Flow Pressure Drop Research Articles

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = −25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Gas–liquid two-phase flow patterns and pressure drop of decaying swirling flow inside a horizontal pipe

Gas–liquid two phase swirling flow has been widely used in industry. Its flow pattern is fundamental to investigate the two-phase flow. In this paper, two-phase air–water flow patterns and pressure drop of decaying swirling flow generated by vane-type swirler inside a horizontal pipe have been systematically investigated by visualization experiment. The range of superficial gas phase Reynolds number is 17–23902, while superficial liquid phase Reynolds number is 12–37871, and gauge pressure is 0.003–0.17 MPa. The five typical flow patterns in a horizontal swirling flow were characterized based on flow visualizations and fluctuation characteristics of pressure drop signals. Then swirling flow regime map nearby the swirler outlet was proposed. As flow patterns altered along the streamwise direction due to swirl decay, flow pattern maps at different positions were proposed, which indicated the swirling flow patterns gradually transformed to non-swirling flow patterns. Finally, a new model to predict frictional pressure drop of air–water swirling flow inside a horizontal pipe containing vane-type swirler was proposed. This correlation performed well on predicting the frictional pressure drop.

Two-layer hydrodynamic network model for redox flow battery stack with flow field design

A two-layer hydrodynamic network model is proposed to analyze the electrolyte distribution within a redox flow battery (RFB). The proposed model consists of a channel, a porous electrode, and an interconnection part through which the electrolyte flows through the channel and porous electrode. The flow rate and pressure drop of each network component are calculated using the Hardy-Cross method. The predicted pressure drop is consistent with experimental and three-dimensional computational fluid dynamics (CFD) results. The velocity and pressure distributions are also in good agreement with CFD results. Furthermore, the proposed model analyzes the flow distribution of cells in RFB stacks with different flow field designs. The results show that the flow rate difference between the first and last cells of the RFB stack with an interdigitated flow field is 20 times higher than that of a flow-through-type.

Experimental investigation and modeling of the pressure drop of ice slurry flow in horizontal pipe

This study was conducted on ice slurry made by 11% of monopropylene glycol with various ice mass fractions through a horizontal pipe. The pressure drops, densities, temperatures, and ice slurry mass flow rates were measured and analyzed. First of all, the values of the pressure drop were validated with experimental results available in the literature. Then a numerical study of the flow of the ice slurry by pseudomonophasic flow model, which assumes the absence of the slip velocity between the phases and treats the ice slurry as a homogeneous and laminar fluid with thermophysical properties of the mixture. The rheological properties confirmed the non-Newtonian character of the ice slurry. The results show that there is a good agreement between the pressure drops of the present work and the literature. It was also found that the numerical analysis is very close to the experimental values in the case of a shear thinning flow.

Experimental investigation of multimodal noise generation by ducted low Mach number flows through orifice plates

Noise generation by low Mach number air flows through circular orifices in rectangular ducts is investigated. In particular, the influence of the number and position of the orifices maintaining a constant flow area is addressed. A review of the available theories suggests a certain importance of such parameters in the excitation of higher-order acoustic duct modes. A qualitative coefficient is proposed for a first characterization of the ability to enhance or lessen a given higher-order acoustic mode by the plate geometry. An experimental campaign is performed to measure the total emitted acoustic power by different plate geometries as well as its modal composition. It is found that the orifices' numbers and positions greatly influence the acoustic emissions while the flow pressure drop caused by the obstacles is similar. The proposed qualitative coefficient shows good agreement with the experimental results. A particle image velocimetry measurement campaign is performed to visualize the near-field average flow behavior upstream and downstream of the orifice plates. An increase in the turbulent velocity fluctuations in the vicinity of the orifices is observed on both sides, further validating previous studies on the subject.

Improvement of air distribution consistency in large-scale proton exchange membrane fuel cell stack manifold

The development of PEMFC (proton exchange membrane fuel cell, PEMFC) a higher power stack in buses and commercial transport vehicles is a growing trend at present. However, the higher power stack requires increasingly consistent flow distribution. In this manuscript, a new air manifold type design of X-shape has been proposed. The differences between the X-shape manifold and the U-shape manifold have been investigated using the CFD (Computational Fluid Dynamics, CFD) model. The model is simultaneously and quantitatively validated with two different variables, precisely, mass flow rate and pressure drop, to ensure its accuracy. The CV (coefficient of variance, CV) value of the X-shape manifold is much lower in comparison to that of the U-shape manifold. A mathematical model was established to explain the key factor responsible for a more uniform distribution of X-shaped manifolds in comparison to-shaped manifolds. The key factor is precisely the smaller magnitude of the pressure drop at the inlet and outlet of the X-shaped manifold in comparison to that of the U-shaped manifold. Based on this, the size reduction of the air entering the bipolar plates is the strategy to improve air distribution consistency. This viewpoint has also been proven by the derivation of a mathematical model and an optimal reduction in size has been observed. The CV of U-shape, X-shape, and X2-shape-50%In-100%Out (entrance geometry narrowed to 50%) are 5.82%,1.32%, and 0.45%, respectively.

