TDCE Question Bank – 2018
Unit I
1. How to represent the energy transformed across the system boundary as a result of energy
imparted to the fluid by a pump, blower or a compressor to make the fluid flow across the
control volume and also generate an equation which explains the work done in stretching
a wire.
2. Deduce expressions for work done and heat transfer for a process which obeys the
equation PVn = Constant
3. How do you prove the temperature of a tank which is being charged from its empty state
and later discharged completely is given by T2 = ᵞ Tp
4. “All the heat engines operating between a given constant temperature source and a given
constant temperature sink, none has a higher efficiency than a reversible engine”
Substantiate your answer
5. Give your comment on the statement “The efficiency of all reversible heat engines
operating between same temperature levels is the same.
6. “ The cyclic integral of (dQ / T ) for a reversible cycle is equal to zero” How do you
prove the given statement
7. Deduce an equation to show cyclic integral of (dQ / T ) is lesser than or equal to zero
8. Arrive at an equation which says in an irreversible process taking place in between state 1
and 2 the change of entropy is
S2 – S1 ≥ ∫ (ds / T)
9. Deduce an equation to prove, the work delivered will be maximum at temperature Tf =
√(T1T2) where T1 and T2 are temperature of two identical bodies of constant heat capacity
Tf – Final temperature
10. “ The exergy is a composite property on the state of both system and surroundings”
substantiate your answer
11. Arrive at an equation for the exergy of a closed system undergoing a change of state from
surroundings at T0
12. Arrive at an equation for the exergy of a steady flow system neglecting its kinetic and
potential energy changes.
13. A gas of Mass undergoes a quasi - static expansion which fallows relationship p=a+bv
where a and b are constants the initial and final pressures are 100kpa and 200kpa
respectively and the corresponding volumes are 0.20m3 and 1.20m3. The specific internal
energy of the gas is given by the relation u=1.5pv-85kj/kg Where p is KPa and v is in
m3/kg. Calculate the net heat transfer and maximum internal energy of the gas attained
due to expansion.
14. The heat capacity at constant pressure of certain system is a function of temperature only
and may be expressed as Cp=2.093+ (41.87/t+100) j/0C where t is the temperature of the
system in 0C. The system is heated while it is maintained at a pressure of 1 atmosphere
unit its volume increases from 0 to 1000C. a) find the magnitude of the heat interaction
b) how much does the internal energy of the system increases?
15. A reversible engine works between three thermal reservoirs A, B and C. The engine
absorbs an equal amount of heat from thermal reservoir kept at temperature T0. The
efficiency of the engine is α times the efficiency of reversible engine which ranges
between resources A and C, prove that
(TA/ TB) = (2α- 1) + [2 (1- α) TA/TC]
16. In a certain process, a vapour, while condensing at 420˚C that is lost due to the
irreversible heat to water evaporating at 250˚C. The resulting steam is used in a power
cycle which rejects heat at 35˚C. What is the fraction of the available energy in the heat
transferred from the process vapour at 420˚C that is lost due to the irreversible heat
transfer at 250˚C?
17. In a steam boiler, hot gases from a fire transfer heat to water which vaporizes at constant
temperature. In a certain case, the gases are cooled from 1100˚C to 550˚C while the water
evaporates at 220˚C. The specific heat of gases is 1.005kJ/kgK, and the latent heat of
water at 220˚C, is 1858.5kJ/kg. All the heat transferred from the gases goes to the water.
How much does the total entropy of combined system of gas and water increase as a
result of the irreversible heat transfer? Obtain the result on the basis of 1 kg of water
evaporated.
If the temperature of the surroundings is 30˚C, find the increase in unavailable
energy due to irreversible heat transfer.
18. Calculate the decrease in available energy when 25 kg of water at 95˚C mix with 35 kg of
water at 35˚C, the pressure being taken as constant and the temperature of the
surroundings being taken as constant and the temperature of the surroundings being
15˚C(cp of water =4.2 kJ/kg K).
19. Air expands through a turbine from 500kPa, 520˚C to 10 kPa, 300˚C. During expansion
10 kJ/kg of heat is lost to the surrounding which is at 98kPa, 20˚C. Neglecting the K.E
and P.E changes, determine per kg of air (a) the decrease in availability, (b) the maximum
work, and (c) The irreversibility. For air, take cp = 1.005kJ/kg, h = cp T where cp is
constant, and the pV =mRT , where p is pressure in kPa, V volume in m3, m mass in kg, R
a constant qual to 0.287 kJ/kg K, and T temperature in K.
