Interface Temperature Research Articles

Simulation of thermal-mechanical coupling in Al alloy/steel inertia friction welding

Inertia friction welding (IFW) is a complicated thermal-mechanical coupling process. In-depth understanding of the thermal-mechanical process can improve the joint quality. In this study, a three-dimensional (3D) thermal-mechanical coupling model was successfully established to simulate the evolution of temperature, energy density, stress, strain, and flow behavior of the IFW process between 2219-O Al alloy and 304 stainless steel. The developed model was validated by comparing it with the measured temperature and deformation. Results show a transforming distribution of interface temperature from a M-shape to a squished V-shape during the IFW process. The characterization is attributed to the transformation of the accumulated friction energy density at the interface from a M-shape to an approximate V-shape due to the combined effect of varying sliding velocity and contact pressure. The Mises stress at the region near the interface is high and low at the steel and Al alloy sides, respectively. A significant portion of the kinetic energy stored in the flywheel is dissipated in the form of plastic deformation energy and cannot be neglected. The tracer particles show that most Al alloy at the initial interface is extruded to form flash, while a small amount of Al alloy is sticky and remains at the interface center. Increasing friction pressure and initial rotation speed result in higher interface temperature, axial shortening distance, and proportion of plastic work in total energy input.

Influences of heat flow on corrosion behavior and interfacial reaction kinetics

Heat transfer surface of heat exchange devices often suffers from severe corrosion, and their corrosion behavior is dramatically influenced by both surface temperature and heat flow. In this work, a novel heat transfer interface corrosion testing system was designed and built based on a simulation calculation analysis (COMSOL Multiphysics 6.0 software). By the aid of it, effects of different heat flux on corrosion performance of steel Q235 was investigated through mass loss and electrochemical methods in 0.5 mol/L H2SO4 solution at controlled interface temperatures. Results indicate that variations in concentration and temperature impose a great contribution to corrosion rate but not corrosion mechanism. However, heat flow not only changed the concentration of reactants near the interfacial surface but also affected the rate and kinetic mechanism of corrosion. Positive heat flow could reduce corrosion rate of heat transfer surface, while negative heat flow increased corrosion rate. Heat flow significantly altered parameters of the corrosion reaction rate constant (such as pre-exponential factor, activation energy, entropy change, and enthalpy change), and an approximate exponential relationship between corrosion rate and heat flux was proposed.

A hovering bubble with a spontaneous horizontal oscillation

Active matters, characterized by multi-mode motions, have been emerging for both engineering and biological applications. Generally, active objects rely on the symmetry-broken structures, compositions, or interfacial activities through a physical or chemical approach. Here, we report an active bubble spontaneously hovering with a horizontal oscillation at the solid/liquid interface by impacting a stationary laser beam into a liquid through a transparent solid cover. This spontaneous oscillation mode of the bubble synchronizes with that of the interfacial temperature and hydrodynamical flow. A physical mechanism is proposed, and the scaling analysis of the oscillation frequency agrees well with experiments in various liquids under different laser powers. Additionally, the bubble trajectory rotates azimuthally, arising from the symmetry breaking of the vortex pair accompanying the oscillation. Moreover, the double pendulum of oscillation bubbles has been demonstrated, achieving a preferable oscillation direction in a controllable way. These findings would not only advance our understanding of active matters but also shed light on the bubble-mediated technological applications, such as microrobots and drug deliveries.

Mesoscopic shear evolution characteristics of frozen soil-concrete interface

The mechanical properties of frozen-concrete interfaces affect the stability and durability of engineering structures in cold regions. To investigate these properties, laboratory tests and numerical simulations were conducted to study the mesoscopic evolution of the shear stress-displacement relationship and the shearing process at the interface. The direct shear tests were performed at different environmental temperatures (−2 °C, −5 °C, and −10 °C) and normal stresses (100 kPa, 200 kPa, and 300 kPa) on the frozen soil-concrete interface, and Particle Flow Code (PFC) model of direct shear was developed. The mesoscopic parameters (particle displacement, rotation, force chain, stress, coordination number, porosity, fabric, etc.) of the interface during shearing were simulated using the PFC model. Moreover, the relationship among the interface temperature, cohesion, and friction coefficient was determined based on experimental data, and the accuracy of the PFC model was verified using previous experimental data. The results of the PFC shear model aligned well with those of the laboratory test, and the formation of shear bands was simulated well. The displacement of the soil particles on the upper layer outside the shear zone was uniform, and the direction was the same, whereas the particles inside the shear zone showed significant differences in the dislocation and rotation of the soil particles. The force chain, stress field, coordination number, and porosity were similar in the shear process and showed a concentrated distribution in the opposite direction of the shear motion, which reflected the consistency of the microcosmic response of the particles under the action of macroscopic external forces. The regression equations for the temperature, cohesion, and friction coefficient in this study can be used to simulate the shear behavior of frozen soil-concrete interfaces under different temperatures and normal stresses.

