When a fluid flows in a conduit, there is friction between the flowing fluid and the pipe walls. The result of this friction is a net loss of energy in the flowing fluid. The fluid pressure is the source of the energy loss. Thus, whenever a fluid flows through a pipe, the pressure of the fluid will decrease in the direction of the flow in the absence of other effects, such as a gravitationalfield, or mechanical devices, such as pumps. Fluid flow can be laminar or turbulent in nature. Turbulent flow is characterized by intense mixing phenomena often observed as eddies within the flow field. Laminar flow is characterizedby a very smooth appearance and is devoid of intense missing phenomena. The third regime of fluid flow is transitional. As the name implies, it occurs when the fluid flow is in transition from laminar to turbulent flow or from turbulent to laminar flow. In general, the flow is considered to be laminar below Re-2000 and turbulent above Re-3000.