air conditioning lab final1
TRANSCRIPT
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Air Conditioning Lab
Authors:
Devon BrownMichael HartleyJames Sabo
Date Performed:
November 15, 2010
Date Submitted:
November 29, 2010
Submitted To:
Matt Feiler 52!0 1"th #ve N$Seattle, %#
9&105
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A. Executive Summary
'he ()r(ose o* this lab was to +ain a better )nerstanin+ o* the va(or
com(ression re*ri+eration cycle- 'o o this we meas)re the tem(erat)re an (ress)re at
.ey (oints thro)+ho)t a stoc. air conitioner- 'his allowe )s to etermine the state o*the /22 that eiste between each com(onent- %e *o)n that in between the eva(orator
an the com(ressor the /22 was a mit)re o* va(or an li)i, with a )ality o* -&" an
an enthal(y o* 21-! .J3.+- Between the com(ressor an the conenser, the /22 was a
s)(erheate va(or with an enthal(y o* 00 .J3.+- Between the conenser an the throttle,
the /22 was a com(resse li)i with an enthal(y o* &&-4 .J3.+ an in between the
throttle an the eva(orator the /22 is a mit)re with a )ality o* -2 an an enthal(y o*
&&-4 .J3.+- %e also meas)re the air velocity at i**erent sections o* the eva(orator eit
in orer to obtain the mass *low o* the air thro)+h the eva(orator o)t()t- 'his
meas)rement allowe )s to *in the total air*low thro)+h the eva(orator, which was 0-142
.+3s, an the eva(orator heat *low, which was 1-49 .%- 'he conenser heat reection rate
was calc)late to be 2-20 .% an the re*ri+erant *low rate was shown to be 0-010 .+3s,
which wo)l ieally remain constant thro)+ho)t the system- Finally, the val)es *or
coe**icient o* (er*ormance an com(ressor e**iciency are 2-09 an 0-"1 .%, res(ectively-
'hese val)es were )ite a bit lower than the ieal val)es, )e to tem(erat)re to several
ass)m(tions an heat lea.in+ to the environment- 'he low e**iciency an coe**icient o* (er*ormance o* this system ma.e it a (oor choice as a re*ri+erator- 6m(rovements, s)ch
as cascain+ or m)ltista+e com(ression with re+enerative coolin+ sho)l be mae to
increase e**iciency an (er*ormance be*ore it is )se in a realworl environment-
B. b!ective
6n this e(eriment, we loo. to )se o)r observe intrinsic val)es to etermine the
state in the i**erent sta+es o* the system- Since there are 2 states that are a mie
sol)tion, it is i**ic)lt to acc)rately etermine the states base solely on the (ress)re an
tem(erat)re- %e there*ore m)st )se o)r thermoynamic (ro(erties to acco)nt *or the
ener+y trans*er into an o)t o* the system- 'his will allow )s to etermine the enthal(y o*
the each state, allowin+ )s to etermine the state- 7ltimately, we loo. to ienti*y the
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thermal e**iciency an the irreversibility o* the system )sin+ the tools an techni)es
+aine in the co)rse-
C. Test Descri"tion
# stoc. air conitioner was chosen to etermine the (er*ormance o* a +eneral
va(orcom(ression re*ri+eration cycle- 'his air conitioner was r)n with /22- 6ts o)ter
casin+ has been remove an several sheaths have been remove an re(lace with
8lei+las to im(rove the visibility o* the system- ne (ress)re +a)+e was set )( be*ore
the com(ressor to rea the low (ress)re an another (ress)re +a)+e was set )( in
between the com(ressor an the conenser to rea the hi+h (ress)re- 'he ass)m(tion was
