transient heat transfer under graduate thesis part 1 level 4 term 1

Aashique Alam Rezwan

Sarzina Hossain

WORK PROGRESS

OF THE LEVEL 4 TERM I,

UNDER GRADUATE THESIS

WEEK 1 & 2

Topic Selection & Discussion

Final Selected Topic:

Transient Heat Transfer Through Flame Resistance Fabrics

WEEK 3

• Submission of Work Plane and other Materials

• Objectives:

1. To study the characteristics of heat transfer from a vertical hot jet of air impinging on

two types of horizontally mounted plate, a flat and a convex plate and to compare the two

results.

2. To study the performance of flame retardant fabrics in contact both with a flat and a

convex plate.

3. To compare the heat transfer characteristics of flat and convex plate (with and without

fabric).

4. Simulation of the heat transfer on flat and convex plate due to hot air impingement.

• Expected Outcomes:

1. Characteristics of convective heat transfer due to air impingement on a convex plate.

2. Characteristics of heat transfer of a flame retardant fabrics used by the local fire fighter.

WEEK 4

• Discussion on Previous Work

• 1. In the flat plate experiment for nozzle to plate separation z/d<3 the maximum Nussult number occurs slightly off the stagnation point. Within this distance the flow parallel to the surface is accelerated. At the end of the accelerated flow region the pressure gradient increases which leads to sudden rise in the turbulence level. The velocity increases slightly off the centre. The result is a sharp increase in the heat transfer co-efficient, h and hence higher Nu.

• 2. For z/d=1 there is secondary peak. Secondary peaks occur in the wall jet as a result of rising turbulence & falling velocity.

• 3. It can be concluded that for z/d<3 there is no specific relation between r/d and Nu because high turbulence. For z/d>3 the Nusselt number exponentially decays with the increasing r/d.

• 4. As the time increases heat flux decreases.

• 5. As the nozzle to plate separation distance increases heat flux also decreases.

WEEK 4 (CONTINUED)

• 6. For larger z/d separation the surface heat flux is fluctuating. This occurs due to the mixing of

surrounding air with hot fluid creates an eddy current which in turns create fluctuation in

reading.

• 7. When the experiment done with fabrics in contact with plate the maximum Nu occurred off

the centre but no secondary peak occurred. So it can be said that the turbulence effect is less

when fabrics is used.

• 8. Another non-contact testing is done where the fabric is 6mm away from the plate. This was

done to compare the energy transfer within the gap. The different FR fabrics give different result

but each of them proves to be more heat resistant when testing with air gap.

• 9. The results obtained using a shim stock testing is scattered with no definite pattern. They

have concluded that the testing apparatus was not perfect to test such situation.

• 10. Adding 6mm air gap contributes to reducing the heat transfer between the plate and warm

jet. As z/d become larger the Nu difference at centre became smaller. This is due to the

appearance of maximum value at the stagnation point.

• Human Tissue Tolerance to Second

Degree Burn

• Stoll, A.M. and Chianta, M.A. “Method

and Rating System for Evaluations of

Thermal Protection” Aerospace

Medicine, Vol 40, 1969, pp. 1232-1238

WEEK 5

STUDY OF SKIN TOLERANCE

• “Transient Heat Transfer Through Thin

Fibrous Layers”

• Performed by, Raul Munoz Anguiano

• Test Condition:

• Velocity of Air Jet: 13m/s

• Temperature: 102±4°

• Nozzle Diameter: 32mm

• Nozzle to Fabrics Distance: 128mm

WEEK 5 (CONTINUED)

SIMULATION OF THE TEST PERFORMED BY THE

PREVIOUS AUTHOR

WEEK 5 (CONTINUED)

• “Heat and Mass Transfer in a

Permeable Fabric System Under Hot

Air Jet Impingement”

• Proceedings of the International Heat

Transfer Conference, August 8-13,

2010 © ASME 2010

• Test Condition:

• Velocity of Air Jet: 32m/s

• Temperature: 100°C and 200°C

• Nozzle Diameter: 20.6mm

• Nozzle to Fabrics Distance: 76.2mm

WEEK 5 (CONTINUED)

