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Facing to the challenges of the lunar regolith resource in-situ utilization, applying an external electric field to manipulate lunar particle becomes a promising space particle control method, which is mainly dependent on the particle charging properties in the applied electric field. In the present work, the surficial lunar regolith sample returned from the Moon by the Chang’E-5 mission (CE5 LS) were used to study its charging properties and particles dynamics under the action of an applied external electric field for high-vacuum condition. Some interesting phenomena regarding the charging process and electrostatic projection were observed and discussed. The experimental data of particle charges, charge-to-mass ratio and the pre-collision parameters of CE5 LS were obtained. Furthermore, the influences of the projected CE5 LS collision on the target colliding surfaces were studied simultaneously. Our work would provide a solid support for the future study of the lunar regolith in-situ utilization and defense.

The M2 muscarinic receptor (M2R) is a prototypical G-protein-coupled receptor (GPCR) that serves as a model system for understanding GPCR regulation by both orthosteric and allosteric ligands. Here, we investigate the mechanisms governing M2R signaling versatility using cryo-electron microscopy (cryo-EM) and NMR spectroscopy, focusing on the physiological agonist acetylcholine and a supra-physiological agonist iperoxo, as well as a positive allosteric modulator LY2119620. These studies reveal that acetylcholine stabilizes a more heterogeneous M2R-G-protein complex than iperoxo, where two conformers with distinctive G-protein orientations were determined. We find that LY2119620 increases the affinity for both agonists, but differentially modulates agonists efficacy in G-protein and β-arrestin pathways. Structural and spectroscopic analysis suggest that LY211620 stabilizes distinct intracellular conformational ensembles from agonist-bound M2R, which may enhance β-arrestin recruitment while impairing G-protein activation. These results highlight the role of conformational dynamics in the complex signaling behavior of GPCRs, and could facilitate design of better drugs.

Precise particle control is crucial to the development of In Situ Resource Utilization (ISRU) devices on the Moon and Mars. The electrostatic method becomes a promising particle control method for the high-vacuum and low-gravity extraterrestrial conditions. In this paper, the dynamics of particle transport by an alternating four-phase travelling-wave electrostatic field is numerically investigated. The discrete element method (DEM) is used for modeling particles' behaviors, and the distribution of electric field is simulated by the finite element method (FEM). The electrostatic force is exerted on each particle at a mesoscopic level and the interaction forces between particles are carefully included. The simulation is validated with existing experimental results, the detailed particle trajectories and macroscopic phenomena, such as particle ensemble transport mode, transport direction and leap heights, are explained by the force analysis in the simulation. The results show that particle transport direction is independent of particle charge polarities. Particle transport velocity and the changes of electrodes’ polarities should be designed in conjunction with each other for particle directed transport. Comparing with the particle forward transport for low excitation frequency, the backward transport of particle under higher frequency conditions could be adopted to realize much faster and more smooth particle directed transport.

Manipulation of a conductive droplet by electrowetting has been a popular topic in microfluidics whereby wettability of the droplet on a solid surface is increased by applying a voltage between the conductive droplet and the insulated surface. However, the opposite phenomenon, e.g., decreasing the wettability of a nonconductive droplet and increasing its contact angle (CA) by the reversed electrowetting (REW) effect, has been scarcely reported. Such a process involves not only the transient dynamics of droplet dewetting but also a critical condition for droplet detachment from the adhesive surface. In this work, actuation of a nonconductive droplet in an aqueous surrounding fluid by REW is studied experimentally. Silicone oil is used for the actuated droplet, and filtered water is used as the surrounding fluid. The solid substrate is made of a glass substrate coated with an indium tin oxide (ITO) film and then deposited by a dielectric layer of Parylene C. Potential difference is applied between the substrate and the surrounding fluid, eliminating the disturbance from the top needle on the motion of the droplet. Three different regimes are identified in the full range of operation. An underactuated regime occurs at low applied voltages, in which the CA of the droplet shows a monotonic increase with the increase of voltage (V). The friction coefficient of the contact line decreases with V before the CA saturation (Vs) but shows little change when V > Vs. At high voltages, the contact line of the sessile droplet is contracted excessively by REW. The droplet shows oscillation, and it refers to the overactuated regime. A combined time scale is proposed, and it verifies that the viscous dissipation of the contact line and liquid inertia show comparable contributions in the droplet dynamics. At sufficiently high voltages, the droplet is rejected completely from the surface. A critical equation for the threshold voltage of droplet detachment is built, and its validity is confirmed by experimental results.

