Flow Pattern Distribution Research Articles

Thermo-mechanical coupling characteristics of the shearer’s guiding shoe during the friction

The reliability and longevity of the guiding shoe are crucial for the proper functioning of coal mining machines. The heavy wear of the sliding surface under thermal stress coupling is the primary factor influencing the service life of the guiding shoe. To reveal the heat flow distribution patterns and the thermo-stress coupling mechanisms of the guiding surface, a thermo-mechanical coupling model of the guiding shoe and the pin row is established. The transient thermodynamic behavior of the guiding shoe under different load and speed conditions is studied using the coupled temp-displacement analysis method in Abaqus. The results indicate that the overall temperature of the guiding shoe friction surface experiences a rapid increase during the initial running-in phase, followed by a progressively slower temperature increase over time. Temperature and stress concentration regions on the friction surface primarily localize at the corners of the shoe groove, and the distribution of temperature and stress shows a strong coupling. Furthermore, elevated traction speed and mechanical load exacerbate the thermo-elastic instability of the guiding shoe, consequently augmenting thermal stress on the friction surface. The increase in support load results in significant thermal shock on the lower area of the left side of the guiding shoe. The research provides a reference for exploring the fatigue failure and wear mechanisms of the guiding shoe while considering thermal effects.

Studi Numerik Pengaruh Sudut Bukaan Damper dan Flue Gas Temperatur Terhadap Distribusi Temperatur Pada Heat Recovery Steam Generator (HRSG)

The Combined Cycle Gas Turbine Power Plant (PLTGU) utilizes the waste heat from the gas turbine to produce steam in a Heat Recovery Steam Generator (HRSG). The steam from the HRSG is then used to generate electricity in a steam turbine. In HRSG operation, several variables significantly impact its performance, including the damper angle and inlet temperature. At the Tanjung Uncang Power Plant in Batam, the manufacturer's standard operating procedure (SOP) requires that the exhaust gas temperature when the damper is open must be below 400°C. However, the gas turbine with an initial load of 5 MW has an exhaust gas temperature of 560°C - 580°C. Therefore, it is necessary to perform a gas turbine load release or FSNL (Full Speed No Load) to reduce the inlet temperature of the gas turbine. During FSNL, there are SOPs for diverter damper angles of 51°, 68°, and 90°. This leads to the need for analyzing the impact of diverter damper angles and inlet temperature on the flow pattern and temperature distribution. The analysis was conducted using CFD (Computational Fluid Dynamics) with ANSYS Fluent 2020 software. The variations used are diverter damper angles of 51°, 68°, and 90°, combined with inlet temperatures of 400°C and 580°C. The simulation outputs include velocity contours, temperature contours, and equivalent stress on the superheater tubes. The HRSG simulation results show that the flue gas is not distributed uniformly. The turbine exhaust gas only spreads along 4 – 11 meters, leading to slower steam production from the superheater. Additionally, when the superheater tubes are empty, the steady-state thermal and structural simulation results indicate that an inlet temperature of 580°C, whether at damper angles of 51°, 68°, or 90°, can cause a larger temperature difference between the inner and outer walls, ranging from 117.04°C to 125.5°C. This temperature difference can lead to thermal stress on the superheater tubes. This is shown in the S-N Curve for SA 213 T22 material, with a convection coefficient of 5 W/m² K (no steam), where the equivalent stress exceeds the endurance limit (infinite zone).