Influence of air inlet and cleaning chamber on the performance of mining cartridge filter

This study is aimed at shedding light on the influence laws of air inlet position, air inlet area and cleaning chamber. To achieve this aim, first, the influences of air inlet position on pressure drop, air flow rate and mass of coal dust collected on the filter cartridges were investigated with the aid of a homemade experimental system. In addition, the effects of air inlet area on dynamic pressure and air flow rate of the air inlet were evaluated. Furthermore, the velocity within 30 cm in front of the air inlet was tested for determining the effective suction range. Finally, the impacts of cleaning chamber height on pressure drop and air flow rate of the cartridge filter were demonstrated. The research is expected to provide guidance for the setting of the air inlet and the cleaning chamber of the cartridge filter.

Numerical evaluation of static and dynamic stability characteristics of a supercritical CO[formula omitted]-driven natural circulation loop

The stability characteristics of closed supercritical natural circulation loop has hardly been explored owing to the mathematical complexity and absence of explicit boundary condition. Present numerical study investigates the nature of both static and dynamic instability in a rectangular loop with carbon dioxide as the working medium. Sharp deterioration in the steady-state circulation rate can be observed, consistent to existing multidimensional analyses. Loop exhibits Ledinegg instability for an intermediate range of heater power, characterized by multiple steady-state solutions. Appearance of static instability has been substantiated following the pressure drop versus mass flow rate profiles, leading to the development of the stability maps. Dynamic instability has also been identified by introducing perturbation during transient simulations, and the range of both static and dynamic instabilities conforms well with each other. A novel approach of approximating the location of the stability threshold using time-series data has also been proposed.

Characteristics of Gas–Solid Flow in an Intermittent Countercurrent Moving Bed

The calculation equations of pressure drop and solid flow rate are given in an intermittent countercurrent moving bed with multiple optimized structures. The flow fields are investigated by experimental methods under different conditions, e.g., ratio of position of the gas distributor to the bed width (rp = 0.5~1.5), gas superficial velocity (ug = 0~0.1591 m/s), solid outlet diameter (Do = 5~25 mm) and cone angle (α = 0~60°). It is found that when rp ≥ 1.0, the flow field in the bed is little affected by rp. Flow patterns are divided into three modes: continuous discharging, intermittent discharging (synchronous, asynchronous) and particle bridging. During continuous discharging, the calculation formula of the solid flow rate, which is closely related to Do and gas–solid slip velocity vslip, is established by referring to the modified De Jong and Beverloo formulas, and its error ≤ ±12.5%. The pressure drop of the total bed consists of the pressure drops of the granular bed and the solid outlets, which are affected by Do, vslip and α; it is built by referring to the Ergun formula, and its error ≤ ±17.0%. As the solid flow rate and pressure drop influence each other through vslip, an iterative algorithm is proposed to enhance the computation accuracy.

A New Two-Phase Multiplier for Flow Pressure Drop in Multiport Minichannel Condensers and Evaporators

Due to flow maldistribution, the condensation and evaporation flow patterns in multiport minichannels are considerably different from single minichannels or macrochannels. This article compiled the friction pressure drop data from experimental phase-change investigations in multiport minichannel condensers and evaporators over the past two decades. The data was reduced to friction pressure gradients, and a new two-phase multiplier was proposed for estimating the phase-change pressure drop in multiport condensers and evaporators. Thirteen hundred and forty-four condensation pressure drop and six hundred and twenty-three evaporation pressure drop data from twenty-nine studies were correlated to yield four predictive two-phase multiplier equations in the laminar and turbulent flow regimes. The predictive correlations fit 67% of the laminar condensation and 80% of the turbulent pressure drop data within ±50%. Further, 57% of the laminar evaporation and 100% of the turbulent evaporation pressure drop data were fit within ±50%. The correlations were compared with widely published correlations and were a significant improvement. Meta-analysis revealed that multiport minichannels are most effective for reducing turbulent flow condensation pressure drop and laminar flow evaporation pressure drop. The compiled data and presented correlations and analysis should be helpful to the process, electronics packaging, aviation, and aerospace industries designing compact, lightweight, and high-efficiency condensers, and evaporators.

