Liquid-solid Contact Research Articles

Droplet trampoline surface for regulating contact time of a bouncing droplet across a wide spectrum of Weber numbers verified by in-situ observation

The dynamic superhydrophobicity of metallic surfaces is crucial for anti-icing and anti-adhesion in the fields of aerospace and transportation. Generally, fabricating micro/nanostructures on metallic surfaces is an effective method for facilitating rapid detachment of droplets, and the micro/nanoscale composite structure can significantly reduce the solid–liquid contact area. Meanwhile, the exploration of the correlation between solid–liquid contact time and the spacing of microstructures across a wide range of Weber numbers is of great significance. In this study, it is observed that the contact time of a bouncing droplet on microstructures with small spacing exhibits a notable correlation with the Weber number. This observation challenges the prevailing understanding that the contact time of a bouncing droplet is commonly perceived as independent of the Weber number, equated to the impact velocity. Increasing the structure spacing appropriately proves advantageous in preventing pinning effect, consequently reducing the duration of solid–liquid contact. Subsequently, a regulatory diagram is generated to demonstrate the correlation between contact time and the dual dimensions of the structure spacing and Weber number. Specifically, a novel theory for predicting the contact time based on the Weber number has been established, which reveals the unconventional correlation and enriches the knowledge of droplet dynamics.

Wetting dynamics and heat transfer of droplet evaporation around boiling point: Facile manipulation by surface roughness

The evaporation of water–ethanol droplets on solid surfaces has vast potential for applications in thermal management, microfluidics, and biomedical sciences, while the approach of manipulating wetting dynamics and heat transfer of droplet evaporation around the boiling point remains open for investigations. The present study proposes a facile approach: fabricating solid surfaces with diverse roughness by sandpaper milling with different grit densities, which can alter the wetting and heat transfer characteristics of droplet evaporation. We discover that when the temperature of the heated surface exceeds the droplet boiling point, the existence of bubbles affects the solid–liquid wetting state; surface roughness alters the ability of bubble departure, thus determining the solid–liquid contact and the contact line retraction time. Consequently, in this case, the solid–liquid contact area and the heat absorbed from heated surfaces for droplets changes with surface roughness, altering the droplet evaporation time and the average heat flux at the solid–liquid interface. Bridged by droplet wetting dynamics, the heat transfer of droplet evaporation above the boiling point can be manipulated by adjusting surface roughness, offering a facile approach to tuning the process of droplet evaporation in the related industrial applications.

Effect of surface roughness on the liquid bridge between two rigid spheres

We aimed to investigate the impact of surface roughness on liquid bridges between spherical particles. Sandblasting was used to control the particle size and produce glass beads and plates with different surface roughness. First, by measuring the advancing and receding contact angles of droplets on different rough surfaces, we analyzed the effects of surface roughness on wettability and hysteresis. Next, we used a custom-made liquid-bridge stretching device to measure the capillary forces of the liquid bridges between spherical particles with different surface roughness values. A charge-coupled device camera acquisition system was set up to capture the morphological changes of the liquid bridge during stretching, and Image View software was used to extract the morphological parameters of the liquid bridge. Theoretically, we reasonably simplified and solved the differential equations for the liquid bridge morphology and used the Young–Laplace equation to calculate the theoretical capillary force of the liquid bridge, providing an in-depth analysis of the influence of surface roughness on the capillary force. Finally, we studied the impact of surface roughness on the volume ratio of the liquid bridge during static stretching and the residual liquid remaining after the liquid bridge breaks. Experimental results indicated that, as the surface roughness increased, the hydrophobicity and wettability hysteresis of the solid surface also increased. The increased hydrophobicity of the surface reduces the solid-liquid contact area of the liquid bridges between the particles, making it easier to form “columnar” or “convex” liquid bridges. Additionally, the enhanced wettability hysteresis causes the solid-liquid contact boundary to lag during the stretching of the liquid bridge, resulting in a decrease in the solid-liquid contact angle. These factors directly alter the geometric shape of liquid bridges during static stretching, thereby affecting capillary forces. Meanwhile, the increase in surface roughness weakens the effect of gravity on the morphology of the liquid bridge, resulting in less liquid mass remaining on the lower sphere after the liquid bridge breaks as the surface becomes rougher.

