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Transpiration cooling have gradually become the lead candidate for thermal protection technology of hypersonic vehicle also due to its excellent cooling performance. The porous medium with exceptional properties can further improve thermal protection capability and reliability of transpiration cooling. This paper investigates the preparation and properties of C f /SiC porous ceramic composite with low density and remarkable permeability, and probes the transpiration cooling performances of ceramic composites (mass ratio of silicon carbide particles and short chopped carbon fibers of 1:1) in the various heat flux conditions. The research results show that C f /SiC porous ceramic composites prepared by adding short chopped carbon fibers have uniform pore size distributions (3～20 μm) and low densities (1.074 g/cm3 ～ 1.377 g/cm3), as well as outstanding wettability and permeability (6.07 × 10−8 mm2 ～ 12.22 × 10−8 mm2). Besides, The C f /SiC porous ceramic composites (mass ratio of 1:1) display excellent transpiration cooling performance, meanwhile a new interesting phenomenon that the water pressure difference increases with the rising of heat flow is discovered. Such studies can provide an essential reference for developing porous medium in transpiration cooling technology. [ABSTRACT FROM AUTHOR]

When a fire occurs onboard a ship, ventilation ducts may become hidden pathways for smoke to spread, and this issue has long attracted attention in the industry. In this paper, an experimental and numerical investigation on the smoke movement and indoor temperature characteristics were carried out. The results show that under the effect of thermal buoyancy, ducts with the openings located on the ceiling can easily become pathways for smoke to spread across the cabins. Compared with the scenario where the ducts are removed, the smoke jets from the ducts make the smoke movement in the adjacent cabin more complicated, and the maximum temperature in the cabin is also significantly increased. Moreover, it is found that the mass flow rate (MFR) of the gas in the duct is mainly determined by the pressure difference Δp between the two ends of the duct, and the MFR increases linearly with the increase of A flow (2Δp)1/2, but its maximum value is limited by the cross-sectional area of the duct. The research results will help to better understand the cross-compartment smoke spread under the effect of ventilation ducts and serve as a reference for the quantitative evaluation of the smoke flow in ducts. [ABSTRACT FROM AUTHOR]

Aiming at the problem of controlling the operating velocity of a large-diameter heavy-duty pipeline inspection gauge (PIG), this paper designs the bypass structure to study the velocity change and flow field state when the Ø1219 mm PIG is operating in pipeline with different bypass rates. Fluent is applied to numerical simulation of the fluid-structure interaction flow field based on the dynamic mesh method. The results show that: the bypass rate of 2%–3% can satisfy the velocity of PIG in 3–5 m/s reasonable interval. The larger the bypass rate is, the larger the turbulence intensity is, and the gradual increase of the pressure difference suffered by the PIG. The operating velocity of the PIG can be regulated more accurately by corresponding to the bypass rate and the pressure difference front and rear. Comparing the experimental and simulation results, the error rate of the velocity decrease with bypass rate of 1%–3% is 12.8 %. • Study of fluid-structure coupling simulation based on the dynamic mesh approach. • Pressure, velocity, turbulence intensity analysis of PIG with 1%–3% bypass rate. • Velocity can be regulated by bypass rate corresponding to pressure difference. • In this paper, scaling experiments are performed and compared with simulation. [ABSTRACT FROM AUTHOR]

• Droplet length is found to be the primary factor influencing the splitting pattern. • The presence of tunnels leads to an exponential decrease in the splitting ratio with droplet length. • Capillary number has a negligible impact on the splitting ratio for large-size droplets. In this paper, the phase-field multiphase lattice Boltzmann method is employed to simulate droplet breakup in a T-junction under different outlet pressures. Three behaviors of droplet breakup: non-breakup (flow pattern I), breakup with tunnels (flow pattern II), and breakup with permanent obstruction (flow pattern Ⅲ) are identified. The evolution of morphological characteristics of droplet breakup is quantitatively characterized, based on which the asymmetric splitting mechanisms and the influencing factors are clarified. Additionally, the factors influencing the droplet splitting volume ratio (V II / V I) are elucidated. The results indicate that there is a non-linear relationship between the V II / V I and the flow rate ratio. Moreover, the curve depicting the final V II / V I versus the initial droplet length exhibits a V-shape and has a minimum value. A conclusion is drawn that the Capillary number mainly influences flow pattern II, with the final V II / V I decreasing as the Capillary number increases. Additionally, for flow pattern III, the final V II / V I increases linearly with rising droplet size at low viscosity ratios, whereas it decreases linearly at high viscosity ratios. The growing outlet pressure difference enlarges the flow difference between the two branches, leading to an increase in the final V II / V I. [Display omitted] [ABSTRACT FROM AUTHOR]

Maintaining high air cleanliness in operating rooms (ORs) can reduce surgical site infections (SSIs). However, door openings and foot traffic during surgery may allow the intrusion of contaminated air and increase microbial contamination in ORs. In this study, numerical methods were applied to investigate the dynamic airflow and bacteria-carrying particle (BCP) dispersion during sliding door opening and foot traffic in an OR. The door movement and realistic human walking were modeled by the dynamic mesh technique. The interfacial exchange of airflow and BCPs was evaluated as the medical staff entered and exited the OR under fixed supply air temperatures and various differential pressures, respectively. Results showed that walking across the door interface caused a sharp increase in airflow exchange between the OR and the anteroom (ANT). An average walking speed of 1.2 m/s induced a maximum inflow rate of approximately 1.32 times greater when entering the OR than when leaving the OR. Once the door was open, the temperature difference convection effect was more significant than the pressure difference outflow effect. Differential pressure outflow indirectly affected airflow exchange at the door interface by changing the direction and temperature of airflow in the ANT. Whether entering or leaving the OR, the BCP intrusion ratios were on average 1.5 times higher at high pressure differentials (15 and 20 Pa) than at low pressure differentials (5 Pa and 10 Pa). This study is expected to improve the understanding of the impact of door opening and foot traffic on OR air quality during surgery. • Airflow and bacteria-carrying particle interface exchanges during foot traffic were evaluated. • Effect of temperature differences was more notable than pressure differences in airflow exchange. • Walking induced more air exchange when entering the operating room than when leaving. • More bacteria-carrying particles invaded the operating room at higher differential pressures. [ABSTRACT FROM AUTHOR]

The multistage hydrogen Knudsen pump based on the thermal transpiration effect has exciting application prospects for hydrogen transport in the micro-power system. The multistage hydrogen Knudsen pump with the silica microchannel is beneficial to its temperature control, which can accurately provide hydrogen transport and storage for the micro-power system. In this paper, the model of the multistage hydrogen Knudsen pump with the silica microchannel is established. The effects of the microchannel height, width and parallel number on the flow and transmission characteristics of the multistage hydrogen Knudsen pump are studied by using the method of N–S equations with the slip boundary. The temperature difference, Knudsen number, thermal transpiration effect, maximum mass flow rate, maximum pressure difference and performance curve under different microchannel parameters are analyzed in detail. The results show that the thermal transpiration effect increases with the microchannel height and decreases with the microchannel width. As the number of parallel microchannels increases, the microchannel is closer to the silicon cantilever, and the thermal transpiration effect becomes stronger. The pumping performance increases with the microchannel height, width and parallel number. The pressurization performance increases with the microchannel height and parallel number. The research results have important guiding significance for the application and design of the multistage hydrogen Knudsen pump in the micro-power system. [Display omitted] • A multistage hydrogen Knudsen pump model without moving components is proposed. • Design and transmission characteristics of multistage hydrogen Knudsen pump are studied. • The hydrogen mass flow rate is higher when the microchannel height is higher. [ABSTRACT FROM AUTHOR]

