Introduction - Exeter



Impact of a JetIntroductionUsing an Armfield F1-10 hydraulic bench, the force of a jet that impacts onto a target plate can be investigated. These reaction forces are produced from the change in momentum. It is expected the greater the momentum transfer, the greater the mass required to balance the plate and jet. MethodApparatusArmfield F1-10 hydraulic benchF1-16 equipmentStopwatchSet-Up19050695960Using four different types of deflector angle (30, 90,120,180 degrees), masses are applied to a plate upon which a water jet is impacting, until the system behaves in equilibrium. The base plate is known to be in equilibrium when the target plate is raised vertically by the impacting water until the weight pan reaches the level gauge as shown in figure one.During this time a reading of the amount of water flowing is required and found by taking a measurement from the sight glass. The volume of water accumulated is in litres and is converted to metres cubed using the conversion factor: 1 litre = 0.001 metres cubed.To find the volumetric flow rate, the time period of the collection of the water is also taken using the stopwatch.This process is repeated for each of the four deflector plates. Altering the valve which controls the flow rate into the apparatus allows the experiment to be undertaken again to obtain at least two sets of data.Figure SEQ Figure \* ARABIC 1- Impact of a jet experiment set upThe data can be processed to obtain relevant information that can be compared to the known theoretical data. Graphically representing the results also will show how accurate the experimental data is. The gradient of the theoretical data is obtained from a regression line and this is compared to the value from:equation 1: s=ρA(cosθ+1)Results -895350647065From the four raw data items obtained from the experiment (deflector angle, volume collected in litres, time to collect, and the mass applied) and using known formulae the mass applied and velocity squared values can be used to represent the results graphically.Table SEQ Table \* ARABIC 1 – Data collected Table 1 shows the collected and calculated data from the experiment. Included in this table is a calculation of accuracy in percentage compared to the theoretical slope.Figure SEQ Figure \* ARABIC 2 – All of the experimental data plotted on the same axisGraphical comparison of the experimental and theoretical data1905075565Figure three shows the comparison of the line of the theoretical data compared to the experimental.The y-axis intercept is not important in this as there would be other coefficients involved. Figure SEQ Figure \* ARABIC 3- 30 degrees deflector The stronger the experimental data is, the more parallel it would be to the theoretical.1905034925Figure four shows the same details as the previous deflector plate.Figure SEQ Figure \* ARABIC 4 – 90 degrees deflectorFigure SEQ Figure \* ARABIC 5 – 120 degrees deflector19050-3810Figure five shows the divergence of the experimental and theoretical data.19050-142875Figure 6 shows the parallel lines on top of each other which are near perfect. Figure SEQ Figure \* ARABIC 6 -180 degrees deflectorConclusionErrorThe average human reaction time to light stimuli is 19ms (0.19 seconds) [2]. This combined with imprecise measurements of the collection of the water has an affect on the accuracy of the results. An estimation of this effect is likely to be a ± 0.1L errorWhen balancing the impact of the jet with the mass applied, the weights are supplied in a set with the lowest weight 10 grams. A load of 55 grams for example, would not be possible. This too has increased the inaccuracy of the results by ± 0.01 Kg.Calculating the error values for velocity squared and applied mass taking into account these errors is shown in table 2. Table 3 (see appendix) is the full table of calculations of the error.190501270Where there was a much lower flow rate (flow rate two) and using the thirty degree deflection plate, the error was abnormally higher and was anomalous to the other data (highlighted). Generally where the forces and velocities were higher the percentage of error was lower. Using the error percentage for the flow rate two and applying these as error bars to the graph provides a more accurate representation.These are the error bars that are used:Table SEQ Table \* ARABIC 2 –Error calculationsDeflection angle (degrees)Horizontal error bar (±%)Vertical error bar (±%)301850907111206718067 Table SEQ Table \* ARABIC 3- Error barsFigure 7 – Collective data as (figure 2) with calculated error bars.Discussions Taking more readings of more flow rates would make a stronger result set. Also repeating the experiment more times the flow rates one and two to get data which averages could be taken would improve the accuracy further than in figure 7.References[1] - [2] - , 1st line , “Mean Reaction Times” paragraph. -190500474980AppendixTable SEQ Table \* ARABIC 4 – Full table of results calculating the error ................
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