Inlet Flow Pattern Research Articles

A hybrid of fast K-nearest neighbor and improved directed acyclic graph support vector machine for large-scale supersonic inlet flow pattern recognition

Inlet flow pattern recognition is one of the most crucial issues and also the foundation of protection control for supersonic air-breathing propulsion systems. This article proposes a hybrid algorithm of fast K-nearest neighbors (F-KNN) and improved directed acyclic graph support vector machine (I-DAGSVM) to solve this issue based on a large amount of experimental data. The basic idea behind the proposed algorithm is combining F-KNN and I-DAGSVM together to reduce the classification error and computational cost when dealing with big data. The proposed algorithm first finds a small set of nearest samples from the training set quickly by F-KNN and then trains a local I-DAGSVM classifier based on these nearest samples. Compared with standard KNN which needs to compare each test sample with the entire training set, F-KNN uses an efficient index-based strategy to quickly find nearest samples, but there also exists misclassification when the number of nearest samples belonging to different classes is the same. To cope with this, I-DAGSVM is adopted, and its tree structure is improved by a measure of class separability to overcome the sequential randomization in classifier generation and to reduce the classification error. In addition, the proposed algorithm compensates for the expensive computational cost of I-DAGSVM because it only needs to train a local classifier based on a small number of samples found by F-KNN instead of all training samples. With all these strategies, the proposed algorithm combines the advantages of both F-KNN and I-DAGSVM and can be applied to the issue of large-scale supersonic inlet flow pattern recognition. The experimental results demonstrate the effectiveness of the proposed algorithm in terms of classification accuracy and test time.

An Experimental Study of In-Tube Condensation and Evaporation Using Enhanced Heat Transfer (EHT) Tubes

A study was carried out to determine in-tube evaporation and condensation performance of enhanced heat transfer tubes (EHT) using R410A, with the results being compared to a plain tube. The test tubes considered in the evaluation include: plain, herringbone (HB) and spiral (HX) microgrooves, herringbone dimple (HB/D), and hydrophobic herringbone (HB/HY). Experiments to evaluate the condensation were conducted at a saturation of 318 K, and at 279 K for evaporation. Mass flux (G) ranged between 40 to 230 kg m−2s−1. Condensed vapor mass decreased from 0.8 to 0.2; and the mass of vaporized vapor increases from 0.2 to 0.8; heat flux increased with G. Inlet and outlet two-phase flow patterns at 200 kg m−2s−1 were recorded and analyzed. Enhanced tube heat transfer condensation performance (compared to a plain tube) increased in the range from 40% to 73%. The largest heat transfer increase is produced by the herringbone–dimple tube (HB/D). In addition to providing drainage, the herringbone groove also helps to lift the accumulated condensate to wet the surrounding wall. Evaporation thermal performance of the enhanced tubes are from 4% to 46% larger than that of smooth tube with the best performance being in the hydrophobic herringbone tube (HB/HY). This enhancement can be attributed to an increase in the number of nucleation sites and a larger heat transfer surface area. Evaporation and condensation correlations for heat transfer in smooth tubes is discussed and compared.

An ensemble radius basis function network based on dynamic time warping for real-time monitoring of supersonic inlet flow patterns

As the basis of protection control, supersonic inlet plays an important role in a supersonic air-breathing propulsion system, so it is of great significance to ensure the safe and stable operation by monitoring its flow patterns. From the perspective of machine learning, this issue can be viewed as a time series classification (TSC) task. Traditionally, several manually-engineered features are extracted as the indicators to evaluate the operation status, which can be heavily dependent on the professional experience and time-consuming. This paper proposes a novel Dynamic Time Warping-Radius Basis Function (DTW-RBF) network to directly determine the flow patterns from the dynamic input signals. DTW-RBF network replaces the Euclidean distance in the static RBF kernels with the DTW distance, which exploits the elastic matching ability of DTW to align the input signals to the kernels. Then, the second-order Levenberg-Marquarelt (LM) optimization algorithm is used to allow the efficient training process of the proposed network. In order to determine the appropriate locations for sensor placement and enhance the robustness and reliability of monitoring flow patterns by a single sensor, an optimal subset of sensors is further selected for ensemble through multi-objective optimization and fuzzy decision. Experimental results demonstrate that the proposed DTW-RBF network works efficiently for TSC tasks on benchmark time series datasets, and has better comprehensive performance for monitoring supersonic inlet flow patterns in terms of classification accuracy and test time. The ensemble classifier further increases the classification accuracy with still meeting the real-time requirements.

