250440967 lab report convefction

7/25/2019 250440967 Lab Report Convefction

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Introduction and Background

Natural convection is a mechanism, or type of heat transport, in which the fluid motion is not

generated by any external source (like a pump, fan, suction device, etc.) but only by density

differences in the fluid occurring due to temperature gradients. Forced convection is a

mechanism, or type of transport in which fluid motion is generated by an external source (like

a pump, fan, suction device, etc.). It should be considered as one of the main methods of

useful heat transfer as significant amounts of heat energy can be transported very efficiently.

Objective

o measure thermal resistance for flat plate, finned heatsink, and pinned heatsink under

natural and forced convection conditions.

Pre-Lab Questions

Lowest Tp Middle Tp Hottest Tp!inned Finned Flat !late

Methodolog

!"peri#ent $ %&orced 'onvection(

$) he fan is placed assembly on the top of the duct.

*) he finned heatsink is placed into the duct.

+) he heater switch is turned on.

,) he heater power control is set to "# $atts (the control knob is turned clockwise).

) he air flow velocity is set to %.# m&s (the control knob is turned clockwise).

.) 'eatsink temperature is recorded in every " minute. $hen the temperature does not

change in " minute, it can be considered that the system reached steady state.

/) Finned and pinned heatsink geometry is measured and their approximate surface areas is

calculated.

0) teady state and ambient temperatures is recorded.

1) he fan speed control knob is set to give a reading of ".%, ".#, and %.% m&s air speed.

$2) tep and * is repeated.

$$) he same experiment for pinned heatsink and flat plate is repeated only for %.#m&s air

velocity case.

$*) he flat plate si+e is measured and its surface are is calculated.

he heatsink temperature is affected by not only natural&forced convection but also

conduction and radiation heat transfer. till, the effect from conduction and radiation heat

transfer is considered negligible for this experiment.

3esults


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4ata sheets

mbient temperature-

urface areas- finned heatsink (%."%m/), pinned heatsink (%.%#m/), flat plate (%.%""m/)

Finned 'eatsink ( c)

'eatsink emperature, p ( c) mbient emperature, p0a ( c)

ime (min) %.# (m&s) ".% (m&s) ".# (m&s) %.# (m&s)

% .# #." ". 1.2

" .* #.% "." *./

/ 3./ 3.1 %.* *.

3.# 3.3 %. *.2

3 3.1 3." %.3 2."

# 3.2 .2 %./ 2.

#." .1 %." 2.#

1 #./ .# %." 2.* #.3 .3 %." 2.*

2 #.1 ./ %." "%."

"% .% .% "%.3

"" ./ /.2 "%.

"/ ./ /.1 "%.

" ./ /. "%.

"3 /.3

"# /.

" /./

"1 /.""* /.%

"2 ".2

/% ".*

/" ".1

// ".

/ ".

/3 ".

!"peri#ent $

Finned heatsink, Input power- "#$

ir velocity

(m&s)

'eatsink

emperature, p

(c)

mbient

emperature, a

(c)

emperature

4ise, p 0 a

(c)

hermal

4esistance

(p5 a)&6

(c&$)

%.% #1. /3.2 /.1 /."*

%.# ./ /#. "%. %.1"

".% /.# /3.1 1.* %.#/

".# ".# /3./ 1. %.32

!inned heatsink, Input power- "# $


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ir velocity

(m&s)

'eatsink

emperature, p

(c)

mbient

emperature, a

(c)

emperature

4ise, p 0 a

(c)

hermal

4esistance

(p5 a)&6

(c&$)

%.% 3*.# /3.* /.1 ".#*

%.# 1.3 /3.# "/.2 %.*

".% ".1 /3./ 1.# %.#%

".# "./ /#." ." %.3"

Flat plate, Input power- "# $

ir velocity

(m&s)

'eatsink

emperature, p

(c)

mbient

emperature, a

(c)

emperature

4ise, p 0 a

(c)

hermal

4esistance

(p5 a)&6

(c&$)%.% 1*.1 /#." #. .#1

%.# 1". /3.2 3.1 .""

