Effect of Working Pressure on the Anticlogging Performance of Micro-Sprinkling Hose with Different Structures

Abstract

A micro-sprinkling hose is a new type of water-saving irrigation equipment, which can become clogged when using sand-laden surface water sources for irrigation. To test the clogging process and mechanism of the micro-sprinkling hose, as well as the influence of working pressure and hose structure, an intermittent micro-sprinkling irrigation experiment was performed using four different micro-sprinkling hoses with different folded diameters (45, 45, 48, and 60 mm). The number of orifices in the single-cycle orifice cluster was three, five, five, and five. The results showed that, when the working pressures were 30 and 40 kPa, the micro-sprinkling hose was prone to complete blockage. When the working pressures were 50 and 60 kPa, the micro-sprinkling hose was partially clogged. The structure of the micro-sprinkling hose affected the mass and gradation of the deposited sediment by mediating the flow rate inside the hose. The particle size range and content of sediment under irrigation using the N48-5 (folded diameter = 48 mm, with five orifices) and N60-5 (folded diameter = 60 mm, with five orifices) hoses were much larger than those of the original soil samples. Micro-sprinkling hose N60-5 had the best anticlogging performance in this study. The results of this study can provide technical support for the application of micro-sprinkler irrigation systems with sand-laden water.

1. Introduction

Since the 1990s, due to affordability and efficiency, the micro-sprinkling hose has emerged as a new type of water-saving irrigation equipment that combines the advantages of drip and sprinkler irrigation. It has been widely used in meadows, tea gardens, and field cash crops, such as corn and wheat [1,2]. However, in practice, blocked orifices in micro-sprinkling hoses affect irrigation uniformity, lead to extra operating costs, and even reduce crop growth [3]. Therefore, investigating the factors and mechanisms behind micro-sprinkling hose blockages is crucial for providing scientific guidance on this equipment’s use.

One of the effective ways to alleviate the problem of water scarcity in irrigation areas along the Yellow River is the rational use of Yellow River water for agricultural irrigation [4]. However, the clogging of irrigation systems is an urgent problem to be solved [5]. In micro-irrigation systems, clogging can be classified according to the water quality as physical, chemical, or biological clogging [6]. Sediment is the main cause of physical clogging when using high-sediment water for irrigation [7,8,9]. Micro-irrigation system blockages are mainly characterized by the impediment of irrigators such as emitters, drip tape, and micro sprayers. One of the main causes of irrigator clogging is the inability of large, suspended particles to pass through the narrow channel of the irrigator [10,11,12,13]. The orifice size of the micro-sprinkling hose is typically <1 mm, and its clogging also occurs in practical applications. The commonly chosen irrigation modes are continuous and intermittent irrigation. It has been proved that the looser the soil texture, the more significant the water saving and energy saving effect of intermittent irrigation. Intermittent irrigation has the advantages of water saving, high uniformity, and higher irrigation efficiency than continuous irrigation [14,15]. In addition, the operation mode of the irrigation system also influences the degree of clogging. Compared with continuous irrigation, intermittent irrigation prevents and reduces irrigator clogging. This is because the vibration during system reboot is very effective in restoring irrigator flow [16,17].

Xu Ru [3] found that the phenomenon of orifice blockage affected irrigation quality under fertigation with a micro-sprinkling hose for spring wheat. There are two aspects of current research on micro-sprinkling hoses. On the one hand, the literature focuses on the hydraulic performance of the micro-sprinkling hose; on the other hand, it focuses on the effect of micro-sprinkling hose application in the field. In terms of the first aspect, Zhou Bin studied the factors influencing water distribution in a single hole of a micro-sprinkling hose [18]. Di Zhigang proposed a model describing the movement of water droplets in the hose based on Newtonian fluid mechanics and derived a formula for the spray width [19]. Wu Zhengwen designed equipment for testing micro-sprinkling hose flow and pressure and proposed an empirical formula for calculating frictional head loss through a regression analysis of testing data [20]. In terms of the second aspect, Wang Wenjuan and Bai Shanshan suggested that the hydraulic performance of micro-sprinkling hoses ensured irrigation uniformity [21,22]. Man Jianguo and Wang Bingxin experimentally determined the suitable length and angle of a micro-sprinkling hose for wheat growth [23,24]. There is a lack of relevant experimental studies on the degree of clogging of micro-sprinkling hoses, as well as its influencing factors, at different working pressures using sand-containing water with high sediment mass concentrations.

