Inlet Branch Research Articles

Design of alveolar biomimetic enhanced heat transfer structure for cylindrical lithium battery pack

Aiming to address the issue of thermal runaway in high energy density batteries during high charge and discharge rates, a heat management system for an alveolar-like honeycomb liquid-cooled power battery was designed. This system is inspired by the bionic concept of cell cooling in biological tissues, with cylindrical batteries serving as cells and cooling channels resembling blood vessels. The cooling system for a battery pack consisting of 24 cylindrical cells was designed and implemented. Numerical simulations were conducted to optimize and study the effects of inlet diameter, branch angle, flow rate, and spiral baffle on coolant flow uniformity and temperature distribution within the battery pack. The results indicate that as the inlet diameter of the fractal channel increases from 2 mm to 20 mm, the coolant flow uniformity improves and the pressure drop decreases. However, the influence of inlet diameter diminishes after reaching a certain limit. When the inlet diameter increases from 10 mm to 20 mm, the relative standard deviation of the velocity at the branch outlet decreases only slightly, from 0.9 % to 0.8 %. Increasing the branch angle from 30° to 75° leads to an increase in the relative standard deviation of velocity, from 0.79 % to 1.24 %. Incorporating a spiral baffle into the internal flow channel of honeycomb cooling significantly enhances temperature uniformity within the battery pack while reducing maximum temperature levels considerably. Furthermore, a smaller pitch for the spiral baffle yields better cooling performance for the immersed liquid cooling thermal management system. After optimization, the maximum temperature difference is only 1.27 °C across the surface of the battery pack, achieving a remarkable temperature uniformity level of just 0.11 %.

A comprehensive study on active mixer performance using liquid metal droplets: an experimental approach

In this experimental study, we delve into the performance of an active mixer that utilizes liquid metal droplets. Our mixer configuration follows an innovative Y-type design, where two liquid metal-based pumping mechanisms operate within the minichannel inlet branches. By applying alternating current voltage to both sides of the liquid metal, we induce a surface tension gradient, propelling the fluid from the reservoirs toward the minichannel. Notably, the two entering liquids are distinctly colored, allowing us to quantify mixing using a Mixing Index (MI) definition and image processing techniques. Our investigation centers on four key variables governing mixer performance: applied voltage, liquid metal droplet diameter, input angle between the branches, and minichannel width. Given the experimental nature of our research, we employ a central composite design method within the framework of design of experiments (DoE). From our obtained experimental results, we establish correlations between MI and the other variables. Our examination of the four mentioned parameters revealed that liquid metal droplet diameter exerts the most significant influence on the mixing index. Following this, in descending order of impact, we find applied voltage, input angle, and channel width. In the optimal dimensions of our mixer, we achieve a remarkable maximum MI of 0.867.

2D and 3D Computational Modeling of Surface Flooding in Urbanized Floodplains: Modeling Performance for Various Building Layouts

AbstractUnderstanding the strengths and limitations of the modeling capacity of surface flooding in urbanized floodplains is of utmost importance as such events are becoming increasingly frequent and extreme. In this study, we assess two computational models against laboratory observations of surface urban flooding in a reduced‐scale physical model of idealized urban districts. Four urban layouts were considered, involving each three inlets and three outlets as well as a combination of three‐ and four‐branch crossroads together with open spaces. The first model (2D) solves the shallow‐water equations while the second one (3D) solves the Reynolds‐averaged Navier‐Stokes equations. Both models accurately predict the flow depths in the inlet branches. For the discharge partition between the outlets, deviations between the computations and laboratory observations remain close to the experimental uncertainties (maximum 2.5 percent‐points). The velocity fields computed in 3D generally match the measured surface velocity fields. In urban layouts involving mostly a network of streets, the depth‐averaged velocity fields computed by the 2D model agree remarkably well with those of the 3D model, with differences not exceeding 10%, despite the presence of helicoidal flow (revealed by the 3D computations). In configurations with large open areas, the 3D model captures generally well the trajectory and velocity distribution of main surface flow jet and recirculations; but the 2D model does not perform as well as it does in relatively channelized flow regions. Visual inspection of the jet trajectories computed by the 2D model in large open areas reveals that they substantially deviate from the observations.

