Turbomachinery MCQs 2026

Impeller eye diameter affects

1. A only discharge flange bolt pattern ✓
2. B suction performance and NPSHr ✓
3. C only paint colour ✓
4. D only foundation rebar ✓

Double-suction impeller splits flow to

1. A increase axial thrust deliberately ✓
2. B eliminate need for bearings ✓
3. C reduce axial thrust and improve inlet area ✓
4. D only pump gases without liquid ✓

Balancing holes or drum in pump impeller reduce

1. A radial seal wear only aesthetic ✓
2. B only motor RPM ✓
3. C axial hydraulic thrust on bearings ✓
4. D only fluid viscosity ✓

Mechanical seal in pump prevents

1. A only radial flow in impeller ✓
2. B leakage along shaft at casing penetration ✓
3. C only cavitation inception ✓
4. D only suction air ingestion always ✓

Wear ring clearance increase in pump causes

1. A higher efficiency always ✓
2. B lower NPSHr always beneficially without limit ✓
3. C internal recirculation leakage reducing efficiency ✓
4. D zero vibration ✓

Turbine blade cooling in gas turbines uses

1. A only water jacket like diesel engine block always ✓
2. B only external ice spray ✓
3. C only vacuum insulation ✓
4. D bleed air from compressor through internal passages ✓

Pump power required is approximately

1. A only Q without head ✓
2. B only H without flow ✓
3. C only density without g ✓
4. D ρ g Q H / efficiency ✓

Nozzle guide vanes in gas turbine direct flow onto

1. A only compressor rotor exclusively without stator ✓
2. B only combustor liner ✓
3. C only afterburner ✓
4. D turbine rotor blades at correct angle ✓

Stator blades in axial compressor

1. A increase pressure and direct flow to next rotor row ✓
2. B only extract power from shaft ✓
3. C only add fuel ✓
4. D only condense steam ✓

Choking in nozzle occurs when

1. A flow is subsonic everywhere always ✓
2. B Mach number reaches unity at throat ✓
3. C pressure ratio is zero ✓
4. D temperature is absolute zero ✓

Turbocharger on diesel engine uses

1. A exhaust gas turbine driving compressor for intake boost ✓
2. B only hydraulic pump for steering ✓
3. C only wind turbine on roof ✓
4. D only steam ejector ✓

Series operation of pumps adds

1. A heads at same flow (approximately) ✓
2. B flows at same head always ✓
3. C only temperatures ✓
4. D only electrical phases ✓

Water hammer in piping is caused by

1. A steady laminar flow only ✓
2. B only water heating without motion ✓
3. C sudden velocity change creating pressure surge ✓
4. D only air filtration ✓

Cavitation erosion on impeller appears as

1. A pitting and material loss on low-pressure side of blades ✓
2. B only uniform polishing beneficially ✓
3. C only paint peeling decorative ✓
4. D only magnetic scaling ✓

Specific speed of a pump indicates whether the design is

1. A only electrical motor RPM nameplate only ✓
2. B centrifugal radial, mixed-flow or axial type ✓
3. C only pipe diameter schedule only ✓
4. D only oil viscosity grade only ✓

Diffuser in compressor or pump casing converts

1. A kinetic energy to pressure energy ✓
2. B pressure to kinetic only wasting energy ✓
3. C only heat to work ✓
4. D only work to chemical energy ✓

Cavitation number or Thoma sigma is used for

1. A only pump NPSH in all fluids identically without context ✓
2. B only compressor surge margin ✓
3. C only boiler TDS ✓
4. D predicting cavitation inception in hydraulic turbines ✓

Synchronization of generator to grid requires

1. A only random connection timing ✓
2. B only maximum current inrush deliberately ✓
3. C only disconnecting excitation ✓
4. D matching voltage, frequency and phase sequence ✓

Runaway speed of hydraulic turbine occurs when

1. A load increases to maximum ✓
2. B water flow stops instantly ✓
3. C wicket gates weld open only without overspeed ✓
4. D load is lost and flow continues accelerating runner ✓

Turbine governing maintains

1. A only constant inlet temperature without control ✓
2. B only maximum vibration ✓
3. C speed or power output under varying load ✓
4. D only colour of lubricant ✓

