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Droplet evaporation is a complex and fundamental topic that holds great scientific interest due to its relevance in numerous physical and biological processes. We systematically study laser-induced nanofluid droplet evaporation under varying light frequencies. Our findings indicate the existence of two spectral regimes where droplet evaporation is either enhanced or inhibited, which is in stark contrast to the constant regime observed under fixed laser power. The enhanced regime is attributed to the rapid heat transfer initiated by the formation of vapor microbubbles inside the droplet, causing an increase in the overall temperature of the droplet. Conversely, the inhibited regime is associated with reduced heat conduction inside the droplet resulting from localized cooling effects brought about by droplet evaporation. Correlations between heat transfer mechanisms and thermal responses at the droplet surface further support these observations. We also demonstrate that both convective and conductive heat transfers determine the critical light frequency to enhance droplet evaporation. Three light-driven flow patterns are additionally identified inside the droplet. These are photophobic, phototropic, and rolling flows, which are driven by the explosive bubble growth, surface tension gradients, and mass shifts in the droplet center, respectively. Understanding these properties is important for developing miniature evaporators, nanoparticle self-assembly, and various biomedicine applications requiring precise temperature and kinetic control. [ABSTRACT FROM AUTHOR]

This paper explores the supercritical heat transfer mechanism by characterizing the boiling contribution ratio qb/q, where qb is the boiling heat flux and q is the applied heat flux. Experiments are performed using nickel–chromium wire in 15 °C liquid carbon dioxide at 5.2, 7.6, 9.0, and 11.0 MPa. The evaporation heat flux qe is the amount of heat used for vapor generation, while qb is the heat transfer in the bulk liquid due to the disturbance of the flow/temperature field by vapor–liquid interface motion. A data processing procedure is developed to measure qb/q from the captured images. Similar trends appear for both supercritical pseudo-boiling and subcritical boiling. The evaporation-like regime at supercritical pressures reaches qb/q = 0.21–0.43, while the film boiling (evaporation) regime achieves qb/q = 0.08. In the supercritical-boiling-like regime, qb/q increases sharply from 0.19 to 0.65, whereas in the subcritical-nucleate-boiling regime, qb/q maintains a value of 0.30 followed by a rapid rise to 0.68 under a vigorous bubble merging and departing mechanism. At both subcritical and supercritical pressures, the heat transfer deteriorates in the evaporation regime, but is significantly enhanced by phase-change-induced flow/temperature field perturbations. The boiling curves differ in the two pressure domains. At supercritical pressures, natural convection transitions smoothly to the evaporation-like regime, then to the boiling-like regime. At subcritical pressures, a steep transition from natural convection to nucleate boiling occurs, and then, film boiling is induced through the action of surface tension. The above findings complete the inverse boiling curves in the two pressure domains. [ABSTRACT FROM AUTHOR]

Supercritical fluids have been widely used in a variety of applications, in which heat transfer under supercritical pressure is of great importance. This paper presents a critical review on supercritical heat transfer, including a summary on the past work focusing on in-tube heat transfer and the pseudo-boiling concept, the understanding of the mechanisms of supercritical heat transfer, and suggestions for future work. For supercritical fluids heated in tubes, the typical characteristics, the effects of various parameters, the buoyancy and flow acceleration effects, and the heat transfer deterioration phenomenon are all discussed, and the heat transfer correlations and numerical methodologies are summarized. For supercritical fluids cooled in tubes, the experimental observations and explanations, the proposed heat transfer correlations, and the numerical results are summarized and discussed. More importantly, this review provides a comprehensive review of the supercritical pseudo-boiling concept, including the experimentally observed pseudo-boiling phenomenon, the theoretical studies for supercritical fluids to reveal their heterogenous two-phase features, and the progress in the application of the pseudo-boiling concept on supercritical heat transfer. Finally, suggestions for future research are provided to further advance the understanding and enable accurate prediction of supercritical heat transfer. [ABSTRACT FROM AUTHOR]

Flow transport of supercritical fluids (SFs) in nanopores widely occurs in shale and deep geothermal systems. Pressure is an important parameter for describing SFs, but the effect of pressure on the flow and slip behaviors of SFs in nanochannels is unknown. In this study, molecular dynamics simulations of the Poiseuille flow of supercritical water (SCW) in graphene nanochannels are performed by applying a driving force to water molecules between two walls. Fluid pressure is realized by varying water density. The effect of pressure on the slip length under different surface wettability is investigated. The results show that the slip length nonmonotonically varies with the pressure, which is divided into three regions according to the three-regime-model of SFs. For the gas phase and gas-like SCW, the slip length gradually decreases with increasing pressure. For two-phase-like SCW, the slip length increases with pressure. For liquid-like (LL) SCW, the slip length decreases with increasing pressure. The slip length nonmonotonically varies due to the nonlinear variation of the fluid viscosity and interfacial friction with pressure. For LL SCW, the slip length is linearly related to the inverse of the density ratio, and the effect of pressure and wettability on the slip length is evaluated using the density ratio and energy barrier. Furthermore, the relationship between the slip length and pressure is verified for application to a wide range of wettability, different channel heights, and different fluid types and solid wall types. This study deepens the understanding of the microscale flow theory under supercritical conditions. [ABSTRACT FROM AUTHOR]

Low-speed driving is an underestimated dangerous behavior that may cause safety issues, such as speed dispersion and traffic flow bottlenecks. To investigate the influence mechanism of low-speed driving behavior, this study constructed the low-speed specific model (LSSM) by extending theory of planned behavior (TPB). The LSSM incorporated two factors, namely, risk perception and behavior habit, into the standard TPB components (attitude, subjective norm, perceived behavioral control, and behavior intention). Web-based questionnaires were used to collect data from a valid sample of 374, of which males accounted for 50%. The participants were aged from 18 to 65 years (M = 35.40, SD = 0.88). The structural equation model was applied to calculate and validate the interrelationships among the components of LSSM. Results showed that the LSSM could explain the variance in low-speed driving behavior and behavior intention by 46% and 76%, respectively. Meanwhile, attitude (β = 0.52, p < 0.001) and behavior habit (β = 0.48, p < 0.001) had the strongest positive influence and prediction power over low-speed driving behavior, respectively, whereas subjective norm (β = 0.05, p > 0.01) and perceived behavioral control (β = -0.12, p > 0.01) showed few significant in influencing the intention. LSSM also showed that people who were sensitive to driving risk perception would avoid low-speed driving behaviors and attitudes. Our findings may provide theoretical support for interventions on low-speed driving behavior. [ABSTRACT FROM AUTHOR]

In emergency scenarios, lane changing can provide a considerable advantage over braking by aiding in the prevention of rear-end collisions. However, executing lane changes on horizontal curves might lead to rollover collisions. This study proposes a systematic methodology for quantifying the rollover safety margin during lane-changing maneuvers by encompassing the complex characteristics of vehicle-road interactions. Specifically, an enhanced six-degree-of-freedom vehicle dynamics model was developed for a tractor-semitrailer and integrates road superelevation. Using this model, the rollover safety margin reduction rate (fS) was calculated. The fS represents the ratio of the difference between the lateral load transfer ratio margins under both reference state and emergency lane change conditions to the lateral load transfer ratio margin in the reference state. The reference state corresponds to vehicles maintaining 80 km·h-1 on a 270 m radius curve, while the emergency condition is defined as lane change durations of less than 4 seconds. The results reveal that emergency lane change maneuvers and roadway alignment significantly affect rollover safety margin. Shorter lane change duration, higher speed, and smaller radius worsen the rollover safety margin; these effects are further amplified when the lane change direction is opposite to the curve's bending direction. When the tractor-semitrailer performs a lane change at 60 km·h-1 within a 4-second duration on a 600 m radius curve, the fS exceeds 100%, indicating an imminent rollover. Consequently, this study contributes valuable evidence to the development of more reliable and secure lane-change strategies. [ABSTRACT FROM AUTHOR]

