Calculation of water consumption over the cross section of a water pipe acts as a starting point in a complex system of hydrodynamic calculations. When constructing or reconstructing a building, when arranging a fire extinguishing system, it is imperative to calculate how much water will flow to the object at a known pressure in the system if pipes of a certain section are installed.
When calculating the water flow, several factors are taken into account, one of the most important is the cross section of the supply pipe and the pressure in the system
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What factors take into account when calculating the flow of water
Determination of water flow by the diameter of the pipe allows you to get data that is very close to real, but not always. In addition to the pipe diameter, a number of factors affect the real flow rate:
- pressure level. At higher pressures in the piping system, consumers will receive more water. Calculation of water flow by pipe diameter and pressure allows you to get more accurate data than using only one parameter. Based on these values, the required pipe wall thickness is determined;
- the water pressure in the system depends on changes in the diameter of the pipes, bends and turns, branches, the presence of shutoff valves. The more complicated the configuration of the water supply system, the more difficult it is to determine the real indicators of the flow rate of water through the pipe at a pressure specified according to SNiP;
- by the frictional force that impedes the movement of the water flow, with a greater length of the system, the flow rate of water through the pipe is significantly reduced, since the speed of the fluid moves;
- roughness of the internal walls of the water supply. Modern polymer structures have about ten percent higher throughput than the latest products from traditional materials - concrete, cast iron and steel;
- during prolonged use, various deposits are clogging the interior of the pipeline. The change in the internal relief due to clogging is hardly possible to calculate using mathematical formulas. So, to accurately determine the amount of water passing through the pipe will be impossible. New polymeric materials allow not to take into account the factor of gradual clogging of the system, since the formation of growths on their inner surface is practically eliminated.
Water consumption will depend on the configuration of the water supply, as well as the type of pipes from which the network is mounted
So, when calculating the water pressure depending on the diameter of the pipe, without taking into account other factors affecting the actual flow rate of the liquid, significant errors can be made.
Methods for calculating the amount of water along the pipe cross section
The pipeline throughput can be calculated using several different methods. You can use:
- physical methods of calculation according to special formulas that are excellent when performing calculations for water supply and sewage;
- tabular methods of calculation, giving approximate values, which in most cases is enough for making subsequent decisions. To obtain accurate values, use Shevelev tables.In addition to the internal section, these tables take into account a number of other parameters, the effect of which affects the throughput of the pipeline;
- special free online calculators;
- special computer programs for calculating various parameters associated with the operation of the pipeline system. Large Russian companies use the paid domestic Hydrosystem program. You can find links on the Internet that allow you to use the TAScope program, which is widely used in many countries.
Calculation of water consumption by diameter and other parameters
Obtaining the calculated data of the water flow allows you to determine:
- with the selection of pipes of the desired diameter, which is linked to the estimated throughput;
- with the thickness of their walls associated with the estimated internal pressure;
- with materials that will be used when laying the pipeline;
- with trunk installation technology.
Calculation of water consumption allows you to choose the type of pipe and their diameter
It is possible to calculate the amount of water consumed by a simple formula:
q = π × d2 / 4 × V
In the above formula, the parameters are used: d - inner diameter of the pipe; V is the flow velocity of the water stream; q is the value of water flow.
Note! For the calculation, the features of the speed of the water flow, which can be both natural, with gravity flow, and created artificially by means of a pumping external source, do not matter.
In a gravity-free system, where water moves by gravity from a water tower, the water flow rate is in the range from 0.7 m / s to 1.9 m / s (in a city water supply system, water flow usually moves at a speed of one and a half meters per second). When using an external source for injection, the speed attached to them is determined by the passport data of the supercharger.
The above formula includes three parameters and allows, knowing two of them, to determine the third.
Determination of water flow with a possible pressure drop
The considered formula for determining water flow by the inner diameter of the pipe and the speed of the water flow is considered simplified. It does not take into account the change in pressure under the influence of circumstances that can lead to lower or higher pressure in the pipeline system. Darcy's formula allows you to make a calculation that takes into account losses at the extreme points of the pipeline. It looks like this:
ΔΡ = λL / D * V2/ 2gρ
The Darcy formula takes into account the following parameters:
P is the viscosity; λ is the coefficient of friction, the value of which is determined by:
- the configuration of the pipeline, straightforward or having complex turns and bends;
- turbulence in the flow of water;
- roughness of the inner surface of the pipe;
- the presence of obstacles in the form of sections using shutoff valves.
The friction coefficient is affected by the presence of locking elements and their number
L is the length of the pipes; D is the value of the internal section; V is the speed of movement of the water stream; g is the acceleration of gravity.
Simplified calculations
Darcy's formula is used in complex hydrodynamic calculations. In most cases, using the usual formula to determine the flow rate is sufficient. Complex calculations can be avoided by resorting to tables based on a combination of four parameters:
- the values of the internal section - D;
- fluid flow rate - q;
- flow rates - V;
- pipe slope - i.
A special case of hydrodynamic calculations is the determination of water flow through the tap hole. The formula q = SV is used, in which, in addition to the values of water flow rate and water flow rate, the value of the cross-sectional area of the tap hole is introduced. It is defined as follows:
S = πr2
If the speed of the water flow is unknown, it is determined by the Toricelli formula V = 2gh. In the Toricelli formula: g is the value of the acceleration of gravity; h is the height of the water column above the tap hole.
It is quite possible to calculate water consumption based on a known value of the internal cross-section of the pipe. The accuracy of this calculation will depend on the effects of several other factors. In some cases, when it is not required to obtain perfectly accurate values, it is quite permissible to neglect them. Naturally, for complex hydrodynamic calculations, simplified formulas are undesirable.
