As MEMS/NEMS advance, compact devices require efficient heat dissipation, making thin film phase transitions a key heat transfer method, but molecular-level understanding of multi-factor regulated liquid film phase transitions and the heat and mass transfer coupling is still limited. In this study, molecular dynamics simulations are employed to systematically investigate how surface wettability, liquid film thickness, and nanopillar sizes jointly regulate phase transition modes and interfacial heat transfer, enabling nanoscale quantification of heat-mass transfer coupling. These factors influenced the phase-change mode and interfacial heat transfer mechanism by modulating bubble nucleation, heat conduction pathways, and local energy barrier distributions. From the phase diagrams of different phase transition modes, it is found that hydrophobic surfaces and thin liquid films favor pure evaporation, whereas hydrophilic surfaces, thicker films, and nanopillars promote local superheating and heterogeneous nucleation, leading to nucleate and film boiling. Moreover, bubble nucleation preferentially occurs at nanopillar corners due to lower local energy barriers, enhancing spatial heterogeneity and boiling heat transfer. Increasing liquid film thickness from 30 Å to 120 Å raises average heat flux by 75.2%, highlighting its dominant role in regulating heat-mass transfer. These results reveal the molecular mechanisms linking nanoscale structure to boiling dynamics and provide design guidelines for optimizing phase-change heat transfer in MEMS/NEMS devices.

With the increasing application of rotating thermal systems in integrated environmental testing equipment, understanding the interplay between Coriolis force, centrifugal forces and thermal buoyancy is crucial. This paper investigates the thermal convection of air within a differentially heated closed cavity subjected to a centrifugal field in order to elucidate how three body forces influence the flow structure, temperature field, and heat transfer performance. Key findings reveal that the thermal buoyancy compresses the thermal boundary layers. Conversely, an intensified Coriolis force leads to the separation and reversal of the core roll, which induces secondary rolls. Changes in centrifugal force exert a negligible effect on heat transfer performance. Finally, a heat transfer correlation for the space-mean Nusselt number applicable to this centrifugal field was developed based on the simulation data. Given the current limited understanding of thermal convection in centrifugal fields, these results strengthens the theoretical foundation for high-precision thermal control in comprehensive environmental testing.

In order to understand the evaporation characteristics of liquids under low-pressure environment, a series of experiments were performed for the evaporations of ethanol and water in bottom-heated pools under low-pressure conditions. A clear temperature discontinuity is observed at the vapor-liquid interface, and the liquid-phase temperature exhibits a non-monotonic axial distribution due to the existence of Bénard-Marangoni convection, except for water at a heating temperature of 4 °C, where the density anomaly suppresses natural convection and yields a nearly linear profile. For ethanol, both the temperature discontinuity and the evaporation rate vary non-monotonically with pressure and heating temperature, whereas water exhibits predominantly monotonic trends. Based on the experimental data, the universal empirical correlations of the interface temperature discontinuity and the evaporation rate are established through linear regression. Furthermore, the flow instability was observed. The critical pressure ratio of the flow destabilization in the ethanol layer increases with heating temperature, while the dominant frequency of temperature oscillations remains nearly constant, reflecting the intrinsic properties of the evaporation system.

The interplay of interfacial behavior, convective flow, and heat transfer significantly influences the evaporation process. This study examines the evaporation of ethanol in a cylindrical pool under low-pressure conditions by integrating experimental measurements with numerical simulations. The findings encompass the average evaporation rate, as well as the axial and radial temperature distributions in both the vapor and liquid phases near the interface. Additionally, the analysis includes the temporal temperature variations at monitoring points throughout the unsteady evaporation process. Flow and temperature profiles, which could not be measured experimentally, are determined through numerical simulation. The results demonstrate that the liquid-layer temperature field is governed by the coupled buoyancy-thermocapillary convection. Increasing the liquid-layer depth enhances evaporation and buoyancy-driven flow, thereby shifting the steady-to-unsteady evaporation transition to higher pressure ratios. Additionally, the interfacial temperature jump increases consistently with the local vapor-side conductive heat flux, and an empirical correlation between these two variables is derived from the experimental findings.