Due to the dynamic nature of work conditions in the manufacturing plant, it is difficult to obtain accurate information on process processing time and energy consumption, affecting the implementation of scheduling solutions. The fuzzy flexible job shop scheduling problem with uncertain production parameters has not yet been well studied. In this paper, a scheduling optimization model with the objectives of maximum completion time, production cost and delivery satisfaction loss is developed using fuzzy triangular numbers to characterize the time parameters, and an improved quantum particle swarm algorithm is proposed to solve it. The innovations of this paper lie in designing a neighborhood search strategy based on machine code variation for deep search; using cross-maintaining the diversity of elite individuals, and combining it with a simulated annealing strategy for local search. Based on giving full play to the global search capability of the quantum particle swarm algorithm, the comprehensive search capability of the algorithm is enhanced by improving the average optimal position of particles. In addition, a gray target decision model is introduced to make the optimal decision on the scheduling scheme by comprehensively considering the fuzzy production cost. Finally, simulation experiments are conducted for test and engineering cases and compared with various advanced algorithms. The experimental results show that the proposed algorithm significantly outperforms the compared ones regarding convergence speed and precision in optimal-searching. The method provides a more reliable solution to the problem and has some application value. [ABSTRACT FROM AUTHOR]

Supercritical fluids (SFs) are classically regarded as single-phase fluids without bubbles or interfaces, but a recent study shows nanobubbles in SFs under unconfined conditions. The objective of this paper is to explore the phase distribution under confined conditions. Molecular dynamics simulations are performed for supercritical argon. Two walls containing the SF have equal fluid–wall interactions with equal and unequal wall temperatures. An external force is applied on the top wall to control the pressure at 1.5Pc, in which Pc is the critical pressure. Periodic boundary conditions are applied on the four side surfaces of the simulation box. The study indicates that the bulk fluid density is not only dependent on pressure and temperature, but also on fluid–wall interactions, this result deviates from the classical theory, where density depends on only pressure and temperature. For strong fluid–wall interactions, three- or five-layer structures are found, including liquid-like (LL) layers on the walls and two-phase-like (TPL) and gas-like (GL) layers (depending on bulk density) in the channel core. For weak fluid–wall interactions, the phase distribution becomes GL on the wall, and TPL and LL (depending on bulk density) in the channel core, which is inverse to those of strong fluid–wall interactions. Correspondingly, the phase distributions for strong and weak fluid–wall interactions can be analogous to annular or Leidenfrost patterns at subcritical pressures, respectively. The density profile is symmetric against the channel centerline at equal wall temperatures, but symmetry-breaking may exist when applying different wall temperatures. This work provides a phase-distribution link between subcritical and supercritical pressures, which is useful for the design and analysis of SF systems. [ABSTRACT FROM AUTHOR]

During the operation of supercritical CO 2 (sCO 2 ) turbomachineries, large pressure ratios, supersonic conditions and non-ideal gas fluid dynamic phenomenon may happen, which will decrease the whole cycle efficiencies. Hence non-standard designs for the turbomachineries geometry are needed. Successfully simulations in capturing non-ideal gas fluid dynamics and coupled with optimization algorithm are hard and currently not available in any commercial CFD software. Therefore, the problem of optimizing sCO 2 turbomachinery is difficult to solve, which has become a major obstacle to obtain compact and high-efficiency sCO 2 turbomachineries. In this study, a modularized geometry optimizer is developed to obtain the non-standard geometric designs for sCO 2 turbomachineries. Multiple techniques are applied to this optimizer, include the Nelder–Mead algorithm, Mahalanobis distance and stochastic algorithm. The newly developed optimizer can successfully find the optimum satisfying the objective function under given weighting factors. The computational cost can be reduced through a stochastic algorithm. To validate the optimizer, a convergent–divergent nozzle for air with a target Mach number equal to 2.4 is optimized. Different starting points and combinations of weighting factors are used to create a Pareto front. Adjust the weighting factors for different terms of the objective function leading the optimizer to go to different directions in n-dimensional spaces. Three optimized cases, one is Mach number optimized, one is outlet flow uniformity optimized and the other is compromised case, are picked out and analyzed. The results show that the optimizer can successfully find optimized geometry than the reference case and potentially save computational cost. Due to the modularized characteristics, the components of this optimizer can be replaced with any available techniques, which mean the optimizer can be applied to solve different types of optimization problems. [ABSTRACT FROM AUTHOR]

Recently, there is an increased interest in supercritical CO2 and organic Rankine cycles (ORC) for their ability to achieve higher thermodynamic efficiency. However, the non-ideal gas thermodynamic in these cycles may affect the flow properties critically, necessitating the research of non-ideal compressible fluid dynamics (NICFD). Thus, simulation tools that can accurately predict fluid flows with NICFD are significant. This study presents a new approximation Riemann solver in OpenFOAM for NICFD. The new solver uses a real-gas (look-up table based) approximate Riemann flux calculator (modified from HLLC ALE flux calculator) through adding a new thermodynamic library tightly coupled with the OpenFOAM®. To validate the solver, three cases are presented, including a NASA transonic nozzle operating with air, to confirm the ability to correctly simulate the transonic flow phenomena and the shock waves; the VKI 2D cascade operated with MDM to assess the ability in simulating non-ideal gas flows typically to industrial applications; and the dense gas flow (MD4M) passing a backward ramp to illustrate the ability of the flux calculator and look-up table mechanism that can work well in the non-ideal region of fluid properties. This study can benefit future engineering applications of computational fluid mechanics of NICFD and the OpenFOAM community. [ABSTRACT FROM AUTHOR]

Roadway multi-fatality crashes have always been a vital issue for traffic safety. This study aims to explore the contributory factors and interdependent characteristics of multi-fatality crashes using a novel framework combining association rules mining and rules graph structures. A case study is conducted using data from 1068 severe fatal crashes in China from 2015 to 2020, and 1452 interesting rules are generated using an association rule mining approach. Several modular rules graph structures are constructed based on graph theory to reflect the interactions and patterns between different variables. The results indicate that multi-fatality crashes are highly associated with improper operations, passenger overload, fewer lanes, mountainous terrain, and run-off-the-road crashes, representing the key variables of factors concerning driver, vehicle, road, environment, and accident, respectively. Furthermore, crashes involving different severity levels, road categories, and terrain are verified to possess unique association rules and independent crash patterns. Moreover, the proportion of severe crashes caused by a combination of human-vehicle-road-environment factors (43%) is much higher than that of normal crashes (3%). This study reveals that the hidden associations between various factors contribute to the overrepresentation and severity of multi-fatality crashes. It also demonstrates that the crash mechanisms involving multi-fatality crashes and their interactions are more complex at the system level than those for normal crashes. The proposed framework can effectively map the intrinsic link between multiple crash factors and potential risks, providing transportation agencies with helpful insights for targeted safety measures and preventive strategies. [ABSTRACT FROM AUTHOR]

Plasmonics offer unprecedented control over light and stimulate fundamental research and engineering applications in solar energy. The surface plasmon resonance is responsible for both enhanced light scattering and absorption. The plasmon excitations in nanostructures can be tuned to control the hot-carrier emission. The damping dissipation of the kinetic energy of surface plasmons releases heat at nanoscale, which can be used to create high-performance nano-heaters and/or radiators. Spectrally and/or thermally engineered plasmonic nanomaterials attract considerable attention for solar energy application due to their distinct thermoplasmonic properties. In light of these advances, this paper provides a critical review of current research in thermoplasmonics with focus on its physic mechanisms, structure tuning strategies and solar energy applications. Basic mechanism of thermoplasmonics is described from the photothermal conversion and heat transfer physics to thermal-induced processes. Structure tuning strategies including self-tunable plasmons, plasmon coupling strategies and active plasmons with tunable gap distances are then fully discussed in terms of their principles and structures. Based on the flourishing development of novel thermoplasmonic structures, potential applications ranging from solar collector, solar radiator, thermo-photovoltaic, solar desalination and sterilization, solar degradation and catalysis, to solar fuels, and solar fertilizers are additionally highlighted. The advantages of using plasmonics over the conventional technologies are identified, and the areas where important basics involved when the thermoplasmonics bringing into application are stressed throughout the text. Finally, we provide our views on future challenges in solar thermoplasmonics, together with a few suggestions for further developments of this technology. This work would bring new insights and inspire innovative works on designing thermoplasmonics for solar energy application. [ABSTRACT FROM AUTHOR]

