Pressure Drop Characteristics Research Articles

Frictional pressure drop correlation of steam-water two-phase flow in helically coiled tubes

Helically coiled tubes are utilized as the heat transfer tubes for High-Temperature Gas-cooled Reactor (HTGR) steam generators due to their compactness, thermal expansion accommodation and high heat transfer coefficient. A clear understanding of the pressure drop characteristics is important for the design and operation of steam generators. In this study, experiments were conducted to investigate the frictional pressure drop characteristics in helically coiled tube with a very large curvature ratio of 0.109. The experiments were carried out in a steam quality range of 0.1–0.9, system pressure range of 3.5–7 MPa, mass flux range of 320–1100 kg/m2s. The results indicate that the frictional pressure drop increased with the increase of mass flux, decreased with the increase of system pressure. It first increased with the increase of steam quality, and reached a maximum value at a steam quality of approximately 0.8, then decreased until steam quality reached unity. Based on the present work and existing experimental database, 25 existing correlations are evaluated and none of them could satisfactorily fit all the data. Therefore, a new correlation based on the Martinelli and Nelson correlation was proposed. Compared with existing correlations, it has a broader range of applicability (operating pressure from 0.75 to 8 MPa, mass flux from 200 to 1100 kg/(m2·s), steam quality from 0.03 to 0.99, and curvature ratio from 0 to 0.109.), and higher accuracy (weighted mean MAPE of 8.92 % and arithmetic mean MAPE of 8.81 %). It also has better compatibility with straight tubes.

Study on the Influence of the Cell Structure on the Pressure Drop of Gasoline Particulate Filter

The cell structure of a gasoline particulate filter (GPF) is made up of thousands of individual cells. Although the symmetric square cell structure of the GPF is commonly used internationally, several cell designs have been proposed to reduce the pressure drop in the GPF trapping process. The aim of this paper was to use AVL-Fire software to establish GPF models of different cell structures, mainly including the symmetric square cell structure, asymmetric square cell structure, and symmetric hexagonal cell structure, and analyze the GPF pressure drop characteristics of different cell structures according to the carrier structural parameters and altitude. The results show that compared with the pressure drop of the symmetric square cell structure, the pressure drop of the asymmetric cell structure with inlet/outlet side length ratios ranging from 1.1 to 1.4 is decreased by 4.61%, 9.07%, 12.19%, and 13.22%, respectively, and the pressure drop of the symmetric hexagonal cell structure is decreased by 33.17%. Both asymmetric and symmetric hexagonal cell structure GPFs can decrease the pressure drop during trapping by increasing the cell density. From 200 CPSI to 300 CPSI, the pressure drop of the asymmetric cell structure with inlet/outlet side length ratios ranging from 1.1 to 1.4 is decreased by 20.43%, 20.53%, 20.39%, and 18.56%, respectively, and the pressure drop of the symmetric hexagonal cell structure is decreased by 18.70%. The pressure drop values of GPFs with asymmetric and symmetric hexagonal cell structures show an increasing trend with an increasing filter wall thickness and inlet/outlet plug length. The pressure drop values of GPFs with asymmetric and symmetric hexagonal cell structures show an increasing trend with an increasing altitude, and the larger the inlet/outlet ratio, the more significant the increase in the pressure drop.

Thermo-fluid performance for helical coils inserted in a tube using hybrid CFD-ANN approach

This paper presents a numerical investigation into the thermal performance of helical coils, assessing the impact of spacing, wire diameter ratio, and coil pitch ratio on the pressure drop and heat transfer characteristics. Heat flux was maintained at 1000 W/m2, while Reynolds numbers ranged from 5000 to 30,000. Coil configurations encompassed pitch ratios within 1 ≤ p/d ≤ 3, wire diameter ratios spanning 0.044 ≤ e/d ≤ 0.133, and spacing intervals of 0.5, 1, and 2 mm. The finite volume method was employed to solve the energy, Navier-Stokes, and 3D continuity equations. Results indicate substantial influences of wire diameter, coil pitch ratios, and spacing on Nusselt number friction factors within the coiled tube. Notably, Nusselt number enhancements within the studied intervals ranged from 16 % to 102 %, with an overall performance criteria improvement reaching 43 %. Furthermore, a machine learning approach utilizing artificial neural networks (ANN) was employed, with comparisons drawn between results obtained from the ANN and computational fluid dynamics (CFD). The congruence between experimental, CFD, and ANN findings underscores the reliability of the study outcomes.