Jet pump (ejector) entrains fluid using

1. A only positive displacement piston ✓
2. B only gear mesh trapping ✓
3. C only nuclear radiation ✓
4. D high-velocity motive fluid ✓

Hydraulic ram pump uses

1. A water hammer effect to lift portion of water without external power ✓
2. B electric motor always required ✓
3. C steam boiler always ✓
4. D only compressed air from factory ✓

Pump turbine (reversible) in pumped storage

1. A only burns natural gas ✓
2. B pumps water uphill off-peak and generates on-peak ✓
3. C only compresses air without water ✓
4. D only distills water ✓

Wind turbine extracts energy from

1. A kinetic energy of moving air ✓
2. B only geothermal steam underground ✓
3. C only tidal salinity gradient ✓
4. D only nuclear fission ✓

Bypass ratio in turbofan is ratio of

1. A fuel to air ratio only ✓
2. B compressor stages to turbine stages only ✓
3. C mass flow through fan bypass duct to core flow ✓
4. D inlet diameter to outlet only ✓

Turbojet engine thrust arises from

1. A only propeller blade lift without exhaust ✓
2. B only boiler steam pressure ✓
3. C only hydraulic ram force ✓
4. D momentum change of exhaust gas plus pressure difference at nozzle ✓

Blower provides

1. A only vacuum 0 absolute ✓
2. B only filtration without pressure ✓
3. C only steam superheat ✓
4. D intermediate pressure rise between fan and compressor ✓

Fan differs from compressor in that fan has

1. A very high pressure ratio multistage always ✓
2. B only handles liquids ✓
3. C only generates vacuum below 0 absolute ✓
4. D low pressure rise with high volume flow ✓

Tip clearance in turbomachinery causes

1. A infinite efficiency gain ✓
2. B leakage reducing efficiency ✓
3. C zero flow always ✓
4. D only structural strengthening without loss ✓

Blade twist in axial machines accommodates

1. A varying relative flow angle along span ✓
2. B only constant incidence at all radii without twist ✓
3. C only paint colour gradient ✓
4. D only bolt pattern ✓

Degree of reaction for turbine stage is

1. A always zero for Francis ✓
2. B always 1 for Pelton impulse ✓
3. C only boiler efficiency ✓
4. D fraction of enthalpy drop in rotor versus total stage drop ✓

Turbine isentropic efficiency compares

1. A only mechanical bearing loss ✓
2. B actual enthalpy drop to isentropic enthalpy drop ✓
3. C only generator copper loss ✓
4. D only cooling tower evaporation ✓

Gas turbine compressor consumes

1. A zero power always ✓
2. B only generates electricity without shaft power split ✓
3. C only heats water ✓
4. D significant portion of turbine output (high back work ratio) ✓

Gas turbine cycle is

1. A Rankine liquid only ✓
2. B Carnot refrigerator only ✓
3. C Brayton cycle (compressor, combustor, turbine) ✓
4. D Stirling regenerator only ✓

Regenerative feedwater heating in steam cycle

1. A only rejects all heat to cooling tower ✓
2. B only burns more coal without recovery ✓
3. C only compresses air ✓
4. D extracts steam from turbine to heat feedwater ✓

Reheat cycle in steam plant

1. A only condenses all steam mid turbine ✓
2. B only bypasses turbine entirely ✓
3. C only heats feedwater in deaerator exclusively ✓
4. D returns steam to boiler for reheating between turbine sections ✓

Pressure compounding (Rateau) drops pressure

1. A only once in condenser ✓
2. B in multiple nozzle stages each followed by moving blades ✓
3. C only in boiler drum ✓
4. D only in feedwater heater ✓

Velocity compounding in steam turbine

1. A only one row without pressure drop ✓
2. B only hydraulic Pelton ✓
3. C uses multiple moving blade rows with stationary reversing blades ✓
4. D only axial compressor ✓

De Laval impulse steam turbine has

1. A only low speed Kaplan hydraulic ✓
2. B only reciprocating piston ✓
3. C single velocity-compounded or simple impulse wheel with high speed ✓
4. D only centrifugal pump ✓

