Swirling Air Flow Research Articles

Development of the Universal Air Collector Design for Measuring the Flow Rate of Swirling Air Flow Using an Integral Thermoanemometer

Measurement of the swirling air flow rate and average speed of air at air distribution units of ventilation systems is a rather difficult task due to the fact that the air flow enters the measuring device at different angles. As a result, significant measurement errors can occur when using point thermoanemometers or other flow meters. The use of integral anemometers facilitates the measurement process. However, it is necessary to eliminate the errors associated with changes in the angle of the air flow to the sensing element of the measuring device. To do this, it is necessary to ensure a rectilinear structure of the air flow using a transitional air collector and rectifier. The aim of this paper is to develop a design of an air collector device that will allow to measure the flow rate of a swirling air flow. The objectives of the paper are to optimize the geometrical parameters of the air collector to ensure a rectilinear flow, minimize its dimensions and aerodynamic drag. The correctness of the air collector design was evaluated by matching the calibration characteristic of the probe of an integral thermoanemometer in the presence of a vortex diffuser in front of the air collector and in its absence. The proposed device has a rectangular shape and consists of a receiver, a rectifying grid, a chamber, an accelerating and stabilizing section, at the outlet of which a thermoanemometer probe is installed. The receiver and the accelerating section are tapered along their length, while the chamber and the stabilizing section have a constant cross-section. The rectifying grid is installed inside the chamber and has a square-shaped honeycomb structure. Several options of the air collector design with different geometrical parameters were studied using computer modelling. The dependence of aerodynamic drag on air flow was plotted. The optimal design of the air collector was chosen, for which a life-size physical model was created. The calibration characteristics of the measuring probe with an air collector were experimentally obtained when a swirling air flow was applied. The developed universal air collector allows the air flow rate measurement at the outlets of almost any air distribution devices of ventilation systems of buildings.

Study the effect of axially perforated baffle plate with multiple opposite-oriented trapezoidal flow deflectors in an air–water tubular heat exchanger

Purpose The research focused on analysing a unique type of heat exchanger that uses swirling air flow over heated tubes. This heat exchanger includes a round baffle plate with holes and opposite-oriented trapezoidal air deflectors attached at different angles. The deflectors are spaced at various distances, and the tubes are arranged in a circular pattern while maintaining a constant heat flux. Design/methodology/approach This setup is housed inside a circular duct with airflow in the longitudinal direction. The study examined the impact of different inclination angles and pitch ratios on the performance of the heat exchanger within a specific range of Reynolds numbers. Findings The findings revealed that the angle of inclination significantly affected the flow velocity, with higher angles resulting in increased velocity. The heat transfer performance was best at lower inclination angles and pitch ratios. Flow resistance decreased with increasing angle of inclination and pitch ratio. Originality/value The average thermal enhancement factor decreased with higher inclination angles, with the maximum value observed as 0.94 at a pitch ratio of 1 at an angle of 30°.

THERMO-FLUID PERFORMANCE COMPARISON OF AN IN-LINE PERFORATED BAFFLE WITH OPPOSITELY ORIENTED RECTANGULAR-WING STRUCTURE IN TURBULENT HEAT EXCHANGER

This research study examined the effects of a novel swirl airflow design on the rate of heat transfer in a tubular heat exchanger with axial flow. The novel design consisted of 16 rectangular air deflectors placed in opposite directions, positioned at varying angles of inclination. These deflectors were embedded on circular perforated baffle plates, which were spaced equidistantly apart at different pitch ratios. Hot water was supplied to heat exchanger tubes whose arrangement remained constant throughout the experiment, while atmospheric air is flown over tube bundle at Reynolds number that ranged from 16 × 10<sup>3</sup> to 3 × 10<sup>4</sup> . The effect of pitch ratio and inclination angle on the thermal enhancement factor was experimentally analyzed. The findings demonstrated that using an opposite-oriented deflector baffle plate with an inclination angle of 30 deg and a pitch ratio of 1 resulted in an average improvement of 1.17 in the thermal enhancement factor compared to a heat exchanger without a baffle plate, tested under similar conditions.

