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The flow characteristics of homogeneous gases in complex systems are an important issue in many areas, including underground mines. The flow in mine excavations and ventilation systems is described by known mathematical relationships that could be applied to various cases. In this paper, a flow in a duct with a local sink of mass and momentum for multiple variants of cooperation of a mechanical fan was analyzed. The relationships for the total and static pressure of air in the duct were derived. In the next stage, a calculation example of how the mass flow rate of air, and the total and static pressure of the flowing air will change in the tested sections for the duct with and without a sink, is presented. The derived formulas and calculated values for the considered calculation case allow the verification of the obtained relationships at the measurement station. Analyzing the results of the examples presented in the article, it can be concluded that the total and static pressure at the sink point differ depending on the equation of motion used. In the case of the classic equation, the value of total pressure is lower than the value calculated from the new equation of motion, and the difference between them is about 20 Pa. In the case of static pressure, this difference is about 46 Pa. Qualitative differences in the static pressure distribution at the release location were also demonstrated. Depending on the applied approach, positive or negative changes in the static pressure are noticed. The presented form of the equation of motion made it possible to determine the flow characteristics in the duct with a point mass and momentum sink in the case of the operation with and without a fan. [ABSTRACT FROM AUTHOR]

An experimental study to investigate the flow of liquid jet issued from a high aspect ratio nozzle slit into an incoming airflow by changing the orientation angle from the incoming free-stream was performed. A two-dimensional liquid sheet emerged from the narrow slit into the subsonic air crossflow. Different orientation angles between 0 and 90 degrees were studied. High-speed photography and shadowgraphy techniques were utilized to visualize the flow physics. The influence of the slit orientation angle on the flow morphology and the flow regimes of liquid sheets was investigated. Some fluid flow parameters were obtained by analyzing the images. The changes in breakup height of different orientations were measured. A model was offered for the breakup height of the liquid sheet based on the liquid-to-gas momentum ratio, gas Weber number, and a new non-dimensional parameter as a representation of the angle of slit orientation. Also, the defined sheet trajectory for each orientation angle was obtained, and the variations were examined. Empirical correlations for the defined trajectory of the sheet in terms of liquid to gas momentum ratio and gas Weber number for each orientation angle were proposed. [ABSTRACT FROM AUTHOR]

This work presents a novel approach to investigating the slip effect in nanofiber filter media. Electrospun nanofiber media with high efficiency and low pressure drop were produced at different concentrations and durations. The surface and cross-sectional morphology of nanofiber media were studied using FE-SEM. Fiber orientation and diameter distributions were also examined. The 3D virtual nanofiber media was modeled using this information along with the experimentally measured porosity and thickness of the media. The effect of the slip phenomenon in nanofiber media was studied numerically, and the results were compared to experimental data. Excellent agreements were found between the measured and simulation results. Additionally, filtration simulations considering aerosols injected with airflow through the nanofibrous filter media were conducted by considering the slip effect, and the effect of filter structure on filtration performance (removal efficiency and pressure drop) was investigated. [ABSTRACT FROM AUTHOR]

Abrupt section changes are a classic problem in the study of flow in cylindrical ducts or pipes. For its analysis, there are a wide set of exiting data from previous studies, among which some authors stand out and will be mentioned. Those previous works have been used to obtain reliable results for the resolution of section changes along a pipe, either due to cross area increases or reductions on a 1D basis. It is also known that a numerical 2D axisymmetric simulation (CFD) could find a consistent result compared to experimental data in almost all fluid flow fields. The main novelty of the present study is the development of a simple numerical approach used to solve the minor loss calculation. Firstly, a theoretical analysis is developed, and then the results of the numerical simulations carried out on the behavior that affects the water and air flow rate in an abrupt section change, for both contraction and expansion problems, are presented. In both cases, the results are analyzed with different meshes (discretizations) and turbulence models. Finally, the obtained numerical results are compared with those in the technical literature. Also, a theoretical approach is shown in order to show a whole frame of the discussion. The core results are the loss coefficient evolution as a function of the section change both for the sudden contraction and the expansion of a pipe flow. As the results follow the existing experimental values, it is concluded that the developed model provides a feasible and quick design tool to analyze possible geometrical changes without the need for further experiments. [ABSTRACT FROM AUTHOR]

Pathfinding algorithms allow for the numerical determination of optimal paths of travel across many applications. These algorithms remain poorly defined for additional consideration of outside parameters, such as fluid flow, while considering contaminant transport problems. We have developed a pathfinding algorithm based on the A* search algorithm which considers the effect of fluid flow behaviors in two dimensions. This search algorithm returns the optimal path between two points in a setting containing impermeable boundaries, allowing for a computational approach to the determination of the most likely path of travel for contaminants or hazards of concern due to fluid flow. This modified A* search algorithm has applications in the statistical modeling of airborne contamination distributions, providing a relative estimate of the statistical relationship between two points in an underground mine's ventilation system. This method provides a significant improvement to the spatial resolution of minimum-cost path methods currently in use in mine ventilation network software. [ABSTRACT FROM AUTHOR]

A technical issue with fluid flow heating is the relatively small temperature increase as the fluid passes through the heating surface. The fluid does not spend enough time inside the heating source to significantly raise its temperature, despite the heating source itself experiencing a substantial increase. To address this challenge, the concept of the multiple circular heating of air was developed, forming the basis of this work. Two PTC heaters with longitudinal fins are located within a closed channel inside housing composed of a thermal insulation material. Air flows circularly from one finned surface to another. Analytical modeling and experimental testing were used in the analysis, with established restrictions and boundary conditions. An important outcome of the analysis was the methodology established for the optimization of the geometric and process parameters based on minimizing the transient thermal entropy. In conducting the analytical modeling, the temperature of the PTC heater was assumed to be constant at 150 °C and 200 °C. By removing the restrictions and adjusting the boundary conditions, the established methodology for the analysis and optimization of various thermally transient industrial processes can be applied more widely. The experimental determination of the transient thermal entropy was performed at a much higher air flow rate of 0.005 m3s−1 inside the closed channel. The minimum transient entropy also indicates the optimal time for the opening of the channel, allowing the heated air to exit. The novelty of this work lies in the controlled circular heating of the fluid and the establishment of the minimum transient thermal entropy as an optimization criterion. [ABSTRACT FROM AUTHOR]

