DEPARTMENT OF MECHANICAL ENGINEERING Academic Year 2014-15
ME 6404
– Terma! e"#i"eeri"# $%e&'i(" )a"*
1
+'a, I"-Car#e Head-Meca"ica!
NIT 1. GA+ (r AIR PO/ER CYCLE+ 1 De"e Term(d"amic cc!e
Thermodynamic cycle is defned as the series o processes perormed on the system, so that energy transer takes place (heat and work) and the system attains its initial state. 2 /a' i& Air &'a"dard (r Air 3(er cc!e&
I air is used as working substance in the thermodynamic cycles, it is called air standard or air power cycles. /a' i& 'e di,ere"ce 7e'ee" 'e Ga& 3(er a"d 8a3(%r 3(er cc!e
In gas power cycle, working medium is undergone dierent processes without phase change. !hereas in a "apour power cycle the working medium is undergone dierent processes and energy transer takes place due to phase change. 4 /a' are 'e a&&%m3'i("& made 9(r air &'a"dard cc!e a"a!&i& 4 Li&' (%' a" 9(%r a&&%m3'i("& 'a' are made i" 'e a"a!&i& (9 air &'a"dard cc!e&
•
the working medium is preect gas throughout i.e. it ollows #$%m&T The working medium has constant specifc heats The working medium does not undergo any chemical change throughout the cycle The compression and e'pansion processes are re"ersible adiabatic i.e. there is no loss or gain in entropy. inetic and potential energies o the working uid are neglected The operation o the engine is rictionless
•
*eat is supplied and re+ected in a re"ersible manner.
• • • • •
5 Name 'e 8ari(%& :#a&; air 3(er cc!e&
arnot cycle, -tto cycle, iesel cycle, ual cycle and /rayton cycle 6 /ri'e 'e 9(%r 3r(ce&&e& i" &e<%e"ce 9(r a" Air 3(er cc!e
i) 0uction process induction o resh charge into cylinder ii) ompression and ombustion process iii) #ower output or 2'pansion process i") *eat re+ection and 2'haust process 3. /a' i& ca!!ed Reci3r(ca'i"# meca"i&m 4echanism which is used to con"ert the reciprocating or linear motion o a piston into rotary motion o crank shat and "ice "ersa = /a' are 'e 7a&ic c(m3("e"'& (9 a Reci3r(ca'i"# meca"i&m 5
i) ylinder ii) #iston iii) onnecting rod i") rank and crank shat > /a' i& 'e +'r(*e
It is the ma'imum displacement o piston during the mo"ement between T and / or "ice "ersa 10 /a' i& 'e +'r(*e (r +e3' 8(!%me
It is the theoretical "olume o charge will be inducted or the mo"ement o piston rom T to / during the suction stroke 11 /a' i& 'e C!eara"ce 8(!%me
It is "olume e'ist between engine head and T (Top ead entre). 12 De"e C(m3re&&i(" ra'i(
It is ratio between "olume o the cylinder beore starting o compression and "olume o the cylinder at the end o compression. RC
=
Compression Ratio =
Volume of the cylinder before starting of compression V1 = Volume of the cylinder at the end of compression V2
1 E?3re&& 'e c(m3re&&i(" ra'i( i" 'erm& (9 c!eara"ce a"d &'r(*e 8(!%me&
$1 % Total "olume o the cylinder % $0 6 $ % 0troke "olume 6 learance "olume RC
=
Compression Ratio = VS
+
VC
VC = 1+ VS VC
$5 % $ % learance "olume
14 P!(' 'e P-@ a"d T-+ dia#ram (9 O''( cc!e
15 /a' i& 'e e?3!(&i(" ra'i(
α
=
!plosion ratio =
Pressure at the end of constant volume heat supplied process = Pressure at the starting of constant volume heat supplied process
16 +*e'c 'e Die&e! cc!e i" 3-8 a"d T-& dia#ram 7
P2' P2 %
1 /ic cc!e i& m(re eBcie"' 9(r 'e &ame c(m3re&&i(" ra'i( a"d ea' i"3%' O''( cc!e (r Die&e! cc!e
8or the same compression ratio and heat input, -tto cycle is ha"ing more e9ciency than iesel cycle 1= /ri'e 'e e?3re&&i(" 9(r eBcie"c (9 'e (''( cc!e η "tto cycle
=
1#
1
( RC )
γ
#1
& % ompression ratio 1> /a' i& 'e c(m3re&&i(" ra'i( 9(r Pe'r(! e"#i"e
ompression ratio or petrol engine is : to 1; 20 /a' i& 'e c%'-(, ra'i( a"d ri'e i'& &i#"ica"ce
ut
ratio Cut off =
Volume of the cylinder at the end of fuel in%ection = Volume of the cylinder at the starting of fuel in%ection
V$ V2
!hen cut o ratio increases e9ciency o iesel cycle decreases 21 E?3re&& 'e c%'-(, ra'i( (9 a Die&e! cc!e i" 'erm& (9 'em3era'%re& ρ
= Cut off ratio =
V$ V2
=
&$ &2
=s cut o period takes place during constant pressure process, "olume is directly proportional to temperature. 22 /a' i& 'e ra"#e (9 c(m3re&&i(" ra'i( 9(r +I a"d die&e! e"#i"e
8or petrol o 0I engine (petrol engine) & is : to 1; 8or diesel engine 15 to 1> 2 /ri'e a" 9(%r di,ere"ce& 7e'ee" O''( a"d Die&e! cc!e
0l,.?o 1
-ttoycle ieselycle -tto cycle consist o Two iesel cycle consist o two @
5 7 @
isentropic and two constant "olume processes *eat a ddition t akes p lace in constant "olume process 29ciency is more than diesel cycle or the same compression ratio ompression ratio is eAual
adiabatic, one constant "olume and one constant pressure processes *eat addition takes place in constant pressure process
to e'pansion ratio
greater than e'pansion ratio
29ciency is less than -tto cycle or the same compression ratio ompression ration is
24 /a' i& 'e &imi!ari' 7e'ee" Die&e! a"d D%a! cc!e
/oth cycle used in I (compression Ignition) engine 25 /a' are 'e ('er "ame& (9 D%a! cc!e
Bimited pressure cycle 26 /a' are 'e ad8a"'a#e& (9 D%a! cc!e (8er Die&e! cc!e
In ual cycle cut o ratio is smaller than diesel cycle and compression ratio o dual cycle is less than iesel cycle hence siCe o the engine working with ual cycle is 2 /a' i& 'e ra"#e eBcie"c (9 a Die&e! cc!e
iesel cycle e9ciency is about 7;D 2= C(m3are 'e c(m3re&&i(" ra'i( (9 a Die&e! i' 'a' (9 D%a! cc!e
ompression ratio o iesel cycle in the range o 5; to 5E whereas compression ratio o the ual cycle is in the range 15 to 1: 2> /a' i& 'e re!a'i(" 7e'ee" c(m3re&&i(" ra'i( a"d e?3a"&i(" ra'i( 9(r O''( cc!e
8or -tto ycle compression ratio is eAual to e'pansion ratio 0 / i& D%a! cc!e ca!!ed a& Limi'i"# 3re&&%re cc!e
#ressure attained at the end o compression stroke o a ual cycle is limited to a smaller "alue compare with that o iesel cycle. *ence ual cycle is called as Bimited pressure cycle. 1 Dra 'e P-@ a"d T- + dia#ram (9 D%a! cc!e
2 Di&c%&& 'e c(m3re&&i(" ra'i( (9 a" O''( Die&e! a"d D%a! cc!e& .
& or -tto cycle is between : to 1; E
Rc or iesel cycle is between 5; to 5E
& or ual cycle is between 15 to 1: F(r 'e &ame c(m3re&&i(" ra'i( a"d ea' reec'ed ic (9 'e 9(!!(i"# cc!e i& 'e m(&' eBcie"' . O''( Die&e! (r D%a! E?3!ai" i' 3-8 a"d T & dia#ram&
8rom # $ diagram work output rom -tto cycle is greater than ual ycle which work output is greater than iesel cycle.