Performance study and improvement of space-folded metamaterial muffler for pipe under grazing flow

A space-folded metamaterial muffler (SMM) for pipe noise attenuation was proposed in this paper, and an improved space-folded metamaterial muffler (ISMM) was formed by arranging wire meshes at the branch inlet. Under the absence of flow and grazing flow, analytical models of SMM and ISMM were developed based on the wave expansion method and Green's function, and correspondingly, the computational fluid dynamics - linear Navier-Stokes (CFD-LNS) numerical models were established. The acoustic characteristics of responsive space (RS) were described through the complex frequency plane. The transmission coefficient of SMM was obtained and verified by sound transmission loss experiments. The results indicate that due to the thermal-viscous effects, the minimum transmission coefficient of RS cannot reach 0. Therefore, the thermal-viscous effect is one of the critical factors. By the parameter retrieving method, it is clarified that the SMM is a single-negative acoustic metamaterial. The effect of the grazing velocity on the transmission coefficient and impedance was revealed quantitatively. The grazing velocity is positively correlated with impedance at the side branch inlet and negatively correlated with total impedance. Therefore, an increase in the grazing velocity will weaken the muffler performance. Since the CFD-LNS model cannot characterize aerodynamic noise, a computational aeroacoustics (CAA) model was established for SMM and ISMM. Numerical results show that the velocity and vorticity at the side branch inlet significantly decrease due to the wire mesh. When Ma is 0.1, 0.05, and 0.01, ISMM reduces aerodynamic noise by 6.11 dB, 9.19 dB, and 2.76 dB, respectively, compared to SMM. Therefore, ISMM has better aerodynamic noise suppression capability. Finally, noise reduction experiments of the ISMM under the grazing flow were performed in an anechoic chamber, and the effectiveness of the ISMM in practical applications was verified by acoustic imaging and spectrogram results.

The Effect of Rotating Speed and Oil Supply Pressure of the Rotating Passage of the Transmission System for a Helicopter

To study the flow field characteristics inside the rotating oil passage of a helicopter with variable speed transmission system, a rotating oil passage model consisting of a single inlet and multiple branch outlets is established, and computation fluid dynamics (CFD) simulation is performed. The influences of rotating speed and oil supply pressure on the distribution of lubricating oil, the flow rate of oil, and the distribution of velocity for the inlet and outlets are discussed. A test rig for studying the lubrication performance of a rotating oil passage is established, with which the oil flow rates of outlets under different conditions were obtained, and the effectiveness of the present simulation approach is validated.

Effects of intersection geometry on flow velocity interference and flow rate redistribution in furcating fractures

Fracture intersections are an essential element of fracture networks in energy extraction. The accurate evaluation of the flow behavior at intersections in the furcating fracture is the key to describing the flow behavior of fractured reservoirs, yet fracture intersections are often oversimplified or even ignored. To fill this knowledge gap, the effect of geometric characteristics internal to the intersection was investigated based on direct numerical simulation by solving Navier-Stokes equations. Two parameters, θ1 and θ2, which are the angles between the normal inlet branch direction and the two sides of a closed triangle, are introduced to characterize the geometry of the intersection in a furcating fracture, and the role of geometrical parameters θ1 and θ2 in the interference effect and flow rate distribution is investigated. The results demonstrate that intersection geometry interferes with the fluid flow passing through the intersection to a certain range. With an increasing hydraulic gradient J and θ, the flow interference range increases. Under the conditions of these simulations (J = 10−3 – 10−2, Re = 101–102), J is linearly correlated with flow rate q, but with an increasing J and θ, the area and percentage of the low-velocity zone caused by an intersection increases leading to the enhancement of nonlinear flow. Furthermore, based on the simulation results, an empirical formula for quantifying the flow redistribution at intersections is proposed, contributing to the effectiveness and accuracy of modeling seepage in the fracture networks. Finally, the physical meanings of geometric parameters θ1 and θ2 are determined. This study advances the understanding of flow behavior at intersections commonly observed in discrete fracture networks from a fresh perspective, despite the difficulty of monitoring.

