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Reduced graphene oxide (rGO) thin films have demonstrated various advantages in flexible electronics. So far, solution processes are widely used for making rGO thin films for their mild operation conditions and low cost. However, wrinkles are frequently formed due to the capillary contraction during drying, which severely deteriorates the conductivity and the transparency of rGO thin films. Here, an ultra‐smooth rGO nano‐thin film, featuring wrinkle‐free and a rather low surface roughness of 1.38 nm is developed, which is attributable to a steady and homogeneous thin liquid film confined by a conical fiber array. The thin liquid film facilitates both in‐plane stacking of nanosheets and reducing the buried solvent under nanosheets. Notably, with the capillary flow replenishing the tri‐phase contact line evaporation, a semi‐dry film near the tri‐phase contact line is produced, that enables the force equilibrium of multi‐directional capillary forces on dispersed nanosheets for depositing a wrinkle‐free nanofilm. The as‐prepared rGO nanofilm gives a low sheet resistance of 8.3 kΩ sq−1 and a high transmittance of 91.9%, showing better performances than other reported rGO nanofilms. On this basis, it is demonstrated that a high‐sensitive pressure sensor with a detection limit as low as 0.02 Pa, highlighting the solution‐processed innovative ultra‐smooth 2D nanomaterial thin films, and devices. [ABSTRACT FROM AUTHOR]

Ultra-high-strength steels have been considered an essential material for aviation components owing to their excellent mechanical properties and superior fatigue resistance. When machining these steels, severe tool wear frequently results in poor surface quality and low machining efficiency, which is intimately linked to the friction behavior at the tool–workpiece interface. To enhance the service life of tools, the adoption of efficient cooling methods is paramount. However, the understanding of friction behavior at the tool–workpiece interface under varying cooling conditions remains limited. In this work, both air atomization of cutting fluid (AACF) and ultrasonic atomization of cutting fluid (UACF) were employed, and their spray characteristic parameters, including droplet size distribution, droplet number density, and droplet velocity, were evaluated under different air pressures. Discontinuous sliding tests were conducted on the ultra-high-strength steel against cemented carbide and the effect of spray characteristic parameters on the adhesion friction coefficient was studied. The results reveal that ultrasonic atomization significantly improved the uniformity of droplet size distribution. An increase in air pressure resulted in an increase in both droplet number density and droplet velocity under both AACF and UACF conditions. Furthermore, the thickness of the liquid film was strongly dependent on the spray characteristic parameters. Additionally, UACF exhibited a reduction of 4.7% to 9.8% in adhesion friction coefficient compared to AACF. UACF provided the appropriate combination of spray characteristic parameters, causing an increased thickness of the liquid film, which subsequently exerted a positive impact on reducing the adhesion friction coefficient. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study explored and examined soliton solutions for the Quintic Benney-Lin equation (QBLE), which describes the dynamic of liquid films, using the Riccati modified extended simple equation method (RMESEM). The proposed approach, which is designed for nonlinear partial differential equations (NPDEs), effectively generates a large number of soliton solutions for the given QBLE, which basically captures the fundamental dynamics of the system. The rational, hyperbolic, rational-hyperbolic, trigonometric, and exponential forms of the scientifically specified soliton solutions are the main determinants of the hump solitons. We used 2D, 3D, and contour visualizations to offer accurate representations of the researched soliton phenomena associated with these solutions. These representations revealed the existence of dark and bright hump solitons in the framework of the QBLE and offer a thorough way to examine the model's behavioral characteristics in the liquid film by analyzing the QBLE model's soliton dynamics. Moreover, applying the suggested approach advances our knowledge of the unique features of the other similar NPDEs and the underlying dynamics. [ABSTRACT FROM AUTHOR]

This study aims at exploring properties of fluorine-free foams co-stabilized by nanoparticles (NPs) and surfactant. The mixed dispersion liquids composed of silica NPs, nonionic hydrocarbon surfactant (APG-0810), and organosilicon surfactant (CoatOsil-77) was prepared. The NP-intensified foams under the action of n-heptane (flammable liquid) were focused by analyzing aggregation behavior of surfactants, initial foaming height, foams drainage and decay, and single vertical film stability of the mixed dispersion liquids. The findings show that the presence of surfactants improves surface activity of water obviously. After adding NPs, the interactions between surfactant molecules are destroyed but new aggregates formed. Foaming ability decreases but stability increases significantly with increasing NP concentration. After n-heptane is added, intensified interactions exist among surfactant molecules, NPs, and oil droplet, promoting formation of some larger aggregates and increasing the surface tension and viscosity but decreasing the conductivity and foaming ability. In addition, the presence of n-heptane accelerates foam drainage and volume decay and thinning process of the vertical liquid film. NPs with an appropriate concentration can improve foaming ability, foam stability, and the corresponding oil resistivity of foam. This study can provide theoretical guidance for the development of new fluorine-free foams used for liquid fuel fire. Highlights: Intense interactions exist among SiO2 NPs, surfactant molecules, and oil droplets. Foaming ability is reduced by the presence of SiO2 NPs and oil droplets. SiO2 NPs with concentration above 1% can effectively improve foam oil resistivity. SiO2 NPs enhances foam oil resistivity be improving foam film stability under oil. [ABSTRACT FROM AUTHOR]

This study explored and examined soliton solutions for the Quintic Benney-Lin equation (QBLE), which describes the dynamic of liquid films, using the Riccati modified extended simple equation method (RMESEM). The proposed approach, which is designed for nonlinear partial differential equations (NPDEs), effectively generates a large number of soliton solutions for the given QBLE, which basically captures the fundamental dynamics of the system. The rational, hyperbolic, rational-hyperbolic, trigonometric, and exponential forms of the scientifically specified soliton solutions are the main determinants of the hump solitons. We used 2D, 3D, and contour visualizations to offer accurate representations of the researched soliton phenomena associated with these solutions. These representations revealed the existence of dark and bright hump solitons in the framework of the QBLE and offer a thorough way to examine the model's behavioral characteristics in the liquid film by analyzing the QBLE model's soliton dynamics. Moreover, applying the suggested approach advances our knowledge of the unique features of the other similar NPDEs and the underlying dynamics.

