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WorksheetsTHERMAL ENGINEERING II MCQ (MODEL EXAM - 3)
Total questions: 50
Worksheet time: 25mins
100 CFM air flow rate is equal to
28.317 liters/s
47.195 liters/s
57.195 liters/s
38.317 liters/s
If the specific heats of dry air and water vapour are 1.00 kJ/kg-K and 1.88 kJ/kg-K respectively and the humidity ratio is 0.011, then the specific heat of moist air at 25°C and 50% relative humidity will be
1.869 kJ/kg-K
1.891 kJ/kg-K
0.9793 kJ/kg-K
1.0206 kJ/kg-K
Air in which of the following classes is cleaner
Class 10000
Class 1000
Class 100
Class 10
The grill temperature of air is
temperature of air entering the cooling coil
temperature of air leaving the room
temperature of air entering the room
temperature of fresh air after mixing with return air
It is desired to condition the outside air from 70% relative humidity and 45°C dry bulb temperature to 50% relative humidity and 25% dry bulb temperature (room condition). The practical arrangement will be
Dehumidification
Cooling and humidification
Cooling and dehumidification
Dehumidification and pure sensible cooling
A cold storage is to be maintained at – 5°C while the surroundings are at 35°C. The heat leakage from the surroundings into the cold storage is estimated to be 29 kW. The actual C.O.P. of the refrigeration plant used is one third that of an ideal plant working between the same temperatures. Find the power required to drive the plant
11.58 kJ/s
12.98 kJ/s
12.90 kJ/s
10.98 kJ/s
In a vapor compression refrigeration plant, the refrigerant leaves the evaporator at 195 KJ/kg and the condenser at 65 KJ/kg. For every kg of refrigerant, the plant can supply per second, a cooling load of
70 KW
130 KW
160 KW
100 KW
If the specific heats of dry air and water vapour are 1.00 kJ/kg-K and 1.88 kJ/kg-K respectively and the humidity ratio is 0.011, then the specific heat of moist air at 25°C and 50% relative humidity will be
1.869 kJ/kg-K
1.891 kJ/kg-K
0.9793 kJ/kg-K
1.0206 kJ/kg-K
It is desired to condition the outside air from 70% relative humidity and 45°C dry bulb temperature to 50% relative humidity and 25% dry bulb temperature (room condition). The practical arrangement will be
Dehumidification
Cooling and humidification
Cooling and dehumidification
Dehumidification and pure sensible cooling
Which one of the following statements is correct
The sensible heat gain is due to the difference in humidity
The latent heat gain is due to the temperature difference between the fresh air through unconditioned space in the building adds to the sensible heat gain
The heat gain through the walls of ducts carrying conditioned air through unconditioned space in the building adds to the sensible heat gain
Maximum heat gain to a building occurs through walls
In the context of cogeneration turbine, the thermodynamic process taking place is
expansion
condensation
contraction
both (a) & (c)
The device used for recovering waste heat from the textile drier exhaust
heat wheel
recuperator
economizer
regenerator
Recuperator as a waste heat recovery system is used mainly in a
boiler
reheating furnace
compressor
gas turbine
The Brayton cycle is a characteristic of
steam turbine
petrol engine
gas turbine
none of the above
Power is to be generated from a cement kiln exhaust gas. The applicable type of cogeneration is called
topping cycle
Carnot cycle
bottoming cycle
Brayton cycle
Combined cycle is a combination of
conventional boiler first followed by cogeneration system
Brayton cycle first followed by a standard Rankine cycle
Rankine cycle first followed by a Brayton cycle
extraction in the first portion and then a condensing cycle
The efficiency of which of the following turbine systems is the highest
condensing
back pressure
double extraction condensing
extraction condensing
Steam enters an impulse turbine at a velocity of 500 m/s and having nozzle angle 20 deg. The symmetrical blades have a mean peripheral velocity of 300 m/s. Consider a mass flow rate of 0.75 kg/s. Calculate the diagram power (kW) for the turbine. Neglect friction effects on blades.
