, Code: MEiOStl

lri,i. i

i intet -lhree Hour. : I\,jaxirlunr Mark: S0 '

-Minimurn Fass Mark: 2g,'i'.lrrti.'

{ i)/;:\l.lll

, (iii)(ir')...:

' i"i)

Q-.I-. Solu,e Any one out of a anrl b" , ,l ,

a. A Simple Singie Stagc vapor: cornpression reliigeratiorr

1:le:ll]piaiipartsof'aqi1estir:ir.inco-ittitrtiii:,'

Assume su itable cJara, if necessaryu39 orrefiigeration and air condiiioning rJaia boolr, srearn tablc and psychrometrictables and chans are perrnitred. -

'

students are here by aovisea !o use preierably' relrigerarion and psvchrorrrerric

?l"p*nj".: tabies ani chart by'M:rir,,- a r,arr,1; il;?;nei;fi;,ffii;J;.::"'"If possi!te students are advisert to enctose the psychroi,riirJiif,|'i"fr,'"ronr,

,'.l

s),stelr based on relrigerant R

. : "^'.

;.:-' - :.a) COP of the systeinb)Wprkinptlt-tocompl:e$Sof.'.'..]...:..:i:1 *.i :lsuperhcar horn (additionai rvort+ requiv/' r'vs ur )upa'ruar norrlr {aoLJrtronar wori<. requirc.d duc [o superhea[)d) Thr-ottling Ioss. (additicnar rvork input due to throttlins in.drace nthrottling in'place of irse.nirooiifoPrcLtlr?,1:iun)

assurrrirrg rlic,isol_,ar ai uorictcnser. pr"Srrr.: ,o loii ncide v,r jth 'saturatedliquid line,

"t]:t.t diagrarn shorvicaicLriafe propenics tikc t:r,)C), p-(Bar),.1r (kJikg), s (kJ/kgrK)

andQualityofeachstatepointinatabIe'

ti,

2.'.'f,- ,2=4

gs'

1,1- z-

t6

QJ Satve alyt 6ag out o,f q anrt b

AExplain iirr.rrtiorr, *.,n; o, u,I .?/1 I {rrvtnuu. O! neql orrof i,.^ ^-_\ l[/,/ , - ^sr8f1llne

alJ'.Jefrieeran.r. Using your erpranari:rii* *';*j:,ffi':;;-',i1;:*;;, c''8i''

"[i, unJ.,.,,,", ;;':;;: ;.,,',ina eci

, -':"'-"'

Discuss in brief Jhe selection of r.efiigerants as for asph_r,sical requirernentp are conierned.

,i6therrnodynamic, chciri ical and

l, {}

irr ltl0

26C 6vi'

:i.:l

'.)

D

lr-q/4,s1ture

anJt orte oril of a nnr! b\/ ,r/'1

,4t ,p, 27.''' April 20I0 , the alrnospheric

J {etnperature of moisf air at Raipur is

piessulg. drv hrr ih tf n l:rrt i ri - :;: .l , ... :

. "...J-v.qrsrv dlrLt 1\/(:t

observed as I atmospheric, 32oC a;id

+'

\ ky.f rr a cooling and dehun:idlficatlon arrar.rgemenr rnltn, ruuorarory of NIT Ruipu,. tn. n -V.-

.air .:nters

tlrrough a cooring coir ar +o ? dry bulb ternperaturg,so-z r13!d sranrrard

'otto'nher:ic Rreslre It leaves ttre eoolilq,coil as saturated air ar20'"a ,r; ";no.nao^rio .: . . ;--'-: .

:' : n:" ltit:' at'20",c The mass flowrate of airis io,o tgy*-in. Determine rheconceniate

,tut" ,ond rhe cooring capacity in TR, Draw sciiemaric:and psychr eor," o,u.;*.L""""'-n'"

RII'andtheoutdoorciesignconditionsare 34ocand40%RFLTrreairissuopliedto,th-eroorn'

:::-::r :ilb'r;rnRerature of i4"c Find a) the required:mas., flow rafe ofiair ui -"ir,u.*conler)r of suppry air, c) sensibre, ratenr heaf roads on the coir, and d) TIie ,*"*- *.i*,

,capacitv oi rbe coir, coir sensible Heat Fador and coir ADp ,r,i. i, ;rr; ;;;1;e coir is,,,0.2.Barometricpressule=latmospheric,Cotnmentonthe]res.,tu,

. '.- i_ -.. i:..rr'! -l:1 .t::

utoour sufr

ratent h:eat

t5

-: i.