The isosteric heat of adsorption (Qst) serves as a fundamental thermodynamic descriptor for gas-solid interfacial interactions, however, its mechanistic evolution from single-molecule formation to capillary condensation remains incomplete. In this study, adsorption cluster theory is applied to quantitatively investigate the evolution of Qst, surface excess potential energy (phi), and Gibbs free energy (Delta G) during adsorption in porous adsorbents. To bridge the gap between single-molecule and condensation phenomena, Zeta cluster theory is adopted and the Langmuir-Zeta model is developed. The Langmuir-Zeta model is applied to argon (non-polar) adsorption, while the Zeta model is employed for water (polar) adsorption. This distinction highlights the different roles of gassolid affinity and lateral adsorbate interactions in governing the progression of adsorption. Results show that argon releases an elevated initial Qst value (11 kJ center dot mol- 1), which exceeds its bulk latent heat (approximately 6.45 kJ center dot mol- 1 at 87 K) due to enhanced gas-solid interactions at low coverage. Further analysis of phi and Delta G reveals that systems with weaker gas-solid interactions exhibit a slower initial decline in both parameters. However, once condensation is initiated, enhanced intermolecular cohesion causes a rapid decrease in both phi and Delta G, indicating a shift in the dominant thermodynamic driving forces. These findings establish a quantitative thermodynamic framework for understanding adsorption transitions and provide a promising insight for the development of porous adsorbents in separation and purification applications.

Industrial heat exchange equipment is easy to form a certain fouling layer at the bottom, which will deteriorate the efficiency of the equipment. To better elucidate the mechanisms of liquid-side particulate fouling, a CFD framework based on the Eulerian approach and integrated with a 3D dynamic mesh is established. Using this model, the deposition behavior in both 2D and 3D rectangular models is examined. Furthermore, particulate fouling in a circular tube is investigated under different operating conditions. The results indicate that, in the rectangular channel, the 3D model better captures the flow complexity, yielding a fouling resistance with a deviation of 13.7 % from the experiments, which is markedly lower than those of the 2D model without and with the dynamic mesh (32.6 % and 26.5 %, respectively) and confirms that dimensional reduction introduces significant errors. Incorporating the dynamic mesh into the 3D model further increases the fouling resistance while reducing the experimental deviation to 0.88 %; the average pressure drops and Nusselt number increase by 50.8 % and 3.73 %, respectively, highlighting the pronounced deterioration of overall thermal-hydraulic performance caused by fouling. The fouling growth can be divided into a rapid deposition stage and a slow equilibrium stage, with a non-uniform layer mainly distributed along both sides of the bottom of the channel. In the range of the parameters studied in the tube, the fouling model combined with the dynamic mesh technology is well verified with the experiment under different operating conditions, and the asymptotic fouling resistance error is kept below 5.0 %. The results further reveal that both the Rf and the xf decrease with increasing flow velocity and inlet temperature, but increase with higher particulate concentration.