Right ventricular (RV) hypertrophy and further heart failure are major co-morbidities, resulting in the premature death of patients with hypoxic pulmonary hypertension (HPH). The regulatory effects of kallikrein-related peptidase (KLK) family members on cardiac function have been extensively studied. However, to the best of the authors' knowledge, the regulatory effects of KLK8 on RV hypertrophy caused by HPH have yet to be reported. The aim of the present study was to assess KLK8 expression in the RV tissue of HPH-modeled rats, and to further explore the effects and underlying mechanism of KLK8 in regulating the hypertrophy of hypoxia-induced H9c2 cardiomyocytes. In HPH model rats, increases in the right ventricle hypertrophy index, the right ventricular systolic pressure, cardiac output, as well as pulmonary artery wall thickness were observed. Western blot analysis revealed that KLK8 expression and MAPK/p53 signaling activity were enhanced in the RVs of rats in an RV HPH rat model. In hypoxia-induced H9c2 cardiomyocytes, KLK8 overexpression promoted cardiomyocyte hypertrophy, whereas KLK8 silencing showed the opposite results. KLK8 overexpression increased the expression levels of ventricular hypertrophy markers, including atrial natriuretic peptide, brain natriuretic peptide and myosin heavy chain 7, which were blocked upon addition of the p38 MAPK inhibitor, SB202190. Conversely, KLK8 silencing caused a decrease in the expression levels of the ventricular hypertrophy markers, which were further reduced via inhibition of the p38 MAPK/p53 signaling pathway. Taken together, the results of the present study have shown that KLK8 may subtly regulate RV hypertrophy, and therefore KLK8 may be a promising therapeutic target for treating HPH-induced RV hypertrophy.

Melatonin receptors (MT1 and MT2 in humans) are family A G protein–coupled receptors that respond to the neurohormone melatonin to regulate circadian rhythm and sleep. Numerous efforts have been made to develop drugs targeting melatonin receptors for the treatment of insomnia, circadian rhythm disorder, and cancer. However, designing subtype-selective melatonergic drugs remains challenging. Here, we report the cryo-EM structures of the MT1–Gi signaling complex with 2-iodomelatonin and ramelteon and the MT2–Gi signaling complex with ramelteon. These structures, together with the reported functional data, reveal that although MT1 and MT2 possess highly similar orthosteric ligand-binding pockets, they also display distinctive features that could be targeted to design subtype-selective drugs. The unique structural motifs in MT1 and MT2 mediate structural rearrangements with a particularly wide opening on the cytoplasmic side. Gi is engaged in the receptor core shared by MT1 and MT2 and presents a conformation deviating from those in other Gi complexes. Together, our results provide new clues for designing melatonergic drugs and further insights into understanding the G protein coupling mechanism., Melatonin receptors (MT1 and MT2) are the targets for melatonin, the major neurohormone involved in circadian rhythm and sleep regulation. Here the authors describe the structures of 2-iodomelatonin and ramelteon bound MT1–Gi and MT2-Gi, revealing that MT1 and MT2 possess distinctive features within the ligand-binding pocket.

Directional fluid transport by electrowetting is an effective method for fluid management both on Earth and in the space environment. Exact control of the process is always hard because the fundamental dynamics of fluid flow and interface are not well understood. In this study, we examine the process of a sensible droplet transported directionally in an electrowetting channel. The electrodes of the channel are programmed to actuate the droplet at the most effective manner. We build a numerical model based on the phase field method, and a dynamic contact angle model is incorporated in the model. Based on simulated results, the basic process of droplet deformation and motion is explained. Three different stages are observed when the droplet starts to move in the electrowetting channel. The droplet can be transported at a high velocity of 17 mm/s at a voltage of V = 80 V. A wide range of influence factors, including voltage, droplet size, friction factor, pinning force, channel height, gravity level, and tilted angle of the channel, are considered. The contact line friction increases almost linearly with the contact line friction coefficient and the pinning force, both retarding the motion of the droplet at parabolic relations. With an increase in the gravity level, the transport velocity of large droplet decreases. However, the droplet smaller than the capillary length shows quite good anti-gravity capability, which can be transported smoothly even when the channel is tilted by 90° in a normal gravity.

Evidence has demonstrated that microRNA-342-5p (miR-342-5p) is implicated in atherosclerosis (AS), but little is known regarding its intrinsic regulatory mechanisms. Here, we aimed to explore the effect of miR-342-5p targeting Wnt3a on formation of vulnerable plaques and angiogenesis of AS. ApoE−/− mice were fed with high-fat feed for 16 w to replicate the AS vulnerable plaque model. miR-342-5p and Wnt3a expression in aortic tissues of AS were detected. The target relationship between miR-342-5p and Wnt3a was verified. Moreover, ApoE−/− mice were injected with miR-342-5p antagomir and overexpression-Wnt3a vector to test their functions in serum lipid levels, inflammatory and oxidative stress-related cytokines, aortic plaque stability and angiogenesis in plaque of AS mice. miR-342-5p expression was enhanced and Wnt3a expression was degraded in aortic tissues of AS mice and miR-342-5p directly targeted Wnt3a. Up-regulating Wnt3a or down-regulating miR-342-5p reduced blood lipid content, inflammatory and oxidative stress levels, the vulnerability of aortic tissue plaque and inhibited angiogenesis in aortic plaque of AS mice. Functional studies show that depleting miR-342-5p can stabilize aortic tissue plaque and reduce angiogenesis in plaque in AS mice via restoring Wnt3a.

