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A dedicated outdoor air system (DOAS) can be designed to supply 100% of the outside air and meet the latent load of the room with dry air. The objectives of this study were to develop a model of a DOAS equipped with a desiccant wheel and a vapor-compression refrigeration system, build a prototype, validate the model with experimental data, and gain knowledge about the system operation. The test facility was designed with the desiccant wheel downstream of the cooling coil to take advantage of the operating principles of cooling coils and desiccants. A model of the DOAS was developed in the TRNSYS environment. The root mean standard error (RMSE) was used for model validation by comparing the measured air and refrigerant properties with the corresponding calculated values. The results obtained with the developed model showed that the DOAS was able to maintain an indoor humidity ratio depending on outdoor conditions. Laboratory tests were also used to investigate the effect of changes in the regeneration air temperature and the process airflow rate on the process air humidity ratio at the outlet of the wheel. The results are consistent with the technical literature. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the platooning of square-back vehicles on top of a road. When two or three bodies are following each other with a short distance between them, the presence of the preceding body changes significantly the pressure force in front of the following one as a weak flow is present in between. The preceding body plays the role of a buckler and so the following body has to face completely different flow conditions. Therefore the drag coefficient of the following bodies can be drastically reduced as shown on the results. But the reduction is strongly linked to the distance between the bodies and the differences are significant. The numerical simulations are performed around simplified vehicles, namely the square back Ahmed body and the simplified European tractor-trailer geometry. The results are also linked to the shape of the bodies. [ABSTRACT FROM AUTHOR]

Recently, multi-rotor unmanned aerial vehicle (UAV) becomes more and more significantly irreplaceable in the field of plant protection against diseases, pests and weeds of crops. The easy takeoff and landing performance, hover function and high spraying efficiency of UAV are urgently required to spray pesticide for crop timely and effectively, especially in dispersed plots and hilly mountains. In such situations, the current researches about UAV spray application mainly focus on studying the influence of the UAV spraying parameters on the droplet deposition, such as operation height, operation velocity and wind velocity. The deposition and distribution of pesticide droplets on crops which depends on installation position of nozzle and airflow distribution characteristics of UAV are directly related to the control effect of pesticide and crop growth in different growth periods. As a preliminary step, this study focuses on the dynamic development law and distribution characteristics of the downwash air flow for the SLK-5 six-rotor agricultural UAV. Based on compressible Reynolds-averaged Navier-Stokes (RANS) equations with an RNG k-ϵ turbulence model and dynamic mesh technology, the efficient three-dimensional computational fluid dynamics (CFD) method was established to analyze the flow field distribution characteristics of UAV in hover. Then the unsteady interaction flow field of the wing was investigated in detail. The downwash wind speed of the marked points for the SLK-5 UAV in hover was also tested by weather tracker. It was found that the maximum velocity value of the downwash flow was close to 10 m/s; the z-direction velocity was the main body of the wind velocity in the downwash airflow, and the comparison of the wind velocity experiment test and simulation showed that the relative error was less than 12% between the experimental and simulated values of the z-direction velocity at the marked points. Then the flow characteristics of the longitudinal and cross section were analyzed in detail, the results obtained can be used as a reference for drift and sedimentation studies for multi-rotor unmanned aerial vehicle. [ABSTRACT FROM AUTHOR]

The linear momentum theory is used to analyze the power-extraction capability of dual-rotor wind turbines with equal-size rotors. The rotors of a dual-rotor wind turbine are modeled as two separate actuator disks. The stream tube encompassing the front rotor is modeled as two (inner and outer) stream tubes, with the rear rotor being fully enclosed within the front rotor inner stream tube. No assumption is made on airflow pressure in between the rotors. The effect of the front and rear rotor interaction on the airflow within the inner stream tube is included in the analysis. With the results obtained, axial thrusts on front and rear rotors are determined and later used as input for computational fluid dynamics simulation to determine flow characteristics across the rotors. Based on the flow pattern between the rotors, the total power coefficient of a dual-rotor wind turbine is related to the rotor separation distance. A general solution for the dual-rotor wind turbine is developed, which shows that the largest total power coefficient that can be obtained is 0.814, occurring at a rotor separation distance of 2.8 times the rotor diameter. The results of this study are compared with those obtained by similar studies reported in the literature. Discrepancies in the largest possible power coefficient of dual-rotor wind turbines reported in various investigations are examined and discussed. [ABSTRACT FROM AUTHOR]

Numerical simulations of fire-induced smoke movement in the stairwell of a high-rise building are conducted using FDS, version 6.0.1, with default settings. Twelve scenarios are considered. The required fineness of the grid has been determined in earlier work by considering both the fire source and the vent flow, and by assessing the velocity profile at the bottom opening and the vertical distribution of temperature in the stairwell. In the present study, the results including the airflow velocity at the bottom opening, vertical distribution of temperature, the temperature at the middle opening, pressure distribution, and neutral plane height in the stairwell, are compared to experimental data. For the average velocity through the bottom opening, a maximum deviation of 16.23% is obtained. Good agreement is achieved for the vertical temperature inside the stairwell (maximum relative deviation of 12.3%). By analyzing the temperature at the middle opening, it is found that the smoke moves faster than in the experiment. The influence of the staircase on the pressure distribution is demonstrated by comparing two cases: one with and one without staircase. The difference between the pressure inside the stairwell and the pressure outside increases with height, due to fire-induced buoyancy. However, the pressure difference evolution is non-monotonic when there are staircases inside the stairwell. The neutral plane height value, as obtained by post-processing the simulation results, is too high in the simulations, compared to experimental data and the corresponding analytical expression. Finally, the influence of the turbulence model is shown to be negligible. [ABSTRACT FROM AUTHOR]