Heterogeneous surfaces are widely employed to regulate droplet evaporation, however, the microscopic mechanisms of interfacial energy and mass transport remain unclear. Molecular dynamics (MD) simulations are conducted to further investigate the evaporation dynamics and interfacial heat and mass transfer of nanoscale droplets on hybrid-wettability surfaces, including functionally graded wettability (FGW) and patterned wettability. Results reveal that at the same wettability ratio, droplet evaporation on patterned surfaces proceeds through mixed, constant contact radius (CCR), and fragmentation-mixed modes, whereas FGW surfaces exhibit sequential CCR, alternating constant contact angle (CCA)-CCR. Patterned surfaces induce mixed to fragmentation evaporation modes and promote stronger local coupling between heat and mass transfer at the three-phase contact line, resulting in more efficient interfacial evaporation compared with FGW surfaces. The interfacial mass transfer rate on hybrid-wettability surfaces increases with temperature difference and hydrophilic fraction. Verification using the Hertz-Knudsen-Schrage equation and Statistical Rate Theory reveals that both models can accurately predict the evaporation mass flux under different temperature differences, elucidating the microscopic mechanism of interfacial mass transfer during evaporation on hybrid-wettability surfaces. From a heat transfer perspective, hybrid-wettability surfaces show the lowest interfacial thermal resistance and highest average heat flux at a hydrophilic fraction of 75%. At the same wettability ratio, the patterned surface can reduce the thermal resistance by up to 49.96% compared to the FGW surface, indicating that the periodic structure significantly enhances interfacial energy coupling and heat transfer efficiency. Moreover, increasing the hydrophilic fraction leads to a higher overlap in the vibrational density of states between the solid and near-surface atoms.

To clarify how eccentricity affects flow stability and the evolutionary process of thermal convection patterns, we conducted a sequence of experiments in deep-liquid pools with an eccentric annular structure. It is found that the bud-shaped flow pattern or straight spoke pattern will appear after the flow destabilization. In contrast to the flow structures appeared in concentric annular liquid pools, these patterns exhibit non-uniform distribution along the circumferential direction, that is, the spacing between adjacent flow modes is not uniform. Specifically, when the working fluid Prandtl (Pr) number is 6.7 and the liquid depth is fixed at 6 mm, the spoke-like patterns in the wide-slit area of the liquid pool will convert into bud-shaped structures with the increasing radial temperature difference, whereas they in the narrow-slit area start to oscillate. At Pr = 16.2 and 25.1, clear radial straight stripes are observed near the inner wall, and these radial straight stripes alternate with the straight spokes. The eccentricity also significantly reduces the critical value for flow destabilization. Notably, although buoyancy is increased in liquid layer depth, the eccentricity weakens the influence of buoyancy on flow stability.

To overcome the limitations of the traditional virtual fouling model (VFM) in describing the coupled evolution of fouling, flow, and heat transfer, a porous-media-based crystallization fouling model (PMM) is developed within a CFD framework. The proposed model is validated against experimental data and then applied to investigate the dynamic growth characteristics of crystallization fouling and the influence of porosity on fouling behavior. The results show that, compared with the VFM, the average prediction error of the PMM is reduced by 3.39%, indicating improved prediction accuracy. The combined resistance and heat source terms increase the predicted crystallization fouling resistance by approximately 16.0%. Moreover, the PMM directly captures the morphology of the fouling layer and reveals its bidirectional coupling effects on both the velocity and temperature fields. The fouling growth process can be divided into a rapid deposition stage and a slow deposition stage. During the rapid deposition stage, fouling resistance and flow-related parameters vary significantly, whereas these indicators gradually approach stable trends in the slow deposition stage. Within the investigated range, porosity markedly affects the flow and temperature distributions in the fouling region; as porosity increases, the fouling resistance first increases and then decreases, reaching its highest value at a porosity of 0.8, while the pressure drop (Δp) decreases monotonically and the Nusselt number (Nu) first decreases and then increases. This study offers a stable and interpretable approach for fouling prediction, control, and industrial heat-exchanger optimization.

To understand the coupled effect of substrate temperature and ethanol concentration on the evaporation characteristics of binary sessile droplets and their induced flow instability, we conducted an experimental study of the evaporation kinetics of ethanol-water binary sessile droplets on a heated substrate. The substrate temperature varies from 30 degrees C to 60 degrees C, while the ethanol volume concentration is from 0 to 90%. The distribution of the droplet surface temperature was observed using infrared thermography. Additionally, the evolutions in droplet surface thermal patterns and droplet morphology were examined. The results suggest that the evaporation of binary mixture droplets (BMD) is influenced by a combination of thermocapillary convection and solute capillary convection, resulting in pronounced flow instabilities, including hydrothermal waves (HTWs) and BenardMarangoni instabilities. The surface thermal pattern of BMD is closely related to the ethanol concentration. At low concentrations of ethanol, "three-convective cell" and "four-convective cell" structures are formed on the surface of the droplets, which are not observed at high ethanol concentrations. Increasing the substrate temperature enhances the droplet evaporation, leading to a higher BMD evaporation rate and an increase in the number of HTWs at the droplet surface. Furthermore, low concentration droplets exhibit a mixed evaporation mode, while high concentration droplets predominantly evaporate in a constant contact radius (CCR) mode.