A Review of Pressure Drop and Mixing Characteristics in Passive Mixers Involving Miscible Liquids.

The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid-liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the type of complexity in shape, size, and configuration. It is observed that the use of different aspect ratios of the microchannel width, presence of obstructions, flow and operating conditions, and fluid properties majorly affect the mixing characteristics and pressure drop in passive micromixers. A regime map for the micromixer selection based on optimization of mixing index (MI) and pressure drop has been identified based on the literature data for the Reynolds number (Re) range (1 ≤ Re ≤ 100). The map comprehensively summarizes the favorable, moderately favorable, or non-operable regimes of a micromixer. Further, regions for special applications of complex micromixer shapes and micromixers operating at low Re have been identified. Similarly, the operable limits for a micromixer based on pressure drop for Re range 0.1 < Re < 100,000 have been identified. A comparison of measured pressure drop with fundamentally derived analytical expressions show that Category 3 and 4 micromixers mostly have higher pressure drops, except for a few efficient ones. An MI regime map comprising diffusion, chaotic advection, and mixed advection-dominated zones has also been devised. An empirical correlation for pressure drop as a function of Reynolds number has been developed and a corresponding friction factor has been obtained. Predictions on heat and mass transfer based on analogies in micromixers have also been proposed.

Investigation of heat exchanger tube fitted with triangular perforated nail head twisted‐tape inserts

AbstractA numerical investigation of the Nusselt number, heat transfer augmentation efficiency, and friction factor in a laminar flow tube with triangular perforated nail head twisted tape (TPNHTT) is reported using ANSYS 19.2 Fluent. The effects of triangular cut (each side 3 mm) in the middle pitch of the tape along the height, diameter, and top diameter of the nail head (10, 2, and 2.5 mm, respectively) have been explored for (300 ≤ Re ≤ 1800) in a tube of 22 mm diameter. In this paper, implementation has been done with a TPNHTT varying width (14 ≤ b ≤ 20) twist ratio (TR) ranging from (3 ≤ TR ≤ 6), inserts in a tube for laminar flow. Twisted tape (TT) produces a swirl flow associated with fluid resulting in heat transfer enhancement and pressure drop characteristics other than that for the plain tube (PT). The performance of the Nusselt number and friction factor increased up to 123.62% and 495.30%, respectively, on the application of TPNHTT as compared with PT. A maximum thermal performance efficiency of 2.98 has been achieved using the twisted‐tape ratio of the current tube in laminar flow at a Reynolds number of 1700. In addition, correlation equations (11) and (12) have been developed for the friction factor and Nusselt number valid for 300 ≤ Re ≤ 1800, 14 ≤ b ≤ 20, and 3 ≤ TR ≤ 6. The study has proved that applying TT is an upgraded approach for laminar convection heat transfer. This novel work finding will be supportive for researchers to design the latest heat exchangers.

Experimental study of hydraulic lifting platform based on multi-ring disc magnetorheological valve

To enhance the operational capabilities of a hydraulic lifting apparatus, a hydraulic lifting platform was engineered based on a multi-ring disc magnetorheological valve. The pressure drop characteristics of the multi-ring disc magnetorheological valve were determined through theoretical analysis, supplemented by magnetic field simulations to assess its performance. The effects of different currents on the stability and response time of the hydraulic lifting platform are studied, and the control accuracy of the hydraulic lifting platform position is verified. The results show that the saturation current of the magnetorheological valve is 2.5 A. The addition of current to the magnetorheological valve leads to a rapid increase in both actuator speed and acceleration, which then levels off. Similarly, the response time of the actuator decreases with an increasing current until it stabilizes. At a coil current of 1.5 A, the actuator achieves a speed of approximately 86 mm s−1, an acceleration of approximately 105 mm s−2, and a response time of approximately 7.15 s. Furthermore, the lifting position accuracy of the hydraulic lifting platform is ±1 mm.