100.25
76.43
150.63
200.36
A partly impulsive and partly reaction force are the driving forces in case of
An impulse turbine
Fifty percent reaction turbine only
Sixty percent reaction turbine only
Any reaction turbine other than hundred & zero percent
Degree of reaction is defined as
Enthalpy drop in the moving blades to the enthalpy drop in the stage
Enthalpy drop in the moving blades to the enthalpy drop in the fixed blades
Enthalpy drop in the fixed blades to the enthalpy drop in the moving blades
Enthalpy drop in the fixed blades to the total enthalpy drop in the moving blades
The driving force in an 50% reaction turbine is partly impulsive force and partly reaction force
True
False
Sometimes true
True only with special attachments
A 50% reaction turbine is rotating at 2400 rpm with a mean blade speed of 100 m/s. The exit angle of blades is 20 deg. and the velocity ratio is 0.56. The mean specific volume of steam is 0.65 cub.m/kg and the mean height of blade is 25 mm. Neglect effect of blade thickness on the annulus area. Calculate the mass flow of steam through the turbine in kg/h.
29340
21147
25365
30285
An impulse steam turbine has a number of pressure stages with each stage having a row of nozzles and a single ring of blades. With reference to the plane of rotation, nozzle angle of first stage is 20 deg and blade exit angle is 30 deg. The velocity of steam leaving the nozzles is 350 m/s and the mean blade speed is 100 m/s. Determine the work done in a stage per kg of steam (kJ/kg). Blade friction factor is 0.8 and nozzle efficiency is 0.85.
56.42
45.98
39.45
40.79
Degree of reaction is defined as
Enthalpy drop in the moving blades to the enthalpy drop in the stage
Enthalpy drop in the fixed blades to the enthalpy drop in the stage
Enthalpy drop in the fixed blades to the enthalpy drop in the moving blades
Enthalpy drop in the fixed blades to the total enthalpy drop in the moving blades
A 50% reaction turbine is rotating at 2600 rpm with a mean blade speed of 120 m/s. The exit angle of blades is 20 deg. and the velocity ratio is 0.56. Calculate the mass flow of steam through the turbine in kg/h. The mean specific volume of steam is 0.65 cub.m/kg and the mean height of blade is 25 mm. Neglect effect of blade thickness on the annulus area.
28044
25365
35236
20365
A steam turbine is to operate between 150 bar, 600 deg.Celcius and 0.1 bar. The bucket velocity is limited to 250 m/s and the average nozzle efficiency is expected to be 95% for impulse and 90% for reaction turbine. All stages operate close to the speed corresponding to maximum efficiency. Nozzle angles can be assumed as 20 deg. for impulse and reaction stages. Estimate the number of stages required if all the stages are 50% reaction stages.
19
5
30
11
A single stage impulse turbine is provided with a steam at mass flow rate of 5 kg/s. Take following data of this turbine:
Rotor diameter: 1.5 m
Rotor speed: 3500 rpm
Nozzle angle 15o
Blade speed ratio: 0.35
Velocity coefficient: 0.86
Assume that outlet blade angle is 2o less than inlet blade angle.
Find Absolute velocity of whirl at exit of moving blade, m/s
147
524
483
785
A binary-vapour cycle operates on mercury and steam. Saturated mercury at 4.5 bar is supplied to the mercury turbine, from which it exhausts at 0.04 bar. The mercury condenser generates saturated steam at 15 bar which is expanded in a steam turbine to 0.04 bar. The thermodynamic states of saturated mercury and saturated vapour are given in the table. Here, h is specific enthalpy, s is specific entropy and v the specific volume; subscripts f and g denote saturated liquid state and saturated vapour state respectively.
