Paper Example on Laminar and Turbulent Flow in Smooth Pipes

The experiment was carried out to investigate the relationship between head loss and mean velocity in a smooth pipe during laminar and turbulent flow. The results of the experiment were used to determine the lower critical velocity, the coefficient of the viscosity of water as well as the roughness of the pipe. The objective of the Osborne Reynolds objective is to illustrate laminar, transitional and turbulent pipe flow and also determine the condition under which these flows exist. Laminar flow is the type whereby there is the movement of particles in a straight line which is in the form of thin parallel sheets (Syahiirah, 2015). There is a steady condition denote in this form of flow whereby the stream lines tend to follow a kind of parallel path. In this case, the fluid continues to be distinguishable without difficulty.

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On the other hand, turbulent flow is where the particles are moving in a zigzag pattern. The condition denoted is unsteady whereby there is the interaction of stream lines hence causing shear plan collapse and hence there is an occurrence of mixing. As there is an increase in the flow rate, transitioning from laminar to turbulent tends to be a gradual process (Syahiirah, 2015). The apparatus used for the experiment are ideal to help in visualizing the flow hence determine its laminar and turbulent. The use of an overflow tank helps to maintain a constant pressure head on the flow tube while the rate of flow is controlled.

Reynolds number is widely used in fluid mechanics. He demonstrated that there are distinctly different types of flow through injecting a thin stream of colored fluid which has the same density as water into a large transparent tube where water is also flowing. The number formula:

R=ULVR= Reynolds number

U= Fluid velocity, (m/s)

L= characteristic length or diameter (m)

V= Kinematic viscosity (m2 /s)

The Reynolds number R is independent of pressure

From the experiment, it was observed that the colored fluid line changes with the increase in the flow rate of water. The change of the shape is from a thin thread to slightly swirling which has smooth thin threads a then fully swirling.

Losses are caused by fitting, bends, enlargement, valves and also contraction. These losses tend to be proportional to the velocity of flow and the geometry of the device being used. It is such that

HL =K (V2 2 g)

The value of K is provided for the devices being used where it denotes the loss factor. In most cases, the cause of energy loss is turbulence. Similarly, the amount of turbulence is also dependent on the differences in the diameters of the pipe. The relation between head loss and mean velocity is that there is an increase in the heat transfer coefficient with an increase in the velocity of the fluid. The intense mixing of the fluid during turbulent flow due to the rapid fluctuation eventually enhance the transfer of momentum between the liquid particles hence an increase in the force of friction on the surface thus requiring more pumping power. At the time when the flow reaches fully turbulent, the friction factor is at its maximum.

The head loss represents the additional height that the fluid should be raised by the pump so as to overcome the losses of friction in the pipe. The head loss is because of viscosity and has a direct relation with the head shear stress. Once the experimenter is aware of the head loss, they seek the requires pumping power so as to overcome the pressure loss. If there is an increase in the angle of the pipe, there is a consequent increase in the minor losses. When the angle decreases, the minor losses also decrease but there is also the requirement of a longer pipe for the transition to occur which means that there are more friction losses and hence a tradeoff and thus minimum loss.

A decrease in the diameter of the pipe leads to a higher velocity at that area. Contraction of the flow and turbulence when there is a change in the diameter lead to an increase of the head loss. The section where the flow is at its narrowest point us the Vena contracta and here, the velocity is at its maximum. The loss factor, in this case, can be computed with its basis on the ratio of the diameter and velocity of flow. However, one important thing that was noted during the experiment, energy losses for sudden contraction tend to be less compared to those of sudden enlargement (Subramanian, 2008).

The graph shows a positive relationship between the scale of rotameter and the flow rate. An increase in millimeters of the scale caused an increase in the corrected flow rate. It is to depict an increase in velocity means hence more head loss and viscosity.

For smooth pipes, the recommendation is to use a correlation of more than 10,000 which is when the flow is between laminar and turbulent. On the other hand, the extent of the roughness of tubes is dependent on the nature of the surface. Rough pipes cause more head loss compared to the smooth pipes.

The experiment reveals that there are a number of ways that one can use to ensure improvements in the experiment to obtain the best results. There is a need to repeat the experiment for a couple of times, say three times so as to get average readings. This way, there will be a reduction in the deviation results hence reliable information to be dispatched (Syahiirah, 2015). The experiment also requires sufficient time. Our group took close to 4 hours to get one and still felt that we needed more time which would have helped to get consistent results as there were some values that did not make sense.

Some of the problems encountered during the experiment included errors of slow response when collecting water in the beaker and getting the need flow. Also, there was a slow response of starting the time taken for the volume of water as well as ensuring accurate regulations of the valve to control the flow. Additionally, the precaution steps are critical and one needs to be alert. We had to work at a suitable and unshaken place so as to get the appropriate laminar smooth stream flow. It was also important to note that there was a need for slow and careful regulation of the clip and the valve for the injection of the colored fluid. The experiment is beneficial in learning more on flow rate in pipes and it was fun making readings from the experiment.

References

Subramanian, R.S., 2008. Heat transfer to or from a fluid flowing through a tube. web2. clarkson. edu/.../subramanian/.../Convective% 20Heat% 20Transfer

Syahiirah, N. 2015. Lab report, Osborne Reynolds Demonstration.