Lab-14.1.pdf

UNIVERSITI SAINS MALAYSIA SCHOOL OF CHEMICAL ENGINEERING EKC 291 CHEMICAL ENGINEERING LABORATORY 1 EXPERIMENT 14: AIR FLOW BENCH

GROUP NUMBER: 1 GROUP MEMBERS: 1. YIAUW DIING YE

(125188)

2. MOHD. RIDZWAN BIN REMLEE

(125147)

3. ONG HOAY YEE

(125169)

LECTURE IN CHARGE

:

DR. MUHAMAD NAZRI MURAT

TECHNICIAN IN CHARGE :

EN. MOHD. ROQIB

DATE OF EXPERIMENT

:

22 MARCH 2016 (AFTERNOON SESSION)

DATE OF SUBMISSION

:

28 MARCH 201

TABLE OF CONTENT NO

CONTENTS

1.0

ABSTRACT

2.0

INTRODUCTION 2.1 A view of Model FM21 Air Flow Bench 2.2 Manometer in Air Flow Bench 2.3 Metering devices in Air Flow Bench 2.4 Industrial Applications of Air Flow Bench THEORY 3.1 Experiment A 3.2 Experiment B 3.3 Experiment C 3.4 Experiment D OBJECTIVE 4.1 Experiment A 4.2 Experiment B 4.3 Experiment C 4.4 Experiment D

3.0

4.0

PAGE NUMBER 1 1 1 2 2 2 3 5 5 6 6 6 6

5.0

EXPERIMENTAL PROCEDURE 5.1 Experiment A 5.2 Experiment B 5.3 Experiment C 5.4 Experiment D

7 7 7 8

6.0

RESULTS 6.1 Experiment A 6.2 Experiment B 6.3 Experiment C 6.4 Experiment D

8 9 11 13

7.0

8.0

DISCUSSION 7.1 Experiment A 7.2 Experiment B 7.3 Experiment C 7.4 Experiment D 7.5 Error Analysis CONCLUSION 8.1 Experiment A 8.2 Experiment B 8.3 Experiment C 8.4 Experiment D

15 16 17 17 18 18 18 19 19

9.0

REFERENCE

19

10.0

APPENDIX A. Calculation B. Raw Data Sheets

20 23

1.0 ABSTRACT In this experiment, we operated the air flow bench to study about the air flow. For experiment A, the centrifugal air blower characteristic is studied through the relationship of static pressure and volumetric air flow rate by adjusting the height of damper. When volumetric flow rate increased, static pressure increased. In experiment B, three types of metering devices, which were orifice plate, venturi nozzle and pitot-static tube were used to conduct flow measurement of air. For the same diameter, orifice plate had a higher pressure drop than venture nozzle. Experiment C was to confirm Bernoulli Theorem apparatus by demonstrating the conservation of energy in Bernoulli apparatus. When total head was held constant, an increase in velocity head resulted in a decrease in pressure head and vice versa. For experiment D, the development of fully turbulent air flow within a pipe was determined. A fully turbulent air flow was develop when the air velocity was constant. Sudden changes in pipe size would lead to changes in velocity profile.

2.0 INTRODUCTION Air Flow Bench is a device used to test the internal aerodynamic qualities of an engine component and also wind tunnel. It is also used to test the flow capabilities of any component that is required to flow gas. It consists of a centrifugal fan of 2 hp of capacity 1100 cfm with inlet diameter of approximately 180 mm. 2.1 A view of Model FM21 Air Flow Bench

2.2 Manometer in Air Flow Bench There are two inclined manometers used. Normally the short one for measurement of static pressure while the long one for measurement of total pressure. 1

2.3 Metering devices in Air Flow Bench Air Flow bench uses three types of metering devices, which are orifice plate, venturi meter and pitot-static tube, which deliver similar accuracy. Orifice plates are simple and able to provide multiple flow ranges easily. While venture nozzle offers substantial improvements in efficiency, its cost is higher. 2.4 Industrial Applications of Air Flow Bench Air Flow Bench is used to test Bernoulli’s Theorem. Beside using for calculation of air flow rate, fan performance curve measurement and thermal resistance, it was also used hot air laminar flow tunnel design for on-line sterilization and depyrogenation of any glass receptacle in pharmaceutical industry. Laminar air flows are also widely used for daily room cleaning activities, pathogen handling, and microbiology and biotechnology applications in various laboratories.

3.0 THEORY Experiment A: Determination Of Centrifugal Air Blower Characteristics The volumetric air flow rate is given by: 𝑞𝑣 = 𝛼(

𝜋𝑑2 4

2∆𝑃

)√ 𝜌

𝐴

(m3/s)

Where: α = 1.0 – 0.5Re – 0.2 when 20000< Re<30000 α = 0.960 when Re>30000 d = diameter of constant diameter duct section, 8.96 x 10-2m ρA = density of upstream air, kg/m3 ∆P = differential pressure measured, Pa.

From the volumetric air flow rate, the average air velocity, v in the 140.4mm duct can be determined: 𝑉=

𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝐷𝑢𝑐𝑡 𝐴𝑟𝑒𝑎

=𝜋 4

𝑞𝑣 ∙ 0.14042

(m/s)

2

The Reynolds Number is then: Re =

𝜌𝐴 𝑣𝑑 𝜇𝐴

Where: μA = viscosity of air at bulk fluid temperature

The dynamic pressure at point PT4 is given by: 𝑃𝑑4 =

𝑣 2 ∙ 𝜌𝐴 2𝑔

(mmH2O)

The static pressure rise across the blower is given by: ∆𝑃𝑆 = (𝑃𝑆𝑃𝑇4 − 𝑃𝑆𝑃𝑇3 ) − (1 − 𝜉24 − 𝜉31 )𝑃𝑑4 Where: (𝑃𝑆𝑃𝑇4 − 𝑃𝑆𝑃𝑇3 ) = pressure drop across the blower 𝛏 = friction coefficient;