A new methodology to calculate interface thermal resistance between intumescent coating and steel substrate

Interface thermal resistance (ITR) plays a very important role in heat transfer and thermomechanical coupling response from intumescent coating to steel substrate in fire. However, the dynamic ITR between intumescent coating and steel substrate during burning is seldom reported. In this paper, a new methodology is presented to calculate dynamic ITR between intumescent coating and steel substrate under high incident heat flux based on the interface conservation equation. The new methodology focuses on measuring the temperature distribution and thermal conductivity of intumescent coating and steel substrate, with fewer variables. In this way, the calculation of ITR can be simplified. Firstly, the temperature variation function curves inside the intumescent coating and the steel substrate were fitted separately based on the temperature measurement data. Secondly, the interface temperatures (Tci,Tsi) were determined separately at the interface position by temperature variation function curves inside the intumescent coating or the steel substrate. Finally, the ITR calculation formula was deduced and the key parameters required for ITR calculation were obtained by cone calorimetry et al. An illustrative example was studied and validate the applicability of the new methodology.

Development of a Single Vial Mass Flow Rate Monitor to Assess Pharmaceutical Freeze Drying Heterogeneity.

During pharmaceutical lyophilization processes, inter-vial drying heterogeneity remains a significant obstacle. Due to differences in heat and mass transfer based on vial position within the freeze drier, edge vials freeze differently, are typically warmer and dry faster than center vials. This vial position-dependent heterogeneity within the freeze dryer leads to tradeoffs during process development. During primary drying, process developers must be careful to avoid shelf temperatures that would result in overheating of edge vials causing the product sublimation interface temperature to rise above the critical (collapse) temperature. However, at lower shelf temperatures, center vials require longer to complete primary drying, risking collapse or melt-back due to incomplete drying. Both situations may result in poor product quality affecting drug stability, activity, and reconstitution times. We present a new approach for monitoring vial location-specific water vapor mass flow based on Tunable Diode Laser Absorption Spectroscopy (TDLAS). The single vial monitor enables measurement of the gas flow velocity, water vapor temperature, and gas concentration from the sublimating ice, enabling the calculation of the mass flow rate which can be used in combination with a heat and mass transfer model to determine vial heat transfer coefficients and product resistance to drying. These parameters can in turn be used for robust and rapid process development and control.

A prediction method of oil recovery for hot water chemical flooding in heavy oil reservoirs: Semi-analytical stream tube model

Abstract Chemical agents (polymer and surfactant) assisted hot water flooding is an effective means of enhancing oil recovery in heterogeneous and heavy oil reservoirs. The rapid prediction of oil recovery through hot water chemical flooding is very important. The stream tube model is a fast analytical method for predicting water flooding recovery, but it is not suitable for hot water chemical flooding. In this paper, a permeability distribution model for multi-stream tubes is established based on permeability variation coefficient using normal distribution function for reservoir heterogeneity, Using GOMPERTZ growth function model to characterize the changes in stream tube temperature, polymer viscosity, and surfactant concentration with injection volume, Using Brooks-Corey model to describe the influence of interfacial tension and temperature on the relative permeability curve. Finally, an analytical stream tube model for hot water chemical flooding of heavy oil reservoirs was established. The time discrete method is used to solve the model, then the graphs of the relationship between oil recovery and water cut are obtained. Compared with numerical simulation methods, the prediction error of oil recovery is less than 2%, and the calculation time is reduced by 89%. This model has been successfully applied to X oilfield. Based on historical fitting, it is predicted that hot water chemical flooding can enhance oil recovery by 6.3% compared to water flooding. This paper provides a fast calculation method for predicting and evaluating the effectiveness of hot water chemical flooding in heavy oil reservoirs.

