Liquid Distribution Research Articles

Investigation on the DNB-type critical heat flux in a fuel assembly with 5 by 5 rods

In this paper, Eulerian two-phase model coupled with wall boiling model was employed to simulate the departure from nucleate boiling (DNB) in a 5 × 5 fuel assembly. The numerical simulation accurately predicted the critical heat flux (CHF) and also its location. Compared with the calculated results from W-3 formula and FLICA subchannel code, the CFD (Computational Fluid Dynamics) calculations showed good agreement against experimental measurements with the deviation of 5%, but presented more detailed flow distribution. Based on CFD results, the method of CHF prediction was discussed with an eye on wall superheat, void fraction and vapor convective heat flux in rod surfaces. The distribution of flow field and liquid–vapor fraction affected by mixing vane were further studied. Mixing vane can continually influence the downstream thermal hydraulic characteristics, forming the diagonal circulation and square circulation with the flow development. As a result, the bubble aggregation firstly occurred on the surface of corner hot rod instead of central hot rod, which induced the local heat transfer crisis. The CFD calculations presenting the evolution process of physical parameters can provide guidance for rod bundle CHF test and fuel assembly design.

Study on liquid dispersion characteristics in trickle bed reactor based on image processing

The liquid flow and distribution are key factors in determining the performance of a trickle bed reactor. It is highly challenging to examine the characteristics of liquid dispersion due to the complexity of the liquid flow mechanism in the trickle bed reactor. In this study, experimental research was performed to determine the impacts of gas/liquid velocity, particle packing method, and liquid properties on the characteristics of liquid dispersion in a pseudo-two-dimensional trickle bed reactor. A high-speed camera system was utilized to record the liquid flow and distribution in the reactor. An image processing method was proposed to obtain the particle surface wetting efficiency for quantifying the liquid distribution in the reactor. By combining liquid distribution images (qualitative information) and particle surface wetting efficiency (quantitative information) in the reactor under different conditions, it is feasible to evaluate the liquid dispersion in the trickle bed reactor in great detail.

Effects of structured prefilmer lip on spray characteristics in planar prefilming airblast atomization

Effective liquid fuel atomization is an ultimate aim for the prefilming airblast atomizer in aero-engines, and the liquid fuel breakup behavior is the key indicator of atomization quality. Whereas, the prefilmer lip structure is unnoticed but of great influence on this breakup process. In this paper, the rectangular block structured prefilmer lip and the triangular prism structured prefilmer lip are delicately designed and adopted in planar prefilming airblast atomization. Accordingly, the spray characteristics, including the liquid film morphology, droplet distributions, and atomization quality are comprehensively investigated under structured prefilmer lips, using a coupled LB-LES model. The numerical results reveal that when the rectangular block structured prefilmer lip is adopted, the multihole morphology appears on the liquid film under the cutting effect of the rectangular sawtooth, thus contributing to the liquid breakup process. The droplet equivalent diameter in the atomization process distributes exponentially, and 70%-80% of the droplet sizes are less than 100 μm. The droplet velocity shows a normal distribution with its average value located from 1 m/s to 2 m/s in the streamwise direction when the air velocity is 20 m/s. Ultimately, according to droplet size, droplet velocity, and atomization angle, along with the atomization efficiency coefficient, the atomization quality under the rectangular block structured prefilmer lip is better than that with triangular prism structured prefilmer lip and unstructured prefilmer lip, and the highest atomization quality is obtained with rectangular block width of 0.3 mm.

Monetary policy transmission through banks when liquidity is abundant but unevenly distributed

We study how the distribution of excess liquidity amongst banks alters the transmission of policy rate hikes to bank interest rates. Using a difference-in-difference approach, we measure the difference in the pricing behavior of the 19 euro-area banking systems depending on their excess liquidity holdings when the European Central Bank’s Deposit Facility Rate (DFR) increases. According to our estimations, every 100 bp increase in the DFR, banking systems holding one additional standard deviation of excess liquidity apply a 1.9 bp higher interest rate on new checking accounts and between 3.2 and 6.8 bp lower interest rates on new loans.