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9 , the maximum liquid-phase superficial velocity is increased by 109 % compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation. [ABSTRACT FROM AUTHOR]

Knowledge of fracture properties and associated flow processes is important for geoscience applications such as nuclear waste disposal, geothermal energy and hydrocarbons. An important tool established in recent years are hydro-mechanical models which provide a useful alternative to experimental methods determining single fracture parameters such as hydraulic aperture. A crucial issue for meaningful numerical modeling is precise imaging of the fracture surfaces to capture geometrical information. Hence, we apply and compare three distinct fracture surface imaging methods: (1) handheld laser scanner (HLS), (2) mounted laser scanner (MLS) and (3) Structure from Motion (SfM) to a bedding plane fracture of sandstone. The imaging reveals that the resolution of the fracture surface obtained from handheld laser scanner (HLS) is insufficient for any numerical simulations, which was therefore rejected. The remaining surfaces are subsequently matched and the resulting fracture dataset is used for detailed fracture flow simulations. The resulting hydraulic aperture is calibrated with laboratory measurements using a handheld air permeameter. The air permeameter data provide a hydraulic aperture of 81 ± 1 µm. For calibration, mechanical aperture fields are calculated using stepwise increasing contact areas up to 15%. At 5% contact area, the average hydraulic aperture obtained by MLS (85 µm) is close to the measurement. For SfM, the measurements are fitted at 7% contact area (83 µm). The flow simulations reveal preferential flow through major channels that are structurally and geometrically predefined. Thus, this study illustrates that resolution and accuracy of the imaging device strongly affect the quality of fluid flow simulations and that SfM provides a promising low-cost method for fracture imaging on cores or even outcrops. Highlights: We evaluate a handheld laser scanner, a mounted laser scanner and the Structure from Motion method for imaging of fracture surfaces. We use the scanned geometries for flow simulations and calibrate the results with air permeameter measurements. Our study reveals that the handheld laser scanner is unsuitable for fracture surface imaging due to low resolution and accuracy. The simulations performed with geometries obtained by the mounted laser scanner and the Structure from Motion method provided comparable results. The Structure from Motion method seems to be promising for fracture investigations in field applications due to the high flexibility and low costs. [ABSTRACT FROM AUTHOR]

This study proposes a mixed-mode dryer with a semi-transparent photovoltaic thermal (PVT) collector for the assessment of drying and thermal performance using computational and experimental findings. The thermal behavior and fluid flow characteristics have been analyzed to optimize the air flow rate in the PVT solar dryer by considering three different inlet velocities of 0.048 m/s (Case 1), 0.096 m/s (Case 2), and 0.144 m/s (Case 3). The temperature distribution is obtained more uniformly for the PVT collector and dryer cabin in Case 2. The results of the investigation show that Case 3 has a positive impact on the PVT solar dryer performance. In numerical and experimental methods, the enhanced thermal efficiency is attained as 30.78% and 29.78% for Case 2, and 33.20% and 31.14% for Case 3, respectively, in comparison to Case 1. Case 3 has improved Reynolds and Nussselt numbers by 3.06 and 2.45 times, respectively compared to Case 1. Experimental results varied by 2.24 to 4.90% from simulated outcomes obtained from CFD. The machine learning approach of ANN has been implemented with different hidden layers network models to choose the best drying conditions by predicting the drying performance parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, an innovative solar photovoltaic thermal (PVT) collector is developed that has a spiral shaped absorber tube fitted underneath the PV panel in such a manner that a bifluid cooling system extracts heat from the PV panel. The methodology adopted in the present study is to conduct a detailed computational investigation in order to understand the impact of important operating and environmental parameters such as mass flow rates and solar radiations on the overall performance of the bifluid PVT collector. One of the fluids, i.e., a nanofluid (Al2O3 in water) with nanoparticle volumetric fraction 5% is passed through the spiral tube, whereas a rectangular air duct is attached below the PV panel for extracting heat from it and delivering the same to the flowing air, thereby making a bifluid coolant system for the PVT collector. Detailed CFD simulations are performed in ANSYS Fluent 19.2 platform for analyzing the thermal performance of the collector. The effects of mass flow rate variations of each individual fluid and in combination (i.e., bifluid) on the PVT efficiency, i.e., thermal, electrical and overall efficiency are observed. The results indicate that with increase in mass flow rate of the fluids, these efficiencies increase up to a certain level but after that, there is only incremental increase with further increase of the latter. When the fluids are used individually or in combination, higher thermal and electrical efficiency are obtained with nanofluid mass flow rate less than that of air. Further, the bifluid is able to transfer heat effectively from the PV panel with less temperature variation between inlet and outlet. Out of all the combinations of varying mass flow rates of individual fluids and bifluid, the best bifluid combination is such that lead to an overall efficiency of 79% corresponding to nanofluid mass flow rate 0.0247 kg/s and air mass flow rate 0.034 kg/s. The computational model developed in this present study will help in designing and developing a more energy efficient, environment friendly and sustainable PVT technology for effective utilization of solar energy. [ABSTRACT FROM AUTHOR]