𝜉24 = 0.37

𝜉31 = 0.8

Experiment B: Flow Metering Devices Pitot Static Tube Measurement The pitot static tube used is modified ellipsoidal-nose type. The minimum velocity past the tube should be greater than 75/tube diameter mm, i.e. 1.875 m/s so as to confirm to BS848 stipulation regarding Reynolds number to be greater than 500. To determine the datum point for the pitot static tube scale, the pitot static tube should be pushed into the duct until the head just touches the side wall. NOTE: Care must be taken not to push too hard and bend the nose of the tube away from the wall. The center of the tube will then be a distance of 2 mm. The differential pressure P across the pitot static tube should be measured at each measuring point. The effective differential pressure is the square of the average of the square roots of the 24 individual differential pressures, as given in the following:

1 Peff =  2

 P   j 1  j  24

Mass flow rate,

0.5 j

2

(Pa)

q m =απD 2 2 Peff / 4

(kg/s) 3

Average velocity,

V av  q m /  A (m/s)

The value of α, the flow coefficient can be derived by evaluating the Reynolds number (Re) based on duct diameter, D (140.4 mm). According to BS 848, this method of flow measurement has an uncertainty value of ±2%

Orifice Plate An orifice plate is a thin plate with a hole in the middle. It is usually placed in a pipe in which fluid flows. When the fluid reaches the orifice plate, with the hole in the middle, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracta. As it does so, the velocity and the pressure changes. The volumetric flow rate is determined from the following: 𝑞𝑣 =

𝐶𝑜 𝐴𝑜 𝑌 √1 − (

Where: C 0

= flow coefficient

𝐷𝑜 4 𝐷𝑖 )

Y = expansibility factor P = pressure drop over orifice plate, Pa

A0

= area of orifice, m 2



= density upstream of the device (i.e. at atmospheric pressure) kg/m 3

D0

= orifice diameter

D i = duct diameter (140.4 mm)

The C 0 value taken from BSS 848 for the orifice plates are as follows: 65 mm orifice: 0.599;

95 mm orifice: 0.596

The Y value for inlet orifice is given by the following expression: 𝑌 = 1 − (0.4 + 35𝛽 4 )

∆𝑃 𝑃1 𝑘

Where: β = Do/Di k = air isentropic constant = 1.4 P 1 = pressure upstream of the device (atmospheric), Pa The uncertainty value of the coefficient may be taken as ±1.5%

4

Venturi Nozzle The volumetric flow rate is determined from expression: 𝑞𝑣 =

𝐶𝑣 𝐴𝑣 𝑌 √1 − (

𝐷𝑣 4 𝐷𝑖 )

Where: C v = flow coefficient (0.98 for Re > 104) A v = area of venture (m 2 ) based on venture diameter D v Y

= expansion factor

The uncertainty of the flow coefficient of a venture device with free inlet is ±1.2%. Experiment C: Bernoulli Principle Observation For Air For single streamline and steady state condition: P u2   g .z  CONSTANT  2 For horizontal ductwork as used in this experiment, Equation C1 is reduced to; P u2   CONSTANT g 2 g Where: U2 P = Pressure Head = Velocity Head 2g g Total Head = Pressure Head + Velocity Head For gas flow, the equation which commonly used: u2 P+  = constant 2g Experiment D: Investigation of The Development of Fully Turbulent Flow Within A Pipe Air boundary layer at the inner pipe surface grows as the air flowing inside the pipe. The boundary layer growth is at minimum at the pipe inlet and reaches its maximum at some point downstream, at which boundary layer fills the pipe completely. Air flow is said to be fully developed at this point. Pitot static tube can be traversed across the pipe diameter to study the pressure profile at specified distance from the inlet and the progressive build-up of a fully developed flow, within the pipe can be laminar or turbulent. Frictional loss in a pipe will cause static pressure drop along the pipe. 5

The static pressure drop: Pf 

4 flV 2 2d

Therefore, friction factor is: f 

(0.5).D2 .Pf

lV 2

V2 D Energy loss due to frictional pipe expansion is given by:  F  i .1  1 2 D2

2

To predict the static pressure drop in pipe inlet, Bernoulli Theorem may be used. There are two flow conditions possible at the inlet. i)When no separation of the streamlines from the wall occurs, as in a bell mouthed inlet. Total pressure will remain constant. Hence, the static pressure drop will be equal to the gain in velocity pressure; P am bient 0  P1  

V2 V12 and P am bient  P1   1 2 2

ii) Vena contracta occurs at the wall hence the velocity will be highest at the vena contracta before slowing down on the subsequent re-expansion. Static pressure will be lower. The net loss in the total pressure is P  k

V2 where k is the pressure loss constant. 2

4.0 OBJECTIVE

Experiment A: To understand the centrifugal air blower characteristic trough the plot of static pressure rise across the blower, against the volumetric air flow rate. Experiment B: To conduct flow measurement of air using three types of flow metering devices, Orifice, Venturi, Pitot Static Tube. Experiment C: To demonstrate the conservation of energy taking place in the Bernoulli apparatus confirm Bernoulli Theorem. Experiment D: To investigate the development of fully turbulent air flow within a pipe.

