A fluid flows through a pipe of diameter 0.1 m with velocity 2 m/s. If the kinematic viscosity is 1×10⁻⁶ m²/s, calculate the Reynolds number.
Answer: A
Re = (ρVD)/μ = VD/ν. Re = (2 × 0.1)/(1×10⁻⁶) = 0.2/(1×10⁻⁶) = 2×10⁵. Flow is turbulent.
Q.202Easy
Which equation relates pressure drop to velocity in laminar flow through pipes?
Answer: A
Hagen-Poiseuille equation (ΔP = 32μLV/D²) is specific for laminar flow. Darcy-Weisbach is general for both laminar and turbulent flows.
Q.203Medium
For turbulent flow in rough pipes at high Reynolds numbers, which friction factor equation is most applicable?
Answer: B
Colebrook-White equation is implicit but accurate for all turbulent regimes including rough pipes. For very rough pipes at high Re, relative roughness dominates.
Q.204Easy
A centrifugal pump operates at 1500 RPM. If the impeller diameter is 0.3 m, what is the tip speed?
Answer: A
Tip speed = πDN/60 = π × 0.3 × 601500 = 23.56 m/s (where N is in RPM).
Q.205Easy
In the Bernoulli equation, which term represents the pressure energy per unit volume?
Answer: C
The Bernoulli equation is P + ½ρV² + ρgz = constant. P itself is pressure energy per unit volume (not P/ρ which is pressure head).
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Q.206Medium
Water flows through a venturimeter with inlet diameter 0.1 m and throat diameter 0.05 m. The pressure difference is 5 kPa. Assuming ideal flow, calculate the velocity at the inlet (ρ = 1000 kg/m³).
Answer: B
Using continuity and Bernoulli: V₁ = √[2ΔP/(ρ(A₁²/A₂² - 1))]. With area ratio 4, V₁ = √[2×5000/(1000×15)] = 2.88 m/s.
Q.207Medium
Which type of pump is most suitable for high-head, low-flow applications?
Answer: B
Reciprocating pumps (piston/plunger) are positive displacement pumps ideal for high-head, low-flow conditions. Centrifugal pumps suit high-flow, low-head applications.
Q.208Medium
What is the relationship between Fanning friction factor (f) and Darcy friction factor (fD)?
Answer: A
Fanning factor is ¼ of Darcy factor: f = fD/4. Both relate pressure drop to flow, but through different equations.
Q.209Easy
A fluid with dynamic viscosity 0.5 Pa·s and density 800 kg/m³ flows in a pipe. Its kinematic viscosity is:
Answer: A
ν = μ/ρ = 0.8005 = 6.25×10⁻⁴ m²/s.
Q.210Medium
In a packed bed, if particle diameter increases while maintaining constant bed porosity and superficial velocity, the pressure drop will:
Answer: B
Ergun equation: ΔP ∝ (1-ε)²V/(ε³dp²). Pressure drop is inversely proportional to dp². Larger particles = lower pressure drop.
Q.211Medium
The drag coefficient for a sphere in creeping flow (Re < 0.1) is given by:
Answer: A
For creeping flow (Stokes law), CD = 24/Re. This is valid for Re < 0.1. For higher Re, additional terms and constant drag apply.
Q.212Medium
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.213Easy
For a Newtonian fluid, shear stress (τ) is related to shear rate (dV/dy) by:
Answer: A
Newton's law of viscosity: τ = μ(dV/dy). Option B is power law (non-Newtonian), C is Bingham plastic model.
Q.214Medium
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).
In fluid mechanics, which dimensionless number represents the ratio of inertial forces to viscous forces?
Answer: A
Reynolds number Re = (Inertial forces)/(Viscous forces) = ρVD/μ. It characterizes flow regime (laminar vs turbulent).
Q.216Hard
For a given pipe and fluid, if the flow velocity doubles, the pressure drop in turbulent flow will approximately:
Answer: C
In turbulent flow, ΔP ∝ f × V^m where m is between 1.8-2 depending on friction factor variation. Not exactly V² due to changing friction factor with Re.
Q.217Medium
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.218Easy
Which pumping principle is used in a gear pump?
Answer: B
Gear pumps are positive displacement pumps. They move fixed volumes of fluid per rotation. Dynamic principle applies to centrifugal pumps.
Q.219Medium
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.220Easy
A fluid with dynamic viscosity of 0.8 Pa·s and density of 900 kg/m³ flows through a circular pipe. What is the kinematic viscosity of this fluid?