This investigation offers valuable perspectives for the development and enhancement of thermal management systems for lithium-ion batteries (LIBs) equipped with three distinct cooling channels, namely open, curved, and rectangular, utilizing both air and water as coolants. The assessment of the battery's thermal behavior involved the examination of temperature distribution, surface Nusselt and Stanton numbers, as well as pressure drop. The open channels proved to be the least efficient for the same operating conditions. Curved conduits employing water as the cooling medium have illustrated the most favorable outcomes in terms of diminished pressure loss and elevated thermal efficacy. Among the three scenarios, the curved channel manifests the highest operating temperature, reaching a maximum value of 305.03 K for airflow and 304.44 K for liquid flow, while the lowest operating temperature recorded is 300 K. Consequently, the curved channel presents a superior cooling efficiency for the battery in comparison to the other conduits. The surface Nusselt values for air flow varied between 60.26 and 77.58%, with the minimum and maximum values, respectively. In the case of liquid flow, these values ranged from 60 to 72.28%. The pressure drop was determined to be approximately 300, 450, and 600 Pa for open, curved, and rectangular channels, respectively. On the other hand, for liquid flow, the corresponding pressure drop values were measured to be 0.8, 1.4, and 1.7 Pa, respectively. These findings underscore the significant impact that the selection of flow channels and cooling fluids has on the thermal behavior of the battery. This study has demonstrated that liquid cooling with a curved channel configuration is an effective approach to enhance the thermal performance of LIBs employed in electric vehicles. As a result, this research provides valuable insights into the design and optimization of thermal management systems for LIBs. [ABSTRACT FROM AUTHOR]

This research presents a detailed transient experimental and computational study of heat transfer and airflow in a scaled room linked with a double-duct vertical roof solar chimney (SC). The analysis was made in the coupled system, varying the heat flux supplied to the roof SC absorber during the day. Experimental temperature profiles were obtained at six different depths and heights, the empirical heat transfer coefficient was computed for the SC absorber, and the variation of air changes per hour was determined. A good agreement between experimental and numerical temperature profiles and average Nusselt number (Nut) is shown in the latter of average difference of 3.41%. The validated computational model was used to analyze the effect of the transient heating of the SC on temperature fields and flow patterns in the thermal system. Almost symmetrical temperature and y-velocity profiles are formed in the ducts at different hours of the day, with thermal boundary layers of about 4 mm. Correlations of the Nusselt number and air changes per hour (ACH) are provided as a function of the modified Rayleigh number. [ABSTRACT FROM AUTHOR]

Techniques for measuring fluid flow have been known since the 19th century. The first solutions based on the use of pressure only allowed relatively slow changes to be observed. It was not until measurement techniques based on the use of electronic components and the phenomenon of thermo-transfer, combined with a method enabling fast signal recording (A/C converters), that it became possible to analyse the flow of a medium (e.g. air) in detail. Although flow sensors based on measuring changes in resistance have been known for many years, new solutions are still being developed. This paper presents the results of a study using three sensors. Their response to laminar airflow was investigated for different velocities (1.2 - 2.6 m/s). The flow forcing was implemented using an axial fan and the signals were measured simultaneously for all the sensors tested. The results showed which sensors had the smallest dispersion of results (PAN and WA sensors) and confirmed that for the investigated velocity variations (0.14 m/s pitch) the results are unambiguously interpretable. It should be noted that sensor research is related to the need to develop a device to measure flow as accurately as possible, while at the same time ensuring the comfort of the test person during the measurements. Therefore, the search was for a sensor that is small in size and at the same time resistant to damage and operation in a harsh humid environment. [ABSTRACT FROM AUTHOR]

The use of solar air heater systems brings with it the convenience of having hot air at discretion for heating households with quite low prices compared to the use of conventional heating sources. The researchers desire to achieve the highest thermal efficiency of these systems has led to the emergence of different ways of improvement. The present work is focused on the available literature in the field of SAH systems made with different types of air flow. The paper also presents the different designs for the realization of airflow types used by researchers for high efficiency during the years 2017-2021. [ABSTRACT FROM AUTHOR]

Study of thermo-fluid flow has its significance in energy analysis of a building. Various thermo-fluid analyses are performed in heating ventilation and air conditioning (HVAC) systems for energy efficient buildings by scientists and engineers to save energy consumption during the life of a building. In order to achieve energy conservation for different HVAC systems, determination of air flow pattern and flow physics are vital parameters. In case of fluid flow postprocessing techniques such as streamlines, vector plots and contours are often employed. These techniques help in understanding the nature of flow and its properties. Each of these postprocessing techniques mentioned are based on Eulerian methods and have certain inherent deficiencies pertaining to the amount of information they can convey about certain aspects of fluid flow. Lagrangian coherent structures (LCS) on the other hand use Lagrangian data for analysis purposes. LCS are generated using finite time Lyapunov exponent fields which in turn depict the rate of expansion or contraction of the trajectories around a certain point. LCS act as the transport barriers across which there is approximately zero mass flux. This property means that LCS can be applied to problems related to separation and reattachment in fluid flow and find virtual boundaries inside flows. In the current study, we focused on the application of LCS for efficient placement of sensors for HVAC systems. We computed LCS using velocity data extracted from the CFD simulations of a 2D room model. Thus, LCS can be used to identify the virtual boundaries in fluid flow. This helps in indication of regions where mixing of particles occurs and also where particles are stagnated. Inlet angles of 0, 15, 22, and 30 degrees are used and analysis shows that manifolds with 30 degree angles provide better ventilation. The outcome of this study can be used to improve the energy efficiency as well as predict the accurate location of HVAC sensor and control units. [ABSTRACT FROM AUTHOR]

This research investigates the fluid flow characterization and thermohydraulic performances (THP) of rib surfaces, using computational and experimental methods. ANSYS computational fluid dynamics (CFD) software was used to predict and validate the findings in the experimental setup. Artificial rib surfaces, including polygonal and forward trapezoidal-shaped ribs, were placed in the absorber plate at different relative pitch distances (p/e) = 6.7, 10, 13.4 and relative height (e/d) = 20, and the mass flow rate of air (working fluid) varied at Reynolds numbers ranging from 2000 to 20,000. According to the validation results, the RNG renormalization k-ε model was selected for the investigation. The results show that strong turbulence occured closer to the wall surface and behind the rib surface, enhancing thermal performances due to the sharp edge shape of the rib. A polygonal rib with a pitch distance of p/e = 6.7 achieved a higher Nusselt number (Nu) and thermohydraulic performance of 2.95 at Re 4000. An empirical correlation between the Nusselt number (Nu) and friction factor (f) was developed using linear regression analysis and was compared with the predicted values. The comparison results show a close range of ±8% between the experimental and predicted values. [ABSTRACT FROM AUTHOR]