Effect of process temperatures on joining aluminum alloy (AA5052) to polypropylene (PP) by friction lap welding

The joining of aluminum alloy 5052 (AA5052) and polypropylene (PP) by friction lap welding (FLW) was investigated under different process temperature conditions. Welding experiments were conducted at different tool rotational speeds, and the process temperatures were monitored using an infrared camera and thermocouples. The temperature distribution at the cross-section was determined using a validated numerical model. The joint quality was assessed by measuring tensile shear strength and examining the joint morphology. It was found that interfacial temperatures in the range of 156 °C–316 °C were optimal for achieving effective mechanical interlocking, attributed to the appropriate flow of molten PP into the textured aluminum alloy surface. Temperatures below 130 °C resulted in inadequate PP flow, leading to poor joint formation, while temperatures above 316 °C caused over-melting of PP, bubble formation, and approached the PP initial decomposition limit. Raman spectroscopy showed that the process temperatures did not cause significant chemical bonding and that mechanical interlocking was the main contributing joining mechanism. The results showed that dissimilar welding of metals and non-polar polymers can be optimized by the precise monitor and control of the temperature of the process.

Dissecting the effect of substrate on polyamide reverse osmosis membranes via regulating substrate pore size by drying shrinkage

Several studies have proved that the substrate significantly influences the chemical properties of reverse osmosis (RO) membranes, whereas the underlying mechanisms remain elusive. Herein, we adjusted the substrate pore size from 8.6 nm to 4.4 nm by drying shrinkage, ensuring the substrate's chemical properties remained consistent. Interestingly, we observed that an intermediate pore size (7.4 nm) of the substrate resulted in the highest exotherm, with the interfacial temperature rising to 26.8 °C, thus showing that larger pore sizes do not necessarily result in more pronounced exothermic interfacial polymerization (IP) reactions. Through multiscale simulations and various characterization techniques, we found that the IP reaction is governed by two competing effects: (1) the storage capacity of MPD, which provides the reactive monomers; and (2) the water content, which absorbs the heat in the IP reaction. Balancing these two competing factors contributes to enhancing the diffusion of MPD, thereby promoting the progression of the IP reaction. This work revealed a new mechanism through which the substrate affects RO membrane formation.

Evaluating the fire resistance potential of functionally graded ultra-high performance concrete

Relevant standards stipulating the concrete surface temperature less than 380 °C and the defects of UHPC prone to fire spalling both limit the direct application of UHPC in specific tunnel fire prevention occasions. In view of this, a two-layered functionally graded ultra-high performance concrete (FGUHPC) was proposed in this paper, where lightweight aggregate concrete (LWAC) serves as the fire-resistant layer and UHPC functions as the structural load-bearing layer. The results showed that LWAC can control its backfire surface temperature to meet the standard requirements under a thickness of 40 mm, and the residual mechanical properties of UHPC before 400 °C were comparable to those at ambient temperature. The straight shear test was adopted to evaluate the FGUHPC interfacial bond strength. The results showed that the interfacial strength of FGUHPC reaches 3.05 MPa at ambient temperature, which is close to or even slightly higher than that of homogenous LWAC. When FGUHPC was treated at 1200 °C for 2h, FGUHPC can still maintains its integrity with its interfacial strength 120.0 % higher than that of LWAC. Compared to the homogenous UHPC member, FGUHPC composed of 40 mm LWAC and 120 mm UHPC effectively avoided explosive spalling, and maintained the interface temperature at around 200 °C. After static loading failure of the post-fire FGUHPC member, the two layers of concrete still remained bonded without delamination, and the loss in load-bearing capacity was less than 20 %. Finally, the design method of FGUHPC members under elevated temperature was discussed.

Interfacial energy conversion mechanism between 3003 aluminum alloy and 321 stainless steel in vaporizing foil actuator welding process

Conventional welding methods encounter significant challenges, including poor weldability, low joint strength, and the formation of brittle intermetallic compounds, primarily due to the substantial disparities in the physical and chemical properties of aluminum and iron. To mitigate these issues, the vaporizing foil actuator welding (VFAW) process has emerged as a highly promising solid-phase welding technology, particularly suitable for joining dissimilar metals with pronounced differences in properties, such as aluminum alloys and stainless steels. The present study provides an innovative quantitative analysis of the interfacial impact energy conversion mechanisms within the VFAW process. The analysis reveals that the energy responsible for accelerating the flyer workpiece comprises burst vaporization energy (Ed\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_d$$\\end{document}) and continuous vaporization energy (Ep\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_p$$\\end{document}), with Ed\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_d$$\\end{document} identified as the primary energy source, contributing approximately 65–80% of the total energy required for acceleration. Further examination elucidates the mechanisms underlying heat generation and transfer during the interface collision. The investigation identifies the formation of an overheating zone at the interface, attributed to the combined effects of plastic deformation energy and adiabatic shear energy within the flyer workpiece. Consequently, the interface temperature can rise significantly, reaching up to 1394 K, with impact velocities as high as 925 m/s. The analyses contribute to establishing a theoretical foundation for understanding the interface bonding mechanisms characteristic of the vaporizing foil actuator welding method.