The search for an appropriate condensation model to simulate wet steam transonic flows

PurposeThe purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.Design/methodology/approachTo find the most suitable condensation model, five nucleation equations and four droplet growth equations are combined, and 20 cases are considered for modelling the wet steam flow through steam turbine blades. Finally, by the comparison between the numerical results and experiments, the most suitable case is proposed. To find out whether the proposed case is also valid for other boundary conditions and geometries, it is used to simulate wet steam flows in de Laval nozzles.FindingsThe results indicate that among all the cases, combining the Hale nucleation equation with the Gyarmathy droplet growth equation results in the smallest error in the simulation of wet steam flows through steam turbine blades. Compared with experimental data, the proposed model’s relative error for the static pressure distribution on the blade suction and pressure sides is 2.7% and 2.3%, respectively, and for the liquid droplet radius distribution it totals to 1%. This case is also reliable for simulating condensing steam flows in de Laval nozzles.Originality/valueThe selection of an appropriate condensation model plays a vital role in the simulation of wet steam flows. Considering that the results of numerical studies on condensation models in recent years have not been completely consistent with the experiments and that there are still uncertainties in this field, further studies aiming to improve condensation models are of particular importance. As condensation models play an important role in simulating the condensation phenomenon, this research can help other researchers to better understand the purpose and importance of choosing a suitable condensation model in improving the results. This study is a significant step to improve the existing condensation models and it can help other researchers to gain a revealing insight into choosing an appropriate condensation model for their simulations.

Measurement of liquid water distribution in GDL under cross-flow-inducing parallel flow field using operando synchrotron X-ray radiography

Baffles in flow field channels for air in a polymer electrolyte fuel cell are known to enhance the performance by inducing convective flow through the gas diffusion layer (GDL) with smaller pressure loss than interdigitated flow fields. This work experimentally correlates performance enhancement with the amount of liquid water in a GDL. A parallel flow field (PFF) that has different inlet and outlet opening sizes is applied to induce cross-flow in the GDL under the rib between adjacent air channels. Operando synchrotron X-ray radiography experiments are conducted to compare the amount of water in the GDL with that for a PFF having the same inlet and outlet sizes. The performance enhancement by application of different opening sizes increases with decreasing relative humidity and increasing air flow rate. A significant performance enhancement is observed when the amount of water in the GDL substrate under the rib becomes almost zero. No performance enhancement is observed under over-humidified conditions, although a decrease in the amount of water in the GDL is still observed, which suggests that the performance becomes insensitive to the difference in the liquid water saturation as the saturation increases.

Influence of porosity and temperature on light non-aqueous phase liquid diffusion in soils

Soil characteristics play an important role in distribution of light non-aqueous phase liquid (LNAPL) spilled from buried pipeline, and enhanced understanding of distribution is significant to the effective design of soil and groundwater remediation strategies. Therefore, distribution of diesel in soils with different porosity and temperature on the temporal evolution of the diesel migration following the saturation profiles of the two-phase flow in soils were investigated in this study. The diffusion ranges, areas and volumes in both the radial as well as in axial directions of leaked diesel in soils with different porosity and temperature increased with time. Soil porosities played an important role in the distributions when soil temperatures had no effect on distributions of diesel in soils. The distribution areas were 0.385 m2, 0.294 m2, 0.213 m2, and 0.170 m2 at 60 min when the soils porosities were 0.1, 0.2, 0.3, and 0.4, respectively. The distribution volumes were 0.177 m3, 0.125 m3, 0.082 m3, 0.060 m3 at 60 min when the soils porosities were 0.1, 0.2, 0.3, and 0.4, respectively. But the distribution areas were 0.213 m2 at 60 min when the soil temperatures were 286.15 K, 296.15 K, 306.15 K and 316.15 K, respectively. The distribution volumes were 0.082 m3 at 60 min when the soil temperatures were 286.15 K, 296.15 K, 306.15 K and 316.15 K, respectively. The calculation formulas of distribution areas and volumes of diesel in soils with different porosity and temperature for developing prevention and control strategies in the future were fitted. The seepage velocities of diesel changed sharply around the leakage port and decreased from about 4.9 m/s to 0 within a few millimeters in soils with different porosity. Additionally, the diffusion ranges of leaked diesel in soils with different porosity were different, indicating that soil porosity had a significant impact on seepage velocities and pressures. The seepage velocities fields and pressures fields of diesel in soils with different temperature were same at the leakage velocity of 4.9 m/s. And the study could provide some supports for determination of the safety zone and formulation of emergency response plans for LNAPL leakage accidents.