ASTM STANDARDS FOR PROTECTIVE CLOTHING

• F2703-08: Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for

Clothing with Burn Injury Prediction

• Heat Flux: 84.6 kW/m2

• Gas Pressure: 55 kPa

• Optional Spacer: 6.4mm

• Minimum Sample Test: 5

• Time of Exposure: 60s

• F2700-08: Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame

Resistant Materials for Clothing with Continuous Heating

WEEK 6

EXPERIMENT ON WIND TUNNEL

13.6

8.5

5.675

3.68

y = -2.31ln(x) + 6.9981

1

2

3

4

1 10 100

Rad

ial P

osi

tio

n

Velocity

Average Velocity Profile of the Wind Tunnel Exit

WEEK 6

COMMENTS

• Centerline Velocity at maximum opening of Wind Tunnel: 4.2 m/s

• Maximum Velocity attained: 19.5 m/s

• Average Velocity attained within the experimental range: 4.75 m/s

• The exit velocity is not uniform due the presence of valve at the end. Velocity

at the outside periphery is higher due to the turbulence created by the valve

blade end. Thus only center portion of the tunnel cross-section is selected for

the upcoming experiment.

PRIMARY DESIGN PARAMETERS

• Nozzle Diameters = 25.4 mm (1 inch)

• Inlet Velocity = 4.75 m/s

• Expected Jet Velocity = 73.62 m/s

• Inlet to Exit Pipe Length = 609.6 mm (24 inch)

• Pipe diameter (internal) = 63.5 mm (2.5 inch)

• Pipe Inlet Reducer = 101.6:63.5 mm (4:2.5 inch)

PRIMARY DESIGN

NOZZLE

PRIMARY DESIGN (CONTINUED)

NOZZLE PIPE ASSEMBLY

PREDICTED VELOCITY ALONG THE SETUP

PREDICTED TEMPERATURE ALONG THE SETUP

PREDICTED TEMPERATURE ON THE WALL

PRESSURE DISTRIBUTION

PRIMARY DESIGN

COMMENTS

• Primary Design Simulation shows a draw back in

experimenting with surface heating for air heater, that it

would require a tremendous amount of surface heat in

short length, under which the material can’t sustain.

Further calculation was recommended for better

design.

ASTM STANDARD

Thermal Sensor

• Copper Slug Calorimeter

• Diameter = 4±0.05cm

• Mass = 18±0.05g

• Electrical Grade Copper

• Thermocouple: ANSI Type J

(Fe/Cu-Ni) or ANSI Type K(Ni-

Cr/Ni-Al)

• Wire Dia = 0.254 mm

Shutter

A manual or computer-controlled

shutter is used to block the heat

flux from the burner (placed

between the specimen holder

and the burner). Water cooling is

recommended to minimize

radiant heat transfer to other

equipment components and to

prevent thermal damage to the

shutter itself. ASTM Standard F 2703 - 08

MATHEMATICAL MODEL PRESENTATION

Special Mid Term Session

IMPINGING JET CHARACTERISTICS

Regions in submerged

impinging round jet:

• Initial Free Jet

• Core Region

• Decaying Jet Region

• Stagnation Region

• Wall Jet Region

INITIAL FLOW REGION

Due to the application of

differential pressure across thin

flat orifice:

• Fairly flat velocity profiles

• Less turbulence

• A downstream flow contraction

(vena-contracta)

INITIAL FLOW REGION

• The shearing at the edges

of the jet transfer

momentum outward

• More fluid is entrained

along with the jet

• Jet losses energy

• The velocity profile is

widened and decreased in

magnitude

THE CORE REGION

• Unaffected by the

momentum transfer

• Higher total pressure

• Experience a drop in

velocity

• Dynamic pressure decays

as result of velocity

gradient presence in the

nozzle exit

DECAYING JET REGION

Juckerman and Lior defines the end of the core region

as the axial position where the centerline flow dynamic

pressure reaches 95% of its original value.

