What does "friction loss" refer to in piping systems?

Friction loss in piping systems specifically refers to the reduction in pressure that occurs as a fluid flows through pipes. This pressure drop is primarily caused by the internal resistance the fluid faces while moving along the inner surfaces of the pipe. Factors influencing this resistance include the type of fluid, the pipe material, the roughness of the internal surface, and the flow rate. As the fluid encounters friction between its layers and the material of the pipe, energy is dissipated, leading to a decrease in pressure. Understanding friction loss is crucial for designing efficient piping systems, as it directly impacts flow rates and can affect the overall performance of fluid transport systems.

The other choices do not correctly define friction loss. An increase in pressure due to resistance would not describe what friction loss entails. The loss of fluid due to evaporation pertains more to phase changes and not to the frictional effects within the pipe. Lastly, while heat loss can occur in thermal pipelines, it is not related to friction loss in terms of fluid pressure.