetrical flow and unobvious asymmetrical flow. The mass transfer could be greatly enhanced in the case of excellent fluid distribution and uniform bubble size, conversely, the mass transfer coefficient would decrease. The increasing leakage flow and internal circulation inside the liquid are conducive to mass transfer performance. Additionally, the honeycomb fractal reactor with variable diameter was designed based on Murray's law and its comprehensive performance was compared with the fractal reactor with equal diameter, which could provide a theoretical basis for the design and optimization of the fractal microreactor.

Effect of channel height on performance of two-phase flow in mini- and microchannels with a T-mixer

Effect of channel height on performance of two-phase flow in mini- and microchannels with a T-mixer

Simulation of refrigerant-lubricant two-phase flow characteristics and performance test in space compressor

The vapor-compression heat pump allows for lightweight heat-control systems and efficient heat emissions. It is considered to be the best choice for future space thermal control systems. To solve the problem of separation and compression deterioration of conventional positive-displacement refrigeration compressors in a microgravity environment, an innovative microgravity solution, mixing refrigerant and lubricant without oil separation, is proposed. A flow model in the compression chamber was developed and simulations were performed to investigate the effects of gravity and lubricant volume fraction on the flow characteristics of the refrigerant-oil mixture in a rolling rotor compressor. A modified compressor performance test bench was built and the effect of compressor speed on parameters such as power and heat dissipation was investigated experimentally. The results showed a maximum difference between the simulated and experimental values of compressor discharge temperatures of 9.16 %. Under microgravity conditions, a lubricant-refrigerant mixture with a volume fraction of less than 5 % can serve as the system working medium. The lubricant volume fraction at the outlet of a compressor cycle in normal gravity was 4.9 %, while it was 3.34 % in microgravity. As the compressor speed increased from 1500 to 5000 rpm, the compressor power increased from 15.5 to 64.5 W and the system heat discharge rate increased from 115.2 to 164.1 W. The system refrigeration coefficient of performance (COPc) decreased from 6.4 to 1.5, while that of heat dissipation, COPh, decreased from 7.4 to 2.5.

Two-Phase Modeling and Simulations of a Polymer Electrolyte Membrane Water Electrolyzer Considering Key Morphological and Geometrical Features in Porous Transport Layers

Polymer electrolyte membrane (PEM) electrolysis has a promising future for large-scale hydrogen production. As PEM electrolysis technology develops, larger operating current densities are required. In order to increase current density, more water should be available at the reaction sites. Moreover, the removal rate of oxygen and hydrogen needs to be effectively improved. This, in turn, necessitates a better understanding of the main mass transport and electrochemical processes. On the anode side, mass transport is particularly crucial because water must be supplied to the catalyst layer (CL) while, at the same time, oxygen bubbles must be eliminated in a parallel flow from the reaction sites into the flow channels. Hence, simulating the two-phase bubbly flow across the cell thickness is necessary to predict PEM electrolysis performance more accurately as a function of the operating current density. This study provides a systematic understanding of how morphological and geometrical features contribute to the polarization curve and performance characteristics of a PEM electrolysis cell. Hence, a multi-phase PEM electrolysis model has been implemented using MATLAB R2022a. Polarization curves have been calibrated against experimental data and then assessed to provide a fundamental understanding of the relationship between the two-phase flow and cell performance.

CO2 chemical absorption into AMP aqueous solution and mass transfer intensification in cascade sudden expansion microchannels

Carbon dioxide chemical absorption into 2-amino-2-methyl-1-propanol (AMP) aqueous solution and mass transfer enhancement in cascade sudden expansion microchannels were investigated by a high-speed digital camera. The influences of the flow rates of gas and liquid phases, the sudden expansion units and the concentration of AMP on the gas-liquid two-phase flow and mass transfer performance are studied systematically. Results showed that the increase of sudden expansion unit is conductive to increase liquid side volumetric mass transfer coefficient and enhancement factor. The maximal enhancement factor could reach to 1.33, and the maximally effective mass transfer efficiency could reach 1.6 under taking the energy consumption into account. The gas phase flow rate has slight effect on mass transfer enhancement factor E, while E decreases with increasing liquid phase flow rate. With the increase of AMP concentration, the volumetric mass transfer coefficient increases, but the enhancement factor decreases. A new correlation with good prediction performance was proposed for the volumetric mass transfer coefficient. Furthermore, the energy consumption and effective mass transfer efficiency were assessed.