Flooding Characteristics and Countermeasures in a PEM Fuel Cell System

PEM fuel cell systems in automotive application face challenging power requirements, as they must provide full load as well as part load efficiently. Especially in systems without an external humidifier, relatively low cathode stoichiometries and increased operating pressures are the key to prevent membrane dry-out by increasing the local relative humidity. During low load operation at increased temperature and pressure, low gas velocities within the flow field occur. Too low gas velocities are known to result in a transition of the two-phase flow from film flow to slug flow regime [1]. This transition within the flow field channel structure can result in a local or global blockage of the reactant paths by liquid water droplets.While the flow regime transition within simple channel geometries is well known in literature, there is a lack of experimental data for full stack situations in fuel cell systems. Some work regarding the stationary minimal flow limitation exists [2], but countermeasures enabled by dynamic operation of the whole system are seldom in focus of systematic studies. However, well guided dynamic operation enables robust low load capability. The negative impact of flooding on stack power and lifetime can be minimized and a possible dry-out can be prevented, while maintaining a relatively low required compressor energy consumption.In the work to be presented, targeted experiments conducted with an automotive fuel cell system confirm the existence of a minimum cathode gas velocity for a stable operation and its relevance in application-like operation. It is shown that during low load operation of a non-humidified system, the targets of sufficient membrane humidification and liquid water drainage are incompatible. Because of a response time of multiple seconds until flooding or dry-out occurs, an intermittent operation with periodic switching between two operating points becomes feasible. During the first phase, the membrane is humidified due to a relatively low cathode stoichiometry and an increased cathode inlet pressure. As the liquid water accumulation becomes critical, the pressure is decreased and the stoichiometry is increased for the second phase, where droplets are blown out by utilizing a high gas velocity, as shown in figure 1.The exemplary results suggest that dynamic water management analysis can widen the operating range of a fuel cell system towards lower loads due to dynamic control. It is expected that a deeper understanding of the underlying processes will allow the development of optimized control strategies in the future.[1] M. Grimm, E.J. See, S.G. Kandlikar. Modeling gas flow in PEMFC channels: Part I – Flow pattern transitions and pressure drop in a simulated ex situ channel with uniform water injection through the GDL. Int. Journal of Hydrogen Energy 37, 12489-12503 (2012).[2] D. Jenssen, O. Berger, U. Krewer. Anode flooding characteristics as design boundary for a hydrogen supply system for automotive polymer electrolyte membrane fuel cells. Journal of Power Sources 298, 249-258 (2015).Figure 1: Normalized current, high frequency resistance, cell voltages, cathode stoichiometry, cathode inlet pressure and cathode inlet velocity, measured on a system test rig during intermittent low load operation. The operating point is periodically switched between membrane humidification (green) and liquid water drainage (orange). Figure 1

Numerical analysis of hydrodynamic and thermal characteristics of three inside channel configurations of a plate and shell heat exchanger (PSHE)

The Plate and Shell Heat Exchanger (PSHE) is a variation of the Plate Heat Exchanger (PHE) with a more compact and robust geometry. This paper presents the analysis of the flow in the inner channel formed by a pair of plates of a PSHE employing computational fluid dynamics to determine the hydrodynamic and thermal characteristics for three Chevron angle configurations, 15° × 15° (High/High-HH), 45° × 45° (Low/Low-LL) and 15° × 45° (High/Low-HL). The ANSYS CFX software was employed with the application of the Standard k-ε and the SST (Shear-Stress-Transport) turbulence models for comparison. Experimental pressure drop data and flow streamlines were used to validate the numerical model and to analyze simplifications in the geometric model. Pressure drop, friction factor, and Nusselt number were evaluated for the three geometries studied. A local analysis of the parameters that describe the channels was also performed in this study.

