Air Jet Velocity Research Articles

Opportunities and Possibilities of Developing an Advanced Precision Spraying System for Tree Fruits.

Reducing risk from pesticide applications has been gaining serious attention in the last few decades due to the significant damage to human health, environment, and ecosystems. Pesticide applications are an essential part of current agriculture, enhancing cultivated crop productivity and quality and preventing losses of up to 45% of the world food supply. However, inappropriate and excessive use of pesticides is a major rising concern. Precision spraying addresses these concerns by precisely and efficiently applying pesticides to the target area and substantially reducing pesticide usage while maintaining efficacy at preventing crop losses. This review provides a systematic summary of current technologies used for precision spraying in tree fruits and highlights their potential, briefly discusses factors affecting spraying parameters, and concludes with possible solutions to reduce excessive agrochemical uses. We conclude there is a critical need for appropriate sensing techniques that can accurately detect the target. In addition, air jet velocity, travel speed, wind speed and direction, droplet size, and canopy characteristics need to be considered for successful droplet deposition by the spraying system. Assessment of terrain is important when field elevation has significant variability. Control of airflow during spraying is another important parameter that needs to be considered. Incorporation of these variables in precision spraying systems will optimize spray decisions and help reduce excessive agrochemical applications.

Importance of cloud motion and two-way momentum coupling in the transport of pharmaceutical nasal sprays

Nasal sprays, which produce relatively large pharmaceutical droplets with sizes mostly higher than 10 μm, are primarily used to deliver locally acting drugs to the nasal mucosa. Due to the large spray droplet size and high spray velocity, these droplets carry significant momentum, which can influence the surrounding gas field (i.e., two-way coupling) and strongly influence the droplet transport mechanics and droplet deposition profile. The objective of this study was to determine if two-way momentum coupling leading to cloud motion is an important factor in simulating pharmaceutical nasal sprays, and if so, to develop a computationally efficient method to capture this effect. The effect of two-way momentum exchange between the nasal spray droplets and the surrounding air was analyzed using Computational Fluid Dynamics (CFD) simulations of sprays from two pharmaceutical nasal spray pumps. The computational spray transport was modeled using different modeling approaches including one-way coupled and two-way coupled Euler-Lagrange and Euler-Euler frameworks. Detailed comparisons of the computational simulation results with in vitro spray transport measurements were performed to establish which modeling approach is more accurate for predicting the nasal spray transport. The simulation results indicated that the coupling effect of the spray momentum exchange with the air molecules created an air-jet velocity profile, which in turn led to a cloud-like motion of the smaller droplets. The airflow created by the cloud of droplets as a whole imparts significant momentum on the smaller droplets and transports them further into the flow field. The comparison study of simulation results and the in vitro measurements demonstrated that the two-way coupled Euler-Lagrange approach was more effective in accurately capturing the nasal spray transport. The spray modeling results indicated that the effect of two-way momentum exchange between the nasal spray droplets and the surrounding air was significant and influenced the spray droplet transport. Calculating the two-way coupling effects was computational resource intensive and time-consuming. Hence, reduced-time and resource modeling approaches including a quasi two-way coupled approach and momentum transfer approach were introduced to simplify the calculation.

Interaction between a Liquid Surface and an Impinging Gas Jet

The water-air and Wood’s metal-air systems are modeled by means of Computational Fluid Dynamics to study the interaction between a liquid surface and an impinging air jet under the near field blowing conditions. The effect of the air jet velocity, the height of the injection lance, and the density of the liquid on the depth of the formed cavity is numerically studied. The CFD results of the cavity depth are compared with results previously reported by other authors. The emergence of the splashing phenomenon is predicted in terms of the critical velocity for each liquid-air system. Besides, the blowing number indicates that the drop generation rate is not significant for jet velocities below the critical velocity, and therefore neither the splashing is significant.

Comprehensive analysis of the effect of air injection on the wake development of an airfoil

The goal of this investigation is to study the effect of air injection on the wake development. As a widely commercial product, airfoil CFJ0025-131-196, is selected, and the profiles for velocity deficit, wake profiles for different attack angles, and profiles for change in the place where the velocity starts to increase are found. For the air jet velocity, the values of 0.0, 20.4, and 33.3 m s−1 are examined while angles of attack are adjusted to 0, 6, and 14°. The main flow speed is 10 m s−1. It is found that when the dimensionless distance from the trailing edge goes up, the velocity deficit has a downward trend. Furthermore, the higher jet velocity is, the smoother the velocity deficit profile becomes. In addition, in a constant dimensionless distance, increasing the angle of attack results in growing the amplitude of the dimensionless velocity profile. The results also reveal that the location at which the velocity starts to increase moves down by the increase in the air jet velocity. Having a broad knowledge about the wake development of an airfoil will help to know its performance better and find more suitable ways to enhance its performance.