This paper presented an experimental investigation on the thermocapillary-buoyancy convection in eccentric annular shallow liquid pools, focusing on the impact of eccentricity on flow stability and flow pattern transitions. By systematically varying eccentricity (e), Prandtl (Pr) number of the working fluid, and liquid layer depth (d), we demonstrated that eccentricity significantly lowers the critical Marangoni number, thereby promoting flow destabilization. Notably, increasing eccentricity narrows the transition region from stable multicellular flows to hydrothermal waves. At e = 0.6, Pr = 16.1, and d = 1.5 mm, the radial waves have been observed. Furthermore, the eccentricity induces an asymmetric temperature gradient, which triggers localized instabilities at the narrowest annular gap. When Pr = 25.2, a distinct transition from multicellular flow to flower-shaped waves will appear, while U-shaped streaks emerge under large eccentricity when Pr = 9.7. These findings certify the pivotal role of eccentricity in modulating convective instabilities. At the same time, the critical parameters of flow instability are determined, and the flow pattern evolution after flow destabilization is also analyzed.

To understand the flow and transport characteristics in the entrance region of Poiseuille-Rayleigh-Benard (P-R-B) double diffusive convection within horizontal channel, a series of three-dimensional numerical simulations are conducted to assess the impact of aspect ratio (B), Reynolds number (Re), buoyancy ratio (N), and Rayleigh number (Ra), with the following ranges: 1 <= B <= 10, 0 <= Re <= 25, - 0.3 <= N <= 0.3, and 40 <= Ra <= 1.2 x 105. The results indicate that the vertical velocity exhibits periodic sinusoidal fluctuations in both space and time as transverse rolls (TRs) develop. The amplitude of these fluctuations increases with Ra and N, while the fundamental frequency decreases as N rises. In the presence of longitudinal rolls (LRs), the vertical velocity is symmetrically distributed in the spanwise direction. If LRs do not fully develop in the entrance region, the vertical velocity will not form regular periodic fluctuations. When stable TRs occupy the entrance region, both temperature and concentration fields fluctuate sinusoidally over time with identical fundamental frequency. Correspondingly, Nusselt (Nu) and Sherwood (Sh) numbers show sinusoidal variations in the streamwise direction, and their amplitudes increase with Ra and N. Moreover, for LRs, the entrance lengths for the onset of secondary flow (L1) and for its full development (L2) decrease with Ra and N, but increase with Re and B. Meanwhile, at high Ra or large positive N, the reductions of L1 and L2 become less pronounced. In addition, the overall transport performance is not improved monotonically with increasing B. Based on simulation data, correlations for L1 and L2 were proposed. Ultimately, the thermal and solute transport correlations including the entrance region were also derived. These findings provide a theoretical foundation for the dimensional design of chemical reactors, heat and mass transfer equipment, and other systems involving P-R-B double diffusive convection.

