Impingement Conditions Research Articles

Experimental study and newly proposed correlations for maximum ceiling gas temperature rise in tunnel fires with natural ventilation

As a critical factor in tunnel fire safety, previous research on model predictions of the maximum ceiling gas temperature rise under natural ventilation has not demonstrated consistent results. These discrepancies are commonly attributed to variations in tunnel dimensions and materials. To address this issue, an experimental investigation utilizing heptane pool fires with different dimensions was conducted in a model-scale tunnel. The results show that the burning rate increases with an increasing aspect ratio of the fire source for the selected diameter range of 0.078–0.169 m. The flame length was characterized using a modified diameter of the fire source considering the air entrainment, and found that the non-dimensional flame length is 2.4 times the 2/5th power of the non-dimensional heat release rate. Finally, incorporating the concept of flame virtual origin, two different forms of correlations were developed to quantify the maximum ceiling gas temperature rise under different impingement conditions of the fire plume, and the coefficients were determined as 0.065 and 0.215 by numerous experimental results from different studies. The newly proposed models demonstrate good applicability to the fire sources with different dimensions, especially for the rectangular fire source with a large aspect ratio, thus solving the problem of insufficient accuracy of classical models under this condition.

The Effects of Mulligan Technique and Ultrasound on Pain and Functional Ability in Shoulder Impingement Condition at EMC Sentul Hospital

Shoulder impingement is a painful shoulder condition caused by injuries to the structures in the subacromial space. The research aims to analyze the effects of the Mulligan Technique and Ultrasound on pain and functional ability in shoulder impingement conditions at EMC Sentul Hospital. The research method used is a quasi-experimental design with pre and post-test control groups. Thirty participants were divided into two groups: an intervention group receiving the Mulligan Technique and Ultrasound (15 participants) and a control group receiving TENS and conventional exercise therapy (15 participants). Each participant underwent six sessions per week, twice a week. Before and after the treatment, each participant's pain level was measured using the Numeric Rating Scale (NRS), and functional ability was assessed using the Shoulder Pain and Disability Index (SPADI). The analysis of the data showed that both treatments in the two groups reduced pain and improved functional ability in shoulder impingement conditions. However, there was a significant difference in the group receiving the Mulligan Technique and Ultrasound, with an average pain reduction from 6.6 NRS to 1.3 NRS and an increase in functional ability from 62.6% to 11.85%. The group receiving TENS and conventional exercise therapy showed an average pain reduction from 3.6 NRS to 6.13 NRS and an increase in functional ability from 61.3% to 40.2%. In conclusion, the study suggests that the application of the Mulligan Technique and Ultrasound is more effective in reducing pain and improving functional abil-ity compared to TENS and conventional exercise therapy in shoulder impingement conditions.

Development of Two-Color pyrometry for flame impingement on oxidized metal surfaces

Measuring the temperature on a metal surface exposed to flame impingement is valuable for studying heat transfer. In this study, a non-intrusive two-color pyrometry was developed. It utilized visible light cameras to measure the two-dimensional temperature distribution on different metal surfaces. The experiment involved measuring the temperature distribution of metals (stainless steel, titanium, molybdenum) ranging from 700 °C to 1200 °C under flame impingement conditions. Thermocouple measurements were used as a reference for accuracy and uncertainty assessment. Two monochrome visible-light cameras equipped with optical filters at wavelengths of 750 nm and 905 nm captured different signal intensities corresponding to relative radiation temperatures. Calibration using a black body furnace at multiple temperature points was performed to enhance measurement accuracy. The variation in correction factor was assessed for shutter speeds ranging from 0.01 s to 0.03 s. An uncertainty analysis accounted for factors such as the grey body assumption, monochromatic wavelength assumption, and thermal radiation sources, and the respective uncertainties for these factors were 4.72 %, 2.5 %, and 1.02 %. Despite the presence of severe oxidation layers on the surfaces being measured, the two-color pyrometer successfully detected surface temperatures within an acceptable margin of error; the maximum relative error between the pyrometer and thermocouples was less than 4 %. This paper presents a technique for measuring temperature that produces a two-dimensional temperature distribution. Additionally, this method mitigates the effects of changes in surface emissivity due to temperature or materials.

