Thermodynamic Cycles
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: To improve actual cycle efficiency, one can:
Minimizing friction and heat losses in actual cycles improves efficiency closer to the ideal case.
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The primary difference between ideal and actual cycles is:
Actual cycles include irreversibilities like friction and heat loss, unlike ideal cycles.
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In an actual Rankine cycle, the steam quality at the turbine exit is:
Turbine inefficiencies increase entropy, reducing steam quality at the exit compared to the ideal cycle.
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The actual Brayton cycle has a lower work output due to:
Inefficiencies in the turbine and compressor reduce the net work output in actual Brayton cycles
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Heat transfer in actual cycles is:
Heat transfer in actual cycles involves temperature differences, making it irreversible.
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In an actual Rankine cycle, the pump work is:
: Pump inefficiencies in actual cycles increase the work required compared to the ideal cycle.
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Turbine efficiency in actual cycles is affected by:
: Blade friction and other losses in the turbine reduce its efficiency in actual cycles.
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In an actual Brayton cycle, compressor efficiency is:
Compressor inefficiencies in actual cycles cause entropy increase, reducing overall efficiency.
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The primary reason for lower efficiency in actual cycles is:
Actual cycles suffer from friction, heat losses, and other irreversibilities, reducing efficiency.
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In an ideal cycle, processes are assumed to be:
Ideal cycles assume reversible processes to maximize efficiency, unlike actual cycles with irreversibilities.
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The Rankine cycle is more practical than the Carnot cycle because:
The Rankine cycle avoids the Carnot cycle’s impractical isothermal compression of a two-phase mixture
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Reheating in the Rankine cycle is used to:
Reheating reduces moisture content in steam, preventing turbine blade erosion and improving efficiency.
Heat is added in the boiler at constant pressure to convert water to steam.
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The boiler in the Rankine cycle adds heat at:
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The Rankine cycle typically operates between:
The Rankine cycle operates between high pressure (boiler) and low pressure (condenser).
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The efficiency of the Rankine cycle can be improved by:
Superheating increases the temperature of steam, improving cycle efficiency.
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The purpose of the condenser in the Rankine cycle is to:
The condenser converts the exhaust steam back into liquid water for the pump
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The component in the Rankine cycle that converts heat into work is:
The turbine expands the high-pressure steam to produce mechanical work.
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In an ideal Rankine cycle, the pump work is assumed to be:
The pump compresses the liquid water isentropically, meaning no entropy change occurs.
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The primary working fluid in the Rankine cycle is:
Water is used as the working fluid, which is converted to steam to drive the turbine.
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The Rankine cycle is primarily used in:
The Rankine cycle is the thermodynamic cycle used in steam power plants to generate electricity.
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The Brayton cycle is less efficient than the Carnot cycle because:
The Brayton cycle rejects heat to the atmosphere, unlike the Carnot cycle, which is fully reversible, reducing its efficiency
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Increasing the turbine inlet temperature in a Brayton cycle:
Higher turbine inlet temperatures increase the work output and efficiency of the Brayton cycle.
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The ideal Brayton cycle consists of how many processes?
The Brayton cycle includes isentropic compression, isobaric heat addition, isentropic expansion, and isobaric heat rejection.
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The exhaust gases in a Brayton cycle are typically:
In an open Brayton cycle, exhaust gases are released to the atmosphere after expansion in the turbine.
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In a Brayton cycle, the turbine work output is used to:
The turbine produces work, part of which drives the compressor, with the remainder as net work output.
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Which component of the Brayton cycle adds heat to the working fluid?
The combustion chamber adds heat to the air at constant pressure in the Brayton cycle.
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The efficiency of an ideal Brayton cycle depends on:
The efficiency of an ideal Brayton cycle increases with the pressure ratio across the compressor, as it affects the work output.
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In an ideal Brayton cycle, the compression process is assumed to be:
The compression in an ideal Brayton cycle is isentropic (adiabatic and reversible), meaning no heat is transferred, and entropy remains constant.
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What is the primary working fluid in a Brayton cycle?
