Question 1

Steam turbine action: classify the nature of steam action  Identify whether the action of steam in a steam turbine is static, dynamic, both, or neither. Choose the correct option.

Accepted Answer

Concept Steam turbines convert the kinetic energy of high-velocity steam jets into mechanical work on the rotor blades. This momentum exchange is a dynamic action. Note Nozzles (often stationary) expand steam (a thermodynamic/static effect) to produce high-velocity jets; the turbine stage itself extracts work dynamically from the jet. Final Answer Dynamic

Question 2

Reheat factor definition in multi-stage turbines  Select the correct definition of the reheat factor (RHF) in terms of heat drops. Choose the correct option.

Accepted Answer

Concept Reheat factor (RHF) accounts for the fact that in multi-stage turbines with reheating/expansion, the sum of actual stage heat drops is slightly greater than the overall isentropic heat drop between inlet and exhaust conditions. Definition RHF = (Cumulative (actual or isentropic stage) heat drop) / (Overall isentropic heat drop) Implication RHF is typically slightly above 1 for practical turbines. Final Answer Ratio of cumulative heat drop to the isentropic heat drop

Question 3

Typical numerical range: reheat factor in steam turbines  Identify the usual range of the reheat factor observed in practice. Choose the correct option.

Accepted Answer

Concept Because cumulative heat drop across multiple stages slightly exceeds the single-step isentropic drop, the reheat factor is a bit greater than unity. Typical values For conventional steam turbines, RHF typically lies in the range 1.02 to 1.06. Final Answer 1.02 to 1.06

Question 4

Flow through fixed (stator) blades in a reaction turbine  When steam flows through the fixed blades (nozzle passages) of a reaction turbine, how do pressure and velocity change? Choose the correct option.

Accepted Answer

Concept In a reaction turbine, the fixed blades act as nozzles. Across a nozzle, steam expands: pressure drops and kinetic energy (hence velocity) rises. Therefore Pressure ↓, Velocity ↑ Final Answer Pressure decreases while velocity increases

Question 5

Critical pressure condition: behavior of discharge (mass flow rate)  Complete the statement about nozzles/orifices: The discharge is ________ at the critical pressure ratio. Choose the correct option.

Accepted Answer

Concept For compressible flow through a converging nozzle, at the critical pressure ratio the flow becomes choked (Mach 1 at the throat) and the mass flow rate reaches its maximum for the given upstream conditions. Implication Further reduction of downstream pressure will not increase the discharge; it remains at the maximum choked value. Final Answer Maximum

Question 6

Stage efficiency relation: combining nozzle and blade efficiencies Given nozzle efficiency (η_N) and blading efficiency (η_B), express the stage efficiency (η_S). Choose the correct option.

Accepted Answer

Concept Stage efficiency reflects cumulative losses in both the nozzle and the moving blades. Assuming the losses are independent, the overall (stage) efficiency is the product: ηS = ηN × ηB Final Answer ηS = ηB × ηN

Question 7

Nozzle inlet state: identify pressure and velocity conditions at entry Select the correct combination for the state of steam at the inlet to a nozzle. Choose the correct option.

Accepted Answer

Concept Nozzles convert pressure energy into kinetic energy. Therefore, at the inlet the steam is at relatively high pressure and low velocity. Across the nozzle, pressure drops and velocity rises. Final Answer High pressure and a low velocity

Question 8

Steam nozzles and flow: identify the correct statement  Options describe expansion, frictional effect on dryness fraction, and the definition of critical pressure at the throat.  Choose the single correct statement.

Accepted Answer

Concept/Approach Ideal nozzle expansion is treated as steady-flow, adiabatic, and approximately isentropic, not a complete Rankine cycle (which is a closed power cycle of boiler–turbine/expander–condenser–pump). With wet steam and friction, entropy rises; moisture generally increases (dryness fraction tends to decrease), not increase. Critical pressure is the pressure at the throat when the mass flow is choked (maximum), so the statement about the throat pressure being called critical pressure is correct. Final Answer The pressure of steam at the throat is called the critical pressure.

Question 9

Reaction turbines: source of axial thrust  Given causes: (a) Pressure drop across the rotor (b) Change in axial component of velocity  Select the correct cause(s) of axial thrust.

Accepted Answer

Concept/Approach In a reaction turbine, static pressure drops across both stator and rotor; a net pressure force acts on rotor disks in the axial direction. Additionally, a change in axial momentum (axial velocity component) across the rotor produces axial thrust. Final Answer Both (a) and (b)

Question 10

Steam turbine blades: definition check for blade velocity coefficient  Statement to judge: “The blade velocity coefficient equals the ratio of the relative velocity of steam at the outlet tip of the blade to the relative velocity at the inlet tip of…

Accepted Answer

Concept/Approach The blade velocity coefficient (sometimes denoted by kb) models frictional loss within the moving blade passage: kb = (relative exit speed)/(relative inlet speed) = Vr2/Vr1 ≤ 1. This definition is general and used in stage loss models. Final Answer Agree — it is the ratio Vr2/Vr1.