COMPARATIVE STUDY OF DIFFERENT CUTTING FLUIDS ON TOOL-WORK INTERFACE TEMPERATURE DURING TURNING OPERATION ON 6061 ALUMINUM ALLOY

This study investigated the impact of tool-work interface temperature during the turning process of a cylindrical workpiece made of 6061 aluminum alloy. The experiment utilized four different cutting fluids: palm oil-based cutting fluid (POBCF), neem seed oil-based cutting fluid (NOBCF), orange seed oil-based cutting fluid (OSOBCF), and mineral oil-based cutting fluid (MOBCF) using uncoated carbide cutting tool of grade H13A. Various machining parameters were considered, including spindle speed (180, 250, 355, 500 rpm), feed rate (0.105, 0.116, 1.4, 1.6 mm/rev), and depth of cut (0.5, 1.0, 1.5, 2.0 mm). The experimental design followed the Taguchi specified L16 (43) orthogonal array and was conducted on a Lathe Machine XL 400. To measure the tool-work interface temperature, an infrared thermometer (KM 690) was employed during the aluminum alloy machining process. Subsequently, a mathematical model for the tool-work interface temperature values was developed through regression analysis using Minitab 16. The significance of the chosen machining parameters and their respective levels on the tool-work interface temperature was determined using analysis of variance (ANOVA) and F-test. The findings indicated that machining under orange seed oil-based cutting fluid (OSOBCF) conditions resulted in a 9.02%, 16.4%, and 21.7% lower temperature at the tool-work interface compared to palm oil-based cutting fluid (POBCF), neem seed oil-based cutting fluid (NOBCF), and conventional oil-based cutting fluid (MOBCF), respectively. This suggests a potential for producing higher-quality products under orange seed oil cutting fluid conditions compared to other wet conditions.

A hybrid mesoscale-continuum approach to understand and predict melting kinetics of Al powders during laser processing

Abstract Laser interaction with metallic powders during additive manufacturing (AM) leads to fast heating and cooling rates that can affect the quality of the final products due to the formation of defects. One of the first steps towards predicting microstructures generated during AM, therefore, requires an accurate understanding of the laser energy deposition mechanisms that determine the melting kinetics at the level of individual powders. The critical challenge, however, is the availability of computational methods that can model the laser energy absorption, heat transfer, and the related microstructure evolution in individual metal powders at the length and time scales of AM. This manuscript demonstrates the capability of a novel scale-bridging methodology that combines the mesoscale quasi-coarse-grained dynamics (QCGD) simulations with a continuum two-temperature model (TTM) to account for the atomistic mechanisms of laser energy deposition and microstructure evolution and predict the kinetics of melting of individual powders at the experimental time and length scales. The scale-bridging capability of the hybrid QCGD-TTM simulations is demonstrated here by investigating the laser-induced microstructure evolution in aluminum powders with various sizes ranging from 200 nm to 20 µm. The analysis of the evolution of temperature, pressure, phase fraction, and melt fronts suggests the melting mechanism is heterogeneous due to the interaction with a laser, and the melting time is observed to decrease exponentially as the laser intensity increases. The solid-liquid interface velocity can be quantified to identify correlations with interface temperatures, and the predicted values satisfy the theoretically reported limits of crystal stability of metals against homogeneous melting. In addition, the pre-melting is found at the grain boundaries of 20 µm polycrystalline aluminum powder, while a minute contribution to melting is observed. This manuscript demonstrates the capability of the QCGD-TTM method to capture laser-powder interaction and allow the investigation of the kinetics of laser melting.