The presence of a thermally conductive cylinder connecting the heated and cooled walls within a cubic enclosure induces a "thermal short-circuit" effect, altering the heat transfer pathways and flow dynamics. Threedimensional numerical simulations were conducted to investigate steady laminar natural convection in a cubic enclosure with a thermally conductive cylinder. Air was used as the working fluid, and Pr = 0.712. The Rayleigh (Ra) number ranges from 103 to 106. The aspect ratio, defined as the diameter of the cylinder relative to the side length of the enclosure, varies between 0.01 and 0.2. The thermal conductivity ratio of the cylinder to the fluid ranges from 487 to 1704. The results show that the cylinder modifies the flow and thermal fields through flow obstruction and solid heat conduction. At low Ra, heat conduction dominates, and the cylinder suppresses the weak natural circulation. At high Ra, stronger natural convection around the cylinder surface enhances local heat transfer and partially offsets the obstruction effect of the cylinder. The mean wall Nusselt (Nu) number Num is mainly governed by Ra and is only weakly affected by the aspect ratio and thermal conductivity ratio because local heat-transfer suppression and enhancement on the heated wall partly compensate for each other. In contrast, the global Nusselt number Nug increases with the aspect ratio and thermal conductivity ratio, indicating that the conductive cylinder provides an additional solid heat-transfer path. Finally, empirical correlations for Num and Nug are proposed. The findings provide insights into the competing effects of solid heat conduction, geometric obstruction, and natural convection in enclosed thermal systems.

Droplet evaporation is a common physical phenomenon in daily life and industrial production. It is of great significance to understand its evaporation characteristics. This study employs the finite element method coupled with moving mesh technology to investigate the influence of gravity on the evaporation dynamics of ethanol-water binary mixture droplets (BMD) under different substrate temperatures and initial ethanol mass fractions. The results indicate that the evaporation rate of BMD is the slowest under zero-gravity condition and the fastest for the sessile droplet. The zero-gravity BMD exhibits a 27.6 % longer lifespan compared with the sessile BMD. As the substrate temperature increases, the lifespan difference between sessile and pendant BMDs becomes more pronounced. With the increasing initial ethanol mass fraction, the volume difference between sessile and pendant droplets decreases in the later stages. This research promotes a deeper understanding of the mass and heat transfer mechanisms in the evaporation process of BMD.

As highly integrated electronic devices exhibit continuously increasing power density, boiling heat transfer based on phase change has become an important approach for efficient heat dissipation under intense heat flux. Nanoscale surface structures and wettability significantly influence boiling heat transfer, particularly hybrid wettability nanostructured surfaces that regulate interfacial nucleation and bubble dynamics. In this work, liquid film boiling on nanopillar arrays and hybrid wettability surfaces was studied by using nonequilibrium molecular dynamics simulations. Different wettability distributions were constructed to analyze the dynamic evolution of bubble nucleation and growth, nucleation and film boiling. Results show that on homogeneous hydrophobic surfaces, the liquid film mainly undergoes interfacial evaporation similar to the Cassie state, whereas homogeneous hydrophilic and hybrid wettability surfaces exhibit evident cavity nucleation, bubble coalescence, and vapor film formation. Hybrid wettability surfaces significantly accelerate bubble growth and promote liquid film instability. Moreover, the phase transition behavior with different thickness under Cassie and Wenzel initial states was further examined. Under the Cassie state, vapor trapped in the cavities forms a thermal resistance layer, and evaporation mainly takes place at the free interface. In contrast, under the Wenzel state the liquid penetrates the cavities, enhancing solid-liquid contact, while local overheating and weakened potential wells induce preferential nucleation. In addition, compared with the smooth surface, nanostructures increase the interfacial heat flux by 7.4 times and reduce interfacial thermal resistance by 90.7%, while hybrid wettability further enhances the heat flux by 20% and reduces the thermal resistance by an additional 28.8% compared with the uniformly wetted nanostructured surface. These findings provide theoretical guidance for designing enhanced boiling heat transfer surfaces.