This paper deals with the development and validation of a unified internal flow model (UIF) for the prediction of fluid behaviour in a network of 3D floodable cells such as an internal ship compartment subdivisions. The UIF model is incorporated in a generic time-domain ship-motion simulation environment. The flow model uses cell-averaged fluid momentum to account for dynamic (inertia) effects in compartments. A compartment is typically given the size of a ship compartment on board. The fluid solver can keep track of the air pressure in and air flow through compartments under isothermal assumption. Simulation results are compared against experimental data from four different configurations: a single tank draining experiment, a two compartment down-flooding experiment, an oscillating water column experiment under pressure, and a transient flooding experiment with a cruise ship in calm water. The general validity of the UIF model is demonstrated through these four examples. The newly developed UIF model overcomes the shortcomings seen in the steady Bernoulli-based simulations. Its application leads to a more accurate prediction of the floodwater progression in the ship, and it captures the fluid dynamics seen in the oscillating water column device very well, which is not possible using the steady Bernoulli approach. The general applicability of the UIF solver for internal fluid response in maritime application is thereby demonstrated. The effect of the internal compartmentalisation of a cruise ship and the effect of viscous roll damping on the transient roll response is discussed. [ABSTRACT FROM AUTHOR]

The objective of this article is to address the challenges associated with visualizing air flow over a heating source in an open laboratory environment. The study uses a combination of experimental visualization and numerical simulation techniques to generate a 3D model of the air flow and heat transfer between the heating source and the environment via natural convection. The Particle Image Velocimetry method is used to experimentally visualize the air flow, which is known for its benefits of high speed and accuracy, and for its ability to avoid disturbing the flow of the fluid being investigated. The data obtained from this experimental method are used as input for numerical simulations using the Ansys Fluent program. The numerical simulations identify air vortices and other elements that disrupt the airflow in the laboratory environment. The resulting 3D model accurately represents the actual situation in the laboratory and could be further optimized by adjusting parameters such as the output of the heater and the heating source temperature. These parameters play a crucial role in ensuring thermal comfort in the laboratory environment, which is of utmost importance for user comfort. In conclusion, the study provides valuable insights into the visualization of air flow over a heating source and demonstrates the effectiveness of combining experimental and numerical simulation techniques to generate accurate 3D models of air flow and heat transfer. [ABSTRACT FROM AUTHOR]

Purpose. Development of a methodology for optimizing the technological parameters of the airlift operation, based on the analysis of the pressure balance in the annulus and in the drill string that occurs during drilling. Methodology. The tasks were solved by a complex research method, which includes a review and generalization of literary and patent sources, analytical studies on existing methods for optimizing the technological parameters of drilling with reverse circulation using an airlift. Findings. It has been established that in the study on the airlift circulation method during rotary drilling with reverse circulation, an important role is played by the analysis of the pressure balance arising in the course of drilling in the annulus and in the drill string. It takes into account both hydrostatic pressures and pressure losses for pumping water and water-air mixture. A technique has been developed for assessing the effect of rate of penetration on circulation parameters. Originality. For the first time, it has been shown that the analysis of the pressure balance makes it possible to establish, with a given accuracy, the average effective values of the output parameters: the density of the water-air mixture, its upward flow rate, and the air flow rate at a given velocity of the upward flow of water as it approaches the mixer. Practical value. The proposed technique makes it possible to establish the dependence of the values of the output parameters on the depth of the well, as well as the required compressor performance to provide a given drilling fluid flow rate. [ABSTRACT FROM AUTHOR]

Unsmooth reversing is one of the most common faults in the four-way reversing valve of the air conditioning system, and the airflow in the valve chamber and the shape of the slider of the reversing valve are the main factors in unsmooth reversing. In order to study the influence of the airflow in the chamber and the slider shape on the reversing process, the fluid flow in the valve chamber of a four-way reversing valve is obtained using computational fluid dynamics (CFD) simulations, and the influence of the slider structure on slider thrust and resistance of the four-way reversing valve is analyzed. Four-way reversing valves with no-cutting, straight-cutting and arc-cutting sliders are employed to evaluate the reversing characteristics. A pressure measuring device for a four-way reversing valve chamber is designed, which is performed to test the chamber pressure of three different types of sliders of four-way reversing valves. The maximum error of experimental tests and simulations is within 5% of engineering tolerance, so as to verify the reliability of numerical simulation. The resistance-to-thrust ratio of the slider is raised to evaluate the performance of the reversing, which can guide the design of the valve and slider. The results indicate that the chamber pressure and resistance-thrust ratio with the cutting slider are reduced, which is beneficial to the reversing of the four-way reversing valve. Compared with the straight-cutting structure, the arc-cutting slider four-way reversing valve has a more stable reversing process and better comprehensive reversing performance. Results demonstrate that both the straight-cutting structure and arc-cutting structure of the slider can improve the process performance but the arc-cutting slider is better. [ABSTRACT FROM AUTHOR]

The "excess salt replication process" is a new simple method of fabrication of open-cell metal foam based on the commonly known salt replication method. Porous materials with porosity between 46% and 66% result when the employed alloy is 25% antimonial lead alloy and when it is 58% to 65% zamak 5. These foams are proposed as structured catalysts instead of packed beds in the treatment of wastewater. The local regimes influencing macroscopic air flow behaviour through these foams are delimited and boundaries are analysed in terms of sample length. Most of the experimental tests in this work exhibited a general trend of air flow in ESR foams dominated by the "strong inertia regime". It was established that the law governing the unidirectional air flow through these foams was the full cubic law. The permeability and inertia coefficient of five samples with a cell diameter between 2.5 and 4.5 mm were calculated, and an empirical correlation was fitted. The irregular cuboid shape of salt grains used in the ESR foam was the origin of the special cell form of ESR foams leading to an anisotropic ordered porous media. This can explain the macroscopic turbulence of air flow because there were many dead zones present in the corner of each cubic cell, thus causing kinetic energy loss starting at earlier regimes. [ABSTRACT FROM AUTHOR]

