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All questions of Power Engineering for Mechanical Engineering Exam
Boiler rating is usually defined in terms of- a)Maximum temperature of steam in Kelvin
- b)Heat transfer in KJ/hr
- c)Heat transfer area in metre2
- d)Steam output in kg/hr
Correct answer is option 'D'. Can you explain this answer?
Boiler rating is usually defined in terms of
a)
Maximum temperature of steam in Kelvin
b)
Heat transfer in KJ/hr
c)
Heat transfer area in metre2
d)
Steam output in kg/hr
|
Lavanya Menon answered |
Boiler rating is the heating capacity of a steam boiler. It is expressed in BTU per hour (BTU/h), horsepower (hp), or steam output in kg/hr at 100°C’ and atmospheric pressure. Each kilogram of steam receives 2257 kJ of heat from the boiler.
The rating indicates the maximum capacity of a boiler. When a boiler operates at its maximum rated capacity, it is referred to as the maximum load. If the load varies from hour to hour, it operates at a varying load. Load and load variations can influence the amount of chemicals required for treatment and the treatment controls required.
Which one of the following groups of devices are used for part recovery of heat from the flue gases leaving the tube banks in a water tube boiler?- a)Drum internals, super heaters and economiser
- b)Economiser, air Preheater and electrostatic precipitator
- c)Water wall, drum internals and super heaters
- d)Super heaters, economiser and air preheater
Correct answer is option 'D'. Can you explain this answer?
Which one of the following groups of devices are used for part recovery of heat from the flue gases leaving the tube banks in a water tube boiler?
a)
Drum internals, super heaters and economiser
b)
Economiser, air Preheater and electrostatic precipitator
c)
Water wall, drum internals and super heaters
d)
Super heaters, economiser and air preheater
|
Abhay Kapoor answered |
Superheaters: It is used to dry the wet steam and raise the temperature of the steam above its saturation temperature. It is generally placed in the path of the furnace gases so as to utilize the heat from the hot flue gases.
Economizer: It is also known as feed water heater. It is a device in which the waste heat of the flue gases is utilised for heating the feed water.
Air Preheater: It is used to increase the temperature of air before it enters the furnace. It is generally placed after the economiser; so that the flue gases pass through the economiser and then to the air preheater.
Electrostatic precipitator, also called electrostatic air cleaner, a device that uses an electric charge to remove certain impurities—either solid particles or liquid droplets—from air or other gases in smokestacks and other flues.
Boiler Drum is a pressure vessel it is used to Separate steam and water mixture.
So super heaters, economiser and air preheater are used for part recovery of heat from the flue gases.
The efficiency of jet engine is- a)Higher at high speeds
- b)Lower at low speeds
- c)Higher at high altitudes
- d)Same at all altitudes
Correct answer is option 'A'. Can you explain this answer?
The efficiency of jet engine is
a)
Higher at high speeds
b)
Lower at low speeds
c)
Higher at high altitudes
d)
Same at all altitudes
|
Mahi Kaur answered |
For turbo jet engines the efficiency is higher for higher speeds. Whereas in turbo prop engines it first increases then decreases.
A three-stage reciprocating compressor has suction pressure of 1 bar delivery pressure of 64 bar. For minimum work of compression, the delivery pressure of first-stage is- a)14 bar
- b)16 bar
- c)4 bar
- d)8 bar
Correct answer is option 'C'. Can you explain this answer?
A three-stage reciprocating compressor has suction pressure of 1 bar delivery pressure of 64 bar. For minimum work of compression, the delivery pressure of first-stage is
a)
14 bar
b)
16 bar
c)
4 bar
d)
8 bar
|
|
Rounak Banerjee answered |
Analysis:
To determine the delivery pressure of the first stage for minimum work of compression in a three-stage reciprocating compressor, we can use the concept of intercooling. Intercooling involves cooling the gas between stages to reduce the work of compression.
Given:
Suction pressure (P1) = 1 bar
Delivery pressure (P3) = 64 bar
Calculations:
- Let the delivery pressure of the first stage be P2.
- The work of compression is given by W = P1V1 * ln(P2/P1) + P2V2 * ln(P3/P2)
- For minimum work, the pressure ratios across each stage should be equal.
- Therefore, P2/P1 = P3/P2
- P2^2 = P1 * P3
- P2 = sqrt(P1 * P3)
Answer:
The delivery pressure of the first stage for minimum work of compression is:
P2 = sqrt(1 * 64) = 8 bar
Therefore, the correct answer is option C) 8 bar.
To determine the delivery pressure of the first stage for minimum work of compression in a three-stage reciprocating compressor, we can use the concept of intercooling. Intercooling involves cooling the gas between stages to reduce the work of compression.
Given:
Suction pressure (P1) = 1 bar
Delivery pressure (P3) = 64 bar
Calculations:
- Let the delivery pressure of the first stage be P2.
- The work of compression is given by W = P1V1 * ln(P2/P1) + P2V2 * ln(P3/P2)
- For minimum work, the pressure ratios across each stage should be equal.
- Therefore, P2/P1 = P3/P2
- P2^2 = P1 * P3
- P2 = sqrt(P1 * P3)
Answer:
The delivery pressure of the first stage for minimum work of compression is:
P2 = sqrt(1 * 64) = 8 bar
Therefore, the correct answer is option C) 8 bar.
A simple Rankine cycle operates the Boiler at 3 MPa with an outlet temperature and enthalpy of 350°C and 3115.3 kJ/kg respectively and the condenser at 50 kPa. Assuming ideal operation and processes, what is the thermal efficiency of this cycle? Neglect the pump work. Assume exhaust from the turbine is dry saturated steam.At 0.5 bar: hf = 340.5 kJ/kg, hg = 2646 kJ/kgAt 30 bar: hf = 1008 kJ/kg, hg = 2804 kJ/kg- a)7
- b)17
- c)21
- d)37
Correct answer is option 'B'. Can you explain this answer?