The effect of high values of relative surface roughness on heat transfer and pressure drop characteristics in the laminar, transitional, quasi-turbulent and turbulent flow regimes

This study investigated the effect of large values of relative surface roughness on the heat transfer and pressure drop characteristics using simultaneously measured heat transfer and pressure drop data. Experiments were conducted using a horizontal circular tube with a base inner diameter of 5 mm and length of 4 m. One smooth and two rough tubes, with relative roughnesses of 0.04 and 0.11, were tested at different constant heat fluxes between Reynolds numbers of 100 and 8 500. Water was used as the test fluid and the Prandtl number varied between 3 and 7. Contrary to the trend in the Moody Chart, a significant increase in laminar friction factors with increasing surface roughness was observed. Both the friction factors and Nusselt numbers as functions of Reynolds number showed a clear upward and leftward shift with increasing surface roughness across the different flow regimes. Furthermore, the boundaries between the flow regimes were the same for the pressure drop and heat transfer results. The width of the transitional flow regime was narrower for rough tubes and had a differing trend. The quasi-turbulent and turbulent flow regimes occurred at lower Reynolds numbers for increasing roughness. When investigating the relationship between heat transfer and pressure drop, it was found that an increase in surface roughness favoured heat transfer in the quasi-turbulent flow regime. This is useful for rough tubes as the quasi-turbulent flow regime onsets early with regards to the Reynolds number in tubes with large roughnesses.

Experimental and numerical pressure drop investigation of a protruding tube microchannel heat exchanger

An experimental and numerical fluid flow study in a micro heat exchanger (microHEX) is conducted in this work to investigate its pressure drop characteristics. The microHEX sample presents a high degree of protrusion of the microchannels inside the inlet and outlet manifolds (Lprot /Dm =0.7), a large manifold-to-branch area aspect ratio (Am/As =37), and a very small flow division in each microchannel (β=1/34). These features configure T-junctions that differ completely from the conventional ones in the literature. Experimental measurements of the microHEX pressure drop were performed for the Reynolds range of 300-2200. The numerical methodology combines a 1D model to evaluate the pressure drop of a single microchannel, adding minor entrance and exit losses due to the change of section and direction. A CFD numerical simulation evaluates the particular pressure loss associated with the dividing T-junction towards the protruded microchannel. The numerical simulation pressure drop results compared well with the experimental measurements, reporting a difference of 3.11% for an initial case. An extension of the work will soon cover all the collected experimental cases.

Transitioning to a Hydrogen Economy: Exploring the Viability of Adapting Natural Gas Pipelines for Hydrogen Transport through a Case Study on Compression vs. Looping

The growing importance of hydrogen as an energy carrier in a future decarbonised energy system has led to a surge in its production plans. However, the development of infrastructure for hydrogen delivery, particularly in the hard-to-abate sectors, remains a significant challenge. While constructing new pipelines entails substantial investment, repurposing existing pipelines offers a cost-effective approach to jump-starting hydrogen networks. Many European countries and, more recently, other regions are exploring the possibility of utilising their current pipeline infrastructure for hydrogen transport. Despite the recent efforts to enhance the understanding of pipeline compatibility and integrity for hydrogen transportation, including issues such as embrittlement, blend ratios, safety concerns, compressor optimisation, and corrosion in distribution networks, there has been limited or no focus on pipeline expansion options to address the low-energy density of hydrogen blends and associated costs. This study, therefore, aims to explore expansion options for existing natural gas high-pressure pipelines through additional compression or looping. It seeks to analyse the corresponding cost implications to achieve an affordable and sustainable hydrogen economy by investigating the utilisation of existing natural gas pipeline infrastructure for hydrogen transportation as a cost-saving measure. It explores two expansion strategies, namely pipeline looping (also known as pipeline reinforcement) and compression, for repurposing a segment of a 342 km × 36 inch existing pipeline, from the Escravos–Lagos gas pipeline system (ELPS) in Nigeria, for hydrogen transport. Employing the Promax® process simulator tool, the study assesses compliance with the API RP 14E and ASME B31.12 standards for hydrogen and hydrogen–methane blends. Both expansion strategies demonstrate acceptable velocity and pressure drop characteristics for hydrogen blends of up to 40%. Additionally, the increase in hydrogen content leads to heightened compression power requirements until approximately 80% hydrogen in the blends for compression and a corresponding extension in looping length until around 80% hydrogen in the blend for looping. Moreover, the compression option is more economically viable for all investigated proportions of hydrogen blends for the PS1–PS5 segment of the Escravos–Lagos gas pipeline case study. The percentage price differentials between the two expansion strategies reach as high as 495% for a 20% hydrogen proportion in the blend. This study offers valuable insights into the technical and economic implications of repurposing existing natural gas infrastructure for hydrogen transportation.

