The aim of the work undertaken was consisted two separate experiments, pipe rush and H2O cock. These are both caused by a decrease in the flow rate within a pipe. They are two alternate dissipations of the kinetic energy of the fluid into another signifier of energy – force per unit area in the instance of the H2O cock, and possible energy in the instance of the rush shaft.
The rush shaft is a device used as a manner of avoiding force per unit area surges which accompany the H2O cock consequence, by leting the fluid up a shaft near the valve, therefore absorbing the force per unit area exerted by the fluid on the valve and the pipe. The purpose of these two experiments was to compare the consequences with the theory derived from Newton ‘s Second Law of Motion.
Water grapevines and distribution systems are subjected to rushs about daily, which over clip can do harm to equipment and the grapevine itself. Rushs are caused by sudden alterations in flow speed that consequence from common causes such as rapid valve closing, pump starts and Michigans, and improper filling patterns. Grapevines frequently see their first rush during make fulling when the air being expelled from a grapevine quickly escapes through a manual blowhole or a throttled valve followed by the H2O.
Being many times denser than air, H2O follows the air to the mercantile establishment at a high speed, but its speed is restricted by the mercantile establishment thereby doing a rush. It is imperative that the make fulling flow rate be carefully controlled and the air vented through decently sized automatic air valves. Similarly, line valves must be closed and opened easy to forestall rapid alterations in flow rate. The operation of pumps and sudden arrest of pumps due to power failures likely have the most frequent impact on the system and the greatest possible to do important rushs.
If the pumping system is non controlled or protected, taint and harm to equipment and the grapevine itself can be serious. The effects of rushs can be every bit minor as relaxation of pipe articulations to every bit terrible as harm to pumps, valves, and concrete constructions. Damaged pipe articulations and vacuity conditions can do taint to the system from land H2O and backflow state of affairss. Uncontrolled rushs can be ruinous as good. Line interruptions can do implosion therapy and line shifting can do harm to supports and even concrete wharfs and vaults. Losingss can be in the 1000000s of dollars so it is indispensable that surges be understood and controlled with the proper equipment.
Water cock is the formation of force per unit area moving ridges as the consequence of a sudden alteration in liquid speed in a piping system. Water cock normally occurs when a fluid flow start or stops rapidly or is forced to do a rapid alteration in way. Quick shutting of valves and arrest of pump can make H2O cock. Valve shutting in 1.5s or less depending upon the valve size and system conditions causes an disconnected arrest of the slow. Since liquid is non compressible, any energy that is applied to is immediately transmitted.
The force per unit area waves created at rapid valve closing can make five times the system ‘s on the job force per unit area. If non considered for, this force per unit area pulsation will quickly speed up to the velocity of sound in liquid, which can transcend 1200 m/s, doing explosion of the grapevine and pump causation every bit good as break in the pipe adjustments. For this ground, it is indispensable to understand under what conditions these force per unit area moving ridges are produced and cut down the force per unit area rise every bit much as possible in a piping system.
In experimental work there are ever some hazards to everyone in the lab, therefore a wellness and safety briefing before get downing the labs. These will aware people to the possible hazards and the appropriate stairss to cut down the likeliness of accidents. Therefore it is important to follow the advice of the staff oversing at all times and utilize the protection equipment provided.
The equipment is set up as shown, where the caput loss can be measured. The inactive caput ( Hs ) is recorded through the degree on the rush shaft when there is no flow, this will be the data point degree throughout the experiment. Then seting the gate valve and supply control valve, so that there is a steady of H2O fluxing into the sump armored combat vehicle, where the new reading in the rush shaft is the speed caput ( hv ) . Then the gate valve is close and delay for the oscillations to halt, once it is stopped the lever is opened to operated gate valve and the H2O degree should drop back to the same value for the speed caput.
The value of Hs and hv are used to cipher the caput loss due to clash which is hs – hv = hafnium. The flow rate will be needed by shuting the shit armored combat vehicle to happen the measure of H2O in the armored combat vehicle in 60 seconds. More reading should be taken for better truth. The flow rate should non be changed for the remainder of the experiment.
The upper limit and minimal rush highs are step by the oscillations and the clip between the gate valves is rapidly closed. The same process is repeated but the clip taken between the rushs go throughing the data point point is measured.