• TNRE increased to 87.89 ± 1.82 % after dosing low concentration exogenous glycine. • Candidatus Brocadia and Candidatus Kuenenia emerged as primary enriched genus. • Glycine modulated nitrogen metabolism by altering the content of Hzs & NirS genes. • High dose of exogenous gly in cross-feeding broke the equilibrium of anammox system. • Gly cleavage system could be the initiating point for the cross-feeding imbalance. Strategies to break the cross-feeding equilibrium by dosing essential metabolites and thus enriching and isolating anammox bacteria (AnAOB) have been proposed, but amino acids have not been investigated as important cross-feeding pathways in anammox consortia. In this study, long-term experiments were designed to verify the effect of exgenous glycine on anammox consortia and changes in the bacterial community and metabolic activity after the addition of glycine in a highly active anammox system were investigated. The results showed that the impact of glycine on the activity of anammox highly depended on glycine concentrations, which was manifested as a promotive effect at low concentrations (0–150 mg/L) and an inhibitory effect at high concentrations (300–600 mg/L). The addition of low concentrations of glycine not only enhanced the diversity and richness of bacterial communities but also promoted the enrichment of Candidatus Kuenenia. The qPCR results showed that the content of functional genes Hzs, NirS and anammox 16S rRNA increased while the expression of amoA and NrfA genes was suppressed when glycine acted positively on AnAOB; Hzs and amoA were suppressed when glycine acted negatively on AnAOB, while the expression of NirS and NrfA genes increased dramatically. Specific anammox activity (SAA) experimental results show that 50–150 mg/L glycine was the optimal amount for promoting the activity of AnAOB. Analysis of community metabolic functions indicated that the addition of exogenous glycine resulted in a imbalance of glycine cross-feeding and promoted AnAOB enrichment mainly by affecting pathways such as other glycan degradation and Lysosome. Overall, this study provided new insights into understanding the glycine cross-feeding, which is essential for improving anammox-based technologies. [ABSTRACT FROM AUTHOR]

• Asymptotic technique is applied to investigate the asymptotic behavior of fluid in near-critical region. • Thermal waves originated from the boundary with a characteristic diffusion coefficient scaled by exponent γ -0.5 α - x L. • Diffusion and wave modes show independent behaviors and the magnitude is proportional to boundary flux. • Divergence of bulk viscosity results in the extra pressure force (scaled by −0.5 α-x b) Abnormal transport phenomena are generally found in supercritical fluids heat transfer due to their unique thermophysical properties on the gas–liquid critical point. In the vicinity of the critical point, static or transport properties of fluids can be scaled by the critical exponents along any thermal path being defined. In this work, with such scaling on the critical isochore, the asymptotic technique is applied to investigate the behavior of the near-critical fluids by studying the response to the thermal perturbation in the acoustic time scale. The full asymptotic governing equations are found in both non-viscous and viscous cases that describe the wave mode in bulk and diffusion mode in the boundary layer. The analytical solutions for the mass transport correlation demonstrate the direct bond between the wave mode and boundary conditions regardless of the motion of boundary layers in both heating and cooling cases. Such correlation shows the asymptotic behavior characterized by exponent −0.5 α - x L = −0.625. Thus, the thermal waves that cause cooling and heating, respectively, can coexist and propagate independently due to the one-to-one bonding with respective boundaries (wave sources). This bonding is still valid even if the enlarged viscosity hinders the fluid flow out of the boundary layers. The viscosity leads to the extra pressure work, whose asymptotic behavior follows the exponent −0.5 α - x b = −1.875, to overcome the viscous stress as the boundary layers expand. [ABSTRACT FROM AUTHOR]

Leidenfrost droplet evaporation on a liquid bath exhibits unique features such as ultra-low resistance to sample transition and low-temperature operation; however, the physical mechanisms responsible for these phenomena are incompletely understood. Droplet size and temperature are two key parameters influencing Leidenfrost droplet evaporation. We report herein the thermal non-equilibrium process of an FC-72 droplet over a thin oil layer. We show that the Leidenfrost droplet radius follows the power law R(t) ∼ (1 − t/τ)n, where τ is the characteristic droplet lifetime and n ranges from 0.63 to 0.91. Based on experimental results and theoretical predictions, the remarkable nonmonotonic variation of droplet temperature departs from the saturation-temperature assumption. For lower oil superheating, a cold (subcooled) droplet can sustain evaporation until it disappears. For higher oil superheating, the droplet goes through both subcooled and superheating stages. This phenomenon is well described by sensible heat absorption and release throughout droplet evaporation. These results are helpful for applications such as drug delivery, wherein a cold droplet can float on a liquid bath, thereby extending the lifetime of the biological sample in a high-temperature environment via a localized, low-temperature system. [ABSTRACT FROM AUTHOR]

The friction coefficient between the tire and the road is one of the key parameters affecting road traffic safety. The purpose of this paper is to quantify the risk of skidding for the vehicles due to the friction evolution caused by the traffic polishing in the horizontal curve. Based on the reliability theory, an innovative dynamic risk assessment model is developed in the present study for passenger cars and trucks. The influence of two traffic characteristics for pavement friction is quantified: cumulative traffic volume (CTV) and annual average daily traffic of trucks (AADTT). The speed distribution on the horizontal curve of the motorway is obtained through field experiments as the basic parameter of the model. The Hasofer-Lind Method is adopted to solve the reliability and the risk probability of vehicle skidding. The results show that in the traffic characteristics, the AADTT has a significant impact on the pavement friction; When the AADTT on the road exceeds 2000 veh/d, the increasing CTV leads to friction decrease rapidly and therefore has a significant impact on the risk of horizontal curve. Especially for roads with more than 50 million vehicles of the CTV, the risk of the horizontal curve shows a sharp increase with CTV rising. The research results can provide reference for the road maintenance department to determine the timing of road maintenance. [ABSTRACT FROM AUTHOR]

Owing to the complicated geometric conditions and increasingly diversified driving environment, freeway curves have become a road section with frequent serious accidents. To ensure safe driving on curves, drivers must first perceive the movement condition and the vehicle's position, and accurately evaluate the characteristics of the road to make the right speed choice. In this process, the perception of speed plays a crucial role. The present study aims to investigate the driver's speed perception characteristics with respect to freeway curves to better understand the driver speed selection mechanism. We first construct six three-dimensional (3D) virtual highway models, which are consistent with the geometric lines and traffic engineering instruments of real freeways. A virtual simulation test is then conducted in a highly immersive environment. After the completion of the simulation experiment, we conduct a field verification experiment, test the actual driving speed and perceived speed of drivers in the same place as the simulation experiment, and verify the effectiveness of the simulation method. Finally, 25 3D curve models of four different types are constructed, and the influence of curve characteristics (e.g., curve radius, curve combination, tangent length between curves) on drivers' speed perception accuracy are tested on the simulation platform. The results show that the driver's perceived speed is lower than the real speed when driving on curves, and the tangent-to-spiral (TS) point is the section where the driver's speed is most underestimated. Radius was the most important factor affecting driver's speed perception, but the tangent length between curves also had a lesser influence. However, the curve combination had no effect on it. Our findings can help researchers and road designers understand the reasons for drivers' speed choice, thus promoting drivers' safety on freeway curves. [ABSTRACT FROM AUTHOR]

On fully enclosed freeways, the service area is the only key node for certain crowd activities such as resting, toileting, and dining. In these activities, using the toilet is the most important purpose for people to enter the service area. A reasonable toilet location and size in the service area is the basis for its efficient operation. This study conducts field surveys on several service areas, including Meicun, Tai'an, and Qianxian, through video recording and crowd tracking questionnaires. We summarize and analyze the characteristics of population flow in Chinese freeway service areas. The key data obtained through field surveys are reported, such as the priority and length of stay of customers in the facilities during peak hours at weekends, to analyze the characteristics of pedestrian traffic in the service areas. Finally, based on a large number of pedestrian simulation methods used in studies on the layout of subways and airport facilities, the AnyLogic simulation software is applied to establish a crowd movement model for these areas. The study not only obtained the pedestrian characteristics of the service area but also showed that only changing the location of toilets has no effect on the efficiency of toilet use without changing the level of service, whereas changing the number of toilets has a significant impact on the efficiency. Most importantly, this paper establishes a relationship model between the toilet size of the service area and the service area pedestrians flow; when the toilet seats 266/158/148 people, the maximum flow of people in the service area is about 3,115/2200/2000 p/h, which can provide help for the scale design of the service area. [ABSTRACT FROM AUTHOR]