Guardrail-based air supply terminal for improving ventilation effectiveness and saving energy in the waiting zone

In the waiting zones of airports, train stations, and other transportation hubs, poor indoor environment is primarily caused by human body-related factors in conjunction with the high density of people. Existing ventilation systems cannot effectively remove the waste heat and pollutants generated by dense crowds. In this paper, a guardrail-based air supply terminal is proposed. Two indices, the velocity target value and temperature target value, were introduced to facilitate the evaluation of the guardrail-based air supply terminal. The jet air velocity, penetration air velocity and width of the unventilated strip are optimized based on CFD numerical simulations; the values obtained were V1 = 0.25 m/s, V2 = 0.15 m/s, and W = 290 mm. The guardrail-based air supply terminal was found to create a homogeneous air velocity of 0.3 m/s to avoid draft sensations. The uniformity and effectiveness of the air supply via the optimized guardrails are verified by full-scale experiments and visual experiments. The temperature of the working area was maintained at 26°C in the summer, creating a comfortable environment. Compared with other existing air distribution systems in high and large spaces, the velocity target value, air age, and temperature target value with the proposed air supply terminal were the smallest. The energy consumption of the guardrail-based air supply terminal was 61% less than that of the vertical wall jets. The results indicate that the guardrail-based air supply terminal not only meets the thermal comfort requirements but also saves energy.

Experimental investigation on controlled cooling by coupling of thermoelectric and an air impinging jet for CPU

AbstractIn this study, experimental tests have been carried out on the coupling thermoelectric cooling module with minichannel heatsink subjected to impinging airflow for cooling desktop central processing unit (CPU). A controlled thermoelectric‐forced test system was designed for this purpose. This was designed using electronic Arduino card. The proposed hybrid cooling system was compared with the conventional forced air‐cooling technique. Three power of heat source (CPU) were adopted, investigated, and compared, namely 60, 87, and 95 W. Performance of controlled thermoelectric cooling with three preset temperature were experimentally examined. The effects of air velocity and thermoelectric input current on the case temperature (Tcase), thermal resistance, and heat transfer coefficient were analyzed. Results showed that the Tcase increases with the increase of its input power. In addition, increasing air jet velocity and thermoelectric input current improve CPU cooling significantly. For a CPU power of 95 W, the recorded Tcase temperature was 57°C with the conventional system. While it was maintained below 50°C in the hybrid system. The thermoelectric cooler has had a major effect on CPU cooling, having 15% improvement over conventional forced air‐cooling. However, this was accompanied by an increase in energy consumption in the range of 45 W.

Modified Bottom Air Entrainment Estimate by Chute Offset Aerator

AbstractOffset aerators are a common design for the prevention of cavitation damage to chute spillways. The aeration capacity is linked to the offset air cavity length and jet velocity. Observation...

Numerical analysis on the characteristic chemical time scale and combustion regime of natural gas MILD combustion

Moderate or intense low-oxygen dilution (MILD) combustion is regarded as a novel combustion technology due to high thermal efficiency and low pollution emissions. Understanding the interaction between turbulence and chemistry can provide a deep insight into the chemical reaction zone structure and MILD combustion regime. Numerical simulation of natural gas MILD combustion in the International Flame Research Foundation (IFRF) test furnace was carried out by using standard k-ε model with Eddy Dissipation Concept (EDC) model. Then a modified Jacobian matrix method with a simplified selection method was developed to calculate the characteristic chemical time scale and the Damköhler number and subsequently to identify the MILD combustion regime of natural gas. All chemical time scales were calculated from the eigenvalues of the chemical source term Jacobian matrix, and the characteristic chemical time scale was chosen out through the simplified and effective selection of major species and chemical time scales. The results show that the characteristic chemical time scale is 10−6–10−4 s in the main combustion zone and about 10−2 s in the post flame zone. The calculated Damköhler number is close to unity and the combustion regime of natural gas combustion is determined as the distributed reaction zone with a higher air jet velocity, which reflects the MILD combustion characteristics. The numerical results confirm that the natural gas MILD combustion in the IFRF furnace is in the finite-rate chemistry regime and disperses throughout the whole furnace volume which is significantly different from the conventional combustion mode.

