Inflow Velocity Research Articles

Numerical study on condensation heat transfer in vertical channel with hydrophilic-hydrophobic patterned surfaces

A numerical study was conducted of condensation phenomenon in a vertical channel with hydrophilic-hydrophobic patterned surfaces. The Volume of Fluid (VOF) method was adopted to detect the phase interface and the Lee's phase-change model was used. An Artificial Neural Network (ANN) model was constructed to predict the heat transfer coefficient using experimental data and model was used for the numerical validation. From the force balance around a liquid droplet, a theoretical relationship between the inflow velocity and the droplet movement angle was derived. The size, arrangement and angle of the pattern were considered as design variables, together with the channel height. The results showed that a decrease of the pattern size and increases of pattern angle and channel height caused heat transfer augmentation. In contrast, increased pressure drop was observed as the pattern size and the channel height decreased and the pattern angle increased. Bridging droplets in the channel were observed depending on the arrangement of patterns between two plates; surfaces with staggered patterns showed better performance. It was found that the thermal performance of the plate was highly influenced by the pattern angle, because of the performance of the condensate liquid removal.

Study on dynamic adsorption characteristics of gangue to heavy metals in goaf and its water purification mechanism under leaching condition

Arid and semi-arid mining areas in Western China are faced with the problems of water shortage, large water inflow of mines and high-salinity of mine water. When the broken gangue is backfilled to the goaf by the solid backfilling mining technology, a large number of voids between the blocks is generated, which can store groundwater and purify water quality. In this study, the real void structure of the gangue backfilling body in the goaf was obtained through CT scanning. By using the COMSOL numerical simulation software, a coupling model of Free and Porous Media Flow and Transport of Diluted Species in Porous Media was established. From the mesoscopic void scale, the effects of particle size distribution, inflow velocity and ion concentration on the flow field characteristics, ion migration and dynamic adsorption characteristics of gangue in the leaching column were explored, and the purification mechanism of broken gangue to heavy metals in mine water was revealed. The results show that: (1) The larger the gangue particle size gradation, the larger the void size, the higher the velocity in the void, and the more significant the average flow velocity difference between the void area and the gangue area. With the increase of inflow velocity, the average velocity in the gangue area and void area also increases, but the average flow velocity in the void area is 5.36 times that in the gangue area; (2) Both the larger particle size gradation of gangue, higher inflow velocity and inlet concentration can improve the velocity of the ion migration in gangue leaching column; (3) The greater the inlet concentration, the faster the flow velocity, the higher the total adsorption rate of gangue in the leaching column; (4) Both decreasing the particle size gradation of the gangue and increasing the inlet concentration can increase the total adsorption capacity of gangue in the leaching column; (5) The removal of heavy metals by gangue is the result of physical adsorption, ion exchange and other reactions. The research results can provide theoretical reference and data support for the treatment of high-salinity mine water in mining areas of Western China.

Prognostic value of right ventricular diastolic dysfunction in patients with inferior ST-elevated myocardial infarction