η "tto cycle
> η 'ual cycle
( η 'iesel cycle
*ence 4 /a' i& 'e eBcie"c (9 a" O''( cc!e ic i& a8i"# c(m3re&&i(" ra'i( i& 10 5 /a' i& 'e e,ec' (9 air &'a"dard eBcie"c (9 Die&e! cc!e i' c(m3re&&i(" ra'i( a"d c%' (, ra'i(
29ciency increases with the increase in compression ratio and "ice<"ersa. The e9ciency decreases with the increase in cut o ratio and "ice<"ersa. 6 De"e Mea" e,ec'i8e 3re&&%re (9 a" IC e"#i"e
4ean eecti"e pressure is defned as the constant pressure acting on the piston during the working stroke. It is also defned as the ratio o work done to the stroke "olume or piston displacement "olume. /a' i& 'e ('er "ame #i8e" '( (''( cc!e
onstant "olume cycle. = De"e 'e 9(!!(i"# 'erm& i" 'e Air +'a"dard cc!e- i Air &'a"dard eBcie"c ii +3ecic (r* 'ra"&9er iii +3ecic air c("&%m3'i(" a"d i8 (r* ra'i( • •
•
=ir standard e9ciency is defned as the ratio o network transer during the cycle to the net heat transer to the cycle 0pecifc work transer is the work transer per unit mass o working substance 0pecifc consumption theow Auantity o working working substance substance or reAuired or doingair work transer oristhe ratio o unit power. :
•
!ork ration% ?et work transer in a cycleFpossible work transer in cycle
> /a' i& 'e di,ere"ce 7e'ee" 'e Ga& T%r7i"e 3(er 3!a"' a"d IC E"#i"e&
Gas turbine cycle is ha"ing rotary compressor whereas I engine cycles are using reciprocating compressor 40 Dra &cema'ic dia#ram 9(r )ra'(" cc!e
41 Dra P@ a"d T& dia#ram (9 )ra'(" cc!e
42 /a' are 'e me'(d& '( i m3r(8e 'e eBcie"c (9 a )ra'(" cc!e
To increase the e9ciency o /rayton cycle the ollowing modifcations are to be pro"ided i) Intercooler ii) &eheater iii) &egenerator 4/a' are 'e e,ec'& (9 i"'r(d%ci"# re#e"era'(r i" 'e 7a&ic #a& '%r7i"e cc!e
i. The uel economy is impro"ed. The Auality o uel reAuired per unit mass o air is less ii. The work output rom turbine, the work reAuired to the compressor will not change. 3
iii. #ressure drop will occur during regeneration i". It increased thermal e9ciency when the turbine operates at low
% =ctual internal work F !ork o isentropic e'pansion !ork o isentropic compression F =ctual internal work
ηcompressor %
45 C(m3are 'e Die&e! a"d )ra'(" cc!e&
ieselcycle 1. It consist o two isentropic, one constant "olume and one constant pressure processes 5. *eat is re+ected at constant "olume 7. Hsed in iesel engines
/raytoncycle 1. It consist o two isentropic, one constant pressure processes 5. *eat is re+ected at constant pressure 7. Hsed in gas turbines
46 / )ra'(" cc!e i& %&ed i" #a& '%r7i"e
Inside the turbine the gas is continuously owing in the processes are ow processes. 0ince the processes has been used asall the cycle or gasin"ol"ed turbine. in /rayton cycle is ow process, it
PART ) 1. = 0i'
kFkg. J4=OK;7M 7. In an oil engine working on dual cycle, the heat supplied at constant pressure is twice that o heat supplied at constant "olume. The compression and e'pansion ratios are > and E.7. The pressure and temperature at the beginning o cycle are ;.L7 bar and 53;. 8ind the e9ciency o the cycle and mean >
eecti"e pressure. Take p % 1.;;EkFkgN " % ;.31>kFkg. J=nna Hni". 4ayFune 5;17M @. The pressure, temperature and "olume o air at the beginning o dual cycle are 1.;7bar, 7E; and 1E;liters respecti"ely. The "olume ater compression is 1;liters @5k o heat is added to constant "olume and :7k at constant pressure. etermine air standard e9ciency, clearance and cut o percentages. J=#&KL>M E. In a /rayton cycle, the air enters the compressor at 1 bar and 5E;. The pressure o air lea"ing the compressor is 7 bar and temperature at turbine inlet is :E;;. etermine per kg o air JiM ycle e9ciency JiiM *eat supplied to air JiiiM !ork input Ji"M *eat re+ected in the cooler and J"M Temperature o air lea"ing the turbine. J4=OK;7M :. In an air standard diesel cycle, the pressure and "olume at the beginning o compression are 1;;k#a and ;.;7m7 respecti"ely. #ressure ater Isentropic compression is @.54#a and ater isentropic e'pansion is 5;;k#a. etermine JiM ompression ratio JiiM utkFkg. J?-$K;@M 3. onsider a stationary power plant operating on an ideal /rayton cycle. The pressure ratio o the cycle is > and the gas temperature at the compressor inlet and turbine inlet are 53; Q 1;53; respecti"ely. etermine the ollowing JiM Gas temperature at the compressor and turbine e'it, JiiM /ack work ratio, and JiiiM Thermal e9ciency. =ssume pr1 % 1.7>: and pr7 % 77;.L. !here pr is the relati"e pressure. J=#&K;EM >. 2'plain a iesel cycle. J=nna Hni". =pr. ;EM L. eri"e an e'pression or the thermal e9ciency o an ideal diesel cycle. J=nna Hni". =pr. ;EM 1;. 0how the dual cycle on p<" and T
13. JaM The mean eecti"e pres sure o an ideal diesel cycle is > bar. The initial pressure is 1 bar and compression ratio is 15. etermine the cut o ratio and air standard e9ciency o the cycle. JbM iscuss the eects o operating "ariables on cycle analysis. J>M J=H., ?o".Fec. 5;1;M 1>. The minimum pressure and temperature in an -tto cycle are 1;; pa and 53S. The amount o heat added to the air per cycle is 1E;; Fkg. JaM etermine the pressure and temperature at all points o the air standard -tto cycle. JbM =lso calculate the specifc work and thermal e9ciency o the cycle or a compression ratio o >1. Take or air " % ;.35 Fkg and P % 1.@. J=H., 4ayFune 5;11M 1L. =n I engine operating on the dual cycle the temperature o the working uid JairM at the beginning o compression is 53S. The ratio o the ma'imum and minimum pressure o the cycle is 3; and compression ratio is 1E. The amounts o heat added at constant "olume and constant pressure are eAual. ompute the air standard thermal e9ciency o cycle. 0tate three main reasons why the actual thermal e9ciency is dierent rom the theoretical "alue. J=H., 4ayFune 5;11M 5;. an air standard diesel cycle has a compression ratio o 1>. The pressure at the beginning o compression stroke is 1 bar and the temperature is 7;S. the heat supplied is 1>;; Fkg. (1) The 29ciency (5) #ressure and temperature at all salient points (7) *eat re+ected (@) mean eecti"e pressure J=H., ?o"Fec 5;17M (b) an air standard otto cycle has a compression ratio o 3. The pressure at the beginning o compression stroke is 1 bar and the temperature is @;S. the heat supplied is 5E1; Fkg. (1) The 29ciency (5) 4a' #ressure and temperature (7) !ork done per o air (@) 4ean eecti"e pressure J=H., ?o"Fec 5;17M 51. =n engine works on a otto cycle. The initial pressure and temperature o the air is 1 bar and @; ;. >5E o heat is supplied per kg o air at the end o compression. 8ind the temp and pressure at all salient points i the compression ratio is :. =lso fnd the e9ciency and mean eecti"e pressure or the cycle. =ssume air is used as working uid and take all idle conditions (b)=n gas turbine works on air standard brayton cycle. The pressure at the beginning o compression stroke is 1 bar and the temperature is @;S. the am' temperature and pressure is limited to 7bar and :E;;. determine (1) The 29ciency (5) 2'haust temperature (7) !ork output 1;
(@) *eat supplied and re+ected per kg o air. J=H., ?o"Fec 5;1@M 55. =n engine works on a otto cycle has an air standerd e9ciency o E:D and re+ects E@@Fg o air. The pressure and temperature o the air is ;.1 4pa and :;;. (1) ompression ratio o the engine (5) #ressure and temperature at the end o compression (7) !ork done per o air (@) 4a' pressure in the cycle (b) raw the actual and theortical #$ diagrams o a our stroke diesel engine and compare them. J=H., =prF4ay 5;1EM
NIT 2- I C ENGINE+ 1 /a' i& e" #i"e 11
!hich system con"erts heat into mechanical work is called as 2ngine. 2 /a' i& maci"e
!hich system con"erts any orm mechanical and electrical energy into mechanical work is called as 4achine. /a' i& 'e ( r*i"# 3ri"ci3!e (9 A %'(m('i8e I C E"#i"e &
=utomoti"e I engines are working in the reciprocating mechanism principle. 4 /a' are 'e mai" c(m3("e"'& (9 a Reci3r(ca'i"# meca"i&m
ylinder, piston, connecting rod, crank and crank shat are the main components o a reciprocating system. 5 H( IC e"#i" e& are c!a& &ied 7a&ed (" c("&'r%c'i("
/ased on the construction, the I engines are classifed as @ stroke and 5 stroke engine. In @ stroke engine "al"es and "al"e actuating components are pro"ided whereas in the a stroke engine there is no "al"es, only ports are pro"ided in the cylinder. 6 H( IC e"#i" e& are c!a& &ied 7a&ed (" 'e i#"i 'i(" me'(d&
/ased on the ignition o uel, I engine are classifed as 0park ignition (0I) engine and ompression ignition (I) engine. In 0I engine carburettor and spark plug is pro"ided where as in I engine uel pump and uel in+ectors are pro"ided. H( IC E"#i"e& are c!a&&ied 7a&ed ( " 9%e!
/ased on the uel, I engines are classifed as #etrol engine and iesel engine. = H( IC E"#i" e& are c!a&& ied 7a&ed (" a33!ica 'i("&
/ased on applications, I engines are classifed or automoti"e "ehicles which are mo"ing whereas I engines used or stationary applications like or (electricity) power production and run the pump in the agricultural orms. > Name 'e di,ere"' c(m3("e"'& (9 a 8a!8e ac'%a'i"# &&'em (9 a 4 &'r(*e e"#i"e
am on the cam shat, ollower rod, rocker arm "al"e stem, "al"e spring are the components o actuating the "al"es. 10 /a' ar e ' e ma i" 3r (ce&&e& 'a *i"# 3! ace i" ( "e c c!e (9 (3era'i(" (9 a" I C E"#i"e
The processes taking during one cycle o operation o an I engines are 1) 0uction o resh charge inside the cylinder 5) compression o uel charge to increase its pressure and temperature 7) combustion o uel charge and e'pansion o high pressure and high temperature gas (power stroke) @) e'hausting o waste gas. 11
/a' i& 'e 3%r3(&e (9 di,ere"' 3i&'(" ri"#& i" 'e 3 i&'("
#iston rings are used gi"e the grip with cylinder to pre"ent the resh uel charge should not leak rom combustion chamber to crank case. 15
12 /a' i& 'e re!a'i(" 7e'ee" &'r(*e !e"#' a"d cra"* radi%&
0troke length B % 5crank radius r 1
De"e &'r(*e (r &e3' 8(!%me (9 a" IC E"#i"e
0troke or 0wept "olume is the theoretical "olume o the resh charge inducted into the cylinder during suction stroke. $
n m 2 ' ) , -. s '# /ore of the cylinder or Piston dismeter in m
Stro)e or S*ept volume =
π
# Stro)e length in m0 n = no of po*er stro)e = for 2 stro)e engine n=
for , stro)e engines0 # speed in rpm 2 ) # no of cylinder
14
/a' i& 'e '3e (9 9%e! %&ed i" +I e"#i"e
In 0I engine, uel with low "iscosity and low density uels with low fring can be used. 15
/a' '3e (9 9%e! c a" 7 e %&ed i " CI e "#i"e
In I engine, uel with high "iscosity and high density uel can be used. 16
/a' i& mea"' 7 4 &'r(*e e"#i"e
In @ stroke engine all the suction, compression and combustion, power and e'haust processes are taking place one ater another in @ stroke mo"ement ( 5 re"olution o crank shat) o piston. 1
/a' i& 'e 2 &'r(*e e"#i"e
In 5 stroke engine all the suction, compression and combustion, power and e'haust processes are taking place in 1 re"olution o crank shat or 5 stroke mo"ement o the piston takes place. 1= / c( m3re&&i(" ra 'i( (9 a + I e" #i"e & (%!d 7e * e3' !( c(m3ared '( CI e"#i"e
I compression ratio o a 0I engines is high then resh charge which contains air and uel mi't ure will gets igni ted on its own called pre< ignition due to high temperature due to high compression ratio. *ence compression ratio fr 0I engines are kept low > to 1;. 1>
/a' i& 'e e,ec' (9 i# c(m3re&&i(" ra'i( (9 a CI E"#i"e
*igh compression ratio in I engine causes the rapid atomiCation o diesel and rapid increase in temperature to start the ignition. 20 /a' are 'e c(m3("e"'& i" 'e +I e"#i"e 9(r 'e c(m7%&'i(" (9 9%e!