6

5.0 EXPERIMENTAL PROCEDURES 5.1 Experiment A The assembly was set up as shown in Figure A.1 (Appendix). Inlet static pressure point PT3 was connected to the limb of long manometer of P010 dual manometer while the outlet static pressure point PT4 was connected to the reservoir of long manometer of P010 dual manometer. Next, the inlet mouth pressure point PT2 was connected to the limb of short manometer P010 dual manometer. The P010 dual manometer with both manometers in the upright position was levelled and being set to zero. The height of P006 damper was set to 0 mm above of P005 damper holder. The P001 blower was switched on. The reading of long manometer (𝑃𝑆𝑃𝑇4 − 𝑃𝑆𝑃𝑇3 ) and short manometer ∆𝑃 were recorded. The inlet air temperature was recorded as well with thermometer. The height of P006 damper was increased until the height is 110 mm above the end of P005 damper holder. The manometer reading was recorded at each setting. 5.2 Experiment B The assembly to include components as outlined in Appendix 1(List of part no. and part description for experimental assembly) is set up as Figure B.2 (Appendix).The P012 (A) orifice 65 mm plate is pushed into P012 inlet adaptor housing. The orifice plate is positioned with the counter sunk side downstream from the inlet, i.e. facing into the housing, where the engraved label should be face upstream. Next, P013 stand is adjusted to a suitable height to support the overhanging section of the assembly. Then P014 pitot static tube I assembly is fit into the 1 meter ductwork at any of the two radial positions (PR1, PR2) with the nose facing the upstream air. The other two radial positions are plugged off. After that, P014 pitot static tube is connected to the long manometer of P010 with the P014 tube top (total pressure) connected to the reservoir and P014 tube side (static pressure) connected to the limb. The pressure tapping PT1 of P012 flow metering device housing is connected to the reservoir of the small manometer P010 dual inclined manometer while the pressure tapping PT2 of P012 flow metering device housing is connected to the limb of the small manometer P010 dual inclined manometer. 5.3 Experiment C The assembly to include components as outlined in Appendix 1(List of part no. and part description for experimental assembly) is set up as Figure C.1 (Appendix).The P021 pitot tube is pushed to maximum insertion. The P021 pitot static tube is connected to P012 dual manometer as follows, 7

where the top (total pressure) connected to the reservoir of long manometer while the side (static pressure) connected to the reservoir of the long manometer. Both manometers are positioned in top inclined position, levelled and being set to zero. P006 damper is set to half open. P001 blower is then being started, the height of P006 damper is adjusted so that the long manometer (total pressure) reading is roughly 0.6kPa. P021 pitot static tube is positioned so that its static pressure holes are aligned to 210 mm position. After that, the readings of long (total pressure) and short (static pressure) manometer are recorded. The step above is repeated with P021 pitot static tube moved in 10 mm increment towards the ductwork end until the static pressure holes of P021 tube are aligned to zero mark on the scale. 5.4 Experiment D The assembly to include components as outlined in Appendix I: List of part and part description for experimental assembly is set up as in Figure D.2. P014 Pilot Static Tube I is fitted at the PT4 position. The tube side (static) and the tube top (total) tapping are connected to the limb and of the long manometer respectively at P010 dual manometer. Both long and short manometer is set to upright position. Long manometer is then levelled and set to zero. Other alternative pitot static measuring points PT3, PT2, and PT1 are plug. A. Determination of volumetric air flow rate using pitot static tube. P006 damper height is set 20mm above the P005 damper holder. Next, P001 blower is started. P014 pitot tube is traversed at positions across the pipe. The manometer reading is recorded. The pitot tube at other positions (PT17, PT18, PT19) are fitted and step above is repeated. B. Determination of volumetric air flow rate using pitot static tube. The limb of the short manometer in upright position was connected to PF1 while the P001 blower is still running from the previous experiment. The reading of the long manometer is recorded, and then is repeated at the other positions (PT2-PT14).

6.0 RESULTS 6.1 Experiment A Inclination of manometer: 30° Inlet air temperature: 25°C (298K)

8

Damper Height (mm)

Total Static Corrected Volumetric PressurePressure at pressure flow rate, Long PI2-Short at PI2, qv manometer, manometer, ∆Pcorrected (m3/s) Pl (kPa) Ps (kPa) (kPa)

Velocity, v (m/s)

Reynolds Number, Re

Dynamic pressure, Pd4 (kPa)

∆Ps (kPa)

0

0.05

0.02

0.010

0.02406

1.55404

13914.73

0.00142

0.05024

10

0.12

0.08

0.040

0.04863

3.14077

28122.15

0.00581

0.12099

20

0.25

0.20

0.100

0.07889

5.09573

45626.63

0.01528

0.25260

30

0.32

0.27

0.135

0.09166

5.92070

53013.36

0.02063

0.32351

40

0.40

0.33

0.165

0.10134

6.54558

58608.47

0.02521

0.40429

50

0.43

0.35

0.175

0.10436

6.74101

60358.36

0.02674

0.43455

70

0.46

0.36

0.180

0.10584

6.83663

61214.55

0.02751

0.46468

90

0.49

0.37

0.185

0.10730

6.93094

62058.93

0.02827

0.49481

110

0.51

0.38

0.190

0.10874

7.02397

62891.97

0.02903

0.51494

Static Pressure Rise Across blower, ∆Ps (kPa)

Table 6.1.1: Result of Experiment A

Graph of Static Pressure Rise Across blower, ∆Ps against Volumetric Flow Rate, qv 0.60000 0.50000 0.40000 0.30000 0.20000 0.10000 0.00000 0.00

0.02

0.04

0.06

0.08

0.10

0.12

Volumetric Flow Rate, qv (m3/s)

Figure 6.1.1: Graph of corrected pressure difference versus volumetric flow rate.