Experimental investigation on a novel external-mixing prefilming atomizer for advanced aircraft engines

As a crucial component of aircraft engine combustors, the external-mixing prefilming atomizer exhibits significant advantages in enhancing combustion efficiency and reducing pollutant emissions. However, the intricate relationship between spray characteristics, droplet breakup mechanisms, flow fields, and geometric parameters of the external-mixing prefilming atomizer remains poorly understood. This paper presents a novel external-mixing prefilming atomizer, aiming to address this knowledge gap. Additionally, particle image velocimetry (PIV), high-speed Schlieren photography, and particle image analysis (PIA) measuring systems were employed to gain insights into the spray characteristics and droplet breakup mechanism of the external-mixing prefilming atomizer under various swirl flow fields. The obtained results reveal the formation of two distinct regions, namely a low-density area and a high-density area. Notably, the number of droplets in the low-density area, located within 0–2 cm from the central axis, is significantly lower compared to the high-density area situated further away from the central axis. The breakup of droplets in the low-density region is primarily attributed to the inner swirl airflow, while the outer swirl airflow induces droplet breakup in the high-density region. As the Reynolds number of the incoming flow increases, the air-liquid ratio (ALR) and Weber number also increase, thereby enhancing the fuel breakup effect. The Schlieren results reveal a two-stage spray development process. The initial stage is characterized by the dominant momentum of the dense spray, with the spray tip penetration (STP) exhibiting a relatively slow increase. The aerodynamic force of airflow plays a crucial role in governing the breakup and transport of droplets, leading to a linear variation of STP over time. As the swirl number increases, there is an enhanced momentum exchange between droplets and airflow, resulting in accelerated spray penetration and droplet breakup.

A counter-swirl design concept for dry powder inhalers

A swirling airflow is incorporated in several dry powder inhalers (DPIs) for effective powder de-agglomeration. This commonly requires the use of a flow-straightening grid in the DPI to reduce drug deposition loss caused by large lateral spreading of the emerging aerosol. Here, we propose a novel grid-free DPI design concept that improves the aerosol flow characteristics and reduces the aforementioned drug loss. The basis of this design is the implementation of a secondary airflow that swirls in the opposite direction (counter-swirl) to that of a primary swirling airflow. In-vitro deposition, computational fluid dynamics simulations and particle image velocimetry measurements are used to evaluate the counter-swirl DPI aerosol performance and flow characteristics.In comparison with a baseline-DPI that has only a primary swirling airflow, the counter-swirl DPI has 20% less deposition of the emitted drug dose in the induction port and pre-separator of a next generation impactor (NGI). This occurs as a result of the lower flow-swirl generated from the counter-swirl DPI which eliminates the axial reverse flow outside of the mouthpiece and substantially reduces lateral spreading in the exiting aerosol.Modifications to the counter-swirl DPI design were made to prevent drug loss from the secondary airflow tangential inlets, which involved the addition of wall perforations in the tangential inlets and the separation of the primary and secondary swirling airflows by an annular channel. These modified DPI devices were successful in that aspect but had higher flow-swirl than that in the counter-swirl DPI and thus had higher drug mass retained in the device and deposited in the induction port and pre-separator of the NGI. The fine particle fraction in the aerosols generated from all the counter-swirl-based DPIs and the baseline-DPI are found to be statistically similar to each other.