Follow to put the equipment up. Where the H2O cock flow control valve should be to the full unfastened and the rush shaft valve is to the full closed, so the measuring of the volumetric flow rate will be taken and therefore cipher the flow speed. The volumetric flow rate can be step utilizing the same process as Pipe Surge. Then the fast acting valve is release to halt the flow of H2O outright doing a force per unit area pulsation to go up and down the pipe.
This is instantaneous closings which mean closing less than 2L/c, i.e. the valve is closed before a reflected moving ridge reaches the valve once more, as this will give us the same force per unit area rise as an instantaneous closing. These pulsations are captured on the CRO where we record the mean amplitude, clip base and the continuance of the pulsation. The clip lags between the two force per unit area transducers are besides recorded.
For the 2nd half of this experiment, the CRO scene is changed so that the clip base scene is increased to 25ms/div. Once it is set up, the same process will be repeated as earlier. The fast playing valve is release and records the mean amplitude value and continuance of the pulsation for the hints that are on the CRO.
Consequences and Analysis
When comparing the values gained by experimentation to the values predicted from the equations, tabulated, it can be observed that the predicted flow rates and the period of oscillation are both rather similar with their experimental values. The ground for the little difference in flow rates is partially due to the fact that the equation that we needed to utilize to happen the flow rate had two unknown values in it, Q and hafnium.
From the clip period is about 8 seconds can be observed, whereas the predicted value is 7.5705 seconds. The disagreement between the two Numberss is most likely to be as a consequence of human mistake, when clocking the points of soap and min rush and besides when the rush crosses the data point a clip factor demands to be taken into consideration for the clip taken between the individual stating when to halt the timer and the other individual really pressing the button. This clip hold could easy explicate the half 2nd difference between the two values.
When comparing the difference between the experimental and predicted values for maximal rush tallness, the first predicted value is enormously different to the existent value achieved. The ground for this is because the equation gives the soap rush from the inactive caput presuming that there are no losingss due to clash, therefore the equation will necessitate to be adjust to take into consideration of the effects of clash.
This acts as a rectification factor. The ground why it need to be use, because the initial caput loss which is due to clash, this is the difference between the inactive caput and the speed caput which is much lower than the inactive caput therefore the initial soaps amplitude should be taken off.
Throughout the effects of clash is of import as covering with a little dullard system whereas in world rush shafts have diameters in metres. The effects of clash can be assumed negligible, every bit long as the initial caput at the valve is assume the same as at the reservoir. However in the flow frictional losingss are comparatively big, this can be seen in the fact that there is a big difference between the inactive caput and speed caput.
This is partially due to the little diameter of the pipe, as the clash occurs at the walls and if the diameter of the pipe is little so the country in which the fluid is unaffected by the clash is traveling to be smaller. In order to take the effects of clash in to account, the equation of the max amplitude must get down from the speed caput therefore the caput loss due to clash can besides be taken into consideration.
From detecting Figure 5 -1 the individual force per unit area moving ridge, it varies somewhat to the symmetrical smooth square shown as in the Fluid Mechanics Lab Manual. The pulse shown on the CRO showed an unsymmetrical, unsmooth rectangle. This abnormality of the line is as a consequence of non all the kinetic energy being transferred into possible energy, which is the force per unit area pulsation, and the staying energy being lost in the signifier of heat, sound and strain.
The strain loss is where the compaction of the H2O attempts to spread out the pipe, i.e. changeless volume therefore alteration the cross sectional country. The ground of that premise is the irregular graph as when deducing the equations as assumed that the kinetic energy lost is equal to the energy gained in the signifier of the force per unit area pulsation, this does non take into consideration the effects of energy losingss like heat noise and distortion.
In another portion of the experiment, the force per unit area transducer set up midway along the pipe. i.e. 1.5meters off from the valve ; this meant there is a clip slowdown between the first moving ridge and the 2nd moving ridge giving the chance to mensurate the velocity of sound in H2O. First the clip slowdown demand to be calculated, utilizing 0.75 per division. In the first set up the clip axis for the CRO to 2.5milliseconds per division, therefore the clip slowdown is 1.5 msecs.