Heat transfer enhancement for flow boiling of zeotropic mixtures with regulating liquid mass transfer resistance

The mass transfer resistance is a significant element leading to heat transfer degradation of zeotropic mixtures in the flow boiling. In this paper, the heat transfer enhancement of zeotropic mixtures in the flow boiling was investigated through regulating the mass transfer resistance by constructing reasonable surface structure. The heat and mass transfer, pressure drop characteristics of stratified bubble flow for R134a/R245fa zeotropic mixtures in a rectangular channel with multi-cone staggered spoiler porous structure were studied experimentally. The bottom of channel was sintered with multi-cone staggered porous layer with thickness/height/diameter of 1/3/2 mm, respectively. The experiments were carried out under an inlet evaporation temperature of 20 ℃, and the ranges for heat and mass fluxes were 10–150 kW/m2 and 100–150 kg/(m2·s), individually. Compared to the rectangular channel with smooth porous structure, liquid mass transfer resistance of zeotropic mixtures in the rectangular channel with multi-cone staggered porous structure was decreased obviously. The decrease degree for Mixture 2 was largest, while the maximum average decrease was 89.61 % at G = 100 kg/(m2·s). The heat transfer coefficients were obviously improved and heat transfer enhancement increased gradually especially under conditions of high heat flux. The enhancement degree for Mixture 2 was the largest, while the maximum average increase was 26.05 % at G = 100 kg/(m2·s). The pressure drop increased significantly, and the increasing degree for Mixture 2 was smallest, while the minimum average increase was 38.18 % at G = 150 kg/(m2·s). Multi-cone staggered structure was helpful to reduce liquid mass transfer resistance and improve heat transfer performance for zeotropic mixture. The zeotropic mixture with higher liquid mass transfer resistance would have better heat transfer intensify and smaller increase of pressure drop with the help of multi-cone staggered structure.

An Experimental Study of the Transfer of Heat in Nanofluid of a Tiny-Channel using Several Innovative Arrangement Designs

This work presents an experimental investigation of the heat transfer (HT) and pressure drop characteristics associated with three different configuration models of minichannel heat sinks. This study utilizes a coolant consisting of TiO2 nanoparticles dispersed in water at a weight concentration of 10%. The performance of this nanofluid coolant is then evaluated and compared to that of distilled water under several heating powers ranging from 100 to 300 W. The findings suggest that the thermal performance of TiO2 nanofluid is significantly influenced by heating power (HP), and its HT efficiency can be enhanced more efficiently at lower levels of HP. However, it has been observed that when the HP decreases, the pressure drop increases. This effect is more pronounced in TiO2 nanofluid than in pure water, which can be attributed to the difference in viscosity with temperature. The Nusselt number remains constant regardless of the increase or reduction in HP. Consequently, when pure water is utilized, the experimental Nusselt number aligns with the Peng and Peterson empirical correlation for all HPs, with an accuracy of 15%. The TiO2 nanofluid was used to test the lowest wall temperature, 40 °C. This measurement was obtained at a Reynolds number of 1100, equivalent to a heat power (HP) of 100 W. Furthermore, it is noted that when the fluid passes through the mini channel, there is an increase in the axial temperature from the input to the outlet of the heat sink (HS). The maximum enhancement observed for a power input of 100 W is 19.59% when utilizing configuration A. This is attributed to the combination of a weak buoyancy force and an increase in the surface area of HT. The HP highly influences the system's thermal performance, and its effective HT characteristics are more pronounced at lower HP levels.