When the unsaturated zone of the unconfined aquifer is covered by a low‐permeability upper layer, significant airflow will be generated in the unsaturated zone during water pumping. However, high permeability preferential flow zones (PFZs) such as fractures and macropores are frequently present in the unsaturated zone, forming the preferential fluid flow paths, which may change the original airflow pattern in the unsaturated zone during the pumping test and consequently affect the precision of obtained aquifer hydraulic parameters. The main objective of this paper is to investigate the effect of PFZs in low‐permeability upper layer on pumping‐induced airflow in the unsaturated zone by numerical simulations of transient three‐dimensional air‐water two‐phase flow and to quantify errors in the aquifer hydraulic parameters obtained during pumping test. The results demonstrate that a large amount of air flows quickly from the atmosphere into the unsaturated zone through the PFZs, and that the PFZs can draw some air from the nearby low‐permeability soils as well. The significant influx of air through PFZs also reduces the negative air pressure in the unsaturated zone and decreases the drawdown in the saturated zone at intermediate times, which are nevertheless still greater than the results obtained in the homogeneous aquifer. Estimations of the aquifer hydraulic parameters reveal that errors of these parameters obtained are smaller when the PFZs with favourable combinations of permeability, width and quantities facilitate more air to flow into the unsaturated zone. [ABSTRACT FROM AUTHOR]

This article pertains to physiognomic behavior of flowing air underneath the absorber plate using artificial roughness to enrich heat transfer coefficient (h) between the absorber plate and the flowing fluid by penetrating the boundary sub-laminar layer developed underside of the SAH duct absorber plate. This article reveals the effect of relative gap width (g/e) on thermal performance of roughened SAH duct using symmetrical arc rib roughness having gaps and staggered rib. The present novel arc rib geometry is obtained by providing additional gap in considerably long continuous arc segment of existing best arc rib geometry so as to break the boundary layer reformation along it. To determine the improvement in the proposed work, experimental results are compared with smooth SAH duct. The investigating parameters for proposed geometry are Re as 3000–16000, p/e as 10, α of 30°, p'/p of 0.4, Ng as 4, ng as 4, g/e as 2–5, e/Dh as 0.043, d/w as 0.65, g'/e as 1 and g/e as 2–5. Optimal escalation is perceived in Nu and f at g/e as 4 and 3, respectively. Maximum THPP is attained at g/e as 4. Under different operating circumstances, correlation development and economic evaluation have been conducted. [ABSTRACT FROM AUTHOR]

Powder mixing is critical in many industries. Despite the wide variety of available mixers, the container blender is favored in industries due to easy manufacturing and convenient operation. As fine powders are frequently encountered in practical mixing, the presence of air during mixing may significantly impact the process. However, a scientific understanding of air–particle interactions in powder mixing has not been established so far. From a physical view, the air drag force on particles might be significant when the gas velocity is high and the particles are fine. Therefore, this novel study numerically investigates the effects of particle size and air presence on powder mixing under typical conditions, such that the relationship between particle–fluid dynamics and mixing performance is clarified for the first time. In the calculation, our advanced computational fluid dynamics–discrete element method, namely, the flexible Eulerian–Lagrangian method with an implicit algorithm, is utilized. To examine the effect of particle size on powder mixing, the coarse-grained discrete element method is employed for fine particle systems. Through the advanced numerical framework, the effect of airflow on powder mixing can be discussed in depth. The numerical results show that airflow accelerates the mixing of fine particles under the investigated rotation speeds. Based on the calculation results of the particle kinetics and fluid velocity distribution, it is clarified that the accelerated mixing results from the fine particle movement under air entrainment. How the movement of fine particles is developed is also elucidated by the continuously circulating gas flow and fluid drag force. Thus, this study provides a new understanding of the effects of airflow on powder mixing, which has not been scientifically clarified in previous studies. [ABSTRACT FROM AUTHOR]

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A computational fluid dynamics study about the aerodynamic loads over a heliostat due to an atmospheric boundary layer flow using a modified k-ɛ turbulence model is presented. A new formulation is used, in which the model quantities vary with the velocity field. Modified wall functions for roughness were used at the bottom of the computational domain to achieve horizontal homogeneity of the airflow. Good horizontal homogeneity for the streamwise and spanwise velocity and turbulence intensity profiles were found. The incident profiles were compared with the inlet ones. The average percentage differences were 0.22% for velocity and 0.43% for turbulent intensity. Good agreement was found between the numerical data and theoretical values of the streamwise and spanwise shear stress at the bottom of the domain. The aerodynamic coefficients of the heliostat at different elevation angles were obtained, and a good agreement was found between the numerical data concerning the wind tunnel experimental values. An average percentage difference of 3.1% was found for drag, 6.5% for lift, and 6.0% for overturning. A significant improvement was obtained by using this new formulation with respect to a non-modified k-ɛ turbulence model. The average differences of the aerodynamic coefficients were 6.6% for drag, 12.4% for lift, and 10.1% for overturning. The velocity, turbulent kinetic energy, and pressure fields at different elevation angles were analyzed. It was found that at an elevation of 60 deg, the stagnation point of the flow occurs at the superior edge of the heliostat, causing the maximum lift force over the structure. [ABSTRACT FROM AUTHOR]