• Begins at 4~8D from the nozzle exit

• Axial velocity component decreased

• Axial velocity and jet width vary linearly

DECAYING JET REGION

• Decaying jet region & free jet region may not exist if

the nozzle lies within a distance of 2D from the target

• Elevated static pressure in the stagnation region

influence the flow immediately at the nozzle exit

STAGNATION REGION

• Flow losses axial velocity and turns

• Builds up a higher static pressure on and above the wall

• Experiences high normal and shear stresses in the

deceleration region

• Stretches vortices in the flow and increases the turbulence

• Martin concluded that the region extends 1.2D above the wall

for round jets

WALL JET REGION

• Flow moves laterally outward parallel to the wall

• Minimum thickness occurs within 0.75~3D from the jet axis,

then continually thickens moving farther away from the

nozzle

• Boundary layers begins within the wall, where its thickness

measures more than 1% of the jet

• Shearing layer influence by velocity gradient with respect to

both at the wall and at the fluid outside the wall

• Entrains flow and grows in thickness

NOZZLE GEOMETRY TYPE ON JET IMPINGEMENT

MAJOR PARAMETERS

• Nusselt Number, 𝑁𝑢 = 𝑕𝐷𝑕

𝑘𝑐

• Convective Heat Transfer Coefficient ℎ = −𝑘𝑐

𝜕𝑇

𝜕𝑛

𝑇𝑗𝑒𝑡−𝑇𝑤𝑎𝑙𝑙

• Recovery factor = 𝑇𝑤𝑎𝑙𝑙−𝑇𝑗𝑒𝑡

𝑈2

2𝐶𝑝

• Sherwood Number, 𝑆ℎ = 𝑘𝑖𝐷

𝐷𝑖, 𝑘𝑖 =

𝐷𝑖𝜕𝐶

𝜕𝑛

𝐶𝑗𝑒𝑡−𝐶𝑤𝑎𝑙𝑙

• Heat to mass transfer rate, 𝑁𝑢

𝑆𝑕=

𝑃𝑟

𝑆𝑐

0.4

OTHER PARAMETERS

• Prandlt Number, Pr

•𝐻

𝐷: nozzle height to nozzle diameter ratio

• r/D: nondimensional radial position from center of the jet

• z/D: nondimensional vertical position measured from the wall

• Turbulence intensity, Tu

• Renolds Number, Re

• Mach Number, M

•𝑝𝑗𝑒𝑡

𝐷 : jet center to center spacing (pitch)

• Free Area, 𝐴𝑓

• Relative Nozzle Area, 𝑓

EMPIRICAL CORRELATIONS

𝑁𝑢 = 𝐶 𝑅𝑒𝑛 𝑃𝑟𝑚 𝑓(𝐻 𝐷 )

• For Single Round Nozzle, Martin correlation

• 𝑁𝑢𝑎𝑣𝑔 = 𝑃𝑟0.42𝐷

𝑟

1−1.1𝐷 𝑟

1+0.1(𝐻 𝐷 −6)𝐷 𝑟 𝐹

• for 2,000<Re<30,000, F = 1.36 Re 0.574

• for 30,000<Re<120,000, F = 0.54 Re 0.667

• for 120,000<Re<400,000, F = 0.151 Re 0.775

EMPIRICAL CORRELATIONS

FLAME IMPINGEMENT

• Transfer heat very effectively and tends to have higher turbulence

• If some fuel travels through the stagnation region without complete

combustion, further reaction in the wall jet will release additional

thermal energy and improve uniformity

• Also transfer heat by radiation from the flame

• 60-70% heat transfer by convection [Malikov et al]