UNIT II
1. Unlike other pure substances volume of water decreases on melting. Prove the above
statement with related PV-diagram.
2. How does the pure substances undergo state change, describe the same with relevant
PT-plot.
3. How to measure its quality of steam. When steam is very wet and pressure after
throttling is not low enough to take the steam to superheated region.
4. Two streams of steam one at 2Mpa, 3000C and other at 2Mpa, 4000C mix is a steady
state flow adiabatic process. The rates of flow of two streams are 5kg/min and
21kg/min respectively. Evaluate the final temperature of emerging stream. If there is
no pressure drop due to mixing process. What should be the rate of increase in the
entropy of the universe? This stream with the negligible velocity now expands
adiabatically in a nozzle to pressure of 1kpa. Determine the exit velocity of stream
and exit area of nozzle.
5. Steam at 10 bar, 2500C flowing wit negligible velocity at the rate of 3kgmin mixes
adiabatically with steam at10bar, 0.75quality flowing also with the negligible velocity
at the rate of 5kg/min. The combined stream of steam is throttled to 5bar and then
expanded isotropically in a nozzle to bar.
Determine a) the state of steam after mixing
b) The state of steam after throttling
c) The increase in entropy due to throttling
d) The velocity of the steam at the exit from the nozzle
e) The exit area of the nozzle
Neglect kinetic energy of the steam at the inlet to nozzle.
6. A spherical aluminum vessel has a inside diameter of 0.3m and 0.62cm thick wall.
The vessel contains water at 250C with a quality of 1%. The vessel is then heated until
water inside is saturated vapour. Considering the vessel and water together as a s/m.
Calculate the heat transfer during this process. The density of aluminum is
2.7g/cm3and its specific heat is 0.896 KJ/KgK.
7. Air is contained in a cylinder fitted with frictionless piston. Initially the cylinder
contains 0.5m3 of air at 1.5bar, 200C. The air is then compressed reversibly according
to the law pvn= constant. Until the final pressure is 6 bar at which the temperature is
1200C. Determine a) polytrophic index n b) final volume of air c) work done on air
and heat transfer d) net change in entropy.
8. The specific heat at constant pressure of air is given by Cp=0.9169+2.577x10-4T-
3.974x10-8T2KJ/KgK. Determine the change in internal energy and that in entropy of
air when it undergoes a change of state from 1atm and 298m to a temperature of
2000K at the same pressure.
UNIT III
1. Arrive at an equation which explains the phase change of a substance satisfying the
following requirements
(i) There are changes of entropy and volume
(ii) The first order derivative of Gibb’s function change discontinuously
2. How do you evaluate thermodynamic properties from an equation of state?
3. Briefly explain what is meant by (i) Zero order reaction (ii) First order reaction
4. Briefly explain what is meant by (i) Rate of reaction (ii) Reaction order & Molecularity
5. Derive the Arrhenius equation.
6. A first order reaction is 30% complete at the end of 140 s. What is the value of the
-1
reaction rate constant in s ? In how many seconds will the reaction be 60% complete?
7. Explain the following
(i) Law of mass action
(ii) Half-life period
(iii) Zero order reactions
(iv) Chain reaction
(v) Activation energy.
8. Distinguish between reaction order and molecularity.
9. Predict the pressure of nitrogen gas at T = 175K at specific volume = 0.00375 m3/ Kg
on the basis of
A) Ideal gas equation
B) The vander waals equation of state
C) The beattie bridgeman equation of state
D) The benedict-webb-rubin equation of state. Compare the values obtained to the
experimentally determined value of 10000kpa.
10. Two vessels A and B, both containing nitrogen, are connected by a valve which is
opened to allow contents to mix and achieve an equilibrium temperature of 27˚C.
Before mixing the following information is known about the gases in two vessels.
Vessel A Vessel B
p =1.5 Mpa p = 0.6 MPa
t = 50˚C t = 20 ˚C
Contents = 0.5 kg mol
Contents = 2.5 kg Calculate the final equilibrium pressure, and the
amount of heat transferred to the surroundings. If the vessel had been perfectly
insulated, Calculate the final temperature and pressure which would have been
reached. Take γ = 1.4
11. A certain gas has cp = 1.968 and cv = 1.507 kJ/kg K. Find its molecular weight and
the gas constant.
A constant volume chamber of 0.3 m3 capacity contains 2 kg of this gas at 5˚C.