.:i ,

: :. '.:

Jime: Three ll,burs.:.. .

:.

Note:' (i),

(ii)'(1u)

,(iv):

: (v)'

, (vi)

Q.1. Solve sny one out of a and b.r',

qf A vappr compression system using R-12 refrigerants works with 2.. . ... ,. _uJT_9tt1or,q

(5p TR , dQ TR nr _0. 1G arrd,.r 30 .oC

valves, 2 individual comlressors and single condeuser at +o oc rn" condition ofrefrigerant leaving'each evaporator ib ciry saturateci anci the iiquid retiigerant leaving

1-"^:::O."ser is sub cooled to 30 oC, Co*pression in "*t "*fr"rr";;r';.;;;:.Draw the schematic and name the system with p-h diagram or trr, ,rr,,

"onrro.i*cofirpressor intake point as ,,1,,. Also calculate:(i) Mass of refrigerant circurated to each evaporator.

Gi) Power consumed by each compressor and totar no**, conrurrred.l(iii) COP of rhe system.

,r^ t6dW A vapor compression refrigeration sysrem using R-12 as refrigerant works between the

: A!,tempf all parts of a question in continuity. ' ' ' .:,' '

:{l.lquestionsarecompulsoryandcarryeq.,atmarks.:.Assurnesuitabledata,_ifnec.,,u,y.1:.:--

Ytt of ref igeratiol and air condiiioning data book and psychrometric tabl€s ancl' charts are permitted. ' . .: : , :

stud'ents ;e here by a6vi11a,l-qr-. preferably refrigemion and psychrometricproperties tables zurd chart by Mathur & M-hd;;i?irr*a by Jain Brothers.s t u d en ts a r e a Is o adv x " a i

" r, i^ t

lh b p s y c hi o in e tr i c; ;t. ;; :;r; ; ;' nts

!#;:! :;, [ !,f " * * n * r "

n i: i ii i i"; ;,, i, i i ii ; ; ;; "; n;i;,"; *, "1]

w u n

'.' r ..' .;:.

gsvTU. ,. ,,,,,'' : \: : : ,- '.it-'I r:- ; j . . ':': .'

;.:.,: ..:(v)_.'-

Q.2. Solve sny one-out of a and b. ' , '

^, In an aircraft fiom Raipur to Mumbai reduced ambient air cooling system is installed

, for 20 TR cooling load. The cooling turbine is receiving rammed ott "1"t

t bar and 27

:

when passes through heat exchanger cools down the temperafure of air coming from

main compressor to 60 oC which is at 4.4 bar. In this heat exchange the temperature of

: cooling turbine uplto cab-in presswe of 1,05 bar according,to law p.Vl32: C. The cabrn

:mperafure is 23 oC, The law followed in compression of rammed air ttiroughrequired te

marn co{npressor is p.Vl5 : C. The transmission efficiency of turbines involved inI

]:....,]..,.'..-..:::':,.-.reduced h*bierrt air refrilgeration system used for aircrafts that should includes only the

followings:

(ii) The u*i"rrs processes for the cycle on the T-s diagram.

And Also Find:

(iii) Mass flow rate of air to cabin'

(iv) Power compressor consuming for refrigeration'

(v) Mass flow rate ot rammed arr used for cooling plrpose through heat exchanger.

(vi) Ne-t power output of all cooling turbines

(vii) COP of the sygtem.

t6

{ l^ air craft from Raipur to Delhi is cruising with a speed of 1000 kT/ht at an altitude

of I krn, the pressure and temperatu:e o'rtside the air craft are 0.35 bar and -15 oC

respectively. The passenger area is supposed to be maintained at 25 oC at 1.013 bar by

' ': .:- ... . '. :. . ^ ,,;,aving,iheeoolingtur6ineis 1:0sbar.The,totalcooling:lciad:=.,f the ,,,". . .: ...r . .. .,Ttl, ,:,lliepressureolalrle .?.. . 1

:: 2r'

-.: . '.....,..: - L.. .. .i . .' ,

'. ,... .:, ,.,

j :, r:.- ' - 'ptane isj'70 kw."Describs,:the working'of'ri*p[e aif-refrigerarion system urlo'ro, ' '

.(i)Schematicdiagramsho-wingthearrangementofallcomponentsinvolvedwith

, (ii) The various processes for the cycre on the T-s diagram.:.: : ' And.AtsoFind:

(iii) Stagnation temperature and pressure. i

::

.'(vr)P.owercontributedbycoo1ingturbine.',:'..'(vii) COP of the arrangement.

