Short Answer:

Major losses in pipes occur due to the frictional resistance offered by the pipe walls to the flow of fluid. When fluid moves through a pipe, some energy is lost in overcoming this resistance, which results in a drop in pressure or head along the length of the pipe. These losses mainly depend on the velocity of the flow, pipe length, pipe diameter, and roughness of the pipe material.

Major losses are generally caused by friction between the fluid and the internal surface of the pipe. The friction loss is calculated using formulas like the Darcy-Weisbach or Hazen-Williams equation. These losses are significant in long pipelines and must be considered while designing efficient piping systems to minimize energy wastage and ensure proper flow.

Detailed Explanation :

Major losses in pipes

When fluid flows through a pipe, a portion of its energy is lost due to friction between the fluid particles and the pipe wall. This energy loss is known as the major loss because it occurs continuously along the entire length of the pipe. Major losses are an important factor in hydraulic engineering, as they directly affect the pressure, flow rate, and efficiency of the system.

The major loss mainly depends on the following factors:

The nature and velocity of the fluid flow (laminar or turbulent).
The pipe length and internal diameter.
The roughness of the pipe surface.
The viscosity and density of the fluid.

These factors influence how much resistance the flow encounters as it moves through the pipe. For accurate design, engineers must calculate these losses to ensure that pumps and systems work effectively.

Causes of major losses

Major losses arise primarily from frictional resistance. As fluid flows, a thin layer of fluid sticks to the inner wall of the pipe due to viscosity. This stationary layer slows down the adjacent fluid layers, creating velocity gradients and frictional shear stress. The longer the pipe and the higher the velocity, the greater the frictional resistance.

When the pipe surface is rough, additional disturbances and eddies are formed, further increasing the energy loss. Therefore, smooth pipes like PVC or copper cause less loss compared to rough pipes like cast iron. The fluid’s viscosity also influences friction—higher viscosity fluids experience more friction and therefore higher energy loss.

Expression for major loss

The most common formula used to calculate major head loss is the Darcy-Weisbach equation:

Where:

= head loss due to friction (m)
= Darcy friction factor (dimensionless)
= length of pipe (m)
= diameter of pipe (m)
= velocity of flow (m/s)
= acceleration due to gravity (9.81 m/s²)

The friction factor depends on the type of flow:

For laminar flow, (where Re is Reynolds number).
For turbulent flow, is found using empirical formulas or charts like the Moody diagram.

Another simplified method is the Hazen-Williams equation, used mainly for water flow in civil systems:

Where is the Hazen-Williams coefficient depending on pipe material.

Importance of calculating major losses

System Efficiency: Major losses reduce the energy available for fluid transport. Knowing these losses helps in selecting proper pump capacity to overcome them.
Pipe Sizing: Proper calculation ensures that the chosen pipe diameter provides an optimum flow with minimal losses.
Cost Reduction: Minimizing friction losses saves energy and reduces operating costs.
Safety and Performance: Correct estimation prevents pressure drops that can affect machinery, valves, and delivery systems.

In long-distance water supply systems or industrial pipelines, major losses are often more significant than minor losses. Therefore, engineers aim to reduce them by selecting smooth pipes, maintaining moderate flow velocities, and avoiding excessive lengths.

Methods to reduce major losses

Use of smooth and corrosion-resistant pipes to minimize surface roughness.
Maintaining moderate flow velocity to avoid turbulence.
Regular cleaning and maintenance to prevent scaling or deposits inside the pipe.
Using larger diameter pipes for high discharge requirements to reduce velocity and hence friction.
Designing shorter and straighter pipelines to minimize length.

By considering these preventive methods, the system efficiency can be improved, and the overall energy loss can be reduced effectively.

Conclusion

Major losses in pipes occur mainly due to friction between the fluid and pipe wall. These losses are continuous and depend on pipe dimensions, fluid properties, and surface conditions. Proper calculation using the Darcy-Weisbach equation is essential to design efficient and cost-effective fluid systems. By selecting suitable materials and maintaining clean, smooth pipelines, major losses can be minimized, ensuring better system performance and energy efficiency.