Steam turbine converts

1. A only chemical fuel without expansion ✓
2. B thermal energy of steam to shaft work ✓
3. C only water head hydraulic ✓
4. D only wind kinetic ✓

Reaction turbine stage has pressure drop

1. A only in nozzles upstream of wheel completely ✓
2. B only in condenser hotwell ✓
3. C in both fixed blades and moving blades ✓
4. D only in feed pump ✓

Impulse turbine stage pressure drop occurs

1. A entirely in runner blades submerged ✓
2. B only in condenser ✓
3. C in fixed nozzles; runner at atmospheric pressure region ✓
4. D only in boiler ✓

Draft tube on reaction turbine recovers

1. A only increases velocity deliberately wasting energy ✓
2. B only filters sediment ✓
3. C kinetic energy at runner exit by decelerating flow ✓
4. D only lubricates bearings ✓

Cavitation in turbines occurs at

1. A runner outlet where pressure may drop below vapour pressure ✓
2. B only inlet penstock high pressure always ✓
3. C only draft tube exit above atmospheric always preventing ✓
4. D only in air ✓

Specific speed for hydraulic turbines classifies

1. A runner type suitable for head and flow ✓
2. B only electrical frequency ✓
3. C only coal ash content ✓
4. D only lubricant ISO grade ✓

Kaplan turbine has

1. A axial flow runner with adjustable blades and guide vanes ✓
2. B only fixed Pelton buckets ✓
3. C only steam nozzles ✓
4. D only gear pump lobes ✓

Francis turbine is

1. A pure impulse jet only ✓
2. B only vertical Kaplan only always ✓
3. C mixed-flow reaction turbine with adjustable wicket gates ✓
4. D only gas turbine ✓

Pelton turbine is

1. A impulse turbine with tangential jets on buckets ✓
2. B reaction runner fully submerged axial only always ✓
3. C only steam turbine condensing ✓
4. D only wind turbine ✓

Hydraulic turbine converts

1. A only electrical to thermal ✓
2. B only compressed air to vacuum ✓
3. C fluid energy (head) to mechanical shaft power ✓
4. D only chemical bond energy ✓

Slip factor in centrifugal impeller accounts for

1. A relative eddy reducing whirl component at exit ✓
2. B only bearing friction ✓
3. C only paint thickness ✓
4. D only foundation vibration ✓

Axial compressor used in

1. A only domestic water well exclusively ✓
2. B only hydraulic press oil only ✓
3. C only boiler feed vacuum only ✓
4. D gas turbines and jet engines for high mass flow ✓

Choke (stonewall) in compressor map is

1. A minimum flow point ✓
2. B maximum flow limited by sonic conditions at some section ✓
3. C only surge point ✓
4. D only shutoff head ✓

Surge in centrifugal compressor is

1. A flow instability with oscillation and possible damage ✓
2. B steady maximum efficiency point always ✓
3. C only lubrication failure ✓
4. D only motor bearing grease colour ✓

Polytropic efficiency of compressor accounts for

1. A only ideal isentropic without losses ✓
2. B only mechanical bearing colour ✓
3. C only inlet filter mesh size aesthetic ✓
4. D real irreversible compression path ✓

Isothermal compression is more efficient than adiabatic because

1. A no work is required ever ✓
2. B pressure never rises ✓
3. C heat is removed keeping temperature constant reducing work ✓
4. D volume is constant ✓

Reciprocating compressor achieves

1. A only very low pressure vacuum always without stages ✓
2. B high pressure ratio with staged cylinders ✓
3. C only axial flow without valves ✓
4. D only isothermal expansion without work ✓

Centrifugal compressor is

1. A only reciprocating piston without valves ✓
2. B only vacuum pump water ring exclusively always ✓
3. C dynamic compressor with radial or axial impellers ✓
4. D only heat exchanger ✓

Compressor raises

1. A only liquid water head without density change much ✓
2. B only solid particles ✓
3. C only vacuum without pressure rise ✓
4. D pressure of gas by doing work on it ✓