mae that this hi+h (ress)re remaine constant over the conenser an the eva(orator- 6n
orer to ma.e s)re that the (ress)res meas)re were acc)rate to the system, the air
conitioner was allowe to r)n *or several ho)rs to warm )(, (rior to ta.in+
meas)rements-
6n orer to *)rther analy:e the air conitioner, thermoco)(les were attache to the
o)ter s)r*aces o* the (i(es at several .ey locations- 'he *irst thermoco)(le was (lace on
the (i(e leain+ into the com(ressor- 'he secon thermoco)(le was (lace on the (i(e in
between the com(ressor an the secon (ress)re +a)+e- 'he thir thermoco)(le was
(lace on the (i(e between the secon (ress)re +a)+e an the conenser- 'he *o)rth an*i*th thermoco)(les were (lace on the (i(e between the conenser an the throttle- 'he
sith an seventh thermoco)(les were (lace on the (i(e between throttle an the
eva(orator- 'he ei+hth thermoco)(le was (lace on the (i(e a*ter the eva(orator- 'he
ninth thermoco)(le was reain+ the ambient tem(erat)re- Finally, the tenth thermoco)(le
was meas)rin+ the hot eha)st an the eleventh thermoco)(le was meas)rin+ the col
eha)st- 'he locations o* each thermoco)(le are shown below in Fi+)re 1- 'hese
tem(erat)re reain+s were meas)re a*ter the air conitioner ha reache a steay state-
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#lso, a c)rrent (robe was )se to meas)re the c)rrent in the air conitioner (owerwire an a voltmeter was )se to meas)re the volta+e at the (l)+ o)tlet- 'his in*ormation
is necessary to calc)late the electrical raw o* the air conitioner- 'hese two val)es were
ta.en twice; once, at the very be+innin+ o* the e(eriment, when only the *ans are
r)nnin+ an then a+ain, once the system ha reache a steay state- 'he *irst set o* val)es
only corres(ons with the (ower cons)me by the *ans, where as the secon set o* val)es
incl)es the (ower raw *rom both the *ans an the com(ressor-
Finally, to analy:e the mass *low o* the col air, the velocity at i**erent (oints in
the eva(orator eit was meas)re )sin+ a (itot static (robe an a i+ital water
manometer- 'he eva(orator eit was ivie 21 sections, as shown in Fi+)re B1
o**? (osition, t)rnin+ o** the *ans- #t this (oint the entire
)nit can be )n(l)++e-
4
Figure 1. Location of thermocouples andpressure gauges.
LowPressure
Condenser
Throttle Compressor
Evaporator
1
2345
6 7 8
HighPressure
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D. #esu$ts
D.%. State o* the /e*ri+erant 'hro)+ho)t the @ycle
'able 1 is(lays the conitions, etermine thro)+h irect meas)rement or calc)lation, at
each state in the re*ri+eration cycle- State 1 corres(ons to the state o* the re*ri+erant
between the eva(orator o)tlet an the com(ressor inlet- State 2 is the state between the
com(ressor o)tlet an the conenser inlet- State is the state between the conenser
o)tlet an the throttle inlet- State 4 is the state between the throttle o)tlet an the
eva(orator inlet- nly inlet tem(erat)res were )se beca)se it was reasone that
tem(erat)re losses between com(onents o* the cycle create inacc)racies in calc)lations
an ca)se com(lications- 7sin+ only inlet tem(erat)res +ives an acc)rate escri(tion o*
the re*ri+erant be*ore it )ner+oes the more rastic chan+es in the com(onents- 'hewebsite, www-thermo*l)is-net, was )se to etermine the conitions o* each state-
