Question 1

Power–head relationship in reaction turbines  For a reaction turbine working under a given set of geometric and efficiency conditions, how does the power produced relate to the head of water?  Choose the correct completion.

Accepted Answer

Concept Shaft power ≈ ηoverall · ρ g Q H. Reasoning For similar operating conditions (η and Q appropriately related), power scales with head H. At fixed discharge, power is directly proportional to H. Final Answer Is directly proportional to head.

Question 2

Speed definitions in turbines: name for speed to develop unit power under unit head Define the engineering term for the speed of an imaginary turbine, geometrically similar to a given turbine, that would develop unit power under unit head

Accepted Answer

Definitions Unit speed: speed at unit head producing the same power as the actual turbine.Specific speed (Ns): speed of a geometrically similar turbine that develops unit power at unit head. Final Answer Specific speed.

Question 3

Impulse turbine efficiencies: identify mechanical efficiency definition Select the correct definition of mechanical efficiency for an impulse turbine. Assume 'energy imparted to the wheel' refers to power at the runner (work done o…

Accepted Answer

Concept Mechanical efficiency ηm accounts for mechanical (frictional) losses between runner and shaft: ηm = Shaft power / Runner power. Option mapping (a) is overall efficiency (shaft power ÷ hydraulic power from head).(b) matches ηm.(c) is hydraulic efficiency (runner power ÷ jet power). Final Answer Actual work available at the turbine shaft ÷ energy imparted to the wheel (runner power).

Question 4

Water wheels: driving cause in overshot wheels  For overshot water wheels, the wheel runs primarily due to which action of water?  Choose the correct completion.

Accepted Answer

Concept Overshot wheels are filled at the top; the descending water in the buckets provides torque mainly by its weight (potential energy conversion). Contrast Undershot wheels rely more on the impulse (kinetic energy) of flowing water. Final Answer Weight of water.

Question 5

Overall efficiency of a reaction turbine: choose the correct ratio Define the overall efficiency (η_overall) for a reaction turbine in terms of power and available hydraulic energy. Choose the correct expression.

Accepted Answer

Definitions Overall efficiency ηoverall = Shaft power / Hydraulic power from head = Pshaft ÷ (ρ g Q H).Hydraulic efficiency = Runner (wheel) power ÷ ρ g Q H.Mechanical efficiency = Shaft power ÷ Runner power. Option mapping (a) matches overall efficiency.(b) matches mechanical efficiency.(c) matches hydraulic efficiency. Final Answer Power produced by the turbine ÷ energy actually supplied by the turbine (ρ g Q H).

Question 6

Effective head in a pipeline/turbine installation: compute net head from gross head and friction loss Let H_g be the gross (total) head and h_f be the head loss due to friction in the conveyance system. Write the expression for …

Accepted Answer

Concept Losses (e.g., pipe friction, fittings) reduce the head available to the runner. Computation Net head: H = Hg − hf. Final Answer H = Hg − hf.

Question 7

Centrifugal pump vane outlet angle and efficiency: statement on backward-curved blades  Consider the choice of blade outlet angle in a centrifugal pump. Assess the statement: “The efficiency of a centrifugal pump will be maximum when the blades are …

Accepted Answer

Concept Backward-curved vanes provide a stable head–discharge characteristic and lower outlet whirl, reducing losses and improving efficiency. Comparison Forward-curved vanes can yield higher theoretical head but suffer from higher losses and unstable characteristics; radial vanes are intermediate. Final Answer True — maximum efficiency occurs with backward-curved blades.

Question 8

Draft tube purpose in reaction turbines  Explain the primary function of the draft tube fitted at the outlet of a reaction turbine runner operating with a tail race below the runner elevation. Choose the correct statement.