Experimental study on the effect of mechanical ventilation on cable tray fires in compartments

This study deals with the effect of ventilation flow rate and the ventilation configuration on the behavior of a cable tray fire in a confined and mechanically ventilated enclosure. Results are based on large-scale fire tests performed within the framework of the OECD Nuclear Energy Agency (NEA) PRISME projects. The fire source, identical for all tests, consisted in five horizontal cable trays measuring 3 m in length, stacked vertically and filled with halogen-free flame retardant cable-type, non-powered cables. The installation consists of two rooms connected by an open doorway. Two ventilation configurations were considered with two different arrangements of the inlet and outlet branches. The analysis demonstrates the effects of ventilation flow rate and air intake position on the fire heat release rate (HRR). Decreasing the ventilation flow rate reduces the maximum HRR and delays combustion on the trays, which burn one after the other rather than simultaneously. This result is the consequence of oxygen vitiation near the cable trays, which reduces the horizontal flame spread on each cable tray. The analysis also discusses the phenomenon of low frequency oscillatory behavior of fire in a ventilated enclosure. The results highlight that the conditions of occurrence of oscillations combine two criteria: a low ventilation flow rate to favor the release of unburnt gases and an appropriate configuration of the ventilation air intake to generate ignition of premixed gases.

Optimal parameter design of a slot jet impingement/microchannel heat sink base on multi-objective optimization algorithm

Jet impingement and microchannel cooling as effective cooling methods have been widely employed for thermal management of high heat flux electronics. In this work, a novel hybrid slot jet impingement/microchannel heat sink, combining the advantages of two cooling technologies, was proposed to achieve vertical flushing of the jet and timely discharge of the waste fluid. To further enhance the cooling performance, a 3-D numerical simulation was applied to evaluate the impact of inlet and outlet branch passage inclination ratios (Hin,1/Hin,2 and Hout,1/Hout,2), channel unit width (W1), channel width ratio (φ) and channel height (H3) on heat sink thermal-hydraulic characteristics. According to the parametric analysis, the variations in the inlet and outlet branch passage inclination ratios have significant effect on the mass flow distribution among the heat transfer channels. Afterward, to acquire the optimal compromise solution for practical applications, the artificial neural network training and multi-objective optimization algorithms, i.e. multi-objective particle swarm optimization (MOPSO) and multi-objective genetic algorithm (MOGA), are utilized to optimize the geometrical parameters, i.e. W1, φ and H3. During the optimization, the average heated surface temperature (T¯heat) and the total pressure drop (ΔP) are two conflicting objectives to evaluate the heat transfer and resistance characteristics. Finally, an optimal compromise solution (W1=1.03mm, φ=0.58 and H3=2.44mm) is chosen from the Pareto front by using the classical decision-making algorithm, i.e. TOPSIS. Compared with one objective minimization in the Pareto front, the optimal compromise solution has a sound balance between heat transfer and resistance performance. Additionally, for the optimal compromise solution, with an inlet velocity of 1.5 m/s and a heat flux of 200 W/cm2, the maximum and average temperature of the heated surface does not exceed 73 °C and 67 °C, respectively, and the total pressure drop is only 5.7 kPa.

Numerical studies on internal flow in pipelines of an aquaculture vessel and flow control using a special branch pipe