BackgroundRight ventricle infarction (RVI) is predominantly a complication of inferior wall myocardial infarction; it occurs in approximately one third of these patients. Right ventricular dysfunction in patients with inferior STEMI and RV infarction was under assessed. Nevertheless, studies which targeted RV assessment by echocardiography, did not routinely evaluate RV diastolic dysfunction. In this study, we aimed to evaluate RV diastolic dysfunction and its prognostic value in patients with inferior STEMI and RVI.ResultsSixty patients with inferior STEMI and RV infarction, who underwent primary PCI were enrolled in the study. Patients with pre-existing clinical conditions that might affect RV function, were excluded. Echocardiography was performed within twenty-four hours following the PCI, to assess the RV systolic and diastolic functions with special focus on tricuspid inflow velocities (E velocity, A velocity and E/A ratio) by pulsed wave (PW) doppler and tricuspid annular velocities by tissue doppler index (TDI) (E′, A′ and E/E′ ratio). Clinical features and MACE, including cardiogenic shock, arrhythmia, stroke, reinfarction and death were analyzed in all our patients within 3 months follow up period. The average age of the study population was 51.58 ± 10.11 years, 10% were females. Five patients developed MACE (death, cardiogenic shock and pulmonary edema, anterior STEMI and cardiogenic shock, recurrent inferior STEMI, and arrhythmia and stroke), of whom four occurred in hospital within the first 48 h. Patients who developed MACE had high filling pressures, as all of them had E/E′ > 6. E′ velocity ≤ 6 cm/sec was associated with increased MACE as 25% of patients with E′ velocity ≤ 6 had MACE compared with 2.3% of patients with E′ velocity > 6 with a p value of 0.015.ConclusionsTricuspid annular velocities by TDI are essential when evaluating RV diastolic dysfunction. E/E′ and E′ velocity have a prognostic value in patients with inferior STEMI and RV infarction; E/E′ > 6 and E′ velocity ≤ 6 cm/sec were associated more MACE in patients with inferior STEMI and RVI.

대형 비행갑판을 갖는 함정과 풍동시험 결과를 활용한 고신뢰도 함정 Airwake 예측

Developing high-fidelity Computational Fluid Dynamics (CFD) simulation methods used to evaluate the airwake characteristics along a flight deck of a large ship, the various kind of data such as actual ship measurement and wind tunnel results are required to verify the accuracy of CFD simulation. Inflow velocity profile at the bow, local unsteady flow field data around the flight deck, and highly reliable wind tunnel data which were measured after reviewing Atmospheric Boundary Layer (ABL) simulation and Reynolds Number effects were also used to determine the key parameters such as turbulence model, time resolution and accuracy, grid resolution and type, inflow condition, domain size, simulation length, and so on in STAR CCM+. Velocity ratio and turbulent intensity difference between Full-scale CFD and actual ship measurement at the measurement points show less than 2% and 1.7% respectively. And differences in velocity ratio and turbulence intensity between wind tunnel test and small-scale CFD are both less than 2.2%. Based upon this fact, the selected parameters in CFD simulation are highly reliable for a specific wind condition.

Study on fast prediction method of hydrodynamic load of floating horizontal axis tidal current turbine with pitching motion under free surface

The floating horizontal-axis tidal current turbine (HATCT) moves with the floating carrier while rotating, resulting in a change in its relative inflow velocity at any time. If the rotating speed of the HATCT is fixed, the HATCT cannot work at the optimum tip speed ratio, resulting in the failure to achieve the optimum power generation efficiency. Therefore, this paper proposes a control strategy for the rotating speed of the HATCT, and obtains the hydrodynamic loads of the HATCT with variable speed rotation and pitching motion under free surface conditions based on the CFD method. Compared with the hydrodynamic load of the HATCT under the same situation but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATCT, but the load fluctuation in terms of the inflow direction load, power, and pitch moment coefficients are more significant than those with fixed speed control. On this basis, according to the variation law of the damping coefficient with pitch period, pitch amplitude, and tip speed ratio, the hydrodynamic load prediction method of the HATCT with pitching motion is established. The validity of this prediction method is verified by comparing the results with those of CFD calculation.

On wake dynamics of a propeller operating under nonuniform behind-hull condition

The wake dynamics of the benchmark propeller INSEAN E779A operating in the nonuniform wake of a typical ship hull are investigated with large-eddy simulations. The flow features and evolution of vortex structures in the propeller wake are analyzed to evaluate the influences of the nonuniform inflow and to identify the instability mechanisms. Unlike the uniform inflow condition, the azimuthal-variant inflow velocity field results in an asymmetric and faster destabilization of the wake. Local mutual interaction among the neighboring tip vortices in the upper region of the wake, which shows a unique bridging-reconnection mechanism of vortex filaments, initiates the decomposition and destabilization of tip vortices and induces instability in the hub vortex. The power spectrum density (PSD) of kinetic energy is employed to analyze the transition characteristics of the tip vortices quantitatively. The hub vortex core circularity and trajectory envelope are calculated to quantify the long- and short-wave instabilities.