The heat transfer and pressure drop (Δ P) of supercritical fluid are crucial for the safety of advanced power cycles. Here, experiments were performed for sCO 2 in a horizontal tube with inner diameter (d in) of 10 mm, covering in the ranges of (G): 496.7–1346.2 kg/m2, heat flux (q w): 97.4～400.3 kW/m2 and pressure (P): 7.53–23.51 MPa. Inspired by the similarity of the outer wall temperature (T ow) distributions between the sCO 2 flow and those of stratified-wavy-flow in subcritical pressures, the multiphase flow theory is introduced in subcritical pressures to deal with the sCO 2 heat transfer. In the two-phase-like (TPL) regime, heat transfer coefficients (HTC) and friction factors (f) of sCO 2 are found to significantly deviate from the correlations based on the single-phase flow theory. Further, the vapor-like Froude number Fr VL is proposed to develop new correlations for both the heat transfer and the flow resistance covering the whole data range. The present paper establishes a connection between the flow resistance and heat transfer in supercritical pressures, which is important for the design and operation of sCO 2 power cycles. • Supercritical heat transfer and flow characteristics of CO 2 is investigated in a horizontal tube. • Thick vapor-like film can reduce the frequency of negative temperature differences occurring. • Flow resistance and heat transfer in the two-phase-like regime both strongly deviates from the single-phase convection. • Fr VL was proposed to be the similarity criterion number to connect flow resistance and heat transfer for horizontal flow. • The new correlations with Fr VL number for heat transfer and friction factor are established. [ABSTRACT FROM AUTHOR]

Icy bridge deck in winter has tremendous consequences for expressway traffic safety, which is closely related to the bridge pavement temperature. In this paper, the critical meteorological conditions of icy bridge deck were predicted by multiple linear regression and BP neural network respectively. Firstly, the main parameters affecting the bridge pavement temperature were determined by Pearson partial correlation analysis based on the three-year winter meteorological data of the traffic meteorological monitoring station on the bridge in Shandong province. Secondly, the bridge pavement temperature is selected as the dependent variable, while air temperature, wind speed, relative humidity, dew point temperature, wet bulb temperature and wind cold temperature were selected as independent variables, and the bridge pavement temperature prediction models of linear regression and 5-layer hidden layer classical BP neural network regression were established respectively based on whether the variables are linear or not. Finally, the prediction accuracy of the above models was compared by using the measured data. The results show that the linear regression model could be established only with air temperature, relative humidity and wind speed, owing to collinearity problem. Compared with multiple linear regression model, the predicted value of the BP neural network has a higher degree of fitting with the measured data, and the coefficient of determination reaches 0.7929. Using multiple linear regression and BP neural network, the critical meteorological conditions of bridge deck icing in winter can be effectively predicted even when the sample size is insufficient. [ABSTRACT FROM AUTHOR]

Under adverse weather conditions, visibility and the available pavement friction are reduced. The improper selection of speed on curved road sections leads to an unreasonable distribution of longitudinal and lateral friction, which is likely to cause rear-end collisions and lateral instability accidents. This study considers the combined braking and turning maneuvers to obtain the permitted vehicle speed under rainy conditions. First, a braking distance computation model was established by simplifying the relationship curve between brake pedal force, vehicle braking deceleration, and braking time. Different from the visibility commonly used in the meteorological field, this paper defines "driver's sight distance based on real road scenarios" as a threshold to measure the longitudinal safety of the vehicle. Furthermore, the lateral friction and rollover margin is defined to characterize the vehicle's lateral stability. The corresponding relationship between rainfall intensity-water film thickness-road friction is established to better predict the safe speed based on the information issued by the weather station. It should be noted that since the road friction factor of the wet pavement not only determined the safe vehicle speed but also be determined by the vehicle speed, so we adopt Ferrari's method to solve the quartic equation about permitted vehicle speed. Finally, the braking and turning maneuvers are considered comprehensively based on the principle of friction ellipse. The results of the TruckSim simulation show that for a single-unit truck, running at the computed permitted speed, both lateral and longitudinal stability meet the requirements. The proposed permitted vehicle speed model on horizontal curves can provide driving guidance for drivers on curves under rainy weather or as a decision-making basis for road managers. [ABSTRACT FROM AUTHOR]

Truck rollover is a problem that seriously endangers the safety of human life. Under special conditions, when the driver takes a sharp turn, the truck is most prone to rollover. Speed seriously affects the driving stability of the truck in a sharp turn, but the calculation of the safe speed is not accurate enough at present. The aim of this paper is to develop a more accurate safe speed calculation method to avoid the truck rollover in a sharp turn. Firstly, the calculation formula of the rollover threshold was derived based on a theoretical model, then, the simulation tests were carried out. We selected a 4-axle truck with a total weight of 30t as the subject, simulated the dynamic process of the truck rollover in a sharp turn with TruckSim, evaluated the dynamic rollover risk levels of the truck during this process, and verified the accuracy of the simulation results by results of the theoretical model. Finally, by analyzing the steering principle of the vehicle, the safe speed threshold and the limit speed threshold of the truck in a sharp turn were calculated according to the lateral acceleration corresponding to the rollover risk levels. The results show that no matter what the loading condition of the truck is, when the rollover margin is reduced to about 0.15g, the truck just reaches the risk level of critical rollover; the result provides an accurate algorithm for speed thresholds of the truck when turning radius is less than 250 m. The research provides a calculation method for safe speed of trucks from a dynamic perspective. The research results can be applied to the speed warning system of trucks, which can make drivers better control the rollover risk of trucks in the process of driving and improve driving safety. [ABSTRACT FROM AUTHOR]

The water film depth is a key variable that affects traffic safety under rainfall conditions. According to the Federal Highway Administration, approximately 5700 people are killed and more than 544 700 people are injured in crashes on wet pavements annually. While several studies have attempted to address water film depth issues by establishing prediction models, a few focused on the relationship among road geometric features, capacity of drainage facilities and water film depth. To ascertain the influence of the geometric features of road and facility drainage capacities on the water film depth, the road geometry features were first classified into four types, and the facility drainage capacities were considered from three aspects in this study. Furthermore, the concept of short-time rainfall grade was proposed according to the results of the field test. Finally, the theoretical prediction model for the water film depth was conceived, based on the geometric features of road and facility drainage capacities with different rainfall intensities. Compared with the traditional regression prediction models, the theoretical prediction model clearly shows the effects of the geometric features of road and facility drainage capacities. When the road drainage facilities have no drainage capacity, the water film depth increases rapidly with the rainfall intensity. This model can be used to predict the water film depth of road surfaces on rainy days, evaluate the effect of rainfall on the driving environment, and provide guidance for determining safety control measures on rainy days. [ABSTRACT FROM AUTHOR]

Due to the limited storage and computing power, edge devices at the network edge cannot train deep learning models locally. Traditional deep learning training requires users to upload a local dataset to a cloud center, and trains the data using massive computation resources of the cloud center. However, it results in two bad effects: uploading a local dataset to a centralized cloud center controlled by a third party leaves user data privacy at risk; and uploading multimedia data will consume huge bandwidth resources of mobile users and storage resources of the cloud center, resulting in low scalability in term of the number of edge devices. To deal with these two problems, we propose an edge-enabled distributed deep learning platform by dividing a general deep learning training network into a front and back subnetwork. Specifically, the front subnetwork consisting of several layers is deployed close to input data and is trained separately at each edge device using the local dataset, and the outputs of all front subnetworks are sent to the back subnetwork for later training at a cloud center; while the back subnetwork is deployed at the cloud center, and its output is sent to each front subnetwork. As no original dataset is transferred from edge devices to the cloud center, the platform can protect data privacy and has high scalability. Above that, another two measures are taken to ensure data privacy: asymmetric encryption technology is adopted to guarantee the safety and integrality of the transferred parameters between edge servers and the cloud center; and blockchain technology is used to monitor the actions of the stakeholders in this platform and thereby ensure trust among the stakeholders. Experimental results show the validation of the proposed method. [ABSTRACT FROM AUTHOR]

The entrance and exit sections of a tunnel are the accident black-spots in an expressway. For a safe operation of road tunnels, it is necessary to understand a driver's physiological indices and driving performance when driving through tunnels. In this study, the UC-Win/Road simulation software was used to build 12 tunnel models of different lengths. A simulated driving experiment was carried out in a 6-DoF motion platform. The lateral position of vehicles characterizing the driving performance was measured using the motion platform. Electrocardiogram and eye movement data of 25 recruited drivers were collected simultaneously through the experiment. The spatial changes in a driver's heart rate (HR) growth rate, RMSSD, pupil diameter growth rate and vehicle lateral deviation within 300 m before and after the tunnel entrance and exit were analyzed to determine the variation rules in the different tunnels. The study identified the length range in the tunnel entrance and exit sections that influences the drivers. A quantitative analysis was further carried out to analyze the relationship between the physiological indices and the driving performance indicator. The results showed that a driver's heart rate fluctuates significantly 250 m before the tunnel entrance and 50 m before the exit. In this region, the pupil diameter increases gradually, and drivers tend to shift the vehicle to the left. At the tunnel exit, the HR and RMSSD are affected significantly by the tunnel length, and the variation is higher in longer tunnels. In comparison, the tunnel length has no significant effect on the physiological indicators and driving performance of the drivers at the entrance and exit. [ABSTRACT FROM AUTHOR]

