Question 1

Meaning of critical pressure (choked condition) in steam nozzles  Statement: The critical pressure corresponds to steam velocity at the throat being equal to the local speed of sound (sonic condition). Decide whether the statement is correct.

Accepted Answer

Concept At the critical pressure ratio, the Mach number at the throat reaches 1 (sonic). The mass flow then attains its maximum for the given inlet state. Therefore The statement equating critical pressure to sonic throat velocity is correct. Final Answer True

Question 2

Components of a binary vapour (mercury–steam) power plant  Identify which of the following are included as core components in a classic binary vapour plant arrangement. Choose the correct option.

Accepted Answer

Concept In mercury–steam binary cycles, a mercury boiler/turbine (high-temperature topping) exhausts heat to generate steam for a steam turbine (bottoming), with associated condensers in each loop. Final Answer All of these

Question 3

Blade geometry in a Parsons reaction turbine  For a Parsons (≈50% reaction) turbine stage, determine the relation between fixed (stator) and moving (rotor) blade shapes. Choose the correct option.

Accepted Answer

Concept In a Parsons reaction stage (degree of reaction ≈ 0.5), the fixed and moving blade passages are designed to be geometrically similar so that pressure drop and acceleration are shared equally. Final Answer Fixed and moving blades are identical (conjugate shapes)

Question 4

Definition of axial discharge from turbine blades  A turbine has axial discharge when the absolute exit steam direction makes what angle with the blade motion (tangential) direction? Choose the correct option.

Accepted Answer

Concept Blade motion is tangential; axial discharge means the absolute exit velocity is along the machine axis, which is perpendicular to the tangential direction. Therefore The angle between exit direction and blade motion is 90°. Final Answer 90°

Question 5

Terminology: axial-flow turbines  Statement: A turbine in which the general direction of steam flow is parallel to the turbine axis is called an axial-flow turbine. Decide whether the statement is correct.

Accepted Answer

Concept By definition, axial-flow machines have working fluid flow predominantly parallel to the axis of rotation. This statement is therefore correct. Final Answer True

Question 6

Critical (throat) pressure in a De Laval nozzle: superheated steam 10 bar → 0.1 bar  Given: Superheated steam expands from 10 bar to 0.1 bar in a De Laval nozzle. Find: Pressure at the minimum area (throat) at choked condition using the standard cri…

Accepted Answer

Given Upstream pressure p1 = 10 bar (superheated)Critical pressure ratio for superheated steam ≈ 0.546 Step-by-step pthroat = 0.546 × p1= 0.546 × 10 bar= 5.46 bar Common pitfall Using the wet-steam critical ratio (≈ 0.577) would give 5.77 bar, which is not applicable here since the prompt specifies superheated steam. Final Answer 5.46 bar

Question 7

Effect of turbine blades on steam direction  Statement: The turbine blades do not change the direction of steam issuing from the nozzle. Decide whether the statement is correct.

Accepted Answer

Concept Moving blades are designed to deflect (change the direction of) the absolute steam velocity to extract momentum and produce torque. In impulse and reaction stages, the exit direction differs from the nozzle exit direction. Therefore The statement is incorrect. Final Answer False

Question 8

Steam turbines — definition of efficiency ratio  The ratio of the total useful heat drop (actual work obtained from the fluid) to the total isentropic heat drop across the turbine/stage.  Choose the correct name of this efficiency.

Accepted Answer

Concept/Approach Isentropic heat drop is the ideal enthalpy drop between inlet and exit pressures with no irreversibility. Useful heat drop equals the actual work extracted from the fluid in the turbine or in a single stage. The ratio (useful drop)/(isentropic drop) within the turbine is called internal efficiency (sometimes called turbine or stage internal efficiency). Common pitfalls Stage efficiency is often used loosely, but strictly it is a product of component efficiencies. The definition asked matches internal (isentropic) efficiency. Rankine efficiency refers to the overall cycle thermal efficiency, not a drop ratio. Final Answer Internal efficiency

Question 9

Steam nozzle losses — where friction is assumed to act  In a practical analysis of a convergent–divergent steam nozzle, the entire frictional loss is assumed to occur in a specific region of the nozzle.  Identify that region.

Accepted Answer

Concept/Approach In steam nozzles, boundary layer growth and condensation effects are most significant in the divergent portion, i.e., from throat to exit; analyses often lump friction there. Assuming losses concentrated after the throat simplifies modeling of velocity loss and exit pressure for choked flow. Final Answer Between throat and exit

Question 10

Maximum efficiency condition for a reaction turbine Let V be the absolute velocity of water at inlet making angle α with the tangent, so its whirl component is V cos α. Find the blade speed V_b for maximum hydraulic efficiency (ideal ana…

Accepted Answer

Given/Definitions Guide vane angle α gives the whirl component at inlet: Vw1 = V cos α. Concept/Approach From Euler's turbine equation and ideal velocity triangles (no losses, outlet whirl minimized), hydraulic efficiency is maximized when blade speed equals Vb = Vw1/2. Step Therefore, Vb = (V cos α)/2. Final Answer Vb = 0.5 × V cos α

Question 11

Meaning of thermal equilibrium for flowing steam  Interpret the term 'thermal equilibrium' in the context of the flow state of steam in a process description.  Choose the most appropriate characterization.

