Pool Surface Research Articles

Numerical and Experimental Analysis of Dual-Beam Laser Polishing Additive Manufacturing Ti6Al4V.

Laser polishing is an emerging efficient technique to remove surface asperity without polluting the environment. However, the insufficient understanding of the mechanism of laser polishing has limited its practical application in industry. In this study, a dual-beam laser polishing experiment was carried out to reduce the roughness of a primary Ti6Al4V sample, and the polishing mechanism was well studied using simulation analysis. The results showed that the surface roughness of the sample was efficiently reduced from an initial 10.96 μm to 1.421 μm using dual-beam laser processing. The simulation analysis regarding the evolution of material surface morphology and the flow behavior of the molten pool during laser the polishing process revealed that the capillary force attributed to surface tension was the main driving force for flattening the large curvature surface of the molten pool at the initial stage, whereas the thermocapillary force influenced from temperature gradient played the key role of eliminating the secondary roughness at the edge of the molten pool during the continuous wave laser polishing process. However, the effect of thermocapillary force can be ignored during the second processing stage in dual-beam laser polishing. The simulation result is well in agreement with the experimental result, indicating the accuracy of the mechanism for the dual-beam laser polishing process. In summary, this work reveals the effect of capillary force and thermocapillary force on molten pool flows during the dual-beam laser polishing processes. Moreover, it is also proved that the dual-beam laser polishing process can further reduce the surface roughness of a sample and obtain a smoother surface.

Towards an Understanding of the Challenges in Laser Beam Welding of Copper – Observation of the Laser-Matter Interaction Zone in Laser Beam Welding of Copper and Steel Using in Situ Synchrotron X-Ray Imaging

The increasing demand for contacting applications in electric components such as batteries, power electronics and electric drives is boosting the use of laser-based copper processing. Laser beam welding is a key for an efficient and high-quality electric vehicle production due to its local, non-contact energy input and high automation capability enabling reproducible weld quality. Nevertheless, a major challenge in process design is the combination of energy-efficiency and precise process guidance with regard to weld seam depth and defect prevention (i.e. spatter, melt ejections), partly caused by the high thermal conductivity of copper. High power lasers in the near infrared range and emerging visible laser beam sources with excellent beam quality can provide a suitable joining solution for this purpose. However, the underlying physical phenomena are currently only partly understood and a reflection on the challenges of laser beam welding of copper compared to well researched steel processing has not yet been carried out. In order to improve the understanding of the effect of the different material properties and the influence of process parameters on the vapor capillary and melt pool geometry in laser beam welding, in situ synchrotron investigations on Cu-ETP and S235 using 515 and 1030 nm laser sources were conducted. The material phase contrast analysis was successfully used to distinguish vapor capillary and melt pool phase boundaries during the welding process with high spatial and temporal resolution up to 5 kHz. A significantly different vapor capillary geometry and sensitivity to parameter variation were found between the steel and copper material. In addition, the visualization of characteristic melt flows revealed different melt pool dynamics and a pronounced eddy close to the melt pool surface for copper, which is assumed to be causal for the observation of pronounced spatter formation during copper welding in a certain process window.

Three Ablation Techniques for Atrial Fibrillation during Concomitant Cardiac Surgery: A Systematic Review and Network Meta-Analysis.

Atrial fibrillation (AF) ablation is a frequent procedure used in concomitant cardiac surgery. However, uncertainty still exists concerning the optimal extent of lesion sets. Hence, the objective of this study was to assess the results of various ablation techniques, aiming to offer a reference for clinical decision making. This review is listed in the prospective register of systematic reviews (PROSPERO) under ID CRD42023412785. A comprehensive search was conducted across eight databases (Scopus, Google Scholar, EBSCOHost, PubMed, Medline, Wiley, ProQuest, and Embase) up to 18 April 2023. Studies were critically appraised using the Cochrane Risk of Bias 2.0 for randomized control trials (RCTs) and the Newcastle Ottawa Scale adapted by the Agency for Healthcare Research and Quality (AHRQ) for cohort studies. Forest plots of pooled effect estimates and surface under the cumulative ranking (SUCRA) were used for the analysis. Our analysis included 39 studies and a total of 7207 patients. Both bi-atrial ablation (BAA) and left atrial ablation (LAA) showed similar efficacy in restoring sinus rhythm (SR; BAA (77.9%) > LAA (76.2%) > pulmonary vein isolation (PVI; 66.5%); LAA: OR = 1.08 (CI 0.94-1.23); PVI: OR = 1.36 (CI 1.08-1.70)). However, BAA had higher pacemaker implantation (LAA: OR = 0.51 (CI 0.37-0.71); PVI: OR = 0.52 (CI 0.31-0.86)) and reoperation rates (LAA: OR = 0.71 (CI 0.28-1.45); PVI: OR = 0.31 (CI 0.1-0.64)). PVI had the lowest efficacy in restoring SR and a similar complication rate to LAA, but had the shortest procedure time (Cross-clamp (Xc): PVI (93.38) > LAA (37.36) > BAA (13.89)); Cardiopulmonary bypass (CPB): PVI (93.93) > LAA (56.04) > BAA (0.03)). We suggest that LAA is the best surgical technique for AF ablation due to its comparable effectiveness in restoring SR, its lower rate of pacemaker requirement, and its lower reoperation rate compared to BAA. Furthermore, LAA ranks as the second-fastest procedure after PVI, with a similar CPB time.

