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Development of a liquid-jet nozzle for fertilizer injection in paddy fields using CFD
Computers and Electronics in Agriculture 167 (2019) 105061
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of a liquid-jet nozzle for fertilizer injection in paddy fields using CFD Wenhan Zhenga, Yu Jiangb, Xu Maa, Long Qia, a b
T
⁎
College of Engineering, South China Agricultural University, 483 Wushan Road, Guangzhou, Guangdong Province 510642, PR China Modern Educational Technology Centre, South China Agricultural University, 483 Wushan Road, Guangzhou, Guangdong Province 510642, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: CFD Fertilizer Injection Jet Liquid Rice
The current broadcasting method for chemical fertilizer applications for rice production causes significant nitrogen losses through volatilization. To minimize this problem, a liquid-jet nozzle was developed for injection of liquid fertilizer in paddy fields. With computational fluid dynamics (CFD), the liquid-jet nozzle was modelled to examine the mass flow rates and velocities as affected by the critical design parameters of the nozzle: fertilizer inlet diameter (df) and nozzle orifice diameter (do). The model was validated with tests, and the performance of the liquid-jet nozzle was evaluated through injecting Urea Ammonium Nitrate solution into a clay loam soil. Simulation results showed that flow velocities decreased and mass flow rates increased at larger do values in a non-linear fashion. Effects of df were less pronounced and depended on the values of do. The model results agreed well with the test results with relative errors between 0.4 and 13.3%. Considering the requirements of nitrogen application rates for rice (60–180 kg ha−1) and soil cutting depths (20–50 mm), the optimal design parameters for the liquid-jet nozzle were the combinations of (df, do): (1.0, 1.0 mm) for producing the highest nitrogen application rate, and (0.6, 0.8 mm) for having the highest ability in cutting soil. The liquid-jet nozzle, a nontraditional injection method, has high potential to become a cost-effective and low soil-disturbance practice for rice production.
1. Introduction In rice production, effective fertilizer application is important for achieving good yield, reducing production cost, and minimizing nitrogen losses due to denitrification and volatilisation. Volatilisation is one of the main nitrogen loss pathways in paddy fields (Deng et al., 2012). The most common fertilization application method for paddy fields, broadcasting, is prone to volatilization. Compared with broadcasting, injection of liquid manure into soil can reduce losses of nitrogen from volatilization (Rahman et al., 2001). This is true for injection of other liquid fertilizers (Nyord et al., 2008). Injection can also increase fertilizer utilisation efficiency, as fertilizer is closely placed to plant roots. However, there are some problems with mechanical injectors, such as performance inconsistency, commercially unavailability, and high cost (Bautista et al., 2001). Most liquid injectors were opener-type injectors, such as coulter-type injectors (Morrison and Potter, 1994). Opener-type injectors caused high soil disturbance, which could potentially damage the plants. In addition, openers are not suitable for paddy fields, as furrows would quickly close behind the openers before the fertilizer is delivered into the furrows. Probe-type
⁎
injectors have been also developed for low soil disturbance applications (Benjamin et al, 1987). Womac and Tompkins (1990) developed a probe-type injector that penetrated soil every 400 mm of travel distance, and deposited liquid fertilizer in the soil at 65 mm depth. Using a similar working principle, a puncher was developed to deliver liquid fertilizer every 300 mm of the travel distance at 90 mm depth (da Silva et al., 2017). A non-traditional injection method using the liquid-jet technology would be a viable alternative to these mechanical injection methods, as discussed below. The liquid-jet technology was adopted from waterjet (WJ) technology. Waterjets have been used in cutting a wide variety of materials, such as plastics, rubber, cardboard, and insulation (Xu et al., 1999). Its working principle is that pressurized water passes through a smalldiameter orifice in a nozzle, forming a coherent stream of water that is powerful enough to cut through materials. For cutting hard materials, such as stone, glass, and metals, abrasive waterjet (AWJ) technology was used, in which an abrasive substance is mixed with the water stream, producing a more aggressive mechanical cutting action. For both WJ and AWJ, the effectiveness of cutting increases with the increase in water pressure (Hashish, 2009). However, high water pressure
Corresponding author. E-mail address: [email protected] (L. Qi).
https://doi.org/10.1016/j.compag.2019.105061 Received 10 July 2019; Received in revised form 5 September 2019; Accepted 18 October 2019 0168-1699/ © 2019 Elsevier B.V. All rights reserved.
Computers and Electronics in Agriculture 167 (2019) 105061
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nozzle outlet, m s−1 nitrogen application rate, kg ha−1 fraction of nitrogen in the liquid fertilizer, dimensionless nozzle spacing on the injector, m injector travel speed, m s−1 hydraulic power, W relative error, % simulated value measured value
Nomenclature CFD df do ṁ f ṁ o uo
RN ω s v P RE S M
Computational Fluid Dynamics diameter of the fertilizer inlet, mm diameter of the nozzle orifice, mm mass flow rate of the fertilizer at the fertilizer inlet, g s−1 mass flow rate of the liquid (water-fertilizer mixture) at the nozzle outlet, g s−1 velocity of the liquid (water-fertilizer mixture) at the
tube, a fertilizer tube, and a mixing chamber (Fig. 1). Connected to the mixing chamber was a water inlet on the top, a liquid outlet at the bottom, and a fertilizer inlet on the side. The working principle of the liquid-jet nozzle was similar to the AWJ. Water was supplied through a pump. Pressurized water entered into the mixing chamber through the water inlet. Water flowed out of the mixing chamber at a high speed through a nozzle orifice. This created a negative pressure within the mixing chamber (Kotousov, 2005), which drew liquid fertilizer into the chamber through the fertilizer inlet. The mixture of water and liquid fertilizer, referred as liquid for simplicity, was discharged from the orifice as a coherent liquid jet. The liquid jet penetrates through paddy soil in the rice field, which have completed the fertilizer injection.
is associated with high cost. If a commercially available pump could be used for pressurizing water, cost for cutting soft materials could be dramatically reduced (Irwansyah et al., 2012). Applications of WJ technology in agriculture have been explored since 1970s. Huang and Tayaputch (1973) proposed liquid-jet injection nozzles which were used to create intermittent or continuous ground openings, such as transplanting. Under a water pressure of 2.8 MPa, the maximum soil penetration depth was only 50 mm. Later, a jet injector for injection of agricultural liquid into the soil was patented by Johnston (1986). The advantages of the jet injector included elimination of tillage and reduction in the tractor power requirement. Tests of a liquid-jet injector were conducted in comparisons with traditional mechanical injectors (disc and spoke wheel injectors) (Nyord et al., 2008). It was found that the liquid-jet injector with a liquid pressure of 2.0 MPa was not able to inject liquid biofertilizer deeper than 20 mm, which was not sufficient to minimize nitrogen volatilization losses. Factors affecting soil cutting using the WJ technology has been studied (Niemoeller et al., 2011). Based on their test results, the recommended parameters for liquid-jet design were a water pressure of 40 MPa, a flow rate of 7.5 l min−1, and a travel speed of 2 m s−1, considering the required injection depths (70–90 mm) and energy consumption. They found that the energy consumption increased near linearly with the water pressure used. The literature results showed that applying the WJ technology to paddy soils with high moisture content would be advantageous. This study aimed to develop a liquid-jet injector that was able to cut paddy soil (with high moisture contents) using reasonably low pressure (10–14 MPa) to reduce the cost. To develop any types of liquid applicators, one needs to understand how the performance of the applicator is affected by design and operational parameters, such as geometrical and operational parameters (Patel et al., 2017). For these, Computational Fluid Dynamics (CFD) was used in this study to model the flow characteristics of a liquid-jet nozzle, such as mass flow rates and velocities. CFD has been recognized as a promising modelling tool for agricultural applications (Bartzanas et al., 2013; Lee et al., 2013) and reducing prototyping cost of applicators (Kashani et al., 2018). CFD was also an effective modelling tool to simulate and design AWJ (Liu et al., 2003; Liu et al., 2004). With CFD, spatial distributions of pressure and velocity in nozzle heads and at outlets could be simulated (Prisco and D’Onofrio, 2008), and multiple fluids (e.g. waste and liquid fertilizer) could be dealt with in one nozzle (Quiroz-Pérez et al., 2016). The objectives of this study were to (1) develop a liquid-jet nozzle for injection of liquid fertilizer (Urea Ammonium Nitrate solution) in paddy fields, (2) simulate the dynamic attributes of the liquid-jet nozzle using CFD to obtain the feasible and optimal design parameters, and (3) validate the model and evaluate the performance of the liquid-jet nozzle using measurements.
2.1.2. Design and operational parameters Parameters for designing the liquid-jet nozzle included lengths and diameters of water tube and inlet, mixing chamber, fertilizer tube and inlet, and nozzle orifice. They should be properly chosen so as to provide appropriate fertilizer application rate and capacity of cutting paddy soil. Through preliminary simulations and testing, the chosen values for these parameters are listed in Table 1, and the most critical design parameters were found to be the diameter of the nozzle orifice (do) and the diameter of the fertilizer inlet (df) (Fig. 1). The feasible and optimal do and df were determined through investigating dynamic attributes of the flows in the nozzle, including the mass flow rate of fertilizer at the fertilizer inlet, the mass flow rate of liquid at the nozzle outlet, and the liquid velocity at the nozzle outlet. These dynamic attributes were simulated using CFD, as discussed later in the paper. To use the liquid-jet nozzle in a fertilizer injector, several operational parameters needed to be considered, including standoff distance (Irwansyah et al., 2012), travel speed of the injector, and nozzle spacing on the injector. A fertilizer injector is required to place fertilizer at a desired application rate, determined based on the agronomic requirement of the crop. Application rate is associated with the mass flow rates of fertilizer, nozzle spacing on the injector, and the injector travel speed in the following relationship:
8 1
7
4
2 5
6 2. Material and methods 2.1. Liquid-jet nozzle development Fig. 1. The diagram of the liquid-jet nozzle; 1-main body, 2-water tube; 3fertilizer tube; 4-water inlet; 5-mixing chamber; 6-nozzle outlet; 7-fertilier inlet; 8-jewel.