An insight on the physical mechanisms responsible of power augmentation in a pair of counter-rotating Darrieus turbines

In recent years, Darrieus turbines have received increasing attention by both the industrial and the academic sector due to their advantages for both wind and hydrokinetic applications. Experimental and numerical investigations showed that the interaction between closely spaced Darrieus rotors can lead to a significant increase in their efficiency. To date, however, the physics underlying this phenomenon has been only argued or qualitatively discussed, since no robust method to determine the actual angle of attack was available.This study provides a novel insight into the physical mechanisms that lead to performance enhancement in twin Darrieus rotors. A pair of counter-rotating, two-blade Darrieus hydrokinetic turbines are investigated while spinning in both the revolution senses, namely, inward and outward, by means of unsteady Computational Fluid Dynamics. After a preliminary analysis on the effect of rotor spacing, an improved flow sampling method is used to analyze the instantaneous flow kinematics past the blades in combination with computed blade loads, thus allowing the calculation of lift and drag forces. Results show that the optimum center-to-center distance for the turbines under consideration is 2D. Also, it is shown that the optimum operating point of the twin rotors tends to shift toward higher Tip-Speed Ratios (TSRs). Compared to the stand-alone turbine, the efficiency improves by 16.1% and 8.7% for the inward and outward twin rotors setups, respectively. A detailed study of the local flow field shows a complete suppression of the streamtube expansion within the area of mutual interactions between the adjacent rotors. This allows more momentum flux to enter the rotor area compared to that of the isolated rotor. More interestingly, it is observed that the change in the inflow velocity direction leads to an increase in the angle of attack for both the inward and outward setups, causing an increase in the generated lift, which is found as the main reason for the efficiency improvement.

Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed

This study investigates the interaction between a premixed methane-air flame and particles inside a model packed bed. The opacity of the spherical packed beds to visible light poses a major barrier to the implementation of highly resolved optical diagnostics, so that no detailed experimental data were so far available for the validation of numerical simulation. Here, a two-dimensional cylindrical packed bed design is set up, which enables direct line-of-sight optical measurements without loss of spatial resolution over the fluid region between the particles. In this study, the case of cold metallic cylindrical particles (T = 377 K) relevant to start-up of a reactor is investigated using internal particle cooling, which also allows cylinder specific heat transfer rate measurements by differential temperature measurements on the coolant streams. The two dimensional assumption is first verified by measuring the inflow velocity and cylinder temperature profile along the cylinders. Chemiluminescence imaging is then performed using a telecentric lens to observe the position and geometry of the two-dimensional flame front with respect to the surrounding cylinders without loss of resolution. Simultaneously, the cylinder-specific flame to cylinder heat transfer rates and cylinder surface temperature are measured. As the flame is closely surrounded by the three cooled cylinders, intense heat transfer is observed in this region corresponding to 25 ± 2.5% of the flame thermal power. Flames were stabilised at different positions depending on inflow velocity and equivalence ratio, and a direct correlation between flame to cylinder stand-off distance and the heat transfer rate normalised to the flame thermal power was found for both top and side cylinders. Also, sidewall quenching distances to the curved cylinder surfaces were evaluated, and seem to be influenced by the presence of a warm recirculation zone behind the cylinders. This investigation provides fully resolved flame front position and heat transfer rates for a known geometry and cylinder thermal boundary conditions, and provides validation data for numerical simulations of this high flame particle coupling case.

A Comprehensive Echocardiographic Assessment of Neonatal Right Ventricular Function in Neonatal Intensive Care Unit Babies.