To better understand the effects of radial air flow quantity and the location of air curtain generator on dust pollution control, the 2–109 2 fully mechanized working face in Xinzhi coal mine (Huozhou Coal Electricity Group Co., Ltd., Shanxi, China) was numerically simulated in the present study. A full-scale physical model of the working face was established; then, based on airflow-dust particle two-phase flowing characteristics, the k-ε-Θ-k p mathematical model was constructed. The comparison between simulation results and field measurements validated the model and the parameter settings. Furthermore, the effects of ventilation parameters on airflow migration and dust diffusion were numerically investigated using FLUENT. The results show that the increase of the radial air flow quantity (denoted as φ ) and the distance of the air curtain generator from working face (denoted as d w ) is beneficial to the formation of a dust-control air curtain. At a constant d w , the dust diffusion distance (denoted as D ) decreases with the increase of φ . At a constant φ , D decreases with the increase of d w when a dust-control air curtain is formed; otherwise, the increase of d w leads to the increase of D . By analyzing the simulation results, the optimal ventilation parameters for 2–109 2 fully mechanized working face and those working faces under similar production conditions are determined as: φ = 240–270 m 3 /min and d w = 20–30 m. [ABSTRACT FROM AUTHOR]

• Higher walking velocity induced significant secondary airflow. • Walking velocity of 1.0 m/s reduced the number of particles settled on patient. • Higher walking velocity potentially reduces the infection risk on a burn patient. An isolation ward requires a highly controlled and contamination-free environment since the settling of bacteria-carrying particles (shed by medical staff) on patients' wounds could cause infections. The present study examines the effect of medical staff's walking movement on airflow distribution and particle dispersion. Three different walking speeds of 0.25 m/s, 0.5 m/s, and 1.0 m/s were assigned to the medical staff. An RNG k-ɛ model based on the Reynolds-Averaged Navier-Stokes (RANS) equation was adopted to predict the airflow, while a Lagrangian tracking approach was selected to track particle dispersion. The reliability of the selected airflow turbulent model and particle tracking approach was validated using published data. The present study showed that the low-pressure region behind the moving medical staff's body has induced wake. The higher walking speed of 1.00 m/s produced a significant secondary airflow of 1.12 m/s, while 0.25 m/s and 0.5 m/s generated lower secondary airflow of 0.41 m/s and 0.53 m/s, respectively. The number of particles settled on the patient at 0.25 m/s, 0.50 m/s, and 1.00 m/s were 31, 18 and 5, respectively. Present finding indicated that a higher walking speed reduces the number of particles settled on the burn patient, therefore potentially reducing the associated nosocomial infection risk. [ABSTRACT FROM AUTHOR]

• The downwash airflow of a coaxial eight-rotor UAV and its effect on droplets are analyzed. • The wind field vortices accompanying the airflow evolution are discussed. • A negative-velocity channel is found to exist in the center of the downwash stream. • The coaxial coupling of rotors offsets the spiral effect of downwash airflow. • The optimum range of spraying distances for coaxial eight-rotor UAV is given. The downwash airflow of a multi-rotor unmanned aerial vehicle (UAV) in hover can improve the penetration rate of droplets in the canopy of fruit trees, but the uncertain distribution of the downwash airflow can also lead to the generation of uneven distribution of droplets. With a co-axial eight-rotor plant protection UAV as the research object, the computational fluid dynamics (CFD) method is adopted in this study to establish the coupled flow field model of the downwash airflow and the two-phase flow model of airflow-droplets in hover. The spatial and temporal distribution law of the downwash airflow is analyzed, and the impact of the motion law of the droplets in the spray field is investigated. The results show that the downwash airflow shifts from an unsteady state to a steady state over time. Various wind vortices such as wake vortex, ground diffusion airflow, and vortex ring are generated during the evolution process, with a "negative velocity channel" of downwash airflow velocity identified in the central region under the rotors. The farther the airflow is from the rotor, the larger the area field of wake vortex airflow. Consequently, there is a gradual coupling of the left and right adjacent wake vortices from mutual independence, with the "spiral effect" of the downwash wind field offset by the mutual coupling of the upper and lower rotors of the UAV. When the installation position of the nozzle falls within the below-rotor region, the distribution of droplet deposition becomes more penetrative than the central axis installation position of the nozzle. It indicates that the below-rotor installation position of the nozzle can prevent droplets from entering into the coupling region of the trailing vortex, which reduces droplet drift. According to the field test, the measurement and simulation results of the downwash air velocity are consistent, with the minimum and maximum relative error reaching 4% and 29%. [ABSTRACT FROM AUTHOR]

An abnormal regulation of the stagger angle deteriorates the internal flow field and pressure pulsation, leading to an augmentation of aero-acoustic noise and vibrations in variable-pitch axial fans. To evaluate the effects of an abnormal stagger angle, the pressure pulsation and transient flow field under normal and abnormal regulations of the stagger angle were simulated using unsteady 3D modelling. The characterization capabilities of the approximate entropy and sample entropy for identifying an abnormal deviation were examined by extracting the features from the static pressure signals. The results indicate that, after an abnormal deviation of stagger angle, the periodic and quasi-periodic pulsation distributions of the static pressure are distinctly hindered, and the impacts of an abnormal deviation angle on the pressure distributions in the time and frequency domains are intensified with increasing deviation degree, resulting in increased pressure fluctuation intensity. The transient flow field clearly changes with time and degree of deviation, and abnormal high- and low-pressure regions are developed. Both the approximate entropy and sample entropy can be used to identify an abnormal blade deviation, but the sample entropy is more suitable for characterizing the effects of deviation degree on the static pressure at the impeller and guide vane outlets. [ABSTRACT FROM AUTHOR]