The Key Role of Wettability and Boundary Layer in Dissolution Rate Test.

The present work proposes a mathematical model able to describe the dissolution of poly-disperse drug spherical particles in a solution (Dissolution Rate Test-DRT). DRT is a pivotal test performed in the pharmaceutical field to qualitatively assess drug bioavailability. The proposed mathematical model relies on the key hallmarks of DRT, such as particle size distribution, solubility, wettability, hydrodynamic conditions in the dissolving liquid of finite dimensions, and possible re-crystallization during the dissolution process. The spherical shape of the drug particles was the only cue simplification applied. Two model drugs were considered to check model robustness: theophylline (both soluble and wettable) and praziquantel (both poorly soluble and wettable). The DRT data analysis within the proposed model allows us to understand that for theophylline, the main resistance to dissolution is due to the boundary layer surrounding drug particles, whereas wettability plays a negligible role. Conversely, the effect of low wettability cannot be neglected for praziquantel. These results are validated by the determination of drug wettability performed while measuring the solid-liquid contact angle on four liquids with decreasing polarities. Moreover, the percentage of drug polarity was determined. The proposed mathematical model confirms the importance of the different physical phenomena leading the dissolution of poly-disperse solid drug particles in a solution. Although a comprehensive mathematical model was proposed and applied, the DRT data of theophylline and praziquantel was successfully fitted by means of just two fitting parameters.

Vibration-Induced Pancake Bouncing of Impacting Droplets on Hydrophobic Surfaces.

Rapid detachment of impacting droplets from solid surfaces is fundamentally interesting and important in many practical applications, including self-cleaning, anti-icing, and energy harvesting. The droplet pancake bouncing is strongly preferred for the reduced contact time and high bouncing velocity. However, the trigger conditions for pancake bouncing are rigorous. Driven by this, this work circumvents the limitations via solid surface vibration. Our results show that the impacting droplet patterns are highly sensitive to the surface vibration parameters (i.e., the vibration amplitude and frequency), and only a reasonable design of vibration parameters enables the impacting droplets to bounce in a pancake shape without the contraction stage. Intriguingly, the pancake bouncing induced by surface vibration exhibits a significant reduction of solid-liquid contact time (up to ≈80%) compared to the traditional bouncing pattern, and the bouncing velocity has been dramatically enhanced. Furthermore, the critical conditions for the pancake bouncing on the hydrophobic surface and the underlying dynamic mechanism are also identified. This work provides an effective method to achieve well-controlled pancake bouncing of impacting droplets for extensive applications.

Wet-adaptive Strain Sensor Based on Hierarchical Core-sheath Yarns for Underwater Motion Monitoring and Energy Harvesting

Bifunctional flexible electronics with motion monitoring and energy harvesting have broad application prospects in day-to-day activities of human society. Nevertheless, conventional electronics are difficult to adapt to the wear comfortability and anti-sensing interference properties in wet environments. Herein, a wet-adaptive spandex/graphene@cotton/polyurethane yarn (SGCPY) sensor is fabricated with excellent sensing and triboelectric performance, which comprises core layer of spandex fibers, middle layer of graphene@cotton sensing fibers and outer layer of spindle-knotted polyurethane nanofibers. Benefiting from its unique structure, as-prepared SGCPY sensor exhibits high mechanical properties (~80%), superhydrophobic performance (>130°), good strain sensitivity (1.82) and fatigue resistance (12000 cycles) even under water condition. The usage of the SGCPY sensor is demonstrated for the stable monitoring of human body motions and human-machine interaction in both air and water environments. When SGCPY sensor weave as plain fabric, the textile also can convert various mechanical energy into electric power for driving electronic device, showing a maximum voltage of ~3.9V and ~0.7V with solid-solid and liquid-solid contact. This work fosters the in-depth study of textile-based electronics for underwater applications and highlights the promising prospects of multi-functional flexible electronics based on textiles.