Tab$e %. @onitions at each state in the re*ri+eration cycle-State % State & State ' State (
Pressure 4!!-9 .8a, 15!9- .8a 15!9- .8a 4!!-9 .8aTem"erature 20-9A@ &4-!A@ 5-4A@ 2-4"A@)ua$ity *x+ 0-&" N3# N3# 0-20Entha$"y *h+ 21-! .J3.+ 00-0 .J3.+ &&-4 .J3.+ &&-4 .J3.+
S"ecific ,o$ume*v+ 0-022 m3.+ 0-019 m3.+ 9-!$4 m3.+ 0-0094 m3.+Entro"y *s+ 0-&12 .J3.+ 0-9&& .J3.+ 0-2 .J3.+ 0-4 .J3.+
State MiS)(erheateCa(or
@om(ressei)i Mi
Fi+)re 2 is a (lot o* tem(erat)re vs- entro(y thro)+ho)t the cycle- Note the (rocess lines
connectin+ states an the ome rawn *rom the sat)rate va(or an li)i lines-
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-igure &. 'em(erat)re$ntro(y Dia+ram o* the System
D.&. 'otal #ir Flow 'hro)+h the $va(orator
'he total air*low thro)+h the eva(orator was calc)late by a((roimatin+ the inte+ral
EC#, an m)lti(lyin+ that val)e by the ensity o* air- C is the velocity o* the air an #
is the i**erential element o* area- 'his inte+ral was estimate )sin+ a s)mmation metho
that is e(laine *)rther in the a((enices- 'he *inal val)e *or air*low was etermine to
be 0-142 .+3s-
D.'. $va(orator Heat Flow
'he eva(orator heat *low is the rate at which heat is ae to the eva(orator *rom the air
stream- 6t is the (ro)ct o* the total air*low m)lti(lie by the s(eci*ic heat o* air an by
the chan+e in tem(erat)re between the ambient tem(erat)re an the col eha)st comin+
o)t o* the eva(orator- 'his val)e was etermine to be 1-49 .%-
D.(. @onenser Heat /eection /ate'he conenser heat reection rate is the rate at which heat is remove *rom the system as
the re*ri+erant +oes thro)+h the conenser- 6t is calc)late )sin+ the balance o* ener+y
e)ation- 6eal conitions may be ass)me so that the heat reection rate is e)al to the
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heat *low into the eva(orator ae to the electrical (ower that is +oin+ into the
com(ressor- 'he heat reection rate was calc)late to be 2-20 .%-
D.. /e*ri+erant Flow /ate
'he re*ri+erant *low rate was etermine thro)+h care*)l analysis o* the re*ri+erant as it
(asses thro)+h the conenser- 'he heat reection rate, calc)late above, is ivie by the
chan+e in enthal(y o* the re*ri+erant between the conenser inlet an o)tlet to calc)late
the *low rate o* the re*ri+erant- 'his was shown to be 0-010 .+3s an ieally remains
constant thro)+ho)t the system-
D./. @oe**icient o* 8er*ormance
'he coe**icient o* (er*ormance *or the re*ri+erator is e)al to 13
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*o)r states- )tlet tem(erat)res were i+nore- 'his oes remove analysis o* the
re*ri+erant )rin+ the transition sta+es o* the cycle in between the com(onents, which
wo)l chan+e the *inal res)lts- However, chan+es are relatively insi+ni*icant, meanin+
the (hysical states o* the re*ri+erant wo)l not chan+e- 6t was also ass)me that the
throttle acts as a constant enthal(y evice, which is not entirely tr)e- 'he (rocess in
which the re*ri+erant (asses thro)+h the throttle may be moele as an aiabatic one, b)t
in reality there is heat trans*er even i* it is small- 'his ass)m(tion can lea to small
errors- #itionally, small (ress)re ro(s in the conenser an eva(orator were i+nore
to ma.e calc)lations easier- 'his also intro)ces errors in calc)lations- 'hese