Heat transfer studies of surface synthesized by chemical vapor deposition

In this paper, heat transfer characteristics of nickel coating over aluminium and mild steel are examined using jet impingement cooling. A rectangular sheet of dimension 10 cm × 3.5 cm × 0.1 cm taken as the test piece is coated with 4 g nickel acetate tetrahydrate precursor in the chemical vapor deposition (CVD) process for 85 mins. Heat transfer characteristics are studied on three layers of nickel coating (no coating, first coating, and second coating) with an impinging air-jet velocity of 3.5 ms−1 and 6 ms−1. The effect of Reynolds number, the thickness of the coating, jet velocity, distance from the stagnation point, and nozzle diameter on the heat transfer coefficient are investigated. The results show an increase in convective heat transfer characteristics with the Reynolds number, the thickness of the coating, and the nozzle diameter and a substantial decrease with deviation from the stagnation point.

An Approximate Analytic Solution to a Non-Linear ODE for Air Jet Velocity Decay through Tree Crops Using Piecewise Linear Emulations and Rectangle Functions

The velocity of air that crosses the canopy of tree crops when using orchard sprayers is a variable that affects pesticide dispersion in the environment. Therefore, having an equation to describe air velocity decay through the canopy is of interest. It was necessary to start from a more general non-linear ordinary differential equation (ODE) obtained from the momentum theorem. After approximating the non-linearity with some piecewise linear terms, analytic solutions were found. Subsequently, to obtain a single equation for velocity decay, a combination of these solutions was proposed by using rectangle functions formed through the hyperbolic tangent function. This single equation was assessed in comparison to the experimental value obtained on a vineyard row by measuring the air velocity at exit of canopy. The results have shown good correspondence, with a mean relative error of 6.6%; moreover, there was no significant difference. To simplify, a combination of only two linearized solutions was also proposed. Again, there was no significant difference between the experimental value and the predicted one, but the mean relative error between the two equations was 3.6%.

Association study between basis weight distribution of melt-blown web and air velocity distribution on the collector

Basis weight distribution of melt-blown fibrous web is attracting considerable interest because it directly affects the application performance of nonwovens. Basis weight distribution is strongly determined by the air velocity distribution on the top surface of the collector. However, how the mentioned air velocity distribution affects basis weight distribution is still unknown. Measurement of the mentioned two distributions is the first step to investigate the influence mechanism. Thus, this work measures air velocity distribution on the collector under different processing conditions. Then the fibrous web is fabricated under same conditions. After fabrication, the basis weight distribution of fibrous web is analyzed by using image analysis method. The effects of processing conditions, including velocity of air jet and suction, die-to-collector distance, and pore size of the collector, on the air velocity distribution and basis weight distribution are quantitatively analyzed. The results demonstrate that higher suction speed and air jet velocity, smaller die-to-collector distance, and larger pores of the collector result in higher air velocity on the top surface of the collector. On the other hand, higher suction speed and air jet velocity, larger die-to-collector distance, and smaller pores of the collector create evenly distributed basis weight. In addition, the correlation between basis weight distribution and air velocity distribution is discussed based on the Spearman correlation analysis method. High correlation demonstrates that air velocity and basis weight display similar distribution on the collector. Namely, both of air velocity and basis weight in the central zone are larger than those in the fringe zone on the collector.

Effect of air flow rate and secondary air jets on the operation of TLUD gasifier cookstove

ABSTRACTThe current article presents experimental results of the operation of top-lit updraft (TLUD) gasifier cookstove. The independent variables for the experiments are secondary airflow rate, the ratio of the secondary to the primary air flow rate, and the secondary air jet velocity. Based on the mass, temperature, and gas measurements the stove performance variables like effectiveness, combustion efficiency, AF, and power are calculated. The results show that varying the secondary airflow rate and jet velocities affect the fuel consumption rate for the flow rates considered. Combustion efficiency is relatively constant around 98%. Increasing the secondary air decreases the CO emission. Effectiveness starts to saturate beyond AF of 10. Useful power is found to be a strong function of secondary air.