This study investigates the effect of roof and façade geometry on the mean wind flow and turbulence in street canyons, as well as the ability of numerical simulation techniques in capturing the flow features. Numerical experiments, using the large eddy simulation FLUENT code, have been conducted under neutral stability conditions to test 5 building geometries: i) flat roof, ii) pitched roof, iii) round roof, iv) terraced building and v) building with balconies. Wind tunnel experiments were also conducted for the first three geometries. The simulation and experimental setups were closely matched and both featured configurations consisting of seven building arrays. The results from the physical and numerical experiments concur that (i) in-canyon vortex dynamics and over-canopy flow conditions, are strongly dependent on the geometric features of the buildings, and (ii) pitched and round roof geometries increase in-canyon mean and turbulent velocities, as well as the depth of the shear layer. The findings provide novel insight on the sensitivity of the flow and turbulence fields, as well as the simulation quality, to urban topography, inflow conditions, and the Reynolds number. They also underline the influence on the flow of small-scale features such as balconies, which are often ignored in prior literature. [ABSTRACT FROM AUTHOR]

Numerical simulations and industrial experiments were conducted to study the effect of the stoichiometric ratio of the fuel-rich flow (0.46, 0.49, 0.51, 0.53, and 0.55) on the flow, combustion, and NOx emission characteristics in a 600-megawatt electric (MWe) super-critical down-fired boiler with multiple-injection and multiple-staging combustion technology. The simulation results indicate that as the stoichiometric ratio of the fuel-rich flow increases from 0.46 to 0.55, the flow fields all form a symmetricW-shaped pattern; this is identical to the symmetric temperature distributions obtained experimentally. The ability of downward coal/air flows to entrain high-temperature gases from the recirculation zone weakens, and the airflow declination angle in tertiary-air regions and the downward flame penetration depth decrease. Coal burnout is enhanced. The temperature in the lower furnace rises, the high-temperature (≥1,700 K) area gradually increases from 64 to 120 m2, the carbon in the fly ash at the furnace exit decreases from 9.41 to 4.23%, and NOx emissions increase from 860 to 1,045 mg=m3 at 6% O2. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) airflows provide a means of generating air motion by a gas discharge across two electrodes without the need for moving parts. A two-dimensional numerical model for a wire-to-grid EHD air blower is developed, validated against previous data, and used to investigate the influence of key design parameters on blower efficiency, including the emitter wire diameter, the blower height, the locations of the collecting surfaces and grid wires, and the collecting grid density. The optimal locations of both collectors from the corona wire are determined based on blower efficiency at a fixed operating power, resulting in improvements in the average outlet velocity between 9% and 15%, depending on blower thickness. The presence of the grid has a strong influence on the electric field distribution and increases the blower performance, with higher flow, lower operating voltage and reduced blower size. An investigation into the effect of grid density reveals that using coarse collecting grids is generally beneficial, leading to higher efficiency with lower pressure losses. [ABSTRACT FROM AUTHOR]

Analysis of the slipstream development around the high-speed trains in tunnels would provide references for assessing the transient gust loads on trackside workers and trackside furniture in tunnels. This paper focuses on the computational analysis of the slipstream caused by high-speed trains passing through double-track tunnels with a cross-sectional area of 100 m2. Three-dimensional unsteady compressible Reynolds-averaged Navier-Stokes equations and a realizable k-ε turbulence model were used to describe the airflow characteristics around a high-speed train in the tunnel. The moving boundary problem was treated using the sliding mesh technology. Three cases were simulated in this paper, including two tunnel lengths and two different configurations of the train. The train speed in these three cases was 250 km/h. The accuracy of the numerical method was validated by the experimental data from full-scale tests, and reasonable consistency was obtained. The results show that the flow field around the high-speed trains can be divided into three distinct regions: the region in front of the train nose, the annular region and the wake region. The slipstream development along the two sides of train is not in balance and offsets to the narrow side in the double-track tunnels. Due to the piston effect, the slipstream has a larger peak value in the tunnel than in open air. The tunnel length, train length and length ratio affect the slipstream velocities; in particular, the velocities increase with longer trains. Moreover, the propagation of pressure waves also induces the slipstream fluctuations: substantial velocity fluctuations mainly occur in front of the train, and weaken with the decrease in amplitude of the pressure wave. [ABSTRACT FROM AUTHOR]

Dust collection plants are widely used in various industrial sectors to collect, transport, and separate dust and solid particles from air and process gases. The dust collection and particle classification performance of the cyclones in such plants is therefore of considerable importance. However, the time characteristics of the performance remain poorly understood. In this study, we measured the dust collection efficiency, partial separation efficiency, and pressure drop of a cyclone using a real powder with different particle diameters. These results were compared with those from a particle tracking numerical simulation of the dust collection process. We found that the dust collection efficiency decreases by approximately 10% over the first 60 min of operation, and then remains constant. A similar trend was observed in the pressure drop. The numerical results for the partial separation efficiency diverge from the experimentally measured values. This is believed to be because the numerical model does not consider the effect of particle motion on the flow, and therefore cannot replicate the reduction in velocity of the swirling flow resulting from an increase in the number of particles. The data reported in this study will enable improved cyclone designs for large-scale dust collection, and also highlight the need for improved numerical techniques to accurately simulate the time characteristics of particles and flow in a cyclone. [ABSTRACT FROM AUTHOR]