Therefore, an indoor sand-laden water irrigation experiment was conducted through intermittent irrigation. The objectives of this study were to investigate the influence of working pressure and structure on the clogging of micro-sprinkling hoses and analyze the dynamic characteristics and clogging mechanism. The findings can provide the necessary theoretical basis and rationale for the application of micro-sprinkling hoses.

2. Materials and Methods

2.1. Material and Devices

The experiment was conducted in the Hydraulics and Sediment Laboratory of Northwest Agriculture and Forestry University, Shaanxi Province, China. The irrigation test system is shown in Figure 1. The experimental device consisted of a water tank, mixer, water pump, precision pressure gauge, main pipe, and branch pipe, amongst other elements. The water tank was a cylindrical box with a diameter of 1.49 m and a height of 1.55 m. A mixer with a double impeller was installed above it. The rated head of the pump was 15 m. The pressure gauge range was 0–0.16 MPa, and the precision was 0.0005 MPa.

Four types of micro-sprinkling hose (Lenong Pipe Co., Ltd., Linyi, China) commonly used in actual production were chosen. The effective spray width of these four types of micro-sprinkling hoses was moderate. Moreover, they had a high spray angle to avoid shading of the jet by surrounding crops. Therefore, the irrigation was more uniform and applicable to a variety of crops. The orifices appeared in clusters on the micro-sprinkling hose. The distance between each orifice within a cluster was equal, and the orifice connection line was at a certain angle with the axis of the micro-sprinkling hose. The orifice clusters were repeatedly arranged at equal intervals. The structural parameters of the micro-sprinkling hoses were different. The folded diameters of the micro-sprinkling hoses with five holes were 45 mm, 48 mm, and 60 mm, whereas the folded diameter of the micro-sprinkling hose with three holes was 45 mm. For convenience, the four kinds of micro-sprinkling hoses were numbered N45-5, N48-5, N60-5, and N45-3, respectively. The pressure–flow relationship of the four micro-sprinkling hoses was measured using fresh water. The structural parameters and pressure–flow relationships of the micro-sprinkling hoses are shown in

Table 1. Structural parameters of micro-sprinkling hose and pressure–flow relationship.

Micro-sprinkling Hose Number	Folded Diameter (mm)	Diameter (mm)	Length of Orifice Cluster L1 (mm)	Orifice Cluster Spacing L2 (mm)	Average Orifice Size (mm)	Number of Orifices in Single Cycle Orifice Cluster	Recommended Working Pressure (kPa)	Pressure–Flow Relationship
N45-3	45	28.65	100	100	0.801	3	25–65	q = 0.43H0.88; R2 = 0.97
N45-5	45	28.65	100	160	0.835	5	25–65	q = 0.95H0.69; R2 = 0.99
N48-5	48	30.56	100	150	0.924	5	25–65	q = 1.38H0.57; R2 = 0.99
N60-5	60	38.20	115	115	0.907	5	25–65	q = 1.07H0.61; R2 = 0.98

Note: q is the flow rate of each cluster of orifices in the micro-sprinkling hose (mL/s); H is the working pressure of the micro-sprinkling hose (kPa).

. The structure of the micro-sprinkling hoses is illustrated in Figure 2 and Figure 3.

Four structures of micro-sprinkling hoses were placed parallelly and horizontally on the experimental platform. Each micro-sprinkling hose specimen was 5 m long. On each micro-sprinkling hose, one orifice cluster per meter was selected for testing. Each micro-sprinkling hose had five test orifice clusters, sequentially recorded as No. 1, 2, 3, 4, and 5 from the head of the hose.

Tap water was used for testing, and the sediment-laden water was prepared in a certain proportion and stirred evenly. Sandy loam was used as sediment, after air-drying and passing through a 1 mm sieve. The sediment gradation after sieving was evaluated using a Malvern laser particle size analyzer (range: 0.01–3500 μm) (Malvern Instruments Ltd., Malvern, UK); the particle size range was 0.01–163.490 μm (

Table 2. Sediment gradation for test.