Cellulose pyrolysis via liquid metal catalysis

Liquid metals are largely unexplored as catalytic media for biomass conversion. Unlike conventional solid-state catalysts which are prone to deactivation, liquid metals, i.e., low-melting metals operated above their melting point, can show resilience against coking, high thermal conductivity, and enhanced liquid-solid contact between catalyst and biomass feedstocks. This promise motivated the present investigation of liquid metals as catalysts for cellulose pyrolysis. Bismuth, tin, and indium were selected as liquid metal candidates, and their impact on cellulose devolatilization kinetics is studied via thermogravimetric analysis. The results indicate that all three metals show catalytic activity, with bismuth catalyzing volatiles formation, while indium and tin enhance char formation. Quantitative analysis of liquid product reveals that bismuth is selective to dehydration and functional rearrangement reactions, leading to anhydro sugars and functionalized furans formation. In contrast, indium and tin are selective towards dehydration, fragmentation reactions, and Diels Alder chemistry, leading to formation of C2-C4 fragments and aromatic compounds, as further confirmed via infrared spectroscopic analysis of the obtained chars. Finally, the Sn and Bi liquid metals’ stability against deactivation via coking is examined against conventional solid-state zeolite catalyst through multiple cellulose pyrolysis runs in the thermogravimetric analyzer (TGA) with the same batch of catalyst. While ZSM-5 zeolite catalyst's activity and selectivity declined and approached non-catalytic sand results (both the TGA curve and the liquid product distribution) within the first few runs, both Sn and Bi fairly maintained their robustness against coking for the conducted durability runs. Overall, the results show significant promise for this new class of catalysts for biomass pyrolysis.

Droplet Friction on Superhydrophobic Surfaces Scales With Liquid-Solid Contact Fraction.

It is generally assumed that contact angle hysteresis of superhydrophobic surfaces scales with liquid-solid contact fraction, however, its experimental verification has been problematic due to the limited accuracy of contact angle and sliding angle goniometry. Advances in cantilever-based friction probes enable accurate droplet friction measurements down to the nanonewton regime, thus suiting much better for characterizing the wetting of superhydrophobic surfaces than contact angle hysteresis measurements. This work quantifies the relationship between droplet friction and liquid-solid contact fraction, through theory and experimental validation. Well-defined micropillar and microcone structures are used as model surfaces to provide a wide range of different liquid-solid contact fractions. Micropillars are known to be able to hold the water on top of them, and a theoretical analysis together with confocal laser scanning microscopy shows that despite the spiky nature of the microcones droplets do not sink into the conical structure either, rendering a diminishingly small liquid-solid contact fraction. Droplet friction characterization with a micropipette force sensor technique reveals a strong dependence of the droplet friction on the contact fraction, and the dependency is described with a simple physical equation, despite the nearly three-orders-of-magnitude difference in liquid-solid contact fraction between the sparsest cone surface and the densest pillar surface.

Miniature and cost‐effective self‐powered triboelectric sensing system toward rapid detection of puerarin concentration

AbstractThe detection of puerarin concentration is an essential capability to study the functional role of the Pueraria root as a natural medicine and dietary source in the treatment of cardiovascular diseases and liver protection. Current methods to detect and measure puerarin concentration, such as ultraviolet–visible spectrophotometry (UV), are bulky, require an external power supply, and are inconvenient to use. Here, we propose a triboelectric puerarin‐detecting sensor (TPDS) which is based on liquid–solid contact electrification, in which liquid–solid interactions generate rapid electrical signals in only 0.4 ms to enable real‐time detection of puerarin concentration in water droplets. The electrical signal of the TPDS decreases with an increase of puerarin concentration, and the sensitivity of the approach is 520 V·(μg/mL)−1. The TPDS represents a miniature and cost‐effective sensor that is 0.2% of the size and 0.01% of the cost of a UV spectrophotometer. Our theoretical analysis verified that the puerarin concentration in droplets can effectively regulate the electronic structure, where higher concentrations of puerarin lead to a narrower energy bandgap, which allows the TPDS to detect puerarin concentration without the need for an external power supply. The TPDS therefore provides a route for the development of a portable and self‐powered method to measure the concentration of an active ingredient in droplets through the conversion of natural energy.image