Influence of weld pool surface depression on burning conditions of an arc with a refractory cathode

Influence of weld pool surface depression on burning conditions of an arc with a refractory cathode

Numerical simulation and experimental investigation of the laser cladding processes of Ti6Al4V with coaxial shroud protection

Laser cladding with coaxial shroud protection offers the possibility to process reactive metals in an open environment. The numerical analysis was performed on the thermal field and dynamics of molten pool with the aim of clarifying the mechanism of the complex effects of the applied extra shielding gas on the resultant microstructure and surface quality of cladding layers of Ti6Al4V. A three-dimensional (3D) computational fluid dynamics (CFD) model was first developed to investigate the extra shielding gas effect on the molten pool. The simulation shows that the extra shielding gas influences both the surface and internal flow field characteristics of the molten pool. The predicted solidification parameters imply fully columnar microstructure in the entire cladding layer. Comparative analysis was then carried out between the numerical simulation and experiments. The electron backscattering diffraction (EBSD) examination reveals that the high cooling rate due to the extra shielding gas inhibits the formation of grain boundary α phase and simultaneously refines the microstructure. The extra shielding gas reduces the surface roughness of cladding layers, and its bunching effect improves the powder utilization. The multi-track cladding experiments reveal that the extra shielding gas can effectively suppress crack formation with a large overlap ratio. This study provides a better understanding of the effect of extra shielding gas flow on molten pool, which helps control and improve the quality of cladding layers.

Modelling and effects of fuel radiation in methanol pool fires

This article proposes a computationally affordable radiative heat transfer model to predict accurately the feedback toward the fuel surface. It combines the multi-scale full-spectrum k (MSFSK) approach to model accurately the radiative interaction between CO2/H2O and the fuel and the rank correlated (RCFSK) scheme. The model achieves the narrow band correlated-k model accuracy with only five quadrature points for each of the two scales. The predictions are also weakly dependent on the Planck temperature which allows to store efficiently the MSRCFSK parameters in a flamelet library. The model is implemented in a well-validated numerical model to provide large eddy simulations of 30 cm and 1 m diameter methanol pool fires. The heat feedback predictions are improved when methanol radiation is considered. The overall radiative contribution of methanol results from two competitive mechanisms: an increase in emission in the hot part of the fuel dome and an increase in absorption close to the pool surface. For both pool fires, the enhancement in emission overall dominates, leading to higher radiative loss and heat feedback. The contribution of absorption increases with the pool size and, as a result, the effects of methanol radiation are more pronounced for the 30 cm pool than for the 1 m one.

Evaporative and non-evaporative droplet impact on a heated phase change material pool: A comparison between ethanol, acetone, and distilled water

The interaction between liquid droplet and phase change material (PCM) underlies the direct contact approach, which is an efficient way for precipitating the melting and solidification processes of PCMs. In this experimental research, to comprehend the direct contact method more profoundly, the impingement of a single droplet on the heated paraffin pool, having a temperature of 70–95 °C, is scrutinized systematically for the first time. Droplet impact solidifies a portion of the pool and may lead to droplet evaporation. Acetone, ethanol, and distilled water are exploited as droplet liquids, whose diameter and impact velocity range from 2.32 to 3.36 mm and from 1.70 to 2.28 m/s, respectively. Through impact visualizations, six distinct regimes are observed, whose regime maps are constructed. Moreover, the effects of fluid properties, pool temperature, and the Weber number on the evolution of crater and jet, crater depth, crater shape, and solidified PCM area (A) generated after the impingement are investigated. It is ascertained that the low PCM temperature instigates the coalescence phenomenon regardless of the Weber number. Additionally, the crater depth is a function of the PCM temperature, Weber number, and Ohnesorge number; thus, a dimensionless correlation is proposed for the maximum crater depth. Furthermore, droplet evaporation augments the extracted heat from the paraffin, provoking a more sizeable solidified area. Interestingly, though absorbing the greatest amount of heat from the PCM, ethanol droplet generates a smaller solidified area than acetone since acetone favorably spreads on the pool surface, enhancing the effective heat exchange area.