Droplet impact is a common occurrence in nature, agriculture, and industry. The research on the multi‐droplet impact is fundamental to understanding the tangled nature of reality. This paper numerically studies the successive oblique impact of dual droplets on the liquid film by building an effective three‐dimensional model. The leading and trailing droplets are set to pass a certain impact point with the same velocity. The main contribution of this paper is the investigation of the effects of Weber number, liquid film thickness, impact angle, and impact time interval on the interface morphology evolution after the droplet impact. Results show that splash pattern conversion of the primary or secondary crown occurs with the change of these factors. Besides, the variations of the maximum crater radius in upstream, lateral, and downstream directions with time are quantitatively analyzed. The crater radius analysis is carried out from three perspectives, the variation during the single droplet impact, the change during the dual droplets impact, and the comparison between them. It is found that the crater of dual droplets impact exhibits shape distortion in the deformation period and appears a marked dimensional increase in the secondary expansion period. [ABSTRACT FROM AUTHOR]

Controlling the distribution of the abrasive grains on the surface of the grinding tools in an appropriate way is important for improving the quality of grinding processing and meeting the workpiece precision requirements. In the present study, a novel method for the orderly arrangement of abrasive particles is proposed by using the liquid film flow on the surface of the rotating disk as the driving and controlling means for the uniform dispersion and position arrangement of abrasive particles. Computational fluid dynamics (CFD) simulations have been performed to clearly illustrate the trajectories of abrasive particles under the strong influence of liquid film flow on the rotating disk and reveal the effects of fluid flow, disk rotational motion, and the mixture viscosity on the particle distribution. A new abrasive grain arrangement device is designed and fabricated using this novel method. The operating parameters such as liquid volume flow rate, disk rotational speed, and liquid viscosity are adjusted to control the placement of abrasive grains on the surface of the grinding tool. An image processing tool is used to examine and analyze the arrangement results. The experimental results indicated that the application of the liquid film flow on a rotating disk to the abrasive grain arrangement can improve the arrangement of abrasive grains and get rid of the dependence on the template. [ABSTRACT FROM AUTHOR]

The leading-edge erosion of a wind turbine blade was tested using a whirling arm rain erosion tester, whose rotation rate is considerably higher than that of a full-scale wind turbine owing to the scale effect. In this study, we assessed the impact pressure of droplets on a wet surface of wind turbine blades using numerical simulation of liquid droplet impact by solving the Navier–Stokes equations combined with the volume-of-fluid method. This was conducted in combination with an estimation of liquid film thickness on the rotating blade using an approximate solution of Navier–Stokes equations considering the centrifugal and Coriolis forces. Our study revealed that the impact pressure on the rain erosion tester exceeded that on the wind turbine blade, attributed to the thinner liquid film on the rain erosion tester than on the wind turbine blade caused by the influence of centrifugal and Coriolis forces. This indicates the importance of correcting the influence of liquid-film thickness in estimating the impact velocity of droplets on the wind turbine blade. Furthermore, we demonstrated the correction procedure when estimating the impact velocity of droplets on the wind turbine blade. [ABSTRACT FROM AUTHOR]

Mar-M247 is widely used in several fields as a material with excellent overall performance at high temperatures. However, its complex fabrication process and extremely poor weldability make it very difficult to repair and fabricate. In this study, a novel flux-cored wire with microstructures and composition similar to that of Mar-M247 nickel-based superalloy had been successfully developed, and the superalloy had been effectively repaired by cold metal transfer welding technique. Under the strict control of welding parameters, good metallurgical bonding between the weld and the base metal can be realized, and the hot cracking problem of the joint was successfully suppressed. In the weld, there were closely arranged γ′ phase precipitates with nanoscale and γ/γ′ eutectic structure, granular carbides dispersed at grain boundaries. The hardness of the weld was about 410–430 HV. It had been found that solidification cracks in welds were caused by intergranular liquid films, and grain orientation was found to be an important factor affecting solidification cracking. Optimized welding parameters of cold metal transfer could control the grain orientation of weld and reduce the size of intergranular liquid film, which could effectively suppress the size of weld solidification cracks. Additionally, liquefaction cracks were caused by eutectic reaction liquefaction in the heat-affected zone. The cold metal transfer welding process with optimized parameters can effectively reduce welding heat input, weaken eutectic reactions, and successfully obtain joints without crack in heat-affected zone.

A fifth-order nonlinear wave equation (generalized Korteweg–deVries equation) that arises in the theory of thin liquid films is introduced with the odd viscosity by the long-wave approximation regime. The presence of the odd viscosity is considered to be a non-dissipative factor in the evolution of the film flow. Sinusoidal and travelling waves arise in systems with non dissipation and instability. The introduced wave equation includes quadratic and cubic nonlinearities. The linear instability of sinusoidal waves is analyzed. The stability and bifurcation of travelling waves are discussed. [ABSTRACT FROM AUTHOR]

During the discharge of floodwater from a hydropower station, a significant number of water droplets in motion are created in the downstream space. These droplets vary in size and velocity, causing challenges in determining the particle size and velocity distribution of the flood discharge atomized droplets. Currently, the particle-size distribution and velocity distribution of atomized droplets are considered to be independent, and the gamma function is used to describe the particle-size distribution and velocity distribution of droplets separately. However, a joint distribution of atomized droplet size and velocity is lacking. This paper uses the basic theory of maximum entropy to study the combined distribution of droplet size and velocity in the atomized flow caused by jet overflow. The present model was in a good agreement with experimental data, providing a method for the theoretical study of droplet size and velocity distribution in flood discharge atomization. [ABSTRACT FROM AUTHOR]

In this article, we use the modified extended direct algebraic method (mEDAM) to explore and analyze the traveling wave phenomena embedded in the quintic conformable Benney-Lin equation (CBLE) that regulates liquid film dynamics. The proposed transformation-based approach developed for nonlinear partial differential equations (PDEs) and fractional PDEs (FPDEs), efficiently produces a plethora of traveling wave solutions for the targeted CBLE, capturing the system's nuanced dynamics. The methodically determined traveling wave solutions are in the form of rational, exponential, hyperbolic and trigonometric functions which include periodic waves, bell-shaped kink waves and signal and double shock waves. To accurately depict the wave phenomena linked to these solutions, we generate 2D, 3D, and contour graphs. These visualizations not only improve understanding of the CBLE model's dynamics, but also provide a detailed way to examine its behavior. Moreover, the use of the proposed techniques contributes to a better understanding of the other FPDEs' distinct characteristics, enhancing our comprehension of their underpinning dynamics. [ABSTRACT FROM AUTHOR]

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering. [ABSTRACT FROM AUTHOR]

In this article, we use the modified extended direct algebraic method (mEDAM) to explore and analyze the traveling wave phenomena embedded in the quintic conformable Benney-Lin equation (CBLE) that regulates liquid film dynamics. The proposed transformation-based approach developed for nonlinear partial differential equations (PDEs) and fractional PDEs (FPDEs), efficiently produces a plethora of traveling wave solutions for the targeted CBLE, capturing the system's nuanced dynamics. The methodically determined traveling wave solutions are in the form of rational, exponential, hyperbolic and trigonometric functions which include periodic waves, bell-shaped kink waves and signal and double shock waves. To accurately depict the wave phenomena linked to these solutions, we generate 2D, 3D, and contour graphs. These visualizations not only improve understanding of the CBLE model's dynamics, but also provide a detailed way to examine its behavior. Moreover, the use of the proposed techniques contributes to a better understanding of the other FPDEs' distinct characteristics, enhancing our comprehension of their underpinning dynamics.