This study investigates four influence factors of flow distribution in multi-circuit evaporators with distributor, including distributor inlet tube length, inclination angle, uneven airflow, and feeder tube length. Experimental tests and numerical simulations were carried out to evaluate the effect of these factors on superheat uniformity and refrigerant distribution performance. Additionally, a feeder tube compensation method for optimizing refrigerant distribution is presented that involves pressure drop fine-tuning of the feeder tube in each circuit coupled with a main expansion device to obtain more uniform superheat performance at all circuit outlets. To adopt this method, a model was developed to predict the best feeder tube length for each circuit. Experimental results show that when using feeder tubes with predicted lengths in condition of uneven airflow, the superheat uniformity was improved significantly, and up to 35% evaporator cooling capacity could be enhanced when airflow non-uniformity coefficient ( F a i r ) was 0.6. [ABSTRACT FROM AUTHOR]

In this work, natural convection heat transfer from two horizontally attached cylinders in air has been studied numerically over the range of Rayleigh number 10 ⩽ Ra ⩽ 10 5 . A new model proposed by Bejan et al. (1995) is applied here, and it has been proved to be a more accurate and effective method for the numerical simulation of the natural convection in free space than other models used previously. Furthermore, the representative results for streamlines, isothermal contours, local Nusselt number and local drag coefficients have been presented with different Rayleigh numbers. It can be observed that there form two recirculation vortexes in the wake region when the two plumes begin to merge, and their sizes grow with the increasing Rayleigh number due to the downstream movement of the front stagnation point and the upstream movement of the separation point. Owing to the interactions of their plumes, the location of the maximum value of local Nusselt number moves downstream along the cylinder surface, i.e., it displaces to 133–150° depending on the Rayleigh number whereas it always occurs at the front stagnation point corresponding to 90° for a single cylinder. However, because the thinnest boundary layer in this work still hardly penetrates the small clearance between them and then influences their heat transfer, their interactions are independent of the Rayleigh number. Finally, a new correlating equation of the average Nusselt number with the Rayleigh number for the present configuration, has been proposed. [ABSTRACT FROM AUTHOR]

The magnitude of air velocity at the fan outlet of agricultural sprayers influences the aerodynamic airflow and is a key factor in the flow structure. The effect of varying the fan output speed in aerodynamic airflow during work at different speeds of movement of the sprayer, using computer simulation (CFD) is analyzed in this work. Simulations of output speeds were conducted in the diffuser fan of 40, 45 and 50 m/s with a fan output width of 115 mm and considering the sprayer without motion and working speeds of 2.18, 4.5 and 6.35 km / h. The aerodynamic behavior of the airflow for each variant was analyzed. The increase in the fan output speed produces an accelerated wear on the core of the current; therefore the use of lower speeds enhances aerodynamic flow. [ABSTRACT FROM AUTHOR]

The direction and distribution of the air flow in the airlock are important basis to ensure the safety of person and equipment in the centralised protection, but its measurement is still not mature at present. This article is based on the three equations. The control volume method is used to carry out the discretisation. With smoke tracking technology in the process of opening the door, the concentration of pollutants in the gradual process is studied. The influence of two kinds of smoke injection modes on the cabin air is obtained when the air supply is 200, 500, 1000 and 1200 m3/h. The results show that when the air supply volume is small, the pollutants will enter into the cabin, and the indoor air is polluted seriously. For two smoke injection methods, we should avoid smog forming pollutants to flow directly in front of the door to obtain better cabin air environment. Through the comparison of the test and CFD numerical simulation results, the experimental data are verified. The accuracy of the obtained data is high, which provides a theoretical basis for the control, isolation and exclusion of the pollutants in the key areas of the ship. [ABSTRACT FROM AUTHOR]

In order to explore the characteristics of airflow field in flat chamber stopes, via combining the similarity theory, we have established the similar experimental models and analysed the time-averaged characteristics of flow field of turbulent jet in flat chambers. Thus, the following results have been obtained: the flow velocity ratio of ambient jet in chambers is the major parameter affecting the jet flow characteristics; the average maximum jet width increases linearly with the increase of flow velocity ratio; the average maximum jet length has a linear relationship with flow velocity ratio; the flow velocity of jet axis decays along the jet; the jet flow at high flow velocity ratio decays more slowly than it at low flow velocity ratio. The research results of experiment play an important practical significance and reference value for ventilation and dust extraction in flat chamber stopes. [ABSTRACT FROM AUTHOR]

In this paper, three-dimensional wind flow patterns over a star dune under a longitudinal (W, 270°) and transverse airflow (ENE, 70°) were examined using computational fluid dynamics (CFD) simulations. New surveying techniques of airborne LiDAR and DGPS allow for establishment of the realistic digital model of the star dune. Simulation results were then validated by field measurement using three-dimensional (3D) ultrasonic anemometers combined with arrays of HOBO cup anemometers. Results show that incident flow conditions (longitudinal or transverse airflow) controlled by the angle between incident flow and dune crestline exert great impact on wind flow patterns over the star dune. In periods of longitudinal airflow, a marked feature of wind flow pattern was flow deflection. Wind erosion occurs on both sides of WNW and S sides during W wind and its main effect was to prolong the star dune longitudinally. However, leeside flow separation and reversal were obvious under transverse airflow. The main effect of ENE wind was to promote the upward growth of the star dune. The CFD simulation of 3D wind flows over complex dune system presents great potential for geomorphological research, enabling new insights into complex dune geomorphology and dynamics. [ABSTRACT FROM AUTHOR]