2.1.1. Structure The liquid-jet nozzle developed comprised of a main body, a water 2
Computers and Electronics in Agriculture 167 (2019) 105061
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(water-fertilizer mixture) at the nozzle outlet (ṁ o ) and the mass flow rate of the fertilizer at the fertilizer inlet (ṁ f ) were measured. Prior to a test, the system was run for approximately 1 min to achieve a stable flow rate in the system. Then, the test was run for 3 min. The weight lost in the fertilizer container was measured using a scale and converted to ṁ f with the given time. Similarly, the weight gained in the measuring cylinder was recorded to calculate the ṁ o . Preliminary tests showed that effects of water pressure on the ṁ f was negligible, and varying the pressure from 10 to 12 MPa, or from 12 to 14 MPa, the ṁ f was increased only by approximately 2%. Therefore, the pressure in simulation was kept at a constant value of 12 MPa for all tests. The liquid velocity from the nozzle was not associated with the soil cutting. Thus, the measure of liquid velocity was done in a free air condition. A high-speed camera (CR600X2, 600 fps) was used to measure the liquid velocity at the nozzle outlet (uo) (Fig. 3a). To prevent damage to the camera from the back splash of the jet hitting the ground, the nozzle was oriented horizontally, held by a horizontal metal bar. It was assumed that the effect of gravity on the liquid jet was negligible. Rulers were placed on a background board as a scale for measuring the shooting distance of the jet. The nozzle, camera, and rulers were positioned properly, so that the camera could capture the image of the jet as it was traveling along the ruler direction. A high-voltage solenoid valve (DC 12 V; 20 MPa; YSV0100, Shanghai Yongzhan Machinery Electric Co.) was used to start and stop the water flow. For a test, a stable flow rate was obtained prior to the measurements by running the system for approximately 1 min. Then water flow was stopped for 2–3 s, and restarted. The shooting liquid jet was captured as picture frames. In a picture frame, the tip location of the liquid jet was indicated by the ruler, as illustrated in Fig. 3b. The travel distance between two consecutive picture frames was the difference between the tip locations on the two pictures. For example, the travel distance would be 42 mm (122 mm − 80 mm), based on the two picture frames shown in Fig. 3b. Then, the flow velocity was estimated as the travel distance divided by the time interval between the two picture frames that was 0.001667 s in this case.
Table 1 Design parameters of the liquid-jet nozzle. Term
Dimension
Value (mm)
Water tube
Diameter Length
5 100
Water inlet
Diameter Length
0.33 1
Mixing chamber
Diameter Length
5 5
Fertilizer tube
Diameter Length
3 5
Fertilizer inlet
Diameter Length
df 1
Nozzle orifice
Diameter Length
do 3
RN =
10ṁ f ω (1)
sv
where RN is the nitrogen application rate (kg ha−1); ṁf is the mass flow rate of fertilizer (g s−1); ω is fraction of nitrogen in the liquid fertilizer (dimensionless); s is nozzle spacing on the injector (m); v is injector travel speed (m s−1). Injector travel speed is adjustable in a field operation. Selection of s is affected by the plant row spacing. The value of ω depends on the type of liquid fertilizer. The ṁf is affected by the design of the liquid-jet nozzle.
2.2. Experiments 2.2.1. Tests of the liquid-jet nozzle For testing, the liquid-jet nozzle was fabricated in a commercial manufacturer. It was tested in a testing platform (Fig. 2a), not in a field fertilizer injector. Tests were conducted in a laboratory in South China Agricultural University, China. As illustrated in Fig. 2b, water through a filter was supplied to a pump (Flow rate: 15.1 l min−1, Pressure: 25 MPa, RRV 4G36, Annovi Reverberi) driven by an engine. Pressurized water flowed to the liquid-jet nozzle through a valve that directed some extra water back to the water reservoir. Liquid fertilizer in a container was connected to the fertilizer inlet of the nozzle through a tube. The liquid (fertilizer mixture) from the nozzle outlet was collected in a measuring cylinder. The data were used to validate the CFD model, described later in the paper. Tests were run for two combinations of the diameters (df, do): (0.6, 0.8 mm) and (0.8, 0.6 mm). Each combination was replicated five times. In the tests, the mass flow rate of the liquid Pressure valve
Pump
2.2.2. Soil cutting experiment Soil is a complex system and its strength varies with soil water content, texture, compaction level, and other conditions. The best way to evaluate the soil cutting ability of the liquid-jet nozzle was to test it in soil. An experiment was conducted in a soil bin (1.60 m long, 0.70 m wide, and 0.45 m deep) containing a typical paddy soil (clay loam) with a moisture content of 50% (dry basis). The soil bin was located at South China Agricultural University. A testing carriage travelled along tracks, and the movable soil bin was positioned below the nozzle (Fig. 4). The carriage was comprised of a DC motor, a controller, a DC power supply,
Engine Water hose
Pressure gauge
Liquid-jet nozzle
Water
Filter
Valve
Pump
Pressure gauge
Liquid-jet nozzle
Fertilizer
Fetilizer mixture
Fertilizer tube
Fertilizer container Scale
Water filter
Liquid collector
(a)
(b)
Fig. 2. Liquid-jet nozzle and the test setup. 3
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Camera Ruler
Valve
Nozzle
(a) Tip of the jet
Tip of the jet
(b) Fig. 3. Measurements of the liquid velocity at the nozzle outlet; (a) measurement setup; (b) two consecutive picture frames from the high-speed camera, showing the image of liquid jet.
wheels and frame, the liquid-jet nozzle and the support. The travel speed of the carriage was adjusted by the controller. The standoff distance of the nozzle could be adjusted along the support. The experimental treatments were the combinations of three different standoff distances (10, 20, and 30 mm) and three different travel speeds (0.6, 0.7, and 0.8 m s−1). Tests were conducted in a completely randomized order with three replicates. For all test runs, the values of df and do were set as 0.6 and 0.8 mm, selected based on preliminary tests. Soil cutting depth was measured by inserting a ruler into the soil slot down to the slot bottom.
Carriage
Support
Track
2.3. Simulations
Soil bin
2.3.1. Model formulation A CFD model of the liquid-jet nozzle was developed using the software Fluent v14.0 in ANSYS as a flow solver. The computational domain comprised of a mixing zone, water zone, and fertilizer zones, which were extended (Fig. 5a). The dimensions of the domain are
Nozzle Fig. 4. Soil cutting experiment setup.
Fig. 5. The CFD model of the liquid-jet nozzle; (a) domain; (b) domain dimensions; (c) discretization. 4
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Model results were used to assess the potential of the liquid-jet nozzle in the context of field injection. When the liquid-jet nozzle was used for fertilizer injection in paddy fields, the following two requirements had to be met:
shown in Fig. 5b. The computational domain was meshed in the ICEM using the tetrahedron element for non-structural components and prism element for exterior walls (Fig. 5c). The discretization scheme was selected as the second-order upwind format. The mesh density of inlet and outlet were increased, and areas with a great change in size were increased as well. A target value of 0.4 was used in smoothing the mesh to ensure a final mesh quality between 0.4 and 1.0. The total number of elements was approximately four million. In the model, the flow was assumed to be in a steady-state condition since the transient variation of internal parameters was not considered in the computational domain. The gravity direction was along the water flow direction and pointed toward the nozzle outlet. The ejection of the water and fertilizer in the nozzle was treated as a round hole jet flow. The turbulence model of Realizable K-ε model was used because of its accuracy and convergence in simulating the round hole jet flow problem (Quiroz-Pérez et al., 2016). The simulation mode of Species Transport was used, assuming that the mixing process of water and fertilizer had no chemical reaction. Computation of energy equations was disabled. The CFD model was solved using the SIMPLEC algorithm. When the residual continuity, momentum, and turbulent flow energy were less than 10−4, and the dynamic attributers (ṁ f , ṁ o , and uo) were stable, the model reached convergence.
(1) to deliver an appropriate nitrogen rate to meet the nutrient requirement of rice crop; (2) to effectively cut soil so that the fertilizer is placed into a desired depth. The typical range of total nitrogen application rate was from 60 to 180 kg ha−1 reported by Peng et al. (2002) for 12 countries. In practice, the total nitrogen requirement is split into applications at multiple times during different rice growing stages (Liu et al., 2016). If two applications were used in the growing season, the nitrogen application rate per application would be from 30 to 90 kg ha−1. The simulated ṁ f values of the nozzle were assessed in terms of meeting the required nitrogen application rates for rice production. In addition, the potential ability of the liquid jet in cutting soil was also assessed.
3. Results and discussion 3.1. Simulation results
2.3.2. Boundary and initial conditions, and model inputs The boundary conditions of water inlet, fertilizer inlet, and nozzle outlet were specified as mass flow inlet, pressure inlet, and pressure outlet, respectively. The mass flow rate of water inlet was constant, and obtained from the experiment. The initial gauge pressures and total gauge pressures were set to zero. Turbulent intensity was set as 5% for all. Initial flow directions were normal to the surfaces. The fluid properties needed as model inputs were density, dynamic viscosity, and relative molecular mass. The liquid fertilizer was Urea Ammonium Nitrate solution with a 32% nitrogen concentration (UAN32). Its density and dynamic viscosity were measured using a glass hydrometer and a digital rotational viscometer. Values of boundary and initial conditions, and fluid properties are listed in Table 2.
