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Revista Ciencias Técnicas Agropecuarias

versión On-line ISSN 2071-0054

Rev Cie Téc Agr vol.26 no.1 San José de las Lajas ene.-mar. 2017

 

Revista Ciencias Técnicas Agropecuarias, 26(1): 50-56, 2017, ISSN: 2071-0054

 

ORIGINAL ARTICLE

 

The air speed in the fan and the flow in an agricultural sprayer

 

La velocidad del aire en el ventilador y el flujo en un pulverizador agrícola

 

 

Dr.C. Mario Ignacio Herrera-Prat,I Dr.C. Armando Eloy García de la Figal-Costales,II M.Sc. Héctor de las Cuevas-Milán,II D.S. Mauri Martins-Teixeira,III

IMinisterio de Educación Superior (MES), Vedado, Plaza, La Habana, Cuba.
IIUniversidad Agraria de La Habana (UNAH), San José de las Lajas, Mayabeque, Cuba.
IIIUniversidade Federal de Viçosa (UFV), Viçosa, MG, Brasil.

 

 


ABSTRACT

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.

Key words: computer simulation (CFD), air flow modeling, aerodynamic flow.


RESUMEN

La magnitud de la velocidad del aire a la salida del ventilador de los pulverizadores agrícolas influye en la aerodinámica del flujo de aire y constituye un factor fundamental en la estructura del flujo. En el trabajo se analiza mediante el uso de la simulación por computadora (CFD), el efecto de la variación de la velocidad de salida del ventilador en la aerodinámica del flujo de aire durante el proceso de trabajo a distintas velocidades de movimiento del pulverizador. Se realizaron simulaciones de velocidades de salida en el difusor de ventilador de 40, 45 y 50 m/s con un ancho de salida del ventilador de 115 mm y considerando el pulverizador sin movimiento y a velocidades de trabajo de 2,18, 4,5 y 6,35 km/h, se analizó el comportamiento de la aerodinámica del flujo de aire para cada variante. El aumento de la velocidad de salida en el ventilador produce un desgaste acelerado en el núcleo de la corriente, por lo que la utilización de velocidades menores favorece la aerodinámica del flujo.

Palabras clave: simulación por computadora (CFD), modelación de flujo de aire, aerodinámica del flujo.


 

 

INTRODUCTION

Aerodynamic air flow fans in agricultural sprayers is one of the root causes of drift. A drift in agricultural spraying produces agronomic and environmental negative impacts causing major crop losses and damage to health. It has been considered one of the most important problems associated with the use of plant protection products (Brazee et al., 1998). The magnitude of fan air velocity is one of the parameters that decides on the pesticide drop transfer to the tree because it influences on its speed, direction and size, and that is corroborated by Delele et al. (2005), when they say that the air speed generated by the spray-assisted air stream, determines the fate of pesticide droplets. Furthermore, Herrera et al. (2004) have related fan parameters with spray quality, so knowing them allows proper operation of the sprayer. Researchers have recently developed models in computational fluid dynamics (CFD), looking for a way to solve this problem with more agility and less resources for experimentation (Walklate, 1992). These models are mainly based on solving numerically the equations of Navier-Stokes flow. CFD work has been complemented with experimental field trials by Walklate et al. (1996), Herrera et al. (2004, 2006), Delele et al. (2005). More recent studies with validated CFD results in a controlled manner were performed by Cross et al. (2001), Tsay et al. (2004), Endalew et al. (2010), Foqué et al. (2012), y Han et al. (2014). In this paper, it will be analyzed, by using computer simulation (CFD), the effect of the variation of air velocity at the fan outlet in the aerodynamic air flow during work at different speeds of the sprayer movement. Deviation and scope of airflow through the interpretation of speed graphics resulting from modeling will be analyzed as response variables. Conclusions are stated about the relationship of the output speed of air in the aerodynamic airflow and its influence on the performance of sprayer.

 

METHODS

The model for the study is based on SS800 model TEYME integral spray fan settings. It has an axial fan with radial model “VL-765” of 750 mm in diameter and of 115 to 135 mm in width of the outlet diffuser, which has been already referred in previous numerical analysis using computational fluid dynamics (CFD) (Herrera et al., 2014). The computational domain used in this work will be utilized as a basis. Fan output speeds of 40, 45 and 50 m / s will be evaluated, while maintaining the width of the fan diffuser outlet to 115 mm, considering the sprayer without movement and work translational speeds of 2.18, 4.5 and 6.35 km / h. Deviation and scope of airflow will be analyzed as response variables, through the interpretation of the velocity distribution charts. The fan used as reference in modeling is shown in Figure 1.

Values of sprayer movement speed and of the air at the fan outlet for the variants studied are shown in Table 1.

Computational modeling analysis was performed using the ANSYS 5.3 program; it bases its numerical analysis in solving the momentum and continuity equations that apply in the dynamics of airflow. The computational domain where the fluid for modeling in CFD moves, was taken from the one designed by (Herrera et al., 2014). In this element, meshing defining nodes for the development of the Navier-Stokes equations is performed; the domain reaches a length of up to 2.4 m away from the source of the flow. In modeling, the properties of air as fluid were density of 1.187 kg / m3 and viscosity of 1.8135 x 10-5 kg / m-5.

 

RESULTS AND DISCUTIONS

Flowcharts obtained in modeling by CFD for the three-speed air outlet studied, represented in figures with the sprayer without movement and the three regimes of translation speed selected are analyzed. In each graph, the scale of speed is presented depending on the colors in the flow development.

