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An oxyacetylene torch tested the ablation of SiC/SiC composites at 1800℃. According to the distribution of ablation product silica, the morphology could be divided into three regions. The fibers in the oval central region were ablated and broken, and the fracture surface is the conical tip. The silica liquid film in the transition region plays a role in resisting the ablation of the material. However, the generation of airflow channels destroys the liquid film's continuity and reduces the material's ablation resistance. Bean sprouts-like nano-sized silica was grown on the surface of the dome-top SiC matrix in the marginal region.

The interfacial shear stress and liquid film thickness are very important to establish the basic model of annular flow in practical applications. In this paper, the liquid film thickness of annular flow in a narrow vertical rectangular channel with a cross-sectional area of 70 mm × 2 mm was measured based on the PCB liquid film sensor. According to the experimental results, the average liquid film thickness, base film thickness and interfacial friction factor were calculated and analyzed. The experimental results showed that the liquid film thickness was affected by the gas phase velocity and the liquid phase velocity, but the effect of the gas phase velocity on the liquid film thickness decreased gradually with increasing gas phase velocity. Moreover, the interfacial friction factor was obvious affected by the liquid phase velocity at low gas phase velocity, but this influence gradually decreased with increasing gas phase velocity. Existing correlations for above parameters were summarized and evaluated with the current data, and there was a large deviation between the predicted results and the experimental results. Therefore, a new correlation for above parameters was proposed, respectively.

Thermal energy transfer (TET) is the main performance of contact interfaces which has been studied at a molecular level. Several investigations on TET were accomplished, however, the influences of liquid film thickness on TET have not been sufficiently examined. Thus, this paper analyses the influences of liquid film thickness on TET across solid–liquid (S-L) interfaces. Two liquid film thicknesses (Lz) of 30 Å and 60 Å have been evaluated, and two shear directions (x- and y-directions) have been tested in the simulation system. It has been found that there is no significant difference in the density distribution of liquid regardless of the shear directions for the same Lz. However, there are differences in the density distribution of liquid between Lz of 30 Å and 60 Å. Based on the results its suggests that, the cut-off of the temperature and velocity at the contact interfaces of solid and liquid is substantially influences by the liquid thickness of the simulation system. It is found that, there are a significant different in the thermal boundary resistance (TBR) for Lz of 30 Å and 60 Å for cases liquid sheared in the x-direction. Whereas TBR for Lz of 30 Å and 60 Å sheared in the y-direction have no significant difference. In conclusion, the TET is affected by the velocity cut-off at the contact interfaces of solid and liquid where larger velocity discontinuity exhibits higher TBR.

Falling film techniques are widely used in various chemical industrial devices because of their high heat and mass transfer coefficients. Since the coverage of a liquid film plays an important role...

With the aim to analyze the flow pattern and heat transfer characteristics of the working fluid in a flat plate heat pipe (FPHP) which was sealed by a transparent tempered glass plate, ethanol, acetone, and R141b were taken as the working medium, and visual experiments were performed at different heat flux when the inclination angle was 90°. The vapor-liquid distribution and the heat transfer characteristics of the FPHP were investigated at different liquid filling ratios. According to the experimental results and the recording of high-speed cameras, some important conclusions had been drawn as follows: (i) As the power increases, the vapor-liquid interface in the FPHP declines and the effects of dryout is significantly intnsified, leading to a sharp increase in temperature. The FPHP with a filling ratios of 25.7% owns better thermal performance than that with the filling ratios of 11.8% and 66% at different heating power; (ii) the bubble generation inside the FPHP became more intense with increasing heat flux, and various bubble movement patterns were found at different the liquid filling ratios; (iii) As the liquid film flowed downward, the thickness of the liquid film increased at first and then decreases. The condensation of steam was reduced due to the thickening of the liquid film on the wall. The liquid film became thinner when it was entrapped and evaporated in the downward flow.