Design and Operation Characteristics of the Horizontal Swirl Flood Discharge System

It is one of the effective methods to increase the reliability of flood discharge buildings with high water head and reduce the project cost to transform the diversion tunnel of temporary buildings into permanent spillway by using the horizontal swirl flood discharge system. Based on Gongboxia hydropower station and combined with prototype monitoring, this paper studies and analyzes the key points of shape layout, structural characteristics and operation effect of horizontal swirl flood discharge system, the results show that the horizontal swirl flood discharge system has strong adaptability to topographic and geological conditions, good energy dissipation effect and hydraulic characteristics, stable inlet and outlet flow pattern, stable cyclone cavity, no obvious signs of adverse negative pressure and cavitation erosion, no adverse structural vibration and dynamic response, and safe operation of the spillway tunnel.

Experimental study on a new gas–liquid separator for a wide range of gas volume fraction

Gas–liquid separation is widely used in various fields. And the centrifugal separator has been witnessed as a worldwide popularity owing to its small size and high efficiency. However, the uncertainty of the inlet flow pattern limits the wide application of centrifugal separators. In this paper, a new gas–liquid separator combining gravity separation and centrifugal separation was proposed for complex and unstable two-phase flow. In this study, the performance of the separator under different liquid flow rates with wide gas volume fraction range from 5% to 90% was investigated experimentally, and the phenomena occurred in the separator were also analyzed. The results show that the separator can keep high-efficiency separation in multiple flow patterns as long as the liquid level in the downcomer is at a reasonable position. Meanwhile, the lowest and highest allowed liquid levels were defined and measured by the pressure difference and a ruler. Furthermore, the bubble column in the downcomer was analyzed.

Phase split of oil-water two phase flow at double-layer T-junctions pipes

Offshore oil and gas production systems are in urgent need of a more compact, high-efficient oil-water separator. T-junction pipes are a potential solution to the need. Combining dynamic separation principle of T-junctions pipes with shallow pond theory, this paper presents a novel design of double-layer T-junctions pipes to realize high-efficient oil-water separation. The separation system consisted of upper and lower double-layer pipes that are connected by two vertical pipes. There exists an axially floating oil pipe along the top of the upper outer pipe. This design makes the Reynolds number decrease, which is beneficial to the formation of oil-water stratified flow. The slender seam at the bottom of inner pipe reduces the turbulence intensity, thus avoiding remixing oil with water. The influence of mixture velocity, oil content, water superficial velocity, oil superficial velocity, and inlet flow pattern on the phase split of oil-water two phase flow at double-layer T-junctions pipes has been investigated. Experimental results showed that the separation performance was less affected by the inlet oil content than by the inlet mixture velocity. Additionally, the phase split in the separation system was very sensitive to the inlet flow pattern. For separated flow pattern, oil-water can be well separated. But for dispersed flow pattern, the oil-water separation efficiency was low. Besides, the using of floating oil pipe can increase the system separation efficiency.

Study on the volute chamber shape of swirling shaft adopted in water diversion project

As an environment-friendly internal energy dissipation technology, the swirling shaft energy dissipation has been more and more applied. In this paper, the influence of the shape of the volute chamber on the flow pattern and energy dissipation rate is studied by the CFD numerical simulation method combined with the physical model test method. The results show that with the increasing of the diameter of the volute chamber, the diameter of the cavity in the volute chamber increases correspondingly, which effectively alleviates the backwater phenomenon on the upstream channel section of the shaft. Increasing the width of the inlet of the volute chamber can promote the flow pattern of the upstream channel section from the pressure flow to the non-pressure flow. The setting of the arc wedge rectification flip bucket can improve the inlet and inner flow pattern of the volute chamber.