Predicting vehicle carbon emissions on vertical curve sections can provide guidance for low-carbon vertical profile designs. Given that the influence of vertical curve design indicators on the fuel consumption and CO2 emissions of vehicles are underexplored, this study filled this research gap by establishing a theoretical carbon emission model of vehicles on vertical curve sections. The carbon emission model was established based on Xu's vehicle energy conversion model, the conversion model of energy, fuel consumption, and CO2 emissions. The accuracy of the theoretical carbon emission model and the CO2 emission rules on vertical curve sections were verified by field test results. Field tests were carried out on flat sections, longitudinal slope sections, and various types of vertical curve sections, with five common types of vehicles maintaining cruising speed. The carbon emission rate effects on the vertical curve are closely related to the gradient and irrelevant of the radius. On the vertical profile composed with downhill/asymmetric/symmetrical vertical curve with a gradient greater than the balance gradient, the carbon emission rate is determined by the gradient and radius. The influence of the gradient on carbon emissions of vehicle on these vertical profiles was more significant than the radius. The radius is irrelevant to the carbon emission rate on the other forms of vertical profile. These results may benefit highway designers and engineers by providing guidelines regarding the environmental effects of highway vertical curve indexes. [ABSTRACT FROM AUTHOR]

We investigate droplet evaporation, which is a natural phenomenon but the mechanism is not well understood. We are surprised to find that sunlight irradiation does not always enhance droplet evaporation, which is against the common sense that "Sun accelerates water evaporation." This is true at least for short-time evaporation. A whole droplet lifetime consists of two regimes of evaporation: a light induced deterioration regime and an acceleration regime. The deterioration regime is explained by the decreased temperature difference from the droplet bottom to apex, weakening Marangoni flow to hinder conduction heat transfer from the substrate to the droplet. The enhanced regime is explained by the reduced light energy reflection via the droplet surface. The substrate conduction heat transfer and radiation heat transfer of light are coupled to dominate evaporation. The two mechanisms create opposite contributions, resulting in a constant evaporation rate for sunlight irradiation on a droplet. However, natural light decreases the evaporation rate vs time. Hence, evaporation rates with and without sunlight irradiation cross at a specific time. Our work enhances the fundamental understanding of droplet evaporation and provides a useful guideline for efficient solar energy utilization. [ABSTRACT FROM AUTHOR]

Carbon emissions are the primary reason that contributes to global warming. The gradient has a significant impact on the carbon dioxide (CO2) emissions produced by trucks. The aim of the current paper is to propose a carbon emission quantification model for diesel trucks on longitudinal slope sections and investigate the influence of gradient on the carbon emissions of trucks for use in the low-carbon highway design. The law of conservation of mechanical energy, the first law of thermodynamics, and the vehicle longitudinal dynamics theory were adopted for deriving the carbon emission model of the trucks on the flat, uphill, downhill and round-trip longitudinal slope segments. Three kinds of common trucks were chosen to conduct the field test. Following the test data, the model demonstrates a high accuracy. The minimum gradient which is expected to impact carbon emissions of trucks on the round-trip longitudinal slope sections was the balance gradient as revealed. The gradient of the longitudinal slope is required to be avoided to be greater in comparison with the balance gradient for the achievement of the two-way traffic low carbon operation on a highway. The results of this study are valuable to researchers interested in low carbon road design and low carbon transportation control. [ABSTRACT FROM AUTHOR]

A new concept of Highway Node Acceptance Capacity (HNAC) is proposed in this paper inspired by a field data observation. To understand HNAC in microscopic view, boundary condition of successful merging is found using car-following behaviours and lane-changing rules, which could also explain traffic oscillations. In macroscopic view, linear positive relationship between HNAC and background traffic volume is obtained based on moving bottleneck. To determine the explicit form of the relationship, data simulation considering car-following behaviours and traffic flow theory is used. In the results, the synchronization phenomenon of oscillation in on-ramp (with respect to main road) and intersected road is found. The explicit equation of HNAC is determined based on standard deviation and correlation coefficient analysis, and also proved to be accurate with model validation, which is helpful in studies related to propagation mechanism of traffic emergencies on highway network. [ABSTRACT FROM AUTHOR]

Using the pseudo-boiling concept, supercritical heat transfer is analogized to the boiling at subcritical pressures. The proposed supercritical-boiling-number SBO represents the competition between the bubble expansion induced momentum force and the inertia force. Sudden changes between normal heat transfer and heat transfer deterioration are found when crossing critical SBO , which is experimentally determined for CO 2 , H 2 O, R134a and R22. The linear law of supercritical heat transfer is discovered. Our study supports the heterogeneous structure of supercritical fluids. • Supercritical-boiling-number SBO dominates supercritical heat transfer mechanism. • Sudden changes in heat transfer behaviors are found when crossing critical SBO. • Critical SBO values are experimentally determined for CO 2 , H 2 O, R134a and R22. • Our study supports the heterogeneous structure of supercritical fluids. Supercritical fluids such as CO 2 , water and organic fluids are frequently applied in power systems. The accurate prediction of heat transfer deterioration (HTD) is important to keep the safe operation of advanced power systems such as solar driven supercritical carbon dioxide Brayton cycle. As described in textbooks, it is impossible to identify liquid from gas beyond the critical point, thus supercritical fluid is assumed to have homogeneous structure with a single-phase. The single-phase assumption cannot explain and predict supercritical heat transfer (SHT). Instead, we investigate SHT by the pseudo-boiling concept. Heat transfer is analogized between supercritical pressure and subcritical pressure to create a new non-dimensional supercritical-boiling-number SBO , representing the bubble expansion induced momentum force against the inertia force when it is coupled with the ratio of liquid density with respect to vapor density. Our study reveals sudden changes from normal heat transfer (NHT) to heat transfer deterioration (HTD) with obvious temperature peak when crossing a critical SBO , which is 5.126 × 10−4, 2.018 × 10−4, 1.653 × 10−4 and 1.358 × 10−4 for CO 2 , H 2 O, R134a and R22, determined by a large quantity of database. Our work paves a new way to understand the SHT mechanism and supports the heterogeneous structure of liquid-like fluid and vapor-like fluid for supercritical fluids. [ABSTRACT FROM AUTHOR]

Piezoelectric (PE) fan is a novel type of active cooling device which enhance heat transfer with less power consumption. In order to achieve the theoretical limit of heat transfer performance of multiple PE fans system in confined volume, the blade location effects on that were investigated in detail by conducting three-dimensional simulations. Here, the blade pitch ranges from 1.6 to 4.2 times the fan width, and the optimal values of blade pitch with respect to four typical vibration phase angles (0°, 60°, 120°, 180°) were obtained, respectively. For all vibration modes, the air volume variation curve follows a parabola trend with blade pitch. The largest air volume is obtained when fans operating in-phase mode (φ = 0°), a conclusion that differs from that in infinite space. We attribute this to the vortex action, and its formation is determined by two effects. The positive one is the attenuation of counteracting effect from normal forces with the increasing blade pitch, where the force was exerted by two blades onto their inner fluid. The negative one is weakening of the coupling effect of two jets formed by the blade tips when spacing of dual fans is gradually increased. In addition, the local hot spot phenomenon was observed in both in-phase and counter-phase mode. It was observed that the distance between local hot spots broadens with the increasing blade pitch for in-phase mode while remains substantially constant for counter-phase mode. Our work provides a design principle for heat transfer optimization of dual PE fans in confined volume and will benefit both theoretical understanding and application in thermal management of PE fan system. [ABSTRACT FROM AUTHOR]