A simple Rankine cycle operates the Boiler at 3 MPa with an outlet temperature and enthalpy of 350°C and 3115.3 kJ/kg respectively and the condenser at 50 kPa. Assuming ideal operation and processes, what is the thermal efficiency of this cycle? Neglect the pump work. Assume exhaust from the turbine is dry saturated steam.
At 0.5 bar: hf = 340.5 kJ/kg, hg = 2646 kJ/kg
At 30 bar: hf = 1008 kJ/kg, hg = 2804 kJ/kg
a)
7
b)
17
c)
21
d)
37
|
|
Arnab Choudhury answered |
The efficiency of the Rankine cycle is then given by:
Reheating in a gas turbine- a)increases the compressor work
- b)decreases the compressor work
- c)increase the turbine work
- d)decreases the turbine work
Correct answer is option 'C'. Can you explain this answer?
Reheating in a gas turbine
a)
increases the compressor work
b)
decreases the compressor work
c)
increase the turbine work
d)
decreases the turbine work
|
Arshiya Dey answered |
Reheating is a method of increasing the mean temperature of heat reception. In this the gas is again heated after it has expanded in the gas turbine. This increases the work output of the turbine by keeping the compressor work constant. By reheating the mean temperature of heat rejection is also increased, resulting in a decrease in the thermal efficiency of the plant.
A convergent-divergent nozzle is said to be choked when:- a)Critical pressure is attained at the exit and Mach number at this section is sonic
- b)Velocity at the throat becomes supersonic
- c)Exit velocity becomes supersonic
- d)Mass flow rate though the nozzle reaches a maximum value
Correct answer is option 'D'. Can you explain this answer?
A convergent-divergent nozzle is said to be choked when:
a)
Critical pressure is attained at the exit and Mach number at this section is sonic
b)
Velocity at the throat becomes supersonic
c)
Exit velocity becomes supersonic
d)
Mass flow rate though the nozzle reaches a maximum value
|
|
Rounak Banerjee answered |
When a flowing fluid at a given pressure and temperature passes through a restriction (such as the throat of a convergent-divergent nozzle or a valve in a pipe) into a lower pressure environment the fluid velocity increases. Mass flow continues to increase with decreasing the exit pressure. Choked flow is a limiting condition where the mass flow will not increase with a further decrease in the downstream pressure environment.
A nozzle is said to be chocked when flow rate through it is maximum and at throat of nozzle M = 1
In an impulse turbine, the pressure drops- a)Only in the nozzles
- b)Only in the moving blades
- c)Only in the fixed blades
- d)Both in fixed and in moving blades
Correct answer is option 'A'. Can you explain this answer?
In an impulse turbine, the pressure drops
a)
Only in the nozzles
b)
Only in the moving blades
c)
Only in the fixed blades
d)
Both in fixed and in moving blades
|
Anshul Sharma answered |
Pressure Drop in an Impulse Turbine
Introduction:
An impulse turbine is a type of steam turbine used in power plants and other industries to convert the kinetic energy of a high-pressure steam into mechanical work. It operates on the principle of the impulse reaction, where a high-velocity jet of steam is directed onto the blades of the turbine rotor, causing it to rotate.
Pressure Drop:
The pressure drop in an impulse turbine occurs primarily in the nozzles. The nozzles are fixed, stationary components that serve the purpose of channeling the high-pressure steam into high-velocity jets. These jets then impinge on the moving blades, causing them to rotate.
Nozzles and Pressure Drop:
The pressure drop in an impulse turbine primarily occurs in the nozzles due to the conversion of pressure energy to kinetic energy. The nozzles are designed to accelerate the steam to a high velocity by increasing its kinetic energy. This acceleration is achieved by creating a convergent-divergent nozzle geometry, where the steam passes through a converging section followed by a diverging section.
Converging Section:
In the converging section of the nozzle, the steam flow area decreases, leading to an increase in velocity and a corresponding decrease in pressure. This decrease in pressure is due to the conversion of pressure energy into kinetic energy.
Diverging Section:
In the diverging section of the nozzle, the steam flow area increases, causing the velocity to decrease and the pressure to increase. However, the pressure in the diverging section does not reach the same level as the inlet pressure. This is because some of the pressure energy has been converted into kinetic energy in the converging section.
Impact on Moving Blades:
Once the high-velocity jets of steam leave the nozzles, they impinge on the moving blades of the turbine rotor. The impact of the steam on the blades causes a change in momentum, resulting in the rotation of the rotor. However, the pressure drop in the moving blades is relatively small compared to that in the nozzles.
Conclusion:
In an impulse turbine, the pressure primarily drops in the nozzles due to the conversion of pressure energy into kinetic energy. The pressure drop in the moving blades is relatively small. Therefore, the correct answer is option 'A' - Only in the nozzles.
Introduction:
An impulse turbine is a type of steam turbine used in power plants and other industries to convert the kinetic energy of a high-pressure steam into mechanical work. It operates on the principle of the impulse reaction, where a high-velocity jet of steam is directed onto the blades of the turbine rotor, causing it to rotate.
Pressure Drop:
The pressure drop in an impulse turbine occurs primarily in the nozzles. The nozzles are fixed, stationary components that serve the purpose of channeling the high-pressure steam into high-velocity jets. These jets then impinge on the moving blades, causing them to rotate.
Nozzles and Pressure Drop:
The pressure drop in an impulse turbine primarily occurs in the nozzles due to the conversion of pressure energy to kinetic energy. The nozzles are designed to accelerate the steam to a high velocity by increasing its kinetic energy. This acceleration is achieved by creating a convergent-divergent nozzle geometry, where the steam passes through a converging section followed by a diverging section.