Air is the primary working fluid in the Brayton cycle, as it is compressed and heated in gas turbines.
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The Brayton cycle is commonly associated with which type of engine?
The Brayton cycle is the thermodynamic cycle used in gas turbine engines, where air is compressed, heated, and expanded to produce work.
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If the cut-off ratio r_c increases in a dual cycle, the efficiency:
Higher rc = V4 / V3 increases constant pressure heat addition, reducing efficiency. It doesn’t make it equal to Otto’s efficiency.
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The constant pressure heat addition in a dual cycle occurs between:
 Constant pressure heat addition occurs from point 3 to 4 after constant volume heating. Other points involve compression or expansion.
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The efficiency of a dual cycle compared to Otto and Diesel cycles is:
 For the same compression ratio, dual cycle efficiency is between Otto (higher) and Diesel (lower) due to hybrid heat addition.
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On a T-S diagram, the dual cycle’s heat addition appears as:
Constant volume heat addition (2-3) is vertical, and constant pressure (3-4) is horizontal on the T-S diagram. Other shapes don’t apply.
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Which dual cycle process has no work done?
 No work is done during constant volume heat addition (2-3) as volume doesn’t change. Other processes involve volume or pressure changes.
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Increasing the pressure ratio rp in a dual cycle:
 Higher rp = P3 / P2 increases constant volume heat addition, boosting efficiency. It doesn’t reduce efficiency or mimic Diesel exactly.
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In a dual cycle, heat rejection occurs at:
 Heat rejection (5-1) in a dual cycle is at constant volume, like the Otto cycle. Constant pressure rejection occurs in the Diesel cycle.
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The compression ratio r in a dual cycle is defined as:
Compression ratio r = V1 / V2 is the volume ratio before and after compression. V4 / V3 is the cut-off ratio, and others are incorrect.
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Which process in a dual cycle is identical to the Otto cycle?
 Constant volume heat addition (2-3) matches the Otto cycle. Constant pressure heat addition is specific to Diesel or dual cycles.
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The dual cycle is primarily used to model:
 The dual cycle models high-speed diesel engines with combined constant volume and pressure heat addition. Gasoline engines use the Otto cycle, and others are unrelated.
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The Diesel cycle assumes:
 Explanation: The Diesel cycle assumes ideal gas behavior for analysis, unlike real gases or irreversible processes. Combustion is at constant pressure, not volume.
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In the Diesel cycle’s adiabatic compression:
 Explanation: Adiabatic compression raises temperature via work input, unlike expansion or isothermal processes. No heat is added; volume decreases.
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Compared to the Otto cycle, the Diesel cycle is:
 Explanation: For the same compression ratio, Diesel is less efficient due to constant-pressure heat addition, unlike Otto’s constant-volume. Efficiency depends on cycle specifics.
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The Diesel cycle is typically modeled in:
Explanation: Piston-cylinders enable isobaric, isochoric, and adiabatic processes, unlike open systems or nozzles in flow cycles. Heat exchangers involve heat transfer.
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The Diesel cycle’s heat rejection occurs at:
 Explanation: Heat rejection is isochoric, unlike constant-pressure in Brayton or isothermal in Carnot. Adiabatic processes involve no heat transfer.
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The efficiency of the Diesel cycle depends on:
 Explanation: Efficiency depends on compression and cutoff ratios (η = 1 - 1/r^(γ-1)/[γ(r_c-1)/(r_c^γ-1)]), unlike temperature in Carnot or pressure in Brayton. Work is a result.
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The adiabatic processes in the Diesel cycle involve:
 Explanation: Adiabatic compression and expansion have no heat transfer, unlike isobaric or isothermal processes. Volume and temperature change, not remain constant.
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In the Diesel cycle, heat addition occurs at:
Explanation: Heat addition is isobaric (constant pressure), unlike constant-volume in Otto or isothermal in Carnot. Adiabatic processes have no heat.
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The Diesel cycle consists of how many processes?
Explanation: The Diesel cycle includes two adiabatic, one isobaric, and one isochoric process, unlike cycles with fewer or more steps. Four processes define its structure.
