Download

bankercordΜηχανική

27 Οκτ 2013 (πριν από 4 χρόνια και 11 μέρες)

74 εμφανίσεις

UNIT


1

16
-

MARKS

BASIC CONCEPTS OF FIRST LAW OF THERMODYNAMICS

1.Derive an expression for constant volume process P,V,T relation and enthalpy, internal energy,heat
transfer and workdone.

2. Derive an expression for constant pressure process P,V,T

relation and enthalpy, internal
energy,heat transfer and workdone.

3. Derive an expression for constant temperature process P,V,T relation and enthalpy, internal
energy,heat transfer and workdone.

4. Derive an expression for adiabatic process P,V,T relat
ion and enthalpy, internal energy,heat
transfer and workdone.

5. (a)Explain briefly about the Quasi


static process with their P
-
V diagram.


(b)
Explain about the Free expansion process.


(c)Explain about the throttling process.

6.(a) Derive an expre
ssion for a steady flow energy equation.


(b)Explain the applications of steady flow energy equations for the following



(i) condenser (ii) compressors (iii) Boiler (iv)Nozzle

7.
o
ne kg of gas expands at Co
nstant pre
ssure from 0.085 m
3

to 0.13 m
3

.if the initial temperature of

the gas is 22.5 °c.find the final. Temperatures, net heat transfer, change in internal energy, pressure of

gas. (16)

8
. A certain quantity of gas is head

at constant pressure from 35

°c
to 185°c. Estimate the

amount of
he
at
transferred, ideal work done, change in internal energy, when the ini
tial volume of the gas is 0.6
m
3
. (16)

9.2kg of gas at a pressure of 1.5 bar. Occupies a volume of 2.5 m
3
. If this gas compresses isothermally
to 1/3 times the initial vol
ume. Find initial. Final temperature, work done, heat transfer. (16)

10
. one kg of air is compressed polytropically (n=1.
3) from 1 bar and 27 2kg of gas at a pressure of
1.5 bar. Occupies a volume of 2.5 m3. If this gas compresses isothermally to

1/3 tim
es the initial volume. Find initial. Final temperature, work done, heat transfer. (16)


11.

one kg of air is compressed polytropically (n=1.3) from 1 bar and 27°c to 3 bar.

Find 1. work transfer 2. Heat transfer 3. Change in internal energy
. (16)

11.0.2
5 kg of the air at a pressure of 1 bar occupies a volume of 0.3 m
3

if this air expands at constant
temperature to a volume of 0.9 m
3

.Find (i) the initial temperature( ii)the final temperature
(iii)External workdone (iv)Heat absorbed (v) Change in

internal energy (vi)Change in enthalpy.

(8)

12. During a non flow process the temperature of the system changes from 100◦c to 200◦c .The
Work done by the system and heat transfer/◦c rise in temperature at each temperature is Given by
dW/dT =(4
-

0.12T) KJ/k and dQ/dT=1.005 KJ/k Determine c
hange in internal energy of the system
during the process (8)

13.
A piston and cylinder machine contains a fluid system which passes through a complete cycle of
three process during the cycle the sum of all heat transfer is +30 KJ

.The system completes 10 cycles
per minute complete the following table showing the method for each item and compute the net rate
of work output in KW.

(10)

PROCESS

Q(KJ/min)

W(Kj/min)


b⡋g/min)
=
a
-
b
=
+50
=
-
=
+20
=
b
-
c
=
-
=
+30
=
-

=
c
-
a
=
-
=
-
=
-
=
=
ㄴ1
A=晬uid=is=con晩ned=in=a=cylinde爠by=a=sp物ng=loaded=晲fctionless=piston=so=that=the=p牥ssu牥=in=a=晬ui
d
=
is=a=linea爠晵nction=o映the=volume=m==a+=b=s
=
the=inte牮al=ene牧y=o映the=晬uid= is=given=by=the=景llowing=
equation=r==34+3.15=ms=,=whe牥=r=䥳=in=kg=,=m=is=in==kpa=,s=in=m
3
.If the fluid changes from an initial
state of 170 kpa ,0.03 m
3

, to a final state of 400 kpa ,0.06 m
3

with no other work than don
e on the
piston find the direction and magnitude of the work and heat transfer.





(8)

15.A frictionless piston

cylinder device contains 2 kg of nitrogen at 100 kpa and 300 K .Nitrogen
is
now compressed slowly according to the law of PV
1.4

= C until it reaches a final temperature of 360
K .Calculate the work input during this process.