IntroductionRegarded as the world’s largest smart-aquaculture vessel so far, Guoxin No. 1, has achieved remarkable success in aim to develop large-scale cruising aquaculture platforms. Guoxin No. 1 is 816 feet long with 15 fish farming tanks, which has a tank capacity of up to 900,000 square feet. It is of great practical interest to study the pipe flow rate distribution involving oxygen and novel flow control schemes for internal flows of aquacultural facilities connecting fish farming tanks.MethodsIn this paper, three-dimensional numerical investigations on internal flow in a T-type pipeline and its flow control are carried out. A single pump is designed to convert water to two separate farming tanks through a pipeline system, which is composed of one main inlet pipe and two outlet pipes with the same diameter as that of the inlet pipe. A horizontal arrangement of the pipes, in which the flow rate of an outlet pipe must be half of the inflow rate, is firstly studied for validation. To guarantee a balanced oxygen supply, equilibrium outflow rates can be achieved as a consequence of using a branch with a smaller diameter installed on the main inlet pipe. 3-D unsteady RANS solvers were employed to simulate the incompressible viscous flow and the pipe walls were assumed as rigid bodies.ResultsA couple of flow rates and three pipe angles were then investigated to assess the change of the outflow rates. Based on the simulations, a flow control scheme was proposed including to optimize the central included angle between the main inlet pipe and the small branch pipe, and the inflow rate of the branch pipe in order to balance the outflow rates. The results show that the central included angle has a significant influence on the flow field and flow rate of the two outlet pipes.DiscussionIf the angle was fixed, it can be indicated that adjusting the flow rate of the branch inlet can be an efficient method to unify the flow rate of the outlet pipes and improve the water exchange among fish farming tanks.

Reproducibility of the computational fluid dynamic analysis of a cerebral aneurysm monitored over a decade

Computational fluid dynamics (CFD) simulations are increasingly utilised to evaluate intracranial aneurysm (IA) haemodynamics to aid in the prediction of morphological changes and rupture risk. However, these models vary and differences in published results warrant the investigation of IA-CFD reproducibility. This study aims to explore sources of intra-team variability and determine its impact on the aneurysm morphology and CFD parameters. A team of four operators were given six sets of magnetic resonance angiography data spanning a decade from one patient with a middle cerebral aneurysm. All operators were given the same protocol and software for model reconstruction and numerical analysis. The morphology and haemodynamics of the operator models were then compared. The segmentation, smoothing factor, inlet and outflow branch lengths were found to cause intra-team variability. There was 80% reproducibility in the time-averaged wall shear stress distribution among operators with the major difference attributed to the level of smoothing. Based on these findings, it was concluded that the clinical applicability of CFD simulations may be feasible if a standardised segmentation protocol is developed. Moreover, when analysing the aneurysm shape change over a decade, it was noted that the co-existence of positive and negative values of the wall shear stress divergence (WSSD) contributed to the growth of a daughter sac.

Validation of a novel numerical model to predict regionalized blood flow in the coronary arteries.

Ischaemic heart disease results from insufficient coronary blood flow. Direct measurement of absolute flow (mL/min) is feasible, but has not entered routine clinical practice in most catheterization laboratories. Interventional cardiologists, therefore, rely on surrogate markers of flow. Recently, we described a computational fluid dynamics (CFD) method for predicting flow that differentiates inlet, side branch, and outlet flows during angiography. In the current study, we evaluate a new method that regionalizes flow along the length of the artery. Three-dimensional coronary anatomy was reconstructed from angiograms from 20 patients with chronic coronary syndrome. All flows were computed using CFD by applying the pressure gradient to the reconstructed geometry. Side branch flow was modelled as a porous wall boundary. Side branch flow magnitude was based on morphometric scaling laws with two models: a homogeneous model with flow loss along the entire arterial length; and a regionalized model with flow proportional to local taper. Flow results were validated against invasive measurements of flow by continuous infusion thermodilution (Coroventis™, Abbott). Both methods quantified flow relative to the invasive measures: homogeneous (r 0.47, P 0.006; zero bias; 95% CI -168 to +168 mL/min); regionalized method (r 0.43, P 0.013; zero bias; 95% CI -175 to +175 mL/min). During angiography and pressure wire assessment, coronary flow can now be regionalized and differentiated at the inlet, outlet, and side branches. The effect of epicardial disease on agreement suggests the model may be best targeted at cases with a stenosis close to side branches.

