Power Engineering MCQ Quiz - Objective Question with Answer for Power Engineering - Download Free PDF

Key Points

• Hydrogen fuel cells produce electricity by combining hydrogen and oxygen through an electrochemical process.
• Water is produced as a byproduct of the reaction, making it an environmentally friendly technology.
• The chemical reaction in a hydrogen fuel cell is 2H₂ + O₂ → 2H₂O + Energy.
• The only byproduct of this reaction is water, which is clean and does not contribute to pollution.

Important Points

• Hydrogen fuel cells are considered a sustainable energy source as they generate electricity with zero emissions apart from water vapor.
• They are used in a variety of applications, including powering electric vehicles, stationary power generation, and backup power systems.
• Hydrogen is stored in pressurized tanks and is supplied to the fuel cell, where it undergoes oxidation to produce energy.

Explanation:

Diaphragm in Steam Turbines

• In the context of steam turbines, a diaphragm refers to a separating wall or partition that is positioned between successive rotors of the turbine. The diaphragm carries stationary nozzles or guide blades, which are essential for redirecting and controlling the steam flow to the moving blades of the rotor downstream. This helps in converting the thermal energy of the steam into mechanical energy efficiently.

Working Principle: The diaphragm is a crucial part of the steam turbine's internal design. After the steam passes through the moving blades of the rotor, it needs to be redirected to the next set of moving blades. The diaphragm achieves this by holding the guide blades or nozzles that direct the steam flow appropriately. The stationary nozzles accelerate the steam and guide it into the next set of moving blades at an optimal angle, ensuring efficient energy transfer and minimizing losses.

Construction:

• The diaphragm is typically constructed from high-strength materials capable of withstanding the high-pressure and high-temperature conditions present in steam turbines.
• It is precisely engineered to ensure proper alignment of the stationary nozzles with the moving blades of the turbine rotor.
• Sealing mechanisms are often incorporated into the diaphragm design to minimize steam leakage and enhance overall efficiency.

Role of the Diaphragm in Steam Turbines:

• Separates successive turbine stages to maintain the desired pressure and thermal conditions for each stage.
• Holds the stationary nozzles or guide blades that direct steam flow efficiently onto the moving blades.
• Contributes to the aerodynamic efficiency of the turbine by ensuring smooth steam flow transitions between stages.
• Helps reduce steam leakage, enhancing the turbine's overall performance and efficiency.

Advantages of Using Diaphragms:

• Improved efficiency due to optimized steam flow direction and reduced leakage.
• Enhanced durability and reliability of the turbine by maintaining proper alignment and minimizing wear on components.
• Flexibility in designing multi-stage turbines with different pressure levels and steam velocities.

Applications: Diaphragms are commonly used in multi-stage steam turbines across various industries, including power generation, petrochemical processing, and marine propulsion systems.

Concept:

We use the principles of boiler thermodynamics to determine the equivalent evaporation, which represents the amount of water that would be evaporated under standard conditions (100°C and 1 atm) using the same heat input as the actual boiler operation.

Given:

• Steam production rate = \( 2000 \, \text{kg/hr} \)
• Enthalpy of steam, \( h_{steam} = 2426 \, \text{kJ/kg} \)
• Feedwater temperature = \( 40°C \)
• Enthalpy of feedwater, \( h_{fw} = 168 \, \text{kJ/kg} \)
• Enthalpy of vaporization at 100°C, \( h_{fg} = 2258 \, \text{kJ/kg} \)

Step 1: Calculate heat added per kg of steam

\( \text{Heat added} = h_{steam} - h_{fw} = 2426 - 168 = 2258 \, \text{kJ/kg} \)

Step 2: Compute equivalent evaporation

\( \text{Equivalent Evaporation} = \frac{\text{Steam production} \times \text{Heat added}}{h_{fg}} = \frac{2000 \times 2258}{2258} = 2000 \, \text{kg/hr} \)

Explanation:

De Laval Steam Turbine

• A De Laval steam turbine is a type of impulse steam turbine that uses a single-stage nozzle to accelerate steam to high velocity before it strikes the turbine blades. The kinetic energy of the steam is converted into mechanical work as the steam passes through the turbine rotor, leading to energy output.