6.2 Experiment B (damper height fixed at 90mm) Testing Apparatus

P012B Orifice 95mm

Height of Pitot Tube (mm) 0 10 20 30 40 50

Long Manometer, Pt (kPa)

Short Manometer, Ps (kPa)

∆Pt,

∆Ps,

corrected

corrected

(kPa)

(kPa)

0.55 0.55 0.53 0.52 0.55 0.54

0.32 0.32 0.32 0.33 0.33 0.33

0.275 0.275 0.265 0.26 0.275 0.27

0.16 0.16 0.16 0.165 0.165 0.165

∆Pt0.5(Pa)

∆Ps0.5(Pa)

16.583124 16.583124 16.2788206 16.1245155 16.583124 16.4316767

12.64911 12.64911 12.64911 12.84523 12.84523 12.84523

9

P012D Venturi 95mm

60 70 80 90 100 110

0.53 0.57 0.55 0.55 0.56 0.55

0.33 0.33 0.33 0.33 0.33 0.33

0.265 0.285 0.275 0.275 0.28 0.275

0.165 0.165 0.165 0.165 0.165 0.165 ∑∆P0.5

16.2788206 16.881943 16.583124 16.583124 16.7332005 16.583124 198.227721

12.84523 12.84523 12.84523 12.84523 12.84523 12.84523 153.5544

0 10 20 30 40 50 60 70 80 90 100 110

0.31 0.29 0.27 0.25 0.27 0.28 0.29 0.29 0.29 0.29 0.29 0.3

0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.24 0.24 0.24 0.24 0.24

0.155 0.145 0.135 0.125 0.135 0.14 0.145 0.145 0.145 0.145 0.145 0.15

0.115 0.115 0.115 0.115 0.115 0.115 0.115 0.12 0.12 0.12 0.12 0.12 ∑∆P0.5

12.4498996 12.0415946 11.61895 11.1803399 11.61895 11.8321596 12.0415946 12.0415946 12.0415946 12.0415946 12.0415946 10.9544512 141.904318

10.72381 10.72381 10.72381 10.72381 10.72381 10.72381 10.72381 10.95445 10.95445 10.95445 10.95445 10.95445 129.8389

Table 6.2.1 Results of Experiment B (top) Testing Apparatus ΔPeff (Pa) qm(kg/s) qv (m3/s) vavg (m/s) Re

P012B

P012D

272.877 0.38774 0.32932 21.2713 190461

139.839 0.27757 0.23575 15.2273 136344

Testing Apparatus ΔPeff (Pa) Y qm qv

Table 6.2.2 Data measured by pitot-static tube (top)

Testing Apparatus

P012B Orifice 95mm

Height of Pitot Tube (mm) 0 10 20 30 40 50 60 70 80 90 100 110

P012B

P012D

163.7428 0.991615 0.092526 0.078585

117.0704034 0.992909603 0.128811376 0.109403241

Table 6.2.3 Data measured by orifice plate and venturi nozzle (top)

Long Manometer, Pt (kPa)

Short Manometer, Ps (kPa)

∆Pt,

∆Ps,

corrected

corrected

(kPa)

(kPa)

0.55 0.55 0.54 0.54 0.54 0.53 0.53 0.53 0.53 0.53 0.54 0.54

0.31 0.31 0.31 0.31 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32

0.275 0.275 0.27 0.27 0.27 0.265 0.265 0.265 0.265 0.265 0.27 0.27

0.155 0.155 0.155 0.155 0.16 0.16 0.16 0.16 0.16 0.16 0.16 0.16 ∑∆P0.5

∆Pt0.5(Pa)

∆Ps0.5(Pa)

16.583124 16.583124 16.4316767 16.4316767 16.4316767 16.2788206 16.2788206 16.2788206 16.2788206 16.2788206 16.4316767 16.4316767 196.718735

12.4499 12.4499 12.4499 12.4499 12.64911 12.64911 12.64911 12.64911 12.64911 12.64911 12.64911 12.64911 150.9925

10

P012D Venturi 95mm

0 10 20 30 40 50 60 70 80 90 100 110

0.33 0.31 0.3 0.3 0.27 0.28 0.27 0.27 0.25 0.25 0.25 0.28

0.2 0.21 0.21 0.21 0.21 0.22 0.22 0.22 0.22 0.22 0.22 0.22

0.165 0.155 0.15 0.15 0.135 0.14 0.135 0.135 0.125 0.125 0.125 0.14

0.1 0.105 0.105 0.105 0.105 0.11 0.11 0.11 0.11 0.11 0.11 0.11 ∑∆P0.5

12.8452326 12.4498996 12.2474487 12.2474487 11.61895 11.8321596 11.61895 11.61895 11.1803399 11.1803399 11.1803399 11.8321596 141.852219

10 10.24695 10.24695 10.24695 10.24695 10.48809 10.48809 10.48809 10.48809 10.48809 10.48809 10.48809 124.4044

Table 6.2.4 Results of Experiment B (side) Testing Apparatus ΔPeff (Pa) qm(kg/s) qv (m3/s) vavg (m/s) Re

P012B

P012D

268.738 0.38479 0.32681 21.1093 189011

139.736 0.27747 0.23566 15.2218 136294

Table 6.2.5 Data measured by pitot-static tube (side)

Testing Apparatus ΔPeff (Pa) Y qm qv

P012B

P012D

158.3245 0.991354 0.090959 0.077254

107.4754189 0.994130855 0.123571716 0.104953046

Table 6.2.6 Data measured by orifice plate and venturi nozzle (side)

6.3 Experiment C Duct Position, d (mm) 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10

Long- Total Pressure, Pt (kPa) -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6

Short- Static Pressure, Ps (kPa) -0.04 -0.09 -0.23 -0.41 -0.46 -0.48 -0.44 -0.35 -0.29 -0.25 -0.22 -0.2 -0.18 -0.17 -0.16 -0.15 -0.14 -0.13 -0.12 -0.1 -0.04

Corrected Total Pressure, Pct (kPa) -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3

Corrected Static Pressure, Pcs (kPa) -0.02 -0.045 -0.115 -0.205 -0.23 -0.24 -0.22 -0.175 -0.145 -0.125 -0.11 -0.1 -0.09 -0.085 -0.08 -0.075 -0.07 -0.065 -0.06 -0.05 -0.02

Velocity Head, P (kPa) -0.28 -0.255 -0.185 -0.095 -0.07 -0.06 -0.08 -0.125 -0.155 -0.175 -0.19 -0.2 -0.21 -0.215 -0.22 -0.225 -0.23 -0.235 -0.24 -0.25 -0.28

Table 6.3.1 Results of Experiment C 11

0

Graph of Corrected Static Pressure Pcs, Corrected Total Pressure Pct, and Velocity Head, P versus Duct Position, d 0

50

100

150

200

250

Pressure, P (kPa)

-0.05 Corrected Total Pressure

-0.1

Corrected Static Pressure

-0.15 -0.2

Velocity Head

-0.25

-0.3 -0.35

Duct Position, d (mm)

Figure 6.3.1 Graph of corrected static pressure, corrected total pressure and velocity head versus duct position.