Particle Size (μm)	Volume Fraction (%)	Particle Size (μm)	Volume Fraction (%)
<0.767	2.436	21.205–31.100	16.901
0.767–2.131	7.012	31.100–45.613	17.938
2.131–5.207	10.066	45.613–66.897	12.510
5.207–12.726	13.147	66.897–86.355	4.101
12.726–21.205	14.134	86.355–163.490	1.754

).

2.2. Experimental Design

It is known that the range of sediment mass concentration in agricultural canals in areas with high-sediment water from the Yellow River used for irrigation (e.g., the Hetao area of Inner Mongolia and the Ningxia irrigation area) is 0.6–1.387 g/L [4,7,25,26]. In this experiment, the sediment content of the irrigation water source was appropriately increased in order to reveal the clogging mechanism of the micro-sprinkling hose better. This also accelerates clogging and shortens the test cycle. Thus, sediment-laden water with a high sediment concentration (1.5 g/L) was utilized for the experiment. The working pressure (H) and structure (S) of the micro-sprinkling hose were selected as experimental factors. As a function of the value of H, the rated working pressure was determined according to the burst pressure of the micro-sprinkling hose. Because the micro-sprinkling hoses used in the test were thin-walled, their water cross-section was greatly affected by the pressure. According to the standard for Agricultural Irrigation Equipment: Micro-Sprinkling Hose (NY/T 1361—2007) [27] and a study by Gou [28], the burst pressure of the micro-sprinkling hose was 1.5–3 times the rated working pressure. The burst pressure of the micro-sprinkling hose used in the test was 80–98 kPa; therefore, the values of H were set to 30, 40, 50, and 60 kPa. The test factors and levels are shown in

Table 3. Factors and levels of sandy water test using micro-sprinkling hose.

Level	Factor
	Working Pressure H (kPa)	Micro-Sprinkling Hose Structure S
1	30	N45-3
2	40	N45-5
3	50	N48-5
4	60	N60-5

, yielding 16 working conditions, which were investigated in triplicate.

2.3. Testing Method

The test method of intermittent irrigation was adopted. Irrigation was conducted at each working pressure 10 times. The irrigation time was set to 20 min for each test according to the clogging test methods for emitters (ISO/TC 23/SC 18/WG5 N4). After each irrigation, the micro-sprinkling hose was allowed to stand for 60 min before the next run. Each micro-sprinkling hose was tested in triplicate at the same working pressure.

The flow rates of the four micro-sprinkling hose orifice clusters were evaluated separately for each irrigation. After 5 min of system irrigation, the weight of water coming out of each test orifice cluster for 1 min was collected. A total of three measurements were taken every 5 min. The flow rate of the orifice cluster was then calculated as a function of the weight of the water. After irrigation was completed, the sediment present in the whole micro-sprinkling hose was collected and weighed after drying, recorded as the sediment mass (m). The sediment gradation was measured using a Malvern laser particle size analyzer.

2.4. Evaluation Index and Determination Method

The relative discharge of the orifice cluster is the flow rate ratio when irrigated with sandy water to when irrigated with clear water. The average of the relative discharges of five test orifice clusters in the micro-sprinkling hose was defined as the average relative flow value (Dra) of the micro-sprinkling hose. The discharge ratio variation (Dra), coefficient of uniformity (CU), and flow rate reduction (q_d) were evaluated as described by Li et al. [29] to evaluate the anticlogging performance of the micro-sprinkling hose irrigation system orifice clusters.

$$\mathrm{Dra}=\frac{{\sum }_1^5\frac{{\mathrm{q}}_{\mathrm{i}}}{{\mathrm{q}}_{\mathrm{i}}^0}}{5} \times 100\%,$$

(1)

where ${\mathrm{q}}_{\mathrm{i}}$ is the flow of the sand-laden water of orifice cluster i (in mL/s), and ${\mathrm{q}}_{\mathrm{i}}^0$ is the flow of the clear water in orifice cluster i (mL/s).