Relationship of local current and two-phase flow in proton exchange membrane electrolyzer cells

A macro segmented Proton exchange membrane electrolyzer cell (PEMEC) with visualized endplates is designed and assembled to investigate the internal performance inhomogeneities. The local current density distribution (CDD) of the four segments of the PEMEC is measured, and the flow in the channel is observed and recorded by visualizing the endplates. The effect of varying operating conditions on the two-phase flow type distribution and performance are analyzed. It is found that the variations of the two-phase flow type from the inlet to the outlet of the electrolyzer cell lead to significant differences in the internal local performance. Large bubbles have a positive effect on the performance improvement, due to they are able to carry bubbles moved backwards along the flow direction, resulting in the region with the best performance moving from the inlet segment to the middle segment. In addition, the electrolytic current density increases as the increase of voltage, and the variation of the two-phase flow type lead to the increase of inhomogeneity. The above investigation provides a better understanding on the internal inhomogenrity of the electrolyzer cell, which is related to the two-phase flow behavior.

Two phase (water/air) suction performance of turbopump inducer

Abstract In the present study, the gas-liquid two-phase flow performance of a turbopump with an inducer has been experimentally investigated. In the performance evaluation test, the air bubbles is released from dissolved air at the upstream valve to realize two-phase flow. By this method, a homogeneous bubbly flow is expected just after the valve. The amount of dissolved oxygen (DO) is an important parameter, and the experiment is carried out under the conditions of DO≅50%, 100%, 200%, where DO[%] indicates the relative amount of DO against the saturated value at the atmospheric condition. Under each DO condition, the experiment is performed at various water flow rates. As a result, a clear trend that the higher DO is, the worse the performance becomes, is observed. It is found that the mechanism for the head drop of the pump differs between at high and low flow rates. At the high flow rate, the performance does not deteriorate up to relatively high volumetric flow rate ratio of air and water. The cause of performance deterioration seems to be the increased number and/or size of bubbles released at the upstream valve. On the other hand, at the low flow rate, the performance deteriorates at relatively low air-water flow rate ratio. Although the air water volume flow ratio is low, the bubbles can precipitate in inlet flow recirculation and back flow vortices, which seems to cause the performance deterioration.

ターボポンプの気液二相流性能に及ぼす液中溶存空気量の影響

In the present study, the gas-liquid two-phase flow performance of a turbopump equipped with an inducer was experimentally investigated. The almost homogeneous bubbly two-phase flow condition was successively set by the uniform aeration of gas dissolved in water upstream of the test pump, which was realized by a sudden pressure decrease with the valve closure. The gas-liquid volumetric flow rate ratio was estimated from the pump inlet pressure and the initial amount of dissolved oxygen under the assumption of mass equilibrium condition of the local dissolved oxygen. The effect of dissolved oxygen content on the gas-liquid two-phase flow performance of a turbopump was investigated. The results showed that low DO conditions are not suitable for evaluating gas-liquid two-phase flow performance because of in-negligible effect of vaporous cavitation. In addition, the effects of a reduced-diameter suction pipe and a swirl brake on the gas-liquid two-phase flow performance of a turbopump were investigated. The results showed that the effect on the gas-liquid two-phase flow performance was small under high DO condition, but the performance deteriorated under low DO condition.

Study on evolution laws of two-phase choking flow and entrainment performance of steam ejector oriented towards MED-TVC desalination system

In this study, a visualizable experimental platform of steam ejector oriented towards MED-TVC desalination system is constructed, and the evolution laws of two-phase choking flow and ejector's entrainment performance under various operating parameters are obtained. Further, a matching double-choking theory with consideration of the condensing flow is developed to explain the inherent reason behind these evolution laws. Key results revealed that the formed two-phase choking flows have great effects on ejector's entrainment performance. The primary jet flow choking area linearly increases as the primary steam pressure raises, and the entrainment choking area experiences a small reduction, while the extended flow area marginally increases. Accordingly, the entrainment ratio significantly decreases, while the choking cross-section is slightly shifted upstream. In addition, the primary jet flow choking area considerably decreases with increasing entrainment pressure, but the entrainment choking area is nearly unchanged and the extended flow area increases by more than 8 times. As a result, the entrainment ratio remarkably increases, the choking cross-section migration distances are much larger than that in the case of primary steam pressure varies. A meaningful guide evolves from fact that priority should be given to restrain the condensing flow for achieving a higher energy efficiency of ejector.

Study on Evolution Laws of Two-Phase Choking Flow and Entrainment Performance of Steam Ejector Oriented Towards MED-TVC Desalination System

Study on Evolution Laws of Two-Phase Choking Flow and Entrainment Performance of Steam Ejector Oriented Towards MED-TVC Desalination System