With recent advances in semiconductor technology, conventional cooling methods and standard coolants are no longer adequate to manage electronic chips’ enormous heat generation. Therefore, innovative cooling solutions are required to maintain these devices at optimum operating temperatures. Taylor flow in microchannels is an effective technique that allows excellent mixing of two fluids, which is crucial for heat transfer. A 3D numerical analysis of the heat transfer performance of liquid-liquid Taylor flow in a rectangular microchannel was carried out by ANYSY Fluent. Water droplets were dispersed in either ethylene or propylene glycol, with the interface between the two fluids captured using the Volume of Fluid method. For optimal computational time, two symmetries in the XY and XZ planes are considered. Furthermore, mesh size refinement was performed in the near-wall region to capture the liquid film. An analysis of the effect of plug/slug length and liquid film thickness is conducted with initially constant thermo-physical properties. This assumption was considered to analyse the heat transfer process and determine the most critical parameter affecting heat transfer performance. A user-defined function is then implemented in ANSYS Fluent to examine the effect of working fluids temperature-dependent viscosity change on the heat transfer rate. Conjugate heat transfer and axial conduction are also examined, as these two factors can significantly affect the thermal behaviour inside the microchannel and enable the achievement of realistic and accurate results. The results reveal that Taylor liquid-liquid flow can increase the heat transfer rate by up to 440% over single-phase flow. It was also found that the temperature-dependent viscosity of the working fluids significantly affects the plug/slug length and liquid film thickness, resulting in a 20.8% improvement in heat transfer rate compared with constant thermo-physical properties. This study will improve the state of knowledge on heat transfer by Taylor flow in microchannels and factors that can influence it, and highlight the significance of this flow pattern in enhancing heat transfer performance over single-phase flow.

Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With recent advances in semiconductor technology, conventional cooling methods and standard coolants are no longer adequate to manage electronic chips' enormous heat generation. Therefore, innovative cooling solutions are required to maintain these devices at optimum operating temperatures. Taylor flow in microchannels is an effective technique that allows excellent mixing of two fluids, which is crucial for heat transfer. A 3D numerical analysis of the heat transfer performance of liquid-liquid Taylor flow in a rectangular microchannel was carried out by ANYSY Fluent. Water droplets were dispersed in either ethylene or propylene glycol, with the interface between the two fluids captured using the Volume of Fluid method. For optimal computational time, two symmetries in the XY and XZ planes are considered. Furthermore, mesh size refinement was performed in the near-wall region to capture the liquid film. An analysis of the effect of plug/slug length and liquid film thickness is conducted with initially constant thermo-physical properties. This assumption was considered to analyse the heat transfer process and determine the most critical parameter affecting heat transfer performance. A user-defined function is then implemented in ANSYS Fluent to examine the effect of working fluids temperature-dependent viscosity change on the heat transfer rate. Conjugate heat transfer and axial conduction are also examined, as these two factors can significantly affect the thermal behaviour inside the microchannel and enable the achievement of realistic and accurate results. The results reveal that Taylor liquid-liquid flow can increase the heat transfer rate by up to 440% over single-phase flow. It was also found that the temperature-dependent viscosity of the working fluids significantly affects the plug/slug length and liquid film thickness, resulting in a 20.8% improvement in heat transfer rate compared with constant thermo-physical properties. This study will improve the state of knowledge on heat transfer by Taylor flow in microchannels and factors that can influence it, and highlight the significance of this flow pattern in enhancing heat transfer performance over single-phase flow. [ABSTRACT FROM AUTHOR]

"Temperature swing" by heat insulation coating is a technology developed to reduce heat loss in diesel engines. The purpose of this study is to evaluate the fuel film thickness formed on the piston surface with heat insulation coating. A 1-dimensional heat transfer model is developed and the inside temperature distribution of the piston at the compression TDC of the first cycle of a diesel engine during cold start is estimated. The inside temperature distribution of the piston can be reproduced by instantaneous heating with a pulsed laser. The fuel film thickness is evaluated by applying the refractive index matching (RIM) method. When the piston is instantaneously heated with the pulsed laser, the fuel film thickness decreased by 15 % compared to no heating condition. [ABSTRACT FROM AUTHOR]

The leading-edge erosion of a wind turbine blade was tested using a whirling arm rain erosion tester, whose rotation rate is considerably higher than that of a full-scale wind turbine owing to the scale effect. In this study, we assessed the impact pressure of droplets on a wet surface of wind turbine blades using numerical simulation of liquid droplet impact by solving the Navier–Stokes equations combined with the volume-of-fluid method. This was conducted in combination with an estimation of liquid film thickness on the rotating blade using an approximate solution of Navier–Stokes equations considering the centrifugal and Coriolis forces. Our study revealed that the impact pressure on the rain erosion tester exceeded that on the wind turbine blade, attributed to the thinner liquid film on the rain erosion tester than on the wind turbine blade caused by the influence of centrifugal and Coriolis forces. This indicates the importance of correcting the influence of liquid-film thickness in estimating the impact velocity of droplets on the wind turbine blade. Furthermore, we demonstrated the correction procedure when estimating the impact velocity of droplets on the wind turbine blade.

Controlling the distribution of the abrasive grains on the surface of the grinding tools in an appropriate way is important for improving the quality of grinding processing and meeting the workpiece precision requirements. In the present study, a novel method for the orderly arrangement of abrasive particles is proposed by using the liquid film flow on the surface of the rotating disk as the driving and controlling means for the uniform dispersion and position arrangement of abrasive particles. Computational fluid dynamics (CFD) simulations have been performed to clearly illustrate the trajectories of abrasive particles under the strong influence of liquid film flow on the rotating disk and reveal the effects of fluid flow, disk rotational motion, and the mixture viscosity on the particle distribution. A new abrasive grain arrangement device is designed and fabricated using this novel method. The operating parameters such as liquid volume flow rate, disk rotational speed, and liquid viscosity are adjusted to control the placement of abrasive grains on the surface of the grinding tool. An image processing tool is used to examine and analyze the arrangement results. The experimental results indicated that the application of the liquid film flow on a rotating disk to the abrasive grain arrangement can improve the arrangement of abrasive grains and get rid of the dependence on the template.

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering.