Impacts of thermally stratified medium on transient convective heat transfer between co‐axial horizontal fixed pipes: Applications of the thermal stratification

AbstractThermal stratification improves coaxial pipe systems’ efficiency and stability. Thermal stratification enables accurate temperature maintenance, reduces thermal stress, optimizes heat transmission performance, and minimizes usage of energy to guarantee the system's long‐term performance. The main aim of the current study is to investigate the impacts of thermal stratification on buoyancy force flow and thermal transmission between coaxial fixed pipes. In the present research, the applications of thermally stratified medium on transient convective heat transfer between two coaxial fixed pipes are studied. A two‐dimensional mathematical formulation in terms of mutually nonlinear partial differential equations is used to analyze the unsteady flow and temperature field between the co‐axial pipes, when the internal pipe is uniformly heated and the outer wall of the external pipe is placed at infinity from the surface of the inner fixed pipe. Flow is assumed along the axial direction of the internal pipe and stationary boundary condition is assumed at the surface of the inner pipe. The coupled equations of the simulated model are solved numerically by applying the Implicit Finite Difference Technique. The computed outcomes in the form of geometrical interpretation are highlighted by using the technically advanced software TECHPLOT‐360. Comprehensive detail of the obtained results for the non‐dimensional parameters included in the flow formulation is predicted for steady state velocity, temperature distribution, time‐dependent surface shearness and time‐dependent energy shearness in results and discussion section of the manuscript. The emphasis is placed on the thermal stratification parameter in the above mentioned chief quantities. From the obtained results, it is predicted that the fluid flow pattern and thermal distribution are both reduced for rising values of the thermal stratification parameter S = 0.001, 0.03, 0.05, and 0.07. Minimum flow and thermal profile are observed at S = 0.07. Further, the amplitude of the time‐dependent surface shearness is uniformly distributed throughout the medium and the amplitude of the time‐dependent energy shearness is reduced effectively for S = 1.0, 5.0, and 10.0.

Coupled CFD-FEM modeling of fluid–thermal–structural interaction in a single-strand tundish

A mathematical model has been developed to study the fluid–thermal–structural interaction in a single-strand tundish based on a coupled computational fluid dynamics (CFD) and finite element method (FEM) approach. The flow pattern and temperature distribution of the molten steel were predicted by the CFD calculation. Heat transfer and thermal stress profiles in the solid layers were investigated by the FEM analysis. Case studies were carried out comparatively to investigate the effect of tundish preheating and thermal insulation. The results show that tundish preheating can maintain the desired temperature of the molten steel at the exit. The heating efficiency drops significantly after 3 h of preheating. Reducing the thermal conductivity of the insulation material will reduce the temperature of the tundish shell and increase the thermal stress on the working lining. The modeling results can be used to improve the reliability and lifetime of the tundish and reduce production costs.

Temporal and Spatial Distribution Characteristics of Inbound Tourism Flow in Guangxi, China

The D-Q model was used to analyze the temporal and spatial distribution characteristics of inbound tourism flow in Guangxi by collecting index data from 2011 to 2019. The results showed that the temporal and spatial distribution of inbound tourism flow presented obvious single-core agglomeration characteristics. The polarization was serious, and the phenomenon of "poverty trap" became more and more obvious. The regional imbalance was prominent. The quantity and quality coordination of inbound tourism flow was poor. The spatial dislocation phenomenon appeared. The overall distribution pattern of inbound tourism flow might remain stable, and the number of cities maintaining a stable state presented a relatively large proportion. Finally, some countermeasures were put forward to promote the development of inbound tourism in Guangxi.

Paleosol-induced early dolomitization with U[sbnd]Pb age constraints and its implications for fluid pathways in ancient sandstone aquifers

In hydrogeology, a key challenge involves identifying patterns within ancient formations to forecast the distribution of fluid pathways and barriers to permeability, as well as comprehending the palaeohydrological system and its changes over time. This study addresses two main research inquiries concerning fluid flow: firstly, the influence of dolomitization induced by paleosols on flow characteristics, and secondly, the implications for fluid flow pattern distribution in continental sedimentary units. The objectives are pursued through: (1) meticulous, high-resolution measurements of porosity and permeability coupled with well-log data from an outcrop and two boreholes; (2) investigation of petrographic features of diagenetic minerals and their ages using the UPb geochronology system; and (3) an integration of these methodologies to grasp rock properties and fluid flow at a broader scale. Findings suggest that early dolomitization in continental sequences significantly affects fluid flow properties across the basin. The development of paleosols triggered early dolomitization, supported by UPb geochronology evidence. Subsequent groundwater migration along hydraulic gradients, influenced by fluctuations in the local aquifer's water table, facilitated the vertical distribution of dolomitization. Dolomitization occurred in residual pores resulting from initial mineral alteration, early lithifying the sediment and preventing mechanical compaction, thus preserving porosity. During migration events, fluids moved vertically along local faults and horizontally through the dolomitized layers of the formation, which likely remained porous at the time, leading to substantial silica mineralization.

