U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

TABLE OF CONTENTS

Page

Front Page

Table of Contents i

Title 1

1. Objective 1

2. Introduction 1

3. Theory 2

4. Equipment 3

5. Experimental Procedure 5

6. Result 5

7. Sample Calculation 6

8. Analysis Result 7

9. Discussion 9

10. Conclusion 12

11. References 15

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

1.0 TITLE

FORCED CONVECTION

2.0 OBJECTIVE:

1. To demonstrate the effect and the use of finned surface and pinned surface to improve

the heat transfer in forced convection.

3.0 INTRODUCTION

Convection is the transfer of energy between a solid surface and the adjacent fluids

that is in motion, and it involves the combined effects of conduction and fluid motion.

Convective heat and mass transfer take place through both diffusion of the random Brownian

motion of individual particles in the fluid and by advection, in which matter or heat is

transported by the larger scale motion of currents in the fluid.

Convection is also the mode of energy transfer between a solid surface and the adjacent

liquid or gas that is in motion, and it involves the combined effects of conduction and fluid

motion. The faster the fluid motion, the greater heat convection heat transfers. In the absence

of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluid is by

pure conduction. The presence of bulk motion of the fluid enhances the heat transfer between

the solid surface and the fluid, but it also complicates the determination of heat transfer rates.

Convection is called forced convection if the fluid is forced to flow over the surface by

external means such as a fan or the wind. In contrast, convection is called natural (or free)

convection if the fluid motion is caused by buoyancy forces that are induced by density

differences due to the variation of temperature in the fluid. Convection can also be qualified

in terms of being natural, forced, gravitational, granular, or thermo magnetic.

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4.0 THEORY

Heat transfer from an object can be improved by increasing the surface area in contact with air by adding fins or pins normal to the surface. This can be seen in Newton`s Law of Cooling, which defines the convection heat transfer rate:

Q̇=hAs (T s−T∞ )

The effect of the surfaces can be demonstrated by comparing finned and unfinned surfaces with a flat plate under the same conditions of power and flow.

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5.0 EQUIPMENT

The surfaces are shown in the figure below. The finned surface consists of 9 fins that are each 0.1 m high and 0.068 m wide. The pinned surface consists of 17 pins that each have a diameter of 0.013 m and are 0.068 m long.

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Finned Plate/Pinned Surface

U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

1. Bench top unit with holder2. Sensors for measuring temperature and flow velocity3. Air duct4. "cylinder" heating element5. Temperature sensor6. Measuring glands7. Fan8. "finned" heating element9. "flat plate" heating element10. Display and control unit11. Handheld sensor to measure airflow velocity

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

6.0 PROCEDURES

Heat exchanger placed into the test duct, and the value of ambient temperature (T) has been record due to the surrounding temperature.

a. The heater then set to 270W to allow the temperature rise until 80°C.b. The heater control is adjust to 20W after its reading reach 80°C and allow the

temperature decrease due to the time allowance 5 minutes by using stopwatch.c. After 5 minutes, the reading of the heater meter has been recorded. d. The next step is by using the fan with speed of 1.0 m/s on the thermal anemometer.e. 5 minutes time allowance as before to stabilize and then take the meter result.f. Finally the fan speed is been increase to 2.0 m/s and 2.5m/s with the same step as

before.g. All the temperature value that been record is base on surface temperature of the

object.h. All steps have been repeated and apply to the other specimen with same procedure.

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

7.0 RESULT

Ambient air temperature, T∞ = 250C

Power input,Q̇ = 20 W

Air Velocity[m/s]

Heater Temperature (Ts)[0C]

FINNED PLATE PINNED PLATE0 66.7 70.2

1.5 53.0 55.22.5 51.3 51.6

DATA ANALYSIS

SAMPLE CALCULATION

i. Surface area of the base plate (Abase);

Abase=L×w¿0 .1×0 .11¿0 .011m2

ii. Surface area of (As) of the finned and pinned plates;

Aalignl¿ finned ¿plate ¿=9×Lw+Abase ¿=(9×0 .1×0 . 068)+0 .011 ¿=0 . 0722m2 ¿¿

Aalignl¿ pinned ¿plate ¿=17×π DL2

+Abase ¿=[17×π (0 .013 )(0 .068)2 ]+0 .011 ¿=0 .0346m2 ¿¿

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

iii. Convection heat transfer coefficient (h);

-For finned plate (at 2.5 m/s);

h=Q̇A s (T s−T∞ )

¿200 .0722(51.3−25 )

¿10 .533W /(m .0C )

-For pinned plate (at 2.5 m/s);

h=Q̇A s (T s−T∞ )

¿200 .0346(51 .6−25 )

¿21 .731W / (m .0C )

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

RESULT ANALYSIS

Surface area of (As) of the finned and pinned plates:

PLATESurface Area, As

(m2)FINNED 0.0722PINNED 0.0346

Temperature difference (Ts-T∞) and convection coefficient, h:

Air Velocity[m/s]

FINNED PLATE PINNED PLATETs

[0C]TS- T∞

[0C]

h[W/(m.0C]

Ts

[0C]TS- T∞

[0C]

H[W/(m.0C]

0 66.7 41.7 6.643 70.2 45.2 12.7881.5 53.0 28.0 9.893 55.2 30.2 19.1402.5 51.3 26.3 10.533 51.6 26.6 21.731

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For finned plate:-

24 26 28 30 32 34 36 38 40 42 440

0.5

1

1.5

2

2.5

3

Air velocity vs Surface Temperature

Surface Temperature

Air V

eloc

ity

For pinned plate:-

25 30 35 40 45 500

0.5

1

1.5

2

2.5

3

Air velocity vs Surface Temperature

Surface Temperature

Air V

eloc

ity

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8.0 DISCUSSION

Prepared by : MUHD ZHARFAN ZUHAIR BIN ZAINURUL ZAHAR2014275902

Prepared by: MUHAMMAD FAIZ BIN MOHAMAD ASRI

2014621946

Prepared by: MUHAMMAD HANIS BIN ROSLI

2014442524

Prepared by: MUHAMMAD KHAIRUDDIN BIN MOHD KHIRZAM

2014691028

Prepared by: MUHAMMAD IZZAT NAQIUDDIN BIN MAT

2014843754

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

9.0 CONCLUSION

Prepared by: MUHD ZHARFAN ZUHAIR BIN ZAINURUL ZAHAR2014275902

Prepared by: MUHAMMAD FAIZ BIN MOHAMAD ASRI

2014621946

Prepared by: MUHAMMAD HANIS BIN ROSLI

2014442524

Prepared by: MUHAMMAD KHAIRUDDIN BIN MOHD KHIRZAM

2014691028

Prepared by: MUHAMMAD IZZAT NAQIUDDIN BIN MAT

2014843754

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U N I V E R S I T I T E K N O L O G I M A R A F A C U L T Y O f M E C H A N I C A L E N G I N E E R I N G T H E R M A F L U I D L A B ( M E C 5 5 4 )

10.0 REFERENCES

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