Forced Convection.docx

UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

TABLE OF CONTENTS Page Front Page Table of Contents i Title

1

1. Objective 2. Introduction

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1 3. Theory 2 4. Equipment 5. Experimental Procedure

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5 6. Result 7. Sample Calculation

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6 8. Analysis Result 9. Discussion 10. Conclusion

7 9

12 11. References 15

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

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.

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

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:

Q  hAs  Ts  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.

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

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.

Finned Plate/Pinned Surface

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

1. Bench top unit with holder 2. Sensors for measuring temperature and flow velocity 3. Air duct 4. "cylinder" heating element 5. Temperature sensor 6. Measuring glands 7. Fan 8. "finned" heating element 9. "flat plate" heating element 10. Display and control unit 11. Handheld sensor to measure airflow velocity

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

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.

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

7.0 RESULT Ambient air temperature, T



= 250C

 Q Power input,

= 20 W Heater Temperature (Ts) [0C] FINNED PINNED PLATE PLATE 66.7 70.2 53.0 55.2 51.3 51.6

Air Velocity [m/s] 0 1.5 2.5 DATA ANALYSIS SAMPLE CALCULATION

i.

Surface area of the base plate (Abase);

Abase  L  w  0.1  0.11  0.011m 2 ii.

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

A finned  9  Lw  Abase plate

 (9  0.1  0.068)  0.011  0.0722m 2 Apinned  17  plate

DL 2

 Abase

 (0.013)( 0.068)     17    0.011 2   0.0346m 2 MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

iii.

Convection heat transfer coefficient (h); -For finned plate (at 2.5 m/s);

h 

 Q As  Ts  T  20 0.0722(51.3  25)

 10.533W /( m.0 C )

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

h  

 Q As  Ts  T  20 0.0346(51.6  25)

 21.731W /( m.0 C )

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

RESULT ANALYSIS

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

PLATE FINNED PINNED

Surface Area, As (m2) 0.0722 0.0346

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

Air Velocity [m/s] 0 1.5 2.5

FINNED PLATE TS- T h  [W/(m.0C] [0C] 66.7 41.7 6.643 53.0 28.0 9.893 51.3 26.3 10.533 Ts [0C]

Ts [0C]

PINNED PLATE TS- T H  [W/ (m.0C] [0C]

70.2 55.2 51.6

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

45.2 30.2 26.6

12.788 19.140 21.731

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

For finned plate:-

Air velocity vs Surface Temperature 3 2.5 2 Air Velocity

1.5 1 0.5 0 24

26

28

30

32

34

36

38

40

42

44

Surface Temperature

For pinned plate:-

Air velocity vs Surface Temperature 3 2.5 2 Air Velocity

1.5 1 0.5 0 25

30

35

40

45

50

Surface Temperature

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

8.0 DISCUSSION Prepared by : MUHD ZHARFAN ZUHAIR BIN ZAINURUL ZAHAR 2014275902

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

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

9.0 CONCLUSION Prepared by: MUHD ZHARFAN ZUHAIR BIN ZAINURUL ZAHAR 2014275902 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

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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UNIVERSITI TEKNOLOGI MAR A FAC U LTY Of M EC H A N I C A L E N G I N E E R I N G THERMAFLUID LAB (MEC 554)

10.0 REFERENCES

MEC 554-THERMALFLUIDS LAB: FORCED CONVECTION

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