The lubrication and cooling design is important for high-speed rolling bearings. A multiphase numerical simulation and the corresponding tests were conducted to investigate the stratified air-oil flow inside jet cooling ball bearings. The simulated results of the volume fraction distribution has the same trend with measured observations. The heat transfer was also considered. It was found that the temperature distribution of the bearing was affected by the volume fraction distribution. The higher temperature always appears in the lower oil volume fraction region. The conventional oil-jet lubrication mechanism cannot achieve an efficient cooling on the inner ring of the high-speed ball bearing. The oil volume fraction increases with an increasing nozzle number. The number should not be larger than six for increasing the oil volume fraction. The jet velocity and the oil flow rate have great effects on the average oil volume fraction inside the bearing rather than the oil volume fraction distribution around the circumference. The flow pattern inside the jet-cooling ball bearing is significant for its temperature forecast and control. [ABSTRACT FROM AUTHOR]

In this study, a fully unsteady computational fluid dynamics (CFD) model was used and the transient airflow properties during the entire breathing cycle, including inhalation and exhalation in a human nasal cavity, were evaluated. Unsteady particle tracking was performed to find the particle motion and deposition in the nasal airway using a Lagrangian approach. In most of earlier computer simulations, the assumption of quasi-steady or steady airflows averaged over the inhalation cycle were typically used to reduce the computational cost. In the present work particular attention was given to assessing the accuracy of these assumptions and their consequence on particle deposition in a human nasal cavity with paranasal sinuses. The simulation results for the airflow field showed significant differences between the unsteady and quasi-steady cases at low breathing rates near the beginning and end of the inspiration cycle. For breathing under a rest condition with a frequency of 0.25 Hz, the quasi-steady airflow assumption in the nasal cavity was found to be reasonable when the instantaneous Strouhal number was smaller than 0.2. The instantaneous deposition of micro-particles was also studied, and the effects of unsteady accelerating and decelerating flows on the deposition fraction were examined. The simulation results showed that the deposition fractions were affected by the accelerating and decelerating airflows during the inhalation phase. The simulated micro-particle depositions under the cyclic breathing condition were compared with those for steady breathing with an equivalent mean airflow rate. It was found that while the general trend was similar, the steady breathing simulation with the mean airflow rate during inhalation cannot accurately predict the total micro-particle deposition for cyclic breathing, particularly for 1–5 µm particles. Furthermore, the predicted regional depositions by the steady breathing were markedly different from those obtained under cyclic breathing. [ABSTRACT FROM AUTHOR]

This study established the three-dimensionally random structures of fibrous filters, with fiber diameters in the range of 10 to 20 μm and solid volume fractions (SVFs) in the range of 12 to 19%, in order to explore the filtration process inside the fibrous filters. The computational fluid dynamics (CFD), coupled with the discrete element method (DEM), was applied to simulate the airflow, the motion of particles, and the interactions between particles, fibers and fluid. The filtration efficiency and pressure drop of the filters were calculated and analyzed in CFD-DEM and the results were validated by the semi-analytical models. In addition, the correlations between filtration performance and fiber structures, particle parameters and fluid properties were investigated. It was found that the changes in key parameters (e.g., particle diameter, fiber diameter and fluid velocity) had significant effects on filtration performance. [ABSTRACT FROM AUTHOR]

The importance of accounting for the temperature dependence of air properties in numerical simulations of air flows over pinned heat sinks is demonstrated by comparisons with recently published experiments. Numerical simulations, based on a conjugate heat transfer analysis, using the RANS-based modified k-ω turbulence model, with temperature-dependent air properties, are shown to be in significantly better agreement with experimental measurements of pressure drop, heat transfer coefficient, and heat sink base temperature, than those which employ constant air properties. [ABSTRACT FROM AUTHOR]

Well-resolved direct numerical simulation (DNS) is applied to investigate strongly heated air flow in a vertical pipe ( L = 30 D ) at inlet Reynolds numbers of Re 0 = 4240 and 6020. The DNS is based on the experimental cases of Shehata and McEligot (1995) and shows excellent agreement with heat-transfer and flow statistical results. Flow relaminarization is observed in the strongly heated cases. We apply a new semi-local wall coordinate to replace the conventional one. With the semi-local wall coordinates, which considers the local property variation, both the velocity and temperature fields show the process of relaminarization. This relaminarization is also indicated by the significant decrease of turbulence intensity and Reynolds shear stress. In the quasi-laminar flow, the viscous sublayer becomes thicker. Turbulence in this layer shows a growing anisotropic character. And turbulence in the pipe center becomes approximately isotropic. This two-layer character is clearly displayed by flow visualization. [ABSTRACT FROM AUTHOR]

Particle deposition in two-dimensional turbulent duct air flows with uniform, expanding or contracting cross-section was studied by CFD simulation. The Reynolds stress turbulent model (RSM) with UDF correction and discrete particle model (DPM) were adopted to predict air flow fields and particle deposition rate. After numerical validation of air velocity profiles and particle deposition velocity in uniform duct, the air flow field structures, flow drag and particle deposition behaviors in expanding and contracting ducts with different air velocities and particle sizes were investigated and compared with uniform duct case. It was found that particle deposition velocity is overall reduced in expanding duct while enhanced in contracting duct. However, the modification magnitude of deposition velocity is significant discrepant for different particle sizes due to the role of near-wall turbulent eddies. For expanding duct cases, the particle deposition velocities are reduced about one or two orders of magnitude for large particles ( d p > 3 μ m ) but less than 5 times for small particles ( d p < 3 μ m ), compared with uniform duct cases. For contracting duct cases, the particle deposition velocities are increased less than 7 times for large particles while about 20–60 times for small particles. Besides, the deposition mechanisms of particles in expanding and contracting duct were also studied and discussed. [ABSTRACT FROM AUTHOR]