Airflow distribution law of multi-branch pipe of pneumatic rice direct seeder based on dimensional analysis

In order to investigate the flow characteristics and distribution law of airflow in multi-branch pipe of pneumatic rice precision direct seeder and obtain the mathematical model between airflow parameters and pipe geometry structure. In this study, the airflow flow law of the multi-branch pipeline of the pneumatic system was studied, the mechanism of airflow flow in the multi-branch pipe was analyzed, and it was clarified that the main factors affecting the airflow flow in the pipe, namely, air density, air dynamic viscosity, the total flow rate of the inlet branch pipe, the length of the closed end of the header, the inner diameter of the outlet branch pipe, and the outlet branch pipe spacing. Numerical simulations were carried out using Fluent simulation software to elucidate the cause of multi-branch pipes of uneven distribution of airflow in multi-branch pipes, the empirical equation among these factors and the flow velocity of the outlet branch pipe are established by dimensional analysis method. The bench test results show that the established empirical equations are applicable in the following ranges: 0.018 m3/s≤Q≤0.054 m3/s, 0.045 m≤d≤0.05 m, 0.075 m≤L≤0.125 m, 0.7 m≤Y1≤0.875 m (0.5 m≤Y2≤0.75 m, 0.36 m≤Y3≤0.45 m), the prediction accuracy can be controlled within 10% of the empirical formula, which can provide a reference for the prediction and optimization design of outlet velocity of the multi-branch pipe. Keywords: pneumatic system, multi-branch pipe, axial momentum conservation, Fluent, dimensional analysis DOI: 10.25165/j.ijabe.20231601.7663 Citation: Qin W, Wang Z M, Zhang M H, He S Y, Wang X G, Jiang Y C, et al. Airflow distribution law of multi-branch pipe of pneumatic rice direct seeder based on dimensional analysis. Int J Agric & Biol Eng, 2023; 16(1): 111–127.

Mean Flow, Turbulent Structures, and SPOD Analysis of Thermal Mixing in a T-Junction with Variation of the Inlet Flow Profile

This paper investigates the effects of different inlet flow profiles on thermal mixing within a T-junction using CFD simulations with the IDDES-SST turbulence model. The different combinations of inlet flow profiles are related to different stage in the flow entry region. The effects of the inlet flow profile on the mean and transient flow behaviour are assessed, while a spectral proper orthogonal decomposition and power spectral density analysis are performed to assess the underlying flow structures and the predominant frequency modes. It is found that the vortical structures associated with the horseshoe and hovering vortex systems consist of a single roll-up vortex for cases with uniformly distributed boundary conditions (BCs) at the branch inlet whereas a double roll-up vortex is observed for the other cases. The double roll-up vortex enhances the mixing locally due to the entrainment of fluid from the branch pipe in these vortical structures, which then results in a lower mean temperature distribution. The appearance of the secondary vortex pair and the nested vortices is delayed for cases with uniformly distributed BCs at the branch inlet, which again results in lower thermal mixing and consequently higher values of mean temperature when compared with the other cases. It is also found that the vorticity related to the counter-rotating vortex pair as well as to the second pair of vortices rotating in the opposite direction is higher for cases with uniformly distributed BCs at the branch inlet. Lastly, the combinations of inlet flow profiles lead to different coherent structures, and the dominant frequencies are of a Strouhal number of around 0.7 for uniformly distributed profiles at the branch inlet and in the range 0.4–0.5 for the other cases.

Numerical modeling of sequential segmentation for enhancement of mixing inside microchannels

This study investigates sequential segmentation as an active mixing technique inside microchannels. In sequential segmentation, the solvent and anti-solvent streams are divided into segments in the axial direction. Due to the non-uniform velocity profile exhibited in laminar flow, Taylor-Aris dispersion can improve mixing by several orders of magnitude as compared with pure molecular diffusion. We built a 3D numerical model using COMSOL Multiphysics® to optimize this technique. We studied the effect of segmentation frequency, duty cycle (DC), flow velocity, microchannel aspect ratio and configuration of the inlet branches on the concentration distribution. We found that channel aspect ratio (H:W) and segmentation frequency had the most significant effect on mixing efficiency. Increasing segmentation frequency was found to increase the mixing efficiency up to a certain limit beyond which mixing efficiency decreased. This decrease was due to the non-complete segmentation of both streams at high frequencies and the formation of continuous trailing stream of both the solvent and anti-solvent. These trailing streams, which mitigate the segmentation effect, also appear in low aspect ratio (i.e. wider) channels and, therefore, reduces the mixing efficiency. Unequal mixing ratios were achievable by changing the segmentation duty cycle without changing the mixing efficiency considerably. Changing the flow velocity did not cause considerable changes in the mixing efficiency. Our 3D model confirms that sequential segmentation can considerably improve mixing inside microchannels and introduces the channel aspect ratio, for the first time, as an important parameter affecting the segmentation mixing efficiency.