Investigation of MHD flow balancing in electrically conductive manifolds of liquid metal blankets

In the liquid metal (LM) blanket design for magnetic confinement fusion reactors, manifolds including main and branch ducts are commonly used to direct fluids to various locations of the blanket to cool its components. The primary objective of this structural configuration is to achieve flow balancing within each branch duct. However, magnetohydrodynamic effects will cause uneven flow distribution, consequently, uncontrollable overheating phenomena in certain blanket segments may be caused by this flow distribution. To assess its impact, the influences of external magnetic fields, inlet velocities and coupling wall thicknesses on the flow partitioning in conductive manifolds are investigated in this study. The results indicate that the flow distribution among the branch ducts becomes less uniform as the external magnetic field strength increases, while varying the inlet velocity has minimal impact. In addition, increasing the coupling wall thickness leads to more even flow distribution when the rectangular branch ducts are perpendicular with the magnetic field direction. Based on above physical understanding, three controlling methods for the flow partitioning in conductive manifolds are proposed to achieve flow balancing in each branch duct and then validated through numerical simulations. The results indicate that flow balancing can be achieved by adjusting the coupling wall thickness when the rectangular branch ducts are aligned with the magnetic field direction, however, it is challenging when they are perpendicular. Furthermore, the flow balancing can be realized by a symmetrical design of the manifold with circular branch pipes and it is independent of external magnetic fields and inlet velocities. These findings will enhance the physical understanding of flow distribution patterns in conductive manifolds under strong magnetic fields, which is important for the flow control and design of manifolds in LM blankets.

In situ analysis of solute and flow fields in directional solidification of immiscible Al–Bi alloy

Segregation of the solidification structure of an immiscible alloy is related to the convection induced by the density differences of the components under gravity during solidification. Here, the solidification of the Al–Bi alloy in both opposing and parallel directions to the gravity force was investigated in situ using radiography and optical flow techniques. A quantitative analysis was performed on the flow, solute, and constitutional undercooling fields at the interface. During upward solidification, a flat solute-enriched layer was observed, with the melt flowing toward the center from both sides of the interface. During downward solidification, the solute-enriched layer was deformed, and solute plumes were observed, with the melt flowing toward the sides from the center of the interface. A high solute concentration gradient enhances the local flow and solute transport. The elongation of the plumes was attributed not only to the convective diffusion of the solute but also to the dispersion of droplet clusters. The forces acting on the droplets were calculated, and it was found that the resultant force on the droplets increased the area of the solute-enriched layer. Convection within the bulk melt and the motion of the droplets have synergistic effects on the flow pattern and solute distribution. Distinct microstructures were observed in opposite directions of solidification owing to the differences in constitutional undercooling and flow instability. This work offers insights into the quantitative measurement and understanding of the multi-physics fields during the solidification process.