Development of a friction factor correlation applicable to both wet and dry foam flow in circular vertical pipes

BackgroundFoam flow, distinguished by its low density and extensive specific surface area, is employed for the cleaning of plant systems. However, its dual nature as a gas-liquid mixture and a non-Newtonian fluid complicates the prediction of the frictional pressure drop. MethodsThis study constructed a laboratory-scale experimental setup to illustrate the upward flow behavior of aqueous foam in a vertical circular pipe, capturing the foam flow using a high-speed camera. Utilizing the collected data and images, a model was developed for the friction factor to predict the frictional pressure drop of the foam flow, under the assumption that the foam flow is a non-Newtonian, quasi-homogeneous, steady, and fully developed laminar flow. Significant findingsWet foam, characterized by small, uniformly distributed spherical bubbles, is observed at lower foam quality levels. In contrast, dry foam, marked by a larger mean bubble diameter, non-uniform bubble distributions, and slugs, is observed at higher foam quality levels. A notable inflection point in the frictional pressure drop is observed during the transition from wet to dry foam within a vertical pipe. The foam regime and frictional pressure drop characteristics of the foam flow show limited sensitivity to surfactant concentration within the experimental range. A correlation for friction factors, applicable to both wet and dry foam flows in vertical circular pipes, was developed based on the Reynolds number, exhibiting a prediction error of 23.6 %.

An experimental study of the effects of porosity and ratio of fin to channel width on water flow boiling in copper foam fin microchannels

Flow boiling in copper foam fin microchannels (FFMC) has demonstrated better heat transfer performance and flow stability. In this work, systematic experiments are conducted to investigate the effects of structural parameters on flow boiling in five FFMCs with porosities ranging from 0.78 to 0.82 and ratios of fin width to channel width ranging from 0.5 to 2. Five mass fluxes ranging from 68 kg/(m2s) to 408 kg/(m2s) and effective heat fluxes ranging from 2 W/cm2 to 297 W/cm2 are tested. The heat transfer, pressure drop, and flow instability characteristics are analyzed. Generally, the heat transfer in FFMCs follows the “three-zone” model. The heat transfer coefficient first increases with increasing heat flux and then decreases. A “synchronous backflow” phenomenon is observed in FFMCs, which is the direct cause of heat transfer deterioration. Due to the interaction of heat transfer area and the transverse flow resistance through the fins, the heat transfer coefficient increases with decreasing porosity in the low-quality region, while the opposite trend is observed in the high-quality region. The utilization efficiency of the fin area decreases as the fin width increases. An optimal ratio of fin width to channel width exists corresponding to the best heat transfer performance, which equals one in this work. A correlation is developed based on 583 data points considering heat transfer mechanisms in channels and fins. The new correlation predicts the experimental values with a mean absolute percentage error of 9 %, and over 99 % of the data are predicted within a 30 % deviation. A performance evaluation criterion is defined to comprehensively compare the FFMCs, and the FFMC with the porosity of 0.78 demonstrates the best flow boiling performance due to higher heat transfer coefficients and lower pumping powers when the ratio of fin to channel width is equal to one.

Experimental study on flow rate and pressure drop characteristics in T-junction pipes under rolling conditions

Numerous T-junction circular channels are used in the pipeline system of marine dynamic platforms. Unlike terrestrial conditions, the fluid inside the channels experiences additional inertial forces due to rolling motion, leading to complex and variable fluid mixing characteristics within T-junction pipes. The flow and pressure drop characteristics were investigated inside the T-junction pipe under rolling motion conditions, including the average value, the fluctuation value, and the instantaneous value. The working fluid is considered as the de-ionized water. The inlet Reynolds number of the main pipe ranges from 2110 to 25 320, and the flow rate ratio is from 1 to 20. The rolling time and angle are 5–15 s and 0°–15°, respectively. The range of rolling Reynolds number is 0–3520. The results indicate that the influence of the rolling motion on the flow and pressure drop characteristics inside the T-junction pipe depends on the inertial force of the fluid itself. When the inertial force of the fluid itself is large, the influence of the rolling motion on the flow parameters will be weakened. The rolling motion has a greater impact on the branch than on the main pipe. Predictive relationships for flow rates and pressure loss coefficients are established under the stationary and rolling conditions, respectively, with a fitting error of less than 10%. In addition, the boundary that ignores the influence of rolling motion on flow fluctuations and the criteria for identifying fluid backflow are also proposed.