Towards the development of liquid ammonia/air spray combustion in a gas turbine-like combustor at moderately high pressure

This study is a numerical investigation of the potentials of liquid ammonia (LNH3) spray combustion in a gas turbine-like combustor at moderately high pressure. The energy costs for the vaporization of LNH3 and the compression of the fuel vapor in the gaseous ammonia (GNH3)/air combustion systems, as well as the capital cost for the equipment involved, can be mitigated by employing LNH3 spray combustion. Additionally, responsiveness to power demand can easily be controlled using direct liquid ammonia. In the first part of this study, the spray characteristics of pure LNH3 were extensively studied numerically and experimentally using a hollow cone nozzle to validate the numerical models and codes. In modeling LNH3 sprays at atmospheric pressure or moderately high ambient pressures, accounting for the flash (superheat) evaporation phenomenon in addition to equilibrium evaporation is very important. Measured and simulated data both show that LNH3 spray (both vapor and droplet phases) reached a minimum equilibrium temperature of 215 K (−60 °C) when LNH3 at a pressure of 0.9 MPa was injected into an environment at 0.1 MPa and 283 K. This minimum temperature is much lower than the saturation temperature of LNH3 of 240 K (−33 °C) at ambient pressure of 0.1 MPa due to occurrence of non-equilibrium flashing. The measured average LNH3 droplet size approximately varied from 15 ∼ 20 µm and the numerical results agreed with these measured values. In the second part of the study, numerical simulations of LNH3 spray combustion were carried out at a moderately high pressure of 0.3 MPa. First, the LNH3 spray was co-fired with gaseous hydrogen (GH2) while maintaining approximately 50 %, 60 %, and 70 % of ammonia in the fuel by energy fraction (ENH3) based on the lower heating value at a moderately high pressure of 0.3 MPa. Finally, 100 % LNH3 spray flame was simulated. Preheated swirling airflow at 600 K was used to enhance the stability of the LNH3 spray flames, enabling stable combustion over a wide range of global equivalence ratios from 0.99 through 1.43. Moreover, the simulated emission characteristics of LNH3/GH2/air flames at ENH3 = 60 % were compared to those of GNH3/GH2/air flames (ENH3 = 60 %) at the same equivalence ratios. The NO and unburnt emissions of LNH3/GH2/air (ENH3 = 50 % ∼ 100 %) flames and GNH3/GH2/air (ENH3 = 60 %) flames show a trade-off relation.

Aerodynamic effect on atomization characteristics in a swirl cup airblast fuel injector

To investigate the influence of swirling air flow field on the spray characteristics and the droplet behaviors of the swirl cup airblast fuel injector, a single swirler cup and a double swirlers cup airblast injector were operated in a wide range of fuel mass flow rates (mf) and relative air pressure drops (ΔPa). Various laser based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high speed particle imaging velocimetry, were employed to provide the information of spray angle, droplet Sauter mean diameter (SMD), droplet velocity, and air flow velocity. The results show that the air flow field was characterized by central toroidal recirculation zone (CTRZ), the double swirlers cup airblast injector generated stronger CTRZ than single swirlers cup airblast injector. The spray characteristics and the droplet behaviors with different size classes were significantly affected by the air flow field. The larger droplets (25–100 μm) with higher initial momentum were likely to keep its velocity when passing through CTRZ, when the mf increased, more large fuel droplets could pass through the CTRZ and expanded to both sides, resulting an increase in a spray angle. On the other hand, smaller droplets (<25 μm) with lower initial momentum were trend to be enrolled by the CTRZ; therefore, the spray droplets at lower mf were confined in the CTRZ. These droplets trend to coalesce with each other resulting in an increase of SMD in this region.

Influence of air swirl orientation on the spray characteristics of a micro-channel-based rotary (MCR) atomizer

In this work, we investigate the atomization and spray characteristics of a novel rotary atomizer with micro-channel grooves, using optical diagnostics. Micro-jets emanate from the grooves provided in the rotating injector. The spiraling liquid jets interact with the surrounding high-speed swirling air flow, resulting in the creation of a well-dispersed fine spray. Attention is focused on the effects of air swirler orientation with respect to that of injector rotation. Accordingly, the co- and counter-swirl cases are investigated. The primary jet breakup process is visualized using back-lit illumination technique, which also provides the measurement of jet breakup length. The jet break-up modes are identified for different air swirl strength and orientation and injector rotational speed. The size, number density and velocity components of the spray droplets are measured using PDPA technique at different axial and radial locations. Air velocity is also measured (in the absence of liquid injection) using the LDV technique. In addition, Laser Sheet Imaging (LSI) is employed to investigate the overall spray structure. Results show that the droplet size significantly reduces when air swirl strength or injector rotational speed is increased. Though not much difference is observed in the characteristic droplet size between the co- and counter-swirl cases, the droplet size distribution is narrower and droplet dispersion is improved for the latter. The current findings demonstrate the potential of the rotary injector to dynamically control the spray characteristics as per requirement.