Accepted Answer

Concept/Approach Thermal equilibrium means no temperature gradients within the system; the temperature is uniform and does not change with time or position, which corresponds to an isothermal description. Isentropic additionally requires reversibility (no entropy change), which is stronger than thermal equilibrium alone. Final Answer Isothermal

Question 12

Steam pressure variation inside a nozzle — key dependencies  Within a steam nozzle, identify the quantities that govern how static pressure changes along the flow passage.  Choose the best option.

Accepted Answer

Concept/Approach Nozzle flow couples momentum and state: velocity rise drives static pressure drop (Bernoulli/energy balance). Steam's specific volume (compressibility) and dryness fraction (quality) affect density and hence acceleration and pressure–area relations. Final Answer All of these

Question 13

Mass discharge in a convergent–divergent steam nozzle after the throat  Statement completion: In an ideally operating C–D nozzle with choked flow at the throat, the discharge (mass flow rate) of steam __________ in the divergent portion after the th…

Accepted Answer

Given/Definitions Steady 1-D nozzle, choked at throat (Mach = 1). Concept/Approach For steady flow, mass flow rate ṁ = ρ A V is constant along the nozzle in the absence of leakage or extraction. After choking, changes in A, ρ, and V adjust so that ṁ stays the same; thus the discharge remains constant along the C–D nozzle. Common pitfalls Velocity increases in the divergent section for supersonic steam, but mass flow rate does not change. Final Answer Remains constant

Question 14

Effect of regeneration on a steam power cycle  Considering a regenerative Rankine cycle with feedwater heating, identify the correct impact on specific work and thermal efficiency.  Choose the correct statement.

Accepted Answer

Concept/Approach Regeneration extracts bleed steam for feed heating, reducing flow through later turbine stages and thus specific work decreases. Raising feedwater temperature increases the mean temperature of heat addition, so thermal efficiency increases. Final Answer Decreased specific work and increased thermal efficiency

Question 15

Nozzle efficiency — definition by heat drops  Definition prompt: The ratio of the useful heat drop (actual enthalpy drop converted to kinetic energy) to the isentropic heat drop across a nozzle equals which efficiency?  Choose the correct option.

Accepted Answer

Concept/Approach Nozzle efficiency is defined as ηn = (actual KE at exit)/(ideal KE) = (actual enthalpy drop)/(isentropic enthalpy drop). It measures how effectively the available heat drop is converted to kinetic energy. Final Answer Nozzle efficiency

Question 16

Critical pressure ratio for choked flow in a nozzle Let p₁ be the inlet (stagnation) pressure and p₂ the throat static pressure at choking. Express the critical pressure ratio (p₂/p₁) in terms of the rati…

Accepted Answer

Concept/Approach For isentropic flow of a perfect gas, the sonic (choked) condition at the throat gives (p2/p1)crit = (2/(γ + 1))γ/(γ − 1). This is derived from the energy equation and isentropic relations at Mach = 1. Final Answer (2/(γ + 1))^(γ/(γ − 1))

Question 17

Nature of flow through a well-designed nozzle  Assume steady, adiabatic expansion with negligible potential energy change and small friction.  How is the flow commonly idealized?

Accepted Answer

Concept/Approach An ideal nozzle converts enthalpy drop into kinetic energy with no heat transfer or irreversibility; thus the expansion is modeled as isentropic. Pressure and density change; volume is not constant, and the process is not isothermal in general. Final Answer Isentropic flow

Question 18

Steam turbines: definition of blading efficiency (diagram efficiency)  The ratio of the work done on the blades to the energy supplied to the blades is called: Choose the correct option.

Accepted Answer

Concept Energy supplied to the blades (from the nozzle) appears mainly as kinetic energy of steam jets. The fraction of that energy actually converted into work on the rotor is the blading (diagram) efficiency. Why others are wrong Nozzle efficiency compares actual and isentropic jet velocities in the nozzle.Stage efficiency combines nozzle and blade effects.Mechanical efficiency accounts for mechanical losses between rotor and output shaft. Final Answer Blading efficiency

Question 19

Turbine blades — prompt incomplete  The stem ‘‘The turbine blades are …’’ is incomplete and does not specify what property is being asked about (shape, material, spacing, stress state, etc.). Select the most appropriate response.

Accepted Answer

Data inadequate

Question 20

Driving force in an impulse–reaction turbine  For an impulse–reaction turbine stage, identify the nature of the driving force acting on the moving blades. Choose the correct option.

Accepted Answer

Concept In an impulse–reaction stage, part of the pressure drop occurs in the fixed nozzles (impulse component) and part within the moving blades (reaction component). The resulting torque arises from both the change in jet momentum (impulse) and from pressure forces across the rotor passages (reaction). Final Answer Partly impulsive and partly reaction

Steam Nozzles and Turbines Questions