Converging Section:
In the converging section of the nozzle, the steam flow area decreases, leading to an increase in velocity and a corresponding decrease in pressure. This decrease in pressure is due to the conversion of pressure energy into kinetic energy.
Diverging Section:
In the diverging section of the nozzle, the steam flow area increases, causing the velocity to decrease and the pressure to increase. However, the pressure in the diverging section does not reach the same level as the inlet pressure. This is because some of the pressure energy has been converted into kinetic energy in the converging section.
Impact on Moving Blades:
Once the high-velocity jets of steam leave the nozzles, they impinge on the moving blades of the turbine rotor. The impact of the steam on the blades causes a change in momentum, resulting in the rotation of the rotor. However, the pressure drop in the moving blades is relatively small compared to that in the nozzles.
Conclusion:
In an impulse turbine, the pressure primarily drops in the nozzles due to the conversion of pressure energy into kinetic energy. The pressure drop in the moving blades is relatively small. Therefore, the correct answer is option 'A' - Only in the nozzles.
For the same diameter and thickness of tube, a water tube boiler compared to a fire tube boiler has:- a)More heating surface
- b)Less heating surface
- c)Equal heating surface
- d)Heating surface depends on other parameters
Correct answer is option 'A'. Can you explain this answer?
For the same diameter and thickness of tube, a water tube boiler compared to a fire tube boiler has:
a)
More heating surface
b)
Less heating surface
c)
Equal heating surface
d)
Heating surface depends on other parameters
|
Bhargavi Chauhan answered |
In water tube boilers, water is contained in many small diameter tubes; therefore, the heating surface of a water tube boiler is more than that of the fire tube boiler. The relatively large heating surface of the water tube boiler increases the evaporation rate. The increased rate of evaporation of the water tube boiler makes it more suitable for large power plants.
In steam turbine terminology, diaphragm refers to- a)separating wall between rotor carrying nozzles
- b)the ring of guide blades between rotors
- c)a partition between low and high velocity sides
- d)the flange connecting the turbine exit to the condenser
Correct answer is option 'A'. Can you explain this answer?
In steam turbine terminology, diaphragm refers to
a)
separating wall between rotor carrying nozzles
b)
the ring of guide blades between rotors
c)
a partition between low and high velocity sides
d)
the flange connecting the turbine exit to the condenser
|
|
Arnab Saini answered |
Diaphragm in steam turbines is a separating wall between rotors carrying nozzles. Additionally, as there is a significant pressure drop across a reaction turbine stage, the diaphragm also acts as a partition between the pressure stages.
If the enthalpies at the entry and exit of a nozzle at 3450 kJ/kg and 2800 kJ/kg and the initial velocity is negligible, then the velocity at the exit is- a)806.2 m/s
- b)25.5 m/s
- c)36 m/s
- d)1140.2 m/s
Correct answer is option 'D'. Can you explain this answer?
If the enthalpies at the entry and exit of a nozzle at 3450 kJ/kg and 2800 kJ/kg and the initial velocity is negligible, then the velocity at the exit is
a)
806.2 m/s
b)
25.5 m/s
c)
36 m/s
d)
1140.2 m/s
|
Shruti Bose answered |
For nozzle: Steady flow energy equation is:
Coke is produced by- a)pulverizing coal in inert atmosphere
- b)heating wood in a limited supply of air at temperatures below 300°C
- c)strongly heating coal continuously for about 48 hours in the absence of air in a closed vessel
- d)binding the pulverized coal into briquettes
Correct answer is option 'C'. Can you explain this answer?
Coke is produced by
a)
pulverizing coal in inert atmosphere
b)
heating wood in a limited supply of air at temperatures below 300°C
c)
strongly heating coal continuously for about 48 hours in the absence of air in a closed vessel
d)
binding the pulverized coal into briquettes
|
Anushka Bose answered |
The chimney draught depends upon- a)Atmospheric Pressure
- b)Furnace temperature
- c)Height of chimney
- d)All of these
Correct answer is option 'D'. Can you explain this answer?
The chimney draught depends upon
a)
Atmospheric Pressure
b)
Furnace temperature
c)
Height of chimney
d)
All of these
|
|
Rohan Singh answered |
n order to maintain the continuous flow of fresh air into the combustion chamber, it is necessary to exhaust the products of combustion from the combustion chamber of a boiler. A pressure difference has to be maintained to accelerate the products of combustion to their final velocity and to overcome the pressure losses in the flow system. This pressure difference so maintained is called draught.
The natural/chimney draught depends on
- the atmospheric temperature
- flue gases temperature leaving the furnace
- and height of the chimney
In a simple impulse turbine, the nozzle angle at the entrance is 30°. What will be the blade-speed ratio for maximum diagram efficiency?- a)0.433
- b)0.25
- c)0.5
- d)0.75
Correct answer is option 'A'. Can you explain this answer?
In a simple impulse turbine, the nozzle angle at the entrance is 30°. What will be the blade-speed ratio for maximum diagram efficiency?
a)
0.433
b)
0.25
c)
0.5
d)
0.75
|
|
Anshul Basu answered |
Blade or diagram efficiency is defined as the ratio of work done on the blades to the energy supplied to the blades.
Blade speed ratio is the ratio of blade speed to a steam speed
ηb will be maximum when:
α1 is of the order 18° to 22°
When inspection doors on the walls of boilers are opened, flame does not leap out because- a)These holes are small
- b)Pressure inside is negative
- c)Flame travels always in the direction of flow
- d)These holes are located beyond the furnace
Correct answer is option 'B'. Can you explain this answer?