ass)m(tions o intro)ce small errors, b)t they o not chan+e the etermine states o*
the re*ri+erant thro)+ho)t the cycle, which ma.es them acce(table errors *or this lab-
'able 1 shows that the re*ri+erant is a sat)rate mi between the eva(orator an thecom(ressor, a s)(erheate va(or between the com(ressor an the conenser, a
com(resse li)i between the conenser an the throttle, an a sat)rate mi between
the throttle an the eva(orator- 'hese res)lts are not chan+e by small errors )e to the
ass)m(tions liste above-
@om(arin+ the 'em(erat)re$ntro(y ia+ram evelo(e *or this lab to an ieal
re*ri+eration cycle yiels some interestin+ res)lts- 'he 's ia+ram *or the ieal
re*ri+eration cycle has state 1 an state 2 at the same entro(y- 6n the e(erimentally
etermine ia+ram, this is obvio)sly not tr)e- State 2 is at has a +reater entro(y- 6n the
ieal cycle, it is also ass)me that at state 1, the re*ri+erant is a sat)rate va(or an at
state , it is a sat)rate li)i- $(erimentally, it was shown that it is a sat)rate mi at
state 1 an a com(resse li)i at state - 'his ma.es sense, since ieal conitions
cannot be a((lie (er*ectly- 'he (rocess that the re*ri+erant )ner+oes when (assin+
thro)+h the conenser is similar in both the ieal an e(erimentally etermine
ia+rams- 'he s)(erheate va(or ro(s in tem(erat)re )ntil it reaches sat)ration an
then )ner+oes a (hase chan+e as entro(y contin)es to ecrease- 6n the ieal case, it
becomes a sat)rate li)i- 6n the e(erimental case, it becomes a com(resse li)i-
'hese is(arities are e(ecte, beca)se it is im(ossible to have a (er*ectly ieal
re*ri+eration cycle- 'he *act that i**erent tem(erat)res are meas)re between each (air
o* inlets an o)tlets shows that this is not an ieal cycle- 6t is worthwhile to com(are to
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an ieal cycle tho)+h since certain ieal conitions were ass)me thro)+ho)t
calc)lations-
'he total air*low can be ass)me to be *airly acc)rate es(ite the *act that it was
a((roimate with a s)mmation metho rather than )sin+ inte+ration- 'he metho o*
estimation is acc)rate eno)+h to +ive a si+ni*icant res)lt- 'his val)e was similar to
val)es calc)late by other +ro)(s- 'he calc)lations *or the heat absor(tion an reection
rates *or the system e(en on the air*low val)e, so any errors in that etermination were
carrie over- 'he heat absor(tion an reection rates are as acc)rate as the air*low val)e-
Similarly, the re*ri+erant *low rate is etermine )sin+ the heat reection rate an
the chan+e in enthal(y across the conenser, so its acc)racy is e(enent on the si:e o*
the errors in those val)es- 'he enthal(y val)es were etermine )sin+
www-thermo*l)is-net, which )ses thermoynamic relationshi(s between (ro(erties- 6tcan be ass)me that these are *airly acc)rate- 'he *low rate is 0-010 .+3s, which is
relatively slow b)t com(arable to other re*ri+eration cycles- 6t has the (ro(er orer o*
ma+nit)e-
'he coe**icient o* (er*ormance *or this cycle is 2-09, which is lower than ieal
val)es *o)n in Thermodynamics: An Engineering Approach- However, it is not that
m)ch lower, an it is e(ecte that it wo)l be lower- 'he coe**icient o* (er*ormance *or
a re*ri+erator is e*ine as the ratio o* the esire o)t()t to the re)ire o)t()t- 'his
means that the esire coolin+ e**ect in the eva(orator is 2-09 times +reater than the wor.