In Vitro Wear of a Novel Vitamin E Crosslinked Polyethylene Lumbar Total Joint Replacement.

A novel, lumbar total joint replacement (TJR) design has been developed to treat degeneration across all three columns of the lumbar spine (anterior, middle, and posterior columns). Thus far, there has been no in vitro studies that establish the preclinical safety profile of the vitamin E-stabilized highly crosslinked polyethylene (VE-HXLPE) lumbar TJR relative to historical lumbar anterior disc replacement for the known risks of wear and impingement faced by all motion preserving designs for the lumbar spine. In this study we asked, (1) what is the wear performance of the VE-HXLPE lumbar TJR under ideal, clean conditions? (2) Is the wear performance of VE-HXLPE in lumbar TJR sensitive to more aggressive, abrasive conditions? (3) How does the VE-HXLPE lumbar TJR perform under impingement conditions? A lumbar TJR with bilateral VE-HXLPE superior bearings and CoCr inferior bearings was evaluated under clean, impingement, and abrasive conditions. Clean and abrasive testing were guided by ISO 18192-1 and impingement was assessed as per ASTM F3295. For abrasive testing, CoCr components were scratched to simulate in vivo abrasion. The devices were tested for 10 million cycles (MC) under clean conditions, 5 MC under abrasion, and 1 MC under impingement. Wear rates under clean and abrasive conditions were 1.2 ± 0.5 and 1.1 ± 0.6 mg/MC, respectively. The VE-HXLPE components demonstrated evidence of burnishing and multidirectional microscratching consistent with microabrasive conditions with the cobalt chromium spherical counterfaces. Under impingement, the wear rates ranged between 1.7 ± 1.1 (smallest size) and 3.9 ± 1.1 mg/MC (largest size). No functional or mechanical failure was observed across any of the wear modes. Overall, we found that that a VE-HXLPE-on-CoCr lumbar total joint replacement design met or exceeded the benchmarks established by traditional anterior disc replacements, with wear rates previously reported in the literature ranging between 1 and 15 mg/MC. The potential clinical benefits of this novel TJR design, which avoids long-term facet complications through facet removal with a posterior approach, were found to be balanced by the in vitro tribological performance of the VE-HXLPE bearings. Our encouraging in vitro findings have supported initiating an FDA-regulated clinical trial for the design which is currently under way.

Machine learning regression tools for erosion prediction of WC-10Co4Cr thermal spray coating

The prediction of erosion in WC-10Co4Cr thermal spray coating is predicted using regression machine learning technique. A pot tester helped to examine the erosion rate of WC-10Co4Cr thermal spray coatings. WC-10Co4Cr thermal spray powder was sprayed onto the SS316L steel. Different impingement conditions (30, 45, and 60°) were tested by using textures designed to simulate erosion. The collected data is used to construct a robust Gaussian Process Regression (GPR) model. The projected values are compared to the actual values obtained via experimentation. To further demonstrate the accuracy of the suggested model, the produced model is compared to various state-of-the-art machine learning methods. The GPR outperforms more commonplace methods of other regression techniques like decision trees, Ensemble boosted trees, and linear regression models. The erosion of coated and bare SS316L austenitic steel was effectively predicted using a GPR model.