Synergistic effects of vapor and gaseous cavitation and mass-transfer mechanism in a mechanical pump

Dynamic gas–liquid mass-transfer processes are extensively encountered in gas–liquid mixture transport systems, where mechanical pumps pressurize the mixture and are accompanied by flow and mass-transfer instabilities. Herein, our proposed gaseous cavitation model was innovatively developed to revolutionize the independent unidirectional absorbed or evolved mass transfers. Complex gas–liquid behaviors under the synergetic effects of gaseous and vapor cavitations were achieved for the first time in an on-orbit refueling mechanical pump. Four coupled mass-transfer processes, namely, evolution, evaporation, absorption, condensation, and gas–liquid distribution, were investigated through numerical calculations. The results indicated that when the solution was close to critical saturation and conversion of the mass-transfer direction, a surge in the mass-transfer rate, and more intense hydrodynamic instability occurred. The vapor drove the accumulation of the evolved gas along the edge of the vapor in the impeller, where the evolved-dominated mass-transfer bands existed on the suction surfaces of the long blade, exhibiting the degassing characteristics of the vapor cavity, and other regions belonged to absorption-dominated region. Continuous dissolution induced by significant positive pressure gradient led to the maximum absorbed oxygen concentration at the impeller outlet. The maximal increments of absorbed oxygen in the suction chamber, impeller, and volute were 98%, 447%, and 694%, respectively, and the volume fractions were attenuated by 18.3%, 12.5%, and 5.0%, respectively. Notably, an increase in the gas volume fraction was the dominant reason for exacerbating the instability of the impeller forces, and the range of the radial force tended to be narrow and concentrated as the concentration increased.

Numerical investigation of gas–liquid two-phase performance in a mixed-flow pump by using a modified drag force model

As key devices to lift deep-sea oil and gas, mixed-flow pumps can transport multiphase flow with high inlet gas volume fraction (IGVF). Performance parameters of mixed-flow pumps may be disturbed by the complex flow and gas–liquid distribution under various conditions that need an accurate two-phase flow numerical methodology for prediction. In this work, the gas–liquid mixed flow performance of a mixed-flow pump is investigated based on the modified drag force model, which considers the bubble deformation at high IGVF. The effects of the IGVF on pressure increment and gas phase distribution are explored. The influences of flow rate and rotational speed are studied as well. Experiments are conducted to obtain performance parameters and gas–liquid distribution images. The results show that performance parameters and gas–liquid distribution predicted in simulations are consistent with those obtained in experiments. The pressure increment of the mixed-flow pump is decreased as the IGVF and flow rate increase. Especially when IGVF increases from 5% to 15%, the pressure increment drops sharply, which is the surging phenomenon. The increased speed may improve the performance. The evolution of gas phase distribution is deeply analyzed to improve the understanding of gas–liquid flow characteristics in mixed-flow pumps.

Role of Hydrogen Bond Defects for Cluster Formation and Distribution in Ionic Liquids by Means of Neutron Diffraction and Molecular Dynamics Simulations.