Electrowetting (EW) is an effective method for droplet manipulation in microfluidics. In traditional EW, a conductive droplet is actuated, which spreads on a solid substrate. Recently, we considered an opposite phenomenon of droplet actuation in EW: inducing nonconductive droplet dewetting and detaching from the substrate. An oil/water system is used in which the oil droplet (nonconductive) is actuated on a flat substrate in surrounding water (conductive) by EW. In this work, alternating current (AC) electric fields are applied to EW, and the transient dynamics of droplet dewetting, oscillation, and detachment with the AC signals are investigated. The droplet is not in contact with electrodes, and it dances freely on the substrate. Experiments are performed in a wide range of voltages and AC frequencies. To demonstrate the droplet dynamics, we divide the full process of droplet manipulation into three distinguishable periods, that is, an initiating period, a steady oscillation period, and a detaching condition. Transient droplet dewetting is considered in the initiating period, and we obtain the distribution of the contact line friction factor. In steady oscillation, the oscillation resonance is verified from the oscillating amplitude of the contact line. Different periodical features are found for the droplet dancing at the resonance frequencies and departure from resonance. The droplet is detached at high voltages, and we provide a map for the detachable and nondetachable zones. The voltage is the dominant factor determining the droplet detachment; however, the AC frequency has notable influences on the critical voltage. The detachment is promoted when the AC frequency is within the region of the oscillation resonance (e.g., 20 < f < 75 Hz). In this region, the detaching process is not monotonic but instead, the droplet rebounds by several times before it is completely detached.

In order to understand the effect of alkali factor on the material properties of carbon fiber composite conductor, the aging behaviors of the composite core are evaluated in alkali solution media. Accelerated aging test was carried out in alkali solutions. The resistance of the composite core was evaluated in terms of alteration in the mechanical (flexural), componential (by fourier transform infrared spectroscopy and thermogravimetic analysis), and microstructural (by scanning electron microscope observation) behaviors of the material. The results showed that alkaline immersion had great effect on the properties of the composite core. It was further proved that chemical aging of composite core occurred in alkaline solution. The performance of the composite core was directly related to the resin matrix and the compound interface due to the effect of resin matrix transferring load to carbon fiber.

Control valves are used to close off piping and prevent backflow. Radiated noise is generated when gas discharges through the check valves. In this study, three-dimensional numerical simulations were conducted to observe the flow patterns and to measure the flow fluctuations when the control value had different valve openings. The internal aerodynamic noise from the check valve was computed by using a frequency domain acoustic analogy, based on the Lighthill acoustic analogy. These results not only provided an understanding of the flow pattern in check values, but also were used to determine the location of the noise and the noise characteristics. The optimized water-microjets system, used for reducing the noise emitted by gas jets, was obtained by Max Kandula. The water-microjet were referenced and designed into the modified check value. The experimental results indicated that the modified value produces lower noise.

Horizontal flow of supercritical fluids is very common in industrial facilities involving heat transfer. The serious inhomogeneity in the thermal field remains as one of the major concerns need to be addressed in horizontal supercritical flow. This work aims to evaluate the effectiveness of internal helical-rib roughness in improving heat transfer of horizontal supercritical flow. A well-validated, three-dimensional numerical model was employed to solve the turbulent mixed convection. Results show that helical ribs easily inhibited buoyancy effect in horizontal flow. Under condition of weak buoyancy influence, helical ribs hardly improved local or integral heat transfer as a result of barely modified flow field. In heavily buoyancy-affecting mixed convection, strong interaction between natural convection and rib-induced swirl flow was observed. The flow field continued evolving along the flow direction, which resulted in a more uniform thermal field and significant improvement in heat transfer. Variation trend of the location where heat transfer was the worst was identified. Finally, it was concluded that though internal helical-rib roughness is less effective in horizontal flow than in upward flow, it can still significantly relieve the serious thermal inhomogeneity and heat transfer deterioration in horizontal smooth pipes at Grq/Grth > 200.