A two-dimensional model for jet splashing rainfall intensity distribution in dam discharge based on laboratory experiments

Flood discharge atomization is a phenomenon of water droplets and mist diffusion caused by dam discharge, which brings heavy rainfall around the dam. The unnatural rainfall is harmful to the safe operation of hydropower stations and the stability of slopes. Jet splashing is the most important factor in the formation of flood discharge atomization. The splashing rainfall intensity and diffusion region are highly dependent on the jet impingement conditions. In this study, a two-dimensional splashing model is derived that describes the splashing rainfall distribution when a jet impinges on a plunge pool surface in terms of the jet impingement conditions. Given the close relationship between the splashing rainfall intensity distribution and the motion trajectories of droplets, it is hypothesized that certain droplet trajectories can accurately represent the distribution of rainfall intensity. The characteristic ejection angle of splashing droplets and the splashing diffusion coefficient are introduced to estimate the characteristic trajectories of droplets. Experimental data from laboratory tests are used to estimate the parameters of the splashing model. The current predictions are compared with the data from laboratory tests and prototype observations. The results suggest that the model accurately predicts the relative rainfall intensity at the upper region of the predicted curves, which corresponds to approximately 1/10 of the total height of the ideal parabola.

Touchdown dynamics of a liquid droplet on a patterned substrate: A generalized lumped parameter-based model

Droplet dynamics post-impingement on a solid surface is of immense technological importance due to its applicability in self-cleaning, anti-frosting, anti-biofouling, anti-icing, thermal management, and inkjet printing. While sustained droplet oscillation is desirable in some applications, a fast seizure of oscillations after the surface touchdown of the droplets is necessary for others. The post-impingement dynamics is a complex non-linear interaction of the fluid and solid properties and a common framework to characterize the short-time response of a droplet is provided here. We describe these post-impact droplet dynamics on a patterned surface in terms of lumped simple harmonic oscillator parameters. We delineate the effect of the substrate and fluid properties and attribute the same to one or more terms in the dynamical model of the oscillator, describing an analogy between the terms. Our analogy gives a universal mapping between the fluid–solid parameters and droplet dynamics, making it feasible to predict with accuracy the post-impact behavior. Here for the first time, we developed a simplified universal approach to predict the droplet oscillation dynamics impacting any solid surface for a broad range of fluid and solid properties and impingement conditions.

Development, characterization, and cavitation erosion analysis of high velocity oxy-fuel (HVOF) sprayed TiC and (70Cu-30Ni)-Cr based composite coatings on SS316 steel

A novel composite coating was developed by depositing powders of Titanium Carbide (TiC) with Cupronickel (70Cu-30Ni) and Chromium (Cr) as binders onto SS316 steel specimens using the High Velocity Oxy Fuel (HVOF) process. The developed coatings were characterized using Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM), and their surface hardness, surface roughness, and porosity were evaluated. The cavitation erosion resistance of the coated and uncoated specimens was tested using a High Stream Water Jet Rig under varying impingement conditions. Coating with TiC+ 50% (70Cu-30Ni)-Cr exhibited better resistance to induced pressure waves than any other proportion of coatings, due to their intermediate hardness and better damping effect. Further, a mixed mode of failure was observed in the TiC+ 50%(70Cu-30Ni)-Cr coating.

SUPPORT VECTOR MACHINE LEARNING ON SLURRY EROSION CHARACTERISTICS ANALYSIS OF Ni- AND Co-ALLOY COATINGS

In this paper, a novel support vector machine (SVM) learning approach has been used to predict the silt erosion of coatings sprayed by the high-velocity oxy-fuel (HVOF) process. The silt erosion resistance of HVOF-coated Co- and Ni-alloys is studied using an erosion tester. Both of these spraying powders were deposited on the 18Cr-12Ni-2Mo austenitic steel substrate. For the erosion experiments, the fixtures were developed to test the erosion characteristics at different impingement conditions (i.e. [Formula: see text], [Formula: see text], and [Formula: see text]). The image processing technique enables an understanding of the erosion mechanisms of coatings. The support vector regression is more effective than the traditional regression models. The proposed model employs support vector regression with parameter tuning. The ideal parameters are selected with the help of the grid search method. The model is trained by supplying 70% data and validated with 15% data. Afterward, the remaining 15% is given to the prepared model as testing data. The dataset obtained is employed for building an effective support vector regression model. The predicted results are compared against the original experimental values. The developed model is also compared with other state-of-the-art machine learning techniques for showing the preciseness of the proposed model. The Ni-based HVOF coating showed superior performance ([Formula: see text]) better than the Co-based HVOF coating under similar experimental conditions. An SVM model was successfully developed to predict the erosion of coated and uncoated 18Cr-12Ni-2Mo austenitic steel. The precision performance of the SVM model was calculated in terms of [Formula: see text], RMSE, [Formula: see text], and MAE as 0.99, [Formula: see text], 0.99, and [Formula: see text], respectively.