The article presents numerical experiments results of the interaction process of the air and the flowing water film on the surface of a cellular humidifier during adiabatic air treatment. Experiments were carried out for irrigated packings of various depths using the StarCCM + program. The results obtained can be applied for improving the methods for calculating heat and mass transfer processes and increasing the energy efficiency of units with irrigated packings.

Liquid droplets impacting on liquid films is common in many industrial and natural processes. It is crucial to understand the impact of droplets on a liquid film resting on soft deformable substrates in some of the applications including 3D printing of engineering structures, prosthetic implants and tissue engineering. By recognizing the practical relevance of soft-substrates, we present an experimental investigation to assess the role of deformable substrates on bouncing-to-merging transition in droplet impact on the liquid film. First, we prepared polyacrylamide (PAAm) soft-gel substrates with various "softness" (i.e., Young's modulus) by modulating the concentration of a crosslinker, N,N-methylene-bis-acrylamide (BIS). We found that the Young's modulus of PAAm initially increases with the concentration of crosslinker, and subsequently becomes almost constant due to inhomogeneity of crosslinking. Next, through the experiments of droplet impact on the liquid film resting on soft substrates with different Young's moduli, we observe that the early merging and corresponding bouncing-to-merging transitional boundaries remain unaffected by the "softness" since such merging occurs further away from the substrate. However, the late merging, which appears during the retraction process of the deformed droplet, occurs relatively close to the substrate, and hence is found to be significantly affected by its "softness". A scaling analysis is presented to quantify the role of change in Young's modulus of the substrate on late merging, which is supported by the experimental data.

The laws of heat exchange between air and a liquid film flowing down along a solid surface with spherical dimples were investigated experimentally. Three cases of heat transfer were considered: quiescent air, air – liquid counter flow, or their cross flow. In all cases, a significant growth of the heat exchange intensity, especially at air – liquid cross flow, was observed. This is caused by the substantial turbulization of flow and mixing of liquid layers in the film. As a result, it was established that surface profiling (manufacture of dimples) under the optimal conditions leads to an increase in heat exchange intensity by an unexpended factor of 2.5 – 2.8 as compared with a smooth surface, other conditions being equal. The obtained experimental data were generalized in the form of dimensionless dependences Nu vs. Re. The best heat transfer surface can be recommended for use in different heat exchangers.

In this article, a novel coaxial three-electrode distributed conductance sensor (CTDCS) is proposed to achieve the salinity and oil content independent measurement of the liquid film thickness in multiphase slug flow. The conductance sensor obtains the liquid film thickness by measuring the conductance between the electrodes. However, the conductance depends on the liquid film thickness and liquid conductivity. For gas–water and oil–gas–water flows in an industrial process, the variations of the salinity and oil content of liquid phase change the liquid conductivity. This will seriously affect the measurement of the liquid film thickness using a conventional two-electrode sensor. Owing to its novel three-electrode configuration, the proposed CTDCS can overcome the problem mentioned above. The optimal geometry of the CTDCS is determined by exhaustive search using a finite-element method, and the electronic circuit suitable for the condition of conductivity variation is investigated. The ratio of two-channel outputs, which is independent of conductivity is acquired and its relationship with the liquid film thickness is established. The advantages of the CTDCS are that it can online compensate conductivity variations and acquire the circumferential distribution of liquid film thicknesses. Hence, the salinity and oil content independent measurement of liquid film thickness is realized for the first time.

The formation and rupture of gas film in the process of formation, rupture and coalescence of antibubbles were investigated by high-speed photography. It was found that a gas film will appear and wrap a droplet when the droplet hit a layer of liquid film or foam before impacting the gas-liquid interface. The gas film may survive the impact on the gas-liquid interface and act as the gas film of an antibubble. A multilayer droplet will be formed when the droplet hits through several layer of liquid films, and a multilayer antibubble will be formed when the multilayer droplet impact a gas-liquid interface or a single layer of foam on the liquid surface. The way to generate antibubbles by liquid films will undergo the formation and rupture of gas films. The coalescence of two antibubbles, which shows a similar merging process of soap bubbles, also undergo the rupture and formation of gas films. The rupture of gas film of antibubble caused by aging and impact is also discussed.

