Flow of a Compressible Fluid Lab Report

Aim
Aim of this lab work is to understand the flow of a compressible fluid inside a tube

Objective
Following are some of the objectives which will lead to completion of above mention aim
1. Study the basic fluids, types of fluids and types of flow of fluid 
2. Perform the numerical analysis to predict the flow of fluid in smooth pipe 
3. Perform experiment of air flowing in smooth pipe
4. Calculate the Reynold number, friction factor and head losses in experiment
5. Compare the experimental result with calculated and numerical analysis

Introduction
Fluid
Fluid is anything which can flow between points of high potential to the point of low potential is called fluid. Ability of the fluid to flow is called its fluidity of fluid and it depends on the viscosity of the fluid. Viscosity of the fluid is much like the density of the solid and it define the weight of the fluid per cubic meter. Higher the viscosity of fluid is higher will its weight per cubic meter and lower will be its fluidity. 

Fluids can be classified in many different types based on the things under discussion for example discussing the Newton law fluids can be classified as Newtonian fluid and Non-Newtonian fluid. Newtonian fluids are those fluids in which stresses at every point of flow are directly proportional and linear to strain and Non-Newtonian fluid are those fluids win which stresses at every point of flow are not directly proportional and linear to strain. 

Based on the ability to compress fluids can be classified as compressible and non-compressible fluids. Compressible fluid has the ability to get compress under high pressure means their particles just their position under pressure and non-compressible fluid are those fluid which does not show any change under pressure means their particle does not change their position under pressure. 
Types of fluid flow
There are three main types of fluid flow and all of them are based on the Reynold number of that particular fluid flowing at any particular speed. Reynold number is a dimension less number which shows the fluid inertial forces as compared to the viscous forces. Based on the Reynold number fluid flow has three types; one is Laminar flow in which the Reynold number of the fluid never exceed 2100 value, transient flow is one in which Reynold number fluid flow lies between 2100 and 4000 value. Turbulent flow in one in which Reynold number of fluid flow exceeds 4000 value.

Numerical Analysis
In order to predict the flow of fluid in any condition numerical analysis of that condition is done. Numerical analysis is a theoretical solution or the answer of the question related to the flow of fluid. Computational fluid mechanics is used to predict the flow of fluid in any required conditions and as this process is very complex computer software like ansys is used to solve the equations involve in this process. 

In order to perform the numerical analysis of this current process first the component involved in this work are needed to be modelled and for this any cad software or work bench of ansys can be used. Figure one shown below is computer added model of pipe which represents the pipe used in this lab work. Second figure is of the fluid domain which represents the fluid which flow inside the pipe. Third figure represent the assembly of the pipe and fluid domain which will be used for analysis purpose. 
In ansys the all components are first named as required like pipe, fluid domain, inlet and outlets and then they are meshed. Inlet of the pipe is on the right side of the pipe and outlet is on the left side (face visible in below figures). In ansys setup the fluid domain is selected as fluid and air is selected as its material. For pipe material does not matter as long as analysis is limited to the flow of fluid. Pipe is made smooth by making the wall roughness zero in ansys setup. In solution section transient solution will be done in order to simulate the flow of fluid inside the pipe with the initial velocity of fluid entering the pipe is as per experiment requirement.






Result of the simulation shown above in figure 4 shows that at the inlet of the pipe the flow of fluid will be very turbulent as different velocities are visible in that region and along the length of the pipe the velocity on the top of the fluid domain and on the centre are different which shows fluid flow will be turbulent throughout the pipe.

Experimental Result


Table 1 Experimental value

Pipe Diameter
Vo m/s
Change in P mbar
m kg/sec
Vpipe m/sec
Re
f
h meter of air
34 mm
51.4
9.8
0.055993
51.41925815
116550.3
0.021004
83.33333333
47.8
8.7
0.052071
47.81790933
108387.3
0.021561
73.97959184
41.9
6.8
0.045644
41.91569876
95008.92
0.021932
57.82312925
35.5
5.1
0.038672
35.51330086
80496.82
0.022915
43.36734694
31.2
4.2
0.033988
31.21168977
70746.5
0.024431
35.71428571
21.3
2.1
0.023203
21.30798052
48298.09
0.02621
17.85714286
15
1.3
0.01634
15.00562008
34012.74
0.032716
11.05442177
24 mm
42.1
23
0.045862
84.52401805
191587.8
0.018243
195.5782313
37.3
14.8
0.040633
74.88707537
169744
0.014955
125.8503401
32.1
8.7
0.034968
64.44705414
146080
0.01187
73.97959184
27.1
2.7
0.029522
54.40857219
123326.1
0.005168
22.95918367
21.6
0.2
0.02353
43.36624204
98296.82
0.000603
1.700680272
14.5
0.4
0.015796
29.11159766
65986.29
0.002675
3.401360544
16 mm
21.7
60.5
0.023639
98.02577627
222191.8
0.035678
514.4557823
18.1
33.4
0.019717
81.76343551
185330.5
0.028311
284.0136054
16.3
28.4
0.017757
73.63226513
166899.8
0.029683
241.4965986
14.2
16.7
0.015469
64.14589968
145397.4
0.022999
142.0068027
12.4
8
0.013508
56.0147293
126966.7
0.014448
68.02721088
10.2
0.3
0.011111
46.07663217
104440.4
0.000801
2.551020408


Comparison

The friction factor mention in the above table is called the experimental frictional factor or the actual frictional factor as the data provided for its calculation was generated by performing an experiment. Another way to get the friction factor is the moody chart which can predict the ideal friction factor based on the Reynold number and relative friction of surface. According the calculation made based on the experimental data the frictional factor for 34 mm diameter pipe and initial velocity of 51.4 meter per second is 0.021. According to the moody char for the Reynold number of 1.1*10^5 and smooth pipe the frictional factor is about 0.017 which is less than the experimental frictional factor. 
 
Figure 7 Moody Chart

Difference in the values of the experimental and graphs friction factor can be due to the fact that the pipe used in the experiment cannot be perfectly smooth that is the internal wall may have produce some extra frictional forces which result is additional pressure drop and increased value of frictional factor. 

Discussion
Numerical analysis of the said experiment was conducted using the computational fluid mechanics in ansys and result show that the flow of air inside the smooth pipe will be turbulent. According to the experimental results the calculated Reynold number of the flow for all conditions is above 4000 mark which shows that the flow of air inside the pipe for experimental setup was turbulent. So it can be concluded that the numerical analysis done for this experiment has successfully predicted the nature of flow of air inside the pipe.

In order observe the effect of mass flow rate on the change in pressure developed across the pipe, a graph was generated using the values obtain during the experiment. According to the graph the mass flow rate and change in pressure developed are directly proportional to each other. This means that the increase of mass flow rate of air inside the pipe increase the pressure difference observed across the pipe and decrease of mass flow rate of air inside the pipe decreases the pressure difference observed across the pipe

In order observe the effect of Reynold number on the frictional factor, a graph was generated using the values obtain during the experiment. According to the graph the Reynold number and frictional factor are directly proportional to each other. This means that the increase of Reynold number of air inside the pipe increase the frictional factor and decrease of Reynold Number of air inside the pipe decreases the Frictional factor for pipe with 24 mm and 16 mm diameter for 34 mm diameter this relation is opposite. 

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