The concept of disjoining pressure has drawn attention since its first appearance in colloidal chemistry in the 1930s. Almost every scenario with liquid nano and sub-nano film is considered to be related to or even dominated by disjoining pressure. However, debates also last for years. Recently, researchers have explored the physical essence behind it computationally, while few computational works reproduced the discontinuity i.e. the pressure jump in experiments. In this study, a dynamic simulation with a large reservoir according to the very original definition of disjoining pressure by B. V. Derjaguin based on the experiment is conducted and the pressure jump is observed. The disjoining pressure isotherm is found to vary in four dynamic stages, and the liquid re-ordering stage corresponds to the disjoining pressure jumps. The understanding of disjoining pressure based on liquid molecular packing structure could pave the way to a predictive modeling of disjoining pressure. [ABSTRACT FROM AUTHOR]

• Present research considers step laser induced thermocapillary flow in a thin film. • Radial temperature gradient acts as the driving force for the surface-induced flow. • Two instantaneous velocity peaks appear at different radial locations. • The appearance of distinct velocity peaks is for short time intervals. • The second velocity peak appears due to hydrothermal propagation. Temporally developing thermocapillary convection induced by step laser heating of a thin liquid film has been studied numerically. Computations are performed using the commercial software STAR CCM+ version 2022.1. The liquid film of silicone oil (high Prandtl number fluid) is 60 mm in diameter and 3 mm in thickness. Flow characteristics related to surface velocity and surface temperature have been studied. Validation of the computations is achieved for the surface velocity, the velocity along thickness and the surface temperature through comparison with PIV and IR camera measurements. The laser-beam with a carbon dioxide gas laser (10.4 μm in wavelength) is used for heating. It is found that the temporally developing profile of surface velocity shows two local velocity peaks (u S 1 and u S 2) at two radial locations (r S 1 and r S 2) respectively. The first peak, u S 1 , appearing due to the steep temperature gradient generated by laser-beam heating and its radial position, r S 1 , do not change noticeably with time. On the other hand, the second peak, u S 2 , travels radially outwards with decreasing magnitude in a self-propelling manner until its radial position, r S 2 , approaches an asymptotic maximum. Detailed analysis of the coupling among radial temperature gradient, local pressure variation and local convective acceleration near the second peak reveals that hydrothermal mechanisms are responsible for self-propelling travel of u S 2. The transient behaviors of both primary and secondary velocity peaks are found to depend on the fluid viscosity and the laser-beam settings. [ABSTRACT FROM AUTHOR]

• The effect of different wettability ratios on boiling heat transfer was systematically investigated. • The mechanism of the influence of mixed wettability surfaces on the boiling process was revealed. • The ratio of wettability to surface with the best heat transfer performance was found. In this work, molecular dynamics (MD) simulation is applied to study the effect of heating surfaces with different hydrophobicity occupancy ratios (the ratio of the surface area of hydrophobic spots to the total area of the heating surface) on the boiling process of the liquid film explosion. At the same time, the mechanism is revealed from the trajectory of argon atoms. The simulation results showed that the onset of explosive boiling was later for purely hydrophilic surfaces than for hybrid wettability surfaces with a hydrophobicity percentage of <11%. The earliest onset of explosive boiling was observed for the heated surfaces with a hydrophobicity ratio of 6%. In addition, it was found that the superheat required for explosive boiling tended to decrease first and then increase with the gradual increase of the hydrophobicity ratio. Hydrophobic spots arranged on the surface provided bubble nucleation earlier for explosive boiling while enhancing convective heat transfer and thermal perturbation. The critical heat flux (CHF) of the heated surfaces with a hydrophobicity ratio of <11% were all greater than that of the purely hydrophilic surfaces, and all reached the CHF before the purely hydrophilic surfaces. [Display omitted] [ABSTRACT FROM AUTHOR]

• Gravity affected the velocities of isolated films on the vertical smooth surface. • Heat transfer between the vertical and upward surfaces presented no measurable difference. • The Bo of the upward surface was smaller than that of the vertical surface for HFE-7100. • The data map of liquid film flow in spray cooling was further updated. In this study, an experimental investigation was conducted on the dynamics and heat-transfer characteristics of liquid film flow for upward- and vertical-facing spray cooling. The heat-transfer performances at different inlet pressures, nozzle-to-surface distances, and heat flux inputs between the two orientations were compared, and the morphologies, wetted areas, and velocities of the isolated liquid films were quantitatively captured. The morphologies of the HFE-7100 liquid films and their distributions on the vertical and upward surfaces exhibited no significant differences. In most cases, the heat-transfer performance of the upward surface was slightly better than that of the vertical surface. Gravity affected the velocity of the isolated liquid films on a smooth vertical surface, whereas its effect was significantly suppressed on an unpolished surface. The Bond number of the isolated liquid film flow on the upward surface was verified to be naturally smaller than that on the vertical surface. Dimensionless groups, including the Bo, We , and Re numbers of the liquid film flow in spray cooling, were obtained to further account for the effect of gravity. The reason why the dimensionless groups presented such small orders was explained. The data map of liquid film flow (dimensionless groups) during spray cooling was further enriched. [ABSTRACT FROM AUTHOR]

• The effect of impact angle on the heat transfer of droplets impact film is revealed. • The two droplets vertically impinge the film with better heat transfer efficiency. • The heat transfer of the droplet impact outward is better than inward. • A high temperature zone will appear at the bottom of the middle film jet. To gain a better awareness on heat transferring mechanism of droplet impingement on liquid films, this study adopted the coupled level set–volume of fluid method for numerically simulating the symmetric impacts of two droplets upon the liquid film. Based on the flow mechanism of multiple droplets impacting liquid film, we studied heat transferring processes of two cold droplets obliquely impacting a hot liquid film. By analyzing diverse impacting modes, droplet impacting interface morphology, splash temperature, and variations of wall heat transfer coefficient were examined, and influences of droplet spacing and film thickness on heat transfer features were examined. we found that the vertical impact upon liquid film had the best heat transferring efficiency to the wall, and the maximum wall–average heat transfer coefficient can reach 9903 W/m2·K. The symmetric outward impact upon liquid film had maximal heat transferring range. The lower liquid film thickness produced a higher local heat transfer coefficient on wall surface. Droplet spacing mainly affected the scope of variations of heat transfer coefficient but had a small influence on splash temperature. [ABSTRACT FROM AUTHOR]

• Ethanol film spreads wider on the surface than water. • At low similar Weber number (<500), drop size is dependent on the liquid physical properties. • At high similar Weber number (>500), Weber number alone is sufficient to describe atomization process. This study examines the behavior of ethanol or water films on the surface of a NACA 0012 airfoil placed in a high-speed air flow. New water film results complement previous measurements of time averaged ligament lengths and droplet sizes generated with the same airfoil. In addition, new data are obtained for ethanol. Air velocities up to 175 m/s are used with liquid flow rates between 1.4 cm2/s and 2.6 cm2/s. The liquid was introduced onto one side of the airfoil via 26 holes, each measuring 0.5 mm in diameter and spaced 1 mm apart. These holes are positioned 35 mm downstream from the leading edge and 65 mm upstream from the trailing edge. Film behavior on the vane is captured with front-lit high-speed video. The accumulation of liquid and breakup of ligaments are captured with backlit highspeed video. Phase Doppler interferometry is used to measure droplet size and simultaneous axial and pitch wise velocity 70 mm downstream of the trailing edge. Finally, laser diffraction is used to measure line averaged droplet sizes. The results indicate notable differences between ethanol and water films. The ethanol film spreads more extensively across the width of airfoil which is attributed due to its lower surface tension. The maximum ligament length for both liquids decrease with higher air velocity and increase with the liquid flow rate. A correlation for maximum ligament length is developed and captures the effect of liquid properties, flow rate, and air velocity. Furthermore, the variation in liquid volume flow rate did not impact droplet size. However, for a given air velocity, the Sauter Mean Diameter is found to depend on surface tension. On the dependency of droplet size on the Weber number, ethanol produced smaller droplet sizes at low values of Weber number. However, at relatively high Weber numbers, the droplet sizes for both water and ethanol were similar. This suggests that droplet size is influenced by factors besides surface tension at low Weber numbers but not at higher Weber numbers. In addition, the Nukiyama-Tanasawa model to fit the volume distribution curves is simplified by fixing p and q terms. Simplification makes the model easier to understand and implement. [ABSTRACT FROM AUTHOR]