omponents or the combustion o uel in the 0I engines are carburetor and spark plug. 21 /a' are 'e c(m3("e"'& %&ed 9(r 'e c(m7%&'i(" (9 9%e! i " 'e CI e"#i"e 17
In the I engines, or the combustion uel, uel pump and uel in+ector are used. 22
/a' i& De'("a'i(" (r *"(c*i"# i" +I e"#i"e
4ultiple ame ront started due to auto ignition o uel ad+acent to the cylinder walls causes the collision o ame ronts and collide with cylinder walls create "ibration in the cylinder and causes the large sound. This is called etonation or knocking. This uncontrolled and une"en combustion causes the engine gets damage. 2
/a' are 'e e,ec'& (9 de'("a'i(" i" +I e"#i"e
etonation or knocking causes the "ibration and collision o"er the cylinder with bell sound causes the engine cylinder and other parts like "al"e seat gets damage. 24
/a' i& a%'( i#"i'i("
$ery hotness o the cylinder walls which is due to deposition o unburned carbon particles causes the uel ad+acent to the cylinder walls gets fring without spark rom the spark plug is called auto ignition. 25
/a' i& 3re i#"i'i("
ue to high compression ratio, the uel and air charge inducted into the cylinder during suction stroke gets fred or ignited beore electric spark is introduced into cylinder is called pre ignition. 26
E?3!ai" Oc'a"e N%m7er
-ctane number indicates the ability o uel resists the detonation or knocking. 2
E?3!ai" 'e I#"i'i(" d e!a i" CI e"#i"e
Ignition delay is the duration starts rom the time o uel in+ection to time o uel gets igni ted. Ignition delay consists o physical delay and chemical delay. 2= /a' ar e ' ( ' 3e& (9 de !a 3e ri(d d%ri"# c(m7%&'i(" (9 9%e! i" 'e CI e"#i"e
physical delay and chemical delay are the two delay period during combustion in I engine. 2>
/a' i& 'e 9%e! i"ec'(r
8uel in+ector is used in diesel engine to in+ect and atomiCe the diesel at the end o the compression stroke. 0 /ri'e a" 9(%r ma(r di,ere"ce& 7e'ee" '( &'r(*e a"d 9(%r &'r(*e IC e"#i"e T( &'r(*e cc!e F(%r +'r(*e cc!e e"#i"e e"#i"e
-ne cycle is completed in two stroke o the piston or one re"olution o the crank shat.
-ne cycle is completed in our stroke o the piston or two re"olution o the crank shat.
1@
8or the same speed, twice the number o power strokes are produced than @ stroke engine. Turning moment is more uniorm and hence lighter ywheel is used. It contains ports which is operated by the piston mo"ement. 1
8or the same speed, hal o the number o power strokes are produced than 5 stroke engine. Turning moment is not uniorm and hence bigger ywheel is used. It contains "al"es which is operated by "al"e mechanism.
/ a' i& mmeans ea"' 7 CI E"#i"e ignition / i' iengine. & ca!!edIn&( Iengine compression I engine the uel
is in+ected by a uel in+ector in atomiCed orm because o high compressed air it gets ignited automatically. *ence it is called as compression ignition engine. 2
/a' i& a '( &'r(*e e"#i"e
= two stroke engine is an engine in which one cycle o operation is completed in two stroke o the piston or one re"olution o the crank shat.
/a' i& a 9(%r &'r(*e e"#i"e
= our stroke engine is an engine in which one cycle o operation is completed in our stroke o the piston or two re"olution o the crank shat. 4
Name 'e 9(%r &'r(*e& (9 a" IC e"#i"e
0uction, compression, power and e'haust stroke. 5
Di,ere"'ia'e 3e'r(! a"d Die&e! e"#i"e& Pe'r(! (r +I e"#i"e& Die&e! (r CI e"#i"e
1. ombustion o air uel mi'ture takes place by spark produced by sparkplug. 5. arburetor is used to mi' the air uel mi'ture. 7. ompression ratio "aries rom : to >.
1. ombustion compressed air.
takes
place
@.It works on -tto cycle.
@. It works on iesel or ual cycle.
by
high
5. 8uel in+ector is used to in+ect the uel in atomiCed orm. 7. ompression ratio "aries rom 15 to 1>.
6 /ri'e 'e im3(r'a"ce (9 !(ad 'e&' c("d%c'ed i" 'e I C E"#i"e&
Boad or perormance test to calculate and analysis dierent e9ciencies (/rake thermal, Indicated thermal, mechanical and "olumetric e9ciency). /ri'e 'e di,ere"ce 7e'ee" )ra*e 3(er a"d I"dica'ed 3(er
/rake power is the actual power a"ailable at the brake shat or any useul output. Indicated power is the theoretical power de"eloped at the piston. =
De"e 8(!%me'ric eBcie"c (9 a" I C e"#i"e 1E
It is the ratio between the actual "olume o resh charge inducted into the cylinder during suction stroke and theoretical "olume or stroke or swept "olume o resh charge inducted. >
/ri'e 'e di,ere"ce 7e'ee" TFC a"d + FC TFC is the Total Fuel Consumption in kgFs and +FC is the +pecifc Fuel Consumption is the consumption o uel to de"elop unit power output
in kgF k!hr. 40
F(r 'e !(ad 'e&' c("d%c'ed (" I C e"#i"e 'e '(r<%e (9 500
000 41Nm a"d E?3&3eed !ai" '(9 eM ea" Er3m ,ec'iCa!c%!a'e 8e Pre&&%'e re )ra*e 3(er
It is the a"erage pressure acting on the piston with same work output as in the air standard cycle with same stroke "olume. It is the ratio between work output and stroke "olume.
42
/ri'e 'e im3(r'a"ce (9 H ea' 7a!a"ce 'e&' ( " a " IC E"#i"e
*eat balance test to calculate the D o heat utiliCed in useul output, D o heat taken by the cooling water, D heat carried by the e'haust gas and D heat loss due to conduction through engine body out o total heat input by burning uel. 4
/a' i!! 'e ma&& (9 e?a%&' #a& 9r(m 'e IC e"#i"e
3ass flo* rate of air and mass flo* rate of fuel consumption is the input to the engine1 4s per the 3ass conservation mass of input e5uals to mass of output1 6ence mass flo* rate of e!haust gas is the sum "f 3ass flo* rate of air and mass flo* rate of fuel consumption1
me m9 ma
PART ) 1. = simple +et carburetor is reAuired to supply E.E kg o air per minute and ;.: kg o uel per minute. The density o uel is 3E;kgFm7. The air is initially at 1 bar and 7;;. alculate the throat diameter o the choke or a ow "elocity o LEmFs. The "elocity coe9cient is taken as ;.3>. I the pressure drop across the uel metering orifce is ;.3: o that at the choke, calculate orifce diameter assuming d % ;.:5.