Background The right ventricle (RV) in the fetus is the predominant chamber, accounting for about 60% of the total cardiac output. The majority of the RV outflow volume is diverted from the pulmonary artery via the ductus arteriosus to the descending aorta. After birth, the RV undergoes extensive structural and functional modifications. The RV undergoes an improper transition from fetal to neonatal circulation in sick neonatal intensive care unit (NICU) babies. Functional echocardiography is now commonly being used in most NICUs as it is a noninvasive and bedside investigation that gives an immediate evaluation of hemodynamics and can be taken into consideration as an extension of clinical assessment to study a critically unwell neonate. Therefore, a study of RV functions in NICU neonates will help in better understanding the neonatal cardiopulmonary response to different diseases. Thus, this study aimed to assess RV functions in neonates getting admitted to the NICU of a tertiary care institute. Methodology This observational, cross-sectional study was approved by the Research & Recognition Committee of Dr. D. Y. Patil Vidyapeeth, Pune. In total, 35 cases of term neonates admitted to the NICU at Dr. D. Y. Patil Medical College, Hospital & Research Centre, Pune who fulfilled the inclusion criteria were enrolled in this study after obtaining consent from their parents. Two-dimensional echocardiography was performed by a trained pediatric cardiologist, and the findings were substantiated by a neonatologist trained in echocardiography. Results Our study found a strong associationbetween tricuspid inflow velocity and neonates with sepsis. Similarly, a significant association was observed betweenabnormal tricuspid Inflow velocity (E/A and E/E')andneonates requiring inotropic support. Conclusions Data on the normal values of different echocardiographic parameters of the systolic and diastolic function of the RV during the neonatal phase of life are currently limited. Our data offer preliminary insights into this topic. Early echocardiography and intervention are advisable, especially in neonates with sepsis and requiring inotropic support.

Leading edge erosion detection for a wind turbine blade using far-field aerodynamic noise

In this paper, the feasibility of using far-field acoustic measurements as a non-contact monitoring technique for wind turbine blade leading edge erosion is assessed. For this purpose, a DU96 W180 airfoil with several eroded leading edge configurations of different severities is experimentally investigated. The eroded leading edges are designed with pits, gouges and coating delamination scaled from a real eroded blade. To assess the feasibility of the technique in quasi-realistic configurations, experiments are carried out under clean and turbulent inflow conditions. Acoustic measurements are performed with a phased microphone array. In the absence of inflow turbulence, because of the low Reynolds number at which the experiments are carried out, the case with minor erosion severity shows similar far-field noise spectra as the clean leading-edge cases, i.e., the presence of tonal peaks caused by laminar boundary layer instability noise through a self-sustained feedback loop but with higher tonal amplitudes. Increasing the damage level (considered as moderate erosion), the spectra of the noise scattered from the suction side show that the tonal peaks shift to higher frequencies and have lower amplitudes, thus suggesting that the damage alters the flow features responsible for the acoustic feedback loop; whereas, the spectra from the pressure side show a broadband noise distribution. For heavy erosion, the far-field noise spectra show broadband features from both airfoil sides, thus suggesting that the damage has fully forced the transition to turbulent flow; in which case, an increase in the low-frequency content is observed. Conversely, in the presence of turbulent inflow, when comparing the noise scattered at the trailing edge, no difference is found. However, leading edge impingement noise decreases at medium–high frequency compared with the baseline case at a chord-length-based Strouhal number StC∼10. The experimental results also suggest that the delamination feature is the one which is the most easily detectable and the approach is valid for a wide range of angles of attack and inflow velocity.

Numerical study on unsteady propeller exciting characteristics considering shafting whirling vibration effect

In this paper, the unsteady exciting characteristics of a marine propeller influenced by the shafting whirling vibration effect are numerically studied by employing the dynamic sliding multi-region method and a Reynolds-averaged Navier–Stokes equation model. The propeller and shafting system inevitably vibrates during operation, where the multiple exciting forces can cause the shafting to rotate and whirl around different center lines at the same time, which is usually ignored in former studies on propeller exciting characteristics. To represent the complex whirling motion of the propeller, it is defined as a combination of revolution around its theoretical center line and rotation around its real center line. Firstly, a model for predicting the unsteady propeller exciting characteristics under different whirling motions is established, and an experiment of propeller transient forces is designed to validate the numerical model. Secondly, the influence mechanism of different whirling motions on the propeller exciting characteristics and propeller velocity field fluctuation are studied. Due to periodic fluctuation of the inflow velocity influenced by whirling, the propeller exciting fluctuates periodically. The linear relationship between propeller exciting and whirling amplitudes is found in the CFD and experimental results, which is caused by the linear increase of inflow velocity fluctuation amplitudes.