Self-sustaining levitation of droplets above a liquid pool

In this Letter, we report the phenomenon of self-sustaining and long-term (>103 s) levitation of millimeter-sized droplets of a variety of liquids without any external forces. The droplet levitation is enabled by solutocapillary convection in the liquid pool, which occurs due to the surface tension gradient originating from non-uniform distribution of vapor molecules from the droplet at the pool surface. The droplet lifetime can be adjusted by adding the droplet liquid into the pool. The maximum levitation duration is achieved at a concentration that reduces the evaporation rate of the droplets and increases the solutocapillary flow in the pool. Such self-sustaining droplet levitation occurs under ambient conditions and can be used as an effective tool for studying the activity of viruses and microorganisms as they are transferred in airborne aerosols.

Effects of silver epoxy reinforcement on graphene nanoplatelets functionalized surface in pool boiling heat transfer enhancement

Silver Epoxy reinforcement is pivotal to enhance the adhesive strength of Graphene nanoplatelets (GNP) on the substrate. This experimental study seeks to scrutinize the effects of Silver Epoxy reinforced GNP functionalized surface on the heat transfer of pool boiling. Three different GNP-based coatings are analyzed: simple GNP, uncured GNP reinforced with Silver Epoxy, and cured GNP reinforced with Silver Epoxy, all applied to copper substrate. For each coating, the surface morphology, chemical bonding, and wettability are examined. Under a heat flux of 550 kW/m2, the experimentally derived heat transfer coefficient improves by 194%, 36%, and 77% respectively on pristine GNP, uncured GNP/Epoxy, and cured GNP/Epoxy compared to the bare copper surface. The epoxy reinforcement weakens the exceptional boiling improvement achieved by a GNP functionalized surface. Although the thermal curing process turns the GNP/epoxy coating from hydrophobic to hydrophilic and recovers partly the level of boiling enhancement, the biphilicity of GNP tends to dominate boiling heat transfer enhancement by enhancing the bubble dynamics. The hydrophilicity has a subordinate effect by re-wetting the dry spots and preventing the vapour blanket. Silver Epoxy reinforcement significantly enhances the adhesive strength of GNP on a substrate but at the expense of boiling heat transfer enhancement.

Effects of Flowrate of Additional Shielding Gas on the Properties of Welded Seam Using Twin-Wire GMAW Welding for Duplex Stainless Steel

Aiming to diminish the defects caused by high-speed pulsed GMAW (Gas Metal Arc Welding), such as lack of penetration, lack of fusion, humping and undercut, this paper proposes an improved twin-wire GMAW welding process by introducing the impact of additional shielding gas on the molten pool, and the effects of different shielding gas flowrates on the mechanical properties and microstructure of the welded seams were investigated. The purpose of introducing additional shielding gas was to use the airflow hood formed by gas injection to isolate air. The impact force generated by the jet might change the original natural solidification mode of the molten pool, which had the effect of improving weld formation and stirring the pool. The airflow hood formed during the process of the additional shielding gas jet impact welding of the molten pool might extend the protection time for the surface of the welding molten pool. The 2205 duplex stainless steel plate was used as the base material for the butt welding test, and the welded seams were subjected to a tensile test, hardness analysis, and metallographic analysis. The results indicated that as the flowrate of additional shielding gas increased in the range of 8 L/min~16 L/min, the width of the welded seam increased and the height of reinforcement decreased gradually. However, a weld seam with a lower middle region and higher sides would appear when the gas flowrate became excessively large. Under the identical welding current and for welding speeds of 160 cm/min, 180 cm/min and 200 cm/min, respectively, the joint formed under the flowrate of 12 L/min had the highest tensile strength (824.3 MPa) among the test specimens under different flowrates of 8 L/min, 12 L/min and 16 L/min. The test results indicated that the jet impact force was relatively moderate when the flowrate of the additional shielding gas was 12 L/min, and thus was optimal for the welded seam.