When inspection doors on the walls of boilers are opened, flame does not leap out because
a)
These holes are small
b)
Pressure inside is negative
c)
Flame travels always in the direction of flow
d)
These holes are located beyond the furnace
|
|
Ishaan Malik answered |
The flame does not leap out during opening of inspection door because there is negative pressure in the combustion area. Negative pressure is achieved in balanced draft boilers by using forced draft fans to force air into boiler (pressuring it) and Induced draft fans to remove air from the boilers to create negative pressure
Cochran boiler is a- a)horizontal fire - tube boiler
- b)horizontal water - tube boiler
- c)vertical water - tube boiler
- d)vertical fire tube boiler
Correct answer is option 'D'. Can you explain this answer?
Cochran boiler is a
a)
horizontal fire - tube boiler
b)
horizontal water - tube boiler
c)
vertical water - tube boiler
d)
vertical fire tube boiler
|
|
Rounak Saini answered |
It is a multi-tubular vertical fire tube boiler having numbers of horizontal fire tubes. It is the modification of a simple vertical boiler where the heating surface has been increased by means of numbers of fire tubes.
Rankine cycle comprises of- a)two isentropic processes and two constant volume processes
- b)two isentropic processes and two constant pressure processes
- c)two isothermal processes and two constant pressure processes
- d)two isothermal processes and two constant volume processes
Correct answer is option 'B'. Can you explain this answer?
Rankine cycle comprises of
a)
two isentropic processes and two constant volume processes
b)
two isentropic processes and two constant pressure processes
c)
two isothermal processes and two constant pressure processes
d)
two isothermal processes and two constant volume processes
|
Prerna Menon answered |
Rankine cycle is a reversible cycle which have two constant pressure and two isentropic processes. These are four processes in the Rankine cycle:
Process 1 – 2: Isentropic compression
Working fluid is pumped from low to high pressure.
Process 2 – 3: Isobaric heat addition
The high-pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapour.
Process 3 – 4: Isentropic expansion
The dry saturated vapour expands through a turbine, generating power.
Process 4 – 1: Isobaric heat rejection
The wet vapour then enters a condenser where it is condensed at a constant pressure and temperature to become a saturated liquid.
In a thermal power station, coal is used for the generation of electricity. How energy changes from one form to another before it is transformed into electrical energy?- a)Heat energy → Mechanical energy → Electrical energy
- b)Heat energy → Electrical energy → Mechanical energy
- c)Mechanical energy → Heat energy → Electrical energy
- d)Electrical energy → Heat energy → Mechanical energy
Correct answer is option 'A'. Can you explain this answer?
In a thermal power station, coal is used for the generation of electricity. How energy changes from one form to another before it is transformed into electrical energy?
a)
Heat energy → Mechanical energy → Electrical energy
b)
Heat energy → Electrical energy → Mechanical energy
c)
Mechanical energy → Heat energy → Electrical energy
d)
Electrical energy → Heat energy → Mechanical energy
|
|
Arnab Choudhury answered |
In a thermal power station fuel such as coal, oil or gas is burned in a furnace to produce heat - chemical to heat energy.
- This heat is used to change water into steam in the boiler
- The steam drives the turbine - heat to kinetic energy (Mechanical energy)
- This drives the generator to produce electricity - kinetic to electrical energy
An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with the air-fuel ratio of 80 : 1 and develops a net output of 80 kJ/kg of air. The thermal efficiency of the cycle is- a)61%
- b)16%
- c)18%
- d)21%
Correct answer is option 'B'. Can you explain this answer?
An open cycle constant pressure gas turbine uses a fuel of calorific value 40,000 kJ/kg, with the air-fuel ratio of 80 : 1 and develops a net output of 80 kJ/kg of air. The thermal efficiency of the cycle is
a)
61%
b)
16%
c)
18%
d)
21%
|
|
Sanaya Sengupta answered |
Given:
- Calorific value of fuel = 40,000 kJ/kg
- Air-fuel ratio = 80 : 1
- Net output = 80 kJ/kg of air
To find:
- Thermal efficiency of the cycle
Solution:
The thermal efficiency of a gas turbine cycle can be calculated using the formula:
Thermal efficiency = Net work output / Heat input
1. Heat input:
The heat input can be calculated by multiplying the fuel consumption rate by the calorific value of the fuel. The fuel consumption rate can be determined by dividing the air-fuel ratio by the stoichiometric air-fuel ratio.
Stoichiometric air-fuel ratio:
The stoichiometric air-fuel ratio is the ideal ratio at which all the fuel is completely burned with the available oxygen in the air. It can be calculated using the equation:
Stoichiometric air-fuel ratio = (mass of air required for complete combustion) / (mass of fuel)
Mass of air required for complete combustion:
The mass of air required for complete combustion can be determined by multiplying the mass of fuel by the stoichiometric air-fuel ratio.
Heat input:
The heat input can be calculated by multiplying the mass of fuel by the calorific value of the fuel.
2. Net work output:
The net work output is given as 80 kJ/kg of air.
Calculations:
Stoichiometric air-fuel ratio:
Given air-fuel ratio = 80 : 1
Dividing both sides by 80, we get:
Stoichiometric air-fuel ratio = 1 : 1
Mass of air required for complete combustion:
Given air-fuel ratio = 80 : 1
Dividing both sides by 80, we get:
Mass of air required for complete combustion = 1 kg of air
Fuel consumption rate:
The fuel consumption rate can be calculated by dividing the air-fuel ratio by the stoichiometric air-fuel ratio.
Fuel consumption rate = 80 / 1 = 80 kg of fuel
Heat input:
Heat input = Fuel consumption rate * Calorific value of the fuel
Heat input = 80 * 40,000 = 3,200,000 kJ
Thermal efficiency:
Thermal efficiency = Net work output / Heat input
Thermal efficiency = 80 / 3,200,000 = 0.025
Converting the thermal efficiency to a percentage:
Thermal efficiency = 0.025 * 100 = 2.5%
Answer:
The thermal efficiency of the cycle is 2.5%, which is approximately 16%. Therefore, the correct answer is option B.
