What is head loss

The head loss from friction is related to the velocity energy of the liquid squared. Thermal Engineering. This is a significant limitation, because most hydraulic systems especially in nuclear engineering include pumps.

This restriction prevents two points in a fluid stream from being analyzed if a pump exists between the two points. In reality, friction plays crucial role. The total head possessed by the fluid cannot be transferred completely and lossless from one point to another. In reality, one purpose of pumps incorporated in a hydraulic system is to overcome the losses in pressure due to friction.

The Hydraulic Head. In general, the hydraulic head , or total head, is a measure of the potential of fluid at the measurement point. It can be used to determine a hydraulic gradient between two or more points.

There are four types of potential head : Pressure potential — Pressure head: The pressure head represents the flow energy of a column of fluid whose weight is equivalent to the pressure of the fluid.

Kinetic potential — Kinetic head: The kinetic head represents the kinetic energy of the fluid. It is the height in feet that a flowing fluid would rise in a column if all of its kinetic energy were converted to potential energy.

Example: Frictional Head Loss. The inlet is fed by a pump at an absolute pressure of 2. The exit is at standard atmospheric pressure kPa and is m higher. Head loss and pressure loss represent the same phenomenon — frictional losses in pipe and losses in hydraulic components, but they are expressed in different units. The friction factor for fluid flow can be determined using a Moody chart.

Why the head loss is very important? Q-H characteristic diagram of centrifugal pump and of pipeline Hydraulic grade line and Total head lines for a constant diameter pipe with friction. In a real pipe line there are energy losses due to friction — these must be taken into account as they can be very significant. Pressure loss form. Darcy Friction Factor for Laminar Flow. For practical purposes, if the Reynolds number is less than , the flow is laminar.

For laminar flow, the head loss is proportional to velocity rather than velocity squared, thus the friction factor is inversely proportional to velocity. Darcy Friction Factor for Transitional Flow. At Reynolds numbers between about and the flow is unstable as a result of the onset of turbulence. These flows are sometimes referred to as transitional flows. The Darcy friction factor contains large uncertainties in this flow regime and is not well understood. Darcy Friction Factor for Turbulent Flow.

If the Reynolds number is greater than , the flow is turbulent. When analyzing piping systems, pressure loss is of upmost importance due to viscous effects along the length of the system, as well as other additional pressure losses arising from attached equipment. The head loss also represents energy used to overcome friction that is caused by the pipe walls and other components, especially in turbulent flow.

There are two types of head loss :. Figure 1. Minor head loss caused by obstacles such as changes in the shape of the pipe and elbow joints. The amount of head loss depends on many factors such as the flow velocity, pipe length and diameter, and the roughness of the pipe, which determines the friction variable and the Reynolds number in the flow.

Head loss resulting from friction produces an equivalent increase in the internal energy, that is, an increase in the temperature of the fluid. Most practiced methods for evaluating head loss due to friction are based almost completely on experimental evidence. Head loss is a measure of the reduction in the total head of the fluid as it moves through a pipe system. Head loss that occurs along the pipe wall is called friction loss.

This column will explore pipelines in detail, consider how they affect the operation of piping systems, and review the method for calculating head loss in pipelines.

A pipeline is a circular conduit used to convey process fluid from one location in the system to another. A pipeline consists of a circular pipe full of fluid, the process fluid, and the valves and fittings used to direct the flow of fluid through the pipe in the operation.

Each of these items affects the head loss in the pipeline. Most fluids used in industrial applications are Newtonian, meaning that their viscosity does not change with the rate of flow.

Water, oils, solvents and petroleum products are examples of Newtonian fluids. For simplification this discussion will be limited to the flow of Newtonian fluids through circular pipelines. When fluid flows inside a pipeline, friction occurs between the moving fluid and the stationary pipe wall.

This thermal energy cannot be converted back to hydraulic energy, so the fluid experiences a drop in pressure. This conversion and loss of energy is known as head loss.

The head loss in a pipeline with Newtonian fluids can be determined using the Darcy equation Equation 1. Evaluating the Darcy equation provides insight into factors affecting the head loss in a pipeline. If the length of the pipe is doubled, the head loss will double. If the inside pipe diameter is doubled, the head loss will be reduced by half.

If the flow rate is doubled, the head loss increases by a factor of four. With the exception of the Darcy friction factor, each of these terms can be easily measured. In this case, little information about the properties of the process fluid or the surface roughness on the inside of the pipe material is available. Although these factors seem to most people to have an effect on head loss, the Darcy equation does not account for them.

The Darcy friction factor takes the fluid properties of density and viscosity into account, along with the pipe roughness. The Crane TP manual provides the tables and formulas needed to perform the head loss calculations. It also includes a copy of the Serghide Explicit equation and the Swamee-Jain formulas allowing for direct calculation of the Darcy friction factor. The Swamee-Jain equation is solved in two parts see Equation 2.

The first step requires calculating the Reynolds number of the fluid in the pipeline. During this step, fluid properties of density and viscosity are considered. The pipe absolute roughness value and Reynolds number are then used to calculate the Darcy friction factor. October 22, EngineeringClicks.

Head loss is the pressure loss over a distance of pipe due to viscous effects Frictional losses and minor losses contribute to total head loss The Darcy-Weisbach equation is the most common equation used to calculate major head losses in a pipe The friction factor helps determine head losses by calculating the degree of roughness in a pipe. Piezometer casing above ground. Head Loss Equation The Darcy-Weisbach equation is an empirical equation, and is one of the most flexible head loss equations for a segment of pipe.

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