Molecular dynamics simulation of deposition of high waxy crude oil on different pipeline walls

ABSTRACT Wax deposition occurs in the process of waxy crude oil pipeline transportation, which seriously affects the normal operation of crude oil pipeline. At present, non-metallic pipes have been proved to be effective in delaying the occurrence of wax deposition. Therefore, based on the pipeline walls of 20 G steel, glass fiber reinforced plastic (FRP), and polyethylene (PE), the microscopic mechanism of wax deposition during the pipeline transportation of waxy crude oil was studied by molecular dynamics simulation. The simulation results show that the waxy crude oil clusters undergo diffusion, deposition, reverse diffusion processes, and finally a wax deposition layer is formed on the pipeline surface. On the pipe walls of different materials, the surface free energy affects the interface energy of the solid-liquid contact surface between the waxy crude oil and the pipe wall, which is the main factor for the low surface free energy pipe to have the anti-wax effect. At the same time, according to the analysis of the contact angle on different materials in the simulation results, the difference in pipeline materials can only delay the formation speed of the wax deposition layer and cannot completely prevent the occurrence of wax deposition..

An experimental study on the wettability of nanofluids

The wettability of nanofluid is a key factor affecting oil recovery and fluid heat transfer. However, the traditional wettability measurement method consisting in determining the contact angle enables to assess the wettability at a solid–liquid contact point only and not within the continuous detection range. Therefore, in this work, a lateral friction detection system is used to continuously measure the wettability of hydroxylated multi-walled carbon nanotubes/deionized water (MWCNT-OH/DIW) nanofluids on polydimethylsiloxane surfaces. Specifically, MWCNT-OH/DIW nanofluids with various mass fractions are configured, and different surfactants are introduced to regulate the dispersion in deionized water. The results reveal that the surface tension and contact angle decrease simultaneously with the increase in MWCNT-OH/DIW mass fraction. Meanwhile, this change also causes an increase in the lateral friction at the nanofluid/PDMS interface. Furthermore, both sodium dodecyl sulfate and cetyltrimethylammonium bromide (CTAB) as surfactants can effectively reduce its surface tension. Notably, when CTAB is added, the maximum static friction (132.62 μN) exceeds that of SDS (113.13 μN). Therefore, the proposed method opens up new prospects in wettability detection of nanofluids.

The simplification and analytical verification of the static liquid bridge force model for particle adhesion in inferior seedling substrates

This study examines the adhesion mechanism in varying water contents of inferior seedling substrate blocks, focusing on the adhesion between particles‒particles and particles‒wall of the seedling tray. A simplified static liquid bridge force model based on the Young–Laplace equation is proposed. The correlation between the liquid bridge force and volume is derived and validated against existing experimental. The results indicate that the static liquid bridge force between particles decreases as the distance increases. A critical distance region is identified, where below this distance, a smaller liquid bridge volume results in a greater static liquid bridge force, and beyond this, the trend reverses, except when the solid–liquid contact angle is 50°. Additionally, the solid‒liquid contact angle has a minimal influence on the liquid bridge force between the particles and the inner sidewall of the seedling tray. This study also analyses the change in critical rupture distance during the transition of liquid bridges from pendulum to ring rope type, and this change increases with the liquid bridge volume.

