forced covection - thermo lab report

8/9/2019 Forced Covection - Thermo Lab Report

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ohammed Zaid Shaikh –00114083This document contains a report on

forced convection around a

cylindrical copper rod of diameter

001!" m

#orced

$ovectionhermo la% &eport


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FORCED CONVECTION – THERMO LAB REPORT

INTRODUCTION

This report covers the heat transfer rate from a cylindrical copper rod to the

surroundin' air movin' at a certain ()ed velocity in an isolated system *esides

sho+in' ho+ the heat transfer rate is a,ected %y varyin' the velocity of air in

the isolated system this e)perimental la% report also sho+s the calculations for

&eynolds num%er- .usselt num%er- as +ell as the (lm heat transfer coe/cient

Moreover- it covers %rief discussion on the comparison of the e)perimental

values of 2 and n2 from the %elo+ euation +ith that of their literature values

Nu= K ℜn

n this e)periment the heat transfer rate associated +ith the cross 5o+ of air

across a cylindrical copper rod at various velocities has %een investi'ated The

aim of the e)periment is to determine the heat transfer characteristics of a

cylinder under cross 5o+ forced convection conditions +hen the cylinder is

isolated The follo+in' euation is used to plot the 'raph and hence the slope of

the 'raph +as used to calculate the estimated heat transfer coefficient 6

( ) ( )a p

a T T t C m

AT T −+−=−

0lnln

α

This e)periment also helps in understandin' the comple)ities in heat transferrin'

durin' the cross 5o+ across a cylindrical copper rod 7n chan'in' the velocity of

the +ind- the &eynolds num%er of the 5o+ chan'es +hich then a,ects the heat

transfer Fig. a9 %elo+ sho+s a 'raphical representation on ho+ increasin' the

&eynolds num%er chan'es the nature of the 5o+

:ractical and &eal ;ife


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report can hence %e used as reference +hen desi'nin' a car radiator +ith copper

metal for am%ient temperature of !3>$

!


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Fig. a

3


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PROCEDURE AND APPARATUS

The follo+in' procedures +ere undertaken for this e)periment=

19 The apparatus +as checked %y the la% supervisor

!9 The air duct +as s+itched on

39 The air speed +as set to 3 m?s usin' the kno%

49 The copper cylindrical rod +as heated up to @A>$ in an electric heated

"9 The copper rod +as then placed inside the air duct throu'h one of the hole

B9 The temperature drop +as noted after every " seconds usin' a thermometer

and stop+atch

A9 Steps 3CB +ere repeated to take readin's at di,erent +ind speed

The follo+in' apparatus +ere used for the e)periment

• $ross 5o+ heat e)chan'er Fig. B9

• Dlectric heater

• $opper cylindrical rod

• Stop +atch

RESULTS

4


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Eiven Fata=


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1!0 B4B "33 "1! 4@1 4AB

$alculated Fata u=3 m/ s

Time(s)

Temp T @

!"m#s($C

)

Amie*+

Temp Ta

($C)

T,Ta ($C) L*(T,Ta)

0 @A0 !3 A4 43040B"" @A0 !3 A4 43040B"10 @!A !3 B@A 4!44!1" @!A !3 B@A 4!44!!0 88B !3 B"B 4183"AB!" 88B !3 B"B 4183"AB30 8A1 !3 B41 41B04443" 8A1 !3 B!1 41!8A4B40 8!0 !3 "@0 40AA"3A4" 8!0 !3 "@0 40AA"3A"0 A@1 !3 "B1 40!A13B"" A@1 !3 "B1 40!A13BB0 AA1 !3 "41 3@@0834B" AA1 !3 "41 3@@0834A0 A4! !3 "1! 3@3"A4A" A4! !3 "1! 3@3"A480 A!4 !3 4@4 38@@@"8" A!4 !3 4@4 38@@@"@0 A04 !3 4A4 38"8B!!