Infiltration and Anti-Filtration Recharge-Pumping Well and Laboratory Recharge Tests

Infiltration and anti-filtration recharge-pumping wells (hereinafter, referred to as IAF recharge-pumping wells) can enable rain-flood flowing in rivers or channel recharge to aquifers, in flood periods, and pump groundwater to be utilized in non-flood periods. In this study, a round IAF recharge-pumping well and a square IAF recharge-pumping well were developed, the structure and characteristic were introduced, the calculation equations of single-well recharge quantity of IAF recharge-pumping wells, in unconfined aquifers were deduced, and the steady-state flow recharge test was conducted in the laboratory. The conclusions were as follows. The theoretical equation of the single-well recharge quantity was reasonable. Compared to existing anti-filtration recharge wells, the new IAF recharge-pumping well had stronger anti-deposit and anti-scour abilities and the single-well recharge quantity increased by 400%. Compared to the square IAF recharge-pumping well, the round IAF recharge-pumping well had a better inlet flow pattern and a larger single-well recharge quantity. With an increase in the test times, the single-well recharge quantity gradually decreased and tended to be stable. The existence of the pumping pipe had a little influence on the single-well recharge quantity.

Equal split of gas–liquid two-phase flow at variable extraction ratio

In this work, a special distributor is proposed to distribute gas–liquid two-phase flow equally at different extraction ratio. A swirl vane is inserted at the entrance to achieve uniform swirling annular flow and ensure all the splitting holes have identical inlet conditions. A balance pipe is also applied to balance the pressure difference between the sample fluid loop and main fluid loop. Experiments were conducted in an air–water two-phase flow loop. The effect of gas and liquid superficial velocity, inlet flow pattern and splitting hole’s diameter were investigated. The results demonstrate that the extraction ratio is only dependent on the ratio of sample fluid hole number to that of main fluid. The fraction of gas and liquid taken off is not influenced by flow gas and liquid velocity, inlet flow pattern and size of the splitting hole. The desired extraction ratio can be obtained by regulating the number of sample fluid holes.

Gas-liquid two-phase flow measurements by the electromagnetic flowmeter combined with a phase-isolation method

The electromagnetic flowmeter has presented excellent performance in single-phase flow. However, there are many fundamental difficulties when it is applied in two-phase flow. The presence of the insulating phase at various positions in two-phase flow strongly influences the distribution of the weight function, consequently resulting in the uncertainty and instability of the electromagnetic flowmeter's output. When the insulating phase contact with the electrode, it even leads to wrong alarm. In this paper, at the upstream of the electromagnetic flowmeter a phase-isolation method was used to change the inlet flow pattern into a uniform and symmetrical swirling core-annular flow, in which gas-liquid mixture was isolated to gas core and liquid annular flows flowing concurrently in the transmission pipe with a clear smooth interface between them. Then we analysed the behavior of the electromagnetic flowmeter performed in this specific flow pattern, and built the liquid flow rate measurement model. Besides, the void fraction was measured by image processing technique. Owing to the clear smooth interface, the difficulty of image processing and the measurement error of the void fraction can be reduced. The experimental results showed that, the combination of the phase-isolation method could improve the measurement accuracy and successfully make the electromagnetic flowmeter available for the gas-liquid two-phase flow where the original phase distribution is not uniform.

Experimental research on liquid-vapor two-phase flow separation of zeotropic mixtures at an impacting T-junction

Impacting T-junctions could work as a partial vapor-liquid separators by enhancing the mal-distribution of phase that occurs naturally therein. Previous studies have mainly concerned the phase splitting of air-water and pure refrigerants but here the performance of a vertical impacting T-junction using zeotropic mixtures as test fluids is reported. Experiments were conducted to investigate the effect of parameters, including inlet mass velocity, vapor quality, splitting ratio, outlet branch diameter and circulating composition of mixtures, on the liquid separation efficiency, based on mixtures R134a/R245fa and R290/R600a. The inlet flow patterns of each test fluid were also identified by using a high-speed camera under various test conditions. It was found that the mixture composition had an obvious effect on phase splitting at high separation loads, but the separation efficiency would not change linearly versus the R134a mass fraction in mixture R134a/R245fa. Overall, pure refrigerant showed better separation performance than zeotropic mixtures, under the same inlet and outlet conditions. Besides, the vaporization due to pressure drop at T-junction was also discussed by conducting a comparison study between air-water mixture and organic fluids. Calculation results indicated that an increase in pressure drop would promote mass transfer from liquid to vapor phase at the impacting T-junction.