Interaction of fuel spray and air swirl on the combustion of residue oils

Effervescent atomization technology was applied in Waste Lubricant Oils (WLO) combustion. The tests were conducted in a 150 kW prototype boiler with a horizontally oriented cylindrical shape combustion chamber in which the combustion process was studied in terms of the interaction between a swirling air flow and fuel spray pattern. The combustion performance was assessed by continuously monitoring gaseous emissions, particularly carbon monoxide (CO) emission. Two different air feeding strategies were tested, varying in swirl number and six different configurations of the injection nozzle orifice. Three nozzles had a single orifice varying in diameter and discharge end geometry, and the others had three divergent orifice arrangement varying in cone angle and diameter. At the same time, the gas-to-liquid ratio (GLR) of the effervescent atomizer was also investigated, allowing to draw important illations about its influence on the combustion efficiency. The results show that the use of effervescent atomizers allows to burn of WLO, with CO emissions as low as 15 ppm at 8% of oxygen (O2) when using a three orifice of 1 mm with 15° of cone angle nozzle. This result was achieved by applying high-intensity combustion air flow swirl. However, the one orifice nozzles with penetrant spray pattern combined with low swirl intensity air flow also produced satisfactory results. With CO emissions of 27 ppm at 8% of O2 with a 1.2 mm single orifice nozzle. Furthermore, it was also demonstrated that the increment of the GLR in a range between 0.25 and 0.35 can be responsible for the reduction of 40 to 50% of the CO emissions when burning WLO.

Identification of swirling air flow velocity by non-neutrally buoyant tracer particle based on machine learning

In the non-intrusive measurement of swirling air flow, helium-filled soap bubbles (HFSBs) are ideal neutrally buoyant tracer particles However, there are some researchers that do not use HFSBs in the non-intrusive measurement of swirling air flow, leading to some kind of measurement inaccuracy. Since the flow velocity data has been implicitly included in the physical equations of any kind of tracer particles, it is possible to extract such hidden flow velocity from particle trajectory. In this study we propose a physics-informed procedure of adopting SINDy algorithm to identify the hidden physical equations of non-neutrally buoyant particle dynamics, so that the implicit flow velocity can be discovered. First of all, the numerical experiment is conducted to generate particle trajectory in a 2D swirling air flow in small cyclone separator. Based on the numerical experiment trajectory data, the input variables for SINDy algorithm are properly constructed. The output of SINDy algorithm, which are the identified physical equations, are evaluated and validated on two different-density particle trajectory data. Our results show that the physical equations of tracer particle dynamics can be identified and the discovered flow velocity data has a maximum deviation of 1.4% from the truth (R2≥0.999). The proposed method may remove the requirement of NB tracer particle in non-intrusive measurement of swirling air flow, and may be applied to recognize the physical equations of complex particle laden flow.

Simulation of the dynamics of a flexible fiber in the swirling airflow in a nozzle containing cylindrical and divergent conical sections