3.1.1. Velocity of liquid at the nozzle outlet Among the simulations for 20 different combinations of df and do, the effects of three different df values with a constant do (0.8 mm) are shown in Fig. 6. In general, the water zone had low velocities which were uniformly distributed in the zone. The fertilizer zone was “quiet” in terms of flow activity. Most actions occurred in the mixing chamber. As the water stream went down the mixing chamber, it became less coherent as well as slower in velocity. The water stream divided the mixing chamber into two “compartments” with different velocity distributions. At df = 0.4 mm (Fig. 6a), on the left compartment of the chamber, the stream hit the bottom wall of the mixing chamber, diverging towards the side wall of the chamber, forming a vertically elongated vortex. On the right compartment of the chamber, the velocity field was different as it was connected with the fertilizer zone where liquid fertilizer was drawn into the chamber. The liquid fertilizer joined the water stream, and the mixed liquid formed a round vortex at the bottom quarter section of the compartment. When increasing df from 0.4 to 0.6 mm (Fig. 6b), the general velocity distribution had little change, however velocities became lower in the right compartment. Further increasing the df to 1.0 mm (Fig. 6c) resulted in a further reduction in velocities. Drawing a substance (fertilizer in this case) into the mixing chamber would more or less slow down the velocities, based on a study on AWJ by Patel and Shaikh (2013). Fig. 7 shows the effects of three different do values with a constant df of 0.8 mm. A distinct phenomenon was observed: the ṁ f was negative
2.3.3. Dynamic attributes monitored The model was used to simulate the critical dynamic attributes that affected the performance of the liquid-jet nozzle for fertilizer injection. Simulations were done for 20 combinations of four levels of df (0.4, 0.6, 0.8, and 1.0 mm) and five levels of do (0.4, 0.6, 0.8, 1.0 and 1.2 mm). Each simulation last for 30,000 time-steps which were found to be sufficient through preliminary simulations. The ṁ f , ṁ o , and uo were monitored to understand how these dynamic attributes were affected by these combinations of the two diameters. With the simulated uo, hydraulic power of the liquid jet was determined as follows based on the literature (Hashish, 2009):
P=
1 ṁ o uo2 2
(2)
where P is hydraulic power of liquid (W). Please notice that the value determined from Eq. (2) was the power at the nozzle outlet, whereas the power that impacted soil would be lower. Thus, P values only indirectly reflected the soil cutting power of the liquid jet.
Table 2 Boundary and initial conditions as well as fluid properties.
2.3.4. Model validation and application Data from the tests of the liquid-jet nozzle were used for the model validation. Model results were compared with those from the tests. Comparisons were made for the ṁ f , ṁ o , and uo. The agreements were assessed by relative errors defined as the following:
RE =
|S − M| 100 M
(3)
where RE is relative error (%); S is simulated value; M is measured value. 5
Boundary
Variable
Value
Water inlet
Mass flow rate (kg s−1) Hydraulic diameter (m) Species mass fraction (fertilizer) Water density (kg/m3) Water dynamic viscosity (Pa·s) Water relative molecular mass
0.0065 1.5 0 998 0.001005 18.02
Fertilizer inlet
Hydraulic diameter (m) Species mass fraction (fertilizer) Fertilizer density (kg/m3) Fertilizer dynamic viscosity (Pa·s) Fertilizer relative molecular mass
3 1 1326 0.00868 62.68
Computers and Electronics in Agriculture 167 (2019) 105061
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(a) df=0.4 mm
(b) df=0.6 mm
(c) df=1.0 mm Fig. 6. Simulated velocity contours in the model domain for different fertilizer inlet diameters (df) with a constant orifice diameter (do) of 0.8 mm.
when do = 0.4 mm (Fig. 7a), meaning that the flow was reversed between the mixing chamber and the fertilizer zone, which was not feasible for fertilizer injector. These phenomena were attributable to the extremely small orifice diameter, which physically blocked the stream from exiting the nozzle outlet. In the right compartment of the mixing chamber, some flow diverged and entered the fertilizer zone before hitting the bottom wall of the chamber, and some entered the fertilizer zone after hitting the bottom wall. At do = 0.8 mm (Fig. 7b), more fertilizer flowed to the mixing chamber, which would increase the fertilizer application rates. Both compartments of the chamber had
lower velocities, due to the drawing of fertilizer, as explained above. This would ultimately increase the effectiveness of soil cutting. At the largest do, 1.2 mm (Fig. 7c), the amount of fertilizer flowing to the chamber was further increased, and the velocities were further reduced. Response surfaces were used to demonstrate the effects of df and do on the flow characteristics. It should be noticed that the response surfaces were generated from the simulation results of only 20 combinations of df and do. The other points on the response surfaces were from interpolating between those 20 simulation points. Also, the range (0.4–1.0 mm) of df and that (0.4–1.2 mm) of do used in the simulations 6
Computers and Electronics in Agriculture 167 (2019) 105061
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(a) do=0.4 mm
(b) do=0.8 mm
(c) do=1.2 mm Fig. 7. Simulated velocity contours in the model domain for different nozzle orifice diameters (do) with a constant fertilizer inlet diameter (df) of 0.8 mm.
was used for a waterjet cutting food (Irwansyah et al., 2012). The response of uo to df depended on the values of do, meaning that there were some interactions between do and df. The results also showed that the df was less critical when compared with do. The dynamics in the fertilizer container was kept minimum due to the zero absolute pressure and near zero velocity in the fertilizer container. Thus, altering df only changed the uo to a small extent. The values of P were plotted against the combination of df and do (Fig. 8b). The P was non-linearly related to df and do, with the higher values at smaller values of df and do. A higher P
were greater than those (0.6–0.8 mm) used in the validation tests. Caution should be taken when using the simulation results which were beyond the measured ranges. The simulated value of uo varied from 7.10 to 32.4 m s−1 within the range of the diameters examined (Fig. 8a). The peak of uo occurred at the smallest do (0.4 mm) and the smallest df (0.4 mm). In general, the uo decreased with the increase of do, which was consistent with fluid dynamics theory. This was why orifice diameters as small as practical were by past researchers. For example, an orifice diameter of 0.5 mm 7
Computers and Electronics in Agriculture 167 (2019) 105061
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Fig. 8. Simulated results for different fertilizer inlet diameter (df) and nozzle orifice diameter (do); (a) velocity of the nozzle outlet; (b) hydraulic power of the liquid.
combinations of large do and df, and the peak value was 15.7 g s−1. In terms of effects of df and do, the same explanations for ṁ f were applied to ṁ o .
potentially has higher power to cut soil, which meant that the diameters resulting in higher hydraulic power favoured soil cutting. This is important information for assessing the soil cutting ability of the liquid-jet nozzle.
3.2. Model validation 3.1.2. Mass flow rates of fertilizer and liquid The response surface of the simulated ṁ f raised as the do increased, and reached to its peak at the largest do and df, where the ṁ o was 9.2 g s−1 (Fig. 9a). Again, effects of df on the ṁf depended on the value of do. The negligible effects of df at a lower range of do implied that the small fertilizer inlet diameter might have physically blocked the fertilizer flow. Thus, one could say that when the fertilizer inlet did not restrict the flow, the amount of fertilizer flowing into the mixing chamber was affected by do, a more dominant factor for ṁ f . Effects of do on ṁ f could be explained by the effects of do on the pressure in the mixing chamber. As the do was increased, the pressure at the outlet of the chamber would decrease, because of the constant pressure at the water inlet. Thus, the pressure difference between the inlet and outlet of the chamber would be increased. This created a higher vacuum in the mixing chamber (Patel and Shaikh, 2013), and therefore drew more liquid fertilizer into the mixing chamber. As the result, the ṁf was increased with the do. At do = 0.4 mm, the mixing chamber had positive pressure, which pushed the liquid from the chamber to the fertilizer container, as discussed above. The ṁo was the sum of ṁ f and the mass flow rate of water that was an initial input of the model (6.50 g s−1). As the water flow rate remained constant in the model, the variation of the simulated ṁ o followed the same trends as the simulated ṁ f , with the response surface being shifted up by 6.50 g s−1 (Fig. 9b). The high ṁ o zone was at the
The simulation results of ṁf and ṁo at two different combination of df and do along with the corresponding test data obtained using the testing platform shown in Fig. 2 are summarized in Table 3. The CFD model slightly over-predicted the mass flow rates with low levels of discrepancy. The maximum relative error of 13.3% was observed for the simulated ṁf at the setting of (0.6, 0.8 mm) for (df, do). The model produced a minimum error of 0.4% for the simulated ṁo at the setting of (0.8, 0.6 mm). The relative errors showed that the simulated and measured mo agreed better than the simulated and measured ṁ f . In terms of uo, the relative errors were also low. Overall, the CFD model was reasonably accurate in simulating the flow dynamics of the liquidjet nozzle system. 3.3. Measured soil cutting depths Soil cutting depth measured from the experiment varied from 19 to 52 mm, depending on the standoff distance and injector travel speed. The cutting depth decreased significantly with the increase in standoff distance (Fig. 10a). The further the nozzle outlet was away from the soil surface, the shallower the soil cutting depth was. This was expected, as the hydraulic power of the jet declined after leaving the outlet, as pointed out by Liu et al. (2004). Cutting depth also decreased significantly with the travel speed of the injector (Fig. 10b). When the
Fig. 9. Simulated mass flow rates under different fertilizer inlet diameter (df) and nozzle orifice diameter (do); (a) at the fertilizer inlet (ṁ f ); (b) at the nozzle outlet. 8
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Table 3 Comparisons between simulation and test results of the liquid-jet nozzle. (df, do) (mm)
ṁ f
50
Model (g s−1)
Test (g s−1)
RE (%)
Model (g s−1)
Test (g s−1)
RE (%)
Model (m s−1)
Test (m s−1)
RE (%)
3.4 0.3
3.0 0.27
13.3 11.1
9.9 6.8
9.5 6.77
4.2 0.4
18.2 23.9
19.2 25.8
5.3 7.2
a
b c
40 30 20 10 0
10 20 30 Standoff distance (mm)
(a)
Soil cutting depth (mm)
Soil cutting depth (mm)
(0.6, 0.8) (0.8, 0.6)
uo
ṁ o
60 50 40 30 20 10 0
a
was assumed that the minimum hydraulic power of 1.15 kW was needed to cut soil. Thus, the combinations of Nos. 1, 2, 5, 6, 10, 11, and 12, which had lower P, were not feasible for the design of the liquid-jet nozzle. In summary, considering the requirements of nitrogen application rate and soil cutting depth, those (df, do) combinations with application rates lower than 30 kg ha−1 and hydraulic powers lower than 1.15 kW were eliminated. Thus, the feasible (df, do) combinations were Nos. 3, 4, 7, 8, and 9, as listed in Table 5. Among them the (1.0, 1.0 mm) combination gave the highest nitrogen application rate, and the (0.6, 0.8 mm) combination had the highest soil cutting ability.
b c
0.6 0.7 0.8 Travel speed (m s-1)
(b)
Fig. 10. Soil cutting depths; (a) for different standoff distances; (b) for different travel speeds. Error bars stand for standard deviations.