• Accumulation of soot may occur on the target which ultimately impede

heat transfer

TRANSIENT HEAT TRANSFER

• Governing equation, 𝜕2𝑇

𝜕𝑥2=

1

𝛼

𝜕𝑇

𝜕𝑡

• Boundary condition, T(x,0) = Ti , T(0,t) = Ts

• Solving, 𝑇 𝑥,𝑡 − 𝑇0

𝑇𝑖 − 𝑇0= erf

𝑥

4𝛼𝑡

• For constant heat flux

• 𝑇 − 𝑇𝑖 = 2𝑞

𝛼𝑡

𝜋

𝑘𝐴𝑒𝑥𝑝

−𝑥2

4𝛼𝑡−

𝑞𝑥

𝑘𝐴1 − 𝑒𝑟𝑓

𝑥

4𝛼𝑡

TRANSIENT HEAT TRANSFER

GOVERNING EQUATIONS FOR THE FABRICS

• For gas phase in the Fabric Layer

• Mass Conservation Equation

• 𝜀𝜕𝜌𝑔

𝜕𝑡+

𝜕

𝜕𝑥𝜌𝑔𝑢𝐷 = 0

• Momentum Conservation Equation

•𝜕 𝜌𝑔𝑢𝐷

𝜕𝑡+

1

𝜀

𝜕 𝜌𝑔𝑢2

𝜕𝑥=

𝜕

𝜕𝑥𝜇𝜕𝑢𝐷

𝜕𝑥− 𝜀

𝑑𝑃

𝑑𝑥− 𝜀

𝜇

𝐾𝑢𝐷 −

𝜀𝜌𝑔𝐶𝐸

𝐾1/2 𝑢2

GOVERNING EQUATIONS FOR THE FABRICS

• Energy Conservation Equation

• 𝜀 𝜌𝑐𝑝 𝑔

𝜕𝑇𝑔

𝜕𝑡+ 𝜌𝑐𝑝 𝑔

𝑢𝐷𝜕𝑇

𝜕𝑥=

𝜕

𝜕𝑥𝜀𝑘𝑔

𝜕𝑇𝑔

𝜕𝑥− ℎ𝑠𝑔

𝐴𝑠𝑔

𝑉𝑓𝑎𝑏𝑇𝑔 − 𝑇𝑠

• Energy Conservation Equation for Fabric Phase

• 1 − 𝜀 𝜌𝑐𝑝 𝑠

𝜕𝑇𝑠

𝜕𝑡=

𝜕

𝜕𝑥1 − 𝜀 𝑘𝑠

𝜕𝑇𝑠

𝜕𝑥+ ℎ𝑠𝑔

𝐴𝑠𝑔

𝑉𝑓𝑎𝑏𝑇𝑔 − 𝑇𝑠

GOVERNING EQUATIONS FOR THE AIR GAP

• Mass Conservation Equation

• 𝑉𝑎𝑔𝑑𝜌𝑔

𝑑𝑡= 𝑚 𝑔,𝑖𝑛 −𝑚 𝑔,𝑜𝑢𝑡

• Where,

• 𝑚 𝑔,𝑖𝑛 = 𝜌𝑔𝐴𝑓𝑎𝑏𝑢𝐷|𝑥=𝐿𝑓𝑎𝑏

• 𝑚 𝑔,𝑜𝑢𝑡 = 𝐶𝑙𝑒𝑎𝑘𝜌𝑔

𝜇𝑔𝑃𝑎𝑝 − 𝑃𝑎𝑚𝑏

GOVERNING EQUATIONS FOR THE AIR GAP

• Energy Conservation Equation

• 𝜌𝑉𝑐𝑝 𝑎𝑔

𝑑𝑇𝑎𝑔

𝑑𝑡= 𝑄 𝑔,𝑖𝑛 − 𝑄 𝑔,𝑜𝑢𝑡 + 𝑄 𝑓𝑎𝑏,𝑟𝑒𝑎𝑟 − 𝑄 𝑐𝑝

• 𝑄 𝑔,𝑖𝑛 = 𝑚 𝑐𝑝𝑇 𝑔,𝑖𝑛

• 𝑄 𝑔,𝑜𝑢𝑡 = 𝑚 𝑐𝑝𝑇 𝑔,𝑜𝑢𝑡

• 𝑄 𝑓𝑎𝑏,𝑟𝑒𝑎𝑟 = ℎ𝑓𝑎𝑏𝐴𝑓𝑎𝑏 1 − 𝜀 𝑇𝑠|𝑥=𝐿𝑓𝑎𝑏 − 𝑇𝑎𝑔

• 𝑄 𝑐𝑝 = ℎ𝑐𝑝𝐴𝑐𝑝 𝑇𝑎𝑔 − 𝑇𝑐𝑝

THERMOPHYSICAL PROPERTIES OF FABRICS

WEEK 7

TYPICAL HEATING & FLOW ARRANGEMENT

WALL TEMPERATURE REQUIRED FOR THE

DESIRED OUTLET TEMPERATURE

0

100

200

300

400

500

600

700

800

900

1000

0 0.5 1 1.5 2 2.5 3 3.5

Tem

per

atu

re

(°C

)

Length (m)