The hydrogen Knudsen compressor has great potential to transport hydrogen and provide the required pressure in MEMS and microfluidic systems. The microchannel composed of cold and hot serrated surfaces is beneficial to the temperature control of the multistage Knudsen compressor. In the present study, a serrated hydrogen Knudsen compressor model is established initially, and the non-equilibrium evolution is numerically studied by using the method of N–S equations with the slip boundary. The key factors affecting the non-equilibrium evolution are comprehensively analyzed. The flow behaviors and performance of the serrated hydrogen Knudsen compressor in different times are studied. It is found that the main factors affecting the non-equilibrium evolution are the thermal expansion flow, thermal transpiration flow, and Poiseuille flow. Meanwhile, the serrated structure affects the local flow in the serrated microchannel at different times. Under the interaction of the thermal transpiration flow and the Poiseuille flow, the pressure difference between the two containers first increases rapidly and then decreases slowly, and finally approaches 1886 Pa. The research reveals the flow mechanisms of the hydrogen Knudsen compressor in the non-equilibrium evolution, which provides theoretical support for the safety and reliability of the hydrogen Knudsen compressor. • The flow evolution in the serrated hydrogen Knudsen compressor can be divided into four stages. • The main factors affecting the non-equilibrium evolution are analyzed. • The serrated structure has a great influence on the local flow in the serrated microchannel. • The pressure difference between the two containers increases first and then decreases. [ABSTRACT FROM AUTHOR]

The membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC) would deform when there is a pressure difference between the cathode and anode. In this study, a three-dimensional PEMFC model that incorporates a two-dimensional MEA deformation model is employed to investigate the effects of the curved MEA on oxygen transport, liquid water removal, pressure drops across cells, and resulting overall cell performances. The results show that the MEA deformation generates a gap between the rib and gas diffusion layer (GDL), thereby enhancing the oxygen transport into and liquid water removal from the cathode porous electrode. At an operating voltage of 0.4 V, the output current density is enhanced by 4.83%, 6.67%, and 8.61%, respectively, for the pressure differences of 10, 20, and 30 kPa between the cathode and anode, as compared with that without a pressure difference. An efficiency evaluation criterion (EEC) that represents a tradeoff between mass transfer enhancement and pressure drop penalty is introduced to evaluate the overall cell performance enhancement. The result shows that the EEC value increases with increasing the pressure difference between the cathode and anode, confirming the performance enhancement by the deformed MEA. In addition, the effects of MEA deformation are also examined at two sets of channel heights (H) and widths (W), i.e., W H =0.5 mm and W H =1.5 mm. At an operating voltage of 0.4 V, the output current density is enhanced by 20.18% at a pressure difference of 30 kPa for the cell with W H =0.5 mm, whereas it is improved only by 2.91% for the cell with W H =1.5 mm. Therefore, increasing the pressure difference between the cathode and anode is a more effective approach to performance enhancement for the cell with a small channel height and width. • The MEA deformation caused by cathode and anode pressure differences is studied. • A gap is generated between the bipolar plate and deformed MEA. • Oxygen transport and liquid water removal are enhanced by the gap. • Cell performances are improved by the deformed MEA. [ABSTRACT FROM AUTHOR]

Traditionally, the measurement of the concentration of a two-phase flow by gauging differential pressure is subject to pressure loss due to the flow friction along the pipe wall. A novel pressure difference method against this issue was proposed in this paper. A theoretic model is developed for the method, from the principle of hydrostatics of particle gravitational settlement. The method was essentially validated with an experiment of particle settling in a stand-alone pipe section by sealing the two terminals to form a static gas-solid two phase medium and supported with a numerical simulation based on a Lagrangian model as well. Inherently, the method is expected to measure the concentration of a two phase flow in a pneumatic conveying pipe, correspondingly by setting a flow branch which contains an erect settlement tube with two dynamically shutting valves to form a transient static particle deposition segment. • A novel differential pressure method was proposed to effectively measure the two phase flow concentration. • The pressure difference in a two phase flow was effectively measured by transiently sealing both the two ends of the sedimentation tube. • An effective model is established for measuring the two phase flow concentration via a static differential pressure measurement. [ABSTRACT FROM AUTHOR]

When the elongated bubbles and liquid slugs of slug flow alternately flow through a throttling element, the strong random fluctuations of pressure difference leads to low accuracy of online measurement of gas-liquid flow rates. In this paper, slug flow is converted into an annular flow before entering a venturi tube using a swirler, and the pressure fluctuation amplitude of the gas-liquid two-phase flow is greatly reduced, and the linear correlation between the pressure difference and the gas-liquid flow rates is more significant. The effects of gas-liquid flow rates on the axial pressure difference Δ P s across the swirler, the radial pressure difference Δ P r on a cross-section downstream of the swirler and the axial pressure difference Δ P o of the venturi tube were studied under the condition of 40%–82% gas volume fraction. The square root of the pressure difference increases linearly with the liquid/gas flow rate, and the empirical correlations between the square root of the pressure differences and the gas-liquid flow rates are established. By combining the empirical correlations in pairs, three flow rates measurement models of slug flow based on double pressure differences are established. When Δ P o and Δ P s are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±2% and ±15%, respectively. When Δ P o and Δ P r are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±3% and ±15%, respectively. It provides high-precision, low-cost and non-radioactive two-phase flow measurement technology for oil-gas gathering and transportation. • Gas-liquid flow rates are measured using a venturi tube with a swirler. • Linear correlations between pressure difference and flow rates are established. • Flow rates measurement models of slug flow are established. • Prediction accuracies of liquid and gas flow rates are below ±2% and ±15%. [ABSTRACT FROM AUTHOR]

• Filtration efficiency of common materials for respiratory masks are investigated. • Effects of materials to the upstream-downstream fluid flow regions are measured. • One-layer masks have similar efficiency; multilayer masks' efficiency is greater than 90%. • Comfortable-effective masks can be made from multilayer cotton and non-woven fabric. • Washing masks reduces effectiveness; masks should be used a limited number of times. Face masks are an important component of personal protection equipment employed in preventing the spread of diseases such as COVID-19. As the supply of mass-produced masks has decreased, the use of homemade masks has become more prevalent. It is important to quantify the effectiveness of different types of materials to provide useful information, which should be considered for homemade masks. Filtration effects of different types of common materials were studied by measuring the aerosol droplet concentrations in the upstream and downstream regions. Flow-field characteristics of surrounding regions of tested materials were investigated using a laser-diagnostics technique, i.e., particle image velocimetry. The pressure difference across the tested materials was measured. Measured aerosol concentrations indicated a breakup of large-size particles into smaller particles. Tested materials had higher filtration efficiency for large particles. Single-layer materials were less efficient, but they had a low pressure-drop. Multilayer materials could produce greater filtering efficiency with an increased pressure drop, which is an indicator of comfort level and breathability. The obtained flow-fields indicated a flow disruption downstream of the tested materials as the velocity magnitude noticeably decreased. The obtained results provide an insight into flow-field characteristics and filtration efficiency of different types of household materials commonly used for homemade masks. This study allows comparison with mass-produced masks under consistent test conditions while employing several well-established techniques. [ABSTRACT FROM AUTHOR]