*Interchange long and short limb. Duct Position, d (mm)

Long - Static Pressure, Ps (kPa)

Short - Total Pressure, Pt (kPa)

Corrected Static Pressure, Pcs (kPa)

Corrected total Pressure, Pct (kPa)

Velocity Head, P (kPa)

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10

0 -0.04 -0.32 -0.66 -0.71 -0.74 -0.65 -0.47 -0.36 -0.3 -0.24 -0.2 -0.17 -0.15 -0.13 -0.11 -0.09 -0.08 -0.06 -0.03 0.06

-0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6 -0.6

0 -0.02 -0.16 -0.33 -0.355 -0.37 -0.325 -0.235 -0.18 -0.15 -0.12 -0.1 -0.085 -0.075 -0.065 -0.055 -0.045 -0.04 -0.03 -0.015 0.03

-0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3

-0.3 -0.28 -0.14 0.03 0.055 0.07 0.025 -0.065 -0.12 -0.15 -0.18 -0.2 -0.215 -0.225 -0.235 -0.245 -0.255 -0.26 -0.27 -0.285 -0.33

Table 6.3.2 Results of Experiment C

12

0.1

Graph of Corrected Static Pressure Pcs, Corrected Total Pressure Pct, and Velocity Head, P versus Duct Position, d

0.05

Pressure, P (kPa)

0 -0.05 0

50

100

150

-0.1 -0.15 -0.2

200

250

Corrected Total Pressure Corrected Static Pressure Velocity Head

-0.25 -0.3 -0.35 -0.4

Duct Position, d (mm)

Figure 6.3.1 Graph of corrected static pressure, corrected total pressure and velocity head versus duct position.

6.4 Experiment D

PT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Corrected Total Static Pressure Volumetric Distance Pressure Pressure, Pressure, Difference, Flow Rate (cm) Difference Pt (kPa) Ps (kPa) ∆P (kPa) (m3/s) (kPa) 2.5 0.92 0.35 0.57 0.285 0.136791 5.6 1.25 0.35 0.9 0.45 0.171886 9.6 1.2 0.36 0.84 0.42 0.166058 12.7 1.22 0.35 0.87 0.435 0.168997 16 1.23 0.35 0.88 0.44 0.169966 24.8 1.02 0.35 0.67 0.335 0.148306 21.3 1.15 0.35 0.8 0.4 0.162056 30.7 1.05 0.35 0.7 0.35 0.15159 35.1 0.86 0.35 0.51 0.255 0.129391 39.2 0.77 0.35 0.42 0.21 0.117421 43.5 0.79 0.35 0.44 0.22 0.120184 47.8 0.75 0.35 0.4 0.2 0.114591 120 0.76 0.35 0.41 0.205 0.116015 197 0.82 0.35 0.47 0.235 0.124214 292 0.86 0.35 0.51 0.255 0.129391 Table 6.4.1 Results of Experiment D

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Velocity (m/s)

Reynolds number, Re

21.69463 27.26065 26.33629 26.80245 26.95605 23.52081 25.70158 24.04163 20.52107 18.62257 19.0608 18.17376 18.39953 19.69989 20.52107

123966.9 155772 150490.1 153153.8 154031.5 134402 146863.3 137378 117260.9 106412.5 108916.7 103848 105138.1 112568.6 117260.9

Fanning Equivalent friction roughness of long factor, f pipe ,Ɛ (m) 1.028599 0.921625 4.6×105 1.028599 0.41144 4.6×105 1.028599 0.240006 4.6×105 1.028599 0.181422 4.6×105 1.028599 0.144004 4.6×105 1.028599 0.092906 4.6×105 1.028599 0.108172 4.6×105 1.028599 0.075051 4.6×105 1.028599 0.065643 4.6×105 1.028599 0.058777 4.6×105 1.028599 0.052967 4.6×105 1.028599 0.048202 4.6×105 1.028599 0.019201 4.6×105 1.028599 0.011696 4.6×105 1.028599 0.007891 4.6×105 Table 6.4.2 Velocity, Re, Kin, f, Ɛ and F values Pressure loss constant, Kin

Friction loss due to sudden expansion, F 82.67788 130.544 121.8411 126.1926 127.643 97.18277 116.0391 101.5342 73.97494 60.92054 63.82152 58.01956 59.47005 68.17299 73.97494

Air Velocity (m/s)

Graph of Air Velocity, v at Different Positions, PT 30 25 20 15 10

Air velocity

5 0 0

5

10

15

PT

Figure 6.4.1 Graph of air velocity at different positions

Static Pressure (kPa)

Graph of Static pressure (kPa) at Different Positions, PT 0.365 0.36 Static Pressure

0.355 0.35

0.345 0

5

PT

10

15

Figure 6.4.2 Graph of static pressure at different positions 14

Pressure Difference (kPa)