The overall efficiency (%) of the plant based on combined cycle is (a)
A certain chemical plant requires heat from process steam at 125° C at the rate of 6 MJ/s and power at the rate of 1000 kW from the generator terminal. Both the heat and power requirements are met by a back pressure turbine with 85% brake (mechanical) and 80% internal (isentropic) efficiency, which exhausts steam at 125° C in dry saturated state. All the latent heat release during the condensation is utilized in the process heater. The thermodynamic states of water and saturated vapour are given in the table. Here, h is specific enthalpy, s is specific entropy and v the specific volume; subscripts f and g denote saturated liquid state and saturated vapour state respectively.
The quality of water vapour at exhaust of water turbine is (a)
At critical point of water, i.e. p=221 bar, the latent heat of vaporization is
maximum
minimum
function of temperature
zero
The evaporation of 15.653 kg of water per hour from and at 100°C is called
evaporative capacity
factor of evaporation
equivalent evaporation
one boiler h.p.
If maximum permissible limit of TDS as in a package boiler is 3000 ppm, percentage make up water is 10% and TDS in feed water is 300 ppm, then the percentage blow down is
1%
2%
3%
5%
The air pressure at the fuel bed is reduced below that of atmosphere by means of a fan placed at or near the bottom of the chimney to produce a draught. Such a draught is called
Natural draught
Induced draught
Forced draught
Balanced draught
The ideal combustion process during which methane is burned completely. The air fuel (AF) ratio for this combustion on a mass basis is
13.76 kg air / kg fuel
17.19 kg air / kg fuel
21.17 kg air / kg fuel
23.12 kg air / kg fuel
65.6 %
86.5 %
72.5 %
80.6 %
when fuel oil with 84.9 % carbon, 11.4 % hydrogen, 3.2 % Sulphur, 0.4 % oxygen and 0.1 % ash by weight is burnt with 20 % excess air, assume complete combustion calculate Total air supplied
6.42 kg/kg of fuel
9.24 kg/kg of fuel
16.72 kg/kg of fuel
19.52 kg/kg of fuel
What is done to increase the rate of heat transfer in the Velox boiler?
The boiler is heated up to very high range of temperature
Combustion gases are circulated through tubes with supersonic speed
High grade fuel is made use for the combustion
The size of the boiler is changed as it is flexible
Which of the following is also known as converging-diverging contoured nozzle?
Bernoulli’s nozzle
Pascal nozzle
de Laval' nozzle
Torricelli’s nozzle
In a nozzle, friction ___________ the dryness fraction of steam at the exit
Decreases
Same
Increases
None of the above
Steam is expanded in a set of nozzles from 4 bar 300 deg. Celcius to 2 bar. What is the type of nozzle? Consider the isentropic index k=1.3.
Convergent-divergent
Convergent
Data insufficient
None of the above
In which part of a converging-diverging nozzle will have unity Mach number in the chocked condition
Convergent portion
Divergent portion
Throat
None of the above
A nozzle is said to be choked when
It is discharging into atmosphere
Flow through it is zero
At the given inlet condition, mass flow rate is maximum
It is not possible to increase the flow by increasing inlet pressure
In a nozzle, friction ___________ the dryness fraction of steam at the exit
Increases
Decreases
Same
None of the above
The condition of steam leaving a nozzle is_______ in comparison with inlet conditions
Low velocity and High pressure
High velocity and high pressure
Low velocity and low pressure
High velocity and low pressure
Air having a flow rate of 3.6 kg/s at 7 bar and 170 deg.Celcius expands through a convergent-divergent nozzle into a space at 1.03 bar. Calculate the throat area (sq.mm) of the nozzle. Assume isentropic flow and neglect inlet velocity
1463
3645
2680
2185
The throat and exit areas of a convergent-divergent nozzle are 1280 sq.mm and 1600 sq.mm respectively. Dry saturated steam at 5 bar enters the nozzle at a velocity of 80 m/s. The exit pressure is 1.5 bar. Estimate the mass flow rate in kg/s. Assume isentropic flow up to the throat and take critical pressure ratio to be 0.58
0.689
0.459
0.958
0.632
The value of critical pressure ratio for superheated steam is
0.546
0.500
0.556
0.582