Effect of jet velocity on LPG to flame stability and flame temperature distribution on Inverse Difusion Flame (IDF)

Liquid Pretolium Gas (LPG) experimental investigation used to Inverse Diffusion Flame (IDF) burners is presented. The effect of fuel jet velocity on the flame stability and flame temperature distribution of LPG Inverse Diffusion Flame (IDF) was investigated. Fuel jet speed (Vf) = 0.154 m/s and 0.330 m/s was chosen for analysis. Air jet velocity varies from Va = 7.431 m/s to Va = 15.924 m/s for Vf = 0.154 m/s and Va = 8.493 m/s up to Va = 21.231 m/s for Vf=0.330 m/s . The results of the observation show that the velocity of the fuel jet affects the ratio of the velocity of the air-fuel jet which will ultimately have a significant effect on the flame. It was found that the stability of LPG IDF flame at Vf = 0.154 m/s occurred at Va = 11.677 m/s, the equivalence ratio (ϕ) = 1.99. The stability of LPG IDF flame at Vf = 0.330 m/s occurs at Va = 14.862 m/s with an equivalence ratio (ϕ) = 1.56. It was observed that the temperature along the IDF centerline increased when the distance from the burner (Z) exit increased. The nature of this temperature distribution shows that central cold air in the air jet is gradually heated towards the IDF downstream. The highest flame temperature is seen in Z between 90-110 mm. It was found that the length of the flame increased with increasing flow of fuel jets. At a constant fuel jet speed the flame length increases but will return again to a certain fuel-air ratio. At Vf = 0.154 m/s the highest flame height is 111 mm and at Vf = 0.330 m/s the highest flame height is 143 mm.

Experimental Characterization of Circumferentially Arranged Fuel Port Inverse Jet Diffusion Flame Burner

ABSTRACT This paper presents experimental studies on flame height, thermal and emission characteristics of Inverse Jet Diffusion Flame (IJDF) using a circumferentially arranged fuel port (CAFP) burner by following two different protocols, namely, Protocol I and Protocol II. Experiments are carried out to investigate the effect of momentum flux ratio (MFR) on flame height and base flame height characteristics for a fixed air jet velocity, by varying fuel jet velocity (Protocol I) and by varying air jet velocity for a fixed fuel jet velocity (Protocol II). For both Protocols, there is a decrease in flame height with MFR due to the deterioration of fuel-air mixing process. Two separate semi-empirical correlations between normalized flame height and MFR are proposed for Protocol I and II, respectively. The center-line temperature characteristics indicate a faster air-fuel mixing at higher MFR for both Protocols. Moreover, Froude number is used to delineate the buoyancy and momentum-controlled regimes in IJDF. A constant temperature plateau is defined to identify the suitability of burner for industrial heating applications and is found to be higher for 32-port burner than that of the 12- port inverse jet diffusion flame burner due to enhanced air-fuel mixing along the jet central axis. Moreover, at lower MFR, emission index (EI) of NO remains independent of both the Protocols, whereas at higher MFR, the variation depends on the type of Protocol due to a larger variation of Froude number. On the other hand, the variation of CO emission index is almost independent of Protocol I and II. The experimental results show that the present 32 port burner design outperforms the emission characteristics of 12-port burner for an overall equivalence ratio less than 1.63. Two semi-empirical correlations for EINO and EICO, respectively, are developed as a function of overall equivalence ratio and MFR, which can be used for design and development of CAFP IJDF burner.

Effect of air jet momentum on the topological features of turbulent CNG inverse jet flame

Inverse jet flame (IJF) configuration is a variant of coaxial nonpremixed jet flame which can produce a nonluminous compact blue flame with independent control of air and fuel jet momentum. In the present work, the effect of central air jet velocity on visible topological features such as, visible flame height and base flame height is investigated experimentally. Also the fluid dynamics behind the evolution of base flame in IJF configuration is unraveled in this study. Notably, buoyancy induced oscillations of IJF, which is relatively unexplored in open literature is studied in this work. Moreover, a systematic classification of IJF based on the evolution of its visible flame features with variation in the central air jet and annular fuel jet velocities is reported. In addition, a semi-empirical correlation for visible flame height of IJF with air-fuel momentum ratio is arrived in the present work which can be useful in the design of IJF based burners utilized for impingement heat transfer applications.