5. The throat diameter o a carburetor is >;mm and noCCle diameter is :mm. The da % ;.>E and d % ;.3. The noCCle lip is :mm. The pressure dierence causing the ow is ;.1bar. 8ind JaM =ir<uel ratio supplied by the carburetor neglecting noCCle lip. JbM =ir<uel ratio considering noCCle lip and JcM The minimum "elocity o air reAuired to start the uel ow. ?eglect air< compressibility. Take Ua % 1.5kgFm7 and U % 3E;kgFm7 7. =ir uel ratio o a mi'ture supplied to an engine by a carburetor is 17. The uel consumption o the engine is 3.EkgFhr. The diameter o the "enture is 5;mm. 8ind the diameter o uel noCCle i the lip o the noCCle is @mm. Take the ollowing data U % 3E;kgFm7, da % ;.>;, d % ;.3 and atmospheric pressure % 1.;17bar and temperature % 53;. 1:
@. The "enture o a simple carburetor has a throat diameter o 5;mm and the coe9cient o ow is ;.>. The uel orifce has a diameter o 1.1@mm and coe9cient o uel ow is ;.:E. The gasoline surace is Emm below the throat, calculate JiM The air<uel ratio or a pressure drop o ;.;>bar when the noCCle lip is neglected. JiiM The air uel ratio when the noCCle lip is taken into account. JiiiM The minimum "elocity o air or critical air "elocity reAuired to start the uel ow when the noCCle lip is pro"ided. =ssume the density o air and uel to be 1.5kgFm7 and 3E;kgFm7 respecti"ely. J=nna Hni". ?o".K;7M E. = single cylinder our stroke diesel engine, ha"ing a swept "olume o 3E;cm7 is tested at 7;;rpm. !hen a braking torAue o :E?;mm 2ngine rpm % @>;rpm 2ecti"e brake load %5Ekg 2ecti"e brake radius % ;.@Em etermine JiM Indicated m.e.p. JiiM Indicated power, JiiiM /rake power and Ji"M 4echanical e9ciency. 3. = rope brake has a brake wheel diameter o 3E;mm and the diameter o the rope is >mm. The dead load on the brake is 53E? and spring balance reads 7E?. I the engine rpm is @>;, fnd the brake power de"eloped. >. = si'
gas % 1;;EkFkg 2'haust gas temperature % @;E; &ope diameter % 5 cm etermine indicated power, brake power, mechanical e9ciency and draw a heat balance sheet on hour basis. J=nna Hni". 4ayFune 5;17M 11. raw the typical portM. J4ay 5;1@M JiiM raw and e'plain the #ort Timing diagram o two stroke cycle diesel engine. J>M J=nna Hni". 4ayFune 5;17M 17. 2'plain how knocking takes place in diesel engines and discuss the "arious methods o controlling it. ompare the knocking in diesel engines with that o the petrol engines. J=nna Hni". ?o".K;7M 1;;. iscuss the signifcance o "arious actors aecting ame speed in 0I engines. J=nna Hni". ?o".K;7M. 1@. JaM iscuss in detail the "arious types o uel supply systems o a I engine. J>M JbM ompare and contrast petrol and diesel engine. J>M J=H. ?o"Fec. 5;1;M 1E. JaM iscuss with neat sketches the "arious types o lubricating systems employed or an I engine. J>M J4ay 5;1@M JbM The petrol used in a 0I engine contains >ED and 1ED *5. The amount o air supplied per kg o uel is 1@ kg. =ssume all *5 is burned, no carbon is deposited and e'haust does not contain ree -5, fnd JiM mass o carbon burning to -5, JiiM mass o each o the gases in the wet e'haust air contains 57D -5 and 33D ?5 by mass. J>M J=H. ?o"Fec. 5;1;M 1:. 2'plain why cooling is necessary in I.. engine. !ith neat sketches describe the working o water cooling system used or multi k! at 75;; r.p.m. and consumed 53 kg o petrol per hour. The calorifc "alue o petrol is @@ 4Fkg. 2stimate JaM The "olumetric e9ciency o the engine i the air – uel ratio is 15 and intake air is at ;.L bar, 75S JbM The brake thermal e9ciency JcM The brake torAue. 8or air, & % ;.5>3 kFkg . J=H. 4ayFune 5;11M 1>. iscuss the working principle o a our stroke engine with sketch. J=H., ?o"Fec 5;17M (b) 2'plain the construction and working principle o /attery coil ignition system 1L. 2'plain the working principle o diesel in+ector with neat 0ketch. (b) alculate the diameter and length o the stroke o a diesel engine working on our stroke constant pressure cycle rom the ollowing data. Indicated power % 1>.3E!,%55;,ompression ratio% 1@, 8uel cuto % 1F5; th o the stroke, Inde' o e'pansion %1.7, Inde' o compression%1.7E,lengthFdiameter%1.E. 1>
assume the pressure and temperature o the air at the inlet are 1bar and @; respecti"ely. J=H., ?o"Fec 5;1@M
;
5;. !ith a neat sketch e'plain the working principle o simple carburetor. (b) 2'plain the working o /attery ignition system. J=H., =prF4ay 5;1EM
NIT III -+TEAM NOJJLE+ AND TR)INE+ 1 /a' are 'e 8ari(%& '3e& (9 "(KK!e& a"d 'eir 9%"c'i("&
?oCCle is a duct o "arying cross
= steam noCCle is a de"ice ha"ing "ariable cross
/a' are 'e e,ec'& (9 9ric'i(" (" 'e ( 'r(%# a &'eam "(KK!e •
•
The fnal raction o the steam is increased as the part o the kinetic energy gets con"erted into heat due to riction and absorbed by steam with n increase in enthalpy. The e'pansion is no more isentropic and enthalpy drop is reduced thereby resulting in lower e'it "elocity. 1L
•
The specifc "olume o steam is increased as the steam becomes drier due to this rictional reheating.
4 De"e "(KK!e eBcie"c a"d cri'ica! 3re&&%re ra'i( N(KK!e eBcie"c It is defned as the ratio o actual enthalpy drop to the
isentropic enthalpy drop ?oCCle e9ciency % =ctual enthalpy drop F Isentropic enthalpy drop. Cri'ica! 3re&&%re ra'i( There is only one "alue o the ratio (#5F#1) which #roduces ma'imum discharge rom the noCCle. The ratio is called critical pressure ratio. ritical pressure ratio #5 F#1 % (5Fn61) nFn61 !here, ##1% pressure 5%Initial Throat pressure. 5 /a' i& 'e &i#"ica"ce (9 cri'ica! 3re&&%re ra'i( • • • •
The critical pressure gi"es the "elocity o sound. The ow in the con"ergent portion o the noCCle is subsonic and di"ergent portion is supersonic 8or e'panding the steam below critical pressure, the di"ergent portion o the noCCle is necessary. !hen p5 approaches the critical "alue the rate o discharge will be ma'imum.
•
6 /a' i& 'e e,ec' (9 9ric'i(" i" "(KK!e • • •
It reduces the "alue o enthalpy drop. The e'pansion will not be isentropic. It increases the entropy.
E?3!ai" 'e 3e"(me"(" (9 &%3er &a'%ra'ed e?3a"&i(" i" &'eam "(KK!e Or /a' i& Me'a &'a7!e (
!hen the supersaturated steam is e'panded in the noCCle, the condensation should occur in the noCCle. 0ince the steam has a great "elocity, the condensation does not take place at the e'pected rate. 0o the eAuilibrium between the liAuid and "apour phase is delayed and the steam continues to e'pand in a dry state. The steam in such set o condition is said to be supersaturated or meta stable ow. = /a' are 'e c("di'i("& 'a' 3r(d%ce &%3er &a'%ra'i(" (9 &'eam i" "(KK!e&
!hen the superheated steam e'pands in the noCCle, the condensation wil occur in the noCCle. 0ince, the steam has more "elocity, the condensation will not take place at the e'pected rate. 0o, the eAuilibrium between the liAuid and "apour phase is delayed and the steam continues to e'pand in a dry state. The steam in such set o condition is said to be supersaturated or meta stable ow.
> /a' are 'e e,ec'& (9 &%3er &a'%ra'i(" i" a &'eam "(KK!e 5;
The ollowing eects in a noCCle on steam, in which super saturation occurs, may be summariCed as ollows. • The dryness raction o the steam is increased. • 2ntropy and specifc "olume o the steam are increased. 2'it "elocity o the steam is reduced. • • 4ass o stream discharged is increased 10 /a' are 'e di,ere"ce& 7e'ee" &%3er&a'%ra'ed ( a"d i&e"'r(3ic ( 'r(%# &'eam "(KK!e& +%3er&a'%ra'ed (
I&e"'r(3ic (
1. 2ntropy is not constant 5. &educe in enthalpy drop 7. !e canot use molier diagram to sol"e problems
2ntropy is constant ?o reduce in enthalpy drop !e can use 4ollier diagram to sol"e problems
11 Te cri'ica! 3re&&%re ra'i( i"i'ia!! dr &a'%ra'ed &'eam i&
#5 F# 1%;.E3 12 De"e &'a#"a'i(" e"'a!3
The stagnation enthalpy represents the enthalpy o uid when it is brought rest adiabatically. 1/a' are 'e rea&("& 9(r 'e dr(3 i" 8e!(ci' (9 'e &'eam 9(r a #i8e" 3re&&%re dr(3 i" &'eam "(KK!e
8riction between the surace o the noCCle and steam ue to internal uid riction in the steam ue to shock losses • •
14/a' are 'e e,ec'& (9 &%3er &a'%ra'i(" i" "(KK!e& • • •
i. The dryness raction o the steam is increased ii. 2ntropy and specifc "olume o the steam are increased iii. 2'it "elocity o the steam is reduced i". 4ass o the steam discharged is increased.
•
15/a' are 'e mai" 9%"c'i("& (9 &'eam "(KK!e& • •
i. To supply high "elocity +et o steam in steam turbine ii. To in+ect eed water in to the boiler in a steam in+ector. 16 Te cri'ica! 3re&&%re ra'i( 9(r i"i'ia!! &%3er ea'ed &'eam i& a& c(m3ared '( i"i'ia!! dr &a'%ra'ed &'eam
Bess. 1 /e" 'e 7ac*3re&&%re (9 a "(KK!e i& 7e!( 'e de&i#"ed 8a!%e (9 3re&&%re a' e?i' (9 "(KK!e 'e "(KK!e i& &aid '( 7e
Hnder damping.
51
1= /a' are 'e 9a c'(r& '(&e ca"#e 'e %i d 3r(3er'ie& i!e a %id (& 'r(%# a "(KK!e i' "( (r* (r ea' 'ra"&9er • •
hange in ow area 8rictional orces.
1> /a' i& a &'eam '%r7i"e
0team turbine is a de"ice which is used to con"ert kinetic energy o steam into mechanical energy. 20 /a' i& 'e 9%"da me"'a! di,ere"ce 7e'ee" 'e (3era'i(" (9 im3%!&e a"d reac'i(" &'eam '%r7i"e& Im3%!&eT%r7i"e
1. It consists o noCCles and mo"ing blades.
Reac'i("'%r7i"e
5. #ressure drop occurs only in noCCles not in mo"ing blades 7. 0team strikes the blades with kinetic energy. @. It has constant blade channels
It consists o f'ed blades and mo"ing blades #ressure drop occurs in f'ed as well as mo"ing blades. 0team passes o"er the mo"ing blades with pressure and kinetic energy. It has "arying blade channels area
area. E. ue to more pressure drop per blade, number o stages reAuired is les.
?umber o stages reAuired is more due to more pressure drop.
21 E?3!ai" 'e "eed (9 c(m3(%"di"# i" &'eam '%r7i"e& :Or; E?3!ai" 'e 3%r3(&e (9 c(m3(%"di"# i" &'eam '%r7i"e&
In simple impulse turbine, the e'pansion o steam rom the boiler pressure to condenser presure takes place in a single stage turbine. The "elocity o steam at the e'it o turbine is "ery high. *ence, there is a considerable los o kinetic energy (i.e. about 1;to 15D). =lso the sped o the rotor is "ery high (i.e. up to 7;;rpm).isThere are se"eral methods o reducing this sped to lower "alue. ompounding a method o absorbing the +et "elocity in stages when the steam ows o"er mo"ing blades. 22 /a' are 'e di,ere"' me'(d& (9 c(m3(%"di"# • • •
$elocity compounding #ressure compounding #ressure<"elocity compounding.