The coefficient of uniformity (CU) was calculated using Equation (2) as follows:

$$\mathrm{CU}=\left(1–\frac{\sum _{\mathrm{i}=1}^5\left|{\mathrm{q}}_{\mathrm{i}}- \stackrel{\mathrm{-}}{\mathrm{q}}\right|}{5\stackrel{\mathrm{-}}{\mathrm{q}}}\right) \times 100\%,$$

(2)

where $\stackrel{-}{\mathrm{q}}$ is the average flow rate of the five test orifice clusters of the micro-sprinkling hose (mL/s).

The degree of blockage of the orifice cluster was evaluated by the flow rate reduction.

$${\mathrm{q}}_{\mathrm{d}}=\frac{{\mathrm{q}}_{\max }- {\mathrm{q}}_{\min }}{{\mathrm{q}}_{\max }}$$

(3)

where q_max is the maximum flow rate of the cluster during 10 irrigations (mL/s), and q_min is the minimum.

3. Results and Analysis

3.1. Dynamic Changes in Dra of Micro-Sprinkling Hoses

During the irrigation process, the Dra of the four micro-sprinkling hoses fluctuated and decreased with the increase in irrigation time (Figure 4). Among them, N45-5 had the best anticlogging performance, with the average relative flow rate decreasing to 87.14–96.19% of the flow rate of clean water. The anticlogging performance of N45-3 was second best, decreasing to a minimum of 70.06%. The anticlogging performance of N48-5 was the worst.

With the increase in working pressure, Dra did not show a clear upward or downward trend. This shows that the working pressure was not monotonically related to the anticlogging ability of the micro-sprinkling hose. The lowest relative flow rate for certain irrigation mostly occurred when the working pressure was lower (30 kPa).

Table 4. Significance analysis of Dra at different working pressures.

H (kPa)	N45-3	N45-5	N48-5	N60-5
30	78.08 b	92.73 b	79.13 a	77.27 b
40	90.76 a	94.07 b	64.01 b	84.78 ab
50	81.48 b	99.21 a	53.59 b	90.20 a
60	92.78 a	99.20 a	68.84 ab	77.09 b

Notes: Different lowercase letters indicate significant differences between different working pressures (p < 0.05). N45-3, N45-5, N48-5, and N60-5 characterize the micro-sprinkling hoses; specific structural parameters are shown in Table 1. The same notes apply to below tables.

shows significant differences between treatments with large pressure variances.

3.2. Dynamic Changes for CU of Micro-Sprinkling Hoses

The CU of the flow rates of the orifice clusters of the four micro-sprinkling hoses varied widely (Figure 5). The CU of N45-5 was above 90%. The uniformity fluctuation of N45-3 with the same folded diameter was larger than that of N45-5. When H was 30 kPa, the uniformity was the lowest at 58.6%. When H was 30 kPa, the CU of N60-5 decreased to 57.8% at the end of 10 irrigations. When H was 40, 50, and 60 kPa, the CU was higher than 75%. The average uniformity of N60-5 was higher than that of N48-5 at all four working pressures (

Table 5. Significance analysis of CU at different working pressures.

H (kPa)	N45-3	N45-5	N48-5	N60-5
30	76.58 b	93.56 a	85.05 a	85.27 ab
40	85.80 a	93.73 a	71.82 b	86.05 ab
50	91.88 a	93.49 a	70.78 b	89.98 a
60	91.24 a	95.16 a	75.99 b	83.28 b

). When H was 40, 50, and 60 kPa, the CU of N48-5 was less than 75% at the end of 10 irrigations.

3.3. Clogging Position of Micro-Sprinkling Hose

After 10 irrigations, the most serious blockages of micro-sprinkling hoses occurred at the end, followed by the head (Figure 6). Most of the orifice clusters at the end were gradually clogged during ten irrigations. The reason might be that the pressure at the end was the lowest in the whole micro-sprinkling hose, the flow velocity at the end was the lowest, and the flow pattern was relatively stable. The sediment that failed to leave with the flow accumulated at the end. Although the pressure at the head of the micro-sprinkling hose was higher compared to the central part, its sediment mass concentration was higher. Moreover, the flow velocity at the head was the largest, which increased the chance of sediment particles colliding to form a floc aggregate.