An analytical double-Gaussian wake model of ducted horizontal-axis tidal turbine

The wake development of a tidal turbine should be fully considered in the array arrangement. There are many studies on wake characteristics, mainly focusing on a conventional horizontal-axis turbine, while a ducted turbine has attracted little attention. This paper investigates the wake characteristic of a ducted turbine using flume experiments and large eddy simulations. An analytical wake model of the ducted turbine is proposed and verified by the wake profile under different inflow velocities and the downstream turbine performance under different tandem arrangements. The results show that a ducted turbine wake still maintains a high self-similarity, and the wake profile is approximately the double-Gaussian curve. Compared with a conventional tidal turbine, a ducted turbine has a faster wake recovery speed, but a larger radial influence range. Therefore, ducted turbine arrays should be configured with wider radial distances and shorter axial distances.

Thermal performance analysis of a counter-flow double-pipe heat exchanger using titanium oxide and zinc oxide nanofluids

In a nanofluid, metals, oxides, or carbides with a diameter of less than 20 nm are combined as one with a base liquid, like water or an oil. Many examinations have recently been completed to inspect the effect of nanofluid on the speed increase of heat transfer rates in various heat exchangers. Heat transfer improvement using nanofluid is dependent on a variety of factors, among them the kind of nanoparticles, their size, shape, and concentration in the base fluid. The proposed article is aimed to study experimentally how a twin-pipe heat exchanger with counter-flow arrangements and two kinds of nanofluid cooling fluid performed. Zinc oxide (ZnO) and titanium oxide (TiO2) are used as base fluids with ethylene glycol (EG) and alkaline water. This study looked at the heat transfer capabilities of a two-pipe heat exchanger with a counter-flow configuration when various quantities of TiO2 and ZnO nanoparticles were combined with EG alkaline water. Alkaline water and nanofluid nanoparticle volume concentrations were 0.5, 0.75, and 1.25. The constant intake temperatures of 60 °C for water and 30 °C for nanofluid in a heat exchanger result in two fluids running at a constant inflow velocity. It was found that nanofluid had higher heat absorption at low flow rates than EG alkaline water and hence improved heat exchanger thermal performance. It was also noticed that when the concentration of nanoparticles increases, the heat transmission rate increases.

Effect on cardiac function among patients with type 2 diabetes following high-dose mineralocorticoid receptor antagonist using echocardiography; data from the MIRAD randomized clinical trial

BackgroundEarly heart failure prevention is central in patients with type 2 diabetes, and mineralocorticoid receptor antagonists (MRAs) have shown to improve prognosis. We investigated the effect of high-dose MRA, eplerenone, on cardiac function and structure in patients with type 2 diabetes and established or increased risk of cardiovascular disease but without heart failure.MethodsIn the current randomized, placebo-controlled clinical trial, 140 patients with high-risk type 2 diabetes were randomized to high-dose eplerenone (100–200 mg daily) or placebo as add-on to standard care for 26 weeks. Left ventricular systolic and diastolic function, indexed left ventricular mass (LVMi), and global longitudinal strain (GLS) were assessed using echocardiography at baseline and after 26 weeks of treatment.ResultsOf the included patients, 138 (99%) had an echocardiography performed at least once. Baseline early diastolic in-flow velocity (E-wave) indexed by mitral annulus velocity (e’) was mean (SD) 11.1 (0.5), with 31% of patients reaching above 12. No effect of treatment on diastolic function was observed measured by E/e’ (0.0, 95%CI [-1.2 to 1.2], P = 0.992) or E/A (-0.1, 95%CI [-0.2 to 0.0], P = 0.191). Mean left ventricular ejection fraction (LVEF) at baseline was 59.0% (8.0). No improvement in systolic function was observed when comparing groups after 26 weeks (LVEF: 0.9, 95%CI [-1.1 to 2.8], P = 0.382; GLS: -0.4%, 95%CI [-1.5 to 0.6], P = 0.422), nor in LVMi (-3.8 g/m2 95%CI [-10.2 to 2.7], P = 0.246).ConclusionIn the present echo sub-study, no change in left ventricular function was observed following high-dose MRA therapy in patients with type 2 diabetes when evaluated by conventional echocardiography.Trial registrationDate of registration 25/08/2015 (EudraCT number: 2015–002,519-14).