The heat transfer performance variations of condensers that are caused by non-uniform distributions of air flows are investigated using a numerical simulation method. A heat exchanger designed for the outdoor unit of a heat pump system is selected and represented using a numerical model. A non-uniform profile of the air velocity is constructed through measuring the air velocity at various locations on the outdoor unit. Numerical analyses are conducted for various refrigerant circuits and air flow conditions. The results demonstrate that the heat transfer capacity is reduced depending on the air flow rate and the refrigerant circuit configuration. It is also demonstrated that the capacity reduction rate is increased as the average air velocity decreases. [ABSTRACT FROM AUTHOR]

Using different tip speed ratios, the near-wake velocity field of a horizontal-axis wind turbine (HAWT) model was simulated. The distributions of the near-wake velocity behind the HAWT rotor are obtained. Furthermore, the development of the wake is shown. The resulting data can be used to identify and better understand the physical attributes of the complex flow field, as well as to aid in the accurate prediction of the HAWT's performance. Calculations indicate that the axial flow downstream of the near-wake region displays obvious three-dimensional properties. The axial component of air flow velocity is larger than the tangential and radial velocity components. For wind turbines of varying heights, the velocity profiles for each component are similar in the near-wake region. Velocity loss exists downstream of the wind turbine's near-wake region, decreasing with an increase in axial position downstream of the turbine. The rate of decrease in center velocity is largest at the near-wake region from the trailing edge of the blade to the position of twice the chord length downstream of the turbine. At the position of four times the chord length downstream, the lowest velocity is restored to over 70% of the free incoming flow velocity. [ABSTRACT FROM AUTHOR]

• The guide vane is added to the air inlet chamber of the intercooler. • An end-to-end model of the intercooler guide vane based on PSO-SVR algorithm. • Structure parameters of guide vane are optimized using genetic algorithm. In order to fundamentally solve the problem of poor air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler, which leads to poor heat exchange effect, this paper innovatively proposes to add a guide vane in the air chamber of the intercooler. The air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler is investigated under different structural parameters of guide vane based on the established end-to-end model. In fact, the end-to-end prediction model is innovatively proposed to characterize the relationship between the structural parameters of guide vane and performance parameters without conducting the high-cost and long-term experiments or numerical simulation. Besides, structure parameters of guide vane with the optimal airflow uniformity coefficient are obtained using genetic algorithm (GA), that is, the diversion angle (α) is 18°, the width of rectangular holes in the guide vane (L) is 6 mm and the number of rectangular holes in the guide vane (N) is 3. To demonstrate the effectiveness of the proposed method, the optimized intercooler is validated and it is found that the airflow uniformity coefficient of the optimized intercooler is 0.983, which is 5.25% higher than the original structure, the outlet temperature is reduced by 8.2 °C. [ABSTRACT FROM AUTHOR]

Drying is a process of removing water from products down to a specific moisture content. It is an energy-intensive process widely-used for grain and biomass processing. Because of the complicated thermodynamics and transport phenomena involved in drying, it is challenging to analyse and optimise drying operations. In this study, computer simulations using a transient model are performed to simulate the real-time paddy drying, and analyse the exergy components, exergy efficiency, exergy loss and destruction of industrial-scale drying process under changing drying air temperature (60–80 °C) and flow velocity (0.56–0.83 m/s) and initial moisture content (0.22–0.3 g water/g wet matter) on a circulation counter-flow paddy dryer. Results show our model can predict paddy moisture content and temperature with mean relative deviations of 5.5% and 1.42%, respectively. Exergy efficiency of drying process is specified to be in the range of 28.75–35.68%. Main factor affecting drying rate and energy consumption in high moisture content regions of drying process is drying air flow velocity while that in low moisture content regions is drying air temperature. We also propose control strategy based on two-stage variable ventilation parameters that achieves high exergy utilization level, high drying rate, and high product quality for grain drying. • Transient model simulation replaced field experiments in industrial-scale grain drying. • Simulated and analysed detailed exergetic components. • Exergy analyses have been reported changing various parameters. • Presented energy-saving strategy of hot air drying based on process control. [ABSTRACT FROM AUTHOR]

The explosion-type phenomenon is an extremely complex physico-chemical process leading to the physical change of objects and objectives met on the propagation pathway as well as to the chemical change of underground atmosphere in the area of influence. Diming the development of the explosion-type phenomenon, due to the energy of the dynamic wave, there are generated significant mechanical effects at the level of the affected mining works as well as at the level of ventilation constructions. In addition, due to intense burning reactions at high temperatures, there occur major effects related to the composition and concentration of the underground atmosphere in the area of influence. Changes, respectively perturbations occurring after the event at the level of underground works or coal faces, endanger the entire working staff and may lead to the occurrence of similar phenomena. An explosion has direct effect upon the ventilation network due to the change of operational parameters of main ventilation fans. This leads to a different post-event natural repartition of air flows at branch level. Also, the underground atmosphere in the coal face changes, fa ct which leads to the increase of the potential risk of a new underground explosion occurrence, respectively to major difficulties regarding the withdrawal of work staff affected and of specialized intervention staff. Prior establishment of post-event work environment is performed through simulations on a ventilation network using the Australian VENTSIM VISUAL ADVANCED software. [ABSTRACT FROM AUTHOR]