2 /a' i& mea"' 7 carr (8er !(&&
The "elocity o steam at e'it is su9ciently high thereby resulting in a kinetic energy los called Wary o"er lossW or WBeading "elocity lossW 24 De"e de#ree (9 reac'i(" 55
It is defned as the ratio o isentropic heat drop in the mo"ing blades to isentropic heat drop in the entire stage o the reaction turbine. 25 /a' 9(r a #(8er"(r i& %&ed
The go"ernor is used to regulate the supply o steam to the turbine in such a way that the speed o the turbine is maintained as or as possible a constant under "arying load conditions. 26 /a' are 'e di,ere"' me'(d& (9 #(8er"i"# &'eam '%r7i"e& •
Throttle go"erning
• •
?oCCle go"erning /y
• •
2 /a' are 'e di,ere"' !(&&e& i"8(!8ed i" &'eam '%r7i"e& • • • • • •
Bosses in regulating "al"es, Bosses due to steam riction, Bosses due to mechanical riction, Bosses due to leakage, &esidual "elocity losses, arry o"er losses,
Bosses due to wetness o steam,c(m3(%"d and 2= /a' are ad8a"'a#e& (9 8e!(ci' im3%!&e '%r7i"e • • • • •
ItKs initial cost is less because o ew numbers o stages. Bess space is reAuired. The system is reliable and easy to start. There is need o strong casing due to low pressure.
•
2> /a' i& /i!&(" !i"e
The limiting condition o under cooling at which condensation commences and is assumed to restore conditions o normal thermal eAuilibrium is called X!ilson lineY. 0De"e de#ree (9 &%3er &a'%ra'i("
The ratio o super saturation pressures corresponding to the temperature between super saturated region is known as the degree o super saturation. 1/ re-ea'er i& "ece&&ar i" #a& '%r7i"e /a' are i'& e,ec'&
The e'pansion process is "ery oten perormed in two sperate turbine stages. he re
Turbine output is increased or the same compression ratio Thermal e9ciency is less.
•
PART ) 57
1. 0team at 1;.Ebar and ;.LEdryness is e'panded through a con"ergent di"ergent noCCle. The pressure o steam lea"ing the noCCle is ;.>Ebar. 8ind JiM $elocity o steam at throat or ma'i mum discharge, JiiM The area at e'i t, JiiiM 0team discharge i the throat area is 1.5cm5. =ssume the ow is isentropic and there are no riction losses. Take n % 1.17E. J=nna Hni". =pr.K;7M 5. ry saturated steam at 5.>bar is e'panded through a con"ergent noCCle to 1.3bar. The e'it area is 7cm5. alculate the e'it "elocity and mass ow rate or JiM Isentropic e'pansion and JiiM 0uper saturated ow. J=nna Hni". =pr.K;7M 7. ry saturated steam at a pressure o >bar enters a con"ergent di"ergent noCCle and lea"es it at a pressure o 1.Ebar. I the steam ow process is isentropic and i the corresponding e'pansion inde' is 1.17E, fnd the ratio o cross sectional area at e'it and throat or ma'imum discharge. J=nna Hni". -ct.K;5M @. 0team enters a group o con"ergentED. J=nna Hni". =pr.K;@M >. 0team at a 7bar with 1;; superheat is passed through a con"ergent noCCle. The "elocity o steam entering the noCCle is L1.EmFs. The backpressure is 1.Ebar. =ssuming noCCle e9ciency o L;D, determine the area o the noCCle at e'it. ischarge though the noCCle is limited to ;.@EkgFsec. Take ps Jsuperheated steamM % 5.5kFkg ;. J=nna Hni". ?o".K;@M 5@
L. = con"ergentM JbM 0team e'pands rom @; bar and specifc "olume o ;.;3@L m7Fkg to a pressure o 5; bar in a noCCle. 0team remains superheated throughout. etermine the e'it area o cross section. J>M J=H., ?o"Fec. 5;1;M 1>. JaM eri"e an e'pression or critical pressure ratio. J>M JbM ompare the throttle and noCCle control go"erning in steam turbines. J>M J=H. ?o"Fec. 5;1;M 1L. ry saturated steam at a pressure o > bar enters a con"ergent
=ssume the inlet and outlet angles to be eAual. J=H. 4ayFune 5;11M 51. JiM !hat are the eects o riction in a noCCleR 2'plain. J>M JiiM = con"ergent – di"ergent noCCle is reAuired to discharge 5kg o steam per second. The noCCle is supplied with steam at 3 bar and 1>;; and discharge takes place against a back pressure o 1 bar. The e'pansion up to throat is isentropic and the rictional resistance between the throat and e'it is eAui"alent to :7kFkg o steam. Taking approach "elocity o 3EmFs and throat pressure o @ bar, estimate J1M 0uitable areas or the throat and e'it and J5M -"erall e9ciency o noCCle based on the enthalpy drop between the actual inlet pressure and temperature and the e'it pressure. J>M J=nna. Hni". 4ayFune 5;17M 55. JiM The "elocity o steam, lea"ing the noCCle o an impulse turbine is 1;;; mFs and the noCCle angle is 5;;. The blade "elocity is 7E; mFs and the blade "elocity o coe9cient is ;.>E. =ssuming no losses due to shock at inlet, calculate or a mass ow o 1.EkgFs and symmetrical blading. J1M /lade inlet angle J7M J5M ri"ing orce on the wheel J7M J7M ='ial thrust on the wheel and J7M J@M #ower de"eloped by the turbine J7M JiiM ierentiate between impulse and reaction turbineR J@M J=nna Hni". 4ayFune 5;17M 57. steam e'pands isentropically in a noCCle rom 14pa to,5E; ; to 1;pa .the ow rate is 1kgFs fnd the ollowing J1M Vuality o steam J5M $elocity o steam J7M 2'it area o the steam (b) 2'plain the pressure and "elocity compounding diagram o an multi stage turbine with sketch. J=nna Hni". ?o"Fec 5;17M 5@. 0team at a pressure o 1;.E bar and ;.LE dry is e'panded through a con"ergent di"ergent noCCle. The pressure o steam lea"ing the noCCle is ;.>E bar. 8ind the "elocity o steam at throat or ma'imum discharge. Take n%1.17E. 5 also fnd the area at the e'it and steam discharge i throat area is 1.7cm . assume the ow is isentropic and there is no riction losses. (b) 2'plain the pressure and "elocity compounding o multi stage turbine with neat sketch. J=nna Hni". ?o"Fec 5;1@M ; 5E. The inlet condition to a steam noCCle are 1; bar and 5E; . the e'it pressure is 5 bar. =ssuming isentropic e'pansion and negligible inlet "elocity determine J1M The throat area J5M $elocity o steam J7M 2'it area o the noCCle
(b) !hat is "elocity compounding R list the ad"antages and limitations. J=H., =prF4ay 5;1EM
5:
NIT I@ - AIR COMPRE+OR :1; C!a&&i9 'e 8ari(%& '3e& (9 air c(m3re&&(r& 1; Acc(rdi"# '( 'e a"d 3ri"ci3!e (9 (3era'i("
a)&eciprocating compressors b) &otary compressors. 2; Acc(rdi"# '( 'e ac'i("
a) 0ingle acting compressors b) ouble acting compressors
; Acc(rdi"# '( 'e "%m7er (9 &'a#e&
a) 0ingle stage compressors b) 4ultistage compressors 4; Acc(rdi"# '( 'e 3re&&%re !imi'
a)Bow pressure compressors b )4edium pressure compressors c) *igh pressure compressors 5; Acc(rdi"# '( 'e ca3aci'
a)Bow capacity compressors b) 4edium capacity compressors. c) *igh capacity compressors :2; /a' i& mea"' 7 &i"#!e ac'i"# c(m3re&&(r&
In single acting reciprocating compressor, the suction, compression and deli"ery o air takes place on both sides o the piston.
:;/a' i& mea"' 7 &i"#!e &'a#e c(m3re&&(r
In single stage compressor, the compression o air rom the initial pressure to the fnal. #ressure is carried out in one cylinder only. :4;/a' i& mea"' 7 d(%7!e ac'i"# c(m3re&&(r
In double acting reciprocating compressor, the suction, compression and deli"ery o air takes place on both sides o the piston. :5;
I"dica'e
'e
a33!ica'i("
(9
i"d%&'r
reci3r(ca'i"#
The applications o compressed air as ollows • #neumatic brakes 53
c(m3re&&(r&
i"
• • • • • • • •
#neumatic +akes. #neumatic drills. #neumatic lits. 0pray painting. 0hop cleaning. In+ecting uel in diesel engines. 0upercharging internal combustion engines. &erigeration, and air conditioning systems.
:6; /a' are 'e ad8a"'a#e& (9 m%!'i &'a#e c(m3re&&i(" i' i"'er"a! c((!i"# (8er &i"#!e &'a#e c(m3re&&i(" 9(r 'e &ame 3re&&%re ra'i( • • • •
It impro"es the "olumetric e9ciency or the gi"en pressure ratio. It reduces the leakage los considerably. It gi"es more uniorm torAue and hence a smaller siCe ywheel is reAuired. It reduces the cost o the compressor.