Introduction. When extinguishing burning solids, the use of water due to its high consumption and low insulating capacity of water films is ineffective. As a result of using viscous hydrogels as a fire extinguishing liquid, its consumption is reduced and a hydrogel film is formed on the burning surface, which has a greater thickness and better insulating ability compared to water. Aims and purposes. The aim of this study was to compare the effectiveness of using water and viscous hydrogels as a fire extinguishing liquid in the extinguishing of solid substances. The following tasks were solved: assessment of the impact of the concentration of gelling additives on the viscosity and evaporation of hydrogels; determination of the effect of viscosity of the fire extinguishing liquid film thickness and flow rate of liquid flowing from a vertical wall; a quantitative comparison of the effectiveness of fire suppression water, and various hydrogels according to their flow rate and film thickness. Methods. The influence of the concentration of gel-forming additives on the viscosity and evaporation of hydrogels was analyzed. An expression is obtained for the viscosity of the “Firesorb” hydrogel depending on the concentration of the polymer additive. The dependences of the evaporated mass of the hydrogel “Firesorb” from time to time at different concentrations of polymer additives. Evaluate the effectiveness of the use of hydrogels in their consumption and the thickness of the hydrogel films. The dependence of the film thickness of the extinguishing liquid flowing from the vertical wall on its viscosity and density is obtained. The coefficient of efficiency of hydrogel use is proposed, which characterizes the efficiency of hydrogel by its consumption and the insulating ability of the hydrogel film by its thickness. The efficiency of using hydrogels of different viscosities in comparison with water is calculated. Results and discussion. By changing the concentration of the gel-forming additive, you can vary the viscosity and evaporation of the hydrogel. The higher the viscosity of the hydrogel flowing from the vertical wall, the thicker the hydrogel film and less its consumption. Compared with water, the efficiency of using hydrogels is 2…4 times higher. Conclusions. The results obtained during the study indicate that the use of viscous hydrogels is effective in extinguishing burning solids.

This paper proposes a contact model between a rigid sphere and an elastic plane covered with a thin liquid film. The elastic contact is determined by Johnson–Kendall–Roberts theory, which deals with the energy equilibrium of elastic and interfacial energies. In elastic contact under presence of thin liquid film, the energy needed to separate the two bodies is defined as the summation of the interfacial energy among the sphere, liquid, and plane. Capillary force affects the two bodies because a liquid bridge is formed between them. Shape of the liquid bridge, assumed by the Clark’s toroidal approximation, determines the capillary force. The hysteresis of the liquid contact angles and that of the liquid volume between loading and unloading processes are considered. In loading process, the liquid film is squeezed out from the contact area and accumulates at the contact edge with increasing the liquid contact angles. In unloading process, the accumulated liquid is dragged to the contact edge, and the contact angles decrease. An irreversible force curve is obtained from these two hystereses, and the effect of liquid bridge is discussed based on the calculated results. In addition, the adhesion-hysteresis mechanisms caused by the capillary force are discussed.

The application of coating films is an important step in the manufacture of pharmaceutical tablets. Understanding the phenomena taking place during coating spray application provides important information that can be used to reduce the number of defective tablets and select the optimal conditions for the coating process. In this work, we investigate spray impact and film spreading on a tablet while this passes through the spray-zone in a rotating coating drum. To simulate spray impingement, we developed an one-dimensional (1D) spreading model that is based on the mechanical energy equation. We assumed the spray to be uniform and we divided it into arrays of droplets that impinge successively on the substrate orthogonally to its surface. In the mechanical energy equation that describes the coating spreading, we accounted for the rate of work done on the surface of the liquid coating film by the impinging droplets that leads to volume change (film spreading and thickness increase). The novel model we propose in this work can calculate the coating spreading rate and thickness. We implemented the mathematical model employing the gPROMS Modelbuilder platform. To study the effect of coating properties and process parameters on the film spreading rate and on the final liquid film thickness, we performed variance-based sensitivity analysis. The model predictions are in good agreement with experimental data found in the literature.