4. Conclusion injector travels faster, the time of the jet impacting soil was less. As the result, the cutting depth was shallower. The factor of standoff distance is limited by the clearance requirement of the nozzle to the soil surface. A smaller standoff distance had a better soil cutting, but it gave a smaller clearance to the soil surface. Paddy fields typically had levelled surfaces, which may allow the use of small standoff distance. Also, it is suggested to inject fertilizer between crop rows, so as to avoid damage the rice plants. Travel speed is easily adjusted. The injector could travel slower to achieve greater soil cutting depth. When the travel speed decreased from 0.8 to 0.6 m s−1, the soil cutting depth increased by approximately 50%.
In this study, a liquid-jet nozzle was developed and modelled for liquid fertilizer injection in paddy fields. The model was validated, and the performance of the liquid-jet nozzle was evaluated using measurements. The following conclusions were drawn:
• The nozzle orifice diameter and fertilizer inlet diameter of the li• •
3.4. Model applications
•
The ṁ f of the liquid-jet nozzle needed to be in a range corresponding to the range of the required nitrogen rates for rice crop. The diameter do = 0.4 mm was eliminated for the design of the liquid-jet nozzle due to its negative ṁ f . The simulated values of ṁ f for the other diameters are summarized in Table 4. With the simulated ṁ f results, assuming that the fraction of nitrogen in the fertilizer (ω) was 0.32, the corresponding nitrogen application rates were determined according to Eq. (1) for three different injector travel speeds (0.6, 0.7, and 0.8 m s−1) and a nozzle spacing of 0.15 m (Table 4). Among the 16 combinations of df and do, the Nos. 13–16 where do = 0.6 mm, had impractically low nitrogen rates. Thus, do = 0.6 mm was eliminated. For the rest of the combinations, the nitrogen rates varied from approximately 32 to 327 kg ha−1, depending on the injector travel speed. These application rates were sufficient to meet the typical nitrogen requirement of a rice crop. For low nitrogen rates, for example, 30 kg ha−1, the liquid-jet nozzle could be used for any travel speeds above 0.6 m s−1. The relationship between the capacity of the injector and the operational parameters could be examined using Eq. (1). Nozzle spacing depends on the plant row spacing. For example, when the plant row spacing is 0.30 m, fertilizer can be injected in between two plant rows, giving a nozzle spacing of 0.30 m. Under the same ṁ f and injector travel speed, the fertilizer application rate in a 0.30 m spacing would be reduced to half. In the case of higher fertilizer rate being desired, fertilizer can also be applied on both sides of the plant row to increase the nitrogen application rates. Another aspect needing to be considered is soil cutting ability of the liquid jet. In theory, soil cutting ability is affected by the P. Preliminary soil cutting tests showed that the (df, do) combinations with do = 1.2 mm did not cut well due to its low P (below 1.15 kW). Thus, it
•
quid-jet nozzle were the most critical design parameters which affected the injection depth and fertilizer application rate. The injector with the liquid-jet nozzles spaced 0.15 m apart was capable of injecting nitrogen at rates from 59 to 231 kg ha−1, depending on the injector travel speed. The liquid-jet nozzle had ability to cut through the given paddy soil to a depth between 19 and 52 mm, depending on the standoff distance and injector travel speed. Considering meeting typical nitrogen application rates for rice production and injection depths, the feasible nozzle orifice diameters (do) were 0.8 and 1.0 mm, and the feasible fertilizer inlet diameters (df) were 0.6, 0.8, and 1.0 mm. Among these feasible diameters, the optimal ones were the combinations of df = 1.0 mm and do = 1.0 mm, in terms of the highest
Table 4 Nitrogen application rates at different injector travel speeds, and hydraulic power determined based on the simulated mass flow rates of fertilizer for a nozzle spacing of 0.15 m. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
9
(df, do) (mm)
(1.0, (0.8, (1.0, (0.8, (0.6, (0.6, (0.6, (1.0, (0.8, (0.4, (0.4, (0.4, (0.4, (0.6, (0.8, (1.0,
1.2) 1.2) 1.0) 1.0) 1.2) 1.0) 0.8) 0.8) 0.8) 1.0) 1.2) 0.8) 0.6) 0.6) 0.6) 0.6)
ṁ f (g s−1)
9.2 7.0 6.5 5.7 4.3 3.7 3.4 2.5 2.2 2.0 1.9 1.2 0.6 0.5 0.3 0.2
Nitrogen rate (kg ha−1)
P
0.6 m s−1
0.7 m s−1
0.8 m s−1
(kW)
327.1 248.9 231.1 202.7 152.9 131.6 120.9 88.9 78.2 71.1 67.6 42.7 21.3 17.8 10.7 7.1
280.4 213.3 198.1 173.7 131.0 112.8 103.6 76.2 67.0 61.0 57.9 36.6 18.3 15.2 9.1 6.1
245.3 186.7 173.3 152.0 114.7 98.7 90.7 66.7 58.7 53.3 50.7 32.0 16.0 13.3 8.0 5.3
1.121 0.737 1.386 1.173 0.407 0.726 1.638 1.272 1.174 0.448 0.210 0.855 2.157 2.091 1.949 1.871
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Table 5 Feasible df and do combinations and the corresponding nitrogen rates at different travel speeds for a nozzle spacing of 0.15 m. (df, do) (mm)
(0.6, (1.0, (1.0, (0.8, (0.8,
0.8) 1.0) 0.8) 0.8) 1.0)
Nitrogen rate (kg ha−1)
Agri. Eng. Res. 78 (4), 333–346. Benjamin, J.G., Cruse, R.M., Blaylock, A.D., Vogl, L.V., 1987. A small-plot point injector for liquid fertilizer application. Soil Sci. Soc. Am. 52, 1194–1195. Lee, I., Bitog, J.P.P., Hong, S., Seo, I., Kwon, K., Bartzanas, T., Kacira, M., 2013. The past, present and future of CFD for agro-environmental applications. Comput. Electron. Agric. 93, 168–183. da Silva, M.J., Franco, H.C.J., Magalhães, P.S.G., 2017. Liquid fertilizer application to ratoon cane using a soil punching method. Soil Till. Res. 165, 279–285. Deng, M.H., Shi, X.J., Tian, Y.H., Yin, B., Zhang, S.L., Zhu, Z.L., Kimura, S.D., 2012. Optimizing nitrogen fertilizer application for rice production in the Taihu Lake Region, China. Pedosphere 22 (1), 48–57. Hashish, M., 2009. Special AWJ nozzles. 2009 American WJTA Conference and Expo, August 18–20, 2009, Houston, TX, USA. Huang, B.K., Tayaputch, V., 1973. Design and analysis of a fluid injection spot and furrow opener. Trans. ASAE 16 (3), 414–419. Irwansyah, I., Masri, I., Hendra, F., 2012. Influence of water-jet nozzle geometry on cutting ability of soft material. J. Rekayasa Kimia Lingkungan 9 (1), 1–6. Johnston, D., 1986. Method and Apparatus for the Jet Injection of Agricultural Liquids into the Soil. United States Patents, No. 4,624,193, USA. Kashani, A., Parizi, H., Mertins, K.H., 2018. Multi-step spray modelling of a flat fan atomizer. Comput. Electron. Agric. 144, 58–70. Kotousov, L.S., 2005. Measurement of the water jet velocity at the outlet of nozzles with different profiles. Trans. Tech. Phys. Gases Liq. 50 (8), 1112–1118. Liu, H., Wang, J., Brown, R.J., Kelson, N., 2003. Computational fluid dynamic (CFD) simulation of ultrahigh velocity abrasive water jet. Eng. Med. Serv. Inform. Technol. 236, 477–482. Liu, H., Wang, J., Kelson, N., Brown, R.J., 2004. A study of abrasive waterjet characteristics by CFD simulation. J. Mater. Process. Technol. 153–154 (2004), 488–493. Liu, X., Wang, H., Zhou, J., Hu, F., Zhu, D., Chen, Z., Liu, Y., 2016. Effect of N fertilization pattern on rice yield, N Use efficiency and fertilizer-N Fate in the Yangtze River basin, China. PLoS ONE 11 (11), 1–21. Morrison, J.E., Potter, K.N., 1994. Fertilizer solution placement with a coulter-nozzle applicator. Appl. Eng. Agric. 10 (1), 7–11. Niemoeller, B., Marms, H.H., Lang, T., 2011. Injection of liquids into the soil with a highpressure jet. Agric. Eng. Int. CIGR J. 13 (2), 1–22. Nyord, T., Sogaard, H.T., Hansen, M.N., Jensen, L.S., 2008. Injection methods to reduce ammonia emission from volatile liquid fertilizer applied to growing crops. Biosyst. Eng. 100 (2008), 235–244. Patel, M.K., Praveen, B., Sahoo, H.K., Patel, B., Kumar, A., Singh, M., Nayak, M.K., Rajan, P., 2017. An advance air-induced air-assisted electrostatic nozzle with enhanced performance. Comput. Electron. Agric. 135, 280–288. Patel, S.R., Shaikh, A.A., 2013. Control and measurement of abrasive flow rate in an abrasive waterjet machine. Int. J. Innov. Res. Sci. Eng. Technol. 2 (19), 7675–7679. Peng, S., Huang, J., Zhong, X., Yang, J., Wang, G., Zou, Y., Christian, W., 2002. Challenge and opportunity in improving fertilizer-nitrogen use efficiency of irrigated rice in China. Agri. Sci. China 1 (7), 776–785. Prisco, U., D’Onofrio, M.C., 2008. Three-dimensional CFD simulation of two-phase flow inside the abrasive water jet cutting head. Int. J. Comput. Meth. Eng. Sci. Mech. 9 (5), 300–319. Quiroz-Pérez, E., Vázquez-Román, R., Castillo-Borja, F., Hernández-Barajas, R., 2016. A CFD model for the FCC feed injection system. Fuel 186, 100–111. Rahman, S., Chen, Y., Zhang, Q., Tessier, S., Baidoo, S., 2001. Performance of a liquid manure injector in a soil bin and on established forages. Can. Biosyst. Eng. 43 (2), 33–40. Womac, A.R., Tompkins, F.D., 1990. Probe-type injector for fluid fertilizers. Appl. Eng. Agric. 6 (2), 149–154. Xu, J., Otterstatter, K., Harkess, M., Sacquitne, R., Lague, J., 1999. Hyper pressure waterjet and abrasive waterjet cutting. 10th American Waterjet Conference, Paper 9. St. Louis. Waterjet Technology Association, MO, USA.