To solve the problem of difficult hazelnut harvesting in mountainous areas of Liaoning, China, a small pneumatic hazelnut harvesting machine was designed, which can realize negative pressure when picking up hazelnut mixtures and positive pressure when cleaning impurities. The key structure and parameters of the harvesting machine were determined by constructing a mechanical model of the whole machine and combining theoretical analysis and operational requirements. To explore the harvesting machine scavenging performance, Liaoning hazelnut No. 3 with a moisture content of 7.47% was used as the experimental object. Firstly, the terminal velocity of hazelnuts and fallen leaves was measured using a material suspension velocity test bench. Secondly, the gas–solid two-phase flow theory was applied comprehensively, and the motion state, particle distribution, and air flow field distribution of hazelnuts from the inlet to the outlet of the pneumatic conveying device were simulated and analyzed using the coupling of computational flow fluid dynamics method (CFD) and discrete element method (DEM) to evaluate the cleaning performance from the perspective of the net fruit rate of hazelnuts in the cleaning box. Finally, a Box–Behnken design experiment was conducted with the sieve plate angle, the distance of the sieve plate, and the air flow velocity as factors and the net fruit rate of hazelnuts as indicators to explore the influence of the three factors on the net fruit rate of hazelnuts. The parameter optimization module of Design-Expert software was used to obtain the optimal combination of parameters for the factors. The experimental results show that the test factors affecting the test index are the following: the air flow rate, the angle of the screen plate, and the distance of the screen plate. The best combination of parameters was an air flow velocity of 14.1 m∙s−1, a sieve plate angle of 55.7°, and a distance of the sieve plate of 33.2 mm. The net fruit rate of hazelnuts was 95.12%. The clearing performance was stable and can guarantee the requirements of hazelnut harvester operation, which provides a certain theoretical basis for the design of a nut harvester. [ABSTRACT FROM AUTHOR]

• The air cooler tubes air cooler tubes at the top of the distillation column suffered from severe leakage during service. • CFD simulation are used to analyze the corrosion behavior of the atmospheric pressure air cooler tubes and the simulation results are validated by experiments. • The gas–liquid erosion corrosion is the main reason for the leakage and the impact angle is the key factor that affects the corrosion. • An improvement measure has been proposed and the corrosion is greatly alleviated. Air coolers are important heat exchangers and widely used in the petroleum and petrochemical industries. The leakage of air cooler tubes due to corrosion frequently happened and seriously affected normal production process leading to unplanned shutdowns, so the corrosion behavior of the air cooler tubes needed to be clarified urgently. In this work, the corrosion behavior of the atmospheric pressure air cooler tubes was investigated by computational fluid dynamics (CFD) simulation and experimental study. It was depicted that the gas–liquid erosion corrosion was the main reason for the leakage of air cooler tubes and the collision angle between the fluid flow and the wall at the inlet of the tubes was the key factor that affects the corrosion behavior of the multiphase flow inside the air cooler tubes. The corrosion was most severe when the collision angle is 30 degree. With the purpose to migrate corrosion, the improvement measure was proposed from the perspective of collision angle elimination. The porous plates were installed and the lifetime of the air cooler tubes was extended to 4 times that of the original conditions, which indicated the installation of porous plates is an effective measure to reduce corrosion. [ABSTRACT FROM AUTHOR]

Pumping is an indispensable operation in microfluidic applications. Numerous simple pumps have been developed to improve the portability of microfluidic systems, but they generally have poor controllability, short duration working time, and narrow pressure range, which compromises the functionality of portable microdevices. To address these limitations, we present a novel handheld, wide-range pressure pump that utilizes a disposable mini gas cylinder as a pressure source and a porous PDMS film as a flow-rate regulator. Specifically, by incorporating a set of parallel porous PDMS films with varying porosity, sectional area, and thickness into the pump system, and selectively switching between the branch flow circuits containing these porous PDMS films, we are able to finely regulate the flow rate of air released from the mini gas cylinder. This capability enables precise control of the pumping pressure applied to microfluidic devices over a wide range, thereby governing the fluid flow rate to accommodate different applications. The compact and lightweight nature of our pressure source renders this pump system particularly advantageous for field-portable microfluidic applications. Additionally, we demonstrate its capabilities through the performance of well-established microfluidic experiments, including concentration gradient generation and emulsion droplet production. We firmly believe that the compactness, operational simplicity, and disposability of our pump will greatly facilitate the widespread adoption of microfluidic technologies, particularly in point-of-care diagnostics and resource-limited settings. [Display omitted] • A compact, low-cost, electricity-free, and wide-range pressure pump is presented. • The pump can finely control flow rates without requiring expensive pressure sensors. • The pump allows performing long-term experiments with a wide range of flow rates. • The pump offers an on-site pumping solution for field-portable detection applications. [ABSTRACT FROM AUTHOR]

The asymmetrical impact of hull-shaped bodies is quite common when a ship sails in oblique waves. In this paper, the impact hydrodynamics of a typical hull obliquely entering water are studied via drop tests. The influence of the bottom bulbous bow and inclination angle on the fluid flow and pressure characteristics are the main concerns. Some special fluid characteristics (jet flows and air cavities) are observed, and the mechanism of load characteristics (i.e., multiple peaks, negative pressure and high oscillations) is explored by combining the free surface characteristics. The existence of the bulbous bow causes obvious fluid separation and jet impact, and the separation degree and jet impact position are affected by the inclination angle. The influence of drop height on impact fluid dynamics is explored. Higher impact velocities result in more intense fluid flow and bubble breaking. The dimensionless pressure coefficient at different entry velocities is different because the affected air cavity flows near the bottom bulbous bow. These findings reveal the law of load and fluid characteristics of hull bodies under asymmetrical impact. • A series of oblique drop tests of a hull-shaped body is carried out to clarify the hydrodynamic impact characteristics. • Mechanism of fluid dynamic behaviors including flow separation, jet flow impact and air cavity is clarified. • Complete dataset (free surface and impact pressure) is provided to fill the gap of oblique water entry of hull-shaped bodies. • Influence of inclination angle and bottom appendage on the fluid dynamic behaviors and load characteristics is clarified. [ABSTRACT FROM AUTHOR]