16.An ideal gas of molecular weight 30 and specific heat ratio 1.4 is compressed according to the law
o
f PV
1.25

= C

from 1 bar absolute and 27
°c to a pressure of 16 bar .Calculate the temperature at the
end of compression ,heat received or rejected, workdoneon the gas during the process and change in
enthalpy.Assume the mass of gas 1 kg.

17.In a vessel 10

kg of O
2

is heated in a reversible non


flow constant volume process so that the
pressure of O
2

is increased two times that of initial value.The initial temperature is 20°c calculate the
final temperature,change in internal energy,change in enthalpy,and

heat transfer.Take R= 0.259
KJ/kgK , C
v

=0.625 KJ/kgK for oxygen.

18. 50 kg/min of air enters the control volume in a steady flow system at 2 bar and 100◦ C and at an
elevation of 100 m above the datum the same mass leaves the control volume at 150 m ele
vation
with a pressure of 10 bar and temperature of 300◦ C the entrance velocityis 2400 m/min and the exit
velocity is 1200 m/min during the process 50000 kj/hr of heat transferred to the control volume and
the rise in enthalpy is 8 kJ/kg calculate the pow
er developed.(16)

19. Air flows steadily at the rate of 0.5 kg/s through an air compressor ,entering at 7 m/s velocity, 100
kpa pressure and 0.9 m
3
/kg the internal energy of the air is leaving 90 kJ/kg greater than that of the
air entering cooling water in the compressor jackets absorbs heat from the air at the rate of 58
kW(a)compute the rate of shaft work input to the air in KW (b) Find the inlet
pipe diameter to the
outlet pipe diameter.








(16)

20.In a steady flow of air through nozzle the enthalpy decreases by 50 KJ between sections Assuming
that there are no other energy changes than the kinetic energy determine the increases in velocity a
t
section 2 if the initial velocity is 90 m/s.

21.A steam turbine operates under steady flow conditions it receives steam 7200 kg/hr from the boiler
the steam enters the turbine at enthalpy of 2800 Kj/kg,a velocity of 400 m/min and an elevation of
4m the s
team leaves the turbine at enthalpy of 2000 Kj a velocity of 8000 m/min and an elevation of
1m due to radiation the amount of heat losses from the turbine to the surroundings is 1580 kj/hr
.Calculate the power output of the turbine.

22.
Air is compressed fr
om 100 kpa and 22
°c to a pressure of 1 Mpa while being cooled at the rate of
16 KJ/kg by circulating water through the compressor casing the volume flow rate of air inlet
condition is 150 m
3
/min and power input to the compressor is 500 kw determine (a)ma
ss flow rate
(b)temperature of air exit neglect datum head.

23.A rec
iprocating air compressor takes in 2 m
3
/min air at 0.11 Mpa ,298 K which it delivers at 1.5 Kpa
,384 K to an after cooler where the air is cooled at constant pressure to 298 K the power
absorbed by
the compressor is 4.15 KW determine the heat transfer in (i) the compressor (ii)the cooler state
your assumptions.

24.A nozzle is a device is increasing the velocity of steadily flowing steam at the inlet to a certain
nozzle the enthalpy of
the fluid pssing is 3000 KJ/kg and the velocity is 60 m/secat the discharge end
the enthalpy is 2762 KJ/kg the nozzle is horizontal and there is negligible heat loss from it (a)find the
velocity at exit from the nozzle (b) if the inlet area is 0.1 m
2

and t
he specific volume at inlet is 0.1
m
3
/kg fid the mass flow rate
(c)if the specific volume at the nozzle exit is 0.498 m
3
/kg find the exit
area of the nozzle.

25.In a turbo machine handling an incompressible fluid with a density of 1000 kg/m
3

the conditions of
the rotor entry and exit are as given below

properties

Inlet

Exit

PRESSURE

1.15 MPa

0.05 MPa

VELOCITY

30 m/s

15.5 m/s

HEIGHT ABOVE DATUM

10 m

2 m




If the volume flow rate of fluid is 40 m
3
/sec

estimate the net energy transfer from the fluid as a
work.







UNIT


5

16


MARKS

PSYCROMETRY

1
.
Dry bulb and wet temperatures of 1 atmospheric air stream are 40°0 and 30°c respectively.
Determine (a)Humidity

(b) Relative humidity (c) Specific humidity. (16)

2. Atmospheric air with barometric pressure of 1.013 bar has 38°c dry bulb temperature and
28°c wet bulb temperature. Determine (a) Humidity ratio (b) Relative humidity (c) dew point
temperature. (16)

3.

