METHOD OF HYDRAULIC CALCULATION OF IRRIGATION PIPELINES AND ITS EXPERIMENTAL VERIFICATION

ABSTRACT

The paper describes a simplified method for the hydraulic calculation of irrigation pipelines, which makes it possible to determine the necessary parameters of the elements of the technology of non-traditional irrigation technology for intensive gardens and vineyards on terraced adyr slopes.

АННОТАЦИЯ

В работе описана упрощенная методика гидравлического расчета оросительных трубопроводов, позволяющая определить необходимые параметры элементов технологии нетрадиционной техники полива для интенсивных садов и виноградников на террасированных адырных склонах.

Keywords: hydraulic calculation, irrigation pipeline, minimum permissible, irrigation technology, flow coefficient, irrigation jet.

Ключевые слова: гидравлический расчет, оросительный трубопровод, технология полива, коэффициент расхода, ирригационная струя.

Introduction.

Polyethylene pipes with an inner diameter of 19 and 28 mm are used as irrigation pipelines in the proposed irrigation network. When developing a method for the hydraulic calculation of such pipelines, we used the results of our own research and the recommendations of V.A. Surin (1976, 1988) on the calculations of irrigation asbestos-cement pipelines of large diameters, as well as materials from other authors [1].

Literature review.

The following method of hydraulic calculation of small diameter polyethylene irrigation pipelines laid on terraces with small positive slopes has been developed and proposed.

Research methodology.

1. By the selection method, the length of the irrigation pipeline is determined depending on the rational values of the specific flow rates of water distribution along the length of the furrows (qsp), the length and longitudinal slope is dense (ter, i). Rational values (qsp) were established as a result of experiments on water absorption into the soil at a variable (gradually increasing in time) water pressure in the furrow sections. For the soil conditions of the studied adyr massifs, the values (qsp) are recommended in the range of 0.002… .0.005 l / s.m (Section 4.1).         According to the set values of the minimum permissible specific flow rate of water distribution qmin beats = 0.002 l / s.m and the longitudinal slope of the terrace canvas (i) according to the graphs (Fig. 1 and 2), the limiting lengths of the pipelines (pr-1) and (pr-2) are determined diameters 19 and 28mm, respectively.

Analysis and Results.

If the specified length of the terrace is L_ter˂ (L_pr-1 or L_pr-2), then the length of the irrigation pipeline is taken to be equal to the length of the terrace L_tr = L_ter. Then, using (L_mp) and (i), the calculated value (q_ud) is specified from the corresponding graph (Fig. 1 and 2).

If L_mer˃L_pr-2, then the ratio n = L_ter / L_pr-2 is determined and the resulting value (if it is not an integer) is rounded up. The length of the irrigation (L _mр) is determined by the ratio L_ter / n. Then, according to (L_mр) and (i), the calculated value (q_sp) is specified according to the graph (Fig. 2).

Determine the water flow in the head of the irrigation pipeline by the formula:

q = q_уд .  _тр , l / s                                                                    (1)

and specify the speed of water movement (ϑ_н) at the beginning of the irrigation pipeline. Froude number is preliminarily determined by the formula:

F_r =                                                                              (2)

where: h - effective piezometric head, m; ϑ - speed of water movement in the pipeline along the holes, m / s; ɡ - = 9.81 - acceleration of gravity, m / s2

The flow coefficient (μ) of the first water outlet according to the formula (3 or 4) depending on the internal diameter of the pipeline.

μ =                                                                        (3)

μ =                                                                        (4)

5. Determine the minimum permissible flow rate of water for an irrigation jet according to the formula

q_min =  0,01392 μ ,                                                               (5)

where: q_min is the minimum allowable flow rate of irrigation jets, l / s;

h - the effective piezometric head at the beginning of the irrigation pipeline, m.

With a minimum flow rate of the irrigation stream, the maximum distribution of water supply along the length of the irrigation furrow is ensured, which improves the uniformity of soil moisture.

Determine the distance between the water outlets using the formula.

∆l =  , m                                                                        (6)

The length of the irrigation pipeline is divided into calculated sections (usually 4 ... .6) and the loss of the piezometric pressure along the length of the pipeline is determined by the formula:

h_дл =J–  (ϑ ²_н – ϑ_k)/g                                                              (7)

Determine the effective pazometric head in the design sections of the pipeline by the formula:

h_х = h_н -  h_дл + ∆h_г ,                                                               (8)

where: hх - losses of piezometric pressure along the length, m; ∆hg is the difference in elevations of the earth's surface, m; hн - piezometric head at the beginning of the irrigation pipeline (recommended to be taken equal to 0.9 ... 1.0 m).

Determine the Froude number and the flow rate coefficients of the water outlets in the design sections of the pipeline sections according to the formulas (1) and (2) or (3).

8. Determine the diameters of the water outlet (irrigation) holes in the design sections according to the formula (4).

The reliability of the method for calculating irrigation pipelines and the obtained design equations was confirmed by experiments carried out at the experimental site. Hydraulic experiments were carried out on polyethylene irrigation pipelines with a length of 120 ... 250 m and a diameter of 19 and 28 mm, laid with a slope of 0.002 ... 0.024. The water pressure in the head of the pipelines was 0.9 ... .1.0 m. The actual operating heads in the design sections of the pipelines were measured with a piezometer, the flow rates of irrigation jets were measured by the volumetric method.

Conclusion and Recommendations.

1) The materials of the experiments carried out are shown in Fig. 4.19. and in the scientific and technical report of the NIS AIK (91). In fig. 1 shows the results of hydraulic studies on an irrigation pipeline 200 m long and 32 mm (28 mm) in diameter, laid with an average slope of 0.007. From the given data it follows that the actual piezometric lines practically coincide with the calculated ones.

2) Measurement of the flow rates of irrigation jets showed that their maximum deviations from the average value do not exceed + 10 %.Consequently, the obtained hydraulic dependencies and the method for calculating irrigation pipelines provide the necessary uniformity of water distribution along the length of the pipeline and can be recommended for use in design practice.

References:

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