In general, for all simulated variants of output and sprayer translation speed in the graphs of flow, the different regions of the stream described by Abramovich (1963) for free flow turbulent are defined. A central core of maximum speed wears as it is away from the source of stream (red), it is accompanied by transition zones with lower speed values that decrease as the distance to the output increases and from the center line of flow to the side as it is described by Schlichting (1972).

Figure 2 shows simulating airflows of the sprayer for output speeds evaluated with the sprayer without movement, that is, flow is shown in calm air. It is noted that the modeling flow has the same structure for the three values ​​of fan air output speed, a central core having the same path and scope in all three cases and disappears at 0.4 m from the fan outlet, in spite of different initial speeds. Analyzing the speed at 2.4 m away from the fan outlet, in this area of ​​flow values were 10.3, 11.5 and 12.8 m / s for initial speeds of 40, 45 and 50 m / s, respectively. Initial speed decreases from 5 m / s to 1 m / s, at that distance. It is because there are higher internal speeds losses in the flow at higher speeds.

The results of the air stream for air speeds at the fan outlet of 40, 45 and 50 m / s are shown in Figure 3. In this case, in the simulation, it is considered that the sprayer is moved at a speed of 2.18 km / h in its working process, so the air flow is subjected to the perpendicular action of this speed.

As it is shown in the figure, the core of the flow represented in red disappears at 0.5 m from the origin. In this case, the core is larger than when the sprayer was static, the component of the speed, product of the translational movement of 0.6 m / s, perpendicular to the flow, produces an elongation of the core. In the transitional zone of the airflow for the three speeds studied, the maximum speed line presents a deviation of 0.15 m with respect to the geometrical axis of the computational domain and in an opposite direction to the sprayer movement. At the distance of 2.4 meters from the outlet, the difference between the speeds in the airflow are less than 1 m / s for speed variants, taking into account that at the beginning the difference is of 5 m / s, which shows greater losses in the flow with higher speeds at startup.

In Figure 4, airflows for speeds at the fan outlet of 40, 45 and 50 m / s, are simulated, but in this case with a higher translational speed of the sprayer at 4.5 km / h. The airflow is subject to greater action of the translational speed of the sprayer.

The figure shows that the core of the flow reaches a length of 0.7 m for the output speed of 40 m / s, 0.75 m for the speed of 45 m / s and 0.80 mm for the outlet speed of 50 m / s, a distinction is made here within the scope of the central core. In all three cases, at 0.5 m away, at the outlet there is already a deviation of 0.20 m with respect to the axis of the computational domain opposite to the sprayer’s direction of movement. In the transitional area of ​​the stream, the deviation of the central axis is 0.5 m for the three cases studied. Analyzing the scope of the stream, it is observed that for the output speed of 40 m / s, the speed of 5.4 m / s in the stream is reached at the distance of 2 m from the outlet, for the initial speed of 45 m / s it is reached at 2.2 m and for 50 m / s initial speed, at 2.4 m. These results demonstrate that the component of translation speed of 4.5 km / h (1.25 m / s) produces a greater effect on the scope of the stream in the output speed in variants with 40 and 45 m / s outlet speed.

In Figure 5, similar to previous cases, flow simulation for air speeds at the output of 40, 45 and 50 m / s are represented. In this case, it is simulated with a higher speed of the sprayer in the working process, at 6.35 km / h, which is the maximum speed for efficient work with that equipment, but sometimes certain conditions are used.

In Figure 5, it is shown that, the core airflow is maintained on the central axis of the domain up to a distance of 0.35 m from here and up to 0.95 m that the core disappears and presents a similar variance for three cases. The scope of flow with respect to the output, for speeds of 6 m / s, in the case of the output speed of 40 m / s, it is reached at 1.8 m, for 45 m / s it is reached at 2 m and for 50 m / s it is obtained at a distance of 2.2 m. That means that as outlet speed increases, the scope of the stream is greater.

By varying the output speed in the ranges studied, in the variants of motionless sprayer and at 2.18 km / h, the scope of the stream is similar and decreases the speed difference at the end of flow with respect to the initial. That indicates that for the translational speed of 2.18 km / h it is possible to consider using lower output speeds (40 km / h) for the similarity in the stream structure and regarding Randall (1971), when he determined better results in the tree coverage for greater airflow and lower air speed at the outlet. In the case of higher translational speeds (4.5 and 6.35 km / h), the variant of highest scope of the stream coincides with the one with highest speed output. A faster flow sprayer can bring other consequences, such as damages to the cultivation, the screen effect occurs in the foliage preventing the liquid pesticide from penetrating into the tree or a very high drop translational speed that reaches kinetic energy values ​​such that prevent it from depositing on the foliage. The results show that, when selecting a sprayer work regime, the fan speed output and the sprayer translation speed should be taken into account.

 

CONCLUSIONS

In all cases of airflow modeling presented in graphs, the precepts of the theory of free flat jet: a stream of turbulent free air full of motionless air or of air in motion, described by Abramovich (1963), are met.

By varying the output speed in the ranges studied, in the variants of the motionless sprayer and at 2.18 km / h, the scope of the stream is similar and decreases the speed difference at the end of flow with respect to the initial.

In the case of higher translational speeds (4.5 and 6.35 km / h), the airflow with higher speed output has higher scope.

 

NOTE

*The mention of commercial equipment marks; instruments or specific materials obey identification purposes, not existing any promotional commitment with relationship to them, neither for the authors nor for the editor.

 

BIBLIOGRAPHY

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Received: 17/02/2016
Approved: 14/11/2016

 

 

Mario Ignacio Herrera-Prat, Inv. y Prof. Tit., Ministerio de Educación Superior (MES), Calle 23 y F, Vedado, Plaza, La Habana, Cuba. Email: herrera@mes.gob.cu

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