Numerical study on the nonwetting ability of trapezoid topography

Pattern texturing has been proved to effectively improve the water repellency on hydrophobic surfaces. To explore the effect of pattern profile on the dynamic wetting state, here, we conduct numerical study of a water droplet impinging on surfaces with a single trapezoid, rectangular, and V-shaped grooves, respectively. Simulations are performed using a volume-of-fluid method based interFoam solver shipped with OpenFOAM. We begin with a numerical validation by comparing with experiment. Subsequently, the wetting states of the droplet on these three substrates are examined, which demonstrate the capability of trapezoid topography to prevent being wetted. Theoretical model well explains that trapezoid structure can lead to a great increase in energy barrier brought by the penetration of liquid–air interface, which in turn improves its non-wetting ability even under impingement conditions. By masking the surface with mix-hydrophobicity, we also prove that wettability in grooves plays a significant role on the dynamic wetting state. A stable dry surface can be obtained by only masking the groove side-wall by superhydrophobic patterns.

Effect of metal foam thickness on the conduction and convection heat transfer for a flat plate with metal foam impinged by multiple jets

ABSTRACT The influence of metal foam thickness on the convection and conduction heat transfer is studied by measuring the local heat transfer of a smooth flat plate, attached and detached metal foamed flat plate under multiple jet impingement conditions. 27 jets of 3 mm diameter are introduced from a jet plate. These jets impinge on a thin stainless steel foil that serves as a targeted plate. The pitch of the jets is 4d in both the spanwise and streamwise directions. The spent fluid is exiting in all directions. The influence of metal foam thickness is investigated for an open-cell aluminum foam with 4, 8, and 12 mm thickness. The porosity of aluminum metal foam is 0.92. The pore density (pores per inch) is 20 PPI. The local heat transfer is measured using infrared thermography and a thin metal foil technique. A smooth flat plate impinged by multiple jets serves as a reference case. The evaluation of the convection and conduction heat transfer offered by the metal foamed flat plate is obtained with the help of the detached foam configuration. The jet diameter-based Reynolds number ranges from 2500 to 15000. The range of the jet to plate spacing covered is 3d to 6d. Depending on the metal foam thickness, the metal foamed flat plate offers additional hydraulic resistance to the jet flow and conduction effect. The additional hydraulic resistance attenuates the convective heat transfer and is represented by attenuation factor (α). For metal foam having 4, 8, and 12 mm thickness, the attenuation factor is around 1.11, 0.99, and 0.64, respectively. The conduction effect offered by metal foam is responsible for the enhancement of the heat transfer. The conduction effect is represented as an enhancement factor (E). For metal foam having 4, 8, and 12 mm thickness, the enhancement factor is around 1.51, 1.58, and 2.32, respectively. The conduction effect presented in the metal foamed flat plate dominates over the attenuation in the convective heat transfer. The overall enhancement offered by 4, 8, and 12 mm metal foamed flat plate is around 1.67, 1.56, and 1.48, respectively.