!fr'r/nx is Kyoto protocol? What do you r-nderstand by " fotal equivalent warmingimpact"?

ffr)Meation the main properties to be considered while choosing a right relligerantfor a refrigeration system.

(iv) Discuss the antifreeze, soiutions and refrigerant dying agents with their purpose.pfHow the inorganic and hydrocarbon refrigerants are designatedz e*jruin n ,

Ammonia, water, air, carbon dioxide, methane, ethane, propane, butzure.

F) wnt R-12 system is susceptihrle to expansion varve freez up?(vii) State how will you carry out "reak detection,, in the refrigerants (i)

Amrnonia (i0 R-12

4x4= 16

(iii)

(iv)

.

1Aes. solve ro

given:

Inside design cqndition: 25 oC DBT ,SIyoRH .

Outside aircondition:43 oC DtsT, 27 )CWBT

Room sensible heat gain: 40 kWRoom latentheat gain: l0 kWBy pass factor: A.2

The return air from the room is mixed with outside air before enlry to the cooling coilin rhe ratio 3:l by weight. Deiermine(i) aOp of cooling coil

(1i) entry and exit conditions of air for cooling coil(iii) Dehumidified air quantitv.

(rv) Fresh air mass flow rate and vorume flow rate(v) Rgfrigeration load on the cooling coil . . . .

:,.,16/ In aadiabatic mixing chamber designed byrMayant Sfour-u of NIT Raipur 0 2 kg/r:;

'lr"itt arr at 45 oc (DBT) and r 0 % RH is mixed with 0.3 kg/s of rnoJ;;; ;;;;;

a humiditv rutio of 0'01s kgwlkgda in an adiabatic mrxrng-chamber-*;i;;,rrlr;'

T':o:t. ir heated to a final temperature or40 o"

"r,4 ";r.;';;;i" n"ut transfer

:1r:t".*.:eater and RH of air a*he exit of heater. Assume the barometri;;;.#;;

and psychrometric diagrams r"Or"rrnr*, ;il;;;right sug$estion? Justlfv. rl : '---'-''|.-1'

lr-:

16Eh{D,:

'4

(OK(t30Code: MEl28l2

\le CSVTU Page 1 of4

B.Tech (Eighth Semester) Examination April-May 2012Subject: Refrigeration & Air Conditioning

Branch: Mechanical EngineeringTime: Three Hours Maximum Mark:80

Minimum Pass Mark: 28Note:

(D Atternpt all parts of a question in continuity.(ii) All questions are compulsory and carry equal marks.(iii) Assume suitable data, if necessary.(iv) Use of refrigeration and air conditioning data book and psychrometric tables and

charts are permitted.(v) Students are here by advised to use preferably refrigeration and psychrometric

properties tables and chart by Mathur & Mehta published by Jain Brothers.(vi) Stadents are also advised to enclose the psychrometric chart or refrigerants

properties chart that has been usedfor solving the problem at proper place withanswer sheet.

Q.1, Solve flny one out of a and b.

a. In the boys hostel of MT Raipur an ammonia vapor-compression refrigeration system

is used which has two separate compartments one for chilled food storage and other for

frozen food storage. The system has two evaporators, one is to provide 20 tons ofrefrigeration at -35oC and another evaporator is to provide 40 tons of refrigeration at

-10oC the system uses two stage compression with flash inter cooling. The condensing

temperature is 35"C and superheat at low stage compression suction valve is 10oC.

Calculate.

1. Mass flow rate of refrigerant through each evaporator.?. Power required by each compressor if compression index is 1.3 for both the

compresso{s.

3. Fiston displacement of each compressor if clearance is 6 percent.

t6b. In an assignment ofjob Abhishek Jain was asked to design a system that uses separate

compressor with multiple expansion valves, using Freon 12 as refrigerant to serve

three evaporators at different loads and temperatures as shown below:

I't -Evaporator 30 tons at -5 oC

Ilnd-Evaporator 20 tons at -10 oC

III'd -Evaporator 10 tons at - 35 oC

Condensing temperature 40 oC

Calculate (i) mass flow rate of refrigerant through each evaporator.

(ii) theoretical piston displacement of each compressor and.