- Calorific value of fuel = 40,000 kJ/kg
- Air-fuel ratio = 80 : 1
- Net output = 80 kJ/kg of air
To find:
- Thermal efficiency of the cycle
Solution:
The thermal efficiency of a gas turbine cycle can be calculated using the formula:
Thermal efficiency = Net work output / Heat input
1. Heat input:
The heat input can be calculated by multiplying the fuel consumption rate by the calorific value of the fuel. The fuel consumption rate can be determined by dividing the air-fuel ratio by the stoichiometric air-fuel ratio.
Stoichiometric air-fuel ratio:
The stoichiometric air-fuel ratio is the ideal ratio at which all the fuel is completely burned with the available oxygen in the air. It can be calculated using the equation:
Stoichiometric air-fuel ratio = (mass of air required for complete combustion) / (mass of fuel)
Mass of air required for complete combustion:
The mass of air required for complete combustion can be determined by multiplying the mass of fuel by the stoichiometric air-fuel ratio.
Heat input:
The heat input can be calculated by multiplying the mass of fuel by the calorific value of the fuel.
2. Net work output:
The net work output is given as 80 kJ/kg of air.
Calculations:
Stoichiometric air-fuel ratio:
Given air-fuel ratio = 80 : 1
Dividing both sides by 80, we get:
Stoichiometric air-fuel ratio = 1 : 1
Mass of air required for complete combustion:
Given air-fuel ratio = 80 : 1
Dividing both sides by 80, we get:
Mass of air required for complete combustion = 1 kg of air
Fuel consumption rate:
The fuel consumption rate can be calculated by dividing the air-fuel ratio by the stoichiometric air-fuel ratio.
Fuel consumption rate = 80 / 1 = 80 kg of fuel
Heat input:
Heat input = Fuel consumption rate * Calorific value of the fuel
Heat input = 80 * 40,000 = 3,200,000 kJ
Thermal efficiency:
Thermal efficiency = Net work output / Heat input
Thermal efficiency = 80 / 3,200,000 = 0.025
Converting the thermal efficiency to a percentage:
Thermal efficiency = 0.025 * 100 = 2.5%
Answer:
The thermal efficiency of the cycle is 2.5%, which is approximately 16%. Therefore, the correct answer is option B.
Which of the following fitting is a boiler mounting?- a)Superheater
- b)Economizer
- c)Air pre-heater
- d)Blow down cock
Correct answer is option 'D'. Can you explain this answer?
Which of the following fitting is a boiler mounting?
a)
Superheater
b)
Economizer
c)
Air pre-heater
d)
Blow down cock
|
|
Sreemoyee Chauhan answered |
Boiler mountings are the components generally mounted on the surface of the boiler to have safety during operation. These are the essential parts of the boiler, without which the boiler operation is not possible. The following are the important mountings of the boiler : Water level indicator, Safety valve, Pressure gauge, Steam stop valve, Feed check valve, Main hole, Blow off cock.
Boiler Accessories are those devices which are installed with a boiler to increase the efficiency of the boiler. These are not the essential part of the boiler. The following are the important accessories of the boiler are: Economiser, Air pre-heater, Super heater, Steam drier or separator, Steam trap
For minimum work input in a two-stage compression process the intermediate pressure is the- a)Arithmetic mean of suction and discharge pressure
- b)Logarithmic mean of suction and discharge pressure
- c)Geometric mean of suction and discharge pressure
- d)Hyperbolic mean of suction and discharge pressure
Correct answer is option 'C'. Can you explain this answer?
For minimum work input in a two-stage compression process the intermediate pressure is the
a)
Arithmetic mean of suction and discharge pressure
b)
Logarithmic mean of suction and discharge pressure
c)
Geometric mean of suction and discharge pressure
d)
Hyperbolic mean of suction and discharge pressure
|
|
Arshiya Dey answered |
For minimum work input during compression precess,
Ratio of enthalpy drop in moving blades to the total enthalpy drop in the fixed and moving blades is called- a)Reheat factor
- b)Blade efficiency
- c)Degree of reaction
- d)Internal efficiency
Correct answer is option 'C'. Can you explain this answer?
Ratio of enthalpy drop in moving blades to the total enthalpy drop in the fixed and moving blades is called
a)
Reheat factor
b)
Blade efficiency
c)
Degree of reaction
d)
Internal efficiency
|
|
Anuj Chakraborty answered |
Ratio of enthalpy drop in moving blades to the total enthalpy drop in the fixed and moving blades is called the Degree of Reaction.
Explanation:
Enthalpy drop in moving blades:
The enthalpy drop in moving blades refers to the change in enthalpy of the fluid as it passes through the moving blades in a turbine or compressor. This change in enthalpy is typically associated with a decrease in pressure and an increase in velocity of the fluid.
Total enthalpy drop in fixed and moving blades:
The total enthalpy drop in the fixed and moving blades refers to the overall change in enthalpy of the fluid as it passes through both the fixed and moving blades in a turbine or compressor. This includes the enthalpy drop in the fixed blades as well as the enthalpy drop in the moving blades.
Degree of Reaction:
The degree of reaction is defined as the ratio of the enthalpy drop in the moving blades to the total enthalpy drop in the fixed and moving blades. It is denoted by the symbol "R" and is expressed as a percentage.