Multi-needle electrospinning is an effective method to increase the productivity of nanofibers. In this paper, the number of single-needle jets was increased to further improve the production efficiency. As the traditional method for increasing the number of single-needle jets has poor controllability and persistence, we proposed a gas-assisted method to increase the yield of nanofibers. A coaxial gas auxiliary needle was designed with an intermediate shaft supplied gas and the outer shaft supplied solution. Innovatively using pulse gas to produce continuous and stable bubbles which are ruptured on the needle. The liquid film is continuously disturbed, which generates jets in the electric field, thereby increasing the number of jets of a single needle. After optimization of the single-needle gas-assisted electrospinning process, the stable spraying process of 16-pin multi-needle electrospinning has been realized. The gas-assisted electrospinning productivity was 4.7 times higher than that of without gas assistance. It provided a new idea for improving the stable production of the multi-needle electrospinning.

The thickness of the thin liquid film and its effects have always been a research hotspot in nuclear power applications and operating nuclear power plants, because the flow phenomenon of the liquid film is extremely common in multiphase flow research. Based on papers published in recent years, novel research progress on thin film thickness is reviewed from the following two perspectives: the experimental measurement and the theoretical model of liquid film thickness. For the experimental measurement, methods mainly include the PLIF method, the capacitance method, and the ultrasonic method. The following contents in this part are mainly reviewed from the PLIF method, the capacitance method, the ultrasonic method, and other methods for the measurement of the liquid film thickness on the wall, the liquid film thickness on the tube wall, and other aspects of the liquid film thickness. For the model, the theoretical model of liquid film thickness on the wall is mainly reviewed from two aspects: vertical flow and horizontal flow. Other models are mainly reviewed from the following aspects. They are annular film thickness, liquid film thickness for gas–liquid annular flow, and film thickness in pipes.

This study addresses multiple droplets impact on a flowing liquid film numerically based on a three-dimensional model developed previously. Major contents include interfacial behavior and h...

International audience; Perforations are one of the recognized geometrical features that contribute to liquid redistribution in corrugated sheet packings. Our experimental study focuses on a simplified but relevant configuration: a thin liquid film flowing on either side of a vertical plate with a circular perforation. We focus on the curtain mode when the liquid fills the perforation. Confocal chromatic imaging reveals a capillary ridge upstream of the perforation, an inertial ridge downstream and a varicose capillary wave standing on the liquid curtain. We show that the wavelength is selected such that the velocity of the wave both satisfies Taylor's dispersion relation and matches the curtain local speed. We examine the effect of perforation size, supply conditions and liquid properties on the curtain transition. Lastly, we propose a simple model based on a momentum balance that describes the effect of these parameters on the Reynolds number at which curtain forms.

Annular gas-liquid two-phase flows, such as the flows attached to the fuel rods of boiling water reactors (BWR), are a prevalent occurrence in industrial processes. At the gas-liquid interface of such flows, disturbance waves with diverse velocity and amplitude commonly arise. Since the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the BWRs, complete knowledge of the disturbance waves is of great importance for the characterized properties of disturbance waves. The properties of disturbance waves have been studied by numerous researchers through extensive experimental and analytical approaches. However, most of the experimental data and analyses available in the literature are limited to the near atmospheric condition. In consideration of the properties of liquids and gases under atmospheric pressure which are distinct from those under BWR operating conditions (7 MPa, 285 °C), we employed the HFC134a gas and liquid ethanol whose properties at relatively low pressure and temperature (0.7 MPa, 40 °C) are similar to those of steam and water under BWR operating conditions as working fluids in a tubular test section having an inside diameter 5.0mm. Meanwhile, the liquid film thickness is measured by conductance probes. In this study, we report the liquid film thickness characteristics in a two-phase HFC134a gas-liquid ethanol flow. A simple model of the height of a disturbance wave was also proposed.