Superhydrophobic surface has attracted enormous interests due to its attractive potential applications. Here, we prepare all carbon nanotube hybrid films simply by depositing multi-walled carbon nanotubes on strong single-walled carbon nanotube films through vacuum filtration. The hybrid films behave some exciting superhydrophobic properties of a large water contact angle of 152° and an ultra-low sliding angle of only 2°. The rebounding height of a water droplet dipping from 5 cm above the hybrid film reaches 9.4 mm, which is 3 times that of on the natural lotus leaf. The superhydrophobic hybrid film also have high specific loading capacity of 627 g/g, more than 12 times that of the natural lotus leaf. The hybrid films can mimic lotus leaf in water repelling, self-cleaning, and carrying heavy things quite well.

Deep understanding of flow and heat transfer of supercritical fluids in rifled tubes with non-uniform heating is of great importance for the safety of modern supercritical steam power equipment. In this paper, the heat transfer of supercritical water flowing in a vertical one-side heated rifled tube was numerically investigated. The differences of flow and heat transfer between the circumferentially non-uniform heated rifled tube (NRT) and uniform heated rifled tube (URT) were investigated. The distributions of temperature field, thermophysical properties, axial velocity and turbulent kinetic energy were analyzed. The mechanism of heat transfer improvement of NRT was comprehensively revealed. Results showed that the maximum inner wall temperature in NRT (Tiw,N,max) was 10 K lower than that in URT for the simulation conditions. Both radial and circumferential heat transfers were improved in NRT due to the swirling flow. Under high q/G (ratio of heat flux to mass flux) conditions, the buoyancy effect was weakened in NRT comparing to that in URT. Flow turbulence in boundary layer of y+ > 30 was intensified in NRT, which was crucial for supercritical fluid heat transfer. The positions of Tiw,N,max were not always at the midpoint of the heated side. And a prediction method for Tiw,N,max was proposed.

A complete set of ordinary differential equations, based on modifications of existing models, is used to investigate bubble growth and collapse under microgravity conditions in this paper. As in previous work, effects of inertia, surface tension and viscosity are taken into consideration in the momentum equation of the liquid phase outside of vapor bubble, while effects of “moving interface”, interface curvature and thermal resistance of surrounding liquid are considered in the evaporation of the vapor bubble. A dimensionless fitting constant b is introduced to account for area change of the moving vapor/liquid interface and the diffusive nature of the interface layer. The values of these fitting constants for bubble growth and bubble collapse in water and ethanol are obtained by matching predicted temporal variations of bubble radii with experimental data. The predicted interfacial dynamics during bubble growth and bubble collapse is analyzed. Different stages during the bubble growth process are characterized. During the early stage of bubble collapse, the simulated bubble radii show some “fluctuations”, which can be attributed to the “rebound effect” of pressure balance in the bubble owing to the initial condition of a sudden drop in temperature.

The alkali metal thermoelectric converter (AMTEC) is a regenerative concentration cell for direct conversion of heat to electrical energy. Optimization of the components in AMTECs has been gained wide interest to improve power output and cell efficiency. A lumped thermal-electrochemical model has been developed in this work based on some previous efforts by Tournier et al. (1997). The main contribution of the present model is to simplify the calculation of radiation heat exchange by rendering the BASE, the condenser and the cell walls as a system of three closed-surfaces. The net radiative heat loss from the BASE is determined using a network method of radiation. For model validation purposes, the lumped model is applied to a PX-3A type cell. Good agreements have been obtained between numerical results and experimental data on variations of voltage, current, power output and cell efficiency within a wide range of external loads. Based on the numerical results, the role and separate influence of each component are quantitatively analyzed, including temperature levels for hot and cold ends, BASE properties, electrode materials, heat reduction methods and conductor leads. Optimum parameters are suggested in the analyses. With the recent advances in BASE and electrode materials, an integrated optimization is made to the AMTEC aiming for extra-terrestrial application. In the new module, the surface area of electrodes is increased, new electrodes materials are used and thermal radiation losses are minimized. With stable parameters, the peak power of the cell has been over 8.0 We. The stable voltage is over 3.0 V when RL > 1.2 Ω and the cell efficiency is over 20% when RL is within 1.2–4.0 Ω.

Controlling of the wettability of micro-nano scale surfaces not only plays important roles in basic science but also presents some significant applications in interference shielding materials, microfluidics and phase-change heat transfer enhancement, etc . Here, the superhydrophobic super-aligned carbon nanotube (SACNT) films are firstly obtained by the chemical vapor deposition method and the annealing process. Then their wettabilities are in-situ switched by the electrowetting strategy. Specifically, the fascinating transformation of superhydrophobicity to the superhydrophilicity is achieved by exerting external DC voltages across the CNT-liquid interfaces, and the transitions of Cassie-to-Wenzel states are observed on the multilayer SACNT films. In addition, the electrowetting induced salt absorption of the porous SACNT is also reported here. Finally, the threshold voltages of the electrowetting behaviors for different liquids on the SACNT films and unit capacitances across the CNT-liquid interfaces are obtained, which reveal that the SACNT films have much more outstanding electrowetting properties than the previously reported works. Our approach reported here demonstrates that the wettability of SACNT films could be simply, effectively and in-situ controlled by the electrowetting method, which will have many profound implications in numerous applications such as phase-change heat transfer enhancement, optical lens with variable focal length and microfluidics, etc .