()t into the com(ressor- 'o im(rove this coe**icient o* (er*ormance, techni)es s)ch as
cascain+ an m)ltista+e com(ression with re+enerative coolin+ may be em(loye2-
@ascain+ is )sin+ two or more va(orcom(ression systems in series- M)ltista+e
com(ression with re+enerative coolin+ )ses a miin+ chamber calle a *lash chamber in
combination with com(ressors o(eratin+ at i**erent (ress)res- 6m(rovin+ the coe**icient
o* (er*ormance allows the re*ri+erator to achieve lower tem(erat)res-
'he calc)late e**iciency o* the com(ressor is 15-"G, which is low b)t e(ecte
)e to the nonieal conitions- 'he system teste in the lab oes not incor(orate newer
e)i(ment or any o* the methos isc)sse above li.e cascain+, which wo)l im(rove
e**iciency o* the system as a whole an o* the com(ressor s(eci*ically- 'he irreversibility
rate was 0-2 .%, which is abo)t 2G o* the (ower absorbe by the system- 'hat means
#
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that 2G o* the (ower is not converte to wor. by the system- J)st as with the e**iciency
o* the com(ressor, this co)l be im(rove by the same methos isc)sse above- #ny
techni)es )se to limit ener+y trans*er between the system an the s)rro)nin+s wo)l
ecrease the irreversibility- 'his irreversibility is ca)se by *riction within the system
an heat trans*er between the com(onents o* the system an the s)rro)nin+ air-
-. Conc$usions
'he re*ri+erant enters the com(ressor as a sat)rate mi- #s it (asses thro)+h the
com(ressor, it becomes a s)(erheate va(or, which then enters the conenser- 6t becomes
a com(resse li)i in the conenser an is then e(ane into a sat)rate mi in the
throttle- 'his *inally (asses thro)+h the eva(orator, an remains a sat)rate mi be*oreenterin+ the com(ressor an starts the cycle over a+ain- 'he coe**icient o* (er*ormance
an com(ressor e**iciency val)es are si+ni*icantly less than the ieal val)es, b)t this is to
be e(ecte- 'he system )se in the lab is a sim(le re*ri+eration cycle that oes not )se
any o* the more avance methos that im(rove e**iciency an ener+y conservation, s)ch
as cascain+ or m)ltista+e com(ression with re+enerative coolin+- 6t is also an oler
system an the testin+ conitions are si+ni*icantly less than ieal- 'he system +ives an
ae)ate re(resentation o* the re*ri+eration cycle an is )se*)l *or sim(le analysis an
isc)ssion o* thermoynamic conce(ts- However, as an act)al system, its low e**iciency
an coe**icient o* (er*ormance ma.e it a (oor choice as a re*ri+erator- 6m(rovements
sho)l be mae to increase e**iciency an (er*ormance be*ore it is )se in a realworl
environment-
1. #eferences
1 8ro*essor S- Bhattacharee-
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A""endix A /aw ata
6n this e(eriment several meas)rements were ta.en- 'he *irst o* which was the
tem(erat)re at several i**erent (oints o* the air conitionin+ cycle, which are as *ollows;
Tab$e A%. 'em(erat)re reain+s *or i**erent (arts o* the cycle
'em(erat)re/eain+s
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Fan nly;@)rrent 1-14 am(sColta+e 121-0 ColtsFan an @om(ressor;@)rrent "-04 am(s
Colta+e120-5Colts
'here were reain+s o* (ress)re ta.en at i**erent sta+es o* the e(eriment- 'he reain+s
were (rovie in 8S6 +a+e, an m)st converte to absol)te (ress)re, )sin+ the
relationshi(
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6n orer to etermine the cross sectional area o* each meas)re velocity we ivie the
circ)lar eha)st into 21 i**erent sections, create with ! concentric circles, all o* which,
besies the mile circle, are ivie into *o)rths as shown below;
Tab$e B%. /aii o* circles
-igure B%. Dia+ram o* col air eha)st areas with rai)s val)es
'he areas o* each o* these re+ions
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22221
2
2 9-==25
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Tab$e B'. meas)re an converte val)es *rom (itot instr)ment
Meas)rement8oint h
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Tab$e B(. @alc)late val)es o* velocity-
Meas)rement8oint
Celocity
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Tab$e B. 8artial an *)ll mass *low rate
Meas)rement#rea
Mass Flow/ate
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D.% Finin+ the 8ower o* the @om(ressor
6n orer to *in the (ower cons)m(tion o* the com(ressor, the relationshi( can be )se;
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Since the state o)t o* the eva(orator is a mie state, the val)es o* ' an 8 cannot be )se
to acc)rately etermine the state- %e there*ore nee to etermine the enthal(y o* the
state, which can be erive *rom a similar *orm as $
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