Indirect mode solar drying of stevia (Stevia rebaudiana) leaves: experimental and numerical investigation of fluid flow pattern, moisture, and temperature distribution profile

Indirect mode solar drying of stevia (Stevia rebaudiana) leaves: experimental and numerical investigation of fluid flow pattern, moisture, and temperature distribution profile

Study on the impact of methanol steam reforming reactor channel structure on hydrogen production performance

The design and operation of embedded reactors involve chemical reaction efficiency issues, with the main consideration being heat and mass transfer characteristics. The contact area of the porous catalytic coating with methanol is affected by the reactor structure, to improve the hydrogen yield and reveal the mechanism of the channel structure on the hydrogen production performance, the hydrogen production performance of circle-triangle, circle-square, square-circle, square-square, and triangle-circle channels was investigated. The reasons for the differences in methanol conversion, hydrogen, and carbon monoxide selectivity were analyzed from the perspective of heat and mass transfer using a three-rate reaction mechanism. The results showed that the circle-triangle channel performed outstandingly in the hydrogen production from methanol steam reforming with 98.61 % methanol conversion, 88.74 % hydrogen selectivity, and 29.06 % CO selectivity. The shapes and sizes of the different channel structures affect the fluid flow pattern and velocity distribution, which in turn affect the mass transfer efficiency and lead to differences in hydrogen production performance. The circle-triangle channel exhibits superior heat transfer and material transport performance, which can improve the hydrogen production efficiency of methanol steam reforming and help provide an important reference for the embedded reactor design.

Numerical study of wave-induced flow and wave set-up on a platform reef with steep slope

A 2D numerical model was developed in this study to investigate the wave-induced flow and wave set-up on a platform reef with steep frontal slope. The model solves the Reynolds Averaged Navier-Stokes (RANS) equations, with the classical k−ε turbulence closure model. The inflow boundary was modified by adding fluid replenishment to balance the water level in the numerical flume to ensure long-term simulation in the platform reef system. The numerical model was first validated by systematically comparing the wave breaking, flow structure, and mean water level against laboratory measurements. The validated model was employed to further analyze the detailed flow field and reveal the influence of the reef morphology on the wave-induced flow and wave set-up. The complex distribution pattern of wave-induced flow and wave set-up on the reef flat were found to be related to the Froude number. The results also reveal that reef slope and reef roughness will not only change the wave breaking morphology but also affect the distribution pattern of wave-induced flow and wave set-up.

Effects of the asymmetric and oscillating turbulent melt flow on the heat transfer and solidification inside the thin slab continuous casting (TSC) mold under the applied electromagnetic brake (EMBr)

The thin slab casting (TSC) is a breakthrough near-net-shape technique for flat products accompanied by rapid casting and solidification rates. The TSC quality hinges on the turbulence, super-heat flow and growth of the solidified shell. The electromagnetic brake (EMBr) is commonly applied to control the fresh melt flow after feeding through a submerged entry nozzle (SEN). Numerical modelling is a perfect tool to investigate the multiphase phenomena in the continuous casting (CC). The presented study considers the heat transfer through the solid shell and water-cooled copper mold including the averaged thermal resistance of the slag skin and the air gap coupled with the turbulent flow and magnetohydrodynamics (MHD) model using an in-house code developed inside the open-source computational fluid dynamics (CFD) package OpenFOAM®. The model is applied to investigate different undesired asymmetric melt flow issues: (i) with the misaligned or (ii) partially blocked SEN; (iii) caused by the mean flow fluctuations with the natural frequencies; (iv) related to the oscillations of the fresh melt jets for the specific SEN designs and casting regimes. The variation of the flow pattern and superheat distribution is studied and presented for different scenarios both with and without applied EMBr.

Rainfall intensity profile induced changes in surface‒subsurface flow and soil loss as influenced by surface cover type: A long-term in situ field study