P (kW)
0.6 m s−1
0.7 m s−1
0.8 m s−1
120.9 231.1 88.9 78.2 202.7
103.6 198.1 76.2 67.0 173.7
90.7 173.3 66.7 58.7 152.0
1.638 1.386 1.272 1.174 1.173
nitrogen application rate, and df = 0.6 mm and do = 0.8 mm, in terms of highest soil cutting ability. The results were obtained from one type of liquid fertilizer and one soil condition, and the simulation results were not validated for all the possible design scenarios. Caution should be taken when applying the results. Injection of liquid fertilizer using the liquid-jet technology is a highly promising technique for rice production. However, there were several drawbacks, including slow travel speeds and shallow injection depths. Currently, the technique and equipment are still in the stage of development. Future research is required before it can be widely used. Acknowledgments This research was supported in part by the National Key R&D Program of China (No. 2018 YFD0200303), the Natural Science Foundation of China (No. 51575195 & 51875217), the Key R&D Program of Guangdong (No. 2019B020221003), Guangdong Science and Technology Support Plant (No. 2017 A020208037), the Earmarked Fund for Modern Agro-industry Technology Research System (No. CARS-01-43). Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.compag.2019.105061. References Bartzanas, T., Kacira, M., Zhu, H., Karmakar, S., Tamimi, E., Katsoulas, N., Kittas, C., 2013. Computational fluid dynamics applications to improve crop production systems. Comput. Electron. Agri. 93, 151–167. Bautista, E.U., Koike, M., Suministrado, D.C., 2001. PM - Power and machinery: mechanical deep placement of nitrogen in wetland rice to receive recommendations. J.
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of a liquid-jet nozzle for fertilizer injection in paddy fields using CFD Wenhan Zhenga, Yu Jiangb, Xu Maa, Long Qia, a b
T
⁎
College of Engineering, South China Agricultural University, 483 Wushan Road, Guangzhou, Guangdong Province 510642, PR China Modern Educational Technology Centre, South China Agricultural University, 483 Wushan Road, Guangzhou, Guangdong Province 510642, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: CFD Fertilizer Injection Jet Liquid Rice
The current broadcasting method for chemical fertilizer applications for rice production causes significant nitrogen losses through volatilization. To minimize this problem, a liquid-jet nozzle was developed for injection of liquid fertilizer in paddy fields. With computational fluid dynamics (CFD), the liquid-jet nozzle was modelled to examine the mass flow rates and velocities as affected by the critical design parameters of the nozzle: fertilizer inlet diameter (df) and nozzle orifice diameter (do). The model was validated with tests, and the performance of the liquid-jet nozzle was evaluated through injecting Urea Ammonium Nitrate solution into a clay loam soil. Simulation results showed that flow velocities decreased and mass flow rates increased at larger do values in a non-linear fashion. Effects of df were less pronounced and depended on the values of do. The model results agreed well with the test results with relative errors between 0.4 and 13.3%. Considering the requirements of nitrogen application rates for rice (60–180 kg ha−1) and soil cutting depths (20–50 mm), the optimal design parameters for the liquid-jet nozzle were the combinations of (df, do): (1.0, 1.0 mm) for producing the highest nitrogen application rate, and (0.6, 0.8 mm) for having the highest ability in cutting soil. The liquid-jet nozzle, a nontraditional injection method, has high potential to become a cost-effective and low soil-disturbance practice for rice production.
1. Introduction In rice production, effective fertilizer application is important for achieving good yield, reducing production cost, and minimizing nitrogen losses due to denitrification and volatilisation. Volatilisation is one of the main nitrogen loss pathways in paddy fields (Deng et al., 2012). The most common fertilization application method for paddy fields, broadcasting, is prone to volatilization. Compared with broadcasting, injection of liquid manure into soil can reduce losses of nitrogen from volatilization (Rahman et al., 2001). This is true for injection of other liquid fertilizers (Nyord et al., 2008). Injection can also increase fertilizer utilisation efficiency, as fertilizer is closely placed to plant roots. However, there are some problems with mechanical injectors, such as performance inconsistency, commercially unavailability, and high cost (Bautista et al., 2001). Most liquid injectors were opener-type injectors, such as coulter-type injectors (Morrison and Potter, 1994). Opener-type injectors caused high soil disturbance, which could potentially damage the plants. In addition, openers are not suitable for paddy fields, as furrows would quickly close behind the openers before the fertilizer is delivered into the furrows. Probe-type
⁎
injectors have been also developed for low soil disturbance applications (Benjamin et al, 1987). Womac and Tompkins (1990) developed a probe-type injector that penetrated soil every 400 mm of travel distance, and deposited liquid fertilizer in the soil at 65 mm depth. Using a similar working principle, a puncher was developed to deliver liquid fertilizer every 300 mm of the travel distance at 90 mm depth (da Silva et al., 2017). A non-traditional injection method using the liquid-jet technology would be a viable alternative to these mechanical injection methods, as discussed below. The liquid-jet technology was adopted from waterjet (WJ) technology. Waterjets have been used in cutting a wide variety of materials, such as plastics, rubber, cardboard, and insulation (Xu et al., 1999). Its working principle is that pressurized water passes through a smalldiameter orifice in a nozzle, forming a coherent stream of water that is powerful enough to cut through materials. For cutting hard materials, such as stone, glass, and metals, abrasive waterjet (AWJ) technology was used, in which an abrasive substance is mixed with the water stream, producing a more aggressive mechanical cutting action. For both WJ and AWJ, the effectiveness of cutting increases with the increase in water pressure (Hashish, 2009). However, high water pressure
Corresponding author. E-mail address: [email protected] (L. Qi).
https://doi.org/10.1016/j.compag.2019.105061 Received 10 July 2019; Received in revised form 5 September 2019; Accepted 18 October 2019 0168-1699/ © 2019 Elsevier B.V. All rights reserved.
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nozzle outlet, m s−1 nitrogen application rate, kg ha−1 fraction of nitrogen in the liquid fertilizer, dimensionless nozzle spacing on the injector, m injector travel speed, m s−1 hydraulic power, W relative error, % simulated value measured value
Nomenclature CFD df do ṁ f ṁ o uo
RN ω s v P RE S M
Computational Fluid Dynamics diameter of the fertilizer inlet, mm diameter of the nozzle orifice, mm mass flow rate of the fertilizer at the fertilizer inlet, g s−1 mass flow rate of the liquid (water-fertilizer mixture) at the nozzle outlet, g s−1 velocity of the liquid (water-fertilizer mixture) at the
tube, a fertilizer tube, and a mixing chamber (Fig. 1). Connected to the mixing chamber was a water inlet on the top, a liquid outlet at the bottom, and a fertilizer inlet on the side. The working principle of the liquid-jet nozzle was similar to the AWJ. Water was supplied through a pump. Pressurized water entered into the mixing chamber through the water inlet. Water flowed out of the mixing chamber at a high speed through a nozzle orifice. This created a negative pressure within the mixing chamber (Kotousov, 2005), which drew liquid fertilizer into the chamber through the fertilizer inlet. The mixture of water and liquid fertilizer, referred as liquid for simplicity, was discharged from the orifice as a coherent liquid jet. The liquid jet penetrates through paddy soil in the rice field, which have completed the fertilizer injection.
is associated with high cost. If a commercially available pump could be used for pressurizing water, cost for cutting soft materials could be dramatically reduced (Irwansyah et al., 2012). Applications of WJ technology in agriculture have been explored since 1970s. Huang and Tayaputch (1973) proposed liquid-jet injection nozzles which were used to create intermittent or continuous ground openings, such as transplanting. Under a water pressure of 2.8 MPa, the maximum soil penetration depth was only 50 mm. Later, a jet injector for injection of agricultural liquid into the soil was patented by Johnston (1986). The advantages of the jet injector included elimination of tillage and reduction in the tractor power requirement. Tests of a liquid-jet injector were conducted in comparisons with traditional mechanical injectors (disc and spoke wheel injectors) (Nyord et al., 2008). It was found that the liquid-jet injector with a liquid pressure of 2.0 MPa was not able to inject liquid biofertilizer deeper than 20 mm, which was not sufficient to minimize nitrogen volatilization losses. Factors affecting soil cutting using the WJ technology has been studied (Niemoeller et al., 2011). Based on their test results, the recommended parameters for liquid-jet design were a water pressure of 40 MPa, a flow rate of 7.5 l min−1, and a travel speed of 2 m s−1, considering the required injection depths (70–90 mm) and energy consumption. They found that the energy consumption increased near linearly with the water pressure used. The literature results showed that applying the WJ technology to paddy soils with high moisture content would be advantageous. This study aimed to develop a liquid-jet injector that was able to cut paddy soil (with high moisture contents) using reasonably low pressure (10–14 MPa) to reduce the cost. To develop any types of liquid applicators, one needs to understand how the performance of the applicator is affected by design and operational parameters, such as geometrical and operational parameters (Patel et al., 2017). For these, Computational Fluid Dynamics (CFD) was used in this study to model the flow characteristics of a liquid-jet nozzle, such as mass flow rates and velocities. CFD has been recognized as a promising modelling tool for agricultural applications (Bartzanas et al., 2013; Lee et al., 2013) and reducing prototyping cost of applicators (Kashani et al., 2018). CFD was also an effective modelling tool to simulate and design AWJ (Liu et al., 2003; Liu et al., 2004). With CFD, spatial distributions of pressure and velocity in nozzle heads and at outlets could be simulated (Prisco and D’Onofrio, 2008), and multiple fluids (e.g. waste and liquid fertilizer) could be dealt with in one nozzle (Quiroz-Pérez et al., 2016). The objectives of this study were to (1) develop a liquid-jet nozzle for injection of liquid fertilizer (Urea Ammonium Nitrate solution) in paddy fields, (2) simulate the dynamic attributes of the liquid-jet nozzle using CFD to obtain the feasible and optimal design parameters, and (3) validate the model and evaluate the performance of the liquid-jet nozzle using measurements.