Numerical studies of gas pull-through and liquid entrainment in gas–liquid flows through multi-branch manifolds

Flows of air–water and saturated steam–water mixtures in a horizontal cylindrical vessel with a single or several cylindrical outlets (branches) were investigated computationally using the volume of fluid (VOF) method to separate the phases and the delayed detached eddy simulation (DDES) model to simulate turbulence. The time-dependent gas–liquid interface was resolved and the vertical distance between the interface elevation and the branch inlet was determined. The computed critical elevations at the onsets of gas pull-through (OGP) and liquid entrainment (OLE) in single-branch vessels were found to be in fair agreement with experimental values under comparable conditions. Simulations of gas–liquid flows in manifolds with three branches also predicted successfully OGP and OLE in the different branches. As an example of the applicability of the present method, we investigated a problem of interest to the CANDU nuclear reactor safety analysis, namely, the discharge of fluid through a small break at the top of a header model with 12 other branches (feeders), focusing on its dependence on the inlet flow rates.

Flow characterization of various singularities in a real-scale ventilation network with rectangular ducts

Flow characterization in ventilation ducts is important for adequate modeling of contamination transfer. Turbulent flow through straight tubes with circular cross-section has been widely studied, but HVAC networks are quite unlike such ideal cases. Industrial ducts are of large scale, their sections can be rectangular, and they include many singularities (bends, T-junctions, reducers). The objective of this paper is to study the effect of such singularities on the flow in an industrial-scale rectangular ventilation network including over ten vertical and horizontal bends, one T-junction, a ventilation damper, and one section reducer, by performing experimental measurements and numerical simulations.Regarding bend flow, simulations of mean velocity profiles downstream of horizontal and vertical bends are validated on the experimental data. The analysis of the T-junction flow shows that this flow is a mix of bend and straight duct flows and probably depends on the flow distribution in the two inlet branches, as well as on the curvature radius of the T-junction. It is also observed experimentally that a deflector inserted inside a bend strongly impacts the velocity profiles up to 8Dh downstream. Experiments conducted on the impact of leakage in a closed ventilation damper show that this leakage flow cannot be ignored in the simulations. Measurements of the flow downstream of an open ventilation damper show significant variations in concentration homogeneity.These tests form an extensive database for flow measurements at industrial scale, useful for CFD validation, a necessary step before simulating gaseous and particulate flow in ventilation ducts.

Analysis of Environmental and Atmospheric Influences in the Use of SAR and Optical Imagery from Sentinel-1, Landsat-8, and Sentinel-2 in the Operational Monitoring of Reservoir Water Level

In this work, we aim to evaluate the feasibility and operational limitations of using Sentinel-1 synthetic aperture radar (SAR) data to monitor water levels in the Poço da Cruz reservoir from September 2016–September 2020, in the semi-arid region of northeast Brazil. To segment water/non-water features, SAR backscattering thresholding was carried out via the graphical interpretation of backscatter coefficient histograms. In addition, surrounding environmental effects on SAR polarization thresholds were investigated by applying wavelet analysis, and the Landsat-8 and Sentinel-2 normalized difference water index (NDWI) and modified normalized difference water index (MNDWI) were used to compare and discuss the SAR results. The assessment of the observed and estimated water levels showed that (i) SAR accuracy was equivalent to that of NDWI/Landsat-8; (ii) optical image accuracy outperformed SAR image accuracy in inlet branches, where the complexity of water features is higher; and (iii) VV polarization outperformed VH polarization. The results confirm that SAR images can be suitable for operational reservoir monitoring, offering a similar accuracy to that of multispectral indices. SAR threshold variations were strongly correlated to the normalized difference vegetation index (NDVI), the soil moisture variations in the reservoir depletion zone, and the prior precipitation quantities, which can be used as a proxy to predict cross-polarization (VH) and co-polarization (VV) thresholds. Our findings may improve the accuracy of the algorithms designed to automate the extraction of water levels using SAR data, either in isolation or combined with multispectral images.