Due to global warming, changes in the rainfall intensity profile (i.e., the temporal intensity distribution within a rainfall event) increase the difficulty of accurate erosion prediction and control. Surface cover has been widely used as a critical measure to control soil erosion worldwide. However, the effects of the rainfall intensity profile (RIP) on soil erosion under different surface covers are not fully understood. In this study, long-term in situ field observations of the rain hyetograph, surface runoff coefficient (SRC), subsurface flow rate (SFR), and soil loss rate (SLR) from bare land, litter cover and grass cover were conducted over 11 consecutive years in the red soil hilly region of southern China. According to the occurrence time of the most intense rainfall, 226 erosive events were classified into four RIP patterns: advanced, intermediate, delayed, and uniform patterns. The results indicated that the advanced pattern with short duration–high intensity and the delayed pattern with long duration–high depth contributed to 73.45% of the total erosive events. For bare land, advanced events were the dominant pattern producing surface runoff and soil erosion, accounting for 57.24% and 75.17%, respectively, of the total surface runoff and erosion. The average SRC and SLR from the advanced pattern were 1.29–2.42 times and 2.52–39.78 times greater than those from the other patterns, respectively. The delayed pattern contributed to subsurface flow, and the average SFR was 1.27–2.17 times greater than that of the other patterns. Furthermore, surface cover significantly reduced surface runoff and erosion and increased subsurface flow, especially under the advanced pattern. Both surface cover measures were equally effective in controlling surface runoff and erosion, but the increase in subsurface flow caused by litter cover was 1.38–2.67 times greater than that caused by grass cover. Advanced pattern events increase the erosion risk on red soil slopes, and surface cover effectively weakens the effect of variation in the RIP pattern on soil erosion. Moreover, surface cover significantly alters the surface‒subsurface flow distribution pattern for all the RIP patterns. This study highlights the crucial importance of rain intensity profiles on water erosion and provides a basis for optimizing measures to effectively control soil and water loss under climate change.

Numerical investigation on unstable oscillation of oxygen jet condensation in cryogenic liquid rocket

Oxygen jet condensation always occurs with intense unstable oscillation in the cryogenic delivery pipe of a space launch vehicle. This phenomenon threatens the safety of the propulsion pipeline. It is essential to explore the transient physical features of oxygen jet condensation precisely, including the spectrum of pressure oscillation. Aiming at a deeper understanding of the thermal hydraulic characteristic of oxygen jet condensation, abundant simulations are carried out using a modified phase change method. In this model, the height function method is introduced to capture the interfacial curvature to reveal the mechanism of periodic fluctuation. The simulation proves that three typical flow patterns are found at variant operating conditions in oxygen jet condensation: chugging, oscillation, and swinging. The condensation regime diagram is summarized according to the flow pattern distribution. The chugging flow, along with the phenomenon of liquid oxygen sucked-back flow, shows the most intense pressure oscillation with a maximum amplitude of 133 kPa. In the oscillation flow, the oxygen vapor plume shrinks periodically with a low frequency of about 10 Hz. The swinging flow is a stable flow pattern with a slight pulsation of oxygen vapor plume wake. Its amplitude of pressure oscillation is approximately 1–3 kPa. The influence of liquid oxygen mass flow rate and subcooling on the unstable characteristic is also obtained. These findings offer ample theoretical direction for the development of the space launch vehicle.

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.

System for recognizing gas flow distribution patterns in blast furnace centre based on computer vision

System for recognizing gas flow distribution patterns in blast furnace centre based on computer vision

Effect of static magnetic field on the molten pool dynamics during laser powder bed fusion of Inconel 718 superalloy

Recent researches show that a static magnetic field (SMF) has an impact on the molten pool dynamics and microstructure of laser powder bed fusion (L-PBF). This work is intended to the multiple effect of SMF on the molten pool dynamics during L-PBF of Inconel 718 superalloy. A three-dimensional (3D) multiphase computational fluid dynamics (CFD) model at the powder-bed scale was established by coupling the electromagnetic braking and Seebeck effect in a static vertically-distributed magnetic field. Results show that the magnetic damping force (MDF) of the order of 104 N/m3∼105 N/m3 within the whole molten pool suppresses the Marangoni convection. The thermoelectric magnetic force (TEMF) of the order of 106 N/m3∼107 N/m3 rotates in the mushy zone and further enhances the melt flow of the whole molten pool. The SMF will not transform the flow pattern and temperature distribution in the molten pool. SMFs of 0.1 T and 0.3 T will suppress the melt flow, while that of 0.5 T will enhance the melt flow. The width of molten pool first decreases and then increases when the magnetic flux density (MFD) increases from 0 T to 0.5 T. In addition, applying a SMF of 0.3 T can effectively inhibit pore defect and spatters. This work can provide insight into the control of molten pool by introducing a SMF during L-PBF.