• Pseudo-boiling of supercritical fluid is investigated using Pt wire and NiCr wire. • Bubble-like interface is tracked by the grey extracting method based on image files. • Evaporation-like mode occurs for Pt wire, both evaporation-like and boiling-like modes occur for NiCr wire. • Intermittent boiling-like heat transfer is caused by the piston motion of the wire. • Continuous boiling-like heat transfer is caused by the temporal-spatial temperature variations of the wire. In this study, we identify whether evaporation-like (EL) mode and boiling-like (BL) mode occur under supercritical pressures by investigating the heat transfer of platinum (Pt) and nickel-chromium (NiCr) wires, with a length of 22.0 mm and diameter of 70 μm, in carbon dioxide liquid at 8 and 10 MPa. Using a direct photographic technique based on the light refractive principle, we analyse the brighter/darker pattern in a varied-density field. The vapor–liquid interface is quantified using the grey extraction method. Our results show that beyond the limit of natural convection (NC), only the EL mode is identified for the Pt wire. However, for the NiCr wire, the EL mode, the transition from EL to BL (TEB) mode, and the BL mode are observed. The opposing gravity and drag forces cause downward bending of the Pt wire and upward bending of the NiCr wire. In the TEB region, the varying importance of interfacial expansion velocity over the buoyancy velocity accounts for the piston motion of the NiCr wire. During falling of the wire, the lighter fluid penetrating the heavier fluid causes interfacial instability to trigger the intermittent BL heat transfer. Beyond the TEB region, continuous BL heat transfer is observed. We introduce the small-perturbation theory to achieve a new non-dimensional parameter, H 3. For the Pt wire, a smaller (either negative or positive) H 3 explains why only the EL mode appears. For the NiCr wire, the negative H 3 in the TEB region proves that the intermittent BL heat transfer is caused by the piston motion of the wire, but the positive and ∼30 times larger H 3 indicates that the continuous BL heat transfer is caused by the temporal-spatial temperature variations. Furthermore, we observe that the BL mode occurs in a vapor-like layer instead of wall cavities, which is different from subcritical boiling. The BL mode displays random and disordered features, like those of subcritical boiling. This work elaborately explores common and uncommon features between supercritical pseudo-boiling and subcritical boiling, and uncovers the secret of two modes of pseudo-boiling. [Display omitted] [ABSTRACT FROM AUTHOR]

• S-CO 2 coal fired power plant was investigated. • The overlap energy utilization (OEU) principle was proposed. • OEU increases the average heat absorption temperature for bottom cycle. • An external air preheater (EAP) recycles extra heat to the system for bottom cycle. • OEU and EAP reaches identical efficiencies for top and bottom cycles. For a coal fired power plant, a combined supercritical CO 2 cycle (S-CO 2) absorbs flue gas energy over entire temperature range. Because top/bottom cycles absorb high and moderate temperature flue gas energy respectively, there is an efficiency gap between the two cycles. To fill the efficiency gap, the overlap absorption of flue gas energy is proposed, using top cycle to absorb high temperature flue gas heat, but bottom cycle to absorb not only moderate temperature flue gas heat, but also a part of high temperature flue gas heat. The overlap energy absorption in a high temperature regime increases CO 2 heat absorption temperature to improve bottom cycle efficiency. A four steps roadmap guides us to construct a combined cycle with RC + DRH as top cycle and RC + DRH + EAP as bottom cycle to reach the maximum efficiency limit, where RC, DRH and EAP represent the cycles of recompression, double-reheating and external air preheater, respectively. The components sharing among top/bottom cycles ensures simple system layout, and EAP recycles extra heat of bottom cycle to the system, keeping a smallest heat dissipation to environment. The net power efficiency reaches 47.99% at the main vapor parameters of 620 °C/30 MPa. The overlap energy utilization can be extended for other systems. [ABSTRACT FROM AUTHOR]

Truck's climbing performance is an important consideration in traffic safety, efficiency, and highway geometric design. With the infrastructure development in high-altitude area in China, more attention needs to be paid on truck's climbing performance in such area. In this article, truck's climbing speed in high-altitude area was examined through field tests on different grade sections at different altitudes. Truck's speed-distance curves were built at different altitudes and the impact of altitude on truck's climbing speed was explored based on the test results. It was shown that, within the altitude range of 3000~5000m, altitude had an obvious influence on test truck's decelerating and accelerating performance. Truck's speed decreased faster on steep grades and increased slower on gentle grades with the increase of the altitude. Also, the stable speed that test truck could maintain on a certain grade was lower at a higher altitude. In addition, test truck's theoretical speed-distance curves at the sea level were estimated through truck's dynamic model. Compared with the theoretical crawl speed, a negative effect of altitude change (from 0 to the altitude above 3000 m) was found on truck's climbing performance. [ABSTRACT FROM AUTHOR]

This research presents an operable zoning approach for phased evacuations adapted to disasters with spatio-temporal randomness. As a criterion for prioritizing evacuation order, evacuation risk is formulated by taking into consideration the estimated residual evacuation horizon associated with the characteristics of the disaster, the estimated time-dependent capacities of outbound lanes related to network supply, and the time-dependent evacuation demand of an evacuation unit. The modeling of the subzone determined for phased evacuation is based on rescue demand, the characteristics of the disaster, and network supply, and is labeled as a high-risk evacuation zone (HEZ). The range of HEZ features a time-evolving pattern in accordance with phased evacuation. The zone partition paradigm can be seamlessly applied to different types of disasters, especially those with high spatio-temporal randomness. It also provides a generalizable approach for subzone partitioning in phased evacuation by minimizing evacuation risk. The proposed approach is examined on numerical experiments through the road network of Xi'an, China, the results of which highlight its strength in increased adaptability to the dynamics of disaster impact and improved performance in evacuation operation. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive analysis of enhanced condensation with phase separation concept is presented, for which mesh-membrane-tube (MMT) is suspended in a tube. A twill Dutch weaved mesh screen and two plain Dutch weaved mesh screens are used to fabricate MMT. Our study reveals that liquid leakage across MMT not only keeps better condensation on condenser wall, but also decreases pressure drop rise penalty. To modulate stratified-flow, the #1 MMT with smallest d p has the largest capillary force to pump liquid towards core region to expose more condenser surface with vapor, where d p is pore diameter. To modulate annular-flow, finest mesh wires of #1 MMT ensure the best wetting to liquid to prevent condenser wall from being impacted by satellite droplets. These mechanisms explain the best performance of #1 MMT, reaching a maximum heat transfer enhancement ratio of 1.82. The three MMTs share a single curve of nozzle discharge coefficient versus Reynolds number. The similar performance of #2 and #3 MMTs is due to identical d p / φ , where φ is mesh open porosity. Fine mesh wires and small mesh pores are suggested to enhance condensation heat transfer. MMT are recommended to be used in condenser tube upstream when vapor mass qualities larger than 0.1. Highlights • Mesh-membrane-tube (MMT) is suspended in tube to enhance condensation heat transfer. • MMT captures droplets with fine mesh wires to resist liquid accumulation on condenser wall. • MMT having smaller mesh pores enhances liquid suction from annular region to core region. • The ratio of mesh pore diameter to open porosity governs liquid flow across membrane. • An overall 82% improvement of heat transfer enhancement is observed, maximally. [ABSTRACT FROM AUTHOR]

Abstract The Organic Rankine Cycle (ORC) driven by low-grade energy can operate in off-grid mode. Here, we report the steady and transient characteristics of an ORC system. A single screw expander and a synchronous generator convert mechanical power to electricity. A lamp array simulates the variable external loads. The quality parameters including electric frequency, electric power and effective voltage are measured by a power meter. We show that at setting frequency of 50 Hz, the maximum system efficiency can be reached when the external load is not larger than the ORC power capacity. The expander isentropic efficiency is above 80% for the vapor superheating of 5–10 K at expander inlet. A control strategy is proposed to achieve better system performance under varied heat source and environment conditions. By use of residual frequency and adjusting pumping frequency, the vapor pressure at expander inlet can be automatically adjusted to reach the optimal value. Transient tests indicate that the electric quality is insensitive to the step change of external loads and heat/cold sources parameters. The thermohydraulic parameters are self-adapted to the change of external parameters. This work provides a self-adapting strategy for ORC operation at varied heat/cold source parameters. Highlights • The steady and transient operation characteristics of an ORC system are investigated. • A single screw expander and a synchronous generator are included in the system. • The electric frequency of 50 Hz is reached if external load is not larger than ORC capacity. • Electric energy quality parameters are insensitive to the step change of external parameters. [ABSTRACT FROM AUTHOR]