Calculation of Hydrodynamic Parameters of the Apparatus of Shock-and-Vortex Action with a Regular Tubular Packing

An analysis of the operation of gas cleaning equipment for gas purification technological schemes, including apparatuses for carrying out a single process, combined apparatuses combining several zones for carrying out various processes, and an apparatus with autonomous irrigation circuits, has allowed developing the design of a two-stage apparatus of shock-vortex action with a regular tubular packing. As a result of the studies carried out for the apparatus’ packed zone, graphical dependences of the hydraulic resistance, the retained liquid amount and the layer’s gas content on the gas velocity and irrigation density, as well as the hydraulic resistance of the tubular bundle during the coolant movement inside the pipes, on the Reynolds number are obtained. In addition, the results of the studies of the hydraulic resistance of the gas-liquid impact zone, the inclined baffle, and the total hydraulic resistance depending on the gas velocity in the inlet branch pipe and the initial liquid level are obtained. Based on the research, a method for calculating hydrodynamic parameters is proposed, including equations for calculating the hydraulic resistance of the ejection zone, the gas flow exit zone from the central pipe, the packed zone and the apparatus as a whole, the retained liquid amount and the layer’s gas content. For this design of a tubular packing, when the coolant moves inside the pipes, equations are obtained for calculating the total hydraulic resistance of the tubular bundle, resistance due to friction, and local resistances.

Linear stability of flow in a 90° bend

This paper considers two-dimensional flow in a channel that consists of straight inlet and outlet branches and a circular 90° curved bend. An incompressible viscous fluid flows through the elbow under the action of a constant pressure gradient between the inlet and outlet. Navier–Stokes equations were solved numerically using a high-fidelity spectral/hp element method. In a range of Reynolds numbers, an adaptive selective frequency damping method was used to obtain steady-state flow. It was found that three separation bubbles and vortex shedding can exist in the bend. The modal stability of two- and three-dimensional perturbations was investigated. The critical Reynolds number of two-dimensional disturbances was found by extrapolation from lower Reynolds number results. It is much greater than the three-dimensional one, but the two-dimensional flow could be subcritically unstable with respect to the externally imposed small-amplitude white noise. For three-dimensional perturbations, the dependence of critical Reynolds numbers on the bending radius was obtained. For the case of a moderate bending radius, a neutral curve is provided and eigenfunctions are studied in detail. Three-dimensional instability can be caused by a periodic or monotonically growing mode, and these unstable modes relate to recirculation bubbles that occur after the bend.

The effect of inlet flow conditions upon thermal mixing and conjugate heat transfer within the wall of a T-Junction

This paper investigates the effects of different inlet velocity profiles on thermal mixing and conjugate heat transfer (CHT) within a T-junction. The flow domain is modelled using the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model implemented within the commercial CFD software STAR-CCM+ 2020.1.1. The thermal analysis of the solid domain is also addressed within the CFD simulations. The OECD/NEA-Vattenfall experimental benchmark database is used to validate the CFD model. The effect of mesh sensitivity within the CFD simulations is also studied qualitatively and quantitatively. The influence of different inlet flow profiles on the CFD simulations is then assessed. Different combinations of inlet flow profiles, uniformly distributed and fully developed, are considered. Compared to the flow profile at the main pipe inlet, the flow profile at the branch pipe inlet presents a much more significant effect on the mean temperature distribution downstream of the T-junction. It is found that the flat flow profile at the branch inlet causes a higher temperature at the top wall, therefore a larger temperature gradient, and may lead to higher thermal stresses due to thermal stratification. The temperature distribution is more uniform for cases with the fully developed flow profile at the branch inlet. The variance of temperature is high at the sides of the pipe, regardless of the velocity profile used. The combination of flat flow profiles at both inlets causes the highest temperature variance. Moreover, the regions of maximum variance of temperature are located at different positions along the pipe section, depending on the combinations of inlet flow profiles.