High Surface Area Metal Oxide Enhanced Self-Powered Microfluidic Device for Real-Time Pathological Detection

Biomarkers based sensing in the realm of disease prevention, its diagnosis, and drug development has shown its unique importance in health care. In particular, the platelet level in blood is strongly linked with the development of several kind of severe diseases like coronavirus disease 2019, diabetes, and microbial infections as well as individuals undergoing cancer diagnosis. Currently, commercial methods employed for platelet level determination in whole-blood are based on Coulter principle, flow cytometry, and image analysis. However, these technologies are intricate, time consuming, expensive, and require a trained operator as well as lack of portability. Considering these issues, we have developed a self-powered portable device for real-time platelet level monitoring, aimed towards point-of-care applications. The fabricated self-powered-microfluidic triboelectric nanogenerator (SPM-TENG) utilized test sample flow-resistance for sensing of platelet level and triboelectric voltage output as sensing signal. For the fine tuning of fabricated SPM-TENG, we compared the triboelectric voltage output from gold electrode measurement setup and terminal electrode measurement setup. In view of further improvement in stability, voltage output and to minimize the noise in sensing signals, the geometrical optimization of microfluidic channel was performed. In conclusion we have optimized the device as a terminal electrode measurement setup with copper tubes on terminals of microfluidic channel and copper oxide nanowires grown on the interior of copper tubes. These copper oxide nanowires provide a high surface area for solid-liquid contact separation and is responsible for enhanced sensing signal. The fabricated SPM-TENG has shown its great potential in platelet level sensing with plasma-based samples as well as whole-blood samples. The proposed device demonstrated its practicality towards real-time rapid sensing of platelet level and portability.

Ag-TiO2 Photovoltaic Synergistic Field-catalyzed Degradation Performance of Tetracycline

Background: Tetracycline (TC), a commonly used antibiotic, is extensively utilized in the medical sector, leading to a significant annual discharge of tetracycline effluent into the water system, which harms both human health and the environment. Objective: A novel technique was developed to address the issues of photogenerated carrier complexation and photocatalyst immobilization. Compared to traditional photocatalytic photoelectrodes, the suspended catalyst used in the photovoltaic synergy field is more stable and increases the solidliquid contact area between the catalyst and the pollutant. Methods: This paper uses sol-gel-prepared Ag-TiO2 materials for the photoelectric synergistic fieldcatalyzed degradation of TC. The study examined how the Ag doping ratio, calcination conditions, catalyst injection, pH, electrolytes, and electrolyte injection affected photoelectric synergistic fieldcatalyzed degradation. The experiments were performed in a photocomposite field with a constant 50 mA current and a 357 nm UV lamp for 60 minutes. The composites underwent characterization using XRD, TEM, and XPS techniques. Results: Ag-TiO2 photoelectric synergistic field-catalyzed reaction with 357 nm ultraviolet lamp irradiation for 60 min and a constant current of 50 mA degraded 5 mg/LTC under preparation conditions of molar doping ratio of Ti: Ag=100:0.5, roasting temperature of 500 °C, and roasting time of 2 h. The photoelectric synergistic field-catalyzed degradation process achieved a degradation rate of 90.49% for 5 mg/L TC, surpassing the combined degradation rates of electrocatalysis and photocatalysis. The quenching experiments demonstrated that the degradation rate of TC decreased from 90.49% in the absence of a quencher to 53.23%, 42.58%, and 74.52%. The presence of •OH had a more significant impact than h+ and •O2 -. Conclusion: The findings suggest that Ag-TiO2 significantly enhanced the efficacy of photoelectric synergistic field-catalyzed degradation and can be employed to treat high-saline and lowconcentration TC. This establishes a benchmark for using photoelectrocatalytic materials based on titanium in treating organic wastewater.