Supercritical water gasification (SCWG) is famous for achieving complete conversion of raw organic matter with the temperature below its ash melting point. Inorganic mineral components associated with raw organic matter will form solid slag particles after the reaction of SCWG is completed. Discharge of the slag particles from reactor is a supercritical water (SCW) transporting particles process under transcritical temperature conditions driven by pressure difference. A comprehensive three-dimensional two-fluid model (TFM) is firstly developed in this study to research the flow dynamics characteristics during the particle transport process. The effect of transport pressure difference (ΔP) and particle outlet position (ΔH) on particle transport are investigated. Results show that the particles can be transported out the reactor smoothly under the action of ΔP , and the solid-containing ratio, s r , can reach to 78.27% with ΔP of 5 MPa and ΔH of 55 mm. Large ΔP can enhance particle transport efficiency, but it may cause fluid overheating in the cooler. When the particle outlet is close to the reactor inlet, a large amount of SCW from reactor inlet will enter the particle outlet, which will decrease the particle transport efficiency. The current model can reasonably describe the flow dynamics characteristics of particle transport process, which may provide theoretical guidance for the design and optimization of slag-discharge system. Unlabelled Image • A CFD model for particle transport driven by pressure difference is developed. • Flow dynamics behaviors of supercritical water transporting particles are studied. • Theoretical guidance for optimizing the slag-discharge system is provided. [ABSTRACT FROM AUTHOR]

Accurate recognition of flow regimes is essential for the analysis of behavior and operation of two-phase flow systems in industrial processes. This paper studies the feasibility of a method for objective recognition of global flow regimes using differential pressure and artificial neural networks. Three main global flow regimes are classified based on differential pressure of the riser. Five statistical parameters are inputted into neural networks classifiers, and good recognition rates of global flow regimes are achieved. With increase of feature parameters, recognition rates of global flow regimes increase, and five selected feature parameters are sufficient to achieve good recognition rates. Recognition rates of two categories are generally higher than those of four categories, and they are found to increase with sample lengths. Average recognition rates of four categories are higher than 94.3% if sample lengths are longer than 240 s and reach almost 100% when sample lengths are sufficient long. Unlabelled Image • Experiments of air-water flow in a long-distance pipeline-riser are carried out. • Differential pressures of the riser reveal different trends in various flow regimes. • Flow regime recognition is performed by differential pressure and neural network. • Influences of feature number and sample length on recognition rate are analyzed. [ABSTRACT FROM AUTHOR]

Optimizing active cooling strategies has become an essential topic in thermal protection due to the increasing structural thermal protection requirements for hypersonic aircraft with higher Mach numbers. This paper proposes a design method for the transpiration cooling structure, taking the isothermal wall as the design target and the pressure difference between the inside and outside of the transpiration matrix and the porosity of the porous medium as the design parameters. The method can achieve the reverse design of the porosity of the transpiration matrix and homogenize the temperature gradient of the surface of porous media. The numerical analysis shows that the porosity design method for pressure difference-controlled transpiration cooling proposed in this research can be used to optimize the porosity design of porous media and achieve maximum utilization of the coolant flow. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of orifice plate separation distance on flame behavior as well as pressure-time histories. Experiments were conducted in a 1 m long, 7 cm by 7 cm square cross-section channel, employing schlieren photography with high-speed camera for visualization to qualitatively identify the propagation mechanisms, and piezoelectric pressure transducers to measure pressure evolution. With two orifice plates in the path of the flame, the flame presents complicated propagating characteristics, i.e., compared to a planar flame, and a corresponding more intricate velocity time-history. It is found that acoustic waves generated in-between orifice plates, after reflection off the second plate, interact with the rear flame front to produce an approximately planar flame. This phenomenon vanishes with decrease in orifice plate separation distance, whereas, with increasing blocking effect the effect is enhanced. In addition, the pressure difference across the second orifice plate correlates with the jet flame length. • The influence of orifice plates space on flame propagation was experimentally studied. • Multiple propagation stages were identified. • Flame propagation mechanism was proposed. [ABSTRACT FROM AUTHOR]

Abstract Multi-zone or multi-seam commingled production in CBM reservoir is an attractive option for extending and/or increasing existing gas production. To solve the problem of interlayer interference during commingled production, with varying permeability and pressure difference between coal seams, numerical simulations are carried out using a gray lattice Boltzmann method. Under different conditions of multi-seam commingled production, the pressure and velocity distributions are obtained. Then, the effects of permeability and pressure contrast on multi-seam commingled production are investigated. The results show that under the condition of commingled production with different permeability contrast, a greater permeability contrast will lead to a greater difference in gas production of each seam. And the smaller the reservoir permeability is, the faster the decrease of reservoir pressure near the wellbore is. For commingled production with different pressure contrast, the interlayer interference coefficient increases linearly with the increase of the pressure contrast. The interference degree of low pressure seam is far greater than that of high pressure seam. A lower reservoir permeability will lead to a greater interference coefficient. The research results provide a basis for revealing the interlayer interference mechanism, production dynamic analysis and production system optimization in multi-seam commingled production. Highlights • The GLBM is validated by simulating the flow between two parallel plates filled with homogeneous porous medium. • With varying permeability and pressure difference between coal seams, simulations are carried out using the GLBM. • The effects of permeability and pressure contrast on multi-seam commingled production are investigated. [ABSTRACT FROM AUTHOR]

Numerous types of liquid, such as water, oil, and so on, are transported via pipelines. Thus, leakage in the pipelines can cause severe hazards to liquid transportation and pose great risks to industries, environment and dwellers. For the purpose of an accurate identification of the leakage location, a novel location algorithm is proposed in this paper based on the attenuation of negative pressure wave (ANPW). As such, this paper presents some of the first efforts in the investigation of the relationship between the pressure difference and leakage location. This is in direct contrast with the traditional method, which relies on the use of the time difference and the velocity of NPW for leakage detection and location. Accordingly, the ANPW method avoids the potential problems of the traditional NPW method – the difficulty for pinpointing the time difference and the disturbance of the velocity of NPW by the liquid flow rate in the pipeline. To explore this new method, this paper firstly deduces the propagation equation of NPW along with the pipeline using the momentum equation and the continuity equation. This is followed by proposing that the ANPW method depends on the change of pressure in place of the time difference. Thirdly, a test of the method in the actual pipeline and comparison between the ANPW method and the time difference method are conducted. Yielding the largest error of 1.161% and the smallest error of 0.355%, the experiment leads to the conclusion that the new method can be applied to the location of pipeline leakage. [ABSTRACT FROM AUTHOR]

