Presentation cooling system

7/25/2019 Presentation cooling system

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Benha University

Faculty of Engineering

Mechanical Engineering Department

Refrigeration & Air Conditioning Course

2006-2007


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1.1 Historical Background

Leonardo da vinci by the end of the 15 thcentury used a ventilating fan.

Boyle in 1659 & alton 1!00 discovered their "ell #no"n la"s.

$he first te%t on heating and ventilating "as "ritten by obertson Buchanan

'1!5(). *ans+ Boiler and adiators has been invented in the ,iddle of 19 thcentury.


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1.1 Historical Background (Cont.)

rof. le%ander $"ining+ /roduced 725 #g of ice a day using a double acting

vacuu, and co,/ression /u,/ e,/loying the 1!( invention of va/or

co,/ression cycle by acob er#ins.


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1.1 Historical Background (Cont.)

W.H. Carrier (1876-1950) '*ather of ir onditioning)

1. evelo/ed for,ulae for o/ti,i3ing the a//lication of forced draft fans.

2. evelo/ed ratings of /i/e-coil heater and setu/ a research lab.

(. 4ngineered and installed the first year-round '- & u,id.-e-hu,id.).

. ade use of air "asher for controlling the de" /oint of air by heating or chilling re-

circulated "ater.

5. n 1911 /resented his re,ar#able /a/er 8ational sycho,etric *or,ulae.

6. n 1922 e,/loyed the centrifugal co,/ressor for refrigeration.


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1.2 The meaning of Air Conditioning

*ull air conditioning i,/lies the auto,atic control of an at,os/heric environ,ent either for co,fort

hu,an beings or ani,als or for the /ro/er /erfor,ance of so,e industrial or scientific /rocess.

*ull ,eans: $he /urity+ ,ove,ent+ te,/erature+ and relative hu,idity of the air to be controlled

; ir onditioning versus


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1.3 Importance of Air

$he individual needs daily about 1.2 #g of "ater+ 2.7 #g of food and 16 #g of air.

ir ,ay carry dusts+ bacteria+ be still+ hot and hu,id and this result in heath

ha3ards.


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1. Comfort Conditions

*or hu,an co,fort the follo"ing fivefactors are to be treated:

1. Dry bulb temperature'cooling or heating is reuired).

2. Humidity Ratio'hu,idification or de-hu,idification is reuired).

(. Air Motion'ir flo" and distribution to feel all /ersons the sa,e feeling).4. Air Purification ir filters to get rid off dust and bacteria.

5. Ventilation'Cse of fresh air)


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!actors affecting human comfort

$here are si% factors that affecting the hu,an co,fort> 8four of them are

en"ironmental and 8t#o are personal

1. ry bulb te,/erature.

2. ean radiant te,/erature.(. elative hu,idity.

. ir velocity.


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1. lothes insulation.

2. $y/e of activity.

$ffecti"e Temperature

t is euivalent to the te,/erature at saturation "hich give the sa,e feeling ofhotness to different te,/eratures and relative hu,ility "hen the air velocity

ranges fro, 15-25 f/,.

n "inter it is 20 o and in su,,er is 22 o.


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%inter Com&inations


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'ummer Com&inations


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o,fort Done


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1. !undamental properties of moist air

$he "or#ing substance in air conditioning is the ,oist air> "hich is considered as a

,i%ture of dry air and "ater va/or.

s the ,oist air /ure substanceE

ry air is a good e%a,/le of /ure substance 'ho,ogeneous and invariableco,/osition).

Fater va/or is also+ a /ure substance> but the ,oist air not a /ure substance in

any /rocess in "hich eva/oration or condensation of ,oisture occurs.


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Composition of r* Air

o,/onent olecular

Feight

@ by

=olu,e

@ by

,ass

G2 2!.02 0.7!0( 0.757

H2 (2.0 0.2099 0.2(19

r (9.91 0.009 0.0129

H2 .0 0.000( 0.0005

2 2.02 0.0001 0.0000


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Cont.

olecular "eight of dry air

I 2!.0!%0.7!0! J ----- I 2!.969 #g?#,ol.

olecular "eight of "ater va/or

I2%1.01J1%16I1!.02 #g?#,ol.'tandard adopted

ensity of air I 1.29( #g?,( at 101(25 a+ 0 o.

ensity of "aterI1000 #g?,(at o.1


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Cont.