Fabrication of superamphiphobic micro-reentrant structures by inverted electrochemical deposition

Due to excellent oil resistance and shortened liquid-solid contact time, superamphiphobic surfaces have promising application prospects in oil transportation, and petroleum pollution control. Although superamphiphobic surfaces have been constructed on various substrates, there is still a lack of high-efficient methods for fabricating micro-reentrant structures on engineering metal substrates. This paper proposes a new method combining laser processing and inverted electrochemical deposition techniques to achieve high-efficient and large-scale fabrication of superamphiphobic surfaces on copper substrates. Firstly, micropillar array structures are constructed by laser processing, and the structures exhibit excellent superhydrophobicity after low surface energy modification. Then, inverted electrochemical deposition is performed after polishing the top of the array, and local angle of the gas/liquid interface can be controlled by adjusting the distance between the top of the micropillar and the electrolyte level, thus regulating micro-morphology of the roof structure. The influences of electrochemical deposition parameters on characteristics of the micro-reentrant structures are systematically investigated. Finally, superamphiphobic micro-reentrant structures (roof diameter > 190 μm, micropillar spacing <250 μm) with water and oil contact angles exceeding 150° are prepared after lowering the surface energy of the deposited structures. After anti-fouling, blowing, ultrasonic vibration, and tape adhesion tests, the prepared superamphiphobic micro-reentrant structures maintained good water and oil repellency, showing excellent chemical stability and durability. The research may provide a simple, efficient, and low-cost method for high-efficient constructing superamphiphobic surfaces on engineering metal substrates, enriching the fabrication techniques of micro-reentrant structures and facilitating their practical applications.

Numerical analysis of fluid flow and heat transfer characteristics in single crystal diamond microchannels with ribs and secondary channels

To meet the heat dissipation requirements of high-frequency and high-power electronic devices, single crystal diamond microchannels (SCD-MC) with secondary channels and rib combinations are proposed. The fluid flow and heat transfer characteristics in SCD-MC with various secondary channels and rectangular rib combinations are investigated through numerical simulations. The comprehensive performance and energy saving effect of the microchannel were evaluated by analyzing the factor of merit and entropy generation performance. The results show that the SCD-MC with secondary channels and rib combinations enhance fluid disturbance and increase the solid–liquid contact area, significantly improving heat transfer. When Reynolds number (Re) is 586, compared with the straight microchannel, the average temperature at the bottom of the SCD-MC with rectangular secondary channels and rectangular rib (Case 5) is reduced by 4.8 K, the heat transfer coefficient is increased by 209.8 %, and the factor of merit is improved by 89.2 %. The entropy generation augmentation number of the Case 5 microchannel was the minimum of 0.52, which has the highest energy saving effect. The factor of merit of the Case 5 microchannel exhibits a tendency to first increase and then decrease with the increase of the relative width of the secondary channel (Ψ), the relative width of the rib (Φ), and the relative position of the rib (Π). At Re = 586, Ψ = 0.933, Φ = 0.667, and Π = 0.5, the factor of merit of the Case 5 microchannel is 2.08, indicating the highest comprehensive performance. This finding provides new ideas and methods for the design and application of microchannel thermal management.

Adhesion switchable transition on bio-inspired Janus surface for multi-directional droplet manipulation

Achieving precise and rapid droplets manipulation in versatile directions transport remains a considerable challenge, however adhesion switchable transitions deemed to be rather serviceable. Here, a double-sided microplate array (DMPA) with bio-inspired Janus surfaces, is proposed to fulfill adjustable adhesion through surface wettability switching and microplate dynamic deformation, thereby executing the droplet multi-dimensional manipulation in response to dynamic magnetic field. The triple-coupled bio-inspired Janus surfaces are newly designed with a convex hull and striped structure respectively, inspired by the respiratory ciliary motion and surface properties of lotus and rice leaves. Leveraging variation in superhydrophobicity and low adhesion of convex hull side on Janus surface, diverse droplet directional transports are achieved in plane, such as high-speed horizontal transport (120 mm/s and 500 µL), anti-gravitational climbing (inclined by 15°), and selective droplet orientation. The adhesion switchable transition of surface striped structure on other side is predominated by solid–liquid contact lines evolution resulting from microplate bending deformation, realizing droplet capture/release for long-distance multi-dimensional transport. Concurrently, a magnetic-responsive droplet switch is developed based on multi-directional droplet manipulation, demonstrating enormous potential for practical application.