Bubble growth in superheated liquid is a fundamental process in vapor-liquid phase change which occurs widely in thermal and chemical engineering. The strong coupling of heat, mass and momentum transfer at the interface brings difficulties to accurately predict the dynamics of bubble growth. At present, bubble growth under three extreme conditions, i.e. the very early growth stage, low superheats and low pressures, cannot be well described by traditional asymptotic solutions. In this work, a mathematical model was presented for better prediction of bubble growth in a superheated liquid. The model was derived from the equations of motion for a bubble and took account of the heat and mass balances at the interface. The model was validated with a series of experiments from the literature, covering a wide range of operating conditions. The newly proposed model can well predict the features of bubble growth at the very early stage (less than 10 −6 s), for superheats varying from 0.8 K to 36 K and for system pressures reduced from 1.0 atm to 0.0124 atm. Analyses on the thermodynamics and hydrodynamics manifested that the bubble growth was characterized by three typical stages, i.e. a thermal delay stage, a fast expansion stage and a steady growth stage. The time lengths of these stages were related to the levels of superheat or system pressure. Characteristics of these stages were further discussed and the roles of interfacial forces under the different operating conditions were demonstrated.

Accurate predictions of the two-phase flow pattern and heat transfer inside the high-pressure tubes is of great importance for the safety of steam power equipment. In this paper, subcooled boiling flow was numerically modeled and the RPI (Rensselaer Polytechnic Institute) wall boiling model was extended to ultra-high pressure conditions up to 15 MPa. Various combinations of closure models for the key parameters in RPI model, including the nucleation site density ( N w ), bubble departure diameter ( D w ) and bubble departure frequency ( f ), were studied in the pressure range of 3–15 MPa. The numerical results were carefully validated by comparing the simulations with the experiments of Bartolemei et al. (1967, 1982). A widely applicable combination of closure models for N w , D w and f was identified for the pressure range from low to ultra-high levels, with the mass flux range of 503–2123 kg/(m 2 s) and the heat flux range of 0.42–2.21 MW/m 2 . The characteristic parameters of wall subcooled boiling were analyzed and the physical process of subcooled boiling was revealed. Based on the optimized models, the influence of operating parameters including mass flux and heat flux was also studied under the pressures of ∼11 MPa and ∼15 MPa.

Deep understanding of nucleate boiling heat transfer mechanism of saline solution is of great importance for the design and safe operation of steam generation equipment. In this paper, the nucleate flow boiling process of saline solution in a vertical heated pipe was experimentally studied within the concentration range of 0 % ∼ 6 %. In order to realize the visualization, the vertical heated pipe was made of transparent silica glass and a transparent ITO heater was used to provide energy for boiling. The high-speed high-resolution camera was used to capture the vapor-liquid two-phase flow structure. The bubble behaviors such as bubble departure diameter, bubble departure frequency, bubble growth time and waiting time were investigated under different operating conditions. The experimental results showed that the heat transfer deterioration did not occur within the solution concentration of 6% in this work. Under some low heat flux conditions, the heat transfer coefficients of solution can be higher than those of pure water. The reason for this phenomenon can be explained by the different bubble behaviors. Comparing to pure water, the bubble departure diameter of saline solution is bigger and bubble departure frequency is lower. The influences of operating parameters, including concentration, mass flux (200 kg/m2s ∼ 600 kg/m2s), heat flux (30 kW/m2 ∼ 180 kW/m2) and subcooling of fluid (5 K ∼ 35 K), on the nucleate boiling heat transfer coefficients and bubble parameters were comprehensively studied.

Droplet actuation by electrowetting (EW) has drawn significant interest due to the potential applications in micro- and nano-fluidics, and the droplet departure is crucial for separation of the drop phase from the solid surface. However, the operating condition for droplet detachment, induced by the traditional electrowetting is quite strict, making it inconvenient for practical application. Recently, we considered the reversed electrowetting (REW) phenomenon, where a non-conductive droplet, settled on an adhesive surface, is dewetted continuously by applying the potential different between the substrate and surrounding fluid (Wang et al. 2020). Detachment of the oil drop is induced naturally and the detaching process is controllable. We have investigated the physical process of REW in the previous experiments. However, the dynamics of droplet detachment and the underlying mechanism are not well explained by the macroscopic experimental approach. For complementation, we build a numerical scheme in this study and examine the transient dynamics of droplet motion in the REW. The interface of the liquid-liquid system is captured by a phase-field method, and a correlation for the dynamic contact angle is incorporated in the numerical model. The simulated results are validated with the experimental cases. The process of droplet detachment and the critical condition are investigated by analyzing the energy transition during the droplet motion.