Statistical analysis of the relationship between Power spectral density of magnetic turbulence and ion velocity in magnetotail bursty bulk Flows

Based on the observation of the THEMIS satellites, we utilize the superposed epoch method to statistically analyze how the p (Power Spectral Density) of compressional and transverse components of the magnetic field is affected by the ion inflow velocity V⊥ which is the peak velocity of BBFs (Bursty Bulk Flows). The analysis demonstrated that a modified scaling relationship p=C0V⊥γflog10C1V⊥χ is more suitable to describe the relationship than p∝f-α. The constant values of C0, γ, C1 and χ vary over the considered frequency ranges, velocity intervals, and components of magnetic field. These illustrate that in the study of turbulence the characteristic spectral index is incomplete to describe the energy cascade process, and the velocity is a key parameter in the study of the magnetotail plasma sheet turbulence.

Numerical Simulation of Ice Crystal Trajectory and Its Influencing Factors Based on Lagrangian Method

Ice crystals are one of the important factors causing aircraft icing, and icing prediction is a major problem in the aviation field. The calculation of ice crystal trajectory is a precondition of the accurate simulation of ice accretion. In this paper, an ice crystal trajectory simulation method based on the Lagrangian method is proposed, and the effects of various parameters on the calculation results are discussed. Control equations of the ice crystal motion trajectory were established, and the solution methods of the equations are given. The method was used to calculate the ice crystal motion characteristics under various conditions, and the calculation results were compared with experimental results and reference results, to verify the correctness of the method. The effects of different particle densities, drag coefficient models, ice crystal diameters, inflow velocities, and angles of attack on the ice crystal collection coefficient were studied. The results showed that the smaller the particle density, the smaller the collection coefficient; the collection coefficient increases with the increase of ice crystal diameter and inflow velocity.

Optimization Study of Marine Energy Harvesting from Vortex-Induced Vibration Using a Response-Surface Method

Vortex-induced vibration (VIV) of bluff bodies is one type of flow-induced vibration phenomenon, and the possibility of using it to harvest hydrokinetic energy from marine currents has recently been revealed. To develop an optimal harvester, various parameters such as mass ratio, structural stiffness, and inflow velocity need to be explored, resulting in a large number of test cases. This study primarily aims to examine the validity of a parameter optimization approach to maximize the energy capture efficiency using VIV. The Box–Behnken design response-surface method (RSM-BBD) applied in the present study, for an optimization purpose, allows for us to efficiently explore these parameters, consequently reducing the number of experiments. The proper combinations of these operating variables were then identified in this regard. Within this algorithm, the spring stiffness, the reduced velocity, and the vibrator diameter are set as level factors. Correspondingly, the energy conversion efficiency was taken as the observed value of the target. The predicted results were validated by comparing the optimized parameters to values collected from the literature, as well as to our simulations using a computational-fluid dynamics (CFD) model. Generally, the optimal operating conditions predicted using the response-surface method agreed well with those simulated using our CFD model. The number of experiments was successfully reduced somewhat, and the operating conditions that lead to the highest efficiency of energy harvesting using VIV were determined.