Molecular dynamics methods are used to investigate the effect of wall wettability and initial fluid density on the nucleation and growth of nanobubbles in a nanochannel with a groove. Surface wettability is controlled by adjusting the parameters of the solid-liquid potential energy and the results show that groove wettability greatly influences the bubble nucleation process. In the case of a groove with a weak solid-liquid interaction, fluid atoms in the groove are strongly affected by repulsive forces attributed to solid atoms, the density of the fluid atoms is low, and atomic collision frequency increases. The local activation energy is concentrated in the groove, resulting in bubble nucleation. In the case of a groove with a stronger solid-liquid interaction, the bubble is formed in the center of the nanochannel. In general, the bubble radius of curvature and contact angle remain unchanged during the growth process in the case of a uniform wettability nanochannel with a groove, while significant changes are observed for a nonuniform wettability nanochannel. The radius of curvature for the generated bubble increases with increasing fluid initial density, while the steady contact angle decreases. [ABSTRACT FROM AUTHOR]

Owing to its mathematical elegance and empirical accuracy, the speed-density model is critical in solving macroscopic traffic problems. This study developed an improved general-logistic-based speed-density model, which is a new method in macroscopic traffic flow theory. This article extensively discusses the properties of the general-logistic-based speed-density model. The physical meanings and values of all the parameters were determined based on the effect of heavy vehicles and the method for the linear and nonlinear regression analysis. The accuracy and versatility of the developed model were also found to be excellent based on the field data and relative error. [ABSTRACT FROM AUTHOR]

Highlights • Condensation experiment on superhydrophobic nanograsses surface (NGS) is performed. • Fresh NGS behaves smaller drop but deteriorates heat transfer compared with polymer surface. • Collapse and breakage of nanograsses worsen heat transfer for long-term operation. • Three mechanisms to induce nanostructure failure are proposed. • There is a limit of decayed heat transfer after nanostructure failure. Abstract Dropwise condensation heat transfer (DWC) on superhydrophobic nanograsses surface (NGS) was investigated for long-term operation. For DWC of pure water-vapor on fresh NGS, two heat transfer regimes are identified: higher heat transfer coefficients with droplet jumping, and constant heat transfer coefficients with droplet rolling. The one-week operation not only deteriorates heat transfer performance, but also changes jumping or rolling mode to sliding mode. The condensation heat transfer coefficients are apparently decreased from first to third day, but they approach a limit value since the third day. In order to identify if the single-molecule-layer of polymer (SML) modified on nanograsses was destroyed, DWC on a smooth single-molecule-layer of polymer surface (SSML) was tested to display stable heat transfer with drop sliding for one-week operation, concluding no failure of the polymer layer. The collapse and breakage of nanograsses were observed to explain the decayed heat transfer versus time on NGS. Compared with SSML, the NGS has smaller droplet departure size but lower heat transfer coefficients, indicating positive and negative effects after introducing nanostructures. Three nanostructure failure mechanisms are proposed. This work suggests a new research field of the nanoscale fluid-wall interaction. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to develop a criterion to predict the onset of heat transfer deterioration (HTD) for supercritical CO 2 heat transfer. A new mechanism is proposed by assuming supercritical pseudo-boiling. Before bulk fluid reaches pseudo-critical temperature (T pc), the tube cross-section contains a vapor layer and a liquid-like fluid. The saturation temperature interface is defined at T = T pc , inside and outside which are a vapor layer (T > T pc) and a subcooled liquid (T < T pc). The subcritical boiling number is extended to supercritical "boiling" number, defined as SBO = q w /(Gi pc), where q w , G and i pc are heat flux, mass flux, and CO 2 enthalpy at T pc , respectively. SBO , by coupling the density ratio between "liquid" and "vapor", represents the competition between vapor expansion induced momentum force and inertia force. The experiment of supercritical CO 2 heat transfer is performed in a 10.0 mm inner diameter tube, covering ranges of P = 7.5–21.1 MPa, G = 488–1600 kg/m2s and q w = 74–413 kW/m2. Surprisingly, the onset of HTD is found to occur at a critical SBO which is 5.126 × 10 − 4 and the critical heat flux is expressed as q C H F = 5.126 × 10 − 4 G i pc . It is shown that our new criterion is also suitable for other experiments reported in literature, providing a general guidance to design and operate S CO 2 heaters to avoid HTD. Graphical abstract Image 1 Highlights • Similarity principle deals with heat transfer deterioration at supercritical pressure. • The analysis results in a new supercritical "boiling" number SBO. • SBO comprehensively considers the effects of a set of variables. • CO 2 heat transfer experiment is performed over wide parameter ranges. • The critical SBO of 5.126 × 10−4 distinguishes two regimes of heat transfer. [ABSTRACT FROM AUTHOR]

Apart from private traffic, the evacuation of transit-dependent population is also an essential component of emergency preparedness, especially under no-notice evacuation scenarios with limit evacuation horizon. In literature, most bus-based evacuation models for no-notice evacuation are established under implicit assumptions of uniform evacuation horizon among different pick-up locations or fixed bus fleet in the evacuation area. These constraints will distance their models from real-world situations, where evacuation horizon is various due to spatial distribution of pick-up locations and fleet size of bus available for allocation will increase over time in no-notice evacuation. This research presents a risk-based bus schedule model which is differentiated from the vehicle routing problem (VRP) and bus evacuation problem (BEP) in literature, including the objective and the time-dependent parameters. A quantified definition of evacuation risk for pick-up location with concerns of disaster dynamics and time-varying supply-demand conditions is proposed in this paper as a criterion for bus allocation, also acting as a reflection of social equity to some extent. A notion of time-evolving disadvantageous evacuation units (DEU) is introduced to represent the pick-up locations selected for bus allocation with limited resource. The binary integer linear programming (BILP) named risk-based bus schedule model incorporated with DEU notion can provide a reference for resource allocation in stage of both evacuation planning and operation for transit-dependent population. The proposed model structure can effectively capture the changes of evacuation risk among pick-up locations over time to realize real-time bus schedule. Numerical experiments are conducted using the transportation network of the city of Xi'an, China, to test the performance of the model. The applicability and comparison of different bus evacuation models are also discussed in this paper. This research provides insights into dealing with disaster dynamics and time-varying supply conditions in realistic bus-based no-notice evacuation operations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Molecular dynamics simulation was performed in nano-Janus-interface system. • Temperature gradients can be steepened by lowering hot wall wettabilities. • Heat transfer is switched by varying wall wettabilities and applied forces to liquid. • The finding helps to develop temperature sensitive nano-energy-devices. Abstract Janus-interface-system is referred as liquid confined between hydrophilic and hydrophobic surfaces, nanoscale energy transfer in Janus-interface-system is not understood. Here, we investigate Poiseuille flow by non-equilibrium molecular dynamics (NEMD) using argon as the working fluid. The two solid walls hold different temperatures and wettabilities. It is found that for pure heat conduction, temperature jumps are negative on hot wall but positive on cold wall to create positive heat flow from hot wall to cold wall (called positive heat transfer). However, the convective energy transfer in Janus-interface-system always behaves positive temperature jumps on the two walls due to viscous heating. We show that, lowering hot wall wettabilities creates more significant velocity and temperature slippages on hot wall than those on cold wall to steepen liquid temperature gradients in nanochannel. We further show that heat flow sign can be switched between positive and negative, by (1) keeping super-hydrophilic hot wall but changing cold wall wettabilities, (2) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying external forces applied to liquid, and (3) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying hot wall temperatures. All the three cases yield non-symmetry velocity profile and more sensitive changes of temperature jumps on cold wall than those on hot wall for heat transfer switch. The transition between positive and negative heat transfer occurs at the zero temperature gradient in the channel. The findings not only enhance the understating of nanoscale energy transfer in Janus-interface-system, but also provide novel working principle for nano-devices behaving temperature sensitive nature. [ABSTRACT FROM AUTHOR]