Question 11

Parsons turbine identification: percentage reaction  Parsons (50% reaction) turbine characteristic.  Choose the correct percentage of reaction.

Accepted Answer

Concept/Approach A Parsons turbine is designed for 50% reaction, i.e., equal isentropic enthalpy drops in stator and rotor. Final Answer 50 percent

Question 12

Improving steam turbine efficiency: pick valid method(s)  Common cycle/plant modifications to raise efficiency.  Choose the best option.

Accepted Answer

Concept/Approach Reheat reduces moisture at turbine exhaust and increases mean temperature of heat addition. Regenerative feed heating increases boiler feedwater temperature, boosting cycle efficiency. Binary/combined vapour plants (e.g., steam with topping/ bottoming) raise overall efficiency. Final Answer Any one of these — each method improves turbine/plant efficiency.

Question 13

Nozzle exit velocity formula (steam): select the correct relation Let K be the nozzle efficiency (or nozzle coefficient) and h_d be the enthalpy (heat) drop during expansion per kilogram. Choose the correct expression for the theoretical…

Accepted Answer

Concept/Approach From steady adiabatic nozzle energy balance: V ≈ √(2 × K × Δh) with Δh in J/kg. With Δh (kJ/kg), conversion gives V (m/s) = 44.72 × √(K × hd) (since √(2 × 1000) ≈ 44.72). Final Answer V = 44.72 × √(K × hd)

Question 14

Definition check: back pressure at nozzle exit  Statement to judge: “The pressure at which the steam leaves the nozzle is known as the back pressure.”  Choose whether the statement is correct or incorrect.

Accepted Answer

Concept/Approach Back pressure is the pressure existing in the receiving space (e.g., condenser or next stage) into which the nozzle discharges; the nozzle exit pressure equals this back pressure in steady operation. Final Answer Agree — the exit pressure equals the back pressure.

Question 15

Thermal states: definition related to supersaturation  Definition prompt: “The difference between the supersaturated temperature and the saturation temperature at the same pressure is called …”  Choose the correct term.

Accepted Answer

Concept/Approach In nozzle flows, supersaturation refers to the fluid being below the saturation temperature (delayed condensation). The temperature deficit relative to saturation at the same pressure is the degree of undercooling (also termed supercooling). Final Answer Degree of undercooling

Question 16

Degree of reaction from enthalpy drops in a turbine stage  Given: Isentropic enthalpy drop in the moving blade (rotor) is two-thirds of the isentropic enthalpy drop in the fixed blade (stator).  Compute the degree of reaction R = (rotor drop)/(stato…

Accepted Answer

Given data Let Δhf = isentropic drop in fixed blades (stator). Δhm (moving/rotor) = (2/3) Δhf. Step-by-Step calculation Total stage drop = Δhf + Δhm = Δhf + (2/3)Δhf = (5/3)Δhf.R = Δhm / (Δhf + Δhm) = ( (2/3)Δhf ) / ( (5/3)Δhf ) = 2/5 = 0.40. Final Answer 0.40

Question 17

Critical pressure condition at a nozzle throat  Choose the correct statement about the steam velocity at the throat when the flow is critical (choked).

Accepted Answer

Concept/Approach At the critical pressure ratio, the mass flow is maximum and the Mach number at the throat is 1 (sonic), so velocity equals local speed of sound. Final Answer Equal to the velocity of sound

Question 18

Critical pressure ratio for initially wet steam  Select the correct value of the critical pressure ratio (p₂/p₁ at the throat corresponding to maximum discharge) for initially wet steam. Choose the correct option.

Accepted Answer

Concept The critical pressure ratio is the downstream-to-upstream pressure ratio at which flow just becomes sonic at the throat (choked flow), giving maximum mass flow for given inlet conditions. For steam, the critical ratio depends slightly on state: Initially wet (near saturation): pthroat/pinlet ≈ 0.577 Superheated: pthroat/pinlet ≈ 0.546 Result For initially wet steam, the standard value used in turbine/nozzle calculations is about 0.577. Common pitfall Do not confuse the superheated value (≈ 0.546) with the wet-steam value. Final Answer 0.577

Question 19

Types of multi-stage steam turbines  Identify which turbine configurations can be multi-stage in practical steam turbine design. Choose the correct option.

Accepted Answer

Concept Multi-staging can be implemented via: Velocity compounding (Curtis): several rows of moving blades to extract jet velocity. Pressure compounding (Rateau): multiple nozzles with pressure drops split over stages. Reaction (Parsons): pressure drop shared between fixed and moving blades over many stages. Final Answer All of these

Question 20

Maximum efficiency of a reaction turbine  The prompt is incomplete and lacks the necessary constraints (e.g., inlet/exit angles, degree of reaction, losses) to state a unique numeric maximum efficiency. Choose the most appropriate statement.

Accepted Answer

Data inadequate — depends on velocity diagrams, reaction, and losses

Steam Nozzles and Turbines Questions