When the core meltdown accident occurs in the nuclear plant, molten corium falls into a coolant pool of the lower plenum. It is considered that the molten corium jet is broken up, cooled, and solidified with fuel-coolant interaction (FCI). However, the coolant pool could be a shallow condition by the leakage and evaporation of the coolant. In this situation, it is considered that the corium jet bottoms and spreads without the jet breakup. From the viewpoint of safety, understanding a jet behavior and estimating a cooling behavior are needed. The purpose of this study is to clarify the mechanism of the liquid jet behavior in a shallow pool as the fundamental process for estimating the cooling behavior in the real machine. In this paper, we discuss the spreading behavior of the liquid jet after bottoming. The jet injection experiment was conducted using test fluids. By using the 3D-LIF method, the 3D visualization of the liquid jet was Successfully implemented. From the visualization result, the following behaviors were seen. After bottoming, the jet spread radially with the liquid film. As the jet spreading behavior, the liquid film was rolled up to the inside, and the vortex was formed. After a certain time, the vortex was broken. Then the flow and the number density of the fragment were changed.

When the dry region on the high-temperature wall is cooled down by liquid, the dry region is transformed into wet region as the temperature shifts in a short time. Vigorous boiling occurs during the temperature transition. Especially, it is called the rewetting phenomenon that liquid contacts dry region on the high-temperature wall in the first time. In nuclear plants, it is essential for nuclear power plant safety to understand this phenomenon. Under severe accidents, a liquid film formed by an emergency core cooling system (ECCS) removes the decay heat of fuel rods. To determine the start time of ECCS, the time required for the liquid film to cover the fuel rods needs to be clarified. Working time is calculated by using rewetting velocity which means the boundary movement speed between liquid and dry region. Previous research reported rewetting velocity was calculated by heat conduction equation using the boundary condition (= heat transfer coefficient (HTC) distribution). However, proposed HTC distributions were not defined directly from experimental data but defined to match experimental results. This is because the temperature was measured by thermocouples which were not enough to obtain temperature distribution. In this study, two kinds of experiments were done to define HTC distribution from experimental results and to elucidate the rewetting phenomenon. First, as liquid film fell along high temperature wall, the transition of temperature distribution of the wall was measured by an infrared camera. Copper plate was used to heat transfer surface. From the results of temperature distribution, HTC distribution was calculated. And then, four critical parameters that consisted of HTC distribution were investigated against experimental parameters. Second, a similar experiment was conducted using silicon wafer which is transparent for infrared rays as the heat transfer surface to observe the rewetting phenomenon, especially the precursory cooling region. The precursory cooling region is considered as one of the important regions to calculate exact rewetting velocity. An infrared camera and high speed camera was used in this experiment. An infrared camera took temperature distribution from the backside which is the opposite side of the liquid film. A high-speed camera took liquid film condition from the front side. Since both cameras were synchronized, this experimental apparatus was able to observe both HTC distribution and liquid film condition at the same time. As a result of observation, the precursory cooling region is the area where drying and wetting are repeated by boiling.

Particle addition is an important method to prepare foam metal, and it is of great significance to clarify the mechanism of particle stabilizing liquid metal foam. In this paper, ethanol-water solution system is used to simulate liquid melt foam. By changing the wettability of particles to adjust the distribution position of particles in foam, two types of particles with different wettability are added, which are mixed and optimized in a certain proportion to improve the foam stability as much as possible. The main mechanism is that the large wetting angle particles at the gas-liquid interface to slow down the gas migration, while small wetting angle particles exist in the liquid film, which can reduce the liquid drainage velocity. The experimental results show that the effect of particle wettability on foam structure is greater than that on viscosity enhancement. The particles with large wetting angle are beneficial to the formation and stability of foam, and the particles with small wetting angle cannot stabilize the foam alone. The effect of two types of particle combinations with different wettability on foam stability is better than that of single type of particle. Considering the height and uniformity of the foam structure, the optimal particle combination is finally obtained.