:; De"e 'e 'erm& a& a33!ied '( air c(m3re&&(r&. @(!%me'ric eBcie"c a"d i&('erma! c(m3re&&i(" eBcie"c :(r; De"e 'e meca"ica! eBcie"c a"d i&('erma! eBcie"c (9 a reci3r(ca'i"# air c(m3re&&(r @(!%me'ric eBcie"c is defned as the ratio o "olume o ree air
sucked intoe9ciency the compressor perocycle stroke o the"olume cylinder. $olumetric $olume ree to airthe taken per "olume cycleF0troke o the cylinder. I&('erma! c(m3re&&i(" eBcie"c Isothermal e9ciency is defned as the ratio between isothermal work to the actual work o the compressor. Isothermal e9ciency % brake powerF Indicated power :=; De"e c!eara"ce ra'i(
learance ratio is defned as the ratio o clearance "olume to swept "olume (or) stroke "olume. C @c@&
$c%learance "olume $s%0wept "olume :>; Di&c%& 'e e,ec' (9 c!eara"ce %3(" 'e 3er9(rma"ce (9 a" air c(m3re&&(r
The "olumetric e9ciency o air compressor increases with decrease in clearance o the compressor. :10; Gi8e '( meri'& (9 r('ar c(m3re&&(r (8er reci3r(ca'i"# c(m3re&&(r • • • •
&otary compressor gi"es uniorm deli"ery o air where compared to reciprocating compressor. &otary compressors are small in siCe or the same discharge as compared with reciprocating compressors. Bubricating system is more complicated in reciprocating compressor where as it is "ery simple in rotary compressor. 5>
:11; / c!eara"ce i& "ece&&ar a"d a' i& i'& e,ec' (" 'e 3er9(rma"ce (9 reci3r(ca'i"# c(m3re&(r
!hen the piston reaches top dead center in the cylinder, there is a dead space between piston top and cylinder head. This space is known as clearance space and the "olume occupied by this space is known as clearance "olume. :12; /a' i& mea"' 7 i"'er c((!er
=n inter cooler is a simple heat e'changer. It e'changes the heat o compressed air rom the low
1. learance "olume. 5. ompression ratio. :14; /a' i& c(m3re&&i(" ra'i(
ompression ratio is defned as the ratio between total "olume and clearance "olume. C(m3re&&i(" ra'i( T('a! 8(!%me C!eara"ce 8(!%me
15 /a' i& mea"' 7 9ree air de!i8ered
The ree air deli"ered is the actual "olume deli"ered at the stated pressure reduced to intake pressure and temperature and e'pressed in m7 Fmin. 16 De"e meca"ica! eBcie"c a"d i&('erma! eBcie"c (9 a reci3r(ca'i"# c(m3re&&(r
4echanical e9ciency is defned as the ratio between brake power to the indicated power. Meca"ica! EBcie"c % /rake powerFIndicated power. Isothermal 29ciency Isothermal e9ciency is defned as the ratio between isothermal work to the actual work o the compressor. I&('erma! EBcie"c % Isothermal workF=ctual work. 1 /a' i& 'e di,ere"ce 7e'ee" 3er9ec' i"'er c((!i"# a"d im3er9ec' i"'er c((!i"# Per9ec' c((!i"# !hen the temperature o air lea"ing the
inter cooler is eAual to the srcinal atmospheric air temperature, then inter cooling is known as perect inter cooling. Im3er9ec' I"'er c((!i"#. !hen the temperature o air lea"ing the inter cooling is more than srcinal atmospheric air temperature, then inter cooling is known as imperect inter cooling. 1= /a' 9ac'(r& !imi' 'e de!i8er 3re&&%re i" a reci3r(ca'i"# c(m3re&&(r • •
To obtain high deli"ery pressure, the siCe o the cylinder will be large. Temperature o air 5L
1> / c!eara"ce i& "ece&&ar a"d a' i& i'& e,ec' (" 'e 3er9(rma"ce (9 reci3r(ca'i(" c(m3re&&(r
!hen the piston reaches top dead center in the cylinder, there is a dead space between piston top and cylinder head. This space is known as clearance space and the "olume occupied by this space is known as clearance "olume. 20 Li&' (%' 'e a33!ica'i(" (9 c(m3re&&ed air
ompressed air is mostly used in pneumatic brakes, pneumatic drills, pneumatic +acks, pneumatic lits, spray painting, shop cleaning, in+ecting uel in diesel engines, supercharging, internal combustion engines, rerigeration and air conditioning systems 21 +'a'e 'e e,ec' (9 c!eara"ce (" (r* d("e i" a reci3r(ca'i"# c(m3re&&(r • • •
=ctual suction "olume decreases 4ass o air is reduced $olumetric e9ciency decreases
22 C(m3re&&(r Ca3aci' i& • • •
$olume o air deli"ered ii. $olume o air sucked iii. /oth a and b i". ?ine o the abo"e
•
2E?3!ai" 'e ( (9 air c("'r(!!ed i" reci3r(ca'i"# c(m3re&&(r&
The ow o air is controlled by three methods such as • entriugal go"ernor mechanisms • 4aintaining the speed o motor constant #ro"iding air pocket ad"ancement to the cylinder. •
24De"e mea" e,ec'i8e 3re&&%re H( i& i' re!a'ed '( i"dica'ed 3(er
eecti"e hypothetical pressure, which The is mean considered to pressure be actingis defned on the as piston throughout the compression stroke. Te i"dica'ed 3(er IP Mea" e,ec'i8e 3re&&%re ? L ? A ? N 25/a' are 'e 9ac'(r& 'a' i"%e"ce 'e 3(er i"3%' '( 'e c(m3re&&(r • • • •
The mass ow o air ii. The pressure ration o the compressor iii. The inlet temperature i". Temperature dierence between the inlet and outlet ". The properties o the working medium
•
26/a' are 'e i"'er"a! a"d e?'er"a! !(&e& i" ce"'ri9%#a! c(m3re&&(r 7;
The internal losses are due to • riction between air and wall o ow passage • ii. isc riction • iii. leakage between impeller and casing • i". turbulence ". shock and the e'ternal losses are mainly due to the bearing riction •
2/a' are 'e di,ere"ce 7e'ee" r('ar air c(m3re&&(r a"d reci3r(ca'i"# air c(m3re&&(r Reci3r(ca'i"# Air c(m3re&&(r
R('ar Air c(m3re&&(r
The ma'imum deli"ery pressure may be as high as 1;;; bar They are suitable or low discharge o air at "ery high pressure The speed o air compressor is low The air supply is intermittent The siCe o the compressor is large or the gi"en discharge The balancing is a ma+or problem
The ma'imum deli"ery pressure is 1; bar only. They are suitable or large discharge o air at low pressure. The speed o air compressor is high The air supply is continuous. The siCe o air compressor is small or the same discharge. There is no balancing problem
2=/a' are 'e ad8a"'a#e& (9 m%!'i &'a#e c(m3re&&(r (8er &i"#!e &'a#e c(m3re&&(r • • • • •
Bess work is done by the compressor to deli"er the same Auantity o air. ii. It impro"es the "olumetric e9ciency or the gi"en pressure ratio. iii. The siCe o the two cylinder may be ad+usted to suit the "olume and pressure o the air. i". It reduces the leakage losses considerably and pro"ides eecti"e lubrication. ". It pro"ides more uniorm torAue and thus smaller siCe o the ywheel is reAuired. "i. It reduces the cost by selecting a cheap material or construction.
2>/a' i& 'e di,ere"ce 7e'ee" ce"'ri9%#a! a"d a?ia! ( c(m3re&&(r& Ce"'ri9%#a! c(m3re&&(r
A?ia! ( c(m3re&&(r
The ow o air is perpendicular to the a'is o compressor It has low manuacturing and running cost
The ow o air is parallel to the a'is o compressor It has high manuacturing and running cost
71
It reAuires low starting torAue It is not suitable or multi staging It reAuires large rontal area or a gi"en rate o ow
It reAuires high starting torAu It is suitable or multi staging. It reAuires less rontal area or a gi"en rate o ow. It makes the compressor suitable or aircrats.
0/a' are 'e ad8a"'a#e& (9 r('ar c(m3re&&(r (8er reci3r(ca'i"# c(m3re&&(r • • • •
4a'imum ree deli"ery is as high as 7;;; m7Fmin. ii. =ir supply is air continuous, more clean. iii. 0mall siCe is reAuired or the same discharge. i". ?o balancing problem
#=&T < / 1. = single stage reciprocating air compressor takes 1m7 o air per minute at 1bar and 1E; and deli"ers it at 3bar. The law o compression is p$1.7 % constant, calculate the indicated power. ?eglect clearance. I the speed o compressor is 7;;rpm and stroke to bore ratio is 1.E, calculate the cylinder dimensions. 8ind the power reAuired i the mechanical e9ciency o compressor is >ED and motor transmission e9ciency is L;D. J?-$K;5M 5. = single acting single stageED and motor transmission e9ciency is L;D. alculate mass or air deli"ered per minute, indicated power, bore and stroke, and the motor power. J=nna Hni". may 5;;@M 7. The ree air deli"ery o a single cylinder single stage reciprocating air compressor is 5.Em7Fmin. The ambient air is at 0T# conditions and deli"ery pressure is 3bar. The clearance "olume is ED o the stroke "olume and law o compression and e'pansion is p$1.5E % . I B % 1.5 and the compressor runs at 1E;rpm, determine the siCe o the cylinders. J2K;7M @. = 0ingle stage single –acting compressor deli"ers 1Em7 o ree air per minute rom 1bar to >bar. The speed o compressor is 7;;rpm. =ssuming that compression and e'pansion ollow the law p$1.7 % constant and clearance is 1F1:th o swept "olume, fnd the diameter and stroke o the compressor. Take BF % 1.E. The temperature and pressure o air at the suction are same as atmospheric air. J2K;7M E. = single stage double acting compressor has a ree air deli"ery J8.=.M o 1@m7Fmin measured at 1.;17bar and 1E;. The pressure and temperature in the cylinder during induction are ;.LEbar and 75; respecti"ely. The deli"ery pressure is 3bar and inde' o compression and e'pansion, n% 1.7. The clearance "olume is ED o the swept "olume. alculate the indicated power reAuired and the "olumetric e9ciency. J=nna Hni". =pr.K;@M :. = three