Graph of Pressure Difference (kPa) at Different Positions, PT 1 0.8 0.6

Pressure change

0.4 0.2

0 0

5

10

15

PT

Figure 6.4.3 Graph of pressure difference at different positions

7.0 DISCUSSION 7.1 Experiment A From the Figure 6.1.1 plotted, it was shown that the static pressure, Ps increased as air volumetric flow rate increased. Another significance was that the static pressure increased at a higher rate than the air volumetric flow rate. The air volumetric flow rate was controlled by the damper height in which an increase in damper height also increased the air volumetric flow rate. The static pressure measured was equivalent to how much the pressure will drop in the system since it was caused by the shear friction force at the wall of the tube which acted against the pressure exerted by the air flow. The shape of the curve in Figure 6.1.1 can be explained by the Bernoulli’s equation: g𝛥𝑧 +

𝛥𝑢2 2

ΔP ρ

+

= 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 . Since 𝛥𝑧 = 0 for this system, plotting pressure drop against air

volumetric flow rate would mean ΔP =

𝛥𝑢2 2

+ 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 [1], where velocity, u was able to be

represented by volumetric flow rate, qv since the area was the same. Hence, any increase in the volumetric flow rate would result in a pressure drop squared increment. Besides, total pressure equals to static pressure plus dynamic pressure. Since the pressures were not negative, it was impossible for static pressure to be greater than the total pressure. However, due to the sum of the friction coefficient across the blower was greater than 1, the static pressure calculated was actually greater than the total pressure. Hence, the issue was either the formula was not complete or friction coefficient was too large.

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7.2 Experiment B In this experiment, pitot-static tube, orifice plate and venture nozzle were used to measure the volumetric flow rate of the system. The results showed that the air volumetric flow rates measured by the three metering devices were constant at the top and the side. The accuracy of these devices should be similar [4]. The volumetric flow rates measured by orifice plate and venture nozzle were close but the volumetric flow rate measured by pitot-static tube was far greater. This error was probably due to the fact that the compressibility of the air was not considered in the calculation for pitot-static tube. Expansion coefficient should be included in the calculation. Plus, the pressure drop across the pitot-static tube was quite high in which it contributed to the larger volumetric flow rate measured. This was probably due to the pitot-static tube not parallel to the air flow and caused the measurement to deviate. Another possibility was at the point where we measured the pressure with pitot-static tube the distance from the air inlet was long and the friction loss across the pipe was larger. If we intend to measure the flow rate of a system, we would not want a very high pressure drop in the system. Therefore, the data shown that venture nozzle was a better option than orifice plate since the pressure drop across the device was smaller and less energy was lost. Besides, the air volumetric flow rate should be constant since the damper height was fixed for the experiment. The velocity at the wall of the tube should be minimum due to shear force and increases until the maximum at the center. Hence, according to Bernoulli’s principle, the pressure drop measured at the wall should be highest and decreased to minimum at the center. The tube diameter was 140.4 mm, so the minimum pressure drop should be measured at around 70 mm from the initial position of the pitot-tube. However, the data obtained in Table 6.2.1 did not show minimum pressure drop at the center, this was due the fluctuation of manometer reading during the experiment. Moreover, the pitot-static tube may not be parallel to the air flow, thus affected the reading. It was also difficult to make sure the pitot-static tube does not move when taking the reading as it is held manually. It was also hard to mark the length on the pitot tube.

7.3 Experiment C According to Bernoulli’s equation, total head is the summation of pressure head and velocity head. Since the total head was held constant, this means that the increase in pressure head will result in a decrease in velocity head and vice versa [5]. The velocity head should equal with the total pressure in terms of magnitude if the pressure head was zero. From Figure 6.3.1, it was clearly illustrated 16

that the sum of velocity head and pressure head at each point equaled to the corrected total pressure. It was assumed that all energy was conserved and the air was ideal fluid. At duct position of 160 mm where the duct area was the smallest, the velocity head reached maximum as the velocity reached maximum and pressure drop reached minimum according to Bernoulli’s Theorem. Velocity head increased from 10 mm to 160 mm then decreased afterwards. This means the duct converged from 10 mm to 160 mm then it started to diverge.

7.4 Experiment D Based on Figure 6.4.1, the graph seemed to be fluctuating but at points between PT 2 and PT 5 and between PT 10 and PT13 the air velocities were quite stable and constant. For a fully developed flow, the velocity was fairly constant. The Reynolds numbers calculated throughout the whole tube were all above 2100, indicating that the flow was turbulent. With these two points, we could say that a fully developed turbulent flow was present between PT 2 and PT 5 and between PT 10 and PT13. Factors that contributed to this occurrence were there was no change in the pipe diameter and no sudden contraction and expansion between the points. From Figure 6.4.2 and 6.4.3, it was observed that the static pressure was rather constant, while the trend of Figure 6.4.3 was similar to Figure 6.4.1. An increase of velocity at PT2, PT7 and PT14 was due to sudden contraction of the tube. Correspondingly, the pressure difference or pressure drop increased at these points. However, at PT6 and PT8 the air velocity decreased due to sudden expansion. Pressure drop also decreased at these points. From PT 8 to PT10 the pressure drop keep decreasing was because the distance between them was too short and the flow was unable to fully develop. As for PT10 to PT13, the distance was very long and turbulence flow was able to fully develop. Inlet loss coefficient, kin is constant throughout the experiment since the same material was used in pipe construction. The equivalent roughness was the same since all the pipes were made of commercial steel. The Fanning friction factor was the highest at PT1 because air was taken in from the atmosphere into the pipe and it was considered a sudden contraction. The shear friction to velocity ratio at PT1 was very high as air in atmospheric had zero velocity and the sudden increase in velocity caused great friction to generate. The friction loss depended on the air velocity and sudden expansion or contraction. From Table 6.4.2, the higher the air velocity, the greater the friction loss. Friction loss also increased when sudden contraction occurred, while sudden expansion decreased its value [2].