2.1.2. Design and operational parameters Parameters for designing the liquid-jet nozzle included lengths and diameters of water tube and inlet, mixing chamber, fertilizer tube and inlet, and nozzle orifice. They should be properly chosen so as to provide appropriate fertilizer application rate and capacity of cutting paddy soil. Through preliminary simulations and testing, the chosen values for these parameters are listed in Table 1, and the most critical design parameters were found to be the diameter of the nozzle orifice (do) and the diameter of the fertilizer inlet (df) (Fig. 1). The feasible and optimal do and df were determined through investigating dynamic attributes of the flows in the nozzle, including the mass flow rate of fertilizer at the fertilizer inlet, the mass flow rate of liquid at the nozzle outlet, and the liquid velocity at the nozzle outlet. These dynamic attributes were simulated using CFD, as discussed later in the paper. To use the liquid-jet nozzle in a fertilizer injector, several operational parameters needed to be considered, including standoff distance (Irwansyah et al., 2012), travel speed of the injector, and nozzle spacing on the injector. A fertilizer injector is required to place fertilizer at a desired application rate, determined based on the agronomic requirement of the crop. Application rate is associated with the mass flow rates of fertilizer, nozzle spacing on the injector, and the injector travel speed in the following relationship:
8 1
7
4
2 5
6 2. Material and methods 2.1. Liquid-jet nozzle development Fig. 1. The diagram of the liquid-jet nozzle; 1-main body, 2-water tube; 3fertilizer tube; 4-water inlet; 5-mixing chamber; 6-nozzle outlet; 7-fertilier inlet; 8-jewel.
2.1.1. Structure The liquid-jet nozzle developed comprised of a main body, a water 2
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(water-fertilizer mixture) at the nozzle outlet (ṁ o ) and the mass flow rate of the fertilizer at the fertilizer inlet (ṁ f ) were measured. Prior to a test, the system was run for approximately 1 min to achieve a stable flow rate in the system. Then, the test was run for 3 min. The weight lost in the fertilizer container was measured using a scale and converted to ṁ f with the given time. Similarly, the weight gained in the measuring cylinder was recorded to calculate the ṁ o . Preliminary tests showed that effects of water pressure on the ṁ f was negligible, and varying the pressure from 10 to 12 MPa, or from 12 to 14 MPa, the ṁ f was increased only by approximately 2%. Therefore, the pressure in simulation was kept at a constant value of 12 MPa for all tests. The liquid velocity from the nozzle was not associated with the soil cutting. Thus, the measure of liquid velocity was done in a free air condition. A high-speed camera (CR600X2, 600 fps) was used to measure the liquid velocity at the nozzle outlet (uo) (Fig. 3a). To prevent damage to the camera from the back splash of the jet hitting the ground, the nozzle was oriented horizontally, held by a horizontal metal bar. It was assumed that the effect of gravity on the liquid jet was negligible. Rulers were placed on a background board as a scale for measuring the shooting distance of the jet. The nozzle, camera, and rulers were positioned properly, so that the camera could capture the image of the jet as it was traveling along the ruler direction. A high-voltage solenoid valve (DC 12 V; 20 MPa; YSV0100, Shanghai Yongzhan Machinery Electric Co.) was used to start and stop the water flow. For a test, a stable flow rate was obtained prior to the measurements by running the system for approximately 1 min. Then water flow was stopped for 2–3 s, and restarted. The shooting liquid jet was captured as picture frames. In a picture frame, the tip location of the liquid jet was indicated by the ruler, as illustrated in Fig. 3b. The travel distance between two consecutive picture frames was the difference between the tip locations on the two pictures. For example, the travel distance would be 42 mm (122 mm − 80 mm), based on the two picture frames shown in Fig. 3b. Then, the flow velocity was estimated as the travel distance divided by the time interval between the two picture frames that was 0.001667 s in this case.
Table 1 Design parameters of the liquid-jet nozzle. Term
Dimension
Value (mm)
Water tube
Diameter Length
5 100
Water inlet
Diameter Length
0.33 1
Mixing chamber
Diameter Length
5 5
Fertilizer tube
Diameter Length
3 5
Fertilizer inlet
Diameter Length
df 1
Nozzle orifice
Diameter Length
do 3
RN =
10ṁ f ω (1)
sv
where RN is the nitrogen application rate (kg ha−1); ṁf is the mass flow rate of fertilizer (g s−1); ω is fraction of nitrogen in the liquid fertilizer (dimensionless); s is nozzle spacing on the injector (m); v is injector travel speed (m s−1). Injector travel speed is adjustable in a field operation. Selection of s is affected by the plant row spacing. The value of ω depends on the type of liquid fertilizer. The ṁf is affected by the design of the liquid-jet nozzle.
2.2. Experiments 2.2.1. Tests of the liquid-jet nozzle For testing, the liquid-jet nozzle was fabricated in a commercial manufacturer. It was tested in a testing platform (Fig. 2a), not in a field fertilizer injector. Tests were conducted in a laboratory in South China Agricultural University, China. As illustrated in Fig. 2b, water through a filter was supplied to a pump (Flow rate: 15.1 l min−1, Pressure: 25 MPa, RRV 4G36, Annovi Reverberi) driven by an engine. Pressurized water flowed to the liquid-jet nozzle through a valve that directed some extra water back to the water reservoir. Liquid fertilizer in a container was connected to the fertilizer inlet of the nozzle through a tube. The liquid (fertilizer mixture) from the nozzle outlet was collected in a measuring cylinder. The data were used to validate the CFD model, described later in the paper. Tests were run for two combinations of the diameters (df, do): (0.6, 0.8 mm) and (0.8, 0.6 mm). Each combination was replicated five times. In the tests, the mass flow rate of the liquid Pressure valve
Pump
2.2.2. Soil cutting experiment Soil is a complex system and its strength varies with soil water content, texture, compaction level, and other conditions. The best way to evaluate the soil cutting ability of the liquid-jet nozzle was to test it in soil. An experiment was conducted in a soil bin (1.60 m long, 0.70 m wide, and 0.45 m deep) containing a typical paddy soil (clay loam) with a moisture content of 50% (dry basis). The soil bin was located at South China Agricultural University. A testing carriage travelled along tracks, and the movable soil bin was positioned below the nozzle (Fig. 4). The carriage was comprised of a DC motor, a controller, a DC power supply,
Engine Water hose
Pressure gauge
Liquid-jet nozzle
Water
Filter
Valve
Pump
Pressure gauge
Liquid-jet nozzle
Fertilizer
Fetilizer mixture
Fertilizer tube
Fertilizer container Scale
Water filter
Liquid collector
(a)
(b)
Fig. 2. Liquid-jet nozzle and the test setup. 3
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Camera Ruler
Valve
Nozzle
(a) Tip of the jet
Tip of the jet
(b) Fig. 3. Measurements of the liquid velocity at the nozzle outlet; (a) measurement setup; (b) two consecutive picture frames from the high-speed camera, showing the image of liquid jet.
wheels and frame, the liquid-jet nozzle and the support. The travel speed of the carriage was adjusted by the controller. The standoff distance of the nozzle could be adjusted along the support. The experimental treatments were the combinations of three different standoff distances (10, 20, and 30 mm) and three different travel speeds (0.6, 0.7, and 0.8 m s−1). Tests were conducted in a completely randomized order with three replicates. For all test runs, the values of df and do were set as 0.6 and 0.8 mm, selected based on preliminary tests. Soil cutting depth was measured by inserting a ruler into the soil slot down to the slot bottom.
Carriage
Support
Track
2.3. Simulations
Soil bin
2.3.1. Model formulation A CFD model of the liquid-jet nozzle was developed using the software Fluent v14.0 in ANSYS as a flow solver. The computational domain comprised of a mixing zone, water zone, and fertilizer zones, which were extended (Fig. 5a). The dimensions of the domain are
Nozzle Fig. 4. Soil cutting experiment setup.
Fig. 5. The CFD model of the liquid-jet nozzle; (a) domain; (b) domain dimensions; (c) discretization. 4
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Model results were used to assess the potential of the liquid-jet nozzle in the context of field injection. When the liquid-jet nozzle was used for fertilizer injection in paddy fields, the following two requirements had to be met:
shown in Fig. 5b. The computational domain was meshed in the ICEM using the tetrahedron element for non-structural components and prism element for exterior walls (Fig. 5c). The discretization scheme was selected as the second-order upwind format. The mesh density of inlet and outlet were increased, and areas with a great change in size were increased as well. A target value of 0.4 was used in smoothing the mesh to ensure a final mesh quality between 0.4 and 1.0. The total number of elements was approximately four million. In the model, the flow was assumed to be in a steady-state condition since the transient variation of internal parameters was not considered in the computational domain. The gravity direction was along the water flow direction and pointed toward the nozzle outlet. The ejection of the water and fertilizer in the nozzle was treated as a round hole jet flow. The turbulence model of Realizable K-ε model was used because of its accuracy and convergence in simulating the round hole jet flow problem (Quiroz-Pérez et al., 2016). The simulation mode of Species Transport was used, assuming that the mixing process of water and fertilizer had no chemical reaction. Computation of energy equations was disabled. The CFD model was solved using the SIMPLEC algorithm. When the residual continuity, momentum, and turbulent flow energy were less than 10−4, and the dynamic attributers (ṁ f , ṁ o , and uo) were stable, the model reached convergence.