Defects fundamentally govern the properties of all real materials. Correlating molecular defects to macroscopic quantities remains a challenge, particularly in the liquid phase. Herein, we report the influence of hydrogen bonds (HB) acting as defects in mixtures of non-hydroxyl-functionalized ionic liquids (ILs) with an increasing concentration of hydroxyl-functionalized ILs. We observed two types of HB defects: The conventional HBs between cation and anion (c-a), and the elusive HBs between cations (c-c) despite the repulsive Coulomb forces. We use neutron diffraction with isotopic substitution in combination with molecular dynamics simulations for measuring the geometry, strength, and distribution of mobile OH defects in the IL mixtures. In principle, this procedure allows relating the number and stability of defects to macroscopic properties such as diffusion, viscosity, and conductivity, which are of utmost importance for the performance of electrolytes in batteries and other electrical devices.

Effects of bubbles on particle dynamic behavior and concentration distribution in High-viscosity liquid under negative pressure

The vacuum method is a widely adopted technique for eliminating bubbles from polymers containing particles. To investigate the influence of bubbles on the behavior of particles and the concentration distribution in high-viscosity liquids under negative pressure, experimental and numerical methods have been employed. The experimental findings demonstrated a positive correlation between the diameter and rising velocity of bubbles and the negative pressure. As the negative pressure increased from − 10 kPa to − 50 kPa, the position of the region where the particles were concentrated in the vertical direction was elevated. Furthermore, when the negative pressure exceeded − 50 kPa, the particle distribution became sparse and layered locally. The Lattice Boltzmann method (LBM) integrated with the discrete phase model (DPM) was utilized to investigate the phenomenon, and the outcomes revealed that rising bubbles have an inhibitory effect on particle sedimentation, and the extent of inhibition was determined by the negative pressure. In addition, vortexes generated by differences in the rising velocity between bubbles resulted in a particle distribution that was sparse and layered locally. This research provides a reference for achieving desired particle distributions using a vacuum defoaming approach and should be further studied to extend its applicability to suspensions containing particles with different viscosities.

Effect of structural parameters of corrugated plate on the evolution of solitary waves and liquid film thickness distribution

The effect of wall distortion of the scrubbing-cooling tube on turbulent falling film is significant. The wall distortion was simplified by using corrugated plates; the effect of structural parameters (amplitude and wavelength) of corrugated plates on the action mechanism of solitary waves and the axial distribution of liquid film thickness were investigated. The results show that the Coanda effect decelerates and accelerates the flowing liquid film attached to the wall, which leads to the generation and extinction of solitary waves on the liquid film. The intensification of the local perturbation easily promotes the solitary waves to form slender water columns. Under the effect of Plateau-Rayleigh instability, the tails of the slender water columns break up to form tiny droplets. The mean liquid film thickness prediction model can accurately predict the mean liquid film thickness on corrugated plates (amplitude/wavelength = 0.02 ∼ 0.08) and the relative errors within ± 15%.

Analysis and Modeling of No-Vent Filling Process for Liquid-Hydrogen Tank in Orbital Conditions

A four-node model is proposed to investigate the no-vent filling performance of liquid hydrogen (LH2) at microgravity. The no-vent filling method can directly prevent the influence of random gas–liquid distributions at microgravity, making it a good choice for cryogenic propellants to achieve orbital refueling. The typical phase distribution of the centrally located ullage was assumed and, in particular, the correlations for the boiling heat transfer of LH2 at microgravity were corrected in this model. After the accuracy of this model was effectively verified, the effects of different filling conditions, including the initial tank pressure, the initial temperature, and the temperature of the inlet liquid, were studied. The results showed that the initial pressure had a major influence on the initial pressure rise but only a slight influence on the final pressure development. A higher initial temperature would have led to an obvious increase in the tank pressure and an obvious decrease in the final filling level when reaching the upper pressure limit. Reducing the temperature of the inlet liquid has certain effects on the pressure control and the improvement of the final filling level. In conclusion, to achieve a higher filling level under a lower pressure level during the no-vent filling of LH2 at microgravity, sufficient pre-cooling of the filling system is required. Furthermore, appropriate evacuation of the receiver tank before filling and subcooling of the inlet liquid within an acceptable range of costs are both suggested. While the proposed model is less accurate than full-resolution CFD for the detailed evolution of physical fields, it offers much greater computational speed for quick parametric studies of key input conditions.