In a steam turbine, the work done per unit mass is equal to the change in kinetic energy of the steam:

\( W = \frac{1}{2} m (V_1^2 - V_2^2) \)

Calculation:

Given:

Inlet velocity, \( V_1 = 30~\text{m/s} \)

Outlet velocity, \( V_2 = 10~\text{m/s} \)

Mass, \( m = 1~\text{kg} \)

Now,

\( W = \frac{1}{2} \times 1 \times (30^2 - 10^2) = \frac{1}{2} \times (900 - 100) = \frac{1}{2} \times 800 = 400~\text{N·m} \)

Explanation:

Critical Pressure Ratio in a Convergent Nozzle

• The critical pressure ratio of a convergent nozzle is defined as the ratio of the outlet pressure to the inlet pressure of the nozzle when the flow through the nozzle reaches its maximum mass flow rate per unit area. This ratio is a critical parameter in the design and operation of convergent nozzles, particularly in applications involving compressible fluid flow, such as in turbines, jet engines, and various industrial processes.

Convergent nozzle:

• A convergent nozzle is a device used to accelerate a fluid by decreasing its cross-sectional area. When a compressible fluid, such as a gas, flows through a convergent nozzle, the velocity of the fluid increases as the cross-sectional area decreases, in accordance with the principle of conservation of mass and energy. The relationship between the pressure, velocity, and density of the fluid is governed by the isentropic flow equations for compressible fluids.
• The critical pressure ratio occurs when the flow at the throat of the nozzle (the point of smallest cross-sectional area) reaches the speed of sound, also known as the Mach number equal to 1. At this point, the flow is said to be "choked," and the mass flow rate through the nozzle becomes maximum for the given inlet conditions. Any further decrease in the outlet pressure below this critical value will not increase the mass flow rate.

The critical pressure ratio of a convergent nozzle is the ratio at which the flow becomes choked and mass flow rate per unit area is maximum.

At this point, further decrease in outlet pressure does not increase the mass flow rate.

\( \left(\frac{P_2}{P_1}\right)_{\text{critical}} = \left(\frac{2}{\gamma + 1} \right)^{\frac{\gamma}{\gamma - 1}} \)

Where \( \gamma \) is the ratio of specific heats, \( P_1 \) is inlet pressure, and \( P_2 \) is outlet pressure.

The correct answer is Mumbai.

• Bhabha Atomic Research Centre (BARC) is located in Mumbai.

Key Points

• Bhabha Atomic Research Centre:
  • It was established in 1954.
  • Its headquarters is in Trombay, Mumbai.
  • Earlier, it was known as Atomic Energy Establishment.
  • At present, BARC house has eight research reactors:
    • Apsara, a one MW Swimming pool-type reactor.
    • Cirus, a 40 MW reactor.
    • Dhruva, a 100 MW high power nuclear research reactor.
    • Zerliana, Purnima I, Purnima II, Purnima III and Kamini
  • It comes under the aegis of the Department of Atomic Energy.

Additional Information

• Other Atomic Research Centres in India: 
  • Atomic Minerals Directorate for Exploration and Research (AMD) is located in Hyderabad.
  • Indira Gandhi Centre for Atomic Research (IGCAR) is located in Kalpakkam, Tamil Nadu.
  • Variable Energy Cyclotron Centre (VECC) is located in Kolkata.

Explanation:

Simple Impulse Turbine (De Laval Turbine):

• It is the first working impulse turbine.
• It consists of a single set of the nozzle and moving blades. Therefore, total pressure drop from boiler pressure to condenser pressure takes place in a single nozzle which gives high rotational speed exceeding pressure limit of 3000 rpm.
• These turbines are mostly used in small power and high-speed purposes.

Additional Information

Concept:

Note that the Rankine cycle has a lower efficiency compared to the corresponding Carnot cycle 2’-3-4-1’ with the same maximum and minimum temperatures. The reason is that the average temperature at which heat is added in the Rankine cycle lies between T₂ and T₂^' and is thus less than the constant temperature T2' at which heat is added to the Carnot cycle.

It is very difficult to build a pump that will handle a mixture of liquid and vapor at state 1' (refer T-s diagram; Carnot Vapor Cycle) and deliver saturated liquid at state 2’.

It is much easier to completely condense the vapor and handle only liquid in the pump (Rankine Cycle)

In the Carnot cycle, the compression is wet compression so the pump work requirement is more compare to the Rankine cycle where the pump compresses only the saturated liquid. Thus the specific work output for the Rankine cycle is more than the Carnot cycle for the same maximum and minimum temperature.

Also, the work ratio is defined as the ratio of net-work to the work done in the turbine.

\(r_w=\frac{W_{net}}{W_T}=\frac{W_T-W_C}{W_T}\)

Thus the work ratio is low for the Carnot Cycle.

Explanation:

Boiler:

• According to A. S. M. E. steam generating unit or boiler is defined as "A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for transferring the heat". So made available to the fluid being heated and vapourised.