(1) to deliver an appropriate nitrogen rate to meet the nutrient requirement of rice crop; (2) to effectively cut soil so that the fertilizer is placed into a desired depth. The typical range of total nitrogen application rate was from 60 to 180 kg ha−1 reported by Peng et al. (2002) for 12 countries. In practice, the total nitrogen requirement is split into applications at multiple times during different rice growing stages (Liu et al., 2016). If two applications were used in the growing season, the nitrogen application rate per application would be from 30 to 90 kg ha−1. The simulated ṁ f values of the nozzle were assessed in terms of meeting the required nitrogen application rates for rice production. In addition, the potential ability of the liquid jet in cutting soil was also assessed.
3. Results and discussion 3.1. Simulation results
2.3.2. Boundary and initial conditions, and model inputs The boundary conditions of water inlet, fertilizer inlet, and nozzle outlet were specified as mass flow inlet, pressure inlet, and pressure outlet, respectively. The mass flow rate of water inlet was constant, and obtained from the experiment. The initial gauge pressures and total gauge pressures were set to zero. Turbulent intensity was set as 5% for all. Initial flow directions were normal to the surfaces. The fluid properties needed as model inputs were density, dynamic viscosity, and relative molecular mass. The liquid fertilizer was Urea Ammonium Nitrate solution with a 32% nitrogen concentration (UAN32). Its density and dynamic viscosity were measured using a glass hydrometer and a digital rotational viscometer. Values of boundary and initial conditions, and fluid properties are listed in Table 2.
3.1.1. Velocity of liquid at the nozzle outlet Among the simulations for 20 different combinations of df and do, the effects of three different df values with a constant do (0.8 mm) are shown in Fig. 6. In general, the water zone had low velocities which were uniformly distributed in the zone. The fertilizer zone was “quiet” in terms of flow activity. Most actions occurred in the mixing chamber. As the water stream went down the mixing chamber, it became less coherent as well as slower in velocity. The water stream divided the mixing chamber into two “compartments” with different velocity distributions. At df = 0.4 mm (Fig. 6a), on the left compartment of the chamber, the stream hit the bottom wall of the mixing chamber, diverging towards the side wall of the chamber, forming a vertically elongated vortex. On the right compartment of the chamber, the velocity field was different as it was connected with the fertilizer zone where liquid fertilizer was drawn into the chamber. The liquid fertilizer joined the water stream, and the mixed liquid formed a round vortex at the bottom quarter section of the compartment. When increasing df from 0.4 to 0.6 mm (Fig. 6b), the general velocity distribution had little change, however velocities became lower in the right compartment. Further increasing the df to 1.0 mm (Fig. 6c) resulted in a further reduction in velocities. Drawing a substance (fertilizer in this case) into the mixing chamber would more or less slow down the velocities, based on a study on AWJ by Patel and Shaikh (2013). Fig. 7 shows the effects of three different do values with a constant df of 0.8 mm. A distinct phenomenon was observed: the ṁ f was negative
2.3.3. Dynamic attributes monitored The model was used to simulate the critical dynamic attributes that affected the performance of the liquid-jet nozzle for fertilizer injection. Simulations were done for 20 combinations of four levels of df (0.4, 0.6, 0.8, and 1.0 mm) and five levels of do (0.4, 0.6, 0.8, 1.0 and 1.2 mm). Each simulation last for 30,000 time-steps which were found to be sufficient through preliminary simulations. The ṁ f , ṁ o , and uo were monitored to understand how these dynamic attributes were affected by these combinations of the two diameters. With the simulated uo, hydraulic power of the liquid jet was determined as follows based on the literature (Hashish, 2009):
P=
1 ṁ o uo2 2
(2)
where P is hydraulic power of liquid (W). Please notice that the value determined from Eq. (2) was the power at the nozzle outlet, whereas the power that impacted soil would be lower. Thus, P values only indirectly reflected the soil cutting power of the liquid jet.
Table 2 Boundary and initial conditions as well as fluid properties.
2.3.4. Model validation and application Data from the tests of the liquid-jet nozzle were used for the model validation. Model results were compared with those from the tests. Comparisons were made for the ṁ f , ṁ o , and uo. The agreements were assessed by relative errors defined as the following:
RE =
|S − M| 100 M
(3)
where RE is relative error (%); S is simulated value; M is measured value. 5
Boundary
Variable
Value
Water inlet
Mass flow rate (kg s−1) Hydraulic diameter (m) Species mass fraction (fertilizer) Water density (kg/m3) Water dynamic viscosity (Pa·s) Water relative molecular mass
0.0065 1.5 0 998 0.001005 18.02
Fertilizer inlet
Hydraulic diameter (m) Species mass fraction (fertilizer) Fertilizer density (kg/m3) Fertilizer dynamic viscosity (Pa·s) Fertilizer relative molecular mass
3 1 1326 0.00868 62.68
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(a) df=0.4 mm
(b) df=0.6 mm
(c) df=1.0 mm Fig. 6. Simulated velocity contours in the model domain for different fertilizer inlet diameters (df) with a constant orifice diameter (do) of 0.8 mm.
when do = 0.4 mm (Fig. 7a), meaning that the flow was reversed between the mixing chamber and the fertilizer zone, which was not feasible for fertilizer injector. These phenomena were attributable to the extremely small orifice diameter, which physically blocked the stream from exiting the nozzle outlet. In the right compartment of the mixing chamber, some flow diverged and entered the fertilizer zone before hitting the bottom wall of the chamber, and some entered the fertilizer zone after hitting the bottom wall. At do = 0.8 mm (Fig. 7b), more fertilizer flowed to the mixing chamber, which would increase the fertilizer application rates. Both compartments of the chamber had
lower velocities, due to the drawing of fertilizer, as explained above. This would ultimately increase the effectiveness of soil cutting. At the largest do, 1.2 mm (Fig. 7c), the amount of fertilizer flowing to the chamber was further increased, and the velocities were further reduced. Response surfaces were used to demonstrate the effects of df and do on the flow characteristics. It should be noticed that the response surfaces were generated from the simulation results of only 20 combinations of df and do. The other points on the response surfaces were from interpolating between those 20 simulation points. Also, the range (0.4–1.0 mm) of df and that (0.4–1.2 mm) of do used in the simulations 6
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(a) do=0.4 mm
(b) do=0.8 mm
(c) do=1.2 mm Fig. 7. Simulated velocity contours in the model domain for different nozzle orifice diameters (do) with a constant fertilizer inlet diameter (df) of 0.8 mm.
was used for a waterjet cutting food (Irwansyah et al., 2012). The response of uo to df depended on the values of do, meaning that there were some interactions between do and df. The results also showed that the df was less critical when compared with do. The dynamics in the fertilizer container was kept minimum due to the zero absolute pressure and near zero velocity in the fertilizer container. Thus, altering df only changed the uo to a small extent. The values of P were plotted against the combination of df and do (Fig. 8b). The P was non-linearly related to df and do, with the higher values at smaller values of df and do. A higher P
were greater than those (0.6–0.8 mm) used in the validation tests. Caution should be taken when using the simulation results which were beyond the measured ranges. The simulated value of uo varied from 7.10 to 32.4 m s−1 within the range of the diameters examined (Fig. 8a). The peak of uo occurred at the smallest do (0.4 mm) and the smallest df (0.4 mm). In general, the uo decreased with the increase of do, which was consistent with fluid dynamics theory. This was why orifice diameters as small as practical were by past researchers. For example, an orifice diameter of 0.5 mm 7
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Fig. 8. Simulated results for different fertilizer inlet diameter (df) and nozzle orifice diameter (do); (a) velocity of the nozzle outlet; (b) hydraulic power of the liquid.
combinations of large do and df, and the peak value was 15.7 g s−1. In terms of effects of df and do, the same explanations for ṁ f were applied to ṁ o .
potentially has higher power to cut soil, which meant that the diameters resulting in higher hydraulic power favoured soil cutting. This is important information for assessing the soil cutting ability of the liquid-jet nozzle.