Foot valve on pump suction prevents

1. A only discharge pressure rise ✓
2. B drainback of liquid when pump stops ✓
3. C only motor overheating electrically always ✓
4. D only cavitation at discharge ✓

Priming of centrifugal pump is needed because

1. A it is positive displacement always ✓
2. B it cannot evacuate air effectively from suction to start pumping ✓
3. C impeller is sealed without clearance ✓
4. D only when pumping mercury always ✓

VFD on pump motor saves energy by

1. A always running at full speed ✓
2. B closing suction valve ✓
3. C reducing speed to match required duty point ✓
4. D increasing static head artificially ✓

Throttling control of pump discharge valve

1. A always improves efficiency at all points ✓
2. B changes impeller diameter ✓
3. C changes speed without VFD ✓
4. D reduces flow but wastes energy as valve loss ✓

System curve for piping network represents

1. A head required versus flow from friction and static lift ✓
2. B only pump efficiency ✓
3. C only impeller diameter ✓
4. D only motor slip ✓

Pump characteristic curve plots

1. A only temperature versus time ✓
2. B head versus flow rate at constant speed ✓
3. C only voltage versus current motor only ✓
4. D only stress versus strain metal ✓

Axial flow pump is suited for

1. A very high head low flow exclusively always ✓
2. B only gases only ✓
3. C high flow low head applications ✓
4. D only molten metal always ✓

Gear pump is

1. A positive displacement rotary pump with meshing gears ✓
2. B only axial fan ✓
3. C only Francis turbine ✓
4. D only steam condenser ✓

Reciprocating pump gives

1. A pulsating flow; needs accumulator sometimes ✓
2. B perfectly steady flow always without devices ✓
3. C only radial discharge ✓
4. D only vacuum without valves ✓

Multistage centrifugal pump uses

1. A several impellers in series on one shaft for high head ✓
2. B only one impeller always ✓
3. C only gear teeth pumping ✓
4. D only steam ejector ✓

Specific speed Ns of pump is indicator of

1. A only motor current ✓
2. B only pipe colour ✓
3. C only oil viscosity without flow ✓
4. D pump type (radial, mixed, axial) best suited ✓

Affinity laws: pump power varies with speed as

1. A N linearly ✓
2. B N cubed ✓
3. C N squared only ✓
4. D independent of N ✓

Affinity laws: pump head H varies with speed as

1. A N squared ✓
2. B N linearly ✓
3. C N cubed for head only wrong ✓
4. D independent of N ✓

Affinity laws for centrifugal pump when speed changes: flow Q varies

1. A with N squared ✓
2. B directly with speed N ✓
3. C inversely with N ✓
4. D independent of N ✓

NPSH required (NPSHr) is

1. A always zero for all pumps ✓
2. B minimum suction energy margin needed by pump design ✓
3. C same as discharge head always ✓
4. D only boiler drum level ✓

NPSH available (NPSHa) depends on

1. A suction conditions and fluid vapour pressure ✓
2. B only discharge valve colour ✓
3. C only motor paint ✓
4. D only foundation bolt torque only ✓

Cavitation in pumps occurs when

1. A pressure always above atmospheric everywhere ✓
2. B only at discharge flange high pressure ✓
3. C local pressure drops below vapour pressure forming vapour bubbles ✓
4. D only in solids ✓

Pump head H represents

1. A only power in kW directly ✓
2. B energy per unit weight of fluid (m of fluid) ✓
3. C only torque in N·m without speed ✓
4. D only temperature rise °C only ✓

Positive displacement pump delivers

1. A infinite flow at zero pressure always without limit ✓
2. B only radial flow without moving parts ✓
3. C only steam expansion ✓
4. D nearly constant volume per cycle regardless of pressure (until relief) ✓

Centrifugal pump imparts energy to fluid primarily by

1. A only positive displacement trapping volume ✓
2. B centrifugal force and diffusion in volute/casing ✓
3. C only electromagnetic field on electrons in metal ✓
4. D only gravity alone without rotation ✓

Turbomachinery includes machines that transfer energy between

1. A only solid gears without fluid ✓
2. B only electrical resistors ✓
3. C fluid and rotor by dynamic action ✓
4. D only belt friction dry only ✓