# Fluid

Objective

To determine the pressure or head loss in different diameters pipes, joints and valves

Theory

Pipe flows belong to a broader class of flows, called internal flows, where the fluid is completely bounded by solid surfaces. In contrast, in external flows, such as flow over a flat plate or an airplane wing, only part of the flow is bounded by a solid surface. The term pipe flow is generally used to describe flow through round pipes, ducts, nozzles, sudden expansions and contractions, valves and other fittings. When a gas or a liquid flows through a pipe, there is a loss of pressure in the fluid, because energy is required to overcome the viscous or frictional forces exerted by the walls of the pipe on the moving fluid. In addition to the energy lost due to frictional forces, the flow also loses energy (or pressure) as it goes through fittings, such as valves, elbows, contractions and expansions. This loss in pressure is mainly due to the fact that flow separates locally as it moves through such fittings. The pressure loss in pipe flows is commonly referred to as head loss. When a fluid flows through pipes, energy is lost inevitably due to frictions which occur as a result of viscous drag. Fluid friction produces eddies and turbulence, and these form of kinetic energy are eventually converted into thermal energy. Losses in energy can be expressed in term of pressure or head loss. This loss of energy due to friction was shown, both theoretically and experimentally, to be related to the Reynolds number for the flow. It has also been found to be proportional to the velocity pressure of the fluid and to a factor related to the smoothness of the surface over which the fluid is flowing.

The total head, H, for a fluid flowing across a pipe is being derived based on Bernoulli's principle and is expressed as follow:

H=P/ƿg + V2/2g + z

Where P/ƿg = pressure head, V2/2g= dynamic or velocity head, z=...

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