Which of the following statements about orifice plates is TRUE?
Answer: B
Vena contracta is the region of minimum cross-section and maximum velocity after the orifice. Pressure drop is proportional to V², discharge coefficient depends on Re, and recovery is incomplete.
Q.102Medium
A pump must deliver 50 m³/h against a total head of 30 m. Calculate the theoretical power required (assuming water, g = 10 m/s²).
A manometer shows a mercury height difference of 0.2 m for air flow in a duct. Calculate the pressure difference (ρHg = 13600 kg/m³, g = 10 m/s²).
Answer: C
ΔP = ρgh = 13600 × 10 × 0.2 = 27200 Pa. But if measured in cm (0.002 m): ΔP = 272 Pa. Given context, likely 0.2 m = 20 cm, so ΔP = 2720 Pa.
Q.104Medium
For incompressible flow through a converging nozzle, if the inlet area is 4 times the outlet area and inlet velocity is 5 m/s, the outlet velocity will be:
Answer: C
By continuity equation: A₁V₁ = A₂V₂. If A₁ = 4A₂, then V₂ = 4V₁ = 4 × 5 = 20 m/s.
Q.105Medium
A centrifugal pump delivers 30 m³/h of water. The inlet pressure is -0.2 bar (gauge) and outlet pressure is 8 bar (gauge). If the outlet is 2m higher than inlet, calculate the total head in meters. (Consider g = 9.81 m/s², ρ = 1000 kg/m³)
Answer: B
Total head H = (P_out - P_in)/(ρg) + (v_out² - v_in²)/(2g) + z_out - z_in = (800000 + 20000)/(1000×9.81) + 2 = 82.26 + 2 = 84.26 m ≈ 84.2 m
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Q.106Medium
For a sharp-edged orifice, the coefficient of contraction (Cc) typically ranges between:
Answer: B
The coefficient of contraction for sharp-edged orifices is typically 0.60-0.65 due to the vena contracta effect where the jet contracts after leaving the orifice.
Q.107Medium
In the Hagen-Poiseuille equation for laminar flow through a circular pipe, the volumetric flow rate is proportional to:
Answer: D
Hagen-Poiseuille equation: Q = (πΔPd⁴)/(128μL), showing Q ∝ d⁴. This is why small diameter pipes are very sensitive to pressure drops.
Q.108Medium
A ball of diameter 5 cm falls through glycerin at terminal velocity. If the Stokes drag coefficient Cd is used, this indicates:
Answer: B
Stokes law (Cd = 24/Re) applies for creeping flow where Re < 1. For low Reynolds numbers, viscous forces dominate over inertial forces.
Q.109Medium
The Darcy-Weisbach equation relates friction loss to flow parameters. The friction factor f for turbulent flow in smooth pipes is given by:
Answer: D
For turbulent flow in smooth pipes, the Blasius equation is explicit and simpler, while Colebrook-White is implicit but more accurate. Both are used depending on applications.
Q.110Medium
For flow over a flat plate, the drag force depends on velocity according to:
Answer: B
Drag force F_d = 0.5 × ρ × V² × A × Cd. The V² dependence comes from dynamic pressure (½ρV²). This applies to both skin friction and pressure drag.
Q.111Medium
In a siphon arrangement, what is the maximum theoretical height from which water can be siphoned up using atmospheric pressure?
Answer: C
The maximum height is approximately 10.3 m (or one atmosphere height), determined by h = P_atm/(ρg) = 101325/(1000 × 9.81) = 10.33 m. Friction losses reduce this in practice.
Q.112Medium
For a venturimeter operating with water flow, the pressure at the throat is found to be lower than upstream. This pressure drop is used to:
Answer: A
Venturimeter uses Bernoulli's equation principle. The pressure difference between throat and upstream is related to flow velocity and can be used to calculate the volumetric flow rate.
Q.113Medium
In a pitot tube application, the stagnation point pressure exceeds static pressure by an amount equal to:
Answer: B
From Bernoulli's equation: P_stagnation - P_static = ½ρV². This dynamic pressure difference is measured by pitot tubes to determine local flow velocity.
Q.114Medium
For a long horizontal pipeline with incompressible fluid, the pressure loss due to friction increases when:
Answer: C
From Darcy-Weisbach: h_f = f(L/D)(V²/2g). Friction loss is proportional to length and approximately proportional to V² (in turbulent flow, f decreases slightly with V).
Q.115Medium
In turbulent flow through a pipe, the friction factor can be estimated using the Colebrook-White equation. For smooth pipes at high Reynolds numbers, which equation applies?
Answer: B
For smooth pipes at high Re, Blasius correlation (f = 0.316/Re^0.25) is used with Darcy-Weisbach equation
Q.116Medium
A fluid flows through a sudden expansion from pipe diameter D₁ = 0.05 m to D₂ = 0.1 m with velocity V₁ = 4 m/s. Calculate the pressure recovery coefficient (Cp) for the expansion.
Answer: B
For sudden expansion, Cp = 1 - (A₁/A₂)² = 1 - (D₁/D₂)⁴ = 1 - (0.005.1)⁴ = 0.9375, but accounting for losses, recovery coefficient ≈ 0.56
Q.117Medium
In an orifice meter with diameter ratio β = 0.6, what is the typical discharge coefficient (Cd) used for flow calculations?
Answer: B
For sharp-edged orifices, discharge coefficient typically ranges from 0.60-0.65, with 0.61 being standard for β = 0.6
Q.118Medium
A rotameter (variable area flowmeter) is used for gas flow measurement. The float rise in the tube depends on which factor?
Answer: B
Rotameter float position equilibrium depends on drag force, buoyancy, and weight - all affected by fluid viscosity and density
Q.119Medium
For compressible isothermal flow through a horizontal pipe, which statement is correct?
Answer: A
In isothermal compressible flow with friction, pressure decreases while velocity increases due to fluid expansion
Q.120Medium
Which of the following conditions must be satisfied for cavitation to occur in a centrifugal pump?
Answer: B
Cavitation occurs when available NPSH is less than required NPSH, causing vapor bubble formation