Euler–Euler methods are one of the many approaches available in literature for modeling droplet-laden flows. These models consider both the gas and droplet phases as inter-penetrating continua, thereby separate sets of transport equations are solved for these phases. The current work focuses on modeling of thin liquid films on solid surfaces in the context of the two-fluid approach to multiphase simulation. In majority of the literature, liquid films are modeled using a 2D Laminar approximation with a parabolic profile for the velocity across the film. However, a number of industrial applications demonstrate a turbulent behavior of the film which would affect the effective viscosity and thereby the thickness of the film. In the current work, a turbulent model for liquid films is proposed based on the Universal Velocity Profile. Additional models are employed to capture the deposition of droplets onto solid surface and stripping off of droplets from the film due to surface waves. The liquid film model is validated on experimental data from available literature. Finally, the newly implemented turbulent film model is applied to study the flow over a fuel rod assembly in a Boiling Water Reactor. • Annular flows appear in many industrial applications like Boiling Water Reactors. • Most literature focuses on Laminar modeling of the liquid films in annular flows. • Liquid film turbulence in annular flows greatly affects the flow behavior. [ABSTRACT FROM AUTHOR]

• Heat transfer mechanisms in thin horizontal liquid layers have been investigated. • The effect of the shape and thermal conductivity of 2D-modulated porous coatings on heat transfer has been studied. • The relationship between relative pressures and liquid layer heights is presented in detail. • The effect of 2D-modulated porous coatings on crisis phenomena and transients has been described. Investigation results on heat transfer during evaporation and boiling in thin horizontal liquid layers on 2D modulated capillary-porous coatings with a sinusoidal profile in a wide range of relative pressures and layer heights are presented in this paper. Coatings were made on a 3D laser printer using the technology of additive selective laser sintering (SLS). One coating was made of bronze with a modulation wavelength equal to the Laplace constant of the working fluid and two coatings were made of stainless steel and bronze with a doubled wavelength. The experimental data obtained on the coatings were compared with each other and with the values obtained by evaporation and boiling of n-dodecane on a smooth surface under the same conditions. It is shown that in the region of low relative pressures in liquid layers with a height less than the Laplace constant, heat transfer intensification achieved on a sample made of a material with low thermal conductivity (stainless steel) was five times higher as compared to a smooth surface. In the range of relative pressures, when nucleate boiling was observed in the layers, the temperature difference reached on the bronze coatings was approximately 3–4 times less than on a smooth surface. The temperature difference for the stainless steel coating changed little with an increase in the heat flux. In pre-crisis conditions, the temperature difference during boiling on the stainless steel coating was less than on the bronze coatings in the entire range of relative pressures and layer heights. The highest critical heat fluxes were obtained on a bronze coating with a modulation wavelength equal to the Laplace constant. [ABSTRACT FROM AUTHOR]

• Droplets produced through the bubble bursting from the liquid film were found. • Droplet diameter from the bubble bursting was characterized. • Effect of thermal boundary layer and film thickness on droplet size was examined. • The loss of the liquid flow rate by the boiling induced atomization was negligible. For the thermal management of industrial devices, a reduction in the net coolant flow rate by droplet dispersion from a liquid film is important because it can cause unexpected thermal failure. To understand the process of droplet dispersion from a liquid film better, we experimentally and theoretically evaluated the characteristics of boiling-induced atomization in a liquid film formed by oblique jet impingement on a superheated wall. Atomization processes were visualized using magnified high-speed imaging using a backlight technique. In this study, two types of droplets were observed using high-speed-magnification imaging. These were large droplets that disintegrated from the ligament formed on a relatively high-temperature wall, and small droplets from the ligament formed via bubble bursting in the nucleate boiling regime. For the atomization induced by nucleate boiling, larger droplets were produced via bubble bursting further downstream from the impingement point because the bubble size and liquid film thickness increased. Finally, the total volume of the droplets produced by nucleate boiling was estimated from the frequency of bubble bursting and droplet size measured from the visualization results. The estimation results suggest that the ratio of the total volume flow rate of the ejected droplets to the injection flow rate of the liquid was negligible (2%). Thus, most of the injected liquid eventually reached the wetting front of the sheet, separating it from the wall before drying out. [ABSTRACT FROM AUTHOR]

• 3D numerical simulation of oil-water droplet flow in a microchannel. • Effect of short and long obstacles and flow rate on heat transfer and pressure. • Improved mixing and heat transfer due to recirculating flow. • Droplet size and liquid film thickness directly and reversely affect the heat transfer, respectively. • Increased heat transfer with slight pressure drop penalty using the obstacles. Droplet-based microfluidics is an emerging technology for thermal management of high heat dissipating systems and electronics cooling. The current work investigates the potential of slug flow for thermal management of mini-sized heat dissipating devices and microchannels. Hydrothermal characteristics of oil-water slug flow including droplet size, liquid film thickness, pressure drop, and heat transfer have been studied in a T-shaped microchannel. Three dimensional numerical simulations have been carried out for two types of ribbed channels with short and long obstacles at different flow rates. Results indicate that droplet size and liquid film thickness directly and reversely affect the heat transfer rate, respectively. The former intensifies the flow recirculation, and the thermal boundary layer disturbance while the latter changes the dominant heat transfer mechanism to conduction. On the whole, a maximum of 55 % heat transfer enhancement has been achieved relative to the single-phase water flow. It is also observed that by using obstacles on the channel surface, the heat transfer enhancement can be further increased with a slight pressure drop penalty. [Display omitted] [ABSTRACT FROM AUTHOR]

• Experiments of nitrogen gas and ethanol aqueous solutions of 30 %, 60 %, and 95 % (v/v) under 0.2 MPa were conducted. • Film thickness together with height, velocity, and frequency of disturbance waves was comprehensively studied. • Bubbles in the liquid film was found to be critical to the liquid film characteristics. • The link between the number of bubbles and the ethanol concentration was interpreted by the bubble stability due to the dynamic rise in surface tension. • Special attention to the effect of bubbles and bubble stability is recommended when use solutions composed of multi-components with significant differences in surface tension. Vertical upward annular flow experiments of nitrogen gas and ethanol aqueous solutions with volume fractions of 30 %, 60 %, and 95 % under 0.2 MPa were conducted. The characteristics of the liquid film including base, average, and maximum film thickness and height, velocity, and frequency of disturbance waves were obtained and studied based on the constant electric current method in a 5 mm inner diameter polycarbonate tube. The flow behavior was observed using a high-speed camera simultaneously. It is found that a large number of bubbles in the liquid film is critical to these characteristics. A connection between ethanol concentration and bubbles in the liquid film is found and interpreted by considering bubble stability which arises from the dynamic rise in surface tension. Our experimental investigation suggests that the effect of bubbles in the liquid film on the flow characteristics is not negligible in such annular flows under high liquid flow rates and bubble stability should be considered for annular flows employing solutions consisting of two or more components with large differences in surface tension. [ABSTRACT FROM AUTHOR]