A molecular dynamics study on the supercritical evaporation of liquid ammonia under forced convection conditions

Although the behavior of the supercritical transition during the evaporation of liquid fuels in engine combustion chambers has been studied by many researchers, the effects of convection on the phase transition of liquid fuel in supercritical environments have been little studied. Previous studies mainly focused on hydrocarbon fuels for supercritical evaporation, with fewer on the zero-carbon liquid ammonia fuel. Aiming at the above deficiencies, this study used molecular dynamics simulations (MD) to explore the phase transition of liquid ammonia in a nitrogen supercritical environment under forced convection conditions. The Peng-Robinson equation of state (PR-EoS) was used to calculate the vapor–liquid equilibrium of the ammonia–nitrogen system to determine the supercritical transition time of liquid ammonia under forced convection conditions. The effects of forced convection on the heat and mass transfer process and the evolution of the liquid-phase region and the vapor–liquid interface region were analyzed. It was found that forced convection can promote the mass and heat transfer process and accelerate the phase transition of liquid ammonia to some extent. Forced convection may have a greater effect on the single-phase diffusive mixing process compared to the two-phase evaporation process. The increase in the interfacial thickness under forced convection conditions is mainly attributed to the temperature increase promoted by convection. The interfacial temperature dominates the development of its thickness and the thickness is approximately linear with temperature during the diffusive mixing stage. The shear effect induced by convection has an inhibitory effect on the diffusion of ammonia molecules within the interface region along the vertical convection direction. The cases in this study indicate that forced convection may promote the supercritical transition of liquid ammonia. In addition, a dimensionless number κ was proposed to explore the possibility of scaling up the MD results to the engineering scale.

Integrating atmospheric water harvester with hydrovoltaics: Simultaneous freshwater production and power generation

Integration of an atmospheric water harvester (AWH) with hydrovoltaic (HV) technology poking a new technology and notification to the arid region people to harvest freshwater and electricity simultaneously from the humid atmosphere even in the non-water region. In this work, we have fabricated a composite material by attaching the sulfonic groups to the graphitic oxide substrate (SGhO) through a one-step reflux method. The material delivers an excellent water absorbing ability of 0.3 g g−1h−1and 2 g g−1in 19 h under a 40–60 % humid environment. The electrical experiments show during moisture absorption, a specific voltage and current are generated indicating the dissociation of sulfonic groups in the graphitic structure creates a drift movement of H+ions through the composite. Our device delivers a voltage of 0.25 V and a high current of 160 µA from a single device during moisture movements through the structure under the relative humidity of 60–65 %. The rapid enhancement of the interfacial temperature from 31 °C to 44 °C within a minute due to the presence of graphitic oxide shows excellent photothermal capacity for the light-induced evaporation mechanism and collecting the condensed water as freshwater. The composite can evaporate all absorbed water within 0.5 h in one sun illumination (1 kW/m2) under the ambient relative humidity (RH) of 40–60 %. Several trials of washing treatments were done to ensure the chemical bonding of sulfonic groups into the graphitic structure. Therefore, it was confirmed the excellent stability, and repeatability for repeatable practical applications. Furthermore, the purity of the collected water is conducted with various analyses such as pH, TDS, and UV–Vis absorption studies and confirmed the excellent purified water which highly meets the global drinking water standards. Therefore, this work demonstrates a single way to achieve dual goals such as water harvesting as well as power generation for a better tomorrow.

On the influence of heat-induced evaporation over interfacial atomization driven by surface acoustic waves

In this work, the influence of evaporative flux over the atomization driven by surface acoustic waves (SAWs) of a Newtonian water drop is studied. The drop is placed on a heated substrate at constant temperature, higher than the saturation temperature at a given vapor pressure. In this manner, an interfacial temperature distribution arises along the drop free surface in terms evaporative mass flux and vapor recoil, which repercussion over aerosol size is studied by determining the asymptotic evolution equation governing the acoustically driven free surface. At such scenario, the connection between surface tension and temperature is also considered; thus, thermocapillary flow is incorporated into our drop model, described in terms of fundamental parameters, like the evaporation number, Marangoni number, and acoustic capillary number. Numerical solution of the evolution equation led us to obtain a simplified representation of the drop interfacial deformation mechanism, capable of predicting atomization and portraying the influence of evaporation over atomization. Subsequent analysis shows that the incorporation of evaporation at SAW atomization traduces in normal stresses counteracting the acoustic and thermocapillary effect, leading to the development of smaller drop aspect ratios with respect to the no-evaporative case. Being aware that the aerosol size is deeply related to the aspect ratio, we propose an analytical expression to estimate aerosol diameter under evaporative conditions. The results show that aspect ratio reduction leads to a decrement on aerosol size, up to two orders of magnitude, with respect to the no-evaporative case. Our study is a first approach providing insight about the importance of evaporation on aerosol regulation at SAW atomization.