High capacity laminate adsorbers: Enhancing separation performance beyond packed beds

In response to the growing demand for more efficient adsorption processes, structured adsorbents have emerged as a promising solution as they offer improved mass transfer and pressure drop characteristics. However, they are often hampered by a lower volumetric capacity due the presence of support structures or a large bed void fraction. This research focuses on the manufacturing and evaluation of self-standing zeolitic laminates of various thickness and spacing, comparing their performance to a traditional packed bed. A shaping method to obtain laminates with a 84 wt% zeolite 13X content is described. Furthermore, a method for precise assembly and spacing of the laminates is detailed. Three such laminar adsorbers with different geometries were evaluated in breakthrough experiments and compared to a packed bed to assess their efficiency in the bulk separation of carbon dioxide. Superior performance of the laminar adsorbers was found, with one configuration employing 1.2 mm laminates and 0.4 mm spacing showing a significant 19 % increase in volumetric capacity compared to a packed bed of pellets. This enhanced capacity is achieved while maintaining efficient heat and mass transfer, resulting in sharp breakthrough profiles. Furthermore, using thinner (0.5 mm) laminates, the length of unused bed was further reduced. Additionally, pressure drop calculations were performed and experimentally validated. The pressure drop over the laminar adsorbers was shown to be significantly lower than over a packed bed. These findings underscore the potential of laminar adsorbers to intensify adsorptive separation processes, reduce energy consumption, and address the demand for more effective adsorption technologies.

Electrospun 3D Curly Electret Nanofiber Air Filters for Particulate Pollutants

Amidst rapid industrialization and urbanization, air pollution has emerged as a global environmental challenge. Traditional air filtration materials face challenges in effectively filtering PM0.3 and often result in discomfort due to high air resistance when used for personal protection, as well as excessive energy consumption in industrial air purification applications. This study initially utilized extremely high environmental humidity to induce fiber formation, resulting in the preparation of a fluffy fiber membrane with a three-dimensional curly morphology, which increased the porosity to 96.93%, significantly reducing air resistance during filtration. Subsequently, rutile TiO2 with a high dielectric constant was introduced, exploiting the low pressure drop characteristic of the fluffy 3D curly fiber membrane combined with the electret effect of TiO2 nanoparticles to notably improve the issue of excessive pressure drops while maintaining filtration efficiency. The microstructure, morphology, and element distribution of the fibers were analyzed using FESEM and EDS. FTIR and XRD were employed to examine the functional groups and crystal structure within the fibers. The electret effect and filtration performance of the fiber membrane were investigated using an electrostatic tester and a particulate filtration efficiency tester. The results demonstrated that inducing fiber formation under high-humidity conditions could produce fibers with a 3D curly structure. The fiber membrane was highly fluffy, significantly reducing the pressure drop. Introducing an appropriate amount of titanium dioxide markedly improved the electrostatic effect of the fiber membrane, enhancing the filtration performance of the 3D curly PVDF/TiO2 composite fiber membrane. With a 0.5% addition of TiO2 nanoparticles, the filtration efficiency of the fiber membrane reached approximately 99.197%, with a pressure drop of about 49.83 Pa. This study offers a new approach to developing efficient, low-resistance air filtration materials, showcasing the potential of material innovation in addressing air quality challenges within the sustainable development framework.

Oil-Water Two-Phase Flow with Three Different Crude Oils: Flow Structure, Droplet Size and Viscosity

The study focuses on the flow patterns and pressure drop characteristics of three crude oils and water in a horizontal pipe. The experimental results showed that the transformation boundary of the flow pattern and phase inversion water fraction were related to the flow parameters. Comparing the three oils, it was found that the viscosity and composition of the oil also significantly influence the flow performance, which can be explained by the adsorption properties of the asphaltenes at the oil-water interface. In particular, the droplet size in water-in-oil dispersion flow was observed and measured. It showed that the water droplet size decreased with the increase of oil viscosity, the decrease of water content, the drop of temperature, and the growth of mixing velocity, probably due to higher shear stress and lower frequency of collision and coalescence between droplets. The apparent viscosity of water-in-oil emulsions was calculated by the rheological model, and the qualitative relation between flow parameters and interfacial area concentration on apparent viscosity was obtained. Taking the influence of interfacial area concentration into consideration, a simple and accurate viscosity model was established based on dimensional analysis, which is of great significance for process design in gathering and transportation systems.