Herein, the effect of the power capacity, W net , on the performance of supercritical carbon dioxide (sCO 2) coal-fired power plants is investigated, with W net in the range of (100–1000) MWe. A comprehensive model was established wherein the sCO 2 cycle was coupled with the models of various components. For the sCO 2 boiler, the total thermal load was assigned to various heaters, and the pressure drop in each heater was calculated. Owing to the strong penalty effect of the pressure drop, both total flow mode (TFM) and partial flow mode (PFM) were applied to the sCO 2 boiler. A fluid network integrating the recuperator units was established for heat recovery in the system. A thermal-hydraulic model was proposed for a single unit and an integration package. Various losses were considered in the prediction of the efficiencies of axial flow turbines and compressors. The thermal efficiency increases, attains a maximum, and then decreases with increase of W net. This parabolic distribution results from the tradeoff between the decreased efficiency owing to pressure drops in the heat exchangers and the increased efficiency of the turbomachinery. The maximum thermal efficiency occurred at W net of 300 MWe and 200 MWe when using the PFM and TFM, respectively. Based on the results, PFM is found to eliminate the penalty effect of pressure drops. Our study provides guidelines for the design and operation of sCO 2 coal-fired power plants. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (sCO 2) cycle can be driven by fossil energy and solar/nuclear energy. Available references maximize cycle efficiency by fixing turbine efficiencies η tt in advance. Here, we provide turbine efficiencies dependent on power capacities W T which are in the range of (50–450) MW. After examination of working mechanism and special characteristic of sCO 2 turbines, a comprehensive model was presented to predict characteristic sizes, irreversible losses and efficiencies of turbines. Characteristic size of turbines (l c) is found to obey the scale law of l c ∼ W T 0.5. Profile loss Y p , secondary loss Y s , clearance loss Y cl and trailing edge loss Y te obey the scaling laws of Y p ∼ W T − 0.075 , Y s ∼ W T − 0.075 , Y cl ∼ W T − 0.39 , Y te ∼ W T − 1 . These scaling laws agree with the correlations based on numerical simulations. With continuous increase of W T , η tt increases but the slope of the curves become gentle. Efficiency maps are provided based on inlet pressures P in and temperatures T in. By fixing W T , η tt decreases with increase of P in and T in. The scaling laws regarding irreversible losses provide the guidance to optimize the turbine design. The efficiency maps can be integrated in the cycle analysis for accurate estimate of system performance, and help to select suitable power capacity. • A comprehensive model is presented to predict the performances of sCO 2 axial turbines. • Scaling laws of characteristic sizes and irreversible losses are theoretically developed. • Turbine efficiencies quickly increase and then the slope of the curve decreases, with increase of W T. • Turbine efficiencies show parabolic variation with respect to expansion pressure ratios. • Efficiency maps are presented based on inlet pressures and temperatures. [ABSTRACT FROM AUTHOR]

Excessively high brake temperature may lead to brake fading and failure, resulting in truck runaway down a graded descent. The accurate prediction of the changes in the brake-drum temperature on downgrades can provide theoretical guidance for truck accident countermeasures, such as determining the maximum safe speeds and the locations of truck escape ramps. By analyzing truck accident mechanisms during graded descents and selecting the initial brake-drum temperature, downgrade percentage and length, and the truck weight and speed as independent variables, with the brake-drum temperature as a dependent variable, the downgrade process of a truck can be divided into two stages: speed control at the grade section and emergency braking at the grade end. The energy conversion process in the forms of brake and nonbrake forces in the two stages are analyzed, based on the energy conservation law. A prediction model for the brake-drum temperature of large trucks on consecutive mountain downgrade routes is established, using the heat quantity formula. The model’s numerical calculation explicitly demonstrates the effect of all the variables. The brake-drum temperature is positively related to the truck weight, and the percentage and length of the downgrade. The temperature increase in the control speed phase is negatively related to the truck speed, whereas that in the emergency braking phase is positively related. The relationship curves between the variables show that the brake-drum temperature does not change significantly with the truck speed. However, the brake-drum temperatures, under different truck weights, downgrade lengths, and percentages, at the same speed, differ considerably. Compared to the existing empirical fitting model based on specific test data, the proposed model clearly shows the effects of main variables. The proposed model can be used for determining the safe truck speeds and locations of truck escape ramps to provide guidance for drivers and builders. [ABSTRACT FROM AUTHOR]

For coal fired power plant, the supercritical carbon dioxide Brayton cycle (S-CO 2 ) is difficult to absorb flue gas heat in a wide temperature range of 120–1500 °C. Here, novel methods are developed to cascade utilize flue gas heat, in which energies in high, moderate and low temperature levels are extracted by top cycle, bottom cycle or flue gas cooler (FGC), and air preheater, respectively. The cascade utilization shall satisfy the criterion that CO 2 temperature entering boiler for top cycle equals to CO 2 temperature leaving boiler for bottom cycle . The separate-top-bottom-cycle (STB) is proposed, in which no any component is shared by top and bottom cycles. Six possible bottom cycles are studied. The thermodynamics analysis is coupled with heat transfer and pressure drop analysis for whole power plant. It is found that the main vapor pressure of bottom cycle can be the “best” parameter to be adjusted over a wide range of 15–35 MPa to couple and optimize top and bottom cycles. Then, the parameter coordination principle is proposed to share specific components for top and bottom cycles. Thus, the separate cycles are converted into a connected cycle to simplify the whole system layout. The connected cycle has a power generation efficiency of 51.82% at main vapor parameters of 700 °C/35 MPa, significantly higher than available supercritical water-steam Rankine cycle power plant. The findings in this paper give a clue to further raise the power generation efficiency for large scale S-CO 2 coal fired power plant. [ABSTRACT FROM AUTHOR]

In order to reveal the main factors affecting the deformation of reinforced soil retaining wall and the influence of various factors on the deformation, the constitutive relation is discretized into four aspects of soil, geogrid, wall panel, and contact surface, and discrete element matrices are, respectively, constructed, with the method of separate finite element. Based on the finite element geotechnical analysis technology platform, the deformation analysis model of reinforced soil retaining wall is established. Taking the modulus of foundation soil as the influencing factor of the foundation soil, taking the geogrid stiffness, length, and spacing as the influencing factors of geogrids, and taking the filling type of limestone, fly ash, and silty clay as the influencing factors of backfill in the wall, the horizontal and vertical deformations of reinforced retaining wall under different factors using the methods of controlling a single variable analysis are calculated. The results show that the increase of elastic modulus of foundation soil will reduce the vertical deformation of the wall but increase the horizontal deformation. The silty clay is not suitable as filler, and lime soil is slightly better than fly ash. The spacing between geogrids is 20 cm ~ 60 cm, which has less effect on wall deformation, but the horizontal deformation rapidly increases after the spacing increases to 80 cm, and other grid performance influencing factors also have the characteristic, where there exists a threshold. The wall will have a greater deformation when the threshold is not reached; a higher indicator of the grid to reduce the deformation of the retaining wall is not obvious after reaching the threshold. [ABSTRACT FROM AUTHOR]

We investigated the effects of four safety facilities in expressway tunnels—information boards, flashing lights, human-voice broadcasts, and siren broadcasts—on driver distance perception by questionnaire surveys and field experiments. Results from a survey questionnaire given to 436 drivers indicated that each of the facilities, except the human-voice broadcast, was perceived to increase the driving safety. Consistently, results from field experiments involving 150 participants in China’s Xingshuliang Tunnel indicated that information boards, flashing lights, and siren broadcasts increased the distance perception accuracy of drivers, while human-voice broadcasts decreased this accuracy. The results of human-voice broadcasts may be due to the fact that drivers could not catch and understand the information they heard from human-voice broadcasts while driving in tunnels. This research can assist engineers in identifying the effective safety facilities in tunnels and provide a basis for prioritizing the implementation of these facilities, ultimately increasing driver distance perception accuracy and decreasing rear-end collisions. [ABSTRACT FROM AUTHOR]

When supercritical carbon dioxide (S CO 2 ) Brayton cycle is used for coal fired power plant, the significantly increased flow rate causes extremely large boiler pressure drops, and residual flue gas energy extraction becomes difficult. This paper contains two consecutive parts to resolve these issues. The first part deals with general analysis. Results show that, introducing intercooling and/or reheating into cycle apparently elevate thermal efficiencies, but cycle performance is obviously deteriorated by large pressure drops. Partial flow strategy was proposed in part 2 to yield boiler module design. Both flow rate and length for each module are cut to be half, reducing pressure drop to 1/8 of that with total flow mode. Surprisingly, we show that CO 2 boiler pressure drop can be equivalent to or even smaller than that for supercritical water-steam boiler. Three flue gas energy extraction schemes are proposed. The case A scheme not only keeps lower exit flue gas temperature (∼120 °C), but also maintains acceptable secondary air temperature. Finally, a 1000 MWe S CO 2 power plant design is given. With main vapor parameters 620 °C/30 MPa, thermal efficiency and power efficiency are 51.22% and 48.37% respectively, showing advantages over supercritical water-steam Rankine cycle. Future works are recommended on S CO 2 power plant design. [ABSTRACT FROM AUTHOR]