Heat is transferred to the gas until the temperature is 100˚C. Find the work done, the
heat transferred, and the changes in internal energy, enthalpy and entropy.
12. Show that for an ideal gas, the slope of the constant volume line on T-s diagram is
more than that of the constant pressure line.
v=c
T p=c
A
S
13. 0.5 kg of air is compressed reversibly and adiabatically from 80 kPa, 60˚C to 0.4
Mpa, and is then expanded at constant pressure to the original volume. Sketch these
processes on the p-v and T-s planes. Compute the heat transfer and work transfer for
the whole path.
14. Discuss equations of state. Explain how Redlich Kwong equation gives good results
at high pressure and is fairly accurate for temperature above critical value.
UNIT IV
1. Mention the factors controlling the rate of flame propagation and explain thermal theory
of laminar flame propagation
2. Explain pre-mixed flames and analyze the structure of laminar flame with temperature
profile
3. The burning velocity of a combustion mixture was determined by employing the nozzle
burner total area method. The data recorded were as follows.
Volumetric flow rate of combustion mixture 220 cm^3
Height of the mean cone of the flame = 3.83 cm
Diameter of the nozzle burner port = 8.3 mm
Calculate the value of flame velocity.
4. Calculate the composition required for maximum mixture and value of maximum flame
velocity of a LPG mixture which has the following volumetric analysis
CH4 = 1.6%, C3H6 = 14.0%; C3H2 = 53.4%; C4H10 (isothermal) = 31.0%
Fuel gas Max burning velocity of fuel air Su max(cm/s)
mixture
% Fuel in mixture (by volume)
CH4 10.05 39
C2H6 6.30 46
C3H8 4.59 45
C4H10 3.52 44
5. A gaseous combustible mixture is contained in a long cylindrical glass tube open at one
end and closed at other end. The internal diameter of the tube is 5.5cm. The speed of the
uniform flame front was determined to be 8.4 cm/s by igniting the combustible mixture at
the open end from the snap shot of the flame front the flame shape was found to be nearly
hemispherical. Calculate the burning velocity of the mixture.
6. Analyze the flame area and flame velocity equation using cylindrical tube method.
7. Analyze the various factors affecting burning velocity.
8. Analyze the effect of flow factors affecting turbulent burning velocity.
9. Analyze flame stretch theory.
10. Analyze theory of diffusion flames.
11. Determine the transfer number of a liquid hydrocarbon (CH2)n fuel droplet burning in an
atmosphere of air. The latent heat of vaporization of the hydrocarbon fuel is 83.5 cal/g and
the specific heat for gases as constant pressure may be taken as 0.3 cal/g0C. Assume the
value of the heat of combustion of fuel (H) as 10550 cal/g. Take T2 - T1 = 565 0C.
12. What is the time of disappearance in second son a liquid droplet of a (CH2)n hydrocarbon fuel
burning in still air when the following data in addition to those given in example in the above
problem(problem 11) . Apply
Density of droplet (Pf) = 0.8 g/cm3
Initial radius of droplet (ro) = 0.002 cm
Exchange co efficient(y) = 0.413*10^3 g/cms
13. Determine the enthalpy of formation (∆Hi) of propane using the table of values of enthalpy of
combustion (∆Hi) of C3H8 (g), enthalpy of formation (∆Hi) of CO, (g) and enthalpy of
formation (∆Hi) of H2O (l).
14. Methane gas at 400 K is supplied along with 120 percent Stoichiometric air (preheated to 500
K) to a furnace. Combustion which occurs at 1 atm pressure, goes to completion and the
temperature of products of combustion is 2000 K. Determine the heat transfer to or from the
furnace in kJ/kmol of fuel.
15. Determine the equilibrium compostion for the constant pressure combustion of CO + i O2 at
3000 K and 10 atm pressure.
16. One mole of CO2 is mixed with one mole of H2. Determine the equilibrium composition for
the reaction C + H2 ↔ CO + H2O, if the temperature and pressure are 2500 K and 1 atm.
Assume that only CO, CO2, H2, H2O and O2 are present in the products.