Types of boiler:

Water Tube Boiler:

• When water is contained inside the tubes (called water tube) which are surrounded by flames and hot gases from outside, then the boilers are named as water tube boilers.
• They are safe, quick steaming, flexible in construction and operation.
• These boilers are extensively used because they can be built for high pressure and large evaporative capacities.

Types of Water Tube Boilers

• Babcock and Wilcox boiler
• Stirling boiler
• Lamont boiler
• Benson boiler
• Loeffler boiler, etc.

Fire Tube Boilers:

• When the flames and hot gases, produced by combustion of fuel, pass through the tubes (called multitube) which are surrounded by water, then the boilers are named as fire tube boilers.

Types of Fire Tube Boilers:

• Simple vertical boiler
• Lancashire boiler
• Cochran boiler
• Locomotive boiler

Supercritical boiler:

• A large number of steam generating units are designed between working ranges of 125 atm and 510°C to 300 atm and 660°C. These are basically characterised as subcritical and supercritical. Subcritical consists, preheater, evaporator and superheater while supercritical boiler requires only preheater and superheater.
• Supercritical boilers operate at a pressure greater than 22 MPa and also referred to as Once through boilers since the feed water circulates only once through boiler in each steam cycle.

Concept:

Centrifugal compressor

• Air is drawn into the centre of a rotating impeller with radial blades and is pushed toward the centre by centrifugal force.
• This radial movement of air results in a pressure rise.
• The airflow rate is more than a reciprocating compressor. but the maximum pressure value is less than the reciprocating compressor.
• Centrifugal compressors were used in jet engines and smaller gas turbine engines.
• For larger engines, axial compressors need a lesser frontal area and are more efficient.

Pressure ratio for centrifugal compressor = 4 : 1

Pressure ratio for axial flow compressor = 1.2 : 1

The correct answer is Anthracite.

• Anthracite contains 86%–97% carbon and generally has the highest heating value of all ranks of coal. It has the highest carbon content.
• Anthracite combusts with a hot, clean flame, containing low content of sulfur and volatiles.
• It is used in domestic applications or other specialized industrial uses that require smokeless fuels.
• In India, it is found only in the Union territory of Jammu and Kashmir.

Additional Information

Concept:

Fire Tube Boiler: In this boiler, the hot flue gases are present inside the tubes and water surrounds them. They are low-pressure boilers. The operating pressure is about 25 bar.

Example to fire tube boilers:

• Cornish boiler
• Cochran boiler
• Locomotive boiler
• Lancashire boiler
• Scotish marine boiler

Water Tube Boiler: In this boiler, the water is present inside the tubes and the hot flue gases surround them. They are high-pressure boilers. The operating pressure is about 250 bar.

Examples of water tube boilers:

• Stirling boiler
• Babcock and Wilcox boiler
• Yarrow boiler
• La mont boiler
• Loeffler boiler
• Velox boiler

In a locomotive boiler, the draught is produced by a steam jet.

The draught is one of the most essential systems of the thermal power plant which supplies the 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 the 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 correct answer is Coal.

• Non-Renewable Resources:
  • The sources that cannot be replaced or reused once they are destroyed are called the Non-renewable resources.
  • These are limited resources. so these are used limitedly.
  • These are not environmentally friendly because the amount of carbon emission is high.
  • The cost of these resources is high.
  • They are not pollution-free.
  • They require low maintenance cost.
  • Coal, oil, nuclear energy, petroleum, natural gas, batteries, shale gas, phosphate are some examples.

Additional Information

• Renewable Resources:
  • Resources that are used by humans since human life exists.
  • These resources are used by our ancestors for their daily purposes like lighting, shelter, transportation, cooking, heating, protection from harm.
  • These are also known as non-conventional sources of energy.
  • For example Soil, water bodies, sun, wind, tidal energy, geothermal, forest, mountains, wildlife, atmospheric resources.
  • These can be used unlimited.
  • They are environment friendly.
  • The cost is low.
  • They are pollution-free.
  • They require high maintenance costs.
  • They are sustainable resources.
  • They cause no harm to life to exist on earth.

The correct answer is Russia.

• Russia has developed the world's first floating nuclear plant.

Key Points

• Akademik Lomonosov is the world’s first floating nuclear reactor. 
• Akademik Lomonosov was named after 18th-century Russian scientist Mikhail Lomonosov.
• Recently, It is completed its epic 5,000 km Arctic voyage in 22 days, despite environmentalists warning of serious risks to the region. 
• The plant was launched by Russia on 19 May 2018 at the St Petersburg shipyard.
• Akademik Lomonosov has painted with signature red, white, and blue colors of the nation's flag at its exterior.