Erosion under turbulent flow: a CFD-based simulation of near-wall turbulent impacts with experimental validation

Engineering systems operating under particle-laden turbulent flow regimes, such as slurry pumps, are prone to erosive wear, where the specific conditions of particle impingement are crucial for determining the wear rate of the eroding surface and thus its relevance for the mechanical or hydraulic system. However, the near-wall interactions under turbulent flows impose a challenge for the formulation and validation of experimental and numerical models that describe the particle’s trajectories close to the surface. This work analyzes the statistics of particle impacts obtained from a Large-Eddy Simulation (LES) with the Wall-Adapting Local Eddy-Viscosity (WALE) model of the flow and its consistency with experimental data on the statistical distributions of particle impact angle and impact direction determined in a slurry pot configuration. The resulting distributions of impact angle, impact direction, and particle velocity derived from the implemented CFD formulation produced characteristic values similar to those derived from experimental data. The LES-WALE approach used in this work offers shorter computational times and is shown valid by comparative analysis with direct simulation. The model’s applicability and prospective dynamic simulation of practical engineering cases are discussed.

Experimental study on spatial distribution characteristics of cylinder-wall oil films under fuel spray impinging condition of GDI engine

This research investigates GDI (Gasoline Direct Injection) fuel spray characteristics, and spray impingement on cylinder-wall oil film were carried out in a constant volume chamber. For studying free spray and spatial distribution characteristics of oil film under spray impinging conditions, the backlight method and LIF (Laser Induced Fluorescence) technology were used, respectively. The influence of injection pressure, ambient pressure, and ambient temperature on the distribution characteristics of oil film with spray impingement were examined. Detailed results on coalescence/splash thresholds criteria of oil film were obtained by considering the incident spray Weber number and the injected fuel mass. In addition, the formation mechanism of oil dilution and splash following the collision were analyzed. It has been found that the incident Weber number is not the only discriminant parameter that can be used to determine the splash criticality of a fuel droplet or spray hitting an oil film. Meanwhile, spray impingement at a higher injection pressure results in a wider spread of oil film, whereas a higher ambient pressure inhibits the spread of oil film.

Which femoral neck for a dual mobility cup? A biomechanical evaluation

PurposeThis study aimed to evaluate polyethylene (PE) damage and wear lesions to the chamfer of mobile components under mobile and fixed femoral neck impingement at the third articulation, and to determine which femoral neck characteristics should be considered with a dual mobility cup to limit those lesions.MethodsTwo femoral neck geometries (cylindrical and quadrangular) with two surface finishing roughness (rough and polished), and two head-to-neck ratios (28- and 22.2-mm diameter femoral heads) were evaluated in a hip simulator testing. For each characteristic, six femoral necks were tested with six dual mobility cups under fixed and mobile femoral neck impingement conditions. Chamfer PE damage and volumetric wear were evaluated and compared for each femoral neck characteristic and impingement condition.ResultsUnder mobile impingement condition, femoral neck characteristics did not significantly affect PE damage and wear lesions to the chamfer (p = 0.283 to 0.810). However, under fixed impingement condition, significantly higher PE damage and wear lesions to the chamfer were produced by the quadrangular geometry compared to the cylindrical geometry (p = 0.004 to 0.025). In addition, with the quadrangular geometry, rough surface finishing was demonstrated to increase volumetric wear of the chamfer (p = 0.009). No significant influence of head-to-neck ratio was observed on PE damage and wear lesions to the chamfer (p = 0.244 to 0.714).DiscussionThis biomechanical study emphasized that femoral neck characteristics are critical with dual mobility cup and tend to favor a cylindrical geometry particularly whether fixed impingement at the third articulation occurs.