Experimental investigation of heat transfer of flowing liquid film with inserted metal foam layer subjected to air jet impingement

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

Study of human response in conditions of surface heating, asymmetric radiation and variable air jet direction

Low temperature radiant heating systems are widely used in buildings being advantageous both from energy use and thermal comfort point of views. However, attention should be paid to asymmetric radiation especially in the case of wall heating. The aim of our research was to analyse the perception of thermal asymmetry in combination with different air velocities. A series of measurements were carried out in controlled environment involving 20 subjects (10 female, 10 male). It was shown that the thermal asymmetry is perceived at low air velocities, but increasing the air velocity to 0.1 m/s, 0.15 m/s or 0.2 m/s the perception of air movement overwrite the perception of thermal asymmetry. The heat removed by convection by the same air flow and air jet velocity was different for women and men group. The higher decrease of the skin temperature in case of women (around 2 K) leads to thermal sensation votes under −0.5 (even though the air and mean radiant temperature were 24 °C). The responses of women and men group regarding draught perception were different as well.

Experimental and Numerical Investigation of LPG-Fueled Inverse Diffusion Flame in a Coaxial Burner

An experimental and numerical investigation of unconfined liquefied petroleum gas (LPG) fuelled inverse diffusion flame (IDF) is presented. The effect of air-fuel velocity ratio on the appearance of the LPG IDF are investigated. A fixed air jet velocity of Va = 11.31 m/s is chosen for the analysis, while the fuel jet velocity is varied from 0.014 m/s to 0.083 m/s. The observations indicate that the air-fuel jet velocity ratio has significant effect on the flame appearance of LPG IDF. It is found that the flame length increases with increase in fuel jet flow. Actual flame in burner is highly complex in nature as it involves momentum, mass and energy transfer in highly turbulent flow regime. To extract detailed information of flow physics, numerical analysis of LPG IDF is performed. It is observed that temperature along the centerline of IDF increases as distance from burner exit (Z) increases. This nature of temperature distribution indicates that the central cold air in the air jet is gradually heated toward the downstream of the IDF. The highest flame temperature is noticed at Z = 30 mm. The highest flame temperature predicted numerically at axial height of 30 mm is central portion of the blue zone of the flame which is main reaction zone.

Hybrid Composite Material and Solid Particle Erosion Studies

Composite is one of the predominant material for most challenging engineering components. Most of the components are in the place of automobile structure, aircraft structures, and wind turbine blade and so on. At the same all the components are indulged to mechanical loading. Recent research on composite material are machinability, wear, tear and corrosion studies. One of the major issue on recent research was solid particle air jet erosion. In this paper hybrid composite material with and without filler. The fibre are in the combination of hemp – kevlar (60:40 wt.%) as reinforcement using epoxy as a matrix. The natural material palm and coconut shell are used as filler materials in the form of crushed powder. The process parameter involved are air jet velocity, volume of erodent and angle of impingement. Experiment performed are in eight different combinations followed from 2k (k = 3) factorial design. From the investigation surface morphology was studied using electron microscope. Mass change with respect to time are used to calculate wear rate and the influence of the process parameters. While solid particle erosion the hard particle impregnates in soft matrix material. Influence of filler material has reduced the wear and compared to plain natural composite material.

Experimental investigation on flame appearance and emission characteristics of LPG inverse diffusion flame with swirl

The flame appearance and emission characteristics of a LPG inverse diffusion flame (IDF) are studied experimentally in a coaxial burner. Flame length, CO and NOx emissions are examined at different equivalence ratio and swirler vane angle. The flame length of non-swirling IDFs steadily increases with increase in the fuel jet velocity. A reduced flame length is observed with the increasing air jet velocity. The IDFs with swirl are wider, shorter and stable compared to the IDFs without swirl due to the generation of internal recirculation zone (IRZ). The soot formation in the IDF is qualitatively estimated with the soot free length fraction (SFLF). The SFLF increases with an increased air jet velocity due to the effective entrainment of the fuel, which leads to an improved premixing of the fuel and air to produce an elongated blue zone of the IDF. The IDFs with swirl are wider, shorter and stable compared to the IDFs without swirl. IDFs with the 30° swirler have comparable characteristics of the CO and NOx emission with that of non-swirling IDFs. The adequate entrainment and the swirl effect for vane angle of 30° produce favourable environment corresponding to low CO and NOx emission.