Previous simulation and observations showed that, the air flow field at windward and leeward side of insulator string will probably be different if the wind velocity is over a certain value, and thus causing the imparity of contamination degree at the two sides. In this paper, fan-shaped non-uniform polluting method was used to artificially simulate the different pollution severity at windward and leeward side of insulator string. Then, the effects of fan-shaped non-uniform pollution on ac flashover performance of 5 types of insulators were discussed. Test results indicate that, SDD, the ratio SDD of windward to leeward side (W/L), the occupation ratio of leeward side (k), will affect the ac flashover performance of insulator string. U50 and SDD still can be expressed by the negative power function. A reduction in W/L from 1/1 to 1/15 would give a decrease about 23% in a value, which causes U50 reducing about 25%, but n value changes little. The correction method proposed by EPRI is also applicable for fan-shaped non-uniform pollution, but has difference. A larger creepage distance of insulator does not mean that the creepage distance utilization rate is higher. Due to the influence of fan-shaped non-uniform pollution, the existing insulation configuration of transmission lines in heavily polluted areas may not satisfy the required insulation margin. The results have certain reference significance for the design and selection of transmission line external insulation. [ABSTRACT FROM PUBLISHER]

This research aimed to reduce excessive dust concentration in flat chambers and to explore the main factors affecting dust motion. Based on the theory of gas-solid two phase flow and airflow field, a physical model was established. Numerical simulation results of dust concentration distributions in flat chambers, which came from fluent, fluid mechanics computational software, were basically concordant with experimental data. Research results showed the following aspects. (1) The main factors affecting dust motion in flat chambers laid in the jet flow zone and reflux zone. (2) When mean flow velocity in flat chambers ranged from 1.0 m/s~3.0 m/s, increases in the mean flow velocity resulted in decreases in dust concentration. (3) With the increase in distance away from working faces, air flow velocity and dust concentrations undulated and appeared to have a downward trend in cross sections. Circulation between the jet flow and reflux resulted in the elimination of dust in flat chambers. [ABSTRACT FROM AUTHOR]

The air flow'field of a foreign fiber separator is simulated numerically. Effects of design parameters such as the nozzle diameter and entrance width of the noil box on the air velocity along nozzle axis, turbulence intensity, and jet deflection distance are studied. Larger nozzle diameters and larger entrance widths of the noil box are advantageous to the elimination of foreign fibers. The results provide a theoretical basis for the design of foreign fiber separators. [ABSTRACT FROM AUTHOR]

The objective of this study is to analyze the solid and fluid flow behaviors inside a rotary drum using computational fluid dynamics (CFD). The CFD model developed was based on an Eulerian–Eulerian multiphase flow approach. The capability of the multiphase CFD model to predict the transverse and axial solid flow patterns, the fluid flow profile, and particle residence time was assessed. The model was used to study the effects of drum rotational speed, filling degree, feed rate, and drum inclination angle. It was verified using experimental results of particle and fluid velocities and residence time. The experiments were conducted on pilot scale rotary drums. As could be proved by measured and simulated results, the particle flow near the bed surface exerted a strong entrainment effect on the transverse air flow in the proximity of the bed surface. The study demonstrated the capability of the multiphase CFD model to predict the particle and fluid flow behaviors inside a rotary drum simultaneously. [ABSTRACT FROM AUTHOR]

Turbulence statistics from two three-dimensional direct numerical simulations of planar n -heptane/air turbulent jets are compared to assess the effect of the gas-phase species diffusion model on flame dynamics and soot formation. The Reynolds number based on the initial jet width and velocity is around 15, 000, corresponding to a Taylor scale Reynolds number in the range 100 ≤ Re λ ≤ 150. In one simulation, multicomponent transport based on a mixture-averaged approach is employed, while in the other the gas-phase species Lewis numbers are set equal to unity. The statistics of temperature and major species obtained with the mixture-averaged formulation are very similar to those in the unity Lewis number case. In both cases, the statistics of temperature are captured with remarkable accuracy by a laminar flamelet model with unity Lewis numbers. On the contrary, a flamelet with a mixture-averaged diffusion model, which corresponds to the model used in the multi-component diffusion three-dimensional DNS, produces significant differences with respect to the DNS results. The total mass of soot precursors decreases by 20–30% with the unity Lewis number approximation, and their distribution is more homogeneous in space and time. Due to the non-linearity of the soot growth rate with respect to the precursors’ concentration, the soot mass yield decreases by a factor of two. Being strongly affected by coagulation, soot number density is not altered significantly if the unity Lewis number model is used rather than the mixture-averaged diffusion. The dominant role of turbulent transport over differential diffusion effects is expected to become more pronounced for higher Reynolds numbers. [ABSTRACT FROM AUTHOR]

Coal and gangue underground pneumatic separation is of key importance for green mining. Two kinds of arrangement schemes for high-pressure value used in pneumatic separation system are proposed in this study. Pneumatic separation effects are examined under different arrangement of high-pressure value. Here, theoretical pneumatic separation distance formulas of mineral particles affected by different airflow directions are derived and validated by a series of numerical simulations and orthogonal experiments. In the following analysis, the effects of gangue diameter (d), conveyor velocity (v0), and the height difference between conveyor belt and air nozzle (hp) are mainly considered. The numerical simulation and experimental results indicate that pneumatic separation effects under the condition of u and v0 being in the opposite direction will be better than that of u and v0 being in the same direction. The pneumatic separation distance ΔS shows a decreasing trend with the increasing of the three factors. The study also shows that gangue diameter has the most significant influence on separation distance, followed by conveyor velocity v0 and height difference hp. [ABSTRACT FROM AUTHOR]