Experimental study of the thermal and burning characteristics of 15 cm pool fires fueled by heptane-toluene mixtures

This article presents an experimental investigation of the effects of the fuel sooting propensity on the thermal and burning characteristics of 15 cm diameter pool fires burning in air. Heptane is used as reference fuel and two other heptane/toluene blends with toluene volume concentration of 5% and 10% are considered to vary the fuel sooting propensity. An exhaustive characterization of the pool fires is performed with measurements of the flame geometry, puffing frequency, mass burning rate, combustion efficiency, local temperature statistics from a dual thermocouple technique, local mean soot volume fraction from laser light extinction, radiative loss to the surroundings and total heat flux to the center of the pool surface. This comprehensive dataset can be used to develop and validate models for soot formation and radiative heat transfer. The experimental results show that the increase in fuel sooting propensity, characterized by a smoke point height decreasing from 12.5 cm to 4.9 cm, results in a significant enhancement in soot production, with the peak of mean soot volume fraction increasing from 0.62 ppm to 1.11 ppm. Radiative loss to the surroundings is also affected, as radiant fraction and total heat flux to the center of the fuel surface increase from 0.37 to 0.45 and 18.5 to 22.2 kW/m2 respectively. This is accompanied by a significant reduction in combustion efficiency from 0.95 to 0.83. In an opposite way, the impact on the temperature statistics is minor.

Short- and medium-chain chlorinated paraffins in agricultural and industrial soils from Shanghai, China: surface and vertical distribution, penetration behavior, and health risk assessment.

The widespread contamination of chlorinated paraffins (CPs) of the soil environment has raised global concern due to their highly persistent and toxic properties. However, little information is available regarding these industrial toxicants' spatial-vertical distribution and penetration potentials. In this study, short- and medium-chain chlorinated paraffins (SCCPs and MCCPs, respectively) were analyzed in pooled surface and core soils (0-45cm) samples collected from agricultural and industrial areas in Shanghai. ∑SCCP concentrations in agricultural and industrial surface soils ranged from 52.6 to 237.6 and 98.3 to 977.1ng/g dry weight (dw), respectively. ∑MCCP levels were comparatively higher and ranged from 417.2 to 1690.8 and 370.9 to 10,712.7ng/g dw in agricultural and industrial soils, respectively. C10Cl5-10 SCCPs and C14-15Cl5-7 MCCPs were the predominant homologues in all samples. Analysis of the soil vertical profiles revealed that MCCP concentrations decreased significantly with depth (P < 0.01). SCCPs more efficiently penetrated into thesoils than MCCPs because of their higher water solubility and less octanol-water partition coefficient (Kow) values. A preliminary risk assessment suggested no potential health risks caused by non-dietary exposure. The daily exposure doses of CPs via ingestion were significantly (P < 0.01) higher for children (5.41 ± 2.11 × 10-3 and 1.68 ± 1.03 × 10-2μgkg-1day-1) and adults (2.56 ± 0.99 × 10-4 and 7.94 ± 4.87 × 10-4μgkg-1day-1) than dermal permeation exposure. Furthermore, CPs at current levels posed low ecological risks (0.1 ≤ RQ < 1) according to the risk quotient model. This study enhanced our understanding of the fates and behaviors of CPs in the terrestrial environment.

Effect of Laser Beam Profile on Thermal Transfer, Fluid Flow and Solidification Parameters during Laser-Based Directed Energy Deposition of Inconel 718.

The profile of the laser beam plays a significant role in determining the heat input on the deposition surface, further affecting the molten pool dynamics during laser-based directed energy deposition. The evolution of molten pool under two types of laser beam, super-Gaussian beam (SGB) and Gaussian beam (GB), was simulated using a three-dimensional numerical model. Two basic physical processes, the laser-powder interaction and the molten pool dynamics, were considered in the model. The deposition surface of the molten pool was calculated using the Arbitrary Lagrangian Eulerian moving mesh approach. Several dimensionless numbers were used to explain the underlying physical phenomena under different laser beams. Moreover, the solidification parameters were calculated using the thermal history at the solidification front. It is found that the peak temperature and liquid velocity in the molten pool under the SGB case were lower compared with those for the GB case. Dimensionless numbers analysis indicated that the fluid flow played a more pronounced role in heat transfer compared to conduction, especially in the GB case. The cooling rate was higher for the SGB case, indicating that the grain size could be finer compared with that for the GB case. Finally, the reliability of the numerical simulation was verified by comparing the computed and experimental clad geometry. The work provides a theoretical basis for understanding the thermal behavior and solidification characteristics under different laser input profile during directed energy deposition.

