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8/17/2019 termo odev

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What is Heat Transfer?

• Heat transfer is the movement ofheat energy from one substance toanother.


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• Heat (energy) always moves from awarmer substance to a coolersubstance.

HotCold



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• Heat will continue to move until bothsubstances are the same temperature.

HotCold WarmWarm



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• The greater the dierence intemperature between the substances!the faster the heat will transfer.



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• There are three types of heattransfer"

# Conduction

# Convection

# $adiation



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%&amples

• 'ou touch a blaccar in the summerand the heat from

the car transfersinto your hand.

• bree*e maesyou feel cooler

because the windtransfers heat awayfrom your body.

• 'ou feel the cold ofa winter daybecause the cold

air transfers intoyou.

• 'our Coe in acooler gets cold

because the coldfrom the ice movesinto the Coe.

nti+%&amples


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Conduction

• Heat transfer by conduction is thetransfer of heat through directcontact.


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Conduction

• ,olecules transfer energy to themolecules ne&t to them.


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Conduction

• The moleculesdo not have tobe the same

substance.

http://www.theelusivefish.com/articles/wp-content/uploads/2007/09/hot-stove.jpg


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%&ample -

http://www.vernier.com/caliper/fall07/images/heat_transfer_large.jpg

The metal conducts heat from the cup

of warm water to the cup of cool water.


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$adiation

• Heat transfer by radiation is the transferof heat through electromagnetic waves.

http://www.nmsu.edu/~safety/images/fire_meaney.gif


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$adiation

• There is no direct contact between thesubstances.


14/31http://www.log.thesietch.org/wp-content/uploads/2007/0!/earth.jpghttp://stardate.org/images/gallery/sun".jpg

Heat from the sun radiates throughempty space to earth.

%&ample -


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Convection

• Heat transfer by convection is thetransfer of heat through the uid(li/uids and gases) movement of

currents.


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Convection

• Warm uids rise! cool down! sin! andthen are warmed again.


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h t t p : / / w w w . e e . u c l a . e

d u / t e s t / f a c u l t y / n e # l i n / $ e c t u r e % / &

i g 0 ' 0 ( . j p g

The radiator warms the room by warming theair around it. Then the warm air transfers heat

to the rest of the room through convection.


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h t t p : / / p h y s i c s . u o r e g o n . e d

u / ~ j i m r a u / ) r a u * m + e w / , h a p 0 7 / & -

0 7_

0 ( . j p g

s air above the road warms up! it rises and is replaced bcooler air! forming a convection current .


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http://www.aos.wisc.edu/~aalope#/aos%0%/w"/heatrans.jpg

This picture illustrates all three type of heat transfer.Can you identify them all?

Conduction

$adiation

Convection


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A heat pipe heat exchanger is a simple device which is

made use of to transfer heat from one location to another,using an evaporation-condensation cycle.

Heat pipes are referred to as the "superconductors" of heatdue to their fast transfer capability with low heat loss.

What is a Heat Pipe

W ki P i i l


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Working Principle

!he heat input region of the heat pipe is called evaporator, the

cooling region is called condenser.

n between the evaporator and condenser regions, there may be

an adiabatic region


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W0$1234 56728The prime requirements are"

compatibility with wic and wall material .

4ood thermal stability.

vapor pressure not too high or low overthe operating temperature range .

high latent heat .

high thermal conductivity .low li/uid and vapor viscosities.

high surface tension.

acceptable free*ing or pour point.


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W2C1 0$ C9266$'

:T$7CT7$%2t is a porous structure made of materials lie

steel!aluminium! nicel or copper in variousranges of pore si*es.

The prime purpose of the wic is to generatecapillary pressure to transport the woring uidfrom the condenser to the evaporator.

2t must also be able to distribute the li/uidaround the evaporator section to any area whereheat is liely to be received by the heat pipe.


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C03T237%8;.Wics are fabricated using metal foams! and

more particularly felts! the latter being morefre/uently used.


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Types of Heat 9ipes6eading edge

$otating and revolving

5lat 9late

,icro heat pipes


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dvantages 0f Heat9ipes,ay reduce or eliminate the need =r reheat.

$e/uires no mechanical or electrical input.

re virtually maintenance free.

9rovide lower operating costs.

6ast a very long time.

re environmentally safe.


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pplications

69T09 H%T 929% :067T203

H i d i


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Heat pipes used inprocessor

: f


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:pace craft


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H%T 929% 23 C97


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Camera

Cooler Combined Heat pipe > water cooling

acet for hi def CC8 camera

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