The mutual result of the magnetic field and Marangoni convection against the thin liquid film of Casson fluid, blood-based carbon nanotube nanofluid has been fruitfully discussed in this article. The influence of various model constraints is focused on velocity, heat transfer, pressure distribution, skin friction and Nusselt number through graphical illustration. In addition, we witness that the thermal field of liquid raises with the growing value of [Formula: see text] and this upsurge is more in single-walled carbon nanotubes and is more dominant than multi-walled carbon nanotubes. The controlling approach of the homotopy analysis method has been used for velocity and temperature distribution. For authentication, the achieved results have been associated with the numerical (ND-Solve) method and displayed. This investigation shows that the velocity profile in the case of Casson fluid single-walled carbon nanotube–blood nanofluid is comparatively less affected and the temperature field of single-walled carbon nanotube–blood nanofluid dominates multi-walled carbon nanotube–blood nanofluid.

In our previous study, we measured the void fraction α, pressure gradient dP/dz, and countercurrent flow limitation in a vertical circular pipe (diameter D = 20 mm) under flooding condition...

The rewetting front propagation may occur when the fuel rod is cooled by the liquid film flow after it is dried out under accident conditions for boiling water reactor cores. Our previous study has...

The effect of Yttrium (Y) addition on hot tearing susceptibility of Mg–6Zn–1Cu–xY–0.6Zr (x = 0, 1, 2, 3) alloys was investigated using a constrained rod casting apparatus which monitored the hot tearing formation with a load sensor and a data acquisition system. The solidification characterization of the investigated alloys was studied through thermal analysis. The thermal analysis results revealed that as-cast Mg–6Zn–1Cu–xY–0.6Zr alloys are composed of primary α-Mg dendrites and several types of second phases, MgZnCu, MgZn2, Mg3YZn6 and/or Mg3Y2Zn3. The hot tearing susceptibility is affected by the addition of Y content that significantly decreases the hot tearing susceptibility of Mg–6Zn–1Cu–xY–0.6Zr alloys due to the grain refinement and high feeding capacity. In addition, the analysis of microstructures and fracture surfaces indicated that liquid film theory and feeding theory are mainly dominant on the hot tearing mechanisms.

Experimental data on the formation of thermocapillary structures and the rupture of a heated liquid film flowing down on a vertical wall have been analyzed and generalized. It is established that the interaction of waves and thermocapillary structures of type A leads to an increase in the critical heat flux (CHF) corresponding to the film rupture as compared to the CHF values known from literature for type B structures.

Liquid films on wettable solid surfaces can be disturbed to dewet when low surface tension liquids or surfactants are added because the surface tension difference gives rise to stresses on the film interface. Here we consider an alcohol drop placed above a thin aqueous film, which punctures a hole in the film starting from underneath the alcohol drop. Such film dewetting is attributed to the Marangoni effects caused by the spatial gradient of alcohol vapour concentration. We measure the liquid–gas interfacial tension of aqueous liquids rapidly responding to the surrounding isopropyl alcohol vapour concentration, and observe evolution of the film morphology consisting of central hole, fringe film, thinning region and bulk. We construct scaling laws to predict the dewetting rates of the film by considering the Marangoni stress, viscous shear stress and evaporation. It is shown that our experiments are consistent with our theory.

The heat transfer efficiency during the pyrolysis process is a key factor to be considered in the design of pyrolysis reactors. In this study, the average apparent heat transfer characteristics of molten plastic pyrolysis in a vertical falling film reactor were explored by experiments and numerical simulation and the apparent heat transfer coefficients were determined. In addition, the temperature distribution and the thickness of the liquid film in the reactor were predicted and the influences of pyrolysis temperatures on the average apparent heat transfer coefficients were discussed.