Numerous types of liquid, such as water, oil, and so on, are transported via pipelines. Thus, leakage in the pipelines can cause severe hazards to liquid transportation and pose great risks to industries, environment and dwellers. For the purpose of an accurate identification of the leakage location, a novel location algorithm is proposed in this paper based on the attenuation of negative pressure wave (ANPW). As such, this paper presents some of the first efforts in the investigation of the relationship between the pressure difference and leakage location. This is in direct contrast with the traditional method, which relies on the use of the time difference and the velocity of NPW for leakage detection and location. Accordingly, the ANPW method avoids the potential problems of the traditional NPW method - the difficulty for pinpointing the time difference and the disturbance of the velocity of NPW by the liquid flow rate in the pipeline. To explore this new method, this paper firstly deduces the propagation equation of NPW along with the pipeline using the momentum equation and the continuity equation. This is followed by proposing that the ANPW method depends on the change of pressure in place of the time difference. Thirdly, a test of the method in the actual pipeline and comparison between the ANPW method and the time difference method are conducted. Yielding the largest error of 1.161% and the smallest error of 0.355%, the experiment leads to the conclusion that the new method can be applied to the location of pipeline leakage. [ABSTRACT FROM AUTHOR]

Abstract Particles can move against gravity inside a vibrating tube inserted in a static granular bed. This offers a new approach for transporting bulk material. In this work, we demonstrate a method to enhance the conveying of powder by sealing the tube top. With the same vibration conditions, a comparison of particle motion in an opened tube and closed top (sealed) pipe is made. Compared to an un-sealed pipe, particle upward motion within a sealed pipe is improved. With low vibration strength, only particles in the sealed tube can ascend. With increasing vibration strength, particles can climb in both tubes while particles in sealed pipe move faster and higher. The enhancement effect works well for particles of smaller size (d < 1 mm), and the positive effect becomes weaker with an increase in particle diameter. In a sealed tube, the final height of the granular column increases as the tube length increases while the growth velocity is reduced. Particle conveying in sealed tube shows less dependence on tube diameter compared to an un-sealed tube. Sealing the tube top introduces air pressure difference during each vibration cycle, which induces an additional upward drag force on the particles in the tube. The drag force becomes significant compared to other relevant forces for small diameter particles at high levels of vibration. Graphical abstract Unlabelled Image Highlights • The conveying of grains is enhanced when the top of the tube is sealed. • The enhancement effect works well for particles with a smaller size (d < 1 mm). • Particle conveying in sealed tube shows less dependence on tube diameter. • Sealing the tube top induces an additional upward drag force (F d) on the particles in the tube. • F d becomes significant for small diameter particles at high levels of vibration. [ABSTRACT FROM AUTHOR]

• Bubble generation process was divided into Formation , Expansion and Contraction stages according to the contact angle between the bubble and the capillary as 90°. Na+, Mg2+, Ca2+ and Al3+ promoted the bubble growth during the Formation and Expansion stages while restrained the growth during the Contraction stage. Al3+ roughly presented the most obvious promotion on the bubble generation. • Bubble internal pressure increased as the bubble grew. Pressure difference inside and outside the bubble generally followed the order Na+ > Mg2+ > Ca2+ > Al3+. Na + presented the thickest hydration layer at the bubble surface and the highest bubble internal pressure. • Net force acting on the bubble first kept constant and then decreased with the concentrations of Na+, Mg2+ and Ca2+, while it first increased and decreased then in the presence of Al3+. Understanding the effect of inorganic cations on dynamic bubble generation is an important precursor for predicting the bubble characteristics in actual coal flotation. Using the high-speed motion acquisition system, we investigated the bubble growth in different inorganic salt solutions. The bubble generation process was divided into Formation , Expansion, and Contraction stages according to the contact angle between the bubble and the capillary as 90°. Na+, Mg2+, Ca2+, and Al3+ were found to promote bubble growth during the Formation and Expansion stages while restraining the growth during the Contraction stage. Al3+ roughly presented the most obvious promotion of the bubble generation. The dynamic bubble width and length during different bubble growth stages were analyzed to discuss the bubble pressure. The internal pressure increased as the bubble grew. The pressure difference inside and outside the bubble generally followed the order Na+ > Mg2+ > Ca2+ > Al3+. The forces acting on the bubble were attempted to be discussed. The net force acting on the bubble first kept constant and then decreased with the concentrations of Na+, Mg2+, and Ca2+, while it first decreased and then increased in the presence of Al3+. Our results can provide valuable insight into the development of the technology for mineral flotation. [ABSTRACT FROM AUTHOR]

Autonomous Underwater Vehicles (AUVs) are high-end marine equipment. In turbid, dimly lit waters that require high concealment, traditional methods struggle to detect targets effectively. Fish, however, can accurately perceive nearby targets using lateral line systems even in harsh environments. This provides inspiration for intelligent detection in AUVs. In this study, the flow field cloud around copepods and visualization of pressure difference matrix are analyzed. A method combining the pressure difference matrix and residual neural network regression is proposed to study how fish lateral lines perceive the direction of cruising copepods. Furthermore, the effects of three key parameters on direction perception are discussed, including perception time scale, initial vertical distance and training angular intervals number. The results indicate that most predicted directions are close to the true directions, with only a small number of misjudgments occurring in the vicinity of the opposite or perpendicular directions to the true direction. Moderate perception time scales (100 ms), shorter vertical distances (2.5 mm), and reasonable training angular intervals number (24 or 36) all lead to lower perception error. This study provides a quantitative analysis of fish lateral line perception mechanism, offering valuable theoretical guidance and technical support for intelligent detection in AUVs. • A method combining pressure difference matrix and Resnet regression is proposed. • Perception mechanism of cruising copepods by fish lateral line is studied. • Effects of time, distance and angular interval on perception are discussed. • The results provide bionic inspiration for the intelligent detection of AUVs. [ABSTRACT FROM AUTHOR]

This study analyzes the throttling pressure control flow field, and the influencing factors of its traction speed regulation and braking mechanism are determined. Throttling pressure control flow field characteristics of the traction speed regulation and braking mechanism are analyzed and the principle experiment of the throttling pressure control flow field is also carried out. The results show that the throttling pressure control flow field of the traction speed regulation and braking mechanism of the pipeline intelligent plugging robot is greatly affected by the structure and shape of the speed control valve. When the opening of the speed control valve decreases, the flow rate of the backward jet increases, and the flow rate is faster. This is convenient for scouring the front pipe wall of the device. Conversely, as the opening of the speed control valve increases, the maximum deceleration effect can be achieved by increasing the pressure difference before and after the device. This study provides a theoretical basis for the structure design and selection of the pipeline intelligent plugging robot. Moreover, it is helpful for providing data reference and theoretical guidance for the design of passive fluid-propulsion robots in pipes equipped with bypass rotary valves. • Influencing factors of TSRBM of the PIPR are determined. • Throttling pressure control flow field characteristics of the TSRBM are revealed. • Less speed control valve opening improves front wall flushing in the PIPR. • More speed control valve opening enhances the PIPR deceleration. • Findings can be helpful for the design and operation of passive fluid propulsion robots in pipelines. [ABSTRACT FROM AUTHOR]