17. Calculate the limits of inflammability of a liquefied petroleum gas (LPG) mixture which has
the following volumetric analysis: CH4 : 1.6 %, C2H6 : 14.0%; C3H8 : 53.4%, C4H10 (iso +
normal): 31.0%
Limit of Inflammability (% by volume)
Gas Lower Upper
CH4 5.3 15.0
C2H6 3.0 12.5
C3H8 2.12 9.35
C4H10 1.83 8.43
18. Calculate the composition required for the maximum mixture and the value of maximum
burning velocity of a liquefied petroleum gas mixture which has the volumetric analysis:
CH4 : 1.6 %, C2H6 : 14.0%; C3H8 : 53.4%, C4H10 (iso + normal): 31.0%
Maximum burning velocity of fuel-air mixture
Fuel gas % Fuel in mixture (by vol.) Su,max
(cm/s)
CH4 10.05 39
C2H6 6.30 46
C3H8 4.59 45
C4H10 3.52 44
19. A gaseous combustible mixture is contained in a long cylindrical glass tube open at one end
and closed at the other end. The internal diameter of the tube is 5.5 cm. The speed of the
uniform movement of the flame front was determined to be 84 cm/s by ignighting the
combutile mixture at the open end. From the snapshot of the flame front, the flame shape was
found to be nearly hemispherical. Calculate the burning velocity of the mixture.
UNIT V
1. A fuel gas has the following percentage volumetric analysis H2:48 , CH4 :26, CO2 : 11,
CO : 5, N2 : 10, the percentage volumetric analysis of the dry exhaust gases is CO2 : 8.8,
O2: 5.5, N2 : 85.7 Determine air/fuel ratio by value if air contains 21% of O2 by volume.
2. A fuel has the following percentage analysis by weight. C : 82, H2 : 10, S: 3, O2 : 2.5,
ash : 2.5 for an air fuel ratio of 12 : 1, calculate
a) The mixture strength as percentage rich or lean and
b) The volumetric analysis of the dry products of combustion air contains 23% oxygen
by weight.
3. Find the dew point temperature of the high temperature products of combustion of
C8H16 with 20% deficiency of air if total pressure is one atmosphere.
4. Determine the equilibrium composition for the constant pressure combustion of
CO + ½ O2 at 3000K and 10 atmospheric pressure.
5. 1 mole of CO2 is mixed with 1 mole H2. Determine the equilibrium composition for
reaction
CO2 + H2 ↔ CO + H2O
If the temperature and pressure are 2500K and 1 atmospheric assume that only CO, CO2,
H2, H2O and O2 are present in the products
6. Carbon monoxide and 200% theoretical oxygen react to give products at high
temperature and one atmospheric pressure. The relative concentrations of CO and CO2 in
the products are determined to be 2:3. Find the Kp for the reaction
7. How do you apply the mode of combustion of fuel droplets in spray combustion process?
8. Analyze the regions in combustion chamber and explain the types of combustion
chamber gas turbine
9. Design a rocket motor which works with a help of gas turbine
11. Analyze the kinetics of heterogeneous combustion
12. Explain the oxidation mechanism of carbon
13. Analyze the properties testing of fuel gas
14. Analyze the combustion of fuel droplets with temperature profile considering the
burning of process as a function of distance from centre of droplet
15. Apply the flame stabilization on quenching distance, penetration distance and dead
space
20. Analyze the mechanism of flame stabilization.
21. Determine the transfer number of a liquid hydrocarbon (CH2) fuel droplet burning in an
atmosphere of air. The latent heat of vaporization of the hydrocarbon fuel is 83.5 cal/g and the
specific heat of gases at constant pressure may be taken as 0.3 cal/g˚C. Assume the value of the
heat of combustion of fuel (H) as 10,550 cal/g. Take T0-T1 = 565˚C.
22. Estimate the life-time of an ethyl alcohol fuel droplet burning in stagnant air. The initial droplet
diameter is 20*10−3 cm. The following data may be used:
Heat of combustion of fuel (H) = 6,700 cal/g
Latent heat of vaporization of fuel (L) = 238 cal/g
Specific gravity of ethyl alcohol = 0.8
Exchange Coefficient (γ = Dρg) = 0.413 * 10−3 gm/cm.
The temperature of the droplet. (Ti) may be assumed to be equal to the atmospheric
temperature (Tg).
23. What is the time disappearance in seconds of a liquid droplet of (CH4)n hydrocarbon fuel burning
in still air when the latent heat of vaporization of the hydrocarbon fuel is 83.5 cal/g and the
specific heat of gases at constant pressure may be taken as 0.3 cal/g˚C. Assume the value of the
heat of combustion of fuel (H) as 10,550 cal/g Take T0-T1 = 565˚C. and the following data:
Density of droplet (ρj) = 0.8g/cm 3
Initial radius of droplet (r0) = 2 * 10−3 cm .
Exchange coefficient (γ = Dρg) = 0.413 * 10−3 gm/cms.