During the actual operation of developing efficient seawater desalination technology, crystallization fouling often occur on the heat exchange surface, leading to severe deterioration of the flow field and heat exchange performance. In this study, a crystallization fouling model incorporating a three-dimensional (3D) dynamic mesh technique was developed based on Computational Fluid Dynamics (CFD), and the model was validated through experimental data. Then, the secondary flow (Se) was used to clarify the fouling behavior in the channel under dynamic-mesh conditions with single rib, different rib numbers and working condition parameters. The results indicate that the introduction of 3D dynamic mesh technology improves the prediction accuracy of the model, and the relative error is reduced from 4.82% to 0.90%. The predicted fouling layer thickness distribution is also in good agreement with its uneven distribution trend. Compared with a smooth channel dominated by stable deposition regions, a single-rib channel significantly disturbs the flow field, forming fouling-variation zones near the rib root and wake. The Se increases by 88%, resulting in a 3.67% reduction in fouling resistance. Within the studied range, increasing the number of ribs further strengthens the secondary flow, thereby enhancing the antifouling capability. Moreover, a strong negative correlation is observed between the fouling-deposition regions and regions of high secondary-flow intensity. Relative to the baseline case, increasing the inlet velocity markedly enhances secondary-flow intensity and effectively suppresses fouling formation, whereas variations in wall temperature or solution concentration cause noticeable changes in fouling but have little influence on Se.

This study integrates molecular dynamics simulations with the Zeta adsorption isotherm to elucidate liquid formation and transport in porous materials. Two critical processes, pore filling and condensate evaporation, are analyzed. The Zeta model accurately predicts adsorption at low relative pressures (<0.45) using parameters from a nonporous surface. Simulations reveal that the vapor-to-liquid phase transition proceeds via molecular clusters nucleation and coalescence. A predictive capillary condensation model was developed to capture the staged evolution of cluster growth. An augmented Young-Laplace equation incorporating disjoining pressure effects reveals distinct regimes: evaporation suppression in the adsorbed film zone (governed by surface interactions) and enhanced mass transfer in the intrinsic meniscus region (dominated by capillary forces). This pressure gradient-driven mechanism enables continuous liquid replenishment while maintaining structural stability. This multiscale approach bridges molecular interactions with macroscopic transport, offering quantitative insights for optimizing porous materials in applications such as thermal energy storage and catalysis.

The binary mixture droplet evaporation is a more intricate process due to the preferential evaporation effect compared to the pure droplet. There is still a lack of research on the evaporation of binary mixture droplets, especially the influence of initial droplet concentration and contact angle on the evaporation kinetics. The current research utilizes a moving-mesh numerical simulation on the basis of the Arbitrary-Lagrangian-Eulerian method to explore the evaporation of water-ethanol binary mixture droplets. The results indicate that the positions and flow directions of the vortices are influenced by the temperature distribution. There is a corresponding relationship between the position of local minima of ethanol concentration and the local low temperatures. An increase in the initial ethanol concentration leads to an enhancement of the flow, thereby accelerating the evaporation of the binary mixture droplet. Influenced by the activity coefficient, the volume variations of the components exhibit linear or concave trends. The activity coefficient modifies the effective vapor pressure of each component by accounting for deviations from Raoult's law in non-ideal solutions. It amplifies the vapor pressure of low-concentration components, thereby enhancing their evaporation. The impact of the initial concentration on the evaporative mass flux of ethanol is significantly greater than that of water, while the initial contact angle has a slightly greater influence on the evaporation flux of ethanol than on that of water. This work can provide valuable guidance in industries such as spray coating and inkjet printing.

Understanding the reversal process of the large-scale circulation will facilitate system recognition of turbulent penetrative Rayleigh-Bénard convection. The present work describes experimental and numerical investigations on the Rayleigh-Bénard flow of water near 4°C in a box-shaped container. The results indicate that the revised Nusselt number is slightly higher than average Nusselt number with adiabatic assumption. The Nusselt numbers from the simulations show good agreement with the experiment values. Large-scale circulation reversal becomes less likely with the increasing Rayleigh number and density inversion parameter. Reversal is not observed at large density inversion parameters and Rayleigh numbers. Large vertical velocity and temperature fluctuations at the center point are found during the reversal process. However, the Nusselt number is slightly affected by the occurrence of the reversal.