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+as ,a#s

BoyleKs la"

3min!andPain"

.

where

ConstpV=

harlesK la"

Kin#min!

#

3andwhere

V =


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The general gas la#

mRTpV=

t is /ossible to co,bine BoyleKs and harlesK la"s as one euation>

Fhere>

/I the /ressure of the gas in a.

=Ithe volu,e of the gas in ,(

,Ithe ,ass of the gas in #g.

Ithe gas constant. ?#g .

$Ithe gas te,/erature in #


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alton-s la# of partial pressure

f a ,i%ture of gases occu/ies a given volu,e at a given te,/erature+ the total

/ressure e%erted by the ,i%ture euals the su, of the /ressure of the

constituents+ each being considered at the sa,e volu,e and te,/erature.

t can be re-e%/ressed as:

1. $he /ressure e%erted by each gas in the ,i%ture is inde/endent of the /resence

of the other gases.

2. $he total /ressure e%erted by a ,i%ture of gases eual the su, of the /artial

/ressures.


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r* &ul& temperature BT or Td&

$he te,/erature recorded by a ther,o,eter "hen its bulb is dry.

%et &ul& temperature %BT or T#&

; $he te,/erature recorded by a ther,o,eter "hen its bulb is covered by a"et cloth or "ic# cotton.

roperties of moist air


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$he "et bulb te,/erature is #no"n as the adiabatic saturation te,/erature

$his is because the heat reuired to eva/orate "ater fro, the "etted "ic# is ta#en fro, the

at,os/heric air /assing through it "hen the te,/erature of the ther,o,eter reaches to its lo"est

value.

$he "et bulb te,/erature is ,easured by a device called sychro,eter


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'ling s*chrometer


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e# point temperature T/ Tdp

$he te,/erature at "hich the "ater va/or e%isting the at,os/heric starts to

condenses if its cooled at cooled at constant /ressure /vGote

t is the saturation te,/erature corres/onding to the /artial /ressure of "ater va/or.


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0oisture content (Humidit* atio) %

t is defined as the ,ass of "ater va/or in #g "hich is associated "ith one #g of

dry air in an air-"ater va/or ,i%ture. t is so,eti,es called ('pecific or

A&solute Humidit*).


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av m$m%=

By using altonKs la" and a//lying the general gas la" to each of the t"o constituents of

,oist air.

a

v

aaaaa

vvvvv

mm%

#&m!"

#&m!"

=

=

=


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vatm

v

a

v

v

a

""

"622.0%

622.0'

'

&

&

ote

=

==

t is clear fro, the above euation that the va/or content 'u,idity ratio) increases "ith the

increase of /artial /ressure of the "ater va/or e%isting the ,oist air and it beco,e ,a%i,u,

"hen the de" /oint beco,e ,a%i,u, i.e. eual to the dry bulb te,/erature $d/I$db


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elati"e humidit* H or

$his is defined as the ratio of the /artial /ressure in ,oist air at a given te,/erature t+ to the

/artial /ressure of saturated "ater va/or in the air at the sa,e te,/erature+ t

100*

)"(

"

satv

v=


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Cont. elati"e humidit* H or


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'pecific "olume

$his is the volu,e in ,(of one #g of dry air ,i%ed "ith " #g of "ater va/or. n the ,i%ture each

constituent occu/ies the sa,e volu,e.

$he general gas la" ,ay be trans/osed to e%/ress the s/ecific volu,e =

"

m

!=


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$nthalp* of moist air

$he enthal/y h used in /sycho,etry is the s/ecific enthal/y of ,oist air e%/ressed in

#?#g dry air+ and is defined as:

hI haJ " hv

haI1.007 t -0.026 '10-60 o) or

haI1.005 t 'do"n to -10 o)

hvI2501J1.! t

hI 1.007 t -0.026 J"'2501J1.! t)


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$ample


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'olution


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Cont.


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Cont.

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Presentation cooling system

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