The article focuses on the robustness of a CFD-based procedure for the quantitative evaluation of the nasal airflow. CFD ability to yield robust results with respect to the unavoidable procedural and modeling inaccuracies must be demonstrated to allow this tool to become part of the clinical practice in this field. The present article specifically addresses the sensitivity of the CFD procedure to the spatial resolution of the available CT scans, as well as to the choice of the segmentation level of the CT images. We found no critical problems concerning these issues; nevertheless, the choice of the segmentation level is potentially delicate if carried out by an untrained operator. [ABSTRACT FROM AUTHOR]

Numerical study is made of heat transfer enhancement in the narrow channel with insulated walls in air steady flow around a heated spherical dimple, when its relative depth is varied from 0 to 0.26 (in terms of spot diameter) at a defined Reynolds number 4 × 10 4 based on bulk velocity and dimple spot diameter. The applicability of multiblock computational technologies for solution of Reynolds and energy equations with the implication of an implicit factorized finite-volume algorithm and overlapping different-scale structured grids of different topology, as well as the verification of the shear stress transfer model (SST model) modified with regard to the streamline curvature within the framework of Leschziner–Rodi–Isaev’s approach is assessed from the comparison of numerical predictions obtained by different SSTM versions. Flow regimes in a spherical dimple, as its depth is increased, are classified on the basis of the analysis of change in the jet–vortex flow structure in the dimple and its wake in the channel. In what follows, special attention is paid to asymmetric flow around a dimple with the greatest vortex heat transfer enhancement. [ABSTRACT FROM AUTHOR]

Numerical simulations are carried out to study the unsteady air flow and heat transfer in a partitioned triangular cavity of differentially heated from inclined walls and heat source placed at the bottom wall. The finite volume numerical method has been employed to solve the governing equations. The grid sensitivity test has been carried out and obtained results have been validated against experimental results. The dependency of several parameters on fluid flow and heat transfer is studied including Rayleigh number from 10 3 to 10 6 , heater size from 0.2 to 0.6, heater position from 0.3 to 0.7 and aspect ratio from 0.2 to 1.0 with a fixed Prandtl number of 0.72 (air). A conductive partition of infinite conductivity is placed at the middle of the enclosure, which means that only heat can freely transfer between two fluid zones through the partition. Results are presented as a form of isotherms and streamlines. Also, heat transfer is presented as a form of Nusselt number. Both transient and steady states of solutions are presented in this study. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the transient 3D numerical simulations of natural convection of air around a circular finned tube (24.9 mm OD ) kept in a small chimney. The annular plain fins are considered in this study. The effects of fin spacing to fin diameter ratio (0.057 mm ⩽ S / D f ⩽ 0.24 mm), chimney height (400–1000 mm) and ambient to surface temperature difference (10 K ⩽ T s ⩽ 65 K) on the heat transfer and the driving force have been investigated. The results are presented in terms of the temperature contours, velocity vectors, heat transfer and the driving force. It has been found that the heat transfer coefficient increases with an increase in the fin spacing upto an optimum value ( S = 8 mm) for all the fin geometries, and beyond S = 8 mm, the heat transfer coefficient decreases. The separation of the thermal boundary layer with a variation in the fin spacing and its effects on the heat transfer and driving force has been shown. For a fixed fin spacing, the heat transfer rate, heat transfer coefficient and the driving force increases with an increase in the fin diameter, however, for D f > 41 mm, the rate of increase in the heat transfer coefficient reduces. The heat transfer coefficient increases with an increase in the chimney height and it has been found that the effect of chimney height on the heat transfer coefficient is a resultant effect of the air outlet temperature and the driving force generated by the chimney. The base to ambient temperature difference has been varied to observe the temperature sensitivity on the heat transfer coefficient and flow patterns. In the last section, various circular and elliptical tube designs have been investigated, and it is found that, the elliptical tube with minimum ellipticity ( b / a = 0.33) and circular tube with smallest diameter (7 mm) provides better heat transfer coefficient than the other circular and elliptical designs. [ABSTRACT FROM AUTHOR]

Draining a viscous liquid from a partially filled, finite-size cylindrical tank through a tube imbedded in the liquid is viewed as selective withdrawal from the lower layer of viscous liquid in an identical tank, with the fluid of the upper layer being air or low-viscosity gas. Contrary to previous approaches that simplify the problem by considering a tank of infinite extent in the horizontal direction and approximating the withdrawal tube as a point mass sink, the model presented here employs a detailed flow geometry of a finite-size tank with a withdrawal tube of comparable radius. An Arbitrary Lagrangian–Eulerian (ALE) method is utilized in the numerical model to track the motion and deformation of the free surface. The results of simulations made with the present model show that the mean curvature at the tip of the free surface depends on the flow rate of drainage and the distance of the unperturbed free surface from the tube inlet; the mean curvature at the free surface tip is not influenced by the size of the tank when the tank-to-tube radius ratio exceeds a value of 30, in agreement with experimental results. The simulations reveal that a critical parameter for the system under investigation is the ratio of tube wall or tube support thickness or the horizontal distance of liquid from the tube inlet, at the level of the inlet, to the tube radius. When this parameter is correctly identified, results of simulations collapse on experimental results regarding the mean curvature of free surface at the tip. [ABSTRACT FROM AUTHOR]