Study on 3D Simulation Performance of Large‐Scale Proton Exchange Membrane Fuel Cell with Distribution Region

The majority of the current research examines fuel cell performance metrics using single channels or small‐area flow fields, but fails to take into consideration the actual shape of the flow field of modern proton exchange membrane fuel cell (PEMFC). The homogeneous distribution of reaction gas concentration and liquid water distribution is examined using 3D computational fluid dynamics simulation on a commercial large‐scale PEMFC with 113.92 cm2 reaction area and distribution region as the object. The results show that the gas distribution in the fluid flow is effectively optimized under the action of the distribution zone, and the maximum concentration error of anode is 4.87%, which is far less than that of cathode, and the higher the flow rate in the flow channel, the stronger the water removal ability; the effects of different working pressure and flow direction of reactant gas on gas concentration in catalytic layer and water content in proton exchange membrane are also studied. The results show that higher working pressure is beneficial to improve the performance of fuel cell, and countercurrent mode is better; finally, the influence of coolant is analyzed, and the results show that coolant can effectively reduce the internal temperature of the fuel cell, which is beneficial to improve the life of the fuel cell.

A falling film design for electrochemical CO2 reduction

Utilizing CO2 as a resource for CO production in electrochemical reactors requires gas diffusion electrodes (GDE) that maintain a stable and highly reactive gas/liquid/solid interface. When scaling the process towards industrial application, the pressure difference in the electrolyte channel increases, amplifying instabilities at the multi-phase boundary inside the GDE. To tackle this challenge, a falling film design where the electrolyte is solely driven downwards by gravity is presented in this work. The hydrostatic pressure is then counter weighed by the hydrodynamic pressure drop, leading to a constant pressure between gas and liquid side over the height of the electrode. Three 3D-printed electrolyte frame designs were compared in a flow cell regarding the liquid distribution in the channel. An even distribution could be achieved with 2 mm channel thickness at an electrolyte flow rate of 4000 mL min−1. Electrolysis experiments were carried out using a 100 cm2 silver GDE. Compared to a conventional electrolyte frame design, the falling film design yielded stable process conditions with a Faraday Efficiency to CO of up to 90 % at 100 mA cm−2 and a cell voltage of 5.5 V. The presented design presents a pathway for scaling CO2 electrolyzers in height and sustains a stable long-term process.

Estimation of Evaporation of Water from a Liquid Desiccant Solar Collector and Regenerator by Using Conservation of Mass and Energy Principles

Solar thermal energy-powered air conditioning technologies are receiving increased attention. Among the solar energy-driven cooling technologies, open type liquid desiccant air conditioning (AC) system is emerging as a promising technology, which has a solar driven desiccant solution regenerator. In this type of system, the evaporation of water and concentrating the desiccant or regenerator performance determines the cooling performance of the AC system, which necessitates its development and experimental performance testing under actual operating conditions. The setup is made of a black painted corrugated solar collector of area 0.8 m × 1.84 m covered with glass, and a liquid desiccant solution tank and distribution system over the absorber. Solar regeneration experiments on calcium chloride–water solution were carried out on the setup and a total of five sets of meteorological, collector and solution property data were collected through concentrating the desiccant from 32.9 initially to 51.3% in five days. The evaporation of water from the regenerator was analyzed using energy and desiccant mass conservation. For a typical day, the mass of water evaporated was estimated to be 3.10 and 3.16 kg over a day, as estimated by conservation of mass and energy principles from a 34.8 kg of calcium chloride solution with initial desiccant concentration of 43.6% stored in the tank.