Numerical analysis of arc and molten pool behaviors in high speed tandem TIG welding of titanium tubes

A high speed tandem TIG welding process was adopted to manufacture titanium welded tubes. A coupled electrode, arc and weld pool numerical model was also developed to investigate the temperature distribution, arc plasma and molten metal flows, and energy propagation of this welding process. Under the driving of the electromagnetic force, arc plasmas under the leading and trailing electrodes flowed towards each other. The Marangoni stress was much higher than the arc shear stress, and was the main driving force for the backward molten metal flow on the top weld pool surface. The calculated arc efficiency of this welding process was 79.8%. The high speed tandem TIG welding process can improve the manufacturing efficiency and quality of titanium welded tubes.

Development and implementation of in-process, orbiting laser-assisted healing technique on fused filament fabrication

Fused filament fabrication is one of the most widely used additive manufacturing processes for producing thermal plastic polymer materials due to the affordable cost and capability to build objects with complex structures. However, parts fabricated with this process exhibit lower mechanical strength when compared to parts manufactured using traditional methods. In this work, an in-process orbiting laser healing technique is developed and implemented on a 3D printer to enhance mechanical strength by improving interlayer adhesion. The orbiting laser assembly can position and align the laser-heated spot before the change of nozzle direction occurs, ensuring that the previous layer is heated prior to material deposition. This laser-heating technique increases the bending strength along the build direction by 40% and reaches 88.9% of the strength along the longitudinal direction. With this technique, the displacement at fracture also increased by 54.3% compared to control sample. The thermal profile of the melting pool and fracture surface was further characterized using a thermal camera and SEM to support the effect of laser heating on polymer microstructure, respectively. Due to its enhanced print quality and lower cost, this technique has the potential to expand the application field of fused filament fabrication to small batch and series production that are currently dominated by injection molding, as well as the high-quality prototyping field.

Pore formation driven by particle impact in laser powder-blown directed energy deposition.

Process defects currently limit the use of metal additive manufacturing (AM) components in industries due to shorter fatigue life, potential for catastrophic failure, and lower strength. Conditions under which these defects form, and their mechanisms, are starting to be analyzed to improve reliability and structural integrity of these highly customized parts. We use in situ, high-speed X-ray imaging in conjunction with a high throughput laser, powder-blown directed energy deposition setup to observe powder particle impact behavior within the melt pool. Through fundamental observations of the stochastic, violent powder delivery in powder-blown DED, we uncover a unique pore formation mechanism. We find that a pore can form due to air-cushioning, where vapor from the carrier gas or environment is entrapped between the solid powder particle surface and liquid melt pool surface. A critical time constant is established for the mechanism, and X-ray computed tomography is used to further analyze and categorize the new type of "air-cushioning" pores. It is shown that the air-cushioning mechanism can occur under multiple laser processing conditions, and we show that air-cushioning pores are more likely to be formed when powder particles are larger than 70 m. By quantifying the effect of powder particle impact, we identify new avenues for development of high-quality laser, powder-blown DED products. Furthermore, we deepen knowledge on defect formation in metal additive manufacturing, which is being increasingly utilized in high performance situations such as aerospace, automotive, and biomedical industries.

Experimental Study on the Interaction of an Impulse Water Jet with Molten Metal

The impingement of a short-duration water jet on a pool of molten Rose’s metal is studied experimentally herein. Short-duration water jet impacting on the free surface of a molten metal pool with a temperature of 300 °C are generated with a pneumatic water delivery system, with two-camera high-speed video registration. A total of 14 experimental series, each containing 5 repeated tests, are performed for a water volume of 0.2–1 mL and a jet impact velocity of 4.1–9.0 m/s. The cavity development in the melt layer is studied, with the main stages described herein. Despite the significantly higher density of melt in comparison with water, the cavity can reach the melt pool bottom; furthermore, its further collapse results in the formation of a central jet rising to the height of a few centimeters. The maximum height of the central jet is shown to depend linearly on the total momentum of the water jet, and a semi-logarithmic correlation is found for the maximum diameter of the cavity. Repeatability analysis is performed within each experimental series, and the relative standard deviation for the melt splash height is shown to be from 8.8% to 26.8%. The effects of the pool depth, the vessel shape, and the water temperature are weaker in the range of the experimental parameters used here.