Wall Temperature Required with the Heating Zone Length

NICHROME WIRE PARAMETERS

Week 7

Ohms/ft at Room Temperature

Gauge Wire Diameter (mm) NiCr A NiCr C

10 2.591 0.06248 0.06488

11 2.311 0.07849 0.08151

12 2.057 0.09907 0.10290

13 1.829 0.12540 0.13020

14 1.626 0.15870 0.16480

15 1.448 0.20010 0.20780

16 1.295 0.24990 0.25950

17 1.143 0.32100 0.33330

18 1.016 0.40630 0.42190

19 0.914 0.50150 0.52080

20 0.813 0.63480 0.65920

21 0.7239 0.80020 0.83100

22 0.6426 1.01500 1.05500

23 0.5740 1.27300 1.32200

24 0.5105 1.60900 1.67100

25 0.4547 2.02900 2.10700

26 0.4039 2.571 2.670

27 0.3607 3.224 3.348

28 0.3200 4.094 4.252

29 0.2870 5.090 5.286

30 0.2540 6.500 6.750

31 0.2261 8.206 8.522

32 0.2032 10.160 10.550

33 0.1803 12.890 13.390

34 0.1600 16.380 17.010

35 0.1422 20.730 21.520

36 0.1270 26.000 27.000

37 0.1143 32.100 33.330

38 0.1016 40.630 42.190

39 0.0889 53.060 55.100

40 0.0787 67.640 70.240

Approximate Amperes to Heat NiChrome Wire

Gauge

Wire

Diameter

(mm)

400°F

205°C

600°

316°

800°

427°

1000°

538°

1200°

649°

1400°

760°

1600°

871°

1800°

982°

2000°

1093°

10 2.591 16.2 23.3 29.7 37.5 46.0 56.0 68.0 80.0 92.0

11 2.311 13.8 19.2 24.8 31.5 39.0 48.0 57.0 67.0 78.0

12 2.057 11.6 16.1 20.8 26.5 33.5 40.8 48.0 56.0 65.0

13 1.829 9.80 13.6 17.6 22.5 28.2 34.2 41.0 48.0 55.0

14 1.626 8.40 11.6 15.0 18.8 23.5 29.0 34.6 40.5 46.0

15 1.448 7.20 10.0 12.8 16.1 20.0 24.5 29.4 34.3 39.2

16 1.295 6.40 8.70 10.9 13.7 17.0 20.9 25.1 29.4 33.6

17 1.143 5.50 7.50 9.50 11.7 14.5 17.6 21.1 24.6 28.1

18 1.016 4.80 6.50 8.20 10.1 12.2 14.8 17.7 20.7 23.7

19 0.914 4.30 5.80 7.20 8.70 10.6 12.7 15.2 17.8 20.5

20 0.813 3.80 5.10 6.30 7.60 9.10 11.0 13.0 15.2 17.5

21 0.7239 3.30 4.30 5.30 6.50 7.80 9.40 11.0 12.9 14.8

22 0.6426 2.90 3.70 4.50 5.60 6.80 8.20 9.60 11.0 12.5

23 0.5740 2.58 3.30 4.00 4.90 5.90 7.00 8.30 9.60 11.0

24 0.5105 2.21 2.90 3.40 4.20 5.10 6.00 7.10 8.20 9.40

25 0.4547 1.92 2.52 3.00 3.60 4.30 5.20 6.10 7.10 8.00

26 0.4039 1.67 2.14 2.60 3.20 3.80 4.50 5.30 6.10 6.90

27 0.3607 1.44 1.84 2.25 2.73 3.30 3.90 4.60 5.30 6.00

28 0.3200 1.24 1.61 1.95 2.38 2.85 3.40 3.90 4.50 5.10

29 0.2870 1.08 1.41 1.73 2.10 2.51 2.95 3.40 3.90 4.40

30 0.2540 0.92 1.19 1.47 1.78 2.14 2.52 2.90 3.30 3.70

31 0.2261 0.77 1.03 1.28 1.54 1.84 2.17 2.52 2.85 3.2

32 0.2032 0.68 0.90 1.13 1.36 1.62 1.89 2.18 2.46 2.76

33 0.1803 0.59 0.79 0.97 1.17 1.40 1.62 1.86 2.12 2.35

34 0.1600 0.50 0.68 0.83 1.00 1.20 1.41 1.60 1.80 1.99

35 0.1422 0.43 0.57 0.72 0.87 1.03 1.21 1.38 1.54 1.71

36 0.1270 0.38 0.52 0.63 0.77 0.89 1.04 1.19 1.33 1.48

37 0.1143 0.35 0.46 0.57 0.68 0.78 0.9 1.03 1.16 1.29

38 0.1016 0.30 0.41 0.50 0.59 0.68 0.78 0.88 0.98 1.09

39 0.0889 0.27 0.36 0.42 0.49 0.58 0.66 0.75 0.84 0.92

40 0.0787 0.24 0.31 0.36 0.43 0.50 0.57 0.64 0.72 0.79

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

110.00

120.00

130.00

140.00

150.00

160.00

170.00

180.00

190.00

200.00

210.00

220.00

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Len

gth

(f

t)