Swirling airflow plays a key role in textile production processes. The structure and properties of a textile processed by utilizing swirling airflow depend to a large extent on the dynamics of the fibers in the flow. This work presents a numerical investigation of the dynamics of a flexible fiber in the tangentially injected swirling airflow in a nozzle containing cylindrical and divergent conical sections, which is frequently encountered during textile production. Simulation of the three-dimensional, transient, compressible and turbulent swirling airflow field in the nozzle is first conducted. A model for the particle-level simulation of a flexible fiber in a wall-bounded flow is consequently adopted for studying the fiber motion in the nozzle. This model assumes the fiber to be composed of several massless elastic rods connected by rigid ball–socket joints where various forces and torques are exerted. The stretching, bending and twisting deformations of the fiber as well as the fiber–wall collision can all be modeled. The motional characteristics of the flexible fiber can be obtained by solving the translational and rotational equations for all the ball–socket joints in the fiber model. Based on the model, the effects of two process and nozzle geometric parameters – the nozzle pressure and radial position of the injectors – on the fiber motion are studied. The results show that the model and methods presented in this work can provide effective and useful insights into the dynamics of flexible fiber in the swirling airflow field inside complex-structured nozzles employed in the textile production processes.

Research on dust removal technology of large eddy dust collecting and swirl airflow distribution in the fully-mechanized excavation face

Aiming at the tricky problem of dust pollution at the fully-mechanized excavation face, the dust removal technology of large eddy dust collecting and swirl airflow distribution was studied. This method divides the space in the tunnel into two air field by airflow distributor. An air-dust coupling model was established to study the law of air field and dust migration. The results show that the upward-tilt angle α and back-tilt angle β of the side outlet of the airflow distributor have a great influence on the formation of reverse swirl airflow. With the increase of α in the range of 20– 35°, the intensity of transverse dust control eddy first increases and then decreases. With the increase of β in the range of 0° ∼ 20°, the dust control effect is enhanced. The back-tilt angle γ of the airflow blown by the end outlet of airflow distributor to the heading face can reduce the air disorder, and the transverse dust control eddy can be formed. Similarity experiments show that the actual dust diffusion distance corresponding to the tracer fog dust is 9.8 m, and the relative error is about 5.1% compared with the simulation results in this paper. With the new technology, the dust removal efficiency is up to 98.3%, and the working environment during the tunneling process will be greatly improved. • A new dust control equipment and strategy was proposed. • The formation mechanism of air curtain were analyzed. • The rules of dust diffusion after using air distributor was obtained.

An experimental investigation of droplet morphology in swirl flow

The interaction of a droplet with a swirling airstream is investigated experimentally using shadowgraphy and particle image velocimetry techniques. In swirl flow, the droplet experiences oppose-flow, cross-flow and co-flow conditions depending on its ejection location, the velocity of the airstream and the swirl strength, which results in distinct droplet morphologies as compared with the straight airflow situation. We observe a new breakup phenomenon, termed as ‘retracting bag breakup’, as the droplet encounters a differential flow field created by the wake of the swirler's vanes and the central recirculation zone in swirl airflow. A regime map demarcating the various modes, such as no breakup, vibrational breakup, retracting bag breakup and bag breakup modes, is presented for different sets of dimensionless parameters influencing the droplet morphology and its trajectory. In contrast to the straight flow, the swirl flow promotes the development of the Rayleigh–Taylor instability, enhancing the stretching factor in the droplet deformation process, resulting in a larger number of fingers on the droplet's surface. In order to gain physical insight, a modified theoretical analysis based on the Rayleigh–Taylor instability is proposed for the swirl flow. The experimental behaviour of droplet deformation phenomena in swirl flow conditions can be determined by modifying the stretching factor in the theoretical model.