".% *. /3.# 33." /.23

".# ." /3.3 *.1 /.#*


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0 0.5 1 1.5 20

0.5

1

1.5

2

2.5

3

3.5

4

Thermal Resistance(c/W) Vs Air Velocity (m/s)

Finned heatsink

Pinned heatsink

Flat plate

Air Velocity (m/s)

Thermal Resistance (c/W)

Figure "- hermal 4esistance against ir 7elocity

8ased on the experiment, figure " shows thermal resistance against air velocity. For %.#m&s

air velocity case, it shows that flat plate thermal resistance is the highest which is ."" ( 9&$)

compare to pinned heatsinks and finned heatsinks which are %.* ( 9&$) and %.1" ( 9&$)

respectively. he thermal resistances for pinned and finned heatsinks are almost same as

compared to flat plate. he relationships between air flow velocity and thermal resistance are

linear for finned heatsinks. s the air flow velocity increase, the thermal resistance decreases.

It shows that air flow velocity and thermal resistance are linear for finned heatsinks. From the

graph, as the air velocity increase, the thermal resistance decrease. It is the same for all of the

three cases which are finned and pinned heatsinks and flat plate. ir velocity % m&s means the

heatsinks is cooled by natural convection. $hen the velocity is % m&s, flat plate shows the

highest thermal resistance which is .#1 ( 9&$) followed by finned heatsinks which is /."*

( 9&$) and pinned heatsinks which is ".#* ( 9&$). he forced convection means that the air

flow velocity is more than % m&s. It shows that the thermal resistance decreased because of

higher air flow velocity. Forced convection was more efficient compared to natural

convection at dissipating heat.


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0 2 4 6 8 10 12 140

2

4

6

8

10

12

Time (min) Vs Temperature Rise (c)

Finned Heatsinks

Time (min)

Temperature Rise (c)

Figure /- emperature 4ise ( 9) against ime (min)

8ased on the experiment, figure / shows temperature rise against time for finned heatsinks.

he relationships between time (min) and temperature rise (9) are not linear. he system has

reached steady state when the temperature rise was constant. he temperature decrease as the

time progress.


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4iscussion

8ased on the experiment, thermal performance (temperature) for pinned heatsinks, pinned

heatsinks and flat plate are different. his is due to the different surface area. he larger the

surface area, the lower the thermal resistance. 8y comparing the three cases which are finned

heatsinks, pinnd heatsinks and flat plate, finned heatsinks is the larger surface area which is

%."% m/as compared to pinned heatsinks and flat plate which are %.%# m /and %.%"" m/

respectively. 8asically, the larger the surface area, the more heat energy is needed to heat the

surface and it needs more time to reach the heatsinks temperature. he plate or heatsinks will

become hot when temperature rise within the time. !reviously, my pre0lab prediction is flat

plate has the hottest heatsink temperature. Followed by finned heatsink as the middle heatsink

temperature and lastly pinned heatsink as the lowest heatsink temperature. he experiment

result agrees with the pre0lab prediction. he heatsinks temperature changes as air velocity

changes because of the heat transfer. 8esides, heat will dissipate faster when the air velocity

contacting the surface of the heatsinks increases. 'igher velocity causes the heat transfer to

the surface lower and the temperature of the heatsink also lower. $hen air temperature has

essentially reached the heatsinks temperature, no cooling take place. fter certain condition,

the air temperature inside finned and the finned surface temperature are same, heat transfer

did not occurs. here are some errors occurs during the experiment. he possible causes of

error in temperature measurement is because of the power is not consistent. It changes

throughout the experiment. It is set to be "# $, but during the experiment it changes to

1. his may happen due to the surrounding and machine itself. he other causes of

errors are the air flow velocity that we set on the machine. he velocity is not consistent

throughout the experiment. It is set to be at a certain value, but during the experiment it

change to 2. :f this cause of error, I supposed that the most significant error was it is

hard to set the power of the heater.


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'onclusions

In conclusions, the larger the surface area, the lower the thermal resistance. 8etween the three

cases which are finned heatsinks, pinned heatsinks and flat plate, finned heatsinks has the

largest surface area. 'ence that, thermal resistance of the finned heatsinks is the lower than

the others. s the air velocity changes, the temperature also changes. Forced convection was

more efficient compared to natural convection at dissipating heat.

3e5erences

http-&&en.wikipedia.org&wiki&Natural;convection

http-&&en.wikipedia.org&wiki&Forced;convection

http-&&www.dummies.com&...&transferring0heat0through0convection0natural0vers...
http://en.wikipedia.org/wiki/Natural_convectionhttp://en.wikipedia.org/wiki/Forced_convectionhttp://www.dummies.com/.../transferring-heat-through-convection-natural-vershttp://en.wikipedia.org/wiki/Forced_convectionhttp://www.dummies.com/.../transferring-heat-through-convection-natural-vershttp://en.wikipedia.org/wiki/Natural_convection

250440967 lab report convefction

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