17

Since air flow rate was the same as damper height was fixed at 90 mm, pipe contraction will result in an increase in air velocity, while pipe expansion will result in a decrease in air velocity.

7.5 Error Analysis Experiment A: Static pressure calculated was greater than the total pressure. The formula was not complete or friction coefficient was too large. Experiment B: Expansion coefficient should be included in the calculation. Pitot-static tube not parallel to the air flow and caused the measurement to deviate. Wrong formula given for calculation of volumetric flow rate across venturi nozzle and orifice plate [3]. Experiment C: Parallax error on reading. Fluctuating readings of manometer. Experiment D: The reading of manometer is fluctuating, leading to inaccurate result obtained. This had affected the following calculations.

8.0 CONCLUSION 8.1 Experiment A For a centrifugal air blower, when the damper height was increased, the volumetric flow rate was also increased, in return, the static pressure which also defined the pressure drop was also increased. The pressure drop increased at a rate greater than that of volumetric flow rate, which satisfied the Bernoulli’s equation for conservation of energy. 8.2 Experiment B Venturi nozzle and orifice plate was used to measure the overall flow measurement whereas pitot tube was used to measure the air flow rate at specific point. All three devices had similar accuracy. Venturi nozzle measured volumetric flow rate close to that measured with orifice plate. However, venturi nozzle had smaller pressure drop compared to orifice meter. The smaller the pressure drop, the smaller the error since less energy will be lost in other forms. Furthermore, a smaller pressure drop will not affect the system much if measurement was taken during system operation.

18

8.3 Experiment C Bernoulli Theorem was about conservation of energy between fluid pressure and velocity. According to Bernoulli Theorem, the sum of velocity head and pressure head will be a constant. However, total head was not a constant in reality due to energy lost in other forms. If total head was a constant, the velocity head reaching its maximum would mean that the pressure head was at its minimum or vice versa which corresponds to the theorem.

8.4 Experiment D We can conclude that a fully developed turbulent air flow was achieved when the air velocity was constant and stable and Re>2100. Factors that helped in fully developing a turbulent flow was a long pipe without contraction or expansion. We also concluded that sudden changes in pipe size can alter air velocity and its pressure differences at different position. Sudden pipe expansion would result in a decrease in air velocity and pressure differences, while sudden pipe contraction would lead to an increase in air velocity and pressure differences.

9.0 REFERENCE [1] “EKC 291 Chemical Engineering Laboratory I Lab Manual”, School of Chemical Engineering, University Science Malaysia, Semester 2, Session 2015/2016. “ [2] ‘Wikipedia’, Air Flow Bench, (wiki article), 19 August, 2015, Available from: https://en.wikipedia.org/wiki/Air_flow_bench. [24 March 2016]. [3] ‘Wikipedia’, Pitot Tube, (wiki article), 2 March, 2015, Available from: https://en.wikipedia.org/wiki/Pitot_tube. [24 March 2016]. [4] The Engineering ToolBox, Types of Fluid Flow Meters. Available from: http://www.engineeringtoolbox.com/flow-meters-d_493.html. [25 March 2016]. [5] Encyclopaedia Britannica, Bernoulli’s Theorem, 7 October, 2015. Available from: http://global.britannica.com/science/Bernoullis-theorem. [26 March 2016].

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10.0 APPENDIX A. CALCULATION Experiment A: The first data of each experiment is taken as example for calculation. Properties of air at 298K and 1atm:   0.960 for Re>30000 Density, ρA = 1.1774 kg/m3 -5 Viscosity, μA = 1.8462 x 10 kg/m.s Since the manometer has an inclination of 30°, Correction Factor = sin (30°) = 0.5 Hence all the pressures that observed from this experiment should be multiplied by the correction factor. I.

II.

Corrected Pressure difference at PI2, ∆Pcorrected ∆Pcorrected = Pressure difference × sin (30°) = 0.02 x 0.5 = 0.01 kPa Volumetric air flow rate, qv d = 8.96×10-2m 𝑞𝑣 = 𝛼 [

𝜋𝑑2 2∆𝑃 𝜋 × (8.96 × 10−2 )2 2(0.01 × 103 ) ]√ = 0.96 [ ]√ 4 𝜌𝐴 4 1.1774

= 𝟎. 𝟎𝟐𝟒𝟗𝟓 𝒎𝟑 /𝒔 Since Re < 30000, iterations were done using 1-0.5Re-0.2 for another few more calculation of qv. At 4th iteration, qv = 𝟎. 𝟎𝟐𝟒𝟎𝟔 𝒎𝟑 /𝒔 III.

Velocity, v d = 0.1404m 𝑣=

IV.

𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑞𝑣 0.02406 = = = 𝟏. 𝟓𝟓𝟒𝟎𝟒 𝒎/𝒔 𝜋 𝜋𝑑2 2 𝐷𝑢𝑐𝑡 𝐴𝑟𝑒𝑎 [ 4 ] 4 (0.1404)

Reynold Number, Re (1.1774)(1.55404)(0.1404) 𝜌 𝑣𝑑 𝑅𝑒 = 𝜇𝐴 = = 𝟏𝟑𝟗𝟏𝟒. 𝟕𝟑 1.8462×10−5 𝐴

V. Pd4 = VI.

Dynamic Pressure, Pd4 𝑣 2 𝜌𝐴 2𝑔

=

(1.554042 )(1.1774) 2(9.81)

= 0.00142 𝑘𝑃𝑎

Static pressure, ∆Ps (kPa)

∆𝑃𝑆 = (𝑃𝑆𝑃𝑇4 − 𝑃𝑆𝑃𝑇3 ) − (1 − 𝜉24 − 𝜉31 )𝑃𝑑4 = 0.05 − (1 − 0.37 − 0.8)(0.00142) = 0.05024 𝑘𝑃𝑎 20

Where: (𝑃𝑆𝑃𝑇4 − 𝑃𝑆𝑃𝑇3 ) = pressure drop across the blower 𝛏 = friction coefficient;

𝜉24 = 0.37

𝜉31 = 0.8

Experiment B: The first data of each experiment is taken as example for calculation. Properties of air at 298K and 1 atm: Density, ρA =1.1774 kg/m3 Viscosity, μA =1.8462  10-5kg/m.s α = 0.986 (for Reynolds number >3  104) = 0.988 (for Reynolds number >105) D = 0.1404m I.