Heat transfer and pressure drop correlations for a gas flow in unidirectional porous copper tubes

In this study, to develop a heat exchanger having small-scale and high performance, the heat transfer performance and the pressure drop in a gas flow are evaluated for six types of unidirectional porous copper tubes fabricated by explosive compaction. Furthermore, correlation equations for the effective heat transfer coefficient and the friction factor are constructed. The maximum enhancement ratio of the effective heat transfer coefficient in the porous copper tubes is four times as high as a swirl tube, which is a typical heat transfer promoter. The performance of these porous tubes becomes high with increasing the Reynolds number based on the superficial velocity. The correlation equation for effective heat transfer coefficient can predict with the error within ±10% regarding 70% of obtained experimental data, that for the friction factor is high accuracy regarding when the number of pores is relatively small and the pore diameter is relatively large.

Machine-learning-aided design optimization of internal flow channel cross-sections

• Artificial neural network-based models are developed for prediction of nusselt number and friction factor. • The predictions apply for fully developed laminar flow in constant cross-section ducts of different cross section shapes. • The machine learning (ML) model predictions are validated and compared against numerical simulations. • Use of ML models in shape optimization of channel cross section for different objective functions is demonstrated. • Guidelines for usage of the developed ML models are discussed. The design optimization of various thermal management components such as cold plates, heat sinks, and heat exchangers relies on accurate prediction of flow heat transfer and pressure drop. During the iterative design process, the heat transfer and pressure drop is typically either computed numerically or obtained using geometry-specific correlations for Nusselt number and friction factor. Numerical approaches are accurate for evaluation of a single design but become computationally expensive if many design iterations are required (such as during formal optimization processes). Correlation-based approaches restrict the design space to a specific set of geometries for which correlations are available. Surrogate models for the Nusselt number and friction factor, which are more universally applicable to all geometries than traditional correlations, would enable flexible and computationally inexpensive design optimization. The current work develops machine-learning-based surrogate models for predicting the Nusselt number and friction factor under fully developed internal flow in channels of arbitrary cross section and demonstrates use of these models for optimization of the cross-sectional channel shape. The predictive performance and generality of the machine learning surrogate models is first verified on various shapes outside the training dataset, and then the models are used in the design optimization of flow cross sections based on performance metrics that weigh both heat transfer and pressure drop. The optimization process leads to novel shapes outside the training data, and so numerical simulations are carried out on these optimized shapes to compare with the surrogate model predictions and show their performance is at least as good as that of shapes with known correlations available. A three-lobed shape was found to reduce friction factor, whereas a pentagon with rounded corners and an ice cream cone-shaped duct, both found using different performance metrics. Although the ML model predictions lose accuracy outside the training set for these novel shapes, the predictions follow the correct trends with parametric variations of the shape and therefore successfully direct the search toward optimized shapes.

Prediction of flow regime boundary and pressure drop for hexagonal wire-wrapped rod bundles using artificial neural networks

This study used an artificial neural network (ANN) regression model in wire-wrapped fuel assemblies to estimate the transition-to-turbulence flow regime boundary (RebT) and friction factor. The ANN models were trained and validated using existing experimental datasets. The bundle dataset comprised several design parameters, such as the number of rods, rod diameter, wire diameter, lattice pitch, edge pitch, and wire helical pitch. The log–log scale Reynolds number and linearity characteristics of the friction coefficient were used to over-sample the friction factor in the laminar and turbulent regimes for resolving the data imbalance. Three-quarters of the entire dataset was used for training, while the remainder was used for validation. The Levenberg–Marquardt approach with the Gauss–Newton approximation for the Hessian of the training cost function was used for training the model. The number of hidden layers for RebT was selected based on the minimum validation error. The pin number effect was additionally considered for the friction factor while selecting the number of hidden layers. The ANN model predicted using the oversampled data set had a 50% reduction in the root mean square error (RMSE) than the model predicted using the original data set. Compared to previous correlations, the prediction of ANN models for the friction factor demonstrated significantly low errors (0.10% mean error and 7.36% RMSE of 142 bundle data).

Unsteady characteristics of flow pattern and pressure drop of flow boiling in single straight microchannel under sudden heat flux increase

Unsteady characteristics of flow pattern and pressure drop of flow boiling in single straight microchannel under sudden heat flux increase

Modeling of pressure drop in waxy oil flows

Modeling of pressure drop in waxy oil flows

Investigation of Gas Turbine Internal Cooling Using Supercritical CO2—Effect of Surface Roughness and Channel Aspect Ratio