Injection over-molding process of PEEK composites

Abstract This study utilizes experimental and microscopic characterization methods to investigate the prospects and feasibility of using the Injection Over-Molding (IOM) process to replace traditional adhesives in the manufacturing of complex ribbed panel structures with Polyether Ether Ketone (PEEK) composites. The results indicate that the IOM process can achieve the optimal bonding strength of adhesives while significantly reducing the processing cycle, demonstrating substantial potential. Additionally, enhancing the melt temperature and mold temperature can further improve interface bonding quality and increase bonding strength. Based on the experimental results, it is inferred that increasing the melt temperature can elevate the interface temperature while raising the mold temperature can slow down the interface cooling rate, suggesting mechanisms by which these parameters influence interface bonding quality.

Prediction of Wear Rate of Glass-Filled PTFE Composites Based on Machine Learning Approaches.

Wear is induced when two surfaces are in relative motion. The wear phenomenon is mostly data-driven and affected by various parameters such as load, sliding velocity, sliding distance, interface temperature, surface roughness, etc. Hence, it is difficult to predict the wear rate of interacting surfaces from fundamental physics principles. The machine learning (ML) approach has not only made it possible to establish the relation between the operating parameters and wear but also helps in predicting the behavior of the material in polymer tribological applications. In this study, an attempt is made to apply different machine learning algorithms to the experimental data for the prediction of the specific wear rate of glass-filled PTFE (Polytetrafluoroethylene) composite. Orthogonal array L25 is used for experimentation for evaluating the specific wear rate of glass-filled PTFE with variations in the operating parameters such as applied load, sliding velocity, and sliding distance. The experimental data are analysed using ML algorithms such as linear regression (LR), gradient boosting (GB), and random forest (RF). The R2 value is obtained as 0.91, 0.97, and 0.94 for LR, GB, and RF, respectively. The R2 value of the GB model is the highest among the models, close to 1.0, indicating an almost perfect fit on the experimental data. Pearson's correlation analysis reveals that load and sliding distance have a considerable impact on specific wear rate as compared to sliding velocity.

Ambient-gas forced convection dictated evaporation kinetics of generic sessile droplets

We probe the temporal evolution of internal thermo-hydrodynamic features of evaporating sessile droplets under external forced convection. A transient numerical model based on Arbitrary Lagrangian-Eulerian (ALE) framework is adopted. The governing equations corresponding to the transport phenomena (mass, momentum and energy) are solved in a fully coupled manner in both the droplet (liquid) and ambient (gaseous) domains while accurately tracing the droplet interface evolution. The role of initial wetting state, external convection velocity and convective heating/cooling effects due to the air-flow are explored in details, and good agreements are noted with previous reports from literature. Results show that although the evaporation rate is augmented significantly in forced convection conditions, the same does not increase in proportion at higher Reynolds numbers. This is primarily due to the enhanced cooling effects that reduce saturated vapor concentration at droplet surface, and thereby supress the diffusion mechanism. Also, depending upon the contact angle, the evaporative cooling effects are compensated partially or completely due to convective heating. This altered thermal profile substantially influences internal hydrodynamic features (Marangoni flow and heat advection) during the transient and stable regimes of droplet evaporation. At higher degrees of convective heating, the droplet interface temperature becomes higher than its base temperature. This condition results in a completely opposite internal Marangoni vortex at stable state compared to that induced due to evaporative cooling effects. We also provide a regime map to show the role of the gas-phase Stefan number on the droplet-phase hydrodynamic regimes.

Laser heat conduction joining of polycarbonate and aluminum alloy

The present work demonstrates the laser heat conduction joining (LHCJ) of polycarbonate and aluminum alloy. The experiments are performed to examine the impact of scan speed and laser power on the joint’s strength and quality. The bonding between the substrates was assessed by examining the cross-section using a scanning electron microscope and conducting energy-dispersive X-ray spectroscopy. The fractured surfaces are inspected by an optical microscope to explore the bond morphology. A finite-element-based numerical model is developed for the estimation of interface temperature and validated with the experimental results. Results of lap shear tests show that the weld strength is significantly affected by the laser power, scan speed, interface temperature, and bubble area. Microscopic observations of the joint interface disclose bubble area and mechanical interlocking between polycarbonate and aluminum. Through X-ray photoelectron spectroscopy (XPS) analysis, it was discovered that the interface experiences chemical bonding facilitated by the formation of Al-O-C bonds, which effectively enhances the strength of the joint.