Experimental investigation of the two-phase flow distribution and pressure drop characteristic within the cathode bending type channel of fuel cell

The accurate prediction of the two-phase flow distribution within the channel is of great significance for enhancing fuel cell water management and improving output efficiency. The current study constructs a novel transparent fuel cell visualization test system and experimentally investigates the characteristics of two-phase flow pattern distribution, pressure drop, and output voltage within the bending type channel. Furthermore, a focused analysis of slug flow which may induce fuel cell flooding is conducted. The results show that the two-phase flow pattern maps of both the bent and straight channels are highly consistent. The force balance analysis is performed to explain the internal mechanism that the bending structure has less influence on the two-phase flow pattern. Additionally, the bending structure has a significant impact on the channel pressure drop magnitude and time-domain characteristics. The two-phase pressure drop can be used as an empirical tool to judge the flow pattern and occurrence position. The fuel cell output voltage jump phenomenon occurs under slug flow pattern, and there is a strong positive correlation between the voltage jump amplitude and current density, with a Pearson correlation coefficient of 0.924. The research results provide theoretical guidance for two-phase flow prediction within the channel and flood prevention of the fuel cell.

CFD Analysis of Pressure Drop Reduction in PEMFC Flow Channels with Distinct Cross-Section Shapes

Proton exchange membrane fuel cells (PEMFCs) have great potential to produce renewable, sustainable and clean energy and reduce air pollutants to mitigate climate change. PEMFCs consist of distinct parts including anode and cathode bipolar plates having flow channels, gas diffusion layers, catalyst layers, and membrane. The flow channel geometry influences the flow and pressure drop characteristics of the channel and cell performance. In this work, a three-dimensional (3D) CFD model is built employing SOLIDWORKS and ANSYS Workbench. The innovative configurations are generated by changing the half of 0.2 x 0.2 mm square channel to 0.3 x 0.1 mm, 0.3 x 0.15 mm, 0.3 x 0.2 mm and 0.3 x 0.25 mm rectangular section at the top. The results showed that increasing rectangular section height significantly reduced pressure drop at the anode and cathode with a slight decrease in the current density at 0.4 and 0.6 V. The new configuration with 0.2 x 0.1 mm half square section at the bottom and 0.3 x 0.25 mm rectangular section at the top decreases the current density, anode and cathode pressure drop of 11%, 69% and 58%, respectively in comparison to 0.2 x 0.2 flow channel at 0.4 V. Taking into account pressure loss along the flow channels, this configuration is a good option to improve the cell performance.

Experimental study on the combustion and pressure drop characteristics of a pintle injector for LOX/kerosene rocket engine

Pintle injectors have attracted much attention in recent years for their excellent throttling and combustion performance. However, the combustion characteristics of cryogenic propellant on pintle injectors with varying operating conditions remain unclear. A LOX/kerosene throttleable rocket engine with a fuel-centered liquid-liquid pintle injector was designed and its pressure drop and combustion characteristics were tested. The pintle engine achieved stable combustion with the total flow rate and oxygen-fuel mixture ratio varying from 59 to 559 g/s and from 0.73 to 1.02. A calculation model for the gas ratio in the LOX channel of the pintle injector was established. The deviation of measurements from the calculated values did not exceed ±10%. The vaporization of LOX from the pintle injector in the hot test was calculated and the positive correlation between gas ratio and combustion efficiency was analyzed. For the phenomenon of low-frequency oscillation of pressure in the hot tests, the source and development process of the oscillation were studied by FFT. The primary frequency and amplitude of low-frequency oscillation had been discovered to exhibit a positive correlation with the gas ratio. Low pressure drop of injection was the main cause of low-frequency oscillation. The strong vaporization of LOX under low operating conditions made the combustion efficiency remain in a high range even if low-frequency oscillation was observed. This work can provide a reference for the design of pintle injectors for cryogenic liquid rocket engines that can be deeply throttled.