Abstract In this paper, an experimental and numerical investigation of internal cooling channels with rib turbulators is presented with sCO2 as the working fluid at process conditions (pressure-20.7 MPa and temperature up to 150 °C). The effect of channel aspect ratio up to 2:1 on thermal-hydraulic performance is explored in additively manufactured rectangular channels and square channels, both with and without 60 deg ribs on the top and bottom sides. The Wilson-plot method is employed to experimentally measure channel-averaged Nusselt number over a Reynolds number range up to 370,000. The friction factor is calculated from pressure drop and mass flow rate and additionally, the overall thermal performance factor (TPF) is reported. A companion computational fluid dynamics (CFD) simulation is performed for the rib turbulated cooling configurations reported in the experiments using the Reynolds average Navier–Stokes-based turbulence model. The objective of the numerical study is to gain insight into the local heat transfer augmentation in the ribbed channels as a result of varying the aspect ratio, channel configuration (square versus rectangular), operating conditions (Reynolds number) and the surface roughness, an inherent outcome of the additive manufacturing process. Surface roughness is simulated using sand grain roughness height (KS) calculated from the experimental data, and a comparison is presented with the corresponding channel configuration with varying surface roughness heights starting from smooth surfaces (KS = 0). Experimental results indicate that the heat transfer augmentation is negligible in the rectangular channels with ribs on the long side compared to the square channel. However, it is enhanced by 60% in comparison to placing ribs on the shorter side. The TPF remains constant at around 1 for the entire range of Reynolds numbers consistent with prior work at the National Energy Technology Laboratory (NETL). The simulation results highlight that increased surface roughness can have a favorable considerable influence on Nusselt number and overall thermal performance enhancement.

Pipe flow experiments of unstable oil-water dispersions with three different oil viscosities: Flow pattern, pressure drop and droplet size measurements

The transport of oil-water dispersions in petroleum production pipelines is difficult to predict and requires special attention since it affects the performance of the entire system. For future field developments it is required to generate accurate predictive models to guarantee an optimal field design. The purpose of this work is to present novel experimental data suitable for improving mechanistic flow models in future works. Oil-water pipe flow experiments were conducted in a stainless-steel flow loop with a L/D ratio of 3766, larger than any comparable setups reported in the literature and sufficient to obtain fully developed flow. A novel level of detail measurements included pressure gradients, density profiles and droplet size distributions.Three oils with different viscosities (oil A: 1.3 cP; oil B: 7 cP; oil C: 22 cP) and brine (3.5 wt% NaCl) as the water phase constituted the three fluid systems used. For each fluid system, several flow rates, and a wide range of water fractions were studied. The fluids were not stabilized by any type of chemical additives.The oil viscosity influences the dispersion behavior, especially for oil continuous flow. For higher oil viscosities the dispersion tends to be more homogeneous, and the pressure drop increases due to increasing wall friction. The droplet size decreases as the oil viscosity increases, presumably due to higher shear stress. Water continuous flows, on the other hand, are less affected by the oil viscosity. A strong drag reduction was found for dispersed flow of all three oils and both oil and water continuous flow. A simple model for the dispersion viscosity and drag reduction was developed based on additional bench scale characterization experiments. With this model the pressure drop could be predicted with good agreement.The data reported in this paper will facilitate the development and validation of mechanistic models for predicting oil-water flows. Previous modelling efforts have been hampered by a lack of detailed measurements, in particular droplet size measurements, hence we believe that this data will allow for significant advancements on the modelling side.

Void Fraction Measurement and Prediction of Two-Phase Boiling Flows in a Tubular Test Section

Abstract Void fraction is one of the most important parameters that affect two-phase flow heat transfer and pressure drop. In this paper, a commercial gamma densitometer and a high-speed X-ray radiography system developed at the University of Michigan (UM) are used to measure the void fraction in two-phase boiling flows, with water as the working fluid, in a tubular test section. The test section is made of Incoloy 800H/HT with a total length of 1.589 m, an inner diameter of 12.95 mm, and a wall thickness of 3.05 mm. These two instrumentation systems are installed on a traversing platform that travels along the vertical test section to perform measurements at multiple elevations. Subcooled flow boiling and natural convection boiling experiments are performed to measure the void fraction in the test section. Flow visualization images are obtained for bubbly and slug flows from the X-ray radiography system. The wall temperature of the test section is measured at 17 elevations by thermocouples. In addition to the experiments, a multiphase computational fluid dynamics (MCFD) model is developed using ansysfluent to simulate the subcooled flow boiling. The measured wall temperature and void fraction from the experiments are compared with the MCFD simulation results. The root-mean-square (RMS) relative deviations are 3.6% and 16.1% for the wall temperature and void fraction, respectively, between the experimental data and MCFD simulations.