Gauge

Characteristics Chart of NiCr A Volt 220V

205C

316C

427C

538C

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

110.00

120.00

130.00

140.00

150.00

160.00

170.00

180.00

190.00

200.00

210.00

220.00

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Len

gth

(f

t)

Gauge

Characteristics Chart of NiCr C Volt 220V

205C

316C

427C

538C

0.0000

50.0000

100.0000

150.0000

200.0000

250.0000

300.0000

350.0000

400.0000

450.0000

500.0000

550.0000

600.0000

650.0000

700.0000

750.0000

800.0000

850.0000

900.0000

950.0000

1000.0000

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Res

ista

nce

(o

hm

s)

Gauge Size

Gauge Size - Resistance Of NiCr C

205C

316C

427C

538C

REQUIRED LENGTH FOR THE AVAILABLE

WALL TEMPERATURE

0

0.5

1

1.5

2

2.5

3

3.5

0 100 200 300 400 500 600 700 800 900 1000

Len

gth

(m

(

Temperature (°C)

Required Length for the Wall Temperature to Raise the Flowing Fluid Temperature to 105°C

RECOMMENDATIONS (WEEK 7)

• The design with only wall heating is complicated in a sense of

physical setup constrain

• For heating purpose, more reliable and higher heat transfer system

may be design

• Internal Fin type heat exchanger may be design with NiChrome

Wire heater

• From the NiChrome Wire Properties, 30 gauge wire with 316°C

heating can be recommended for design

• Further study required for designing other type of heat exchanger

WEEK 8

BUDGET ESTIMATION Item Description Unit Price No. of Unit Required Total Price

Piping for Jet Impingement for both Air & Steam

2½ʺ GI Pipe

For heating space & flow

control

240/- per feet 5 ft 1200/-

1ʺ GI Pipe

For jet impingement both

in Air and Steam

80/- per feet 5 ft 400/-

4ʺ x 2½ʺ Socket

To reduce the flow

600/- 1 600/-

2½ʺ x 1ʺ Socket

To make the jet

300/- 1 300/-

1ʺ 90° Bends

To control the steam

60/- 5 300/-

Flange with 4ʺ hole

For setting up with the

wind tunnel

85/- per kg

Specimen Holder

½ʺ Plastic Pipe

To flow shield cooling

water

15/- per feet

Steel Sheet 28 gauge

For thermal shield

140/- per running feet 2 x 2 sq. feet 560/-

Wood Structure

Thermocouple

Measuring Plate

BUDGET ESTIMATION (CONTINUED)

Type Size Wattage Rating Unit

Price

Rod Shape 8ʺ ~ 18ʺ 400W ~ 3000W 200/- ~

1200/-

12ʺ 2000W 450/-

12ʺ 1200W 350/-

8ʺ 400W 250/-

Ring Shape (Finned) 8ʺ 600W 400/-

U Shape 12ʺ 500W 350/-

Locally assembled Coil 4 feet

400/-

Heating Coil

CALCULATION WITH INTERNAL FIN HEATER CONFIGURATION 1: TUBE BANKS PARALLEL TO THE FLOW DIRECTION

• Initial Condition:

• Inlet Air Temperature = 30°C

• Heater Wall Temperature =

205°C

• Correlation: Nu=0.37 〖Re〗^0.8

for 17 < Re < 70000

• McAdams, W. H., Heat

Transmission, 3rd ed., New York,

McGraw-Hill, 1954

CALCULATION (CONTINUED)

CONFIGURATION 2: TUBE BANKS ACROSS THE FLOW


• Initial Condition:

• Inlet Air Temperature = 30°C

• Heater Wall Temperature = 205°C

• Correlations: Knudsen and Katz suggested,

• Nu=C 〖Re〗^n 〖Pr〗^(1⁄3)

• For Tube Banks of 4 rows high and 6 rows deep,

• C = 0.27

• n = 0.63

• From Table 6-6 and Table 6-7

• [Zukauskas, A., Heat Transfer from Tubes in Cross Flow, Adv. Heat Transfer, vol 8, pp 93-160, 1972]

• Temperature Increased per Stage: 20.2°C

WEEK 8

COMMENTS

• The calculation shows better heating can be achieved

with this type of arrangement.