Atmospheric air at 760 mm of Hg has 45°c DBT and 30°c WBT, using psychometric chart

calculate R.H, Humidity ratio, DPT, enthalpy, specific volume of air. (16)

4.Atmospheric

air at 1 bar pressure has 2.5

°c
DBT and 75% RH using psychometric chart,
calcul
ate DBT, enthalpy, vapour pressure. (16)

5. Explain sensible heating process, sensible cooling, and

cooling and

humidification process

,

cooling and
dehumidification process
. (16)

6. An air water

vapour mixture at 0.1 Mpa, 30 °c

,80% RH. Has a volume of

50 m
3

Calculate
the specific humidity, dew point, wet bulb temperature, mass of dry air and mass of water
vapour. (16)

7.Explain the following terms


(a)adiabatic mixing of air streams (b) Adiabatic evaporative cooling

8.

explain the following heating
and humidification process ,heating and dehumidification
process.

9.Air at 20
°c

,40 % RH is mixed adiabatically with air at 40
°c

,40% RH in the ratio of

1 kg
of former with 2 kg of the latter (on the dry basis ) .find the condition of air .

(16)

10. 1
kg

of air at 24
°c

,70% RH is mixed adiabatically with 2 kg of air at 16
°c

,10% RH
.Determine the final condition of the mixture (16)

11
.The air in a room has a pressure of 1 atmosphere a dry bulb temperature of 24
°c

and a wet
bulb temperature 17
°c
comp
ute the following (a) the specific humidity (b)dewpoint
temperature (c) relative humidity (d)the degree of saturation

12
.
30 m
3
/min of moist air at 15
°c

DBT and 13
°c

WBT are mixed with 12 m
3
/min of moist air
at 25
°c

DBT and 18
°c

WBT .Determine DBT and WBT of the mixture assuming the
barometric pressure is one atmospheric.

13.
80 m
3

of air /min at 35
°c

and 50%DBT and 50%RH is cooled to 25
°c

DBT keeping its
specific humidity constant Determine (i) RH of cooled air (ii) Heat removed

from the air
using psychrometry chart

14.60 m
3

of air per minute at 35
°c DBT and 50% RH is cooled to 20

°c

DBT by passing
through a cooling coil .Determine the following (i) RH of outcoming air (ii) WBT of
outcoming air (iii) cooling capacity of coil in

tonnes of refrigeration (iv) Amount of water
vapour removed from per hour .

15.120m
3

of air per minute is passing through the adiabatic

humidifier the condition of air at
inlet is 35°c DBT and

20 % RH and the outlet condition is 20°c DBT and 15 °c WBT
.Determine the following
(i) Dew point temperature (ii) Relative humidity of the exit air (iii)
Amount of water vapour added to air per minute .

16.Air conditi
oning plant is required to supply 60
m
3

of air per minute at a DBT of 21°c and
55 % RH.The outside air is at DBT of 35 °c and 60 % RH .Determine the mass of water
drained .and capacity of the cooling coil .Assume the air conditioning plant is first to
dehumidify and then cool the air.

















UNIT


2

16


MARKS

SECOND LAW OF THERMODYNAMICS AND ENTROPY,AVAILABILITY

1.(a) Explain the two statements of second law of thermodynamics


(a) Explain the HEATPUMP and REFRIGERATOR .

2.Explain about the carnot

cycle with its P
-
V diagram and also derive an expression for the
efficiency.

3. (a)Explain about the thermodynamic temperature scale (8)


(b)Explain about the claucius inequality

(8)

4.
Derive the general relation for the entropy interms of (P
,T) and (P,V) and (T,V)

5.Derive an expression for the entropy

for the following process with its T
-
S diagram


(a) constant pressure (b) constant volume (c) constant temperature (d) polytropic process

6. Air flows through an adiabatic compressor at 3 kg
/s the inlet conditions are 2 bar and 310k and exit
conditions are 20 bar and 560 k. compute the net rate of availability transfer and irreversibility. (16)

7
. Air in a closed vessel of fixed volume of 0.15 m 3, exerts pressure of 12 bar at 250 °c ,if the

vessel
is cooled so that the pressure falls to 3.5 bar, determine the final temperature, heat transfer and change
of entropy. (16)

8
. Explain the term availability and unavailability. (16)

9
. A heat engine operates between a source a 600 °c and a sink a
t 60

°c

Determine the least rate of
heat rejection per KW net output of the engine. (16)

10.