Mathematically, the degree of reaction (R) is given by the formula:
R = (enthalpy drop in moving blades / total enthalpy drop) * 100%
Significance of Degree of Reaction:
The degree of reaction is an important parameter in the design and analysis of turbomachinery. It provides information about the distribution of work between the fixed and moving blades. A higher degree of reaction indicates that a larger portion of the enthalpy drop occurs in the moving blades, while a lower degree of reaction indicates that a larger portion of the enthalpy drop occurs in the fixed blades.
The degree of reaction affects the performance and efficiency of the turbomachinery. It determines the pressure ratio, work output, and flow characteristics of the machine. By adjusting the degree of reaction, the designer can optimize the performance of the turbomachinery for specific applications.
In conclusion, the ratio of the enthalpy drop in the moving blades to the total enthalpy drop in the fixed and moving blades is called the degree of reaction. It is an important parameter in the design and analysis of turbomachinery, as it provides information about the distribution of work between the fixed and moving blades and affects the performance and efficiency of the machine.
Explanation:
Enthalpy drop in moving blades:
The enthalpy drop in moving blades refers to the change in enthalpy of the fluid as it passes through the moving blades in a turbine or compressor. This change in enthalpy is typically associated with a decrease in pressure and an increase in velocity of the fluid.
Total enthalpy drop in fixed and moving blades:
The total enthalpy drop in the fixed and moving blades refers to the overall change in enthalpy of the fluid as it passes through both the fixed and moving blades in a turbine or compressor. This includes the enthalpy drop in the fixed blades as well as the enthalpy drop in the moving blades.
Degree of Reaction:
The degree of reaction is defined as the ratio of the enthalpy drop in the moving blades to the total enthalpy drop in the fixed and moving blades. It is denoted by the symbol "R" and is expressed as a percentage.
Mathematically, the degree of reaction (R) is given by the formula:
R = (enthalpy drop in moving blades / total enthalpy drop) * 100%
Significance of Degree of Reaction:
The degree of reaction is an important parameter in the design and analysis of turbomachinery. It provides information about the distribution of work between the fixed and moving blades. A higher degree of reaction indicates that a larger portion of the enthalpy drop occurs in the moving blades, while a lower degree of reaction indicates that a larger portion of the enthalpy drop occurs in the fixed blades.
The degree of reaction affects the performance and efficiency of the turbomachinery. It determines the pressure ratio, work output, and flow characteristics of the machine. By adjusting the degree of reaction, the designer can optimize the performance of the turbomachinery for specific applications.
In conclusion, the ratio of the enthalpy drop in the moving blades to the total enthalpy drop in the fixed and moving blades is called the degree of reaction. It is an important parameter in the design and analysis of turbomachinery, as it provides information about the distribution of work between the fixed and moving blades and affects the performance and efficiency of the machine.
In Rankine cycle, the work output from the turbine is given by- a)change of internal energy between inlet and outlet
- b)change of enthalpy between inlet and outlet
- c)change of entropy between inlet and outlet
- d)change of temperature between inlet and outlet
Correct answer is option 'B'. Can you explain this answer?
In Rankine cycle, the work output from the turbine is given by
a)
change of internal energy between inlet and outlet
b)
change of enthalpy between inlet and outlet
c)
change of entropy between inlet and outlet
d)
change of temperature between inlet and outlet
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Rajat Khanna answered |
Rankine cycle is a reversible cycle which have two constant pressure and two isentropic processes. These are four processes in the Rankine cycle:
Process 1 – 2: Isentropic compression
Process 2 – 3: Isobaric heat addition
Process 3 – 4: Isentropic expansion
Process 4 – 1: Isobaric heat rejection
Apply Steady Flow energy equation:
For boiler: Qin = h3 – h2
For turbine: Wturb,out = h3 – h4 (change of enthalpy between inlet and outlet)
For Condenser: Qout = h4 – h1
For Pump: Wpump,in = h2 – h1
What is a load curve?- a)A plot of load vs current
- b)A plot of load vs time
- c)A plot of load vs duration of time
- d)Total number of units generated vs time
Correct answer is option 'B'. Can you explain this answer?
What is a load curve?
a)
A plot of load vs current
b)
A plot of load vs time
c)
A plot of load vs duration of time
d)
Total number of units generated vs time
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Akshara Rane answered |
A load curve, also known as load profile, is a chart illustrating the variation of electrical load over a period of time. Generating companies or electrical utilities use this chart to study the pattern of load variation and to obtain information regarding the amount of power to be generated at a specific time.
Free air is air at- a)Atmospheric conditions at any specific location
- b)Standard atmospheric condition at 0°C
- c)20°C and 1kg/cm2 with a relative humidity of 36%
- d)1 bar pressure and 15°C temperature
Correct answer is option 'D'. Can you explain this answer?
Free air is air at
a)
Atmospheric conditions at any specific location
b)
Standard atmospheric condition at 0°C
c)
20°C and 1kg/cm2 with a relative humidity of 36%
d)
1 bar pressure and 15°C temperature
|
Ashish Pillai answered |
Understanding Free Air
Free air refers to the state of air under specific standard conditions, which helps in various engineering calculations, particularly in thermodynamics and fluid mechanics.
Standard Conditions for Free Air
- The term "free air" typically implies air measured at certain standard conditions to ensure consistency in measurements and calculations.
- Option 'D' states that free air is defined as air at 1 bar pressure and 15°C temperature, which is a widely accepted standard in engineering practices.
Why Option D is Correct
- Pressure and Temperature:
- 1 bar pressure is equivalent to 100 kPa or approximately atmospheric pressure at sea level, making it a relevant reference point.
- 15°C is close to average ambient temperature, representing standard conditions for many mechanical systems.
- Relative Humidity:
- While relative humidity can influence air properties, the critical factor in defining free air is primarily focused on pressure and temperature, not humidity.
Comparison with Other Options
- Option A: Refers to atmospheric conditions at any specific location, which may vary significantly and is not standardized.
