Points of Loss
Fluid may loose energy at different points in the course of flow and different methods for estimation of these losses are used.
Inlets and Exits
If the inlets to any system of flow are not designed properly and have sharp edges, then it results in head losses. When a fluid enters through inlets with sharp edges, its flow area contracts at the entry point. This increases the fluid speed at entrance. To fill the area, fluid decelerates after entry point. These sudden changes cause abrupt mixing of fluid resulting in some loss in mechanical energy.
Similarly, when a fluid exits to a larger reservoir its kinetic energy is almost completely lost. A part of the kinetic energy can be recovered by providing a diffuser at the exit of the fluid.
Change in Area of Flow
Sudden changes in flow area, such as contraction or enlargement, cause separation of flow and turbulence which results in loss in energy of fluid. Loss in such cases is estimated using the loss coefficient with the kinetic energy per unit mass of the flow in the larger section of flow.
These losses can be reduced by installing nozzles or diffusers between the different cross sections. It makes the transition more gradual.
The head loss in a bent pipe is more than a straight pipe of the same length. An equivalent length of straight pipe for the bend can be found which causes same head loss as the bend. This equivalent length is used for calculation of minor losses due to bends.
Different types of fittings such as valves or joints in any system add to minor losses in the flow. Manufacturing defects increase the loss. Losses due to fittings are also given in terms of the equivalent length. This data is found experimentally and generally provided by the manufacturer.
In the last two articles we have considered the losses part of modification in the Bernoulli Equation. In the next article we will discuss real velocity distribution to modify the velocity term in the energy equation.