(iiD power required by the system

16

CSVTU Page2 of 4 Code: M812812

Q.2. Solve any one oat of a and b.

a. The following data refers to a reduced ambient air refrigeration system used for an

aircraft. Speed of aircraft = 1500 kmph; Ambient pressure = 0.g bar. AmbientTemperature = 5oC; Ram effrciency = 100% Pressure of cooled air leaving the firstCooling turbine : 0.8 bar. Temperature of cooled air leaving the heat exchanger =100'C. Pressure ratio of main compressor = 3. Pressure loss between the outlet ofsecond cooling turbine and the cabin =0.1 bar; Temperature in the cabin = ZZ"C;Loadin cabin = l0 TR; Isentropic efficiency of compressor = 85Zo; Isentropic efficiency ofboth cooling turbines :80%o.

Find:

(l) Mass flow of air passing through the second cooling turbine.(2) Quantity of ram air passing through the heat exchanger, if the rise in temperature islimited to g0 K.(3) COP of the system.

16b. An aircraft is cruising with a speed of 1000 kmlhr at an altitude of g000 meter, where

the ambient conditions, pressure and temperature are 0"35 bar and -l5oC respectively.The cabin of plane is maintained at 25nC by using simple air refrigeration system. Thepressure ratio of compressor is 3. The air is passed through heat exshanger aftercompression and cooled to its origina! oondition entering into the plane. In heatexchanger pressure loss of 0.1 bar takes place. The pressure of air leaving of thecooling turbine is 1.06 and the air pressure in the cabin is 1.0i3 bar. Consiclering thetotal cooling load of plane is 70kW. Draw the schematic sketch and T-S diagramDetermine:

(a) Stagnation temperature and pressure(b) Mass flow rate of air circulated through the cabin,(c) Volume handled by the compressor and expander.(d) Net power delivered to the refrigeration system and c.o.p. ofthe system.

l6Q.3. Solve any one out of a and b

a. Explain the following Indices for thermal comforti. The mean radiant temperafure Tn,,,,

ii. Effective temperature (ET):iii. Operative temperature (T ):

Draw the comfort chart and explain uuo,llthe region where summer and winter comfortzones overlaps.

l6

CSVTU Page 3 of4 Code: MEl2812

b. Explain the Ozone depletion and global warming issues. Discuss why CFC refrigerants

are to be phased out. List the alternative refrigerants.

16

Q.4. Solve any (a+b) or c.

a. On a moderate day at NIT campus the dry bulb temperature of atmospheric air reads

35"C while wet bulb temperature reads 22oC. The barometric pressure reads 760 mm

Hg. Calculate by the first principle assuming that you do not have the psychometric

charfi (i) The relative humidity (ii) Specific humidity (iii) degree of saturation (iv) dew

point temperature. The saturation pressures at 35oC and 22"C are 0.05622 bar and

0.02642bar.

08

b. An air conditioning plant is required to supply 60 m3 /min of air at a DBT of 2l oC and

55% RH. The outside air is at DBT of 28oC and 60% RH. Determine the mass of the

water drained per min, and capacity of cooling coil. Assume the plant to dehumidiff the

air first and then to cool the air.

08

Outdoor condition= 38 oC DBT and 28 oC wBT

Room Sensible Heat load:46.4 kW

Room Latent heat load: 11.6 kW

Quantity of infiltration: 1200 m3 /hr

ADP = l0 oC, Quantity of recirculate d ab : 60a/o

If the quantity of recirculated air is mixed with conditioned air after the coolins coil

find:

(l) Condition of air leaving the coil

(2) Condition of air entering the hall.

(3) The mass flow rate of air entering the cooler

(a) The mass flow rate of total air passing through the hall.

(5) By-pass factor

(6) The refrigeration load on the cooling coil in TR.

16

CSVTU

Q.5. Solve

Page 4 of4Code: MEl2gt2

respectively:Lights anO"A 75 \M and 45 W

fflilHffilfatn'ri l;33iw

Bt;;fffifforffi- L 80.m3/min

*:"Trj#":o"\:*ffi *@,,ulione-thirdorrreshairares;flb"'o,""ute,inon""ooiiii-iiir,:;;;fi #lfi ffi "#:lf,:.ff :x.:'J,fr lffiDetermine:

1. Apparatus dew point2. Room sensible heat load3. Room latent heat load4. Room sensible heat factor5. Coil sensible heat load6. Coil latent heat load7. Coil sensible heat factor8. Effective sensible heat factor

A conference room folseatlng 80 persons is proposed in administrative buildihg ofNITRaipur The data rerated t" th";;p"Jloor is given berow.Inside design condition: ^^ ^_ _out iiJ. o'ilie,i."iiijlit ??:9!!r ss r0 RHs*"uir""Jl?it#r'"jir"lm 38 oc osr, zs oCilnr

t6

END

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