Accepted Answer

Given / Concept A draft tube is a gradually enlarging passage fitted at the runner exit of a reaction turbine. The tail race level is below the runner outlet level. Approach / Why draft tube The draft tube converts a part of the exit kinetic energy into static pressure (pressure recovery) and allows the runner to be set above tail race while still utilising that elevation difference as useful head. Key relations Effective head gained ≈ elevation difference (runner outlet to tail race) + portion of velocity head recovered in the diffuser-like draft tube. Common pitfalls Thinking it merely 'transports' water. Its main duty is head recovery and permitting the runner to run full under sub-atmospheric pressure at outlet. Final Answer It increases the effective head by an amount about equal to the runner outlet elevation above the tail race (plus some recovered velocity head).

Question 9

Hydraulic accumulator capacity: definition  State how the capacity of a hydraulic accumulator is specified in design and selection. Choose the correct definition.

Accepted Answer

Concept A hydraulic accumulator stores energy in the form of pressurised fluid (via weight, spring, or gas precharge). Definition Its capacity is specified as the maximum energy that can be stored and made available between two pressure limits.For a gas-charged accumulator, energy ≈ ∫ p dV over the usable pressure range; for a weight-loaded type, ≈ average pressure × volume change. Common pitfall Equating capacity with volume only. Volume matters, but capacity is fundamentally the energy deliverable. Final Answer Maximum amount of energy stored.

Question 10

Purpose and placement of air vessels in reciprocating pumps  Identify where air vessels are installed and why, in a typical single-cylinder reciprocating pump. Choose the correct statement.

Accepted Answer

Concept Reciprocating pumps produce pulsating flow, causing large acceleration/retardation of fluid in suction and delivery lines. Function of air vessels Air vessels act as hydraulic flywheels, absorbing and supplying flow to smooth the discharge, thereby reducing acceleration head, friction losses, and power fluctuation.Best effectiveness is achieved when fitted close to the cylinder on both suction and delivery lines. Benefits Reduced risk of separation/cavitation on suction, smaller pipe sizes, and lower power requirement. Final Answer They are fitted to both suction and delivery pipes near the cylinder to smooth flow and reduce acceleration head losses.

Question 11

Why use multi-stage centrifugal pumps?  State the principal reason for employing multi-stage centrifugal pumps (impellers in series). Choose the best answer.

Accepted Answer

Concept In series arrangement, each impeller contributes head; the total head is the sum of heads developed by all stages, at approximately the same discharge. Result Multi-stage pumps are therefore chosen primarily for high head duties (e.g., boiler feed pumps). Common pitfall High discharge is typically increased by parallel pumps or larger single-stage impellers, not by series staging. Final Answer To produce high heads.

Question 12

Breast water wheel: operating principle  Characterise how a breast water wheel develops torque relative to overshot and undershot wheels. Choose the correct description.

Accepted Answer

Background Water enters a breast wheel near the level of the wheel axis (breast height). Operating principle The wheel develops torque from both the weight of water contained in the buckets and the impulse of the incoming stream. Final Answer Partly by weight and partly by impulse.

Question 13

Definition of mechanical efficiency for turbines  Fill in the blank: The ratio of actual work available at the turbine shaft to the energy imparted to the wheel (runner) is called ________ efficiency. Choose the correct term.

Accepted Answer

Efficiency taxonomy Hydraulic efficiency = Runner power / Water power at runner inlet. Mechanical efficiency = Shaft power / Runner power (accounts for mechanical losses in bearings, windage, etc.). Overall efficiency = Shaft power / Water power at turbine inlet. Therefore 'Actual work available at the turbine' (shaft output) divided by 'energy imparted to the wheel' (runner input) is mechanical efficiency. Final Answer Mechanical efficiency.

Question 14

Device classification: hydraulic coupling  Identify the correct category for a hydraulic coupling used between prime mover and driven machine. Choose the correct category.

Accepted Answer

Concept A hydraulic (fluid) coupling transfers torque hydrodynamically from input to output without changing the energy form; it does not create (develop) or primarily absorb power. Therefore It is an energy transfer / power transmitting device. Final Answer Energy transfer (power transmitting) machine.