Leading edge impingement cooling analysis with separators of a real gas turbine blade

• Experiments of impingement cooling at real temperature conditions are conducted. • A new cooling design containing separators is suggested to prevent cross flow. • Deviation by using low temperature conditions of impingement cooling is presented. • Heat transfer data of impingement cooling are compared with published studies. This paper reports an analysis on leading edge impingement cooling of a turbine blade under real operation conditions of gas turbine. In the experiments, both mainstream and cooling air are heated to real high temperatures, and overall cooling effectiveness on the external blade mid-span surface is measured. Numerical strategy including RNG k-ε turbulence model is validated by the experimental data. Impingement cooling models with and without separators (Model A and Model B) are used as specimens, and the effects of high temperature conditions, separators and temperature ratios are discussed. The results indicate that: 1) When jet Reynolds number, mass flow ratio and temperature ratio are matched to the real conditions, the Nusselt numbers predicted by low temperature conditions can be generally matched, exclude the forepart of the internal surface at the blade leading edge. But the error of overall cooling effectiveness on the blade external surface is not neglected. 2) The application of separators can prevent the heat transfer deterioration caused by cross flow with extending the heat exchange area, thus the leading edge with separators can be further cooled over 30 K compared to the traditional design. 3) Under the real operating conditions of gas turbine, two new correlations between the surface averaged Nusselt number with jet Reynolds number and temperature ratio are suggested.

A simulation study of fracture toughness for a solid rocket motor contains a cracked propellant grain: Consideration of gas impingement effect

It is essential to understand the fracture characteristics of a cracked propellant grain in a solid rocket motor during the motor ignition. In this paper, a finite element model of a solid rocket motor is developed, including the gas impingement flow field and the structural field. A circumferential crack is prefabricated on a round-hole type propellant grain. The gas pressure inside the cracked grain is obtained as a function of time by calculating the flow field. Then applying this pressure to the structural field, and J-integral at the crack tip can be calculated. The J-integral can represent the fracture toughness of the propellant. The results show that the circumferential crack in the propellant grain opens up as the gas pressure gradually increases. The J-integral values at the crack tip show an oscillating trend and are not monotonically increasing. This paper predicts the moment of crack propagation in the rocket motor grain under gas impingement conditions by comparing the JIC of the propellant.

Modeling the Effects of Drop Impingement Frequency on Heated Walls at Engine Conditions

<div class="section abstract"><div class="htmlview paragraph">Understanding the fundamental details of drop/wall interactions is important to improving engine performance. Most of the drop-wall interactions studies are based on the impact of a single drop on the wall. To accurately mimic and model the real engine conditions, it is necessary to characterize spray/wall interactions with different impingement frequencies at a wide range of wall temperatures. In this study, a numerical method, based on Smoothed Particle Hydrodynamics (SPH), is used to simulate consecutive droplet impacts on a heated wall both below and above the Leidenfrost temperature. Impact regimes are identified for various impact conditions by analyzing the time evolution of the post-impingement process of n-heptane drops at different impingement frequencies and wall surface temperatures. For wall temperature below the Leidenfrost temperature, the recoiled film does not leave the surface. Recoiling of the film takes place at a rapid rate at wall temperature above the boiling point of the liquid. For the given impingement conditions, at low impingement frequency, the succeeding drops meet the secondary drop, coalescing into a large drop. An increase in the impingement frequency promotes splashing. For the same impinging conditions, with the wall temperature above the Leidenfrost temperature, at low impingement frequency, recoiling and rebounding of the secondary droplets is seen along with the secondary droplets above the heated wall. On the other hand, at higher impingement frequencies, the succeeding drops impinge on thin liquid films about to be raised above the wall by the vapor film on the wall and splash forming isolated chunks of secondary droplets. Results of this study can further lead to the development of spray/wall impingement models that consider the impact frequency and wall temperature at realistic engine conditions.</div></div>

Protection of material applied in heat exchanger under submerged jet impingement condition with Boswellia serrata: electrochemical approach