Abstract Indoor air environment inside operating room (OR) is crucial for the success of surgical operation. The opening and closing process of sliding door is very common in OR. In this case, the designed positive pressure will disappear. Since the air exchange characteristic at the interface of the sliding door will influence the Surgical Site Infection risk, the combined effects of temperature and pressure differences on interface airflow along with the air infiltration volume and intruding particles caused by the airflow are studied by theoretical and numerical methods. Two different cases are compared, where the temperature of OR is lower or higher than that of anteroom, respectively. Results show that the contaminants accumulate in the upper space of the OR due to the airflow pattern between two rooms when the temperature of OR is lower than the anteroom. This will increase the possibility that airflow carrying contaminants intrudes into OR. On the contrary, the contaminants are controlled in the lower space of the OR when the temperature of OR is higher than that of anteroom. On average, the particle intrusion ratio of the second case decreases by 55% compared with that of the first case. So, it is helpful to protect the clean environment of OR when the temperature of OR is higher than that of the anteroom. Moreover, the air infiltration volume of the closing phase is found unequal to that of the opening phase. This study provides the useful information for maintaining a clean indoor environment under operational condition. Highlights • Interface airflow of sliding door with temperature/pressure differences is studied. • Theoretical model was established for interface flow under the coupled effect. • Air infiltration rate of the closing phase is more than that of the opening phase. [ABSTRACT FROM AUTHOR]

The air permeation caused by the pressure difference at both sides of the magnetic seal accounts for a significant part of energy loss in a refrigerated room. The purpose of this study is to model the air permeation rate. Based on momentum equations of air flow along the permeation paths, the air permeation rate is deduced as a function of the average height of permeation paths and the flow factor. The average height is obtained by a resultant force of magnetic attraction and pressure difference under the assumption of parabolic asperity profile in the permeation paths; and the flow factor is calculated by semi-empirical correlations based on the average height of the permeation paths. An experiment is designed to validate the model, and the results show that the predicted air permeation rate can describe 98% of the experimental data within a deviation of ± 15% and the mean deviation is 5.6%. [ABSTRACT FROM AUTHOR]

Inflatable membrane structure employs flexible membranes as main constructive materials, as well as pressurized gas in the membrane envelope aiming to provide the bearing capacity and structural integrity. Therefore, the internal pressure control and load simulation method are very significant to estimate the structural behavior of inflatable membrane structure. This paper presents an automatic system for pressure control and load simulation of inflatable membrane structure, including a pressure control subsystem and a load simulation subsystem. For pressure control, internal pressure of inflatable membrane structure is controlled by switching the high-speed on/off valves which connect air compressor to the structure. For load simulation, wind pressure and wind suck loads, acting on membrane surface in the normal direction, are simulated by controlling the solenoid valves to allow the vacuum pumps to inflate air into or pump air out from the load simulation chamber which is closely connected to inflatable membrane structure with an airtight space. More importantly, the coupling control of two subsystems can be automatically carried out to simulate the inflatable membrane structure under resisting the varied wind loads. These above actions are automatically performed based on the control logic coded in software module. In order to estimate the proposed automatic system, the internal pressure control, load simulation and coupling control tests were performed on a square double-layer ETFE (ethylene tetrafluoroethylene) cushion model. Control performance and accuracy of the proposed system are proved by analyzing the measured pressures. It is thus demonstrated that the proposed automatic system is considerably automatic, accurate, efficient and reliable for pressure control and load simulation of inflatable membrane structures. [ABSTRACT FROM AUTHOR]

An experimental study of the flow disturbances induced by an orifice plate in an air-water slug flow is carried on a horizontal test section with 0.026 m and 1009 pipe diameters long. Three orifices with distinct area contraction ratios are tested at three axial positions along the test section. The instantaneous orifice pressure difference as well as the absolute pressure and void fraction along the test section are measured. The data is further processed to get the bubble nose velocities and the slug frequency. The pressure difference at the orifice and the absolute pressure along the test section reveal a pulsatile pressure behavior due the intermittent passage liquid slugs and elongated bubble through the orifice. The spectral analyses disclose a match between the frequency of passage of slugs through the orifice and the frequency of the orifice pressure fluctuations. The orifice disturbances on the void fraction, bubble nose velocity and frequency of passage exhibits a dependency on the orifice size and to the distance from the mixer. [ABSTRACT FROM AUTHOR]

The recovery of methane in the slits with varying surface activity is simulated through a NEMD-extraction molecular dynamics workflow. [Display omitted] Understanding the production process of shale gas in the complex geological environment is important for the recovery prediction of shale gas development. The adsorption/desorption and extraction of methane in the slits with varying surface activity simplified by tuning the force field parameters are studied with molecular dynamics (MD) simulations. The density of free gas in the slits does not change with the surface activity, while the density of adsorbed gas increases with the surface activity. A minimum pressure difference to initiate the desorption is characterized by the non-equilibrium molecular dynamic (NEMD) simulation. The high surface activity results in not only the slow flow of free gas, but also the slow desorption of the adsorbed gas. Thus, the extraction presents a slow rate and long-tail with extraction times. The adsorption/desorption and the extraction computations in the MD simulations provide a useful reference for the production prediction of shale gas. [ABSTRACT FROM AUTHOR]

Opposed Piston Two Stroke (OP2S) engines are widely used for its high power density and high thermal efficiency. For OP2S diesel engines, the scavenging process is accomplished by the pressure difference between intake chamber and exhaust chamber. 1-D model of OP2S diesel engine is built and the accuracy of the model is validated by tracer gas method. Based on the 1-D model, the influence of pressure difference to OP2S diesel engine scavenging process is studied. The results illustrated that: (1) in order to obtain higher pressure difference, the pressure in exhaust chamber should also be higher; (2) pressure difference has vital influence in gas exchange process. With the incensement of pressure difference, the delivery ratio increases but the trapping ratio decreases; (3) under the condition of the same pressure difference, the delivery ratio decreases and the trapping ratio increases in higher engine speed; (4) the scavenging efficiency range of OP2S diesel engine is 0.7-0.96.（5）the increment of pressure difference or back pressure is beneficial in improving engine thermal efficiency. [ABSTRACT FROM AUTHOR]

Airtightness measurement standards using the fan pressurization method are widely used for measuring residential units such as detached houses and apartment units. The measurement of airtightness for small buildings can be readily conducted through existing fan pressurization methods. However, it can be difficult to achieve accurate measurement results for large buildings, as the height and volume of the buildings are considerably increased. This paper empirically investigates factors that are to be considered in regard to airflow rate (Q) and pressure difference (ΔP), which are measurement values required for deriving more accurate airtightness values for large buildings. The specifications of the standards ISO 9972, EN 13829, ASTM E779 , JIS A 2201, ATTMA TS 1, and CAN/CGSB 149.15 relating to Q and △P are compared. Test conditions with respect to Q and △P are discussed for large building airtightness measurements. In measuring airtightness, a method is proposed in which the pressure difference at each floor of the building is measured and an average pressure difference value is used. Experiments were conducted on two multi-story office buildings using the method based on measuring pressure difference according to existing standards in tandem with the proposed pressure difference measurement method. The results of the experimental study show that the vertical pressure distribution across the overall building envelope can be significantly different when a building is pressurized. The airtightness values may also be different according to the measurement methods. This paper demonstrates how important it is to derive accurate △P values in measuring large building airtightness. [ABSTRACT FROM AUTHOR]