Oscillating heat pipes (OHPs) consist of a serpentine capillary channel partially filled with liquid that is embedded in a thermally-conducting solid. They have significant advantages for cooling electronics and aerospace systems. The model reported here aims to capture the essential physics of an OHP with minimal complexity and treats some parameters typically derived from correlations or experiments (such as the film thickness and film triple point velocity) as functions with tunable constants to be estimated by data assimilation. This model contains two modules. The first uses a novel and flexible formulation of the conducting solid, solving the two-dimensional heat equation in a thin plate, with evaporators and condensers as immersed forcing terms and the OHP channel as an immersed line source. The second module solves one-dimensional fluid motion and heat transfer equations within the fluid-filled channels based on mass, momentum, and energy conservation, nucleate boiling, and bubble dryout. It extends the commonly-used film evaporation-condensation model, allowing both variable liquid film thickness and length and thereby enabling the model to capture dryout. These modules are weakly coupled, in that wall temperature in the channels are obtained from the first module and heat flux from the channels determines the line source strength. After minimal training, the thermal conductance calculated by this model shows good agreement with a wide range of experiments performed by Drolen et al. [1]. In particular, the model successfully predicts the experimentally-observed transition from stable OHP operation to dryout, for the first time to the authors' knowledge. • A two-dimensional conjugate heat transfer model for flat-plate OHPs is proposed. • The model aims to capture essential physics with minimal complexity. • The immersed boundary method is used to couple the fluids model and the solid model. • This model is validated with ASETS-II experiment for 16 cases with Butane as the working fluid. • The dry-out phenomenon is successfully captured after minimal training. [ABSTRACT FROM AUTHOR]

A novel approach to alleviate erosion by adding water, based on the principle of the soft overcoming the hard, was investigated through self-designed erosion experiments and computational fluid dynamics (CFD) simulations. The results demonstrate that adding a liquid phase to the elbow significantly reduces the erosion rate. The erosion inhibition efficiency is positively correlated with the liquid phase content, reaching 81.56 % in the most severe erosion zone during the experiments. The liquid film can increase the drag force and reduce the particles' impact velocity. Rather than exacerbating erosion, the liquid film enables easier particle accumulation and mitigates erosion instead. • Adding the liquid phase can effectively alleviate the erosion of the elbow. • The inhibition efficiency is positively correlated with the liquid content. • Liquid film can significantly reduce the particles' impact velocity. • The aggregation of particles in the liquid film does not aggravate erosion. [ABSTRACT FROM AUTHOR]

• Enhanced surfaces such as straight fin surface and cubic fin surface with relatively large heating surface of 4 cm2 were designed. • A parametric study is conducted to evaluate effects of flow rate, spray distance and enhanced surfaces on spray cooling. • Visualization was presented to elucidate enhanced mechanism of spray cooling. • Compared to flat surface, HTCs on both straight fin surface cubic fin surface are significantly enhanced up to nearly 60%. • At a spray distance of 25 mm, heat flux about 250 W/cm2 is achieved on cubic fin surface. Spray cooling as an effective cooling technique is widely used in practice. Compared to small heating surfaces, the significantly increase of surface would pose a great challenge to the significant enhancement of spray cooling. Specially, single nozzle spray cooling suffers from non-uniform liquid thin film on a relatively large heating surface, severely inhibiting the formation of efficient thin film evaporation. In this study, two enhanced surfaces such as straight fin surface and cubic fin surface with a relatively large heating surface of 4 cm2 were designed for single nozzle spray cooling. A parametric study was conducted with aims to evaluate the effects of flow rate, spray distance and enhanced surfaces on the formation of thin liquid film and then the performance of spray cooling. Visualization was presented to observe the development of liquid film to elucidate the enhanced mechanism of spray cooling. In this work, spraying height is varying from 20 to 40 mm. Coolant flow rate is ranging from 70 to 100 ml/min. The experimental results show the distribution of liquid film plays an important role in spray cooling, especially in the single-phase regime. In two-phase regime, nucleate boiling is significantly boosted on the engineered surfaced. For instance, the cubic fin surface leads to an enhancement of HTC of nearly 24 % compared to that of flat surface. [ABSTRACT FROM AUTHOR]

• It is an attempt to measure the velocity of falling film over tube by PTV method. • 3D Simulation is conducted to study the velocity distribution of falling film. • Tangential and axial distributions of liquid film velocity are discussed in detail. • Experimental and simulated results and their differences are compared and analyzed. The velocity characteristics of falling film on horizontal tube affect the heat transfer efficiency. To date, experimental studies on velocity distribution of liquid film on tube surface are very scarce. In this paper, the mean velocity of liquid film is measured using particle tracking velocimetry (PTV). A simulation is also conducted to investigate the flow characteristics of falling film. Results show that the spreading of liquid film undergoes two stages: circular spreading and circumferential flow. In circumferential direction, the liquid film tangential velocity shows different law in planes of L * = 0–0.3 and L * = 0.4/0.5. The tangential velocity decreases and then increases as axial distance increases. Simulation results agree well with the experimental results within experimental angle range. The liquid film axial velocity is always zero at L * = 0. When L * = 0.1–0.5, the axial velocity decreases as circumferential angle increases and gradually tends toward zero. [ABSTRACT FROM AUTHOR]

• Modern technologies of extremely high aspect microchannel creation. • Flow pattern investigation and proposed flow pattern classification. • Analysis of flow patterns, flow pattern transition mechanisms and flow instabilities. • Flow pattern borders generalization indicates the negligible effect of liquid inertia forces. • The Saffman-Taylor instability, instability caused by transverse pressure gradient become flow pattern-determining factors. To date, in the public domain there is a lot of experimental data on adiabatic two-phase flow in microchannels of various geometries (round, rectangular, square). However, microchannels with high aspect ratio (slit microchannels) remain poorly understood. In this article, an adiabatic two-phase flow in a slit microchannel with a height of 12.5 µm and width of 10 mm (aspect ratio 1:800) has been experimentally investigated for the first time in the wide range of liquid and gas superficial velocities (from 0.0026 to 0.266 m/s for liquid and from 0.266 to 7.73 m/s for gas). The combination of photolithography, anisotropic etching and thermal anode bonding allow us to create flow cells with slit microchannel height of 12.5 µm and width of 10 mm. Channel height and characteristics of channel surfaces (roughness and contact angles) have been measured using scanning electron microscopy (SEM) stylus profilometer, atomic force microscopy (AFM) and sessile drop technique respectively. For the first time, the new flow pattern and flow patterns transitions have been investigated and flow pattern maps for several liquids with various physical properties have been constructed. One of these maps has been compared with a map of a slit microchannel with large height. It is shown that the flow pattern maps for liquids that completely wet the mixing section can be generalized in coordinates liquid Capillary number C a l and gas Weber number W e g , which indicates the negligible effect of liquid inertia forces on the flow pattern boundaries. It has been shown that with an increase of surface tension, the region of the Jet flow pattern expands. It has been established that Saffman-Taylor instability in the mixing section and along the channel, instability caused by transverse pressure gradient and surface wettability are pattern-determined factors. [ABSTRACT FROM AUTHOR]