@" A04 !3 4A4 38"8B!!100 B83 !3 4"3 381330A10" B83 !3 4"3 381330A110 BB4 !3 434 3AA04"@11" BB4 !3 434 3AA04"@1!0 B4B !3 41B 3A!81

$alculations=

@u=3 m /s

u=3 m / s

v= u

0.9=

3

0.9=3.33

µ=18.3808 Pa . s

ρa

=1.17656 kg/m3

B


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d=0.0125 m

b=0.125 m

h=0.125 m

k =0.0259 W /(m . K )

Heat transfer ceff!c!ent " # =−$%pe f graph 1 & m & C p

A

# 3=−−0.0048 &0.21 &380

0.00404

# 3=94.8 W /(m2

. K )

Similarly- @u=5,7,9,∧11 heat transfer coe/cient is calculated

# 5=150.12 W /(m2

. K )

# 7=167.9 W /(m2

. K )

# 9=169.87 W /(m2

. K )

# 11=185.67 W /(m2

. K )

Nusse%t number " Nu=# d

k

Nu3=

94.8& 0.0125

0.0259=46

Similarly- @u=5,7,9,∧11 .usselt num%er is calculated

Nu5=73

Nu7=82

A


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Nu9=83

Nu11=90

ℜ= ρ a v d

µ

ℜ3=1.17656 &3.333 & 0.0125

18.3808=2667

Similarly- @u=5,7,9,∧11 &eynolds num%er is calculated

ℜ5=4445

ℜ7=6315

ℜ9=8119

ℜ11=9924

:randlt .um%er- Pr=C

p& '

k

Pr=0.27

Eraphical $alculations=

8


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0 !0 40 B0 80 100 1!0 1403

3"

4

4"

"

-() ! , / 0 1."

Ln (T-Ta) vs t

ln ITCTaJ

;inear ln ITCTaJ9

Time

2* ()T,Ta

3RAPH 4

0 !0 40 B0 80 100 1!0 140

0

10

!0

30

40

"0

B0

A0

80

-() ! &".% ep( / )

(T-Ta) vs t

ITCTaJ

D)ponential ITCTaJ9

Time

T,Ta

3RAPH 45

@


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!000 4000 B000 8000 10000 1!000 14000

0

10

!0

30

40

"0

B0

A0

80

@0

100

-() ! .% 6/.1%

Nu vs Re

:o+er 9

Re7*829s *:me;

N:sse2+ *:me;

3RAPH 4"

Kalues from Eraphical Duations=

#rom Eraph L1= Slope C 00048

#rom Eraph L3= Nu= K ℜn

Ghere-

K =1.5066 - n=0.4462

DISCUSSION

The $orrelation literature value for ( k ( and ( n 2 for the euation Nu= K ℜn

+ere found as follo+s=

K =1.15

n=0.5

Drror


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)rrr = )*per!menta% va%ue− +!teratureva%ue

+!terature va%ue &100

)rrr fr K =1.5066−1.15

1.15

&100=31

)rrr fr n=0.4462−0.5

0.5& 100=−10.7

Nsin' a%ove values of K and n - +e (nd Nu theoretical

Kelocity u m /s 9 &eynolds .um%er ℜ¿ .usselt .um%er Nu 9

3 2667 59

5 4445 77

7 6315 91

9 8119 103

11 9924 114

:lottin' the 'raph for literature value of

Nu

vs

ℜ +e 'et-

11


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!000 4000 B000 8000 10000 1!0000

!0

40

B0

80

100

1!0

f)9 11B )O0"

Nu vs Re

.u

:o+er .u 9

Re7*829 *:me;

N:sse2+ *:me;

3RAPH 41

$omparin' the 'raph L3 and 'raph L4=


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!000 4000 B000 8000 100001!000

0

!0

40

B0

80

100

1!0

f)9 0@8 )O0"

f)9 11B )O0"

.u literature

:o+er .u literature9

.u

:o+er .u9

Re7*829s *:me;

N:sse2+ *:me;

3RAPH 4%

:ossi%le errors durin' the e)periment=

• Karyin' am%ient temperature

• Slo+ di'ital thermocouple

• Timin' calculation +hile usin' the stop+atch

• Karyin' +ind speed from the air duct

CONCLUSION

The e)perimental results +ere almost as e)pected Drror P for the calculations

+as less This e)periment sho+s ho+ the heat transfer rate chan'es under the

circumstances of forced convection n conclusion to the e)perimental result the

follo+in' points can %e noted=

1 7n increasin' the +ind speed the copper rod cools faster! The thermal coe/cient increases +ith the increase in &eynolds num%er

3 $opper is a 'ood conductor of heat4 $onvection is an important part of real life applications and can cause

serious en'ineerin' pro%lems if not dealt +ith properly

REFERENCE

1 ;ienhard- QH- K R ;ienhard- QH K- < Heat Transfer Te)t%ook- 4th Dd-

$am%rid'e- M

forced covection - thermo lab report

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