II.

Corrected Pressure difference, ∆Pcorrected ∆Pcorrected = (pressure difference) × sin (30°) = 0.55 x 0.5 = 0.275 kPa Effective Differential Pressure, Peff 𝑗=12

∆𝑃𝑒𝑓𝑓

2

2 1 1 0.5 = [ ∑ ∆𝑃𝑗 ] = [ (196.718735)] 12 12 𝑗=1

= 𝟐𝟔𝟖. 𝟕𝟑𝟖 𝐏𝐚 III.

Mass Flow Rate, qm 𝛼𝜋𝐷2 𝑞𝑚 = √2𝜌∆𝑃𝑒𝑓𝑓 4 (0.988)𝜋(0.1404)2 √2(1.1774)(268.738) = 4 = 𝟎. 𝟑𝟖𝟒𝟕𝟗 𝒌𝒈/𝒔

IV.

Volumetric flow rate, V q m 0.38479 kg/s V= = ρA 1.1774 kg/m3 = 𝟎. 𝟑𝟐𝟔𝟖𝟏 𝐦𝟑 /𝐬

V.

Average velocity, vavg 𝑉 0.32681 𝑣𝑎𝑣𝑔 = =𝜋 2 𝜋𝐷 2 [ 4 ] 4 (0.1404) = 𝟐𝟏. 𝟏𝟎𝟗𝟑 𝐦/𝐬

21

VI.

VII.

Reynolds Number, Re 𝜌𝐴 𝑣𝑎𝑣𝑔 𝐷 𝑅𝑒 = 𝜇𝐴 (1.1774)(21.1093)(0.1404) = 1.8462 × 10−5 = 𝟏𝟖𝟗𝟎𝟏𝟏 Expansion coefficient, Y 𝑌 = 1 − (0.4 + 35𝛽 4 )

∆𝑃 𝑃1 𝑘

0.08964

158.3245

= 1 − (0.4 + 35 (0.1404 )) (101523)(1.4) = 0.991354

Experiment C: The first data of each experiment is taken as example for calculation. For d = 240mm, I. Corrected Total Pressure, Pct Pct = sin (30°) x Total pressure = 0.5 x (-0.6) = - 0.3 kPa

II.

III.

Corrected Static Pressure, Pcs Pcs = sin(30°) x Static pressure = 0.5 x -0.04 = -0.02 kPa Velocity Head, P Velocity Head = Corrected total pressure - Corrected Static pressure P = -0.3 – (-0.02) = -0.28 kPa

Experiment D: The first data of each experiment is taken as example for calculation. Properties of air at 298K and 1 atm: Density, ρA = 1.1774 kg/m3 Viscosity, μA = 1.8462  10-5kg/m.s α = 0.9860 (for Reynolds number > 3  104) D1=0.1404m & D2 = 0.0896m I.

Pressure difference, ∆P ∆P = Total pressure - Static pressure = 0.92 – 0.35 = 0.57 kPa

22

II.

III.

Corrected Pressure difference, ∆Pcorrected ∆Pcorrected = (pressure difference) × sin (30°) = 0.57 x 0.5 = 0.285 kPa Volumetric air flow rate, qv πd2 2∆P π × (8.96 × 10−2 )2 2 × 0.285 × 1000 qv = α ( )√ = 0.986 [ ]√ 4 ρA 4 1.1774 = 0.136791 m3/s

IV.

V.

VI.

VII.

VIII.

IX.

Average air velocity, v 𝑞𝑣 0.136791 𝑉= = π = 𝟐𝟏. 𝟔𝟗𝟒𝟔𝟑 𝐦/𝐬 𝐷𝑢𝑐𝑡 𝐴𝑟𝑒𝑎 ( × 0.08962 ) 4 Reynolds number, Re ρA vd 1.1774 × 21.69463 × 0.0896 Re = = = 𝟏𝟐𝟑𝟗𝟔𝟔. 𝟗 μA 1.8462 × 10−5 Pressure loss constant, kin 0.285 × 1000 P 𝑘𝑖𝑛 = = = 𝟏. 𝟎𝟐𝟖𝟓𝟗𝟗 0.5 × 1.1774 × (21.69463)2 0.5   A  v 2

Fanning Friction Factor, f 0.5  D2  Pf 0.5×0.0896×(0.285×1000) 𝑓= = 1.1774×0.025×(21.69463)2 = 𝟎. 𝟗𝟐𝟏𝟔𝟐𝟓 2 lv Equivalent Roughness of long pipe, 𝛏 The Ɛ/D can be read from the Moody Chart based on the f and Re calculated. The value is the multiply by D to get the roughness. For this experiment, by assuming the material of pipe is commercial steel, relative roughness of pipe, ε = 4.6×10-5 m. (Taken from Figure 2.10-3 in the Lab Manual) Friction loss due to sudden expansion, F ℎ𝑓𝑒 = 𝐾𝑒

𝑉𝑎 2 2

= (1 −

𝑆𝑠𝑚𝑎𝑙𝑙 2 𝑉𝑎 2 ) 2 𝑆𝑏𝑖𝑔

(𝜋×0.08962 )⁄4

2

21.694632 ) 2

= (1 − (𝜋×0.14042 )⁄4) (

= 𝟖𝟐. 𝟔𝟕𝟕𝟖𝟖 m

B. RAW DATA SHEETS

23