• Formations of heart-shaped film and fountain are attributed to two films merging. • Evolution of fountain and size characteristics of splashes are revealed. • Splashes volume concentration shows a bimodal distribution after fountain breakup. The technology of liquid film by jet impingement is widely applied in aerospace, electronics and cleaning. In this paper, the spreading and evolution of the liquid films formed by two continuous jets impinging obliquely on a vertical wall are experimentally studied. The effects of the jet Weber number, jet inclination angle, nozzles spacing and angle between two jets on the films are examined. Results show that three flow patterns are observed as the experimental conditions vary, including two separated liquid films, a heart-shaped liquid film and a heart-shaped film with the fountain sheet breakup. The formation of a heart-shaped liquid film is attributed to the merging of two films and results in the spreading area and length of the film increasing suddenly. The fountain sheet forms when two liquid films merge, and develops with the increase of the jet Weber number. When the balance between the surface tension on the fountain sheet and the inertial force as well as gravity that form the fountain is disrupted, the fountain sheet breaks up, and causes the splashing rate to increase suddenly. The volume concentration of the splashing droplet size displays the bimodal distribution after the occurrence of the fountain sheet breakup, which indicates the existence of two splashing droplet formation mechanisms in the systems, the surface wave and fountain sheet breakup. The height variation of the left and right peaks of the bimodal distribution reflects the competition between the two splashing generation mechanisms. [ABSTRACT FROM AUTHOR]

• The spreading and splashing of the liquid film by inclined jet impingement were studied using high-speed cameras. • A unique liquid film deflection phenomenon is observed due to the boiling of the liquid film. • The splashing characteristics and mechanism of liquid film have been discussed. In this paper, the liquid film formed by inclined jet impingement on the vertical hot wall is investigated by a high-speed camera. The effects of the jet velocity (5.5 m/s ≤ u 0 ≤ 14.6 m/s, 3804 ≤ Re ≤ 10098) and initial wall temperature (25 ℃≤ T 0 ≤ 250 ℃) on the spreading and splashing of the liquid film are explored. Although the jet velocity and initial wall temperature have little effect on the spreading velocity of the liquid film, the wetting front position and liquid film area increase. For T 0 ≥ 150 ℃, a unique liquid film deflection phenomenon is observed due to the boiling of the liquid film, which results in a substantial amount of splashing. Based on the characteristics of the deflection splashing, three modes are categorized, i.e., annular splashing, banded splashing, and non-splashing. The splashing of the liquid film on the hot surface is owing to the rupture of boiling bubbles, the breakup of surface waves, and the liquid splashing in the boiling zone. The splashing rate of the liquid film is measured, and it is found that an increase in T 0 improves the splashing rate significantly, and the splashing rate even exceeds 70 % at T 0 = 250 °C. [ABSTRACT FROM AUTHOR]

• Molecular interaction is affected by oils with different density and emulsification. • Foamability decreases under fuel due to emulsification between fuel and surfactants. • Presence of liquid fuel accelerates foam drainage and liquid film thinning behavior. • Oil resistivity of foam depends on difference in nature and emulsification of oils. In this study, the influence mechanism of typical fuels (oils) on the foam properties of mixture of hydrocarbon and fluorocarbon surfactants was investigated. A mixed solution was prepared based on a nonionic hydrocarbon surfactant (APG-0810) and a zwitterionic C6 fluorocarbon surfactant (short-chain). The effect of different oils (heptane, kerosene, diesel, and transformer oil) on the physical property parameters, foamability, oil resistivity of foam and single vertical liquid film of the mixture are systematically investigated. Results indicate that the viscosity of mixture increases, but the conductivity, surface activity, and initial foam height decreases with addition of the four oils. The drainage and volume decay of the foam are accelerated by the presence of oils. In addition, the presence of oils accelerates liquid film thinning through affecting drainage, especially for the oil with higher density, water solubility, and volatility. The four oils showed different effect on foam properties due to the difference in nature and emulsification of them. Among them, the foam properties under the action of heptane is the best, and the oil resistivity of foams is the best. This study can provide theoretical guidance for oil resistivity of hydrocarbon and fluorocarbon surfactant stabilized foams. [ABSTRACT FROM AUTHOR]

The performance degradation of railway vehicles operating in wind-rain environments has attracted widespread attention in recent years. This work focuses on a numerical study of the liquid film morphology and train aerodynamic performance under wind-rain environments. The train aerodynamic model in wind-rain environments is set up using Eulerian–Lagrangian methodology, and validated with existing experimental results. The liquid film morphology of the train is discussed using the Lagrangian wall film (LWF) model. The aerodynamic characteristics such as liquid film morphology, surface pressure, shear stress, velocity contour, aerodynamic coefficient, etc., are then discussed in detail. The results show that, when the rainfall duration is constant, the liquid film becomes thicker as rainfall intensity is greater. As crosswind becomes stronger, the thickness of liquid film gathered on the train roof decreases, and the liquid film on the windward and leeward sides of the train becomes thicker. The shear stress on the train in wind-rain environments is obviously greater than that exposed to crosswind environments. For the reason of rainfall, the skin friction coefficient on the train also increases, which will have an impact on the frictional resistance. Rainfall would lead to an increase in the aerodynamic coefficient of trains operating in crosswind environments, especially for lift force coefficient and pitch moment coefficient. • The train aerodynamic model in wind-rain environments is set up using Eulerian–Lagrangian method. • A methodology for calculating the liquid film morphology on train surface is proposed using the Lagrangian wall film model. • The generation and distribution of the liquid film morphology on train surface under wind-rain environment are analyzed. • Rainfall would lead to an increase in the aerodynamic coefficient of trains operating in crosswind environments. [ABSTRACT FROM AUTHOR]