The electrohydrodynamic (EHD) is an effective method to enhance boiling heat transfer in the terrestrial and space applications. To simplify the coupling effect of hydrodynamics and heat transfer processes, a varieties of adiabatic researches have been carried out recently, mainly for the upward surfaces. Actually, in industrial application, the boiling heat surface can be in any direction. The EHD effects on bubble dynamics on vertical surfaces and downward surfaces should be paid particular attention. In this work, a systematic experimental research was performed to study the effect of EHD on bubble behaviors considering the different bubble injection directions. A uniform DC electric field was applied to the testing zone with coarse bubbles generated from an orifice of 1.5 mm. Both the positive and negative directions of the electric field were considered in the measurement. The retarding effect of EHD on bubble detachment was demonstrated from the experimental results. This phenomenon was confirmed in all the three bubble injection conditions and was proved to be related to the bubble size by an extra experimental case. To explain the mechanism of the influence of electric field on the bubble dynamics, the main forces acting on the single bubble were analyzed qualitatively based on the evolution characteristics of the bubbles. The force distribution around the coarse bubble was proved to be in imbalance and the net force inhabited the bubble growth, prolonging the bubble detaching time.

The interphase forces play a crucial role in gas–liquid two-phase flow modeling as they construct the mechanical equilibrium between phases and determine the phase distribution pattern across/along the flow channel. In this work, the predictive features of different correlations for the interphase forces were analyzed, and corresponding simulations were conducted to validate the accuracy of each correlation. Three experimental cases with a wide range of bubble Renolds number (Reb) were considered in the modeling validation in order to verify the predictive ability of each model on different bubbly flow regimes. The models differences were clarified. The results showed that there was no standard models that could be universally used for all flow conditions. Selection of the correlations for the drag force, lift force and wall lubrication force should take in account of the bubble regimes and the flow patterns in different Reb ranges. Changes of the turbulence dispersion force model and the turbulent model showed minor influences on the phase distribution in the simulated results, but variation of the turbulent viscosity model significantly affected the turbulent structure in the gas–liquid flow. The optimal models for different Reb ranges had been determined in the simulated results. Based on the results in this work, a modeling strategy route was finally summarized for easier selection of the interphase force models in arranging/optimizing simulations. The strategy route can also be used as the validating steps for new interphase models proposed for bubbly flows.

Optimization of geometric parameters for rifled tube is of great importance for safe operation of heat exchangers. In this paper, the influences of geometry, including rib height, pitch and rib shape, on the heat transfer performance of supercritical water in circumferentially non-uniformly heated rifled tubes were comprehensively studied. The differences of geometry effects on heat transfers in rifled tubes under uniform heating and non-uniform heating conditions were compared. The impact extent of geometry changes for forced convection and mixed convection heat transfer conditions were obtained by conducting simulations under relatively low q/G and high q/G conditions respectively. Finally, the mechanism of heat transfer enhancement resulting from the changes of geometric parameters was revealed. The results show that different geometric parameters have different influences on the overall heat transfer performance of supercritical water in rifled tubes. There exists an optimum value for rib height. According to the analysis, the optimum rib height is 0.45 mm for the present study. Heat transfer is enhanced with the decrease of pitch and the influence of rib shape is negligible. The changes of geometric parameters, which can improve the turbulence intensity in the boundary layer range of 30

A careful evaluation on the wall heat flux partitioning is of great importance for the deep understanding the nucleate flow boiling heat transfer to saline solution. In this work, the portion of each heat transfer contribution was analyzed through wall heat flux partitioning model after model validation. The key parameters used in the model were discussed and the reasonable values were determined. The experimental data of bubble departure diameter, departure frequency, active nucleation site density, bubble waiting time and growth time, were combined into the model to eliminate the uncertainties of empirical closure sub-models. The comparison of heat flux partitioning of subcooled flow boiling between NaCl solution and pure water was presented under different operating conditions. The results showed that for the operating conditions of Qw > 180 kW/m2 or G

One important phenomenon in coal beneficiation fluidized bed (CBFB) is the accumulation of fine coal particles in beneficiation due to poor screening efficiency and attrition of coal samples. The effect of fine coal accumulation is numerically studied in this work using a TFM–DEM hybrid model. The gas phase and medium solid phase are modeled by a two-fluid model (TFM), while the fine coal particles are modeled by the discrete element method (DEM). Particles with a diameter of 0.9 mm are used as the fine coal sample in the simulation. The gas–solid flow pattern and particle dynamics are investigated with different concentrations of fine coal particles accumulated in the bed. For model validation purpose, the mean bed density distributions are compared with the experimental reports from He et al. (2013). The results show that a critical particle concentration exists in the fine coal accumulation process in CBFB. When the fine coal particles are less than 11 wt% in the bed, the flow pattern of medium phase is little affected and the coal particles are well mixed in the bed. However, when the particle concentration exceeds this threshold, the uniformity of bed density distribution is destroyed and particle stratification occurs along the bed height according to their density difference. Flow dynamics of the dense bed and main forces acting on the fine coal particles are analyzed to explain the underlying mechanism. With a large number of particles accumulated in the bed, the mixing effect of medium flow is suppressed. Motion of the fine coal particles is less dependent on the bed disturbance, instead, the particle gravity plays a decisive role in the particle distribution and results in the particle segregation in the fine coal accumulation process.