Steam assisted gravity drainage (SAGD) is an effective method for bitumen and heavy oil reservoirs. In SAGD process, steam is injected into the reservoir with a high pressure from the upper horizontal well, and the injected steam will heat the surrounding oil sands through a conduction and convection heat transfer process. In this paper, a novel unified model is developed to investigate the heat transfer mechanism in SAGD process. Typically, the multiphase flow assumption at the edge of steam chamber is introduced in our model. And the effect of both the conduction and convection heat transfer in steam chamber are considered. Especially, in this model, the convective heat transfer process caused by pressure difference and gravity is studied. Then the simulation results are compared against the UTF field data to confirm the accuracy of our model. Results indicate that our model can match the UTF field data very well, and it can be used to investigate the heat transfer process in SAGD process. It is found that the oil production rate decreases as the interface velocity increases. The optimal interface velocity is about 1.5–2.5 cm/d. In this range, the oil production rate is about 0.4 m 3 /(m·d) and oil cut is approximately 31%. The variations of condensate liquid mobility and density lead to that oil production will decrease as the pressure difference increases. Finally, it can be concluded that a suitable injection pressure should be chosen to guarantee the optimal interface velocity in SAGD process. This new model will benefit to understanding the convective heat transfer mechanism and guiding the field production behavior in SAGD process. [ABSTRACT FROM AUTHOR]

Impacts of energy retrofits on air pressure differences across building envelope, air change rate (ACR), and indoor carbon dioxide (CO 2 ) concentrations were studied. Measurements were performed before and after the retrofits of multi-family buildings during heating season in two Northern European countries: Finland and Lithuania. In the Finnish case buildings (N apartments = 128), pressure differences against outdoor were within national guideline values before the retrofits in 52% and after the retrofits in 42% of the buildings with mechanical exhaust ventilation system. The values were within the guidelines before the retrofits in 33% and after the retrofits in 20% in buildings with natural ventilation, correspondingly. In the Lithuanian case buildings (N apartments = 31), pressure differences against outdoor were within the same guideline values before the retrofits in 77% and after the retrofits in 52% of the buildings. After the retrofits, higher air pressure differences and ACR, as well as lower CO 2 concentrations, were observed in Finnish buildings with mechanical ventilation. On the contrary, lower air pressure differences and ACR, as well as higher CO 2 concentrations, were observed in Lithuanian buildings with natural ventilation. [ABSTRACT FROM AUTHOR]

Deposition of α-alumina film by spraying alumina granules in a vacuum at room temperature was performed using a modified aerosol deposition system that had a supplemental gas flow line in addition to the carrier gas flow line. The pressure difference between the nozzle inlet and deposition chamber was increased by increasing the supplemental gas flow rate or by decreasing the nozzle throat width. For the same nozzle, the alumina film thickness per granule consumption increased as the pressure difference was increased. However, the film obtained by using the wide throat nozzle was thicker than that by using the narrow throat nozzle in spite of the smaller pressure difference except for the case without using the supplemental gas. The deposition behaviors according to the supplemental gas flow rate and the nozzle throat width were explained in part by the friction-affected layer near the nozzle throat wall and a critical granule velocity for film deposition. Alumina granules and films were characterized by scanning electron microscopy, X-ray diffractometry, surface profilometry, and transmission electron microscopy to assess and correlate the film quality to the deposition conditions. [ABSTRACT FROM AUTHOR]

Recently, steam assisted gravity drainage (SAGD) has been widely adopted in thermal recovery for heavy oil. However, challenges remain in SAGD development: the close distance between injector and producer makes it easy to cause steam breakthrough, which means lower thermal efficiency as well as higher investment. It is generally acknowledged that there is a liquid level existing between the injector and producer, a reasonable liquid level could prevent steam from being produced directly. The existence of liquid level generates a temperature difference between two wells, i.e., subcool. Subcool has generally been used to describe liquid level in practice and in many researches, yet it is inaccurate. In order to characterize the liquid level precisely, it is necessary to fully clarify the relationship among subcool, liquid level and pressure difference between injector and producer. By analyzing the features of subcool and pressure difference shown in SAGD experiments, it is found that the value of subcool may be not directly relevant with the distance between injector and producer, considering the huge difference between experiments and the measured data from actual oilfield. Correspondingly, liquid level is supposed to be treated as a dimensionless variable, to be specific, named as dimensionless liquid level, defined as liquid level divided by the distance between two wells. Afterwards, over 40 cases of CMG numerical simulations are run to investigate the liquid levels with different injector-producer distances and different subcools. Based on the analysis of simulation results, the dimensionless liquid level increases with subcool, while for a given subcool, dimensionless liquid level is inversely proportional to pressure difference between injector and producer. Accordingly, liquid level could be accurately controlled under a given subcool and pressure gradient, which is applicable and be of great significance for the SAGD operation on the field. [ABSTRACT FROM AUTHOR]

• Review of the literature of the forced convective heat transfer of molten salts in enhanced tubes. • Measurement of the forced convective heat transfer of Solar Salt in a spirally grooved tube for 11000 < R e < 285000. • Comparison of the measured friction factor in a spirally grooved and a smooth tube to correlations from the literature. • Measurement of the Nusselt number at film temperatures above the chemical stability temperature limit of Solar Salt. The forced convective heat transfer and pressure difference of molten nitrate salt in a spirally grooved tube with a relative groove height e/2r i =0.017, a relative groove pitch p/2r i =0.913 and groove angle α=73.8° is experimentally investigated using a water-cooled induction heater setup. The data is provided for Reynolds numbers ranging between 11000 up to 285000 and Prandtl numbers from 3.7 to 10. The experiments are carried out for bulk salt temperatures ranging between 300 and 550 °C and for heating flux densities between 330 and 930 kW/m². Inner wall temperatures up to 633 °C are achieved with the setup, thus providing data on the behavior of the forced convective heat transfer as a function of inner wall temperature. The data is compared to the measurement results obtained with the same setup and a circular smooth tube as well as correlations and data from the literature in order to deduce relative Nusselt numbers and friction factors. [ABSTRACT FROM AUTHOR]

Pilot-Control Globe Valve (PCGV) can utilize pressure difference caused by fluid flow through the orifice on valve core as its power, for open and close the main valve with a small pilot valve. It has obvious advantages of energy conservation and quick response. Orifice structure on the valve core is the main component to determine the pressure difference, which is used to push the valve core. In this paper, the numerical model with User Defined Functions (UDFs) method is carried out, and the experimental device is arranged. The numerical and experimental results of valve core displacements achieve agreements. Then, analysis of pressure difference under different static pressures, inlet velocities and different orifice diameters are carried out. It shows that pressure difference has no relationship with static pressure, thus PCGV can be adopted in hydrogen pipelines. Meanwhile, higher inlet velocity can turn out larger pressure difference with quicker response of PCGV. In addition, there exits an unbalanced moment, and 15 mm is the extreme diameter of the orifice for DN150 PCGV. Finally, the design method of the orifice structure in PCGV is proposed with design formulas. This work can help the precise design work of PCGV, and it can be referred by other researchers who are also deal with orifice structures in similar valves design work. [ABSTRACT FROM AUTHOR]