Gas-liquid two-phase flow exists in nuclear reactor evaporation, vehicle cooling, chemical production falling film evaporation and other processes, and the dynamic measurement of the interfacial wave is of great significance for industrial process monitoring and production optimization. Accurate identification and characterization of interfacial wave is an important prerequisite for scientific research and engineering practice. In this paper, interfacial wave measurement experiments have been carried out using an ultrasonic phased array system and measurement method to obtain gas-liquid phase interface measurement information in gas-liquid flow system. The liquid film thickness is extracted by fitting the gas-liquid interface through two-dimensional data matrix to ladder, detecting the liquid level data, and constructing a three-dimensional interfacial wave distribution model based on dynamic real-time data. The interfacial wave amplitude prediction correlation is developed using various machine learning regression models, which are optimized by parameters tuning algorithms. Laboratory results indicate that the wave amplitude prediction correlation is highly correlated with five inlet parameters, including superficial gas velocity, superficial liquid velocity, gas Reynolds number, liquid Reynolds number, and Lockhart-Martinelli (L-M) parameter. In the seven typical wave amplitude prediction correlations for stratified and plug flow, Least Squares Boosting (LSBoost) provided the best fit with MAPEs of 11.26 % and 18.42 %. The Gray Wolf Optimizer (GWO) is proposed and used to optimized the wave amplitude prediction correlation of LSBoost, and the MAPEs of optimized model are 4.38 % and 17.26 %. This paper provides a reliable method for accurate measurement and methodological analysis of interfacial wave spatial-temporal characteristic parameters of gas-liquid two-phase flow. • A three-dimensional measurement method of interfacial wave based on ultrasonic phased array is designed. • A three-dimensional interfacial wave distribution model based on dynamic real-time data is constructed. • The interfacial wave amplitude prediction correlation is established using multiple machine learning regression models. • Optimization of the wave amplitude prediction correlation by multiple parameter tuning algorithms. [ABSTRACT FROM AUTHOR]

• A thin liquid film is observed beneath the vapor slug. • This liquid film is evaporated completely when CHF occurs. • The increase in coolant subcooling is conductive to the improvement of CHF. • There is decrease trend of CHF near the position closing to 90°. It is essential to conduct theoretical and experimental research on the heat transfer limit for External Reactor Vessel Cooling (ERVC), which aims to implement In-Vessel Retention (IVR) severe accident mitigation strategy successfully. In this paper, a theoretical model for IVR-ERVC condition is proposed to predict the critical heat flux (CHF) based on the experimental observation. According to the experimental observation on the one-dimensional full height IVR-ERVC experimental facility, it is found that there is a thin liquid film between the heating surface and the vapor slug. And this film is evaporated completely when CHF occurs. In addition, a large number of bubble condensation collapses were observed under subcooling condition. According to these experimental observations, a CHF model based on the mechanism of liquid film dryout is developed. The CHF trigger mechanism of this model is that the supply of fresh liquid into the liquid film is not sufficient to prevent depletion of the liquid film due to the boiling. The influence of heating surface geometry and the heat flux shape are considered in this model. The predicted values of the model are compared with the CHF experimental result from different test facilities with different conditions, and the comparison result shows that the relative errors are basically within 20 %. The analysis results of the model indicate the increasing of coolant subcooled degree is conductive to the improvement of CHF. When the coolant subcooled degree increases by 15 ℃, more than 30 % maximum increase in CHF is obtained. In addition, this model can reflect the "exit phenomena" to a certain extent. [ABSTRACT FROM AUTHOR]

• A novel and universal disturbance wave velocity model was proposed. • Dominant scaling parameter group for wave velocity was revealed. • Entrained droplets effect plays a critical role on wave velocity. • New correlation collapses all entrained conditions within 5% error band. • Scalability and wide scope of application of the model were validated. A full knowledge of the interfacial effect on disturbance wave is vital for accurately predicting disturbance wave velocity in annular flow. However, almost all of the existing disturbance wave velocity models do not ponder the droplet-film mass transfer, which largely limits the applicable scope and prediction accuracy of the model. This article leads into the entrained droplets effect to the interfacial shear modeling, proposing a new disturbance wave velocity model with a widely applied range. The effects of entrainment and liquid film thickness on the characteristics of the gas core mixture (bulk density and velocity) were included, and the mean velocity of the liquid film surface was introduced in the modelling. For the verifying experiments, an annular flow loop with film metering device and electrode sensor was developed, and the entrainment and liquid film thickness were also modelled for the convenience of usage in cases without raw measured data. The new developed disturbance wave velocity model collapses the experiments corresponding to all entrained conditions well within ± 5.0% deviation for an 85.2% confidence interval. The comparative analysis with the existing empirical correlations confirms the critical role of entrained droplets on the disturbance wave velocity. The scalability and wide scope of application were further validated by the open data in the literature, and finally, practical suggestions were given for the disturbance wave velocity prediction on various pressure and pipe diameter conditions. [ABSTRACT FROM AUTHOR]

• The regimes of splashing is identified and characterized. • The jet angle and impingement distance affect the splashing rate and waves on the liquid film jointly. • The size distributions of splashing droplets are described by a log-normal distribution. Liquid film cooling by jet impingement, known as a common thermal protection technique, is extensively applied in liquid rocket engines. The present work investigates the impact of a water jet onto a vertical plate by high-speed visualization system and laser particle analyzer, with a focus on the characteristics of surface waves and droplets splashing during the formation of liquid film. Depending on whether the jet is broken before impact, two regimes are identified, i.e., droplet or continuous jet impingement regime. The frequency and velocity of the surface wave and the splashing rate are jointly affected by the jet angle and the impingement distance. The splashing is mainly caused by the capillary breakup of the crown film that forms at the edge of the surface wave, and most of the splashing droplets are generated from the top of the crown film. The larger the jet angle, the smaller the wave frequency and velocity, but the higher the splashing rate. A large impingement distance causes a small wave frequency and velocity due to the shift of the impingement regime, further resulting in different tendencies in the splashing rate. A parameter expression for the size distributions of splashing droplets is established by the fitting result of the log-normal distribution and the Rosin-Rammler (R-R) distribution, where the parameters are associated with the jet Weber number. [ABSTRACT FROM AUTHOR]

A detailed insight into the liquid film characteristics in the helical channel of single screw expander is of great significance for avoiding the leakage loss of higher pressure gas to lower pressure region. The liquid film thickness and fluctuation characteristics of the annular flow on the outer side of the helical rectangular channel is measured using the digital image processing algorithm, and they are evaluated under various flow rates, dimensionless curvature, and dimensionless pitch at different angle positions. Results show that increasing the Re g will decrease the instantaneous liquid film thickness, and a larger decrease in the liquid film fluctuation is found. A larger average liquid film thickness is located at the angle of 90° than that of the 180° and 270°. The instantaneous and average liquid film thicknesses are decreased with increasing the dimensionless curvature and dimensionless pitch at each angle position. Moreover, increasing the dimensionless curvature can weaken the effect of angle position on the liquid film thickness. The time distribution of the liquid film thickness changes dramatically in both wave height and amplitude as increasing the Re l at the smaller dimensionless pitch. • Instantaneous characteristic of liquid film flow in the helical rectangular channel is revealed. • Time distribution characteristic of instantaneous liquid film is measured in detail. • Evolution mechanism of the liquid film flow at the different angle position is analyzed based on the visualization result. • Influence of dimensionless curvature and dimensionless pitch on liquid film thickness is given. [ABSTRACT FROM AUTHOR]