7;; ater each stage o compression. The deli"ery pressure o the compressor is 1E;bar. The &.#.4. o the compressor is 7;;. The clearance o B.#., I.#., and *.#. cylinders are ED o the respecti"e strokes. The inde' o compression and re;D. J=nna Hni". ?o".K;@M 3. onsider a single> through a pressure ratio o L to 1. /oth the stages ha"e the same pressure ratio and the inde' o compression and e'pansion in both stages is 1.7. =ssume a complete inter cooling, fnd the indicated power and the cylinder swept "olumes reAuired. =ssume that the clearance "olumes o both stages are ED o their respecti"e swept "olumes. J=nna Hni". =pr.K;EM >. 2'plain with the help o a neat sketch the principle o operation o a reciprocating air compressor. J=nna Hni". =pr.K;@M L. !ith the help o a neat sketch e'plain the principles o operation o a centriugal compressor. J=nna Hni". =pr.K;@ Q ?o".K;@M 1;. ompare reciprocating and rotary air compressors. J=nna Hni". =pr.K;@M 11. iscuss the merits and demerits o rotary and reciprocating compressors. J=nna Hni". ec.K;7 Q ?o".K;@M 15. !ith the help o schematic and p<$ diagrams, e'plain the working o a "ane type compressor. J=nna Hni". =pr.K;EM 17. JaM 0how that in a reciprocating air compressor, with perect inter cooling, the work done or compressing air is re+ected to cooling medium. JbM !ith the aid o #<$ diagrams discuss the reasons or the use o multi stage compressors. J=H. ?o"Fec.5;1;M 1@. JaM ompare reciprocating and rotary compressors and discuss. JbM !hat are the ad"antages o multi stage compressors o"er single stage compressorsR eri"e the condition o minimum work with complete inter cooling in a two stage compressor. J=H. 4ayFune 5;11M J4ay 5;1@M 1E. = two stage single acting compressor takes in air at the rate o ;.5 m7Fs the intake pressure and temperature are ;.1 4#a and 1:S. The air is pressed to a fnal pressure o ;.3 4#a. The intermediate pressure is ideal and inter cooling is perect. The compression inde' in both the stages is 1.5E and the compressor runs at :;; r.p.m. ?eglecting clearance, determine JaM The intermediate pressure JbM The total "olume o each cylinder JcM The power reAuired to dri"e the compressor and JdM The rate o heat re+ection in the inter cooler. Take p % 1.;;E Fkg and & % ;.5>3 Fg . J=H. 4ayFune 5;11M
77
1:. JaM 2'plain the working o a single stage single acting reciprocating compressor with a neat sketch and p<" diagram. JbM = single stage double acting reciprocating air compressor is reAuired to deli"er 1@ m7 o air minute measured at 1.;17 bar and 1ES. The deli"ery pressure is 3 bar and the seed 7;; r.p.m. Take the clearance "olume as ED o the swept "olume with the compression and e'pansion inde' o n% 1.7. alculate JiM 0wept "olume o the cylinder JiiM The deli"ery temperature JiiiM Indicated power. J=H. 4ayFune 5;11M 13. = single acting reciprocating air compressor has a piston diameter o 5;;mm and a stroke o 7;;mm and runs at 7E;rpm. =ir is drawn at 1.1 bar pressure and is deli"ered at > bar pressure. The law o compression is p$ 1.7E % constant and clearance "olume is :D o the stroke "olume. etermine the mean eecti"e pressure and the power reAuired to dri"e the compressor. J=nna Hni". 4ayFune 5;17M 1>. eri"e the work done by a two stage reciprocating air compressor with inter cooler and deri"e the condition or minimum work input and the e'pression or minimum work reAuired or two stage reciprocating compressorR J=nna Hni". 4ayFune 5;17M 1L In a two stage compressor in which intercooling is perect pro"e that work done in the compressor is minimum when the pressure in the intercooler geometric mean between the initial and fnal pressure. raw the #$QT0 diagram or two stage compression (b) 2'plain the construction and working principle o multi stage compressor and discuss the perect and imperect intercooling with neat sketch. J=nna Hni". ?o"Fec 5;17M 5;. eri"e an e'pression or "olumetric e9ciency o a air compressor. J4ay 5;1@M 51. eri"e an e'pression or "olumetric e9ciency o a reciprocating air compressor. (b) (b) 2'plain the construction and working principle o multi stage compressor and discuss the perect and imperect intercooling with neat sketch. J=nna Hni". ?o"Fec 5;1@M 55. = single stage single acting reciprocating air compressor deli"ers 1Em 7 o ree air per min rom 1.1 to > bar pressur e. =ssuming that compression and e'pansion ollow p$ 1.7E % constant and clearance "olume is 1F: th o the swept "olume. 8ind the diameter and stroke o the compressor. Take BF %1.E. the temperature and pressure o air at the suction are 5; ; and 1 bar respecti"ely.
7@
J=H., =prF4ay 5;1EM
NIT @- REFRIGERATION AND AIR CONDITIONING 1 /a' i& 'e di,ere"ce 7e'ee" a ea' 3%m3 a"d a re9ri#era'(r
*eat pump is a de"ice which operating in cyclic process, maintains the temperature o a hot body at a temperature higher than the temperature o surroundings. = rerigerator is a de"ice which operating in a cyclic process, maintains the temperature o a cold body at a temperature lower than the temperature o the surroundings. 2 De"e 'e 'erm COP
o
The amount o heat e'tracted in a gi"en time is known as rerigeration eect. 4 /ri'e 'e e?3re&&i(" 9(r COP (9 a ea' 3%m3 a"d a re9ri#era'(r COP O9 ea' 3%m3 :COP;
HP
T2T2-T1
COP (9 Re9ri#era'(r :COP;REF T1T2-T1 5 E?3!ai" 'e 'erm &(%rce a"d &i"*
0ource is a thermal reser"oir, which supplies heat to the system and sink is a thermal reser"oir, which takes the heat rom the system. 6 /a' d( (% %"der&'a"d 7 'e e"'r(3 3ri"ci3!e
The entropy o an isolated system can ne"er decrease. It always increases and remains constant only when the process is re"ersible. This is known as principle o increase in entropy or entropy principle. 7E
De"e '("e (9 re9ri#era'i("
= tone o rerigeration is defned as the Auantiy o heat reAuired to be remo"ed rom one tone o water (1;;kg) at ; to con"ert that into ice at ; in 5@ hours. In actual practice, 1 '("e (9 re9ri#era'i(" 210*mi"5*/ = De"e '("e (9 re9ri#era'i(" Hea' i& rem(8ed 9r(m a &3ace a' a ra'e (9 4200* E?3re&& 'i& ea' rem(8a! ra'e i" '("&
= tone o rerigeration is defned as the Auantity o heat reAuired to be remo"ed rom one tone o water (1;;kg) to con"ert hat into ice at ;Z 5@ hours. > Te 8a3(%r c(m3re&&i(" re9ri#era'(r em3!(& 'e -- cc!e
&e"ersed arnot. 10 Te d((r (9 a r%""i"# re9ri#era'(r i"&ide a r((m a& !e9' (3e" /a' i!! a33e"
The room will be gradually warmed up. 11 I" a 8a3(r c(m3re&&i(" re9ri#era'i(" &&'em ere 'e !(e&' 'em3era'%re i!! (cc%r
=t inlet o e"aporator 12 H( d(e& 'e ac'%a! 8a3(%r c(m3re&&i(" cc!e di,er 9r(m 'a' (9 'e idea! cc!e • •
In actual cycles, pressure loses occur in both condenser and e"aporator. 8riction loses occur in compressor.
1 Name 9(%r im3(r'a"' 3r(3er'ie& (9 a #(d re9ri#era"' • •
Bow boiling point. *igh critical temperature and pressure. Bow specifc heat o liAuid
14 /a' i& re9ri#era'i("
'e
di,ere"ce
7e'ee"
air
c("di'i("i"#
a"d
&erigeration is the process o pro"iding and maintaining the temperature in space below atmospheric temperature. =ir conditioning is the process o supplying su9cient "olume o clean air containing a specifc amount o water "apour and maintaining the predetermined atmospheric condition with in a selected enclosure. 15 /a' i& 'e 9%"c'i(" (9 'e 'r(''!i"# 8a!8e i" 8a3(%r c(m3re&&i(" re9ri#era'i(" &&'em
The unction o throttling "al"e is to allow the liAuid rerigerant under high pressure and temperature to pas to controlled rate ater reducing its pressure and temperature. 7:
16 I" a 8a3(%r c(m3re&&i(" re9ri#era'i(" &&'em ere 'e i#e&' 'em3era'%re i!! (cc%r
=ter compresion. 1 Te 8a3(%r a7&(r3'i(" &&'em ca" %&e !(-#rade ea' e"er# i" 'e #e"era'(r I& 'r%e (r 9a!&e
True. 1= Name a" '( c(mm("! %&ed re9ri#era"'& • •
=mmonia (?*7) arbon dio'ide (-5).
1> E?3!ai" %"i' (9 Re9ri#era'i("
Hnit o rerigeration is e'pressed in terms o tone o rerigeration. = tone o rerigeration is defned as the Auantity o heat reAuired to be remo"ed rom one tone o water (1;;kg) to con"ert hat into ice at ;Z in 5@ hours. 20 / 'r(''!e 8a!8e i& %&ed i" 3!ace (9 e?3a"&i(" c!i"der 9(r 8a3(%r c(m3re&&i(" re9ri#era"' maci"e
In throttling process, enthalpy remains constant and pressure is reduced so is used throttle "al"e 21 /a' are 'e e,ec' 39 &%3erea' a"d &%7 c((!i"# (" 'e 8a3(%r c(m3re&&i(" cc!e
0uperheating increases the rerigeration eect and -# may be increased or decreased. /ut sub cooling always increase the -# o the rerigeration and also decrease the mass ow rate o rerigerant. 22 /a' are 'e 3r(3er'ie& (9 #(d re9ri#era"'
=n ideal rerigerant should poses ollowing desirable properties. shouldthe ha"e low reeCing point. • The rerigerant • It must ha"e high critical pressure and temperature to a"oid large power reAuirements. • It should ha"e low
&erigerating eect is the total heat remo"ed rom the rerigerant in the e"aporator. COP Re9ri#era'i(" e,ec' /(r* d("e Re9ri#era'i(" e,ec' COP /(r* d("e 73
24 Name 'e 8ari(%& c(m3("e"'& %&ed i" &im3!e 8a3(%r a7&(r3'i(" &&'em • • • • • •
=bsorber #ump Generator ondenser. Throttle "al"e. 2"aporator.
•
25 De"e re9ri#era"'
=ny substance capable o absorbing heat rom another reAuired substance can be used as rerigerant. 26/a' are 'e meri'& a"d demeri'& (9 air re9ri#era'i(" &&'em Meri'&. • • •
The rerigerant air is cheap and easily a"ailable ii. There is no danger o fre o to'ic eects due to leakages. iii. The eAuipment weight to tonne o rerigeration is low
Demeri'&. •
The Auantity o rerigerant used per o rerigeration is high
• •
ii. The -# o the system is "ery low iii. The danger o rosting at the e'pander "al"es is more as air contains moisture.
•
2Name &(me im3(r'a"' re9ri#era'i(" a33!ica'i("&
Ice making, ood preser"ation, milk processing, industrial air< conditioning, chemical related industries, medical and surgical aids, oil refning and treatment o metals.