A molecular dynamics workflow to simulate the desorption–extraction of shale gas is proposed for predicting the production of shale gas. [Display omitted] • A novel desorption–extraction MD workflow based on the EF-NEMD is proposed. • Some factors affecting the recovery are examined. • Large amount of methane in micropores is unrecoverable due to the stronger adsorption. • The recovery decline curves could be obtained in the proposed MD workflow. • Models of enhancement of recovery by pressure difference and temperature are built. Understanding microscopic process of gas desorption is important to production forecast in shale gas development. In usual simulations on the gas desorption process, the desorption occurs in a non-equilibrium state, but stops when the desorption–adsorption equilibration is reached. This is contrary to the continuous process in gas production. A workflow based on non-equilibrium molecular dynamics (NEMD) is proposed in this work to simulate the continuous desorption in the illite nanoslits by introducing an intermittent extraction into the whole process. A production curve is obtained in the workflow, and a pseudo decline-curve analysis (PDCA) can be provided in molecular simulation. The variation of desorption–extraction with pore size (H), temperature (T) and pressure difference (ΔP) is discussed. The attraction of illite–methane in the narrower slits is stronger than that in the wider slits. In the early stage, the extraction is dominated by the free gas in the wider slits. And in the later stage, the desorption of adsorbed gas in the narrower slits is the main process. The ΔP and T promote the desorption and extraction mainly in the early stage. The ΔP promotes the desorption in the wider slits more remarkably, while the desorption in the narrower slits is enhanced more by a higher T. The enhancement of desorption by ΔP and T in the early stage is modeled. The newly developed MD workflow and obtained PDCA model can be readily extended to study the extraction and production prediction of shale gas. [ABSTRACT FROM AUTHOR]

Clean indoor air is a prerequisite for the welfare of the society. The Indoor Air Quality simulator (IAQ simulator) offers a research tool for building physic and building material research to evaluate the effect of the complicated causal connections of indoor air quality and multilayer building structures, materials and their unexpected exposure to moisture and microbial growth. In Microdiverbuild-project, the IAQ simulator was used to assess the drift of microbial metabolites (e.g. volatile metabolites of micro-organisms, MVOC) from a moisture damaged wall structure into indoor environment under various material moisture loads and pressure differences over the structure. Even low under-pressure has been found to cause infiltration of impurities in the indoor environment but unnecessary high under-pressure indoors increases further concentrations of impurities from the building structures. Also, infiltration of microbial gaseous contaminants from active mould growth inside the structure decreases indoor air quality. The wood laths were covered by active mould growth, and represented a mould damaged wall structure (mould index 4-5). These laths were assembled inside the wall and simulated a hidden active mould growth having air leakage routes through the envelope. Two pressure difference levels simulated normal (low pressure difference) and unbalanced ventilation when pressure difference may increase as high as -20 Pa.The simulation test showed clearly MVOCs indicating hidden microbial growth. In our previous study, VOC profiles were developed based on building occupants complaints about poor IAQ, and found high ketone concentrations indicate mould problem which is equal with results of this study. However, it is known that MVOCs can be released from other sources in real buildings and the impact of relative humidity of the material is remarkable. [ABSTRACT FROM AUTHOR]

Pressure differences between outdoors and indoors influence indoor environmental quality (IEQ) and building physics of the building envelope. This paper focuses on measurements of pressure difference values of about 152 apartments from 26 multi- family buildings in Finland. Measured data include pressure differences between indoor spaces and both outdoors and staircases before and after renovation. In buildings equipped with mechanical exhaust, the pressure differences between indoors and outdoors before renovation varied from +10,1 to -95,0 Pa (average -7,8 Pa), and between indoors and staircases from -3,5 to -6,0 Pa (average -18,6 Pa), being lower than -5 Pa in 36% of the buildings. In naturally ventilated buildings, the pressure differences between indoors and outdoors were lower than -5 Pa in 44% of the buildings. The average pressure differences after renovation in nine buildings equipped with mechanical exhaust were slightly higher (-19,1 Pa against outdoor and -9,0 Pa against staircase). A possible reason for higher negative pressure could be that the airtightness of building was improved by renovation, but the ventilation system was not balanced accordingly. Improving energy efficiency (EE) could effect on pressure difference either positively or negatively. Measured pressure difference between indoors and outdoors or staircase before and after renovation could be a possible indicator when assessing the impacts of improving EE on IEQ and occupant satisfaction. [ABSTRACT FROM AUTHOR]

• A novel embedded discrete fracture networks (EDFM) EGS was proposed. • A 3D fluid flow and heat transfer for multi-fracture was presented. • Effects of fracture distribution, well spacing & length on EGS were studied. • Sensitivity analysis on injection, fracture, and well parameters were investigated. This study proposed a doublet horizontal well injection enhanced geothermal systems(EGS) model for heat extraction via the embedded discrete fracture network. Thermal-hydraulic(TH) coupling was established and applied in this model. The performance of thermal exploitation by the comparison of four specific models (reservoir without fractures, reservoir with hydraulic fractures, reservoir with discrete fractures, and reservoir with hydraulic and discrete fractures) to optimize the base model were investigated. Meanwhile, the sensitivity analysis of reservoir parameters and injection parameters were conducted. Four specific indexes including fractures permeability, injection temperature, injection mass flow rate and well layout schemes were selected for evaluating the performance of heat extraction. The results shown that increasing the fracture number and improving the connectivity can obtain an excellent heat extraction effect. Firstly, there is a threshold for fracture permeability. Only the adequate stimulation measures were applied to increase the fracture permeability, did the stimulation of thermal power output can be reached. Secondly, increasing injection temperature will induce the enhancement of viscosity and pressure loss, and thus decrease the velocity of fluid and the temperature difference. Which is reflected in the descending of thermal power output finally. Furthermore, increasing the injection mass flow rate will give rise to the thermal power output greatly. However, it will also require greater injection pressure and energy input. Therefore, it is necessary to strike a balance between the injected mass flow and the thermal output power. Finally, the results of simulation in various well layouts illuminate that the area of the fluid flowing through the reservoir determines the temperature of the production fluid. Overall, this study provides reasonable suggestions and guidance for field-well layouts design and analysis, and heat extraction sensitivity parameters optimization under the condition of complex embedded discrete fracture networks. [ABSTRACT FROM AUTHOR]