3.2. Model validation 3.1.2. Mass flow rates of fertilizer and liquid The response surface of the simulated ṁ f raised as the do increased, and reached to its peak at the largest do and df, where the ṁ o was 9.2 g s−1 (Fig. 9a). Again, effects of df on the ṁf depended on the value of do. The negligible effects of df at a lower range of do implied that the small fertilizer inlet diameter might have physically blocked the fertilizer flow. Thus, one could say that when the fertilizer inlet did not restrict the flow, the amount of fertilizer flowing into the mixing chamber was affected by do, a more dominant factor for ṁ f . Effects of do on ṁ f could be explained by the effects of do on the pressure in the mixing chamber. As the do was increased, the pressure at the outlet of the chamber would decrease, because of the constant pressure at the water inlet. Thus, the pressure difference between the inlet and outlet of the chamber would be increased. This created a higher vacuum in the mixing chamber (Patel and Shaikh, 2013), and therefore drew more liquid fertilizer into the mixing chamber. As the result, the ṁf was increased with the do. At do = 0.4 mm, the mixing chamber had positive pressure, which pushed the liquid from the chamber to the fertilizer container, as discussed above. The ṁo was the sum of ṁ f and the mass flow rate of water that was an initial input of the model (6.50 g s−1). As the water flow rate remained constant in the model, the variation of the simulated ṁ o followed the same trends as the simulated ṁ f , with the response surface being shifted up by 6.50 g s−1 (Fig. 9b). The high ṁ o zone was at the
The simulation results of ṁf and ṁo at two different combination of df and do along with the corresponding test data obtained using the testing platform shown in Fig. 2 are summarized in Table 3. The CFD model slightly over-predicted the mass flow rates with low levels of discrepancy. The maximum relative error of 13.3% was observed for the simulated ṁf at the setting of (0.6, 0.8 mm) for (df, do). The model produced a minimum error of 0.4% for the simulated ṁo at the setting of (0.8, 0.6 mm). The relative errors showed that the simulated and measured mo agreed better than the simulated and measured ṁ f . In terms of uo, the relative errors were also low. Overall, the CFD model was reasonably accurate in simulating the flow dynamics of the liquidjet nozzle system. 3.3. Measured soil cutting depths Soil cutting depth measured from the experiment varied from 19 to 52 mm, depending on the standoff distance and injector travel speed. The cutting depth decreased significantly with the increase in standoff distance (Fig. 10a). The further the nozzle outlet was away from the soil surface, the shallower the soil cutting depth was. This was expected, as the hydraulic power of the jet declined after leaving the outlet, as pointed out by Liu et al. (2004). Cutting depth also decreased significantly with the travel speed of the injector (Fig. 10b). When the
Fig. 9. Simulated mass flow rates under different fertilizer inlet diameter (df) and nozzle orifice diameter (do); (a) at the fertilizer inlet (ṁ f ); (b) at the nozzle outlet. 8
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Table 3 Comparisons between simulation and test results of the liquid-jet nozzle. (df, do) (mm)
ṁ f
50
Model (g s−1)
Test (g s−1)
RE (%)
Model (g s−1)
Test (g s−1)
RE (%)
Model (m s−1)
Test (m s−1)
RE (%)
3.4 0.3
3.0 0.27
13.3 11.1
9.9 6.8
9.5 6.77
4.2 0.4
18.2 23.9
19.2 25.8
5.3 7.2
a
b c
40 30 20 10 0
10 20 30 Standoff distance (mm)
(a)
Soil cutting depth (mm)
Soil cutting depth (mm)
(0.6, 0.8) (0.8, 0.6)
uo
ṁ o
60 50 40 30 20 10 0
a
was assumed that the minimum hydraulic power of 1.15 kW was needed to cut soil. Thus, the combinations of Nos. 1, 2, 5, 6, 10, 11, and 12, which had lower P, were not feasible for the design of the liquid-jet nozzle. In summary, considering the requirements of nitrogen application rate and soil cutting depth, those (df, do) combinations with application rates lower than 30 kg ha−1 and hydraulic powers lower than 1.15 kW were eliminated. Thus, the feasible (df, do) combinations were Nos. 3, 4, 7, 8, and 9, as listed in Table 5. Among them the (1.0, 1.0 mm) combination gave the highest nitrogen application rate, and the (0.6, 0.8 mm) combination had the highest soil cutting ability.
b c
0.6 0.7 0.8 Travel speed (m s-1)
(b)
Fig. 10. Soil cutting depths; (a) for different standoff distances; (b) for different travel speeds. Error bars stand for standard deviations.
4. Conclusion injector travels faster, the time of the jet impacting soil was less. As the result, the cutting depth was shallower. The factor of standoff distance is limited by the clearance requirement of the nozzle to the soil surface. A smaller standoff distance had a better soil cutting, but it gave a smaller clearance to the soil surface. Paddy fields typically had levelled surfaces, which may allow the use of small standoff distance. Also, it is suggested to inject fertilizer between crop rows, so as to avoid damage the rice plants. Travel speed is easily adjusted. The injector could travel slower to achieve greater soil cutting depth. When the travel speed decreased from 0.8 to 0.6 m s−1, the soil cutting depth increased by approximately 50%.
In this study, a liquid-jet nozzle was developed and modelled for liquid fertilizer injection in paddy fields. The model was validated, and the performance of the liquid-jet nozzle was evaluated using measurements. The following conclusions were drawn:
• The nozzle orifice diameter and fertilizer inlet diameter of the li• •
3.4. Model applications
•
The ṁ f of the liquid-jet nozzle needed to be in a range corresponding to the range of the required nitrogen rates for rice crop. The diameter do = 0.4 mm was eliminated for the design of the liquid-jet nozzle due to its negative ṁ f . The simulated values of ṁ f for the other diameters are summarized in Table 4. With the simulated ṁ f results, assuming that the fraction of nitrogen in the fertilizer (ω) was 0.32, the corresponding nitrogen application rates were determined according to Eq. (1) for three different injector travel speeds (0.6, 0.7, and 0.8 m s−1) and a nozzle spacing of 0.15 m (Table 4). Among the 16 combinations of df and do, the Nos. 13–16 where do = 0.6 mm, had impractically low nitrogen rates. Thus, do = 0.6 mm was eliminated. For the rest of the combinations, the nitrogen rates varied from approximately 32 to 327 kg ha−1, depending on the injector travel speed. These application rates were sufficient to meet the typical nitrogen requirement of a rice crop. For low nitrogen rates, for example, 30 kg ha−1, the liquid-jet nozzle could be used for any travel speeds above 0.6 m s−1. The relationship between the capacity of the injector and the operational parameters could be examined using Eq. (1). Nozzle spacing depends on the plant row spacing. For example, when the plant row spacing is 0.30 m, fertilizer can be injected in between two plant rows, giving a nozzle spacing of 0.30 m. Under the same ṁ f and injector travel speed, the fertilizer application rate in a 0.30 m spacing would be reduced to half. In the case of higher fertilizer rate being desired, fertilizer can also be applied on both sides of the plant row to increase the nitrogen application rates. Another aspect needing to be considered is soil cutting ability of the liquid jet. In theory, soil cutting ability is affected by the P. Preliminary soil cutting tests showed that the (df, do) combinations with do = 1.2 mm did not cut well due to its low P (below 1.15 kW). Thus, it
•
quid-jet nozzle were the most critical design parameters which affected the injection depth and fertilizer application rate. The injector with the liquid-jet nozzles spaced 0.15 m apart was capable of injecting nitrogen at rates from 59 to 231 kg ha−1, depending on the injector travel speed. The liquid-jet nozzle had ability to cut through the given paddy soil to a depth between 19 and 52 mm, depending on the standoff distance and injector travel speed. Considering meeting typical nitrogen application rates for rice production and injection depths, the feasible nozzle orifice diameters (do) were 0.8 and 1.0 mm, and the feasible fertilizer inlet diameters (df) were 0.6, 0.8, and 1.0 mm. Among these feasible diameters, the optimal ones were the combinations of df = 1.0 mm and do = 1.0 mm, in terms of the highest
Table 4 Nitrogen application rates at different injector travel speeds, and hydraulic power determined based on the simulated mass flow rates of fertilizer for a nozzle spacing of 0.15 m. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
9
(df, do) (mm)
(1.0, (0.8, (1.0, (0.8, (0.6, (0.6, (0.6, (1.0, (0.8, (0.4, (0.4, (0.4, (0.4, (0.6, (0.8, (1.0,
1.2) 1.2) 1.0) 1.0) 1.2) 1.0) 0.8) 0.8) 0.8) 1.0) 1.2) 0.8) 0.6) 0.6) 0.6) 0.6)
ṁ f (g s−1)
9.2 7.0 6.5 5.7 4.3 3.7 3.4 2.5 2.2 2.0 1.9 1.2 0.6 0.5 0.3 0.2
Nitrogen rate (kg ha−1)
P
0.6 m s−1
0.7 m s−1
0.8 m s−1
(kW)
327.1 248.9 231.1 202.7 152.9 131.6 120.9 88.9 78.2 71.1 67.6 42.7 21.3 17.8 10.7 7.1
280.4 213.3 198.1 173.7 131.0 112.8 103.6 76.2 67.0 61.0 57.9 36.6 18.3 15.2 9.1 6.1
245.3 186.7 173.3 152.0 114.7 98.7 90.7 66.7 58.7 53.3 50.7 32.0 16.0 13.3 8.0 5.3
1.121 0.737 1.386 1.173 0.407 0.726 1.638 1.272 1.174 0.448 0.210 0.855 2.157 2.091 1.949 1.871
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Table 5 Feasible df and do combinations and the corresponding nitrogen rates at different travel speeds for a nozzle spacing of 0.15 m. (df, do) (mm)
(0.6, (1.0, (1.0, (0.8, (0.8,
0.8) 1.0) 0.8) 0.8) 1.0)
Nitrogen rate (kg ha−1)
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P (kW)
0.6 m s−1
0.7 m s−1
0.8 m s−1
120.9 231.1 88.9 78.2 202.7
103.6 198.1 76.2 67.0 173.7
90.7 173.3 66.7 58.7 152.0
1.638 1.386 1.272 1.174 1.173
nitrogen application rate, and df = 0.6 mm and do = 0.8 mm, in terms of highest soil cutting ability. The results were obtained from one type of liquid fertilizer and one soil condition, and the simulation results were not validated for all the possible design scenarios. Caution should be taken when applying the results. Injection of liquid fertilizer using the liquid-jet technology is a highly promising technique for rice production. However, there were several drawbacks, including slow travel speeds and shallow injection depths. Currently, the technique and equipment are still in the stage of development. Future research is required before it can be widely used. Acknowledgments This research was supported in part by the National Key R&D Program of China (No. 2018 YFD0200303), the Natural Science Foundation of China (No. 51575195 & 51875217), the Key R&D Program of Guangdong (No. 2019B020221003), Guangdong Science and Technology Support Plant (No. 2017 A020208037), the Earmarked Fund for Modern Agro-industry Technology Research System (No. CARS-01-43). Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.compag.2019.105061. References Bartzanas, T., Kacira, M., Zhu, H., Karmakar, S., Tamimi, E., Katsoulas, N., Kittas, C., 2013. Computational fluid dynamics applications to improve crop production systems. Comput. Electron. Agri. 93, 151–167. Bautista, E.U., Koike, M., Suministrado, D.C., 2001. PM - Power and machinery: mechanical deep placement of nitrogen in wetland rice to receive recommendations. J.
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