3.4. Mass of Sediment Particles

The mass of sediment deposited in the micro-sprinkling hose increased with the increase in working pressure (Figure 7). The structure of the orifice cluster of the micro-sprinkling hoses also affected the mass of deposited particles. The mass of sediment deposited in N45-5 with the same folded diameter was always lower than that deposited in N45-3. The deposited sediment mass of the three micro-sprinkling hoses with five orifices in a single circulating orifice cluster gradually increased with the increase in folded diameter. When H was 60 kPa, the mass of deposited sediment in N45-5 was 59.55% and 50.28% of that in N48-5 and N60-5, respectively.

3.5. Characteristics of Deposited Sediment

The particle size distribution of the sediment deposited in the micro-sprinkling hose is shown in Figure 8. They were classified by particle size. The sediment particles deposited in the four micro-sprinkling hoses were mainly silt (Figure 9). The soil particle composition of the original soil sample used to prepare the sand-laden water was as follows: clay 18.97%, silt 66.20%, and sand 14.83%. Compared with the original soil sample, the content of sand increased while the content of clay decreased with the increase in the folded diameter of the three micro-sprinkling hoses (N45-5, N48-5, and N60-5) under the same pressure conditions. The proportions of sand, silt, and clay in N45-3 and N45-5 were close. Therefore, the folded diameter was the main factor influencing the particle gradation of deposited sediment.

Table 6. Particle size range (μm) of deposited sediment.

Working Pressure (kPa) Label	30	40	50	60
N45-3	0.31–143.90	0.31–86.36	0.31–185.75	0.31–185.75
N45-5	0.31–111.47	0.31–143.90	0.31–126.65	0.31–111.47
N48-5	0.31–859.45	0.31–665.79	0.31–665.79	0.31–665.79
N60-5	0.36–185.75	0.36–211.04	0.36–515.77	0.36–239.78

shows the particle size range of sediment deposited in each micro-sprinkling hose. The particle size range of sediment deposited in N45-5 was lower than that of the original soil sample (0.31–163.49 μm) at all four working pressures. In contrast, the particle size ranges of N48-5 and N60-5 were both larger than that of the original soil sample. The particle size range of the deposited sediment within N48-5 was widest at the four working pressures. In other words, the sediment developed the largest size aggregates within N48-5.

The coefficient of nonuniformity (ϕ) was further used to reflect the uniformity of deposited sediment [30]. A larger ϕ denotes a more nonuniform sediment. The ϕ was calculated using Equation (4).

$$\mathsf{\phi }=\sqrt{{\mathrm{d}}_{60}/{\mathrm{d}}_{10}},$$

(4)

where d₆₀ and d₁₀ indicate that the sediment content smaller than this size is 60% and 10%.

The deposited sediment of N60-5 was uniform and coarsened compared to the other three micro-sprinkling hoses (Figure 10). In addition, the median particle size (d₅₀) of N60-5 was higher than that of the original soil sample (23 μm). N48-5 also showed coarsening, but the degree of coarsening was less than observed for N60-5. Therefore, a larger folding diameter allowed the sediment particles to aggregate into stable and unbreakable aggregates within the micro-sprinkling hose. A high proportion of these large aggregates in the deposited sediment was the main reason for the decrease in micro-sprinkling hose discharge.

4. Discussion

4.1. The Effect of Working Pressure on Micro-Sprinkling Hose Clogging

In the pressure range of this study, the clogging of the micro-sprinkling hose was more serious when the working pressure was small. According to the pressure–flow relationship of the micro-sprinkling hoses (Table 1), a lower working pressure led to a smaller flow rate through the orifice. Therefore, the particles leaving the micro-sprinkling hose with water were mostly clay particles that struggled to settle, whereas larger sediment particles remained in the micro-sprinkling hose as aggregates of larger agglomerates. This increased the probability of orifice clogging during irrigation. Moreover, at the end of irrigation, the negative pressure formed at the orifice increased with the increase in working pressure, more air was sucked into the micro-sprinkling hose from the orifice, and the process was more intense. This process dislodged the clogging substance cemented at the orifice, thereby reducing the clogging degree of the micro-sprinkling hose. However, there was also more serious clogging when the working pressure was high; for example, the Dra of N48-5 was lowest at H = 50 kPa for all but the fifth of the ten irrigations. The Dra of N60-5 was similar at H = 60 kPa and 30 kPa but lower in between. The flow velocity in the micro-sprinkling hose differed with working pressure, while the trajectory and interaction of sediment particles also changed. The following mechanism is proposed: When the pressure was low, the water flow was relatively smooth, and the aggregate structure formed by the sediment particle flocculation could not be easily dispersed, gradually developing into larger and more stable floc aggregates, which were consolidated around the orifice of the micro-sprinkling hose when flowing out with water. When the pressure was high, the flow velocity in the micro-sprinkling hose increased, and the turbulence was more intense, which increased the collision chance of sediment particles, gradually forming a clogging substance with higher shear strength. Therefore, the working pressure and the clogging of the micro-sprinkling hose did not exhibit a monotonic relationship, mostly affecting the anticlogging performance of the micro-sprinkling hose as a function of its structure.