0.2 kg of air at 1.5 bar and 27 "c is compressed to a pressure of 15 bar according to the law

pv (l.25) =c. determine work done heat flow to or from the air,
increase or decrease in entropy
(16)

11.
An inventor claims to have developed an efficient hot engine which would have a heat source at
1000 °c and reject heat to a sink at 50°c and gives an efficiency of 90 %
justify whether his claim is
possible or not

12.A heat engine of 30% efficiency drives a heat pump of COP 5 the heat is transferred both from
engine and the heat pump

to circulating water for heating building in winter .Find the ratio of heat
transfer to the circulating water from the heat pump to th
e heat transfer to the circulating water from
the heat engine .

13.A reversibile heat engine operating between reservoirs at 900 K and 300K drives a reversible
refrigerator operating between reservoirs at 300 K and 250 K .The engine receives 1800 KJ heat f
rom
900 K reservoir the net output from the combined
engine and refrigerator is 360KJ .Find the heat
transferred to the refrigerator and the net heat rejected to the reservoir at 300 K
.

14. A reversibile heat engine operating between reservoirs at 1000 K
and 400K drives a refrigerator
o
perating between reservoirs at 4
00 K a
nd 250 K .The engine receives 20
00 KJ heat from 10
00 K
reservoir the net output from the combined engine and refrigerator is
40
0KJ .Find the heat transferred
to the refrigerator and the

net hea
t rejected to the reservoir at 4
00 K .

15.A carnot heat engine receives heat from 600
°c source the efficiency of the engine is 59% .Find the
amount of heat supplied and heat rejected per KW of work output.

16.A refrigerator removes heat from a
refrigerated space at 2°c at a rate of 300KJ/min and rejects heat
to kitchen air at 26°c at a rate 345 KJ/min.Verify whether it violates ii law by (i) clacius inequality
(ii) carnot theorem

17.Three carnot engines A,B,C are operating in series between ex
treme temperatures of 1200K and
300 K find the intermediate temperatures if the work produced by the engines is in the ratio of 1:1:1

18.Two reversible heat engine A and B are arranged in series A is rejecting heat directly to B .A
receives 200 KJ at 421
°c from a hot source
while B is in communication with a cold sink at 4.4 °c .If
the work output of

A is twice that of B find(a) the intermediate temperature A and B (ii)the
efficiency of each engine (c) the heat rejected to the cold sink


















UNIT


4

16


MARKS

IDEAL GASES AND REAL
GASES, THERMODYNAMIC

RALATIONS

1. Derive

an expression for the Maxwell relations.

2. Derive

an expression for clausius clapeyron equation
.

3. Derive

an expression for joule Thomson coefficient .

4. Derive

an expression

for Tds or Entropy relations ,Enthalpy.

5. Prove

that C
p


C
v

= R and C
p


C
v

= Tβ
2
V / K

6.

(
A)
Explain about the vanderwaals equation

of state. (8)


(b)
Define compressibility factor and compressibility chart (8)

7. A

cylinder of 120
lit capacity contains CO
2

at 100 bar and 20
°c .Determine (1)mass of the gas
(2)molar volume (3)density of the gas (4) specific volume .

8. A

mixture of ideal gases consists of 2.5 kg of N
2

and 4.5 kg of CO
2
at a pressure of 4 bar and a
temperature of
25°c

.Determine (a)mole fraction of each constituent (b)Equivalent molecular weight
of the mixture (c)Eqivalent gas constant of mixture (d) the partial pressure and partial volumes (e)The
volume and density of the mixture.

9.A tank contains 0.2 m
3

of gas
mixture composed of 4 kg of nitrogen ,1 kg of oxygen and 0.5 kg of
CO
2

if the temperature is 20°c determine the total pressure ,gas constant and molar mass of the
mixture.

10.
A closed vessel has a capacity of 0.5 m
3

it contains 20% nitrogen and 20 % oxyg
en ,60% CO
2

by
volume at 20°c and 1Mpa calculate
the molecular mass ,gas constant ,and mass percentages and the
mass of mixture.

11.A mixture of 2 kg oxygen (MW =32 kg/k mol ) and 2 kg argon (MW =40 kg/k mol )

is present in
an insulated piston /cylinder ar
rangement at 100 kpa ,300K .The piston now compresses the mixture
to half its initial volume
.Find the final pressure,temperature and piston work .Asuume C
V

for oxygen
and argon as 0.1668 KJ/kg K and 0.3122 KJ/kg K.

12.
A closed r
igid cylinder is divided
by a diaphragm in to two equal compartments each of volume
0.1 m
3

.Each compartment contains air at a temperature of 20°c
the pressure in one compartment is
2.5 MPa