Determination of head loss in water pipes

. This article is devoted to the problems of water supply to the population, which are associated with the current water management situation, such as the shortage of water resources, the decline in the quality of surface and groundwater, the technical condition of pipelines. In this situation, there is a need to eliminate or mitigate the current situation, so the study of hydraulic friction losses in water conduits is of national economic and scientific importance.The article deals with the issues of determining the pressure loss in water pipes under various modes, the causes of clogging of pipelines in water supply systems and the basic formulas of engineering hydraulics under conditions of insufficient water supply to the population. Solving the problem will increase the reliability of pipeline operation, meet the requirements of the population, and meet the minimum of the reduced costs for construction and operation.


Introduction
At present, the current shortage of water resources is further exacerbated by their qualitative depletion, that is, salinization and pollution of surface and groundwater.Against this hydroecological background, a very difficult situation with the water supply of the population has formed in Uzbekistan.Estimates show that annually 1.9-2.0km 3 of water is used for household and drinking purposes in Uzbekistan.At the same time, significant water losses are observed in the water supply network, which on average in Uzbekistan amount to 26.4% or more than 1.1 million m3 / day.The efficiency of water use is reduced by its losses and accounting in transportation systems through pressure conduits.First of all, this is due to a violation of the hydraulic mode of water supply in the pipes and the appearance of additional hydraulic resistance during operation, which ultimately leads to significant losses in water pressure.Experience in the operation of water conduits shows that the sources of additional hydraulic resistance are: clogging with organic substances, the development of corrosion processes, the appearance of cracks and the destruction of individual pipe sections.Therefore, the study of hydraulic friction losses in water conduits is of national economic and scientific importance.

Methods
The pressure loss during the movement of water through the pipes is proportional to their length and depends on the diameter of the pipes,water flow (flow rate), the nature and degree of roughness of the pipe walls (i.e. on the type and material of the pipes) and from the area of the hydraulic mode of their work.The main formula of engineering hydraulics, linking all these characteristics, is the Darcy-Weisbach formula where: -section head loss; -coefficient of hydraulic resistance of this section; and -length and diameter of the section pipe; v ik -the speed of water movement in the pipe; g -acceleration of gravity.
For calculations of plumbing systems, it is more convenient to modify this formula, in which the speed is replaced by the flow rate: where:k -coefficient; -water consumption on the site; m -exponent.Both presented formulas are a special case (for pressure movement in pipes) of a more general formula, covering the cases of pressure and non-pressure movement in channels and pipes: [1,2,3,4] where: С-Chezy coefficient; R -hydraulic radius; i -hydraulic slope.The coefficients, k and C are of the same nature and are related by the following relationships: When pipes operate in the region of quadratic resistance, the values of these coefficients depend only on their diameter and roughness.In our region, as experiments have shown, non-new steel and cast iron pipes work at the speed of water movement When pipes operate in the transition region of the turbulent regime (up to the quadratic region), the values (k and C) depend on the diameter and roughness of the pipes, as well as on the Reynolds number, i.e., on the speed (or flow rate) at a given diameter and on the viscosity of the liquid.Non-new steel and cast iron pipes work in this area at a speed of , as well as new metal and asbestos-cement pipes at almost all used water flow rates.[5,6,7,8] When pipes are operated in the "hydraulically smooth" region, the values of these coefficients depend on the diameter of the pipes and the Reynolds number and do not depend on their roughness.Plastic and glass pipes work in this area.The influence of the roughness of the inner surface of pipes on their hydraulic resistance is taken into account by various empirical formulas derived for pipes of different types either on the basis of experimental data or using some numerical characteristics of roughness.The number of different calculation formulas proposed for determining the coefficients (k and C) is very large.[9,10,11,12,13] Based on the fact that the pressure loss is proportional to the length of the water line, it is possible to determine the pressure loss per unit length by a dimensionless value -the hydraulic slope [14,15,16] and find the total pressure loss for a water line of any length: F. A. Shevelev proposed the following formulas for determining unit pressure losses in pipes: non-new steel and cast iron, working in the quadratic region at , non-new steel and cast iron, working in the transition region at , asbestos-cement

Plastic
For new metal pipes operating only in the transition region, there are special calculations -if there is a guarantee that internal corrosion and deposits will not be observed during operation.[17,18,19,20]

Results and Discussion
In recent years, due to the deterioration of the quality of surface waters and the use of coagulants in many existing water supply systems, corrosion overgrowth of the inner surface of cast-iron and especially steel pipes has been observed.This leads to an increase in the hydraulic resistance of metal pipelines, sometimes by a factor of 2 or more.For reconstructed networks and water pipelines, measures should be taken to restore and maintain their throughput.If it is technically impossible or economically impractical, then it is allowed to increase the hydraulic resistance of the pipes.When determining the hydraulic slope of reinforced concrete pipes, the following dependencies can be used: for vibrohy dropressed [21,22,23] forcentrifuged To facilitate and speed up the determination of pressure losses, auxiliary tables, graphs and nomograms are widely used.However, there are many tasks in which the calculation of pressure losses using tables is inconvenient, for example, when linking a network.
If the general formula for head loss is represented as then the value will include all factors characterizing the hydraulic resistance per unit length of the line.The value is called specific hydraulic resistance.Total .For pipes operating in a non-quadratic region, the quantity includes the flow (or velocity) to some fractional power.Thenthegeneralformulaforheadlossis The degree of β is in the range of 1.75-2.Some formulas, including the formulas of F. A. Shevelev, cannot be reduced to the indicated form.When using them, the head loss is determined by quadratic dependencies, and then a correction factor is introduced into the loss value, depending on the speed: When carrying out hydraulic and technical and economic calculations, the use of formulas containing a two-term factor leads to certain difficulties.A number of authors have proposed approximate one-term formulas of the form approximating the above.
In particular, for non-new metal pipes at a water velocity of up to 3 m/s, M. M. Andriyashev proposed the formula For asbestos-cement pipes, N.N.Abramov obtained the following single-term formula: In order to calculate the head loss in free-flowing motion, it is necessary to determine the value of the Chezy coefficient (C).It can be calculated by N. N. Pavlovsky's formula where,n -pipe roughness coefficient taken according to Table 1; -hydraulic radius corresponding to the calculated filling (here -wetted perimeter at calculated filling: -central angle in the pipe corresponding to the calculated filling: -flow cross-sectional area corresponding to the calculated filling):y -exponent, determined by the formula

Conclusions
1.During operation, the water supply system must operate without unacceptable reductions in the flow of water and pressure.Ensuring the reliability of the water supply and distribution system is achieved by structural and temporary redundancy.Structural redundancy involves the use of redundant elements in the system.
2. The required reliability when transporting water from a water supply source to the city network can be ensured by laying several parallel water conduits instead of one and switching devices to them.In the water distribution system, it is provided by the device of ring networks.
3. The reliability of the system can be increased by installing several power sources, equipping pumping stations with standby units, etc.

Table 1 .
Specific resistances of pipes