Numerical study of the vortex-induced vibration of a riser taking into account the variation of the tension

ABSTRACT Previous studies of the marine riser VIV have primarily considered the constant values of the tension, but limited work has been done to consider the variations of the tension with riser vibrations. In addition, previous studies have mainly focused on the effect of the inflow velocity profile on a riser VIV, while a study of a riser VIV at a wide range of velocities is still lacking. This study presents a model that can take into account the variation of the tension with riser vibrations. The VIV characteristics of the riser were investigated based on the fluid-structure coupling methods. It is shown that the model that takes into account the variation of the tension is able to accurately capture the bimodal character of the amplitude-ratio curve and the vortex shedding pattern, and to calculate the vibration frequencies accurately.

Simulation of Particulate Matter Structure Detachment from Surfaces of Wall-Flow Filters for Elevated Velocities Applying Lattice Boltzmann Methods

Rearrangement events in wall-flow filters lead to the formation of specific deposition patterns, which affect a filter’s pressure drop, its loading capacity and the separation efficiency. A universal and consistent formulation of probable causes and influence factors does not exist and appropriate calculation models that enable a quantification of respective influence factors are missing. In this work, a previously developed lattice Boltzmann method, which has been used with inflow velocities of up to 2 m s−1, is applied to elevated velocities of up to 60 m s−1. The particle-free flow, a single layer fragment and a deposition layer during break-up are investigated as three different scenarios. One goal of this work is a comprehensive quantification of the stability and accuracy of both particle-free and particle-including flows, considering static, impermeable deposition-layer fragments. A second goal is the determination of the hydrodynamic surface forces and the deduction of the local detachment likelihood of individual layer fragments. Satisfactory stability and accuracy can be shown for fluid velocity, fluid pressure and the hydrodynamic forces. When considering layer fragments, the parameter domain turns out to be limited to inflow velocities of 28 m s−1. It is shown that fragment detachment rather occurs consecutively and regions of no possible detachment are identified. The work contributes to an understanding of rearrangement events and respective deposition pattern predictions and enables potential optimizations in engine performance, fuel consumption and the service life of wall-flow filters.

Pore-scale numerical simulation and LTNE analysis for fully-developed forced convective heat transfer in packed beds of mono-sized rough spheres covering near-wall and core regions

This work presents a novel method to acquire the effective convection heat transfer coefficients on the interfaces of wall-fluid contacts and sphere-fluid in both the near-wall region and core region of sphere-packed beds. Pore-scale numerical simulations are first conducted for different porosities pertaining to two regular body-centered cubic and face-centered cubic packings, packing lattice angles, inflow velocities, and ratios of the thermal conductivities of the solid and fluid. A finite-thickness metal reactor wall is included in the pore-scale simulation to make the heating boundary conditions more realistic. The outer surface of the metal wall is subjected to a uniform heat flux. The heat then passes through the metal wall and dispenses into the solid and liquid phases of the packed bed through the wall-sphere and the wall-fluid interfaces at the inner wall according to the physical mechanisms. Within the reactor, the heat transfer mechanism is separately considered in the near-wall region and the core region due to the intrinsic differences in the flow pattern. For each packing, different inflow angles are examined and exhibit different flow patterns and heat transfer performances. After the whole domain is hydrodynamically and thermally fully-developed, the local effective convection heat transfer coefficients can then be calculated. These coefficients reflect the realistic local convection either on the reactor wall or on the sphere-fluid interface. These convection heat transfer coefficients, along with the effective solid thermal conductivity through the contacting spheres obtained in our previous work, are implanted into a modified two-equation LTNE model. This modified LTNE model yields linear longitudinal fully-developed temperature distributions within the reactor having discrepancies in the temperature slopes less than ±10% from those by the pore-scale numerical simulations. In contrast, the conventional model even fails to reach linear distributions of the solid- and liquid-phase temperatures, which are expected for fully-developed packed-bed flows.