2= H( d(e& %midi' a,ec' %ma" c(m9(r'
I the humidity is abo"e a certain le"el, water "apour rom human body moisture cannot be absorbed by the atmospheric air. It results in discomort because o sweating. 2> /a' are 'e ad8a"'a#e& a"d di&ad8a"'a#e& (9 air re9ri#era'i(" &&'em Ad8a"'a#e&. • • •
The rerigerant used namely air is cheap and easily a"ailable. There is no danger o fre or to'ic eects due to leakages. The weight to tonne o rerigeration ratio is less as compared to other systems.
Di&ad8a"'a#e&. •
The Auantity o rerigerant used per tonne o rerigeration is high as compared to other systems. 7>
• •
The -# o the system is "ery low. Thereore running cost is high. The danger o rosting at the e'pander "al"es is more as the air contains
0. +'a'e a" '( ad8a"'a#e& (9 8a3(%r a7&(r3'i(" &&'em (8er c(m3re&&i(" &&'em • • • • •
?o need o electric power. !ear and Tear is less. Tonne capacity is high. There is no leakage o rerigerant. 0pace reAuirement is less.
1 /a' i& G+HF G+HF T+HGTH T+HTLHT+HQ
T0* % Total sensible heat load. GT* % Grand total heat load. TB* % Total latent heat load. G0*8 % Grand sensible heat actor. 2 Me"'i(" 'e de&ira7!e 3r(3er'ie& (9 re9ri#era"' • • • • • • • •
The rerigerant should ha"e low reeCing point. It must ha"e high critical pressure and temperature to a"oid large power reAuirements. It should ha"e low
De"e &e"&i7!e ea'i"# a"d &e"&i7!e c((!i"# 3r(ce&& +e"&i7!e ea' 3r(ce&&. In sensible heating process, air is heated at
constant specifc humidity. It means, heating is done without adding moisture. uring this process, dry bulb temperature is increased. +e"&i7!e c((!i"# 3r(ce&& In sensible cooling process, air is cooled at constant specifc humidity. uring this process, the dry bulb temperature is reduced. 4 /a' i& %midica'i(" a"d de%midica'i("
*umidifcation is defned as the process o adding moisture at constant dry bulb temperature. ehumidifcation is defned as the process o remo"ing moisture at constant dry bulb temperature. 5 E"%mera'e 'e c(m3("e"'& (9 c((!i"# !(ad e&'ima'e 7L
• • • •
*eat ow through the e'terior walls,ceilings,oors, doors and windows. *eat by solar radiation *eat recei"ed rom the occupants *eat recei"ed by infetrated air etc..
6 Di,ere"'ia'e 8a3(%r a7&(r3'i(" &&'em a"d 8a3(%r c(m3re&&i(" &&'em @a3(%r a7&(r3'i(" &&'em
@a3(%r c(m3re&&i(" &&'em
ue to compressor and an more wear and tear 2lectrical power is essential to operate the system
-nly mo"ing part is liAuid pump, less wear and tear 2lectrical power is not essential to operate the system (heat energy is used) The compressor is used to compress ompressor is replaced by absorber the and rerigerant generator 8reon 15, 8reon 55, ?*7, #ropane, ?*7 water "apour system, Bithium Isobutane – used as rerigerants /romide water "apour system is used. -ccupiesless space. -ccupiesmore space. #erormance is poor at partial loads #erormance is not aected at partial loads.
Par' ) 1. = Etonne rerigeration plant uses &15 as rerigerant. It enters the compressor at
T; 75
#JbarM 3.>E 5.:1
2nthalpy kFkg h hg 17;.E 5:@.E <<<< [email protected]
2ntropy kFkg sg 1.E@5 1.EE3
5.= rerigerator works between <3; and 53;. The "apour is dry at the end o adiabatic compression. =ssuming there is no under cooling determine JiM The .-.# JiiM #ower o the compressor to remo"e a heat load o 151@;kFhr. the properties o rerigerant are gi"en table. J=nna Hni". 4ay ;7M T;
0ensible
Batent heat
2ntropy o
2ntropy o
heat, JhM JkFkg
JhgM kFkg
BiAuid JsM kFkg
$apour kFkgJsgM
@;
<3 53
<5L.7 113.57
15L3.L 1135.7
<;.1;L ;.@53
@.3@> @.777
7.= "apour compression rerigeration system using &15 has a condensing temperature o E;; and e"aporating temperature o ;;. The rerigeration capacity is 3tons. The liAuid lea"ing the condenser is saturated liAuid and compression is isentropic. The "apour lea"ing the e"aporator is dry saturated. =ssume that enthalpy at the end o isentropic compression % 51;kFkg. etermine JiM The rerigeration ow rate. JiiM The power reAuired to run the compressor. JiiiM The heat re+ected in the plant. Ji"M -# o the system. The properties o &15 are listed below J=nna Hni". ?o".K;7 Q ec.K;@M Temp #ressure hJkFkgM hg JsM sg J;M JbarM JkFkgM kFkg JkFkgM E; 15.1LL >@.>:> 5;:.5L> ;.7;7@ ;.:3L5 ;
;.;>:
7:.;55
1>3.7L3
;.1@1>
;.:L:;
@. 5> tonnes o ice rom and ;; is produced per day in an ammonia rerigerator. The temperature range in the compressor is rom 5E; to <1E;. The "apour is dry and saturated at the end o compression perormance o :5D o theoretical, alculate the power reAuired to dri"e the compressor. The properties o ammonia are gi"en in the ollowing table J=nna Hni". =pr.K;@M
Temperature 5E <1E
2nthalpy JkFkgM BiAuid $apour 1;;.@ 171L.55
2ntropy JkFkgM BiAuid $apour ;.7@37 @.@>E5 <5.177> E.;E>E
E. =ir enters the compressor o an aircrat system at 1;;k#a, 533 and is compressed to 7;;k#a with an isentropic e9ciency o 35D. =ter being cooled to 75> at constant pressure in a heat e'changer the air then e'pands in a turbine to 1;;k#a with an isentropic e9ciency o 3>D. The low temperature air absorbs a cooling load o 7tons o rerigeration at constant pressure beore re< entering the compressor. !hich is dri"en by the turbine. =ssuming air as ideal gas, fnd the -#, the dri"ing power reAuired and the air mass ow rate. J=nna Hni". 4ay.K;EM :. JiM =n o9ce is to be air
@1
3. =n air<"apour mi'ture at ;.1 4#a, 7;;, >;D &* has a "olume o E;m7, alculate the specifc humidity, dew point temperature, wet bulb temperature, mass o dry air and mass o water "apour. J=nna Hni". =pr.K;EM >. !ith a neat ow diagram, e'plain the working o a "apour compression rerigeration system. J4H, =prKL:, =pr.KL> Q =nna Hni". =pr.K;@ Q =pr.K;EM J4ay 5;1@M 5:1. !hat are the desirable properties o good rerigerantsR J=nna Hni". =pr.K;EM L. !ith a neat sketch, discuss briey the ammonia absorption rerigeration cycle. J=nna Hni". pr.K;EM 1;. iscuss the ad"antages and disad"antages o "apour absorption rerigeration system o"er "apour compression system. J=nna Hni". ec.K;7M 11. efne &0*8 and =0*8. J=nna Hni". ec.K;7M 15. raw a neat diagram o air conditioning system reAuired in winter season. 2'plain the working o dierent components in the circuit. Is it possible to use steam or such air conditioning system. J=nna Hni". ec.K;7 Q apr.K;7M 17. escribe the working o summer air conditioning system suitable or hot and wet weather and or hot and dry weather with simple component diagrams. J=nna Hni". =pr.K;7 Q =pr.K;@M 1@. JaM 2'plain with a neat sketch the working principle o lithium bromide rerigeration system. JbM =n & – 15 system is operating at conditions such that the "aporiCing temperature is < 1ES and the condensing temperature is @;S. I it is assumed that no sub cooling o the liAuid occurs so that the temperature o liAuid at the rerigerant control is also @;S, fnd the ollowing JiM the rerigerating eect per kilogram JiiM the mass o rerigerant circulated in kilograms per second per kilowatt JiiiM the mass o rerigerant circulated per second or a ton system. J=H., ?o"Fec.5;1;M 1E. !rite short notes on the ollowing. JiM G0*8 JiiM &0*8. J=H., ?o"Fec.5;1;M 1:. 2'plain "apour absorption rerigeration system with a neat sketch. =lso bring out the dierence between "apour compression and absorption rerigeration systems. J=H., 4ayFune 5;11M 13. =n airS !/T &eAuired indoor conditions 5;S /T and :;D &.*. =mount o air circulation ;.7 m7FminFperson 0eating capacity o the o9ce E; The reAuired condition is achie"ed frst by heating and then by adiabatic humidiying. 8ind the ollowing JaM *eating capacity o the coil in k! and the surace temperature reAuired i the bypass actor o the coil is ;.75. JbM The capacity o the humidifer. J=H. 4ayFune 5;11M 1>. JiM !hat are the properties o a good rerigerantR J@M J=nna Hni". 4ayFune 5;17M @5
JiiM =n ammonia rerigerator produces 7; tons o ice at ;; in a day o 5@ hours. The temperature range in the compressor is rom 5E; to <1E;. The "apour is dry saturated at the end o compression. =ssume a -# o :;D Theoretical "alue. alculate the power reAuired to dri"e the compressor. =ssume latent heat o ice is 77EkFkg. 8or properties o ?*7, reer the table below. J15M Temperature J;M h hg 0 0g kFkgk kFkgk kFkgk kFkgk 5E 5L>.L 1@:E.> 1.15@ E.;7L <1E 115.7@ 1@5:.E ;.@E35 E.E@L 1L. The temperature limits o =mmonia rerigeration system are 5E ; and <1;;. i the gas is dry at the end o the compression calculate the -# o the cycle assuming no undercooling o the liAuid =mmonia the properties o ammonia are Temperature J;M liAuid heat latent heat liAuid entropy 5E 5L>.L 11::.> 1.5@5; <1; 17E.7@ 15L3.E ;.E@@7 (b) 2'plain the construction and working o "apour compression rerigrigeration system with neat sketch. J=nna Hni". ?o"Fec 5;17M 5;. 2'plain the construction and working o "apour absorption rerigeration system. (b) e'plain the desirable thermodynamic properties and en"ironmental saety aspects o alternati"e rerigents. J=nna Hni". ?o"Fec 5;1@M 51.
J=H., =prF4ay 5;1EM
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