A TFM–DEM hybrid model is introduced for modeling of the complex gas–solid flows in a pilot scale Coal Beneficiation Fluidized Bed (CBFB). The gas and the dense solid phases are modeled using an Eulerian-Eulerian or two fluid model (TFM), while the beneficiated coal particles are modeled as a dilute phase by the discrete element method (DEM). In this work, the influence of some key operation parameters on particle segregation behavior is studied, including fluidized air velocity, bed depth, and coal feed ratio and bed medium properties. Their effects are evaluated using a single coal sample of diameter 4.3 mm. Particles are divided into five different density fractions to represent the wide density range of raw coal samples. The simulation results demonstrate that by increasing the fluidizing air velocity from 1.2 u mf to 1.8 u mf of the dense medium solids, the segregation degree of beneficiated coal particles is significantly reduced, but the segregation time is only slightly decreased. Increasing the particle feed mass or decreasing the bed depth has a similar influence on CBFB operation. Both help to improve particle segregation, but a shallower bed is demonstrated to be more effective for coal beneficiation. A decrease in the medium density can reduce the bed cut density as well as the beneficiation limit for lighter samples, while a decrease in the medium size will increase the back-mixing effects, resulting in reduced beneficiation quality. Hydrodynamic forces acting on the beneficiated particles are also quantified from the simulation results. By analyzing the magnitude and direction of each force acting on discrete particles, the mechanisms influencing particle segregation under different operation conditions are explained at the particle scale.

Ionic fluids are essential to energy conversion, water desalination, drug delivery, and lab-on-a-chip devices. Ionic transport in nanoscale confinements and complex physical fields still remain elusive. Here, a nanofluidic system is developed using nanochannels of heterogeneous surface properties to investigate transport properties of ions under different temperatures. Steady ionic currents are observed under symmetric temperature gradients, which is equivalent to generating electricity using waste heat (e.g., electronic chips and solar panels). The currents increase linearly with temperature gradient and nonlinearly with channel size. Contributions to ion motion from temperatures and channel properties are evaluated for this phenomenon. The findings provide insights into the study of confined ionic fluids in multiphysical fields, and suggest applications in thermal energy conversion, temperature sensors, and chip-level thermal management.

Particle segregation behavior in a coal beneficiation fluidized bed (CBFB) is numerically studied using a TFM–DEM hybrid model, in which the gas and the dense solid phases are modeled using a Eulerian–Eulerian or two fluid model (TFM), while the beneficiated coal particles are modeled as a dilute phase by the discrete element method (DEM). For validation purpose, the numerical model was setup using geometric and operating conditions similar to a laboratory experimental model with the bed thickness set to one particle diameter to save computational cost. For a fixed gas injection velocity, the influence of particle size and density of the beneficiated samples was studied. It was found that the particles would segregate along the bed height due to the density differences with the degree of segregation being strongly influenced by particle size. Obvious segregation occurs for the coarse samples (6.7 mm and 4.3 mm) and little segregation occurs for the particles smaller than 3 mm. The flow patterns and segregation kinetics were qualitatively comparable with those observed in physical experiments conducted under similar conditions. On this basis, the underlying mechanisms governing particle segregation have been explained in terms of the hydrodynamic forces acting on individual particles. It was demonstrated that the segregation of coarse particles was mainly controlled by the balance between gravity and the local pressure force, while fine particles were more strongly affected by the direct drag forces from the gas phase and the continuum solid phase, thus making them difficult to separate.

The dynamics of liquid penetration in porous wire mesh are experimentally studied in this work by particularly considering the influence of gravity. Similar experimental setups are used on the ground and in a drop tower facility in order to compare the experimental results directly. Visualization of the liquid penetrating process is realized by using single-layered wire mesh which is put between a pair of transparent parallel plates. The dependence of wire mesh on the parallel plates is confirmed. The dimensional results show that liquid penetration in the wire mesh stops at an equilibrium height in normal gravity, while the liquid penetrates ceaselessly in microgravity following a parabolic relation between the liquid height and time. The fast rising early period of liquid rise in normal gravity reduces to a slow climbing period in microgravity. Different to that in normal gravity, liquid rises faster in the coarse wire mesh than in the fine wire mesh in microgravity. The effective contact angle of fluid in the parallel plates increases when it changes from normal gravity to microgravity, while it shows weak dependence on the gravity level as well as the pore radii in the wire meshes. Dimensionless analysis is performed to the results. Good consistency is obtained between the dimensionless experimental data and the theoretical solution, providing a generalized explanation to the dynamics of liquid penetration in metal wire mesh under both normal gravity and microgravity environments.