Stack-induced pressure differences cause various problems in high-rise buildings. In particular, the reopening problem, which involves difficulty in closing elevator doors, and which arises from large stack-induced pressure differences across the elevator shafts, can be especially troublesome. This paper performs an experimental study that uses a full-scale mock-up to evaluate the effects of pressure differences on the functioning of elevator doors. Pressure distribution measurements were taken and simulations were performed for 25 actual buildings to analyze problems related to pressure differences. The analysis shows that the threshold value for malfunctions is different from the previously suggested threshold of 25 Pa. After a theoretical study on the principles governing the operation of elevator doors in an elevator shaft, experiments were performed with a full-scale mock-up that is capable of simulating four airflow directions associated with the stack effect, the reverse stack effect, and the location of the elevator car at either the uppermost or the lowermost floor. The results of the experiments, which were conducted with various conditions for the direction of the stack effect, location of the elevator car, and door type, show that the reopening problem of elevator doors occurs when there is a pressure difference of approximately 40 Pa. It is observed that the problem of elevator door malfunction is more severe at the lower floors during the heating mode and at the higher floors during the cooling mode. • The elevator reopening problem is analyzed based on the stack pressure data of 25 buildings. • A full-scale mock-up was built to depict how elevators operate under the stack effect. • A new threshold pressure difference value for preventing the reopening problem is suggested. [ABSTRACT FROM AUTHOR]

The pilot-control globe valve (PCGV) is a new kind valve with simple structures and low driving energy consumption. It can utilize the pressure difference before and after the valve to control the action of the valve core. However, systematic theoretical research and numerical analysis are deficient at present. In this paper, the mathematical model of PCGV is established and Computational Fluid Dynamics (CFD) method is employed to numerically simulate its dynamic characteristics. Through the analysis of the internal flow field distribution, its working principle is verified. Then three different opening processes with the same spring stiffness are analyzed under different static inlet pressures, and the best design point is obtained by studying the characteristic curves of the valve core’s displacement. The relationship of static inlet pressure and the valve core’s displacement is summarized and the selection formula for the valve design is generalized which can reduce the various design work for further optimization and engineering applications of PCGV. [ABSTRACT FROM AUTHOR]

Highlights: [•] Theoretically proposed models of water flow rates for multiple parallel chillers. [•] Both the total and partial flow rates of chillers can be determined by the models. [•] Providing a method to determine the distribution of water flow rates in chillers. [•] Providing actual water flow rate of each chiller for other researches such as FDD. [Copyright &y& Elsevier]

Abstract: This paper mainly investigates the transient conjugate heat transfer characteristic that the high speed airflow invades into the gap–cavity–gap structure. For this purpose, a simplified and effective quasi-steady approach in order to improve the numerical computational efficiency in multi-domain transient conjugate problems is presented. In this quasi-steady approach the pretty difference of the characteristic time step between the fluid and solid domains is utilized, so the computational expense can be reduced by alternating the solution sequence between coupled convection/conduction analysis and conduction analysis. The control factors to impact on the accuracy of this quasi-steady state method are analyzed further, by analyzing the process that high speed airflow aerodynamically heats the solid cylinder. Based on this quasi-steady approach, the computational fluid dynamics model combined convection, conduction and surface thermal radiation is established. Then, the transient conjugate heat transfer for the gap–cavity–gap structure is discussed. The computational results and the experimental data are compared with each other and the relative errors between them are summarized. After that, during the transient process, the features of the temperature contour inside the structure are discussed. Finally, from viewpoint of initial pressure difference between high speed airflow outside the structure and the cavity, the transient conjugate heat transfer characteristics of this structure are analyzed. [Copyright &y& Elsevier]

Abstract: Air motion problems in ventilation systems of buildings, underground facilities (mines, the underground), etc. can be simulated by means of the motion of an incompressible homogeneous viscous fluid. The aim of this work is to develop a method of solving stationary traffic in the channel of an incompressible homogeneous viscous fluid with the given pressure at the inlet and outlet of the channel and to study the stability of the solutions. [Copyright &y& Elsevier]

Abstract: In the present study, high-speed horizontal water entry behaviors of flat, ogival and hemispherical-nose projectiles were studied experimentally and theoretically. Particular attention is given to characterizing the projectile dynamics and the cavity evolution before a deep pinching starts. An analytical cavity model based on the solution to the Rayleigh–Besant problem was developed to describe the cavity dynamics of projectile water entry. Three parameters in the cavity model were discussed and determined theoretically and experimentally. Numerical simulations using the AUTODYN-2D Lagrange–Euler coupling techniques were conducted to specially study the drag coefficients of projectiles. Based on the experimental and numerical results, a drag coefficient model independent on the cavitation number was proposed. The results indicated that there are two variation laws for the three parameters in the cavity model; Additionally, the drag coefficients increase with the impact velocities with holding the projectile nose constant and decrease with an increase in the projectile nose coefficient (CRH) value. Good agreements were observed between analytical results and experimental observations. [Copyright &y& Elsevier]

Abstract: Pulsating blood flow patterns in the left ventricular (LV) were computed for three normal subjects and three patients after myocardial infarction (MI). Cardiac magnetic resonance (MR) images were obtained, segmented and transformed into 25 frames of LV for a computational fluid dynamics (CFD) study. Multi-block structure meshes were generated for 25 frames and 75 intermediate grids. The complete LV cycle was modelled by using ANSYS-CFX 12. The flow patterns and pressure drops in the LV chamber of this study provided some useful information on intra-LV flow patterns with heart diseases. [Copyright &y& Elsevier]

Abstract: Study on steam-carrying effect in static flash of both pure water and aqueous NaCl solution was present. Properties, including steam-carrying ratio, waterfilm height drop and equilibrium concentration of waterfilm, were measured in experiments. Their dependences on separating height, initial waterfilm concentration and mean pressure difference were analyzed. Particularly, steam-carrying ratio was defined as the mass ratio of be-carried liquid and generated steam. Results suggested that this ratio increased with the decreasing of separating height or the rising of initial waterfilm concentration, and a peak value existed in its evolution versus mean pressure difference. At last, according to experimental results and basic principles a calculating model for steam-carrying effect in static flash was built. [Copyright &y& Elsevier]

Abstract: This paper is devoted to the study of the peristaltic transport of viscoelastic non-Newtonian fluids with fractional Maxwell model in a channel. Approximate analytical solutions have been constructed using Adomian decomposition method under the assumption of long wave boundary layer type approximation and low Reynolds number. The effects of relaxation time, fractional parameters and amplitude on the pressure difference and friction force along one wavelength are received and analyzed. The study is limited to one way coupling model with forward effect of the fluid on the peristaltic wall. It is evident from the result that pressure diminishes with increase in relaxation time and the effects of both fractional parameters on pressure are opposite to each other. The influences of these parameters on friction force are opposite to that of pressure. [Copyright &y& Elsevier]

[Display omitted] • Methods to improve response and sensitivity are proposed. • Research the effect of sensing structure on the response fluctuation. • Analyze the response fluctuation variation with the constant temperature. • The increase of response fluctuation can cover the improvement in sensitivity. The gas sensing technique based on the differential pressure principle is quite suitable to evaluate the effectiveness of gas fire extinguishing system. This paper is focused on the study of the change rule of its response fluctuation that is critical to the concentration measuring accuracy. The variation of response fluctuation and sensing performance with sensing structure and constant temperature was explored. Results show that it will often enlarge the response fluctuation when promoting the response/sensitivity or response rate by changing the sensing structure, which can cover the improvement in sensitivity causing the decrease in measuring precision, especially for high concentration. However, the increase of temperature will reduce the response fluctuation while improving the response/sensitivity and response rate, which is a good way to promote sensing performance. The research in the paper can provide suggestions for the optimization design of the sensor. [ABSTRACT FROM AUTHOR]