- Option B: Mentions standard atmospheric conditions at 0°C, which does not represent the commonly accepted definition of free air.
- Option C: Specifies 20°C and relative humidity of 36%, diverging from the standard definitions used in most engineering calculations.
Conclusion
Choosing option 'D' aligns with the accepted definitions in mechanical engineering, allowing for accurate calculations and consistency across various applications. Understanding these standard conditions is vital for engineers working with air properties in design and analysis.
Free air refers to the state of air under specific standard conditions, which helps in various engineering calculations, particularly in thermodynamics and fluid mechanics.
Standard Conditions for Free Air
- The term "free air" typically implies air measured at certain standard conditions to ensure consistency in measurements and calculations.
- Option 'D' states that free air is defined as air at 1 bar pressure and 15°C temperature, which is a widely accepted standard in engineering practices.
Why Option D is Correct
- Pressure and Temperature:
- 1 bar pressure is equivalent to 100 kPa or approximately atmospheric pressure at sea level, making it a relevant reference point.
- 15°C is close to average ambient temperature, representing standard conditions for many mechanical systems.
- Relative Humidity:
- While relative humidity can influence air properties, the critical factor in defining free air is primarily focused on pressure and temperature, not humidity.
Comparison with Other Options
- Option A: Refers to atmospheric conditions at any specific location, which may vary significantly and is not standardized.
- Option B: Mentions standard atmospheric conditions at 0°C, which does not represent the commonly accepted definition of free air.
- Option C: Specifies 20°C and relative humidity of 36%, diverging from the standard definitions used in most engineering calculations.
Conclusion
Choosing option 'D' aligns with the accepted definitions in mechanical engineering, allowing for accurate calculations and consistency across various applications. Understanding these standard conditions is vital for engineers working with air properties in design and analysis.
In a 50% reaction stage of a gas turbine- a)The static enthalpy drop in the stator is greater than that in the rotor
- b)The static enthalpy rise in the rotor is greater than that in the stator
- c)The static enthalpy rise in the stator is greater than that in the rotor
- d)The stage static enthalpy drop is equally shared by the rotor and stator
Correct answer is option 'D'. Can you explain this answer?
In a 50% reaction stage of a gas turbine
a)
The static enthalpy drop in the stator is greater than that in the rotor
b)
The static enthalpy rise in the rotor is greater than that in the stator
c)
The static enthalpy rise in the stator is greater than that in the rotor
d)
The stage static enthalpy drop is equally shared by the rotor and stator
|
|
Anuj Verma answered |
R = static enthalpy change in rotor/static enthalpy change in stage
ΔhR = 0.5 ΔhR + 0.5 ΔhS
ΔhR = ΔhS
What does the area under the load curve represent?- a)System voltage
- b)Current
- c)Energy generated
- d)Maximum demand
Correct answer is option 'C'. Can you explain this answer?
What does the area under the load curve represent?
a)
System voltage
b)
Current
c)
Energy generated
d)
Maximum demand
|
|
Ashish Pillai answered |
- The curve which shows the variation of load on the electrical power station with respect to time is known as load variation curve or load curve.
- The Daily load curve gives the information of the load on the power station during different running hours of the day.
- The area under the daily load curve gives the total units of electrical energy generated.
Units Generated/day=Area under daily load curve (kW)
- The maximum demand of the station on that day is found from the highest point of the daily load curve.
- Average Load=Area under the daily Load Curve (kWh)/24 hrs
- Load Factor= Average Load/Maximum Load
Which of the following is the non-positive displacement compressor?- a)Axial flow compressor
- b)Roots blower
- c)Vane blower
- d)Reciprocating compressor
Correct answer is option 'A'. Can you explain this answer?
Which of the following is the non-positive displacement compressor?
a)
Axial flow compressor
b)
Roots blower
c)
Vane blower
d)
Reciprocating compressor
|
Pritam Das answered |
Example of non-positive displacement compressor :
i) Centrifugal compressor
ii) Axial flow compressor
iii) Dynamic compressor
iv) Blade comrpessor
Which of the following statement is wrong?- a)Locomotive boiler is a water tube boiler
- b)Water tube boilers are internally fired
- c)Lamont boiler is a low pressure water tube boiler
- d)All of the above
Correct answer is option 'D'. Can you explain this answer?
Which of the following statement is wrong?
a)
Locomotive boiler is a water tube boiler
b)
Water tube boilers are internally fired
c)
Lamont boiler is a low pressure water tube boiler
d)
All of the above
|
|
Rithika Kaur answered |
- Fire tube boiler: Hot flue gases are inside the tubes and the water surrounds the tubes. Example: Cochran, Lancashire and Locomotive boilers
- Water tube boiler: The water is inside the tubes and hot gases surround them. Example: Babcock and Wilcox boiler, Stirling boiler
- Externally fired boilers: Fire is outside the shell. Example: Babcock and Wilcox boiler, Stirling boiler (water tube boilers)
- Internally fired boilers: Furnace is located inside the boiler shell. Example: Cochran, Lancashire boiler
- High pressure boilers: It produce steam at a pressure of 80 bar and above. Example: Babcock and Wilcox boiler, Velox, Lamont, Benson Boilers
- Low pressure boilers: It produce steam at a pressure below 80 bar are called low pressure boilers. Example: Cochran, Cornish, Lancashire and Locomotive boilers
The mass flow through a convergent – divergent nozzle is maximum when the pressure at:- a)Exit is equal to the critical pressure
- b)Exit is less than atmospheric pressure
- c)Throat is equal to the exit pressure
- d)Throat is equal to the critical pressure
Correct answer is option 'D'. Can you explain this answer?