The objective of this study was to experimentally and analytically investigate the lubrication condition and visualize the fluid flow in a ball bearing cage under various operating conditions. To achieve the experimental aspects of this investigation, a test apparatus incorporating a transparent cage was designed and developed. The transparent cage was manufactured based on the original geometry of the bearing cage. The transparent cage was positioned in the test rig relative to the ball using a precision XYZ table. This allowed for critical observation and examination of air and oil entrapment conditions within the cage. A high-speed camera was utilized to capture the fluid flow and air distribution inside the cage. To address the analytical aspects of this study, Ansys Fluent computational fluid dynamics (CFD) software was used to develop a multiphase lubrication model simulating the same conditions as the test apparatus. Lubricant and air distribution within the cage were investigated for various operating speeds and cage positions relative to the ball. Results from the experimental and analytical studies were corroborated and found to be in good agreement. The results demonstrate that as the cage was moved closer to the ball, lubrication conditions changed and fluid striated over the ball surface, resulting in greater air entrapment within the cage. The CFD model predicted similar trends and results. Increasing ball speed promoted starvation of lubricant supply to the cage. The CFD model confirmed that lubricant surface tension plays a key role in the striation patterns over the ball surface. [ABSTRACT FROM AUTHOR]

Power losses in gearboxes result in frictional heating. Sufficient heat transfer from the gearbox to the environment is required for reliable operation. The heat dissipation from gears is linked to their interaction with fluids in the gearbox. Recent research has demonstrated the use of Computational Fluid Dynamics (CFD) to predict the gearbox fluid flow and no-load losses in an isothermal manner. This study focuses on a numerical analysis of the heat dissipation within a dry-lubricated gearbox under atmospheric conditions. Spur gears and helical gears are investigated. The air flow in the gearbox as well as the heat dissipation over the gear surfaces are evaluated in detail. The results show that the gear geometry and the circumferential speed have a strong impact on the air flow. Especially, the axial inflow of air to the gears has a great influence on the heat dissipation. Conveying effects of helical gears lead to a multidirectional airflow, resulting in higher values of the heat transfer coefficient on the gear surface compared to spur gears. [ABSTRACT FROM AUTHOR]

The water vapor present in the atmosphere may be one of the sources of fresh and clean water. It is well known that 70% of the earth is covered with water. However, only less than 1% of fresh water is of direct use for humankind on earth. Several techniques have been devised to mitigate the availability of fresh water for humans. In this paper, a novel approach has been discussed to study the mass transfer from water vapor on a flat surface, and a moisture harvesting technique has been developed as a non-conventional source using the Peltier module to produce water condensate. The characterization of the flat surfaces has been done for the thermal homogeneity and the temperature gradient. The droplet nucleation process and the mass flux of water vapor from the air on the vertical surface at different temperatures have been devised. The results have been discussed for the mathematical calculation of the Reynolds number, Schmidt number, and Sherwood number using the experimental data. The comparison of experimental and theoretical mass fluxes was presented with an airflow velocity of less than 1.0 ms−1. The airflow on the condensing surface was a mixed type, and the coefficient of proportionality of the fluid flow was calculated as 0.23 for the proposed blunt-faced structure. The outcome was theoretically validated for the rate of condensation of water vapor from humid air and the mass flux produced. The technique developed may have several applications ranging from mass transfer in biotechnology to the nonconventional source of water production. [ABSTRACT FROM AUTHOR]

Energy harvesting induced from flowing fluids (e.g., air and water flows) is a well-known process, which can be regarded as a sustainable and renewable energy source. In addition to traditional high-efficiency devices (e.g., turbines and watermills), the micro-power extracting technologies based on the flow-induced vibration (FIV) effect have sparked great concerns by virtue of their prospective applications as a self-power source for the microelectronic devices in recent years. This article aims to conduct a comprehensive review for the FIV working principle and their potential applications for energy harvesting. First, various classifications of the FIV effect for energy harvesting are briefly introduced, such as vortex-induced vibration (VIV), galloping, flutter, and wake-induced vibration (WIV). Next, the development of FIV energy harvesting techniques is reviewed to discuss the research works in the past three years. The application of hybrid FIV energy harvesting techniques that can enhance the harvesting performance is also presented. Furthermore, the nonlinear designs of FIV-based energy harvesters are reported in this study, e.g., multi-stability and limit-cycle oscillation (LCO) phenomena. Moreover, advanced FIV-based energy harvesting studies for fluid engineering applications are briefly mentioned. Finally, conclusions and future outlook are summarized. [ABSTRACT FROM AUTHOR]

During storage, pallets of food product generating heat (e.g., cheese, fruit, and vegetable) are exposed to low velocity ventilation. In addition, the boxes have often little perforation. Therefore airflow is weak inside the boxes located downstream of the pallet; and if the product generates heat, its temperature can rise above the recommended one. Computational fluid dynamics modeling can predict these phenomena but needs an expertise of numerical fluid flow, a detailed description of product and packaging and leads to expensive computational costs. A simplified model is here developed based on a hydraulic network analogy. Given the vent holes areas of the boxes and the heat generation, it predicts the global air flow (flow through the box faces) and the product temperature. The predictions are in good agreement with experimental data. The software (Matlab executable) is easy to use and needs only some seconds to compute. It can be used to predict temperature evolution along a cold chain and to improve packaging and logistic operating conditions. Practical applications: Based on a on a hydraulic network analogy, a simplified zonal model of airflow and heat transfer in a pallet of food generating heat is built with the Matlab software. It takes into account the vent holes areas of the boxes and the heat generation, and allows predicting the distribution of air fluxes through the box faces and the product temperature. The major advantage of this model is that it is easy to use and needs only some seconds to compute. Therefore, it can be easily used in industrial field. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study carried out to investigate the influence of different performance parameters on heat transfer and fluid flow characteristics of a roughened double pass duct provided with combination of discrete multi V and staggered shaped ribs. The investigation has covered the range of operating parameter, i.e. Reynolds number (Re) from 3000 to 21000, and roughness parameters, i.e. relative inclined gap distance (Ig/Lv) from 0.4 to 0.8, and angle of attack (α) from 30° to 75° while the other roughness parameters are kept as constant. The Nusselt number, friction factor, and thermohydraulic performance for the artificially roughened double pass duct have been investigated. The results of the study have been compared with that of double-pass channel without roughness and considerable enhancement in the performance of the duct has been achieved. Based on the experimental results, the optimum values of roughness and operating parameters have also been identified. Further, the pumping power reduction to circulate the air has also been investigated. [ABSTRACT FROM AUTHOR]