Ethanol spray tubular flame established in a swirling air flow

This study proposes an efficient technique to burn ethanol spray in an intense swirling air flow and investigates the mechanism of flame lift-off. On the basis of typical tubular burners for gaseous fuels, ethanol spray was axially induced and mixed with the tangentially injected air under room temperature, yielding the ethanol spray tubular flames under various operating conditions. The results show that from an ultra-lean condition of global equivalence ratio of 0.1 to the rich condition, two typical flames, namely attached and lifted tubular flames, were established. Then, the structure of the ethanol spray tubular flame was specified by temperature measurements, OH-PLIF imaging, indicating its overwhelming aerodynamic and thermal stability with low pollutant emissions. Meanwhile, a flue gas analyzer was used to characterize the gas composition in the hot exhaust. It is found that the burner can achieve very low emissions of both CO and NOx, illustrating high combustion completeness under both attached and lifted flame conditions. To give a better understanding and make fully utilization of spray tubular flames, a parametric study was carried out to investigate the effects of the tangentially swirling air flow, the flow rate and oxygen concentration of atomizing gas, and the flow rate of liquid ethanol. Generally, an attached flame is lifted under a higher tangential velocity of air flow; increasing oxygen concentration of the atomizing gas flow leads to the height decrease of the flame lift-off, even the reattachment of the lifted flame; by raising the ethanol flow rate to exceed a critical value, the flame also lifts off. Furthermore, the evaporation time of droplets, residence time and chemical reaction time were calculated to quantify the flame lift-off behavior. The lifted flame can be established only when the evaporation time is larger than both the reaction time and the residence time.

Modeling the airflow field of vortex spinning

Vortex spinning technology adopts a high-speed swirling airflow to rotate the fibers with open-ends to form yarn with real twists. The airflow behavior within the nozzle has a great effect on the yarn-formation process. In this study, a three-dimensional calculation nozzle model and corresponding three-dimensional airflow region model were established to enable the numerical calculation; airflow behavior—pressure, velocity, and the turbulent airflow field, and the streamline of airflow—was investigated in the presence of fiber bundles within the vortex spinning nozzle. Hybrid hexahedral/tetrahedral control volumes were utilized to mesh the grids in the calculation region. To consider airflow diffusion and convection in the nozzle, the Realizable k- ε turbulence model with wall function was adopted to conduct the calculation. Dynamic and static pressure values were obtained by numerical analysis to predict the action of the inner surface of nozzle and the wall resistance on the high-speed swirling airflow. The numerical simulation of dynamic airflow behavior can generate great insight into the details of airflow behavior and its distribution characteristics, and is helpful for understanding the spinning mechanism and promoting optimization of the spinning process.

Experimental Study on the Stabilization Mechanism of Diffusion Flames in a Curved Impinging Spray Combustion Field in a Narrow Region

HVAF (High Velocity Air Flame) flame spraying can generate supersonic high-temperature gas jets, enabling thermal spraying at unprecedented speeds. However, there is a problem with the energy cost of this device. This study focused on combustors that used cheap liquid fuel (kerosene) as the fuel for HVAF. In this research, we have developed a compact combustor with a narrow channel as a heat source for the HVAF heat atomizer. Using this combustor, the stability of the flame formed in the combustor, the morphology of the flame, and the temperature behavior in the combustion chamber were investigated in detail. As a result, the magnitude of the swirling airflow had a great influence on the structure of the flame formed in the combustor, and the stable combustion range of the combustor could be determined. As the swirling air flow rate changes, the equivalent ratio of the entire combustor changes significantly, and the flame structure also transition from the premixed flame to the diffusion flame. From this study, it was confirmed that the temperature inside the combustor has great influence on the flame structure.

Aerodynamic characteristics of the sawdust combustion process in a vortex furnace

The article presents the results of a numerical study of the behavioral characteristics of the process of burning sawdust with a diameter from dmin = 25 μm to dmax = 750 μm in a vortex furnace with counter swirling air flows. The fields of static pressure and absolute velocity in the furnace volume are given. The change in flow density, volume concentration of particles along the height of the furnace is shown. Consumption concentration of particles is 0.094 kg / kg of air. Currently, one of the main directions of Ukraine's strategic development is to achieve energy independence. To achieve this, it is necessary to implement systems for the use of energy resources available in our country. Since a significant part of the country's economic activity is occupied by agricultural activities, the use of low-grade fuels, most of which are waste in this area, is relevant and profitable for economic and environmental reasons. Reconstruction of boilers, improvement of methods and ways of combustion in vortex furnaces of low-grade fuels will significantly reduce the consumption of imported natural gas and bring the country closer to the status of energy-independent state. coke burnout is 100%. The value of the volume concentration of particles β <3 · 10-2 characterizes the aerodynamic mode of motion of particles in the furnace as the mode of gas suspension. In the course of research, the main characteristics of the process of burning sawdust in a vortex furnace with counter-swirling air flows, namely: higher gas velocity is observed in the near-wall area in the lower part of the furnace; when the diameter of the fuel particles increases, the zone with the maximum coke content in them moves from the lower zone of the furnace to the upper; the gas pressure varies slightly both in height and in the cross section of the furnace.