At a lower working pressure (30 and 40 kPa), the four micro-sprinkling hoses showed lower uniformity and lower average relative flow. At a higher working pressure (50 and 60 kPa), the four micro-sprinkling hoses showed higher average relative flow rates and lower uniformity. This denotes that the micro-sprinkling hose was prone to complete clogging at lower working pressures, whereas clogging mostly occurred locally at higher working pressures.

4.2. The Effect of Micro-Sprinkling Hose Structure on Deposited Sediment

The four micro-sprinkling hoses had large orifices with diameters above 0.8 mm. At the same working pressure, a larger diameter of the orifice led to greater flow, facilitating the removal of larger sediment particles.

The structure of the micro-sprinkling hose directly affected the flow rate of the orifice clusters, and the flow rate is the main factor affecting the mass of deposited sediment in the micro-sprinkling hose. At the same working pressure, a greater flow rate of the orifice cluster resulted in less sediment being deposited in the micro-sprinkling hose. According to the pressure–flow relationship of the micro-sprinkling hoses (30–60 kPa), the flow rate of the orifice group of N45-5 was greatest, resulting in lower sediment mass deposition.

The structure affected not only the mass of sediment in the micro-sprinkling hose but also the gradation of sediment, thus influencing the clogging development of the micro-sprinkling hose. At the four working pressures, the particle size range of the deposited sediment in N48-5 and N60-5 was larger than that of the original soil sample and N45-5, indicating sediment aggregation behavior in the micro-sprinkling hose, due to an increase in the proportion of sand particles. Aggregation behavior was mainly due to the flocculation and adhesion of sediment particles in the process of collision [31,32]. The fine particles of sediment aggregated by this action were not easily dispersed during analysis using a laser particle size analyzer [33,34]. This is closely related to the electric double-layer structure on the surface of sediment particles and the van der Waals force between particles [32], as well as factors such as microorganisms and medium ions [34,35]. In addition, the main reasons for sediment aggregation were the large specific surface area of fine particles, the formation of an adsorbed water film on the surface due to a negative charge, and the strong cohesion generated by mutual contact [36], whereby the particles were bonded to each other to form larger aggregates [37]. Moreover, various cations in the water and sediment with negative charge characteristics formed an electric double-layer structure, resulting in salt flocculation [38]. In conclusion, the good anticlogging performance of N45-5 was due to its structure, which allowed larger particles of sediment in the water source to be discharged from the micro-sprinkling hose, whereas the sediment particles remaining in the hose could not easily form larger aggregates. However, the specific relationship between the structural parameters and the anticlogging performance of the micro-sprinkling hose needs to be further studied.

5. Conclusions

Three conclusions can be drawn from the research:

• When the working pressure was lower (30 and 40 kPa), the micro-sprinkling hose was prone to overall clogging, as well as more severe clogging. However, when the working pressure was high (50 and 60 kPa), the micro-sprinkling hose mostly exhibited local clogging. The working pressure and the structure of the micro-sprinkling hose together affected the anticlogging performance.
• The structure of the micro-sprinkling hose affected the clogging development through its influence on the mass and gradation of sediment deposited. The larger the folded diameter, the more serious the sediment coarsening within the micro-sprinkling hose.
• Considering the uniformity and anticlogging performance, this study suggested prioritizing N45-5 micro-sprinkling hoses in practical applications among the four kinds of micro-sprinkling hoses, followed by N45-3.