Estimating lane utilization for variable approach lanes using explainable machine learning

This study investigates the flow distribution patterns at intersection approaches with variable approach lanes (VALs) and proposes a new lane utilization adjustment factor specifically for VALs. Unmanned aerial vehicles (UAVs) were used to collect naturalistic data, including traffic flow, approach geometry, and signal control-specific information, at selected intersections in Hangzhou, China. Machine learning techniques were employed to develop accurate regression models for estimating lane utilization, separately for the two VAL statuses. Preliminary analyses indicate different VAL utilization patterns across sites, suggesting the presence of external factors, beyond the VAL control itself, influencing the VAL utilization. The machine learning regression models provide insights into these factors by ranking them based on the importance and the impact magnitude. From a practical standpoint, this study recommends the implementation of uniform lane guiding signs, lane geometry improvements, and driver education to enhance the operational efficiency of variable approach lanes.

Experimental study and prediction of two-phase flow pattern distribution diagrams in multi-channel cylinder dryer

The multi-channel cylinder dryer (MCD) is designed to improve heat transfer. Although there are numerous research studies on the pressure drop, heat transfer characteristics, and flow pattern in static state of MCD, there is little research on the flow pattern in the rotating state. In this paper, the distribution of flow pattern in MCD under different rotating speeds and steam mass flow rates is studied. Furthermore, the logistic regression method (LR) is used to predict the flow pattern diagrams. The results show that in the front section of the flow channel, the flow pattern is basically annular flow, which is not affected by mass flow rate and rotating speed. On the other hand, wavy flow, vortex flow, slug flow, and bubble flow can be observed when the fluid enters the middle and the end section. The higher the rotating speed and the steam mass flow rate, the more the flow pattern tends to be an annular and wavy flow. At the end of the passage, the flow pattern is mainly slug flow. The predicted flow pattern diagrams are in good agreement with the experimental result, and to obtain an effective flow pattern in the middle and the end section of the flow channel, the influence of increasing rotating speed is greater than that of increasing steam mass flow rate. However, the specific rotating speed, steam mass flow rate, and other parameters should still be set by combining with the actual situation. This work can provide some references for the further study of MCD flow characteristics.

Effects of blade-tip squealer geometry on the working performance of a helico-axial multi-phase pump

Tip-leakage flow occurs in the tip-clearance region of helico-axial multi-phase pumps, and this reduces their working performance. In this study, a structural modification, in the form of the inclusion of “squealers” on the impeller blade tips, was adopted to reduce the tip-leakage flow in a helico-axial multi-phase pump, thereby improving its working performance. Numerical simulations were conducted to examine the impact patterns of geometric parameters such as the depth, shape, and size of the squealer on the external characteristics and tip-leakage flow. The results of this study show that the presence of squealer tips has significant effect on the performance of a multi-phase pump. The depth of the squealer and the ratio of the squealer length to the blade-tip length were found to be the critical structural parameters of the squealer. There is an optimal value for the relative squealer depth, and this was found to be 9%. Larger ratios of squealer length to blade-tip length were also found to be more favorable for improving the performance of the multi-phase pump. The width and location of the squealer were found to have relatively low impacts on the performance of the multi-phase pump considered in this study. The presence of squealer reduced the tip-leakage flow rate and also alter the structure of the flow field in the impeller blade-tip region, changing the periodic distribution pattern of tip-leakage flow to some extent. The results of this study have important guiding significance for improving the performance of helico-axial multi-phase pumps.