Gas-liquid two-phase flow distribution in parallel micro-channels with different header and channels’ orientations

An experimental investigation was conducted to study the effect of header and channels orientations on the two-phase flow distribution in parallel micro-channels. The parallel micro-channels was composed of a header with hydraulic diameter of 0.667mm and three parallel channels with hydraulic diameter of 0.500mm, all with rectangle cross sections. Nitrogen and 0.03wt% sodium dodecyl sulfate (SDS) solution were used as the test working fluids. The inlet superficial velocities of gas and liquid varied from 0.200 to 16.0m/s and from 0.0246 to 0.650m/s, respectively. The fluid dynamics of two-phase flow splitting in parallel micro-channels was captured by high speed recording technique and three flow patterns were observed at the inlet. It was found that the phase distribution characteristics of two-phase flow in parallel channels highly depended on the inlet flow patterns and the orientations of header and channels. For slug flow, a uniform phase distribution was achieved in horizontal header with vertically downward channels, whereas the distribution of slug-annular flow was improved in vertically upward header and horizontal channels. For annular flow, two-phase inhomogeneous distribution reached the highest when the header was vertically downward.

Investigating the liquid film characteristics of gas–liquid swirling flow using ultrasound doppler velocimetry

A novel gas–liquid two‐phase flow metering method was proposed. A spiral vane mounted in the inner pipe was used to transform inlet flow patterns into gas–liquid swirling annular flow. The thickness and velocity profile of liquid film were measured by ultrasound Doppler velocimetry. The liquid flow rates were obtained by integrating of velocity profile during the liquid film zone. Experiments were carried out in an air–water two‐phase flow loop and an ultrasonic transducer was installed under the bottom of the test section with the Doppler angle of 70°. The flow patterns included stratified wavy, annular, and slug flows. Compared with non‐swirling flow, the liquid film thickness at the bottom reduces greatly. The measurement accuracy of liquid flow rate was independent of inlet flow patterns, gas and liquid velocities. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2348–2357, 2017

Phase split characteristics of slug and annular flow in a dividing micro-T-junction

The characteristics of slug and annular gas–liquid two-phase flow when moving through a rectangular micro-channel dividing T-junction were investigated with experiments focusing on the relationships between the phase split and the two-phase superficial velocity, liquid surface tension, and liquid effective viscosity. The effects of the pipe sizes and pipe cross section shapes on phase split were compared and analyzed. Phase split was tested using a 100×800μm rectangular dividing micro-T-junction. Air was used as the gas medium and the liquid mediums were water, 0.01% SDS solution, 0.5% SDS solution, 0.1wt% PAAm, 0.25wt% PAAm, and 0.5wt% PAAm. Results showed that whether the inlet flow pattern was slug or annular flow, the liquid taken off from side branch at the dividing T-junction decreases with an increase in liquid superficial velocity and that there is little effect of inlet gas flow rate on the liquid taken off. It was also found that the liquid taken off from side branch decreases with a decrease in liquid surface tension and increases with an increase in liquid effective viscosity. When results were compared to those from studies using channels of other diameters, it was seen that the phase split of the slug flow was similar at different sized dividing T-junction, while the phase split of annular flow varied at different pipe sizes. It was also seen that the phase split characteristics of a dividing micro-T-junction are dependent on the aspect ratios of the channel’s cross section. A predictive model of phase split characteristics studied in this investigation was formulated with the regression analysis of the experimental data and verified by calculations showing little error.

Phase distribution of nitrogen–water two-phase flow in parallel micro channels

The present work experimentally investigated the phase splitting characteristics of gas–liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.