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The Diesel cycle is primarily used in:
 Explanation: The Diesel cycle models compression-ignition engines like diesel engines, unlike spark-ignition in Otto or gas turbines. Refrigeration uses other cycles.
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The Otto cycle is less efficient than:
 Explanation: The Carnot cycle sets the maximum efficiency limit, unlike Diesel, Brayton, or Rankine cycles. Otto efficiency depends on compression ratio.
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In the Otto cycle’s adiabatic compression:
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The Otto cycle assumes:
Explanation: The Otto cycle assumes ideal gas behavior for analysis, unlike real gases or irreversible processes. Combustion is at constant volume, not pressure.
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The Otto cycle is typically modeled in:
Explanation: Piston-cylinders enable isochoric and adiabatic processes, unlike open systems or nozzles in flow cycles. Heat exchangers involve heat transfer.
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The Otto cycle’s heat rejection occurs at:
Explanation: Heat rejection is isochoric, unlike constant-pressure in Diesel or isothermal in Carnot. Adiabatic processes involve no heat transfer.
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The efficiency of the Otto cycle depends on:
Explanation: Efficiency increases with compression ratio (η = 1 - 1/r^(γ-1)), unlike pressure ratios in Brayton or temperature in Carnot. Work output is a result.
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The adiabatic processes in the Otto cycle involve:
 Explanation: Adiabatic compression and expansion have no heat transfer, unlike isobaric or isothermal processes. Volume and temperature change, not remain
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In the Otto cycle, heat addition occurs at:
Explanation: Heat addition in the Otto cycle is isochoric (constant volume), unlike constant-pressure in Diesel or isothermal in Carnot. Adiabatic processes have no heat.
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The Otto cycle consists of how many processes?
 Explanation: The Otto cycle includes two isochoric and two adiabatic processes, unlike cycles with fewer or more steps. Four processes define its structure.
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The Otto cycle is primarily used in:
Explanation: The Otto cycle models spark-ignition engines like petrol engines, unlike diesel engines or gas turbines. Refrigeration uses vapor-compression cycles.
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The Carnot cycle assumes:
Explanation: Reversible, frictionless processes maximize efficiency, unlike irreversible or real gas cycles. Heat transfer varies, not remains constant.
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In the Carnot cycle’s adiabatic expansion:
 Explanation: Adiabatic expansion lowers temperature via work, unlike isothermal processes or heat absorption in expansion. Internal energy changes, not stays constant.
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The Carnot cycle is typically modeled in:
Explanation: Piston-cylinders allow volume changes for isothermal and adiabatic processes, unlike rigid containers or pipes in other systems. Heat exchangers involve heat transfer.
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During the Carnot cycle’s isothermal compression:
Explanation: Isothermal compression rejects heat to the cold reservoir, unlike absorption in expansion or temperature changes in adiabatic processes. Work is non-zero.
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The Carnot cycle is significant because it:
Explanation: The Carnot cycle defines the maximum efficiency for heat engines, unlike real gas cycles or constant-volume processes. Work is produced, not zero.
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The efficiency of a Carnot cycle is determined by:
 Explanation: Efficiency relies on hot and cold reservoir temperatures (η = 1 - Tc/Th), unlike work or volume in other cycles or pressure ratios in real engines.
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The adiabatic processes in the Carnot cycle involve:
Explanation: Adiabatic processes have no heat transfer, unlike isobaric or isothermal processes with heat exchange. Volume and temperature change, not remain
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In the Carnot cycle’s isothermal expansion, the system:
Explanation: Isothermal expansion absorbs heat at constant temperature, unlike rejection in compression or no heat in adiabatic processes. Work is done, not zero.
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The Carnot cycle operates between:
Explanation: Heat transfer occurs between hot and cold temperature reservoirs, unlike pressure or volume-based systems in other cycles. Entropy reservoirs are not relevant.
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The Carnot cycle consists of how many processes?
Explanation: The Carnot cycle includes two isothermal and two adiabatic processes, unlike cycles with fewer or more steps. Four processes define its reversible structure.
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