Question 15

Jet on a fixed inclined plate: force component normal to the original flow  A water jet of velocity V and area a strikes a fixed flat plate inclined at angle θ to the jet direction. Find the force exerted by the jet on the plate in the direction <em…

Accepted Answer

Given Jet: speed V, area a, density ρ → mass flow rate ṁ = ρ a V. Plate: fixed, inclined at θ to jet. Approach Take x along the jet and y normal to the jet. The plate eliminates the normal-to-plate velocity component; in x–y, the outgoing flow has zero y-component. Step-by-step Incoming momentum flux in y = ṁ (V sin θ) = ρ a V · V sin θ = ρ a V^2 sin θ.Outgoing momentum flux in y = 0 (fixed plate, flow slides along the plate).Force on plate in +y (on fluid in −y) = Δ(momentum flux in y) = ρ a V^2 sin θ. Checks θ = 0° ⇒ F = 0 (plate parallel to flow) ✔θ = 90° ⇒ F = ρ a V^2 (plate normal to flow) ✔ Final Answer F = ρ a V^2 sin θ

Question 16

Energy conversion in a reaction turbine runner  Assess the statement: As water flows over the vanes of a reaction turbine, its pressure head decreases and is converted into kinetic head before leaving the wheel. Choose the correct judgment.

Accepted Answer

Concept In a reaction turbine (e.g., Francis, Kaplan), pressure drop occurs across the runner itself. Energy changes As water passes through the moving passages, part of its pressure head converts to kinetic head and mechanical work on the runner.Residual velocity head at exit is then partially recovered by the draft tube. Final Answer True.

Question 17

Head range suitability: Francis turbine selection  Identify the usual range of available water head for which a Francis (mixed-flow reaction) turbine is preferred. Choose the correct range.

Accepted Answer

Concept Francis turbines are medium-head mixed-flow reaction machines. Kaplan suits low head; Pelton suits high head. Typical ranges Francis: ≈ 25–250 m, depending on specific speed and site conditions. Final Answer 25 m to 250 m.

Question 18

Jet propulsion of a ship: propelling force with side inlets at right angles to motion  Given: water is drawn through inlet orifices at right angles to the ship's direction of motion. Symbols: a = jet area, V = jet velocity relative to still water (i…

Accepted Answer

Concept / Approach Thrust in jet propulsion comes from the rate of change of momentum in the direction of motion. Mass flow rate through the ship's system (as seen on the ship) = ρ a Vr. Velocity component change along the ship's axis between inlet and exit = (V − v) − 0, because the inflow through side inlets has no axial component. Step-by-step Thrust F = (mass flow rate) × (axial velocity change) F = (ρ a Vr) × (V − v) Verification If the ship is stationary (v = 0), then Vr = V, and F reduces to ρ a V × V = ρ a V², as expected for a stationary nozzle. Common pitfalls Adding velocities instead of taking the difference (V − v) in the momentum change term. Using ρ a V instead of ρ a Vr for the mass flow seen by the moving ship. Final Answer ρ a Vr (V − v)

Question 19

Centrifugal pump discharge formula at inlet For a centrifugal pump, let D be the impeller diameter at inlet, b the impeller width at inlet, and V_f the flow velocity at inlet. Write the discharge Q in terms of these quantities (neglecting…

Accepted Answer

Concept Discharge = (flow area at inlet annulus) × (radial/flow velocity). Calculation Inlet annulus area A = π D b. Therefore, Q = A Vf = π D b Vf. Common pitfalls Forgetting the circumference factor π D and using only b Vf. Final Answer Q = π D b Vf

Question 20

Pump performance ratio: name the ratio based on delivered flow  Definition: The ratio of liquid actually discharged per second by the pump to the liquid passing per second through the impeller. Identify the correct efficiency term for this ratio.  C…

Accepted Answer

Definitions Volumetric efficiency = Qactual / Qimpeller (accounts for leakage and slip). Manometric efficiency relates head rise to theoretical head. Mechanical efficiency accounts for mechanical losses. Overall efficiency = (product of hydraulic × volumetric × mechanical). Final Answer Volumetric efficiency

Hydraulic Machines Questions