Liquid film generated by a jet slit injector on a wall was analyzed experimentally. Liquid film characteristics were investigated by measuring the liquid film thickness distribution for various experimental conditions. At first, the distributions were qualitatively analyzed using backlight imaging. Furthermore, quantitative measurements were performed using a liquid film thickness sensor based on the electric conductance method, which was applied to the high-speed wire-mesh method. The injection angle (15, 30, 45 °), jet velocity (7, 10.5, 13.5 m/s), and injection distance (45, 55, 65 mm) were varied, and the responses of the liquid film were observed. Having increased the injection angle, the main stream thickness decreased and the position of the maximum film thickness moved upstream. A faster jet velocity corresponded to a wider liquid film area and larger perturbation of the liquid film. The injection distance did not affect the characteristics of the liquid film considerably. A hydraulic jump effect was also observed, and a large hydraulic jump affected the film thickness distribution of the main stream. The results of this study can be applied to the development of liquid rocket engines or thrusters using the film-cooling method.

Scaled-down electric vehicle battery cooling plates were formed from multi-layered Al brazing sheets in the O and H24 sheet tempers between room temperature and 250 °C. The formed plates were joined using an industrial furnace brazing process. All brazed assemblies were leak-free when an internal pressure of 0.28 MPa was applied, demonstrating the integrity of the components. Digital radiography of the brazed assemblies revealed only localized defects within individual samples, with no obvious patterns appearing across all samples of a given forming condition. Thus, no clear difference in brazing performance between forming conditions was noted at the component level, although slightly more consistent brazed fillets were noted for the H24-250 °C condition compared to H24-RT. Strain distributions throughout the formed plate were predicted using a finite element model, to facilitate microstructure analysis of the brazed assemblies. The post-braze microstructure in plates formed from O temper sheet depended on the local strain, but did not strongly depend on forming temperature: liquid film migration and a non-recrystallized core were observed at locations of relatively low strain, while coarse recrystallized core grains and a clad residue were found at locations of high strain. Conversely, the microstructure was homogeneous throughout H24 temper plates formed at room temperature and at 250 °C, and consisted of a recrystallized core alloy and a clad residue layer at the sheet surface. It is concluded that warm forming does not adversely affect the brazing performance of Al brazing sheet and, therefore, is a promising manufacturing technique for the production of next-generation heat exchangers.

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

The present study reports a study of water droplets impacting on cold thin water films on a superhydrophilic surface. A thermal infrared imager was used to record the surface temperature distribution after the droplet impact on the liquid films. A ring-shaped high temperature zone was found after impact with the temperature first increasing and then gradually decreasing in the radial direction. Numerical simulations were then used to study the velocity distribution and the droplet motion inside the liquid film. The droplet spreading motion was restricted by liquid in the film for lower We which then reduces the heat transfer in that area and causes the formation of a ring-shaped high temperature distribution. The ring structure shape then changes with the increasing of We. This hot ring becomes wider and the temperature difference between the ring and the impact center decrease with the increasing of We. As We continues to increase, the ring-shaped temperature distribution disappears with the highest temperature at the center and the temperature in radial direction monotonically decreasing from the center to the edge. The initial film thickness also affects the temperature distribution after droplet impact. A thicker film causes the ring-shaped hot region to gradually move inward until it reaches the center and forms a hottest region in the impact center. Thus, the ring-shaped temperature distribution only occurs for lower We and thinner films. The shape and position of the temperature distribution after droplet impact on the cold, thin liquid films can then be precisely controlled by regulating the impact We and the initial film thickness. These results will greatly facilitate the design of precision spraying processes.

A three-dimensional model is applied to simulate the liquid film spreading process and liquid film thickness distribution. The volume-of-fluid (VOF) method is used to trace the gas–liquid interface. The mutual influences on the liquid film flow behavior between liquid columns are discussed in detail. It is found that the liquid film spreading and the distribution of the liquid film thickness are influenced by liquid column impact and the wave crest formation process. The wave crest forms in the vicinity of the center point of the adjacent liquid column. The Reynolds (Re) number is an important factor in the spread of the liquid film and the distribution of the liquid film thickness, but the tube spacer has almost no influence on it when the Re number is 188.