Friction Loss Along Pipe

Topics: Fluid dynamics, Reynolds number, Viscosity Pages: 12 (2637 words) Published: September 23, 2013
This experiment of the friction loss along a smooth pipe shows that there are existence of laminar and transitional flows as stated in Graph 2.0 and Graph 2.1. It is proven that the higher velocity along the smooth bore pipe, the higher is the head loss of water. As shown in Table 3.0, when the Reynolds’ number increases, the value of pipe coefficient friction, f decreases along the decreasing stead laminar line. On top of that, there are energy loss from the water to the surface of the pipe and therefore, the temperature increases when velocity, flow rate and head loss increases respectively. The percentage difference of obtained head loss and calculated head loss are 2.5%, 19.0%, 32.0%, 27.0% and 30.0% whereby the differences are not major and in the acceptable range. There are few factors in affecting the head loss which are flow rate, inner diameter of the pipe, roughness of the pipe wall, corrosion and scale deposits, viscosity of the liquid, fittings and also straightness of the pipe. There are existence of both human errors, parallax errors and environmental effect but there are always error counters to be taken place to increase the accuracy of the results.

Basically, friction loss refers to the loss of energy which occurs in the pipe flow due to viscous effects generated by the surface of the 3mm ID pipe. It is understandable that friction loss is a major loss rather than minor loss including energy lost due to obstructions. Loss of head occurred by the mixing of fluid which occurs at fittings such as bends or valves, and also frictional resistance at the pipe wall. Besides, the major part of the head loss will be due to the local mixing near the fittings.

Figure 1.0 Illustration of Fully Developed Flow along a Pipe
Based on the figure above shows how the flow goes along the length of 0.52m with 3mm ID pipe which can be found in our experiment. Those fittings such as valves or bends are sufficiently remote to reduce any disturbance from them to ensure the distribution of velocity across the pipe does not vary with the length of the pipe. This flow is known as a “fully developed”. The head loss depends on the wall shear stress, τ in between the fluid and pipe surface. On top of that, the shear stress of a flow is also dependent on whether the flow is turbulent or laminar.

Nevertheless, the Reynolds number is provided by
Re = =
whereby Q shows volumetric flow rate and the shows the molecular viscosity. This quantity varies with temperature whereby the higher the head loss of water and mercury, the higher the change in temperature. The Reynolds number determines whether the flow is laminar or turbulent. For a smooth pipe, the Re < 2100 shows laminar flow properties while Re > 4000 signifies turbulent flow properties. On the other hand, transitional flows refer to range 2100 < Re < 4000.

Figure 1.1 Laminar and Turbulent Flows Along a Pipe
Illustrations above shows the flows of laminar and turbulent properties along a smooth pipe whereby velocity increases from zero (minimal) at the wall to a maximum value U at the centre of the pipe. Therefore, the mean velocity, V is of course less than U in both flows. In laminar flow, the velocity profile is parabolic and the ratio U/V of the centre line velocity to mean velocity is = 2

Meanwhile, the velocity distribution is much flatter over most of the pipe cross section for the turbulent flow. The flatness of the profile is proportional to the Reynolds’ number whereby the ratio of maximum to mean velocity reduces slightly.

Graph 1.0 Graphs of h against u and log h against log u
The graphs shown above relates on how velocity, v along the pipe affects the head loss, h of both water and mercury. It increases steadily shows the existence of laminar flow then follow by random curves which represents transitional flow for both graphs. Besides, for graph of h against u has a curvy increase after the...
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