Heat exchangers are widely used for cooling and heating in every process industry. Here, a laboratory-scale experimental setup is used to investigate the thermal performance of inserted helical tube three-fluid heat exchanger using three different concentrations of graphene/water nanofluid (viz. 2, 4, and 6 volume percentage) as a working fluid. The influence of fluid flow in parallel configuration (viz. the flow of hot water, nanofluid, and air) is examined on the overall heat transfer coefficient, effectiveness and Nusselt number. The overall heat transfer coefficient increases with increasing all fluid flow rates. Significant improvements of the heat transfer coefficient between hot water and nanofluid and between nanofluid and air are found for the cases of nanofluids at the hot water flow or air flow rates, while a negligible effect of nanofluids between hot water and nanofluid is observed with increasing nanofluid fluid flow. Additionally, effectiveness decreases up to a minimum, after that it increases with increasing flow of hot water or nanofluid, while the effectiveness increases with increasing air flow and an improvement is found for the case of high concentration of nanofluid. A comparison between Nusselt numbers and correlations of a double-pipe helical tube heat exchanger shows a significant variation in results. Therefore, we proposed semiempirical correlations to estimate the Nusselt number and friction factor for the triple-fluid helical tube heat exchanger, and the correlations agree well with the experimental results. The semiempirical correlations would be useful for the flow of multiple fluids and several thermal communications in heat exchangers. [ABSTRACT FROM AUTHOR]

• Wind regimes of the largest central-tower CSP plant in the world were simulated. • Heliostats increase surface roughness and decrease the wind speed by 20%. • The wind and sand barriers reduced the wind speed within 100 m. • Suggestions were proposed for managing and designing CSP plants in desert regions. Concentrated solar power (CSP) plants in desert regions disturb the wind regime and blowing sand, thus altering surface erosion and accumulation processes. We investigated wind regimes around the largest central-tower CSP plant in the world in Dubai in a desert environment using computational fluid dynamics to simulate the flows for the entire area, the wind and sand barriers, the central tower, and the heliostats. Over the entire area, increased surface roughness caused by the heliostats reduced wind speed by 20%, but the wind gradually returned to its original speed and direction after the return-flow region. Wind and sand barriers significantly reduced wind speed within 100 m and up to 200 m after the barrier. The area downwind of these barriers showed obvious airflow disruptions, with wind speeds decreasing by more than 50% at a distance of 100 m. The heliostat array reduced wind speed by about 20% locally, but had no effect on the overall wind field. Upwind and downwind of the central tower, the pressure and wind changed greatly, resulting in upwind erosion and downwind sand accumulation. We provide several recommendations regarding the management and design of CSP plants in desert regions. [ABSTRACT FROM AUTHOR]

The vapor compression cooling devices operate on the same principle as heat pumps. In these types of machines thermal energy is transferred from the cold environment to the warmer side using provided power by the compressor. In this study, the effect of air flow rate on the cooling performance of vapor compression cooling devices has been investigated by simulating a designed system in AVL CRUISE™ M program. The simulated model is air-to-air cooling machine and refrigerant R134a was used as circulated gas inside the system. COP value of the system has been calculated in different working conditions and obtained results have been fully discussed. Accordingly, enthalpy variation in every element of the heat pump has been calculated in different working conditions and discussed on P-h diagram. This study presents a simulation method that is a practical solution method in the field of heat pumps, cooling machines and refrigerators which can be considered before installing device in order to have a proper prediction of the system performance. [ABSTRACT FROM AUTHOR]

An experimental investigation has been designed and performed to determine the fluid flow characteristics in a rotor-stator cavity with large gap ratio and inlet at low radius. In this investigation, the particle image velocimetry (PIV) technique is employed for the velocity measurements of airflow in the rotor-stator cavity. Local swirl ratios are calculated from these velocity distributions. A range of parameter combinations of interest in fluid flow characteristics is covered, including combinations of variations in axial location, rotational Reynolds number (denoted as Reφ), and inlet nondimensional mass flow rate (denoted as CW). The results indicate that the flow in the rotor-stator cavity is still dominated by circumferential motion. The velocity is basically unchanged along the circumference. However, the velocity increases with the increase of radial position. In different axial positions, the velocity distribution is different. The closer to the rotor, the more uneven the flow in the rotor-stator cavity is. The disturbance of the rotor rotating motion to the fluid mainly occurs in the high radius region, which should be paid more attention to in the process of reforming the flow field characteristics. To the circumferential velocity of low radius fluid, the Reφ is in direct proportion, while the CW is in inverse. The swirl ratio in the core region is very close to that in the high radius near the wall region of the rotor, which can be inferred to be caused by the backflow in the rotor-stator cavity. [ABSTRACT FROM AUTHOR]

Fluid flow and heat transfer characteristics past four elliptic cylinders arranged in square configuration are numerically investigated in this study. An in-house finite element method code based on streamline upwind Petrov - Galerkin algorithm has been used for simulations of two-dimensional, incompressible and laminar flow of air. Analyses are carried out by changing geometric parameters such as spacing ratio, axis ratio and incident angle. Results in terms of vorticity and temperature contours, Strouhal number, drag and lift coefficients and Nusselt number are studied for all cases. These results show that fluid flow patterns are strongly influenced by geometric parameters, based on which flow can be categorized into different types. A critical spacing ratio is found for some of the configurations, where a steep increase in drag coefficient is encountered. From this study, it is observed that incident angle 22.5 degree gives a higher heat transfer rate compared to the other two configurations (0 and 45 degree). Also, elliptic cylinders (axis ratio of 0.8 and 0.5) have similar Nusselt number value with less drag force compared to circular cylinders (axis ratio of 1.0) which justifies the utilization of elliptic cylinders as an alternative for circular ones. [ABSTRACT FROM AUTHOR]