Application of multi-slot sampling method for gas-liquid two-phase flow rate measurement

A novel approach to measure the individual mass flow rates of gas-liquid two-phase flow was proposed. Gas-liquid two-phase flow was divided into eighteen equal parts by a specially designed sampler and three parts were applied as sample fluid. The total gas and liquid flow rates are determined according to the flow rates of sampled fluid and the extraction ratio. The correlation of extraction ratio is deduced from the relation of resistance between the main loop and the division loop. Experiments were carried out in an air-water two-phase flow loop and the gas quality ranged from 0.008 to 0.66. The observed flow pattern included stratified smooth, stratified wavy, annular and slug flows. It was found that the gas and liquid extraction ratios are very close to the theoretical value (0.167) and independent of inlet flow pattern, gas and liquid velocities. The error of gas and liquid mass flow rates measurements was less than ±5.0%.

Effect of non-uniform inlet flow rate on the heat-up process of a solid oxide fuel cell unit with cross-flow configuration

This study simulates the heat-up process of a solid oxide fuel cell unit with the cross-flow configuration, and investigates the effect of the non-uniform inlet flow pattern and the non-uniform deviation on the maximum temperature gradient and preheating time. The numerical method is precise and reliable through the comparison with the analytical solution of previous literature. The results show that the effect of non-uniform inlet flow pattern on the maximum temperature gradient is obvious, and the effect in the fuel side is more obvious than that in the air side. The best choice of the inlet flow pattern is C, which the fuel side is uniform and the air side is the progressively increasing profile. Additionally, the effect of non-uniform inlet flow pattern on the preheating time can not be neglected, and this effect becomes larger when the non-uniform deviation increases.

Experimental investigation of phase split of gas–liquid two-phase flow through small holes at the pipe wall

An experimental and analytical study on phase split of gas–liquid two-phase flow through small holes at the main pipe wall has been performed in this paper. The inner pipe diameter of the test section is 40mm and the diameter of sampling hole is 2.5mm. Experiments were conducted in an air–water two-phase flow loop and four types of sampler with different arrangement of sampling-holes were tested. Stratified-wavy, annular and slug flows were observed. Experimental results show that phase splitting behavior is significantly influenced by the number and positions of the sampling-holes and the superficial velocities of the gas and liquid. If a swirl vane is mounted at the upstream of the four-hole sampler, an interesting phenomenon that the liquid extraction ratio maintains constant and is independent of the inlet flow patterns can be observed.

Parametric Studies of Pipe Diffuser on Performance of a Highly Loaded Centrifugal Compressor

Pipe diffusers with several different geometries were designed for a highly loaded centrifugal compressor originally using a wedge diffuser. Parametric studies on the effect of pipe diffuser performance of a highly loaded centrifugal compressor by varying pipe diffuser inlet-to-impeller exit radius ratio, throat length, divergence angle, and throat area on centrifugal compressor performance were performed using a state-of-the-art multiblock flow solver. An optimum design of pipe diffuser was obtained from the parametric study, and the numerical results indicate that this pipe diffuser has remarkable advantageous effects on the compressor performance. Furthermore, a detailed comparison of flow visualization between the pipe diffuser and the wedge diffuser was conducted to identify the physical mechanism that account for the beneficial effects of the pipe diffuser on the performance and stability of the compressor. It was found that the performance enhancement afforded by the pipe diffuser is a result of the unique diffuse inlet flow pattern. Alleviating flow distortion in the diffuser inlet and reducing the possibility of a flow separation in discrete passages are the physical mechanisms responsible for improving the highly loaded centrifugal compressor performance.

Kerosene-Water Flow Pattern in T-Junction Vertical Diameter Ratio 0.5 (Variation of Inclination Branch)

The separation is one of the important processes in exploration and production oil technology. Phase separation across T-junction with orientation vertical up branch is simplicity method to achieve maximum efficiency, but useful information is rather limited. This paper is presented only for inlet flow pattern and T-junction flow pattern of kerosene water mixture with inlet diameter 36 mm and branch diameter 19 mm (diameter ratio 0.5) on the variation inclination branch are 30o, 60o and 90o. Regulating flow by closing valve at downstream was done to obtain three flow resistance in the downstream. The flow pattern obtained in this study were : stratified (ST), three-layer-13 (3L-13) , three layer-2 (3L-2), and three layer-3 (3L-3). The results of the phase separation is best achieved under conditions inlet flow pattern stratified (ST) and T-junction three layer-3 (3L-3) flow pattern, angle 90 ° and downstream resistance 6471 Pa.Keywords: phase separation, T-junction, flow patterns, downstream resistance.