Investigation on the heat discharge performance of a bioinspired latent heat exchanger with leaf-like fins

The low energy efficiency of phase-change thermal storage technologies leads to slow progress in promoting sustainable energy. To address this, here constructs a creative leaf-like fin and designs a bioinspired latent heat exchanger (LHE) using phase change materials (PCMs). A two-dimensional model of solidification processes considering natural convection is developed and solved numerically. The phase-change behaviors and dynamic thermal characteristics of different LHEs are investigated. Moreover, material selections and operating conditions of LHEs are studied, focusing on their effects on discharge performance. The results imply that the innovative leaf-like fin strengthens discharge performance. Compared to conventional LHEs, bioinspired LHEs shorten complete solidification time by 41.6% and increase average discharge power by 69.9%. Since the solidification procedure is driven by heat-conduction, the temperature stratification is only apparent in the early stage, while the solid–liquid phase interface and temperature distribution are almost axisymmetric for most solidification processes. For material selections, aluminum is recommended based on the trade-off between cost and thermal enhancement gain, and Stearic acid has apparent advantages in achieving satisfactory heat discharge performance for PCMs selected in this paper. Moreover, the lower temperature of the heat transport fluid facilitates the discharge rate enhancement for practical engineering.

Phase Distribution Measurement of Liquid–Solid Media Using Multimode Ultrasound

Ultrasound tomography (UT) is an emerging technique for phase distribution measurement in industrial multiphase flow monitoring. A multimode UT combining the ultrasound transmission and reflection modes is proposed to measure stratified phase distribution and sound speed of liquid–solid mixtures in the horizontal pipe. First, the acoustic attenuation is used to reconstruct the phase distribution with a modified matrix regularization algorithm, and the time-of-flight (TOF) of ultrasound is used to extract the boundary of multiphase layers with the weight Akaike information criterion algorithm. Second, a wavelet fusion method based on the principal component averaging is proposed to fuse the reconstruction images of UT transmission and reflection. Third, numerical investigations are carried out to validate the feasibility of the proposed method. According to the quantitative indexes, the proposed method can effectively reconstruct the phase distribution of multiphase media. Finally, an experimental test pipeline Section is established, and sand–water and oil–water–sand liquid–solid media are investigated. The minimum relative error (RE) and the maximum correlation coefficient (CC) of experimental fusion results can reach 0.33 and 0.94, respectively, and the average measurement error (ME) of the layer height is 3.80%.

Analysing operando 2D X-ray transmission images for liquid water distribution in polymer electrolyte fuel cells

Analysing operando 2D X-ray transmission images for liquid water distribution in polymer electrolyte fuel cells

Matching the Liquid Atomization Model to Experimental Data Obtained from Selected Nozzles

The spraying procedure is one of the most difficult operations in agricultural production. Achieving the desired effectiveness of the procedure is dependent on obtaining an appropriate level and uniformity of liquid distribution. The aim of this paper was to present a liquid decomposition model generated on the basis of experimental data. The tests were carried out on a test stand, which consisted of a container with nozzles and a grooved table. The experiments were carried out with the use of selected standard, anti-drift, and air-induction single-stream nozzles at constant liquid pressure. The optimization process was carried out in Microsoft Excel Solver. Furthermore, in order to compare the data generated by the model with the data from the virtual boom, we applied an analysis of correlation and linear regression in the Statistica 13.1 software. Based on the results obtained, it can be concluded that the model is a good fit to the experimental data (R2 > 0.95). The model, which was generated on the basis of experimental data, will facilitate control of the operation and degree of wear of nozzles, which will contribute to ensuring uniform spraying.