The segregation behaviors of fine coal particles in a coal beneficiation fluidized bed (CBFB) were investigated in this work. The size range of 1–8 mm was taken into account and three separate size fractions were studied comparatively in the experiments, e.g. 1–2 mm, 3–5.5 mm and 5.5–8 mm. Both a clean coal sample and a gangue sample were used as the processed material to study the segregation behaviors of both light particles and heavy particles. The dense bed was divided as seven layers from bottom to top and the particle distribution in each layer for each sample was fully demonstrated. The influences of the particle density, particle size and the fluidized air velocity were revealed, the segregation patterns under different conditions were compared and the segregation mechanism was carefully analyzed. The results showed that the flotation and sedimentation of the particles in CBFB were still largely influenced by the particle density for the fine size range particles, and density stratification occurred even within each size fraction sample. The weight fraction in each layer showed a quadratic increase along the bed height for the coal particles. For gangue particles, a large fraction deposited in the bottom while the mass proportions in the middle layers also showed an increased tendency. With a decrease of the particle size, both the particle segregation and the density stratification phenomena deteriorated seriously. It was proved that particle feed size should be above 3 mm as the separation effect was quite inefficient for finer particles. By increasing the fluidized air velocity, the bed density slightly decreased but the bed turbulence was largely strengthened by the increasing bubble boiling effect. The flotation and sedimentation of the particles in 5.5–8 mm were obviously affected while no clear influence occurred to the rest of the two size fractions. Moreover, the results in this work provide a group of data that are quite suitable for CBFB numerical modeling studies.

The oscillatory regime for liquid rise in vertical capillaries has been observed but the analytical solution that can be applied for this regime is still in shortage. Some lack terms in the existing analytical solutions make them show deviations when predicting the oscillatory behavior of liquid rise. An improved dynamic model is built in this work for the oscillatory regime. Two main contributions are made, concerning the non-equal pressure losses at the entrance for liquid rise and fall, and the receding dynamic contact angle for the regions with negative capillary numbers. Experiments are performed to correlate the empirical parameters in the submodels and to validate the combined dynamic model. Good accuracies of the present model are obtained by comparing with the experimental data both in literature and from the present study. Inclusion of the non-equal pressure loss equations for the end effect makes the model well capture the high asymmetry of oscillations, while the two-stage dynamic contact angle models correct the local bouncing of the meniscus. The dynamics of liquid in the oscillatory regime is discussed by comparing the contribution of each pressure force. Occurrence criteria of the oscillatory regime is obtained through a non-dimensional analysis. It is shown that the oscillatory regime is affected not only by the combined parameter (ω), but also by the immersed height of tube (H0) and the pressure head loss coefficients (ξ).

Concentrated salt solutions are used as working fluids in heat exchangers for heavy oil drilling to meet the requirements of environmental protection. Deep understanding the nucleate flow boiling heat transfer mechanism of salt solutions is of great importance for the design and safe operation of modern steam power equipment. In this work, the nucleate flow boiling for NaCl solution and pure water was experimentally studied within the concentration (C) range of 0%–6% in a vertical heated tube. To simultaneously obtain the heat transfer coefficient (HTC) and bubble parameters, the test section was built to be transparent and the energy for boiling was provided by a transparent ITO heater. The bubble parameters, including bubble departure diameter (Dw), bubble departure frequency (f), bubble growth time (tg) and waiting time (tw), were measured in the experiments. A wide range of operating conditions is considered in this study, covering the inlet fluid temperature (Tinlet) between 337 and 365 K, the mass flux (G) between 200 and 600 kg/m2s and the heat flux between 10 and 180 kW/m2. Based on the experimental results, the difference of nucleate flow boiling heat transfer performance between pure water and solutions was compared. It was found that the HTC of pure water was higher than that of salt solutions under the operating conditions of Tinlet 351 K and q > 180 kW/m2, in some cases, it was lower than that of solutions. Dw in the solution is bigger than that in pure water while f in the solution is lower. The corresponding reasons for those heat transfer differences between pure water and solutions were revealed by considering the differences in bubble behaviors, physical properties and mass transfer rate. In addition, the influences of operating parameters on the heat transfer characteristics and bubble behaviors of salt solution during nucleate flow boiling were demonstrated.