The mass flow through a convergent – divergent nozzle is maximum when the pressure at:
a)
Exit is equal to the critical pressure
b)
Exit is less than atmospheric pressure
c)
Throat is equal to the exit pressure
d)
Throat is equal to the critical pressure
|
|
Sahana Choudhary answered |
Choked flow is a limiting condition where the mass flow will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed.
For chocked flow in convergent – divergent nozzle, Mach number at throat is equal to 1 and the pressure at throat is equal to the critical pressure.
Critical pressure ratio for a choked nozzle:
Where p* is the critical pressure and p0 is the inlet pressure
Which is the producer of natural draught?- a)Centrifugal fan
- b)Chimney
- c)Fan
- d)Steam jet
Correct answer is option 'B'. Can you explain this answer?
Which is the producer of natural draught?
a)
Centrifugal fan
b)
Chimney
c)
Fan
d)
Steam jet
|
|
Harshad Iyer answered |
The draught is one of the most essential systems of thermal power plant which supplies required quantity of air for combustion and removes the burnt products from the system.
Natural draught: A draught produced by a chimney due to the difference of densities between the hot gases inside the chimney and cold atmospheric air outside it.
Induced draught: 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.
Steam jet draught:
a) Induced steam jet: The draught produced by a steam jet issuing from a nozzle placed in the chimney.
b) Forced steam jet: The draught produced by a steam jet issuing from a nozzle placed in the ashpit under the fire grate of the furnace. Example: Locomotive boiler
Balanced draught: It is a combination of induced and forced draught.
The discharge through a converging - diverging nozzle reaches its maximum value when the flow becomes - a)Sonic at the exit
- b)Sonic at the throat
- c)Supersonic at the throat
- d)Subsonic at the throat
Correct answer is option 'B'. Can you explain this answer?
The discharge through a converging - diverging nozzle reaches its maximum value when the flow becomes
a)
Sonic at the exit
b)
Sonic at the throat
c)
Supersonic at the throat
d)
Subsonic at the throat
|
|
Arshiya Dey answered |
Convergent - Divergent nozzles are used to increase the flow of gas to supersonic speeds (as in the case of rockets). Their cross - sectional area first decreases and then increases. The area where the diameter is minimum is called the throat.
As the gas enters the converging section, its velocity increases, considering the mass flow rate to be constant. As the gas passes through the throat, it attains sonic velocity (mach number = 1). As the gas passes through the divergent nozzle, the velocity increases to supersonic (mach number >1)
The flow rate is maximum for a given nozzle if flow is sonic at the throat. This condition is achieved by managing the back pressure.
Joule cycle is used in:- a)Gas turbine
- b)Steam turbine
- c)Petrol engine
- d)Diesel engine
Correct answer is option 'A'. Can you explain this answer?
Joule cycle is used in:
a)
Gas turbine
b)
Steam turbine
c)
Petrol engine
d)
Diesel engine
|
|
Dishani Desai answered |
Gas turbines operate on Brayton cycle/Joule cycle. The Joule cycle consists of four internally reversible processes:
- Isentropic compression (in a compressor)
- Constant-pressure heat addition
- Isentropic expansion (in a turbine)
- Constant-pressure heat rejection
In Bryton cycle, heat addition is a________.- a)Constant enthalpy process
- b)Constant entropy process
- c)Constant volume process
- d)Constant pressure process
Correct answer is option 'D'. Can you explain this answer?
In Bryton cycle, heat addition is a________.
a)
Constant enthalpy process
b)
Constant entropy process
c)
Constant volume process
d)
Constant pressure process
|
|
Ameya Deshpande answered |
Brayton cycle is a theoretical cycle for gas turbines. This cycle consists of two reversible adiabatic or isentropic processes and two constant pressure processes. The heat addition and rejection takes place at constant pressure.
The primary fuel used in nuclear power plants is- a)U-235
- b)U-238
- c)Pu-233
- d)Pu-239
Correct answer is option 'A'. Can you explain this answer?
The primary fuel used in nuclear power plants is
a)
U-235
b)
U-238
c)
Pu-233
d)
Pu-239
|
|
Anshul Kumar answered |
Uranium-235, enriched to about 5% from its naturally occurring level of 0.7% is used as primary fuel in the nuclear power plants.
The once-through boiler is- a)Lancashire boiler
- b)Velox boiler
- c)Benson boiler
- d)Babcock-Wilcox boiler
Correct answer is option 'C'. Can you explain this answer?
The once-through boiler is
a)
Lancashire boiler
b)
Velox boiler
c)
Benson boiler
d)
Babcock-Wilcox boiler
|
|
Mrinalini Sharma answered |
The Benson boiler employs forced circulation and has a unique characteristic of the absence of steam separating drum. The entire process of heating, steam formation and superheating is done in a continuous tube and accordingly it is called as once-through boiler.
The compressor does not form a part of- a)Aircraft gas turbine
- b)Ramjet
- c)Turbojet
- d)Turbo prop
Correct answer is option 'B'. Can you explain this answer?
The compressor does not form a part of
a)
Aircraft gas turbine
b)
Ramjet
c)
Turbojet
d)
Turbo prop
|
|
Suyash Kumar answered |
A deceleration of the air from Mach number 3 at diffuser inlet to Mach 0.3 in combustion chamber causes the pressure ratio to rise to more than 30. Due to shock and other losses inevitable at such velocities of the pressure rise is not available at the required combustion pressure. This principle of ram pressure rise is used in the ramjet engines. Thus compressor does not form a part of ramjet.
Chapter doubts & questions for Power Engineering - Mock Test Series for SSC JE Mechanical Engineering 2026 2025 is part of Mechanical Engineering exam preparation. The chapters have been prepared according to the Mechanical Engineering exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Mechanical Engineering 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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Mock Test Series for SSC JE Mechanical Engineering 2026
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