Design and Computational Fluid Dynamics Analysis of a Novel Compact Mixing Chamber in Blast Furnace Ironmaking

Abstract Homogeneous mixing of hot air from the hot blast stove with suitable quantity of cold air in a mixing chamber is very essential to maintain uniform temperature of hot air at all tuyers of a blast furnace. Proper design of the mixing chamber is very important for stable and efficient operation of blast furnace, lower energy consumption, and lower carbon dioxide emission. Comprehensive understanding of the physics of the mixing process is very essential for efficient design of the mixing chamber. In this paper, computational fluid dynamics (CFD) simulations are conducted to analyze the mixing of hot and cold air in a tangential cold gas inlet type and in a radial cold gas inlet type mixing chambers, which are commonly used in the industry. Results show that both types of mixing chamber produce very non-homogeneous mixture of cold and hot air despite having large mixing length in the long hot blast main. Also, design of a novel compact mixing chamber is presented and CFD analysis of this mixing chamber is conducted. The new mixing chamber is found to produce almost homogeneously mixed air stream within a very short length due to very high turbulence of the intensely swirling air flow. Also, the new mixing chamber is found to save large amount of high-quality thermal energy, which is wasted in the other two designs through the wall of the long hot blast main.

Improvement of production efficiency of spray-synthesized HKUST-1

Spray synthesis of metal–organic frameworks (MOFs) is desirable for scaled production. In this study, we designed a new apparatus for spray-synthesizing MOFs, wherein an upward spraying and swirling air flow was applied to prevent loss of the precursor solution. We evaluated the effects of the flow rate and temperature of swirling air, temperature of the reactor tube, initial feed rate of the precursor solution, and precursor concentration on the yield, purity, space–time yield (STY), BET surface area, and average particle size. The swirling air flow along with re-spraying of the solution accumulated on the upward spray nozzle improved yield significantly. The highest STY was 45.7 kg/m3/day obtained at a precursor feed rate of 5 mL/min; the highest surface area was 1,872 m2/g obtained at a precursor concentration of 1.38 mol/L. The sample with the highest surface area exhibited 2.60 wt% of hydrogen adsorption capacity at 77 K and 1 bar, with 7.6–6.1 kJ/mol of heat of hydrogen adsorption.

CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities

In order to explore the performance of the B-ULV-616A knapsack sprayer, computational fluid dynamics (CFD) was used to simulate the B-ULV-616A knapsack air-assisted device, which features an ultra-low-volume electric sprayer. Field experiments were carried out to test the spraying effects, and the KANOMAX anemometer was used to verify the simulated results. First, the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established. The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device. The high-speed airflow (maximum of 83.5 m/s) generates negative pressure (minimum of 0.099 MPa) and causes a rapid increase in the droplet velocity and a secondary droplets spray, allowing droplets to reach a longer distance. Then, the maximum relative error was 20.14%, and its average value was 9.59%, indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device. Finally, based on the greenhouse experiment, the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop, increase the droplet density (maximum of 81/cm2; droplet density of conventional electric sprayer is 64/cm2), and reduce the deposition amount and coefficient of variation (below 20%) within and between regions. Further, it managed to reduce pesticide use (by 69.85%) and rural non-point source pollution. Keywords: CFD simulation, air-assisted sprayer, ultra-low spraying rate, deposition, air-velocity field, relative error DOI: 10.25165/j.ijabe.20211402.6013 Citation: Lu X Y, Gong Y, Liu D J, Wang G, Chen X, Zhang X, et al. CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities. Int J Agric & Biol Eng, 2021; 14(2): 26–34.