• Further calculation on the same arrangement but

different configuration was recommended.

• Final design was encouraged to submit within the next

week.

• Simulating using CFD module was planned for the final

design.

WEEK 9

• Provisional Advanced Bill was submitted for sanction

• Extended Abstract was submitted for participating in the

ICME 2011

WEEK 10 SIMULATION OF THE TESTING EQUIPMENT DESIGNED

WITH ADIABATIC WALL CONDITION

DESIGN CHECK 2

DESIGN CHECK 2 (CONTINUED)

DESIGN CHECK 3

DESIGN CHECK 3 (CONTINUED)

WEEK 10

COMMENTS

• The simulation showed a major drawback in the design that

- the surface temperature increased tremendously at the end of

the tube

- the temperature attained using fixed heat transfer is not

perfectly correct due to the physical constrain and the nature of

heat transfer in the air

• Further modification was recommended by using baffle or

extended chamber

WEEK 11

REDESIGN

REDESIGN (CONTINUED)

REDESIGN

COMMENTS

• Temperature of the air attained is about 110°C - which is required for the testing of fabric

• But the surface temperature of the Fin/Tube Heater is maximum about 2437°C at some places - which will cause the heater to melt or break away before it reaches that high temperature

• Modification is recommended for the design

FINAL DESIGN

AIR JET IMPINGEMENT SETUP

SECTIONAL VIEW OF SETUP

SPECIMEN HOLDER

FINAL DESIGN SIMULATION

FINAL DESIGN (CONTINUED)

COMMENTS

• Air Temperature Expected: 120°C

• Maximum Surface Temperature of Heater: 630°C

• Jet Velocity Expected: 74 m/s

CONSTRUCTION OF THE SETUP

CONSTRUCTION

2½ INCH PIPE & REDUCER

CONSTRUCTION (CONTINUED)

4 INCH PIPE WITH FLANGE


2½ INCH PIPE & 1 INCH REDUCER


FLANGE


WOODEN FABRIC HOLDER

PLAN FOR NEXT TERM

• 1. Testing of the setup:

• (a) After establishing the structure, the data acquisition system will be assembled with it.

• (b) Then the calibration of testing equipment will be done.

• 2. Experiment on flame resistant fabric:

• Testing upon fabric will be performed by hot air jet impingement.

• 3. Calculation on the experimental value

• Calculation on the experimental value and later comparison on the result will be done .

PLAN FOR NEXT TERM (CONTINUED)

• 4. Comparing experimental result with Computer simulation

• Computer simulation will be made using ANSYS CFX and ANSYS FLUENT. The

experimental result will be compared with the simulation. The mathematical model will be

verified by using the appropriate technique

• 5. Analysis on skin burning effect

• The result will be analyzed with the skin burning effect on heat flux and will be determined

whether the fabric can reduce the flame heating on skin

PLAN FOR NEXT TERM (CONTINUED)

• 6. Study on steam impingement and steam exposures

• •Further study will be done on steam and a comparative study will be presented on steam

impingement technique.

• •The previous research on flame impingement shows that the significant difference

between the air impingement and steam impingement.

• •The momentum effect of steam is more acute than air.

• •Further, the condensation occurs in the stagnation point will cause more heat flux upon

the fabric material.

• •Some recommendations will be presented on steam modeling and experimental

constrained.

• •The effect of steam exposures can also be studied because in many cases, the steam

exposure may causes accident during working and emergency situation.

Under Supervision of

Dr. Ashraful Islam

Professor, Department of Mechanical Engineering

Bangladesh University of Engineering & Technology

PREPARED BY

AASHIQUE ALAM REZWAN (06 10 012)

IN ASSOCIATION WITH

SARZINA HOSSAIN (06 10 063) SPECIAL THANKS FOR CONSTRUCTION WORK OF THE SETUP

A K M NAZRUL ISLAM (MASTER’S STD)

transient heat transfer under graduate thesis part 1 level 4 term 1

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