Hydrovoltaic–piezoelectric hybridized device for microdroplet-pressure dual energy harvesting and piezo sensing

Previous droplet-based nanogenerators have made significant advancements in mechanical energy harvesting from liquid–solid contact electrification. However, these generators still face certain issues, such as neglecting substrate deformation energy, inability to store energy, and surface deterioration due to continuous impact of droplets, thus narrowing the scope of their potential applications. Here, a novel hydrovoltaic-piezoelectric hybridized device (HPeD) is reported that integrates hydrocapacitor, aluminum–air (Al–air) battery, and piezoelectric nanogenerator technologies through a green design strategy, which can effectively address the proposed problems. Impinged by a 40-μL water droplet, the HPeD yields a potential window of 1.54 V within approximately 1 min, further boosting to 1.86 V under external vertical pressure. The generated energy was greatly stored for up to 5.7 days. This all-solid-state device effectively inhibits electrolyte leakage during idle periods and controls reversible reactions to minimize corrosion, thereby extending its lifespan. Furthermore, the HPeD is successfully used as a piezoelectric nanogenerator/sensor that can operate continuously to detect external mechanical stimulus. In piezo sensor mode, the device demonstrated good sensitivity of 0.098 kPa−1 in the low-pressure range (0–8.2 kPa), a remarkable response/relaxation time of 0.3 s, and durability lasting over 8000 cycles. This study paves the way for the advancement of next-generation flexible hybrid devices capable of multifunctionality in both energy harvesting and sensing.

Measuring thermal contact resistance across solid and liquid interface mediums by thermal imaging technique: Applications on bearing steel

This study introduces a versatile method for measuring thermal contact resistance in bearing steel with solid–solid and liquid–solid interfaces using lock-in thermography (LIT) technique. The method relies on analyzing the lock-in thermal response across the layers of the bearing structure induced by periodic surface-laser heating. Thermal contact resistance is determined from the discontinuous behavior analysis of the thermal response at the solid–solid or liquid–solid contact interface, based on the resolved heat equation for the multilayered structure. The usability of the method is demonstrated through measurements conducted on a conventional bearing steel configuration, using air and lubricating oil as the interface mediums. Furthermore, the versatility of the method allows for investigating the impact of mechanical load on thermal contact resistance. This proposed approach represents an advanced tool for analyzing thermal contact resistance with applications beyond bearing steel to various multilayered materials. It has the potential to assist in enhancing thermal analysis, improving reliability, extending the lifetime, and reducing maintenance costs of different thermal engineering applications including bearings.

Monitoring atmospheric corrosion under multi-droplet conditions by electrical resistance sensor measurement

This paper presents a novel approach to investigate atmospheric corrosion kinetics of carbon steel under multi-droplet conditions. A homemade climate chamber has been developed to accurately control and monitor environmental conditions, including temperature (T) and relative humidity (RH), during exposure. Carbon steel corrosion kinetics are monitored with a custom-designed Electrical Resistance (ER) sensor pair. Savitzky-Golay (S-G) based filtering technique has been used for the corrosion signal processing. In parallel, top-view droplet temporal evolution has been recorded by microscopic imaging and analyzed for both droplet size distribution and the solid-liquid contact angle. The droplet size distribution can typically be described with a power-law form curve. The curve shows a decrease in height and a concurrent expansion in width with progressive drying. The introduction of NaCl into the electrolyte and surface roughness variations have also been identified to substantially influence the carbon steel corrosion rate. A strong correlation between the corrosion rate derived from the ER monitoring method and the RH can be observed. This correlation is further analyzed to incorporate the impact of droplet-based electrolyte conditions. This study offers valuable insights into the development of mechanistic and kinetic prediction models for atmospheric corrosion.