In any movement there are losses of energy - even though it will be a car, although the aircraft, even though the fluid in the pipeline.Always part of the energy is spent on overcoming the resistance movement.Reducing the pressure of the liquid and is usually determined as the hydraulic resistance.In fact, there are two types of this resistance - the local and linear.Local due to the loss of energy in the valves, gate valves, bends, expansion and contraction of the pipe.
It should be noted that the source of loss is always fluid viscosity.Local loss or flow resistance calculation formula is related to the parameters of valves, pipes and valves, is determined by a special technique.But the line losses are largely dependent on the nature of fluid flow in the pipe.
Research mode liquid flow conducted by Reynolds in 1883.When these studies used the flow of water, to which is added the paint and the glass tube could be observed character of the movement of paint and water.This was done by measurement of pressure, velocity and pressure of the liquid.
first mode of motion was observed at low speed water.In this case, ink and water are not mixed with each other and move together along the tube.The rate and pressure at constant during this time.This mode is called laminar flow of liquid.
If the movement speed will increase, the largest in its specific picture of fluid motion will change.The jet ink begins to stir the entire volume of the pipe becomes visible vortex-formation and rotation of liquid.The measured values of the velocity and pressure of the fluid begin to pulsate.Such a motion is called turbulent.If the flow rate is reduced, the laminar flow is restored again.
In laminar flow of the liquid flow resistance is minimal, when it is much more turbulent.It is necessary to make the clarification that there are losses due to friction on the pipe wall.Speed in laminar flow in the tube wall is minimal and maximal at the center of the flow, but the flow of water moves smoothly along the entire tube.When turbulent flow turbulence arising obstruct the movement of water and an additional hydraulic resistance.
There is another phenomenon which contributes to losses.It is called cavitation.Cavitation occurs when the motion of the liquid in the tube appears bottleneck.Then, at a position and velocity increases, according to Bernoulli's law, pressure decreases.The pressure decrease causes the selection that begins dissolved gases in the liquid and the water begins to boil at the current temperature.
After passing through a narrow section of the flow velocity decreases, the pressure increases and a boil disappears.Cavitation causes additional losses caused by local disturbances laminar flow.Usually, it occurs in the taps, valves, and other similar sites.This phenomenon is considered to be extremely undesirable, sinceIt can damage the whole pipeline system.
Thus, it turns out that the flow resistance - a concept that is determined by several factors.These include design features of the pipeline system (length, bends, valves and cranes), including the material from which pipes are made.On the loss also affects the character of the liquid.It helps to understand what should be the pipeline system and what to avoid in its design and operation.
The submission considered such a thing as the flow resistance with respect to the pipeline system.A description of various modes of fluid flow and its behavior in the tubes.