Erosion–corrosion of 6061 aluminum alloy was attenuated with a green inhibitor Boswellia serrata (BWS) under submerged jet impingement condition by using artificial seawater slurry. Erosion–corrosion rates in the absence and in the presence of inhibitor were achieved by potentiodynamic polarization techniques (PDP). Experiments were performed under the varying concentration of inhibitor at different flow rates and temperatures. Conditions were optimized to obtain maximum inhibition efficiency. Mechanistic aspects of the corrosion and inhibition process were studied in detail by the electrochemical impedance spectroscopy (EIS) technique by correlating the data with appropriate equivalent circuit models. Adsorption of inhibitor was confirmed by surface morphology studies using scanning electron microscopy technique (SEM). Suitable mechanism was proposed for corrosion inhibition process. The inhibition efficiency increased with an increase in its concentration and it decreased with an increase in the flow rate and temperature. The inhibition efficiency of 70% was obtained for 1000 ppm of inhibitor at 303 K at the flow rate of 4 L min−1. It was proved that the mechanism of corrosion inhibition under this tribological condition is charge transfer controlled. The effect of hydrodynamics on the inhibitor efficiency of Boswellia serrata extract was remarkable. Boswellia serrata emerged as an efficient green inhibitor of erosion–corrosion control of 6061 aluminum alloy under submerged jet impingement conditions.Graphical abstract

Electrochemical Evaluation of the Effect of Different NaCl Concentrations on Low Alloy- and Stainless Steels under Corrosion and Erosion-Corrosion Conditions

The main objective of this study was to assess the influence of salt concentration on the corrosion behaviour, including the role of hydrodynamic conditions, of two broad classes of ferrous engineering materials. These are comprised of alloys, typified by a low-alloy steel (UNS G43400) that corrodes actively in aqueous conditions and a range of passive-film-forming stainless steels (UNS S31600, UNS S15500 and UNS S32760). Corrosion monitoring employed electrochemical (potentiodynamic polarisation) techniques. Three concentrations of aerated sodium chloride were utilised: 0.05 wt% NaCl, 3.5 wt% NaCl and 10 wt% NaCl. In quiescent, liquid impingement and solid/liquid impingement conditions, the corrosion rate of the low-alloy steel was observed to peak at 3.5 wt% NaCl, followed by a reduction in 10 wt% NaCl solution. These findings expand the range of previously reported trends, focused on static conditions. Such corrosion rate/salinity trends were observed to be dictated by the progress of the anodic reaction rather than influence on the cathodic reaction. Detailed studies were undertaken using segmented specimens to facilitate comparisons of the influence of hydrodynamic variations on corrosion behavior; these revealed that such variations influence the corrosion rates of low-alloy steel to a much lesser extent than the effect of changes in salinity. For the stainless steels, in quiescent and flowing conditions, when surface passive films are stable, there was a constant increase in corrosion rate with salinity. In solid-liquid conditions, however, the periodic film-destruction/repassivation events resulted in a similar corrosion rate/salinity trend to that displayed by the low-alloy steel, but with a much larger effect of hydrodynamic conditions. Additonally, the study revealed an underlying influence of stainless steel composition that mirrored, to an extent, the corrosion behaviour in pitting/re-passivation situations

Effects of the surface roughness on the separation efficiency of oil–gas mixture impingement on the vertical wall

This paper investigated the effect of the surface roughness (0.3 μm, 1.1 μm, 2.5 μm, and 4.5 μm) on the oil–gas separation efficiency. Through spraying the oil–gas mixture onto the vertical wall, the droplets impingement in inertial separators was imitated. The impact separation efficiency on a wall was calculated by comparing the volume of the collected oil flowing down from the wall with the volume of the impinging oil. Experiments were conducted three different impingement conditions. The impinging velocity and droplets size distributions on the impingement surface were characterized by the Malvern particle size analyzer and the particle image velocimetry (PIV) technique, respectively. The droplets impinging velocities varied in the range of 3−5 m/s, and the Sauter mean diameter was observed around 40 μm. The collecting process can be divided into the initial stage and the steady stage according to the film flow state. It was found that the surface roughness has both advantages and disadvantages effect on the film flow. These two opposite effects are of different importance at different roughness levels. Under the studied impingement conditions, the separation efficiency was all above 80%, and the surface of the middle roughness (1.1–2.5 μm) performed better than the smoothest 0.3 μm surface and the roughest 4.5 μm surface.