Multi-phase flow simulation of powder streaming in laser-based directed energy deposition

As a promising additive manufacturing technique, laser-based directed energy deposition has been widely applied in part fabrication, surface cladding, and part restoration. During the powder feeding process, the gas, particles, and laser interact and further affect the molten pool flow. To study the powder feeding process, a multi-physics gas-particle multi-phase flow model coupled with a laser ray-tracing heat source model is developed to predict the powder particle temperature, velocity, and concentration distribution as well as laser energy loss, which is then validated against experimental results. The single-nozzle simulation shows that powder particles out of the nozzle follow a radial Weibull distribution instead of a 2D Gaussian distribution from the inlet of the nozzle. In the four-nozzle powder feeding process, the particles converge further after passing the focal plane, and setting the focal plane above the molten pool surface could potentially increase the powder catchment. Moreover, the laser ray-tracing model incorporates laser reflection and laser incident angle into laser energy loss calculation, which would be more accurate than those models based on the Beer-Lambert law. Additionally, by increasing the powder feed rate or decreasing the carrier gas flow rate, the laser energy loss linearly increases. The predicted powder velocity, temperature distribution, and attenuated laser can be further implemented into the molten pool flow model to more comprehensively study the interaction between particles and the molten pool in the future.

Numerical analysis of coupling dynamics of keyhole and molten pool in vertical-up laser mirror welding of 2219 aluminum alloy

In vertical-up laser mirror welding, the keyhole dynamics and flow behavior of molten pool play crucial roles in weld quality, yet the mechanisms of these coupling dynamics have not been well clarified. In this work, a three-dimensional transient model for simulation of vertical-up laser mirror welding process was carried out to account for the flow behavior of molten pool and dynamic evolution characteristics of keyhole. Two laser heat sources with regard to laser mirror welding were also taken into consideration in the combined heat source model. It is proved that the simulation results are basically consistent with the experimental data. The simulation results indicate that the morphology and flow field distribution of upper and lower molten pool both exhibit a high degree of consistency on the X–Y section, while significant difference is visible on the X-Z section. Before keyhole coupling, the high velocity fluid exists on the surface of molten pool and tends to increase the diameter of keyhole, of which the maximum velocity reaches 5.26 m s−1. During the keyhole coupling process, the coupled keyhole in the center area is found to fall, which results in deteriorated coupling process. Force analysis of keyhole illustrates that the resultant force on the X–Y section points to the direction of increasing the depth and diameter of keyhole before and during the keyhole coupling process. In contrast, the resultant force on the X-Z section is conductive to keyhole coupling occurring at the lower position. After keyhole coupling, the diameter of coupled keyhole in the center zone is increased and the fluid velocity is reduced to 0.109 m s−1, contributing to a firm connection.

Mass Transfer of Hydrogen Sulfide at Turbulent Water Surface by Falling Drops or a Single Jet

Hydrogen sulfide (H2S) is a primary cause of odor and corrosion in sewer systems. In drop structures, falling wastewater impinges the surface of bottom water pool as a jet or numerous drops, triggering a high level of turbulence and thus enhancing the emission of H2S and the absorption of oxygen (O2) at the pool surface. In this study, laboratory experiments were conducted to study the mass transfer at the pool surface with falling water drops or a single jet of water. In the test range of falling flow rate of 49–223 mm/h and falling velocity of 3.1–5.2 m/s [kinetic energy flux (KEF)=0.11–0.80 J/(m2·s)], the mass transfer coefficient KL for the pool surface was found to be 2.6–14.8×10−5 m/s for H2S. In addition, KL was found to be 76% larger when the pool surface was impinged by water drops than by a single jet. KL was 27%−47% larger in the half of the water surface directly receiving the drops or jet than the other half. The increase of water depth in the pool promoted the mass transfer, especially for the scenario of falling jet. Equations were proposed to predict KL under drops or jet. Moreover, KL for H2S and for O2 was found almost the same, indicating O2 can be a safe surrogate gas for H2S. Finally, the research results were applied to estimate H2S emissions at the pool surface of a prototype drop structure with a falling height of up to 10 m, which showed that turbulent wastewater surface can enhance mass transfer over 100 times compared with a quiescent surface.