The clip slowdown should approximately be a one-fourth of the clip period, so it is as expected the clip slowdown is 1.5625 msecs, which is really near to what by experimentation gained hence proposing that the value has a little mistake but non as important mistake that the value ca n’t be used to work out Ce. As a consequence the value of the clip slowdown in the equation can be used
An experimental value was given for the velocity of sound in the water/pipe system which is 960m/s. This value is used to cipher the clip it takes a individual force per unit area pulsation to go a complete circuit of the pipe, in this instance 6 metres, and the value is 4.523 msecs compared to 6.25 msecs from the study. The difference between these two values could be due to non reading the figure of divisions accurately plenty and besides where the step of the period from, both of which could hold made the consequence closer to the consequence calculated.
However the disagreement might besides be due to pulsate going further than it is assumed. For the computations, premise is made that it is merely going the length of the pipe, nevertheless the pulsation might go some distance into the heading armored combat vehicle alternatively of being reflected back at the border. This would so account for why the mensural clip period is longer, as it could be going further than the 6 metres as assumed.
When looking at the tabular array 6 -2 for the H2O cock experiment, the predicted and experimental values for the velocity of sound in H2O can be compared, peak force per unit area and besides the continuance of the first pulsation. There is non much difference the experimental and predicted values of velocity of sound in the water/pipe system, this indicates that the experiment went good and that the computations and therefore the equations used are right.
However there is a important difference between the peak force per unit area and besides the continuance of the pulsation, it is rather likely that measured the continuance of the pulsation inaccurately as determined a unsmooth value for how many divisions the period was, similarly with the amplitude of the pulsation. Furthermore when ciphering the experimental speed of sound in H2O the clip slowdown was used as the clip in the equation and the clip slowdown once more was measured by reading how many divisions it took up and as a effect was unfastened to human mistake in reading it.
From can be observe several reflected force per unit area moving ridges. When the pulsation is reflected as a low force per unit area moving ridge, the pulsation is traveling lower than the original start point. The force per unit area moving ridge is really making the vapour force per unit area of H2O and as a effect the H2O is boiling and vaporizing making bubbles, this causes a vacuity to be created therefore decelerating down the pulsation.
The energy created from the boiling H2O shortly dissipates and when there are non adequate bubbles to decelerate down the pulsation so a 2nd pulsation starts and the whole procedure repeats itself. The fact that the pulsation is slowed down in the force per unit area trough by the vacuity and bubbles means that the pulsations are non symmetrical.
Analyzing the Figure 5 – 1 more closely, on the 2nd pulsation moving ridge there is a little spike half manner between the first pulsation and the 2nd pulsation can be observe, this could be due to a figure of grounds but the most likely is that it is the pulsation that has been reflected back from the dorsum of the Header armored combat vehicle. Ideally the experiment would be set up such that the heading armored combat vehicle has a large adequate alteration in volume and force per unit area compared to the pipe that it would move as a discontinuity and reflect the pulsation back straight off.
However in this instance some of the pulsation could be being reflected from the back wall of the heading armored combat vehicle. This would besides explicate why there is a difference between some of our experimental and predicted consequences for the velocity of sound in H2O, as we could be presuming that the distance travelled by the pulsation is somewhat shorter than it travelled in world, therefore holding different values when ciphering C.
The ground why the amplitudes of the pulsation moving ridge are non symmetrical is partially due to the vaporization of the H2O and besides as a effect of clash, as the flow is slowed the frictional caput loss besides reduces and so the caput at the valve increases to the equilibrium place of the inactive caput, that is why the amplitudes converges towards the inactive equilibrium can be observe.
In decision, the consequences between theoretical and experimental were similar and close to each other. However, the little disagreements might due to human mistake, e.g. non entering the clip as accurately and besides the effects of clash will necessitate to be taken in consideration. Therefore if the experiment is repeated to acquire better truth for the consequence can be more dependable to utilize.
- Douglas JF, Gasiorek JM and Swaffield JA, Fluid Mechanics, 4th erectile dysfunction, Prentice Hall, 2001. ( ISBN 0582414768 )
- Massey, B, Mechanics of Fluids, 8th erectile dysfunction, Taylor & A ; Francis, 2006 ( ISBN 0-415-36206 )
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