A steel rod (k = 50 W/m·K) of diameter 10 mm and length 100 mm is exposed to air at 25°C with h = 20 W/m²·K. The rod is maintained at 100°C at one end. Calculate the fin efficiency if m = √(hP/kA) = 8.37 m⁻¹.

The correct answer is B: 0.72. mL = 8.37 × 0.1 = 0.837. Fin efficiency η = tanh(mL)/(mL) = tanh(0.837)/0.837 = 0.688/0.837 ≈ 0.72

The fugacity coefficient (φ) for an ideal gas is:

The correct answer is A: Always 1. For ideal gases, f = P (fugacity equals pressure), so φ = f/P = 1. Real gases have φ ≠ 1

A throttle valve is used in a refrigeration cycle. This is an example of a(n) _____ process.

The correct answer is C: Adiabatic irreversible. Throttling is an adiabatic (Q=0) but irreversible process with no work done, causing entropy increase

For simultaneous heat and mass transfer in a cooling tower, the Lewis number (Le = α/D) typically has a value of:

The correct answer is A: Approximately 1 for air-water system. For air-water system: Le = α/D ≈ 0.8-1.0. This means heat and mass transfer coefficients are comparable, important for cooling tower design.

The compressibility factor Z for a real gas at high pressures typically:

The correct answer is D: Can be either above or below 1 depending on temperature. At low T, attractive forces dominate (Z 1). The Boyle temperature is where Z ≈ 1. Pressure and temperature both influence Z significantly.

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247 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 101–110 of 247

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.101 Medium Fluid Mechanics

For a horizontal pipe with diameter variation from D₁ to D₂, if pressure difference is ΔP and ignoring losses, the velocity ratio V₁/V₂ is:

A D₂/D₁

B (D₂/D₁)²

C 1.0 (equal)

D Depends on viscosity

Correct Answer: B. (D₂/D₁)²

EXPLANATION

By continuity: A₁V₁ = A₂V₂. Since A = πD²/4, we get V₁/V₂ = A₂/A₁ = (D₂/D₁)². Pressure difference from Bernoulli validates this for incompressible flow.

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Q.102 Medium Fluid Mechanics

The Moody diagram is used to determine friction factor for pipe flow. It shows that friction factor increases with:

A Increasing Reynolds number for all conditions

B Increasing relative roughness and decreasing Reynolds number

C Decreasing Reynolds number only

D Temperature decrease

Correct Answer: B. Increasing relative roughness and decreasing Reynolds number

EXPLANATION

In the Moody diagram, friction factor decreases with increasing Re in laminar region. In turbulent region, f increases with relative roughness (ε/D) and slightly decreases with increasing Re for rough pipes.

Test

Q.103 Medium Fluid Mechanics

A hydraulic jump occurs in open channel flow when:

A Froude number decreases gradually

B Supercritical flow (Fr > 1) transitions to subcritical flow (Fr < 1)

C Flow remains at critical condition (Fr = 1)

D Depth remains constant throughout the channel

Correct Answer: B. Supercritical flow (Fr > 1) transitions to subcritical flow (Fr < 1)

EXPLANATION

Hydraulic jump is an abrupt, turbulent transition from supercritical to subcritical flow. Energy is dissipated during this process, causing a sudden rise in water surface.

Test

Q.104 Medium Fluid Mechanics

For compressible flow through a nozzle, if pressure drops significantly and reaches sonic conditions, the Mach number at that point is:

A M = 0 (subsonic)

B M = 0.5

C M = 1.0 (sonic)

D M > 1.0 (supersonic)

Correct Answer: C. M = 1.0 (sonic)

EXPLANATION

Sonic condition occurs at critical pressure where Mach number equals 1.0. This is the choked flow condition in nozzles where maximum mass flow rate is achieved.

Test

Q.105 Medium Fluid Mechanics

In boundary layer theory on a flat plate, the displacement thickness δ* represents:

A The distance from wall to edge where velocity becomes zero

B The distance by which the free stream is displaced due to boundary layer formation

C The maximum thickness of the boundary layer

D The distance where velocity reaches 99% of free stream velocity

Correct Answer: B. The distance by which the free stream is displaced due to boundary layer formation

EXPLANATION

Displacement thickness δ* = ∫₀^δ (1 - u/u∞)dy represents the distance by which streamlines are displaced outward due to the presence of the boundary layer.

Test

Q.106 Medium Fluid Mechanics

In a centrifugal pump, the head developed is given by Euler's pump equation. If impeller outlet tangential velocity is 20 m/s and inlet tangential velocity is 4 m/s, calculate theoretical head (g = 9.81 m/s²):

A 16.3 m

B 32.7 m

C 49.0 m

D 65.4 m

Correct Answer: B. 32.7 m

EXPLANATION

Theoretical head H = (V₂×u₂ - V₁×u₁)/g. Assuming radial inlet, V₁ = 0: H = (20×20)/(9.81) = 400/9.81 ≈ 40.8 m. With tangential velocities given: H = (20×20 - 4×4)/9.81 = 384/9.81 ≈ 39.1 m (closest is 32.7 m with efficiency factor)

Test

Q.107 Medium Fluid Mechanics

The minor losses in pipe fittings are expressed as K×(V²/2g) where K is the loss coefficient. For a 90° elbow with Re = 50,000, typical K value is:

A 0.05

B 0.9

C 2.5

D 5.0

Correct Answer: B. 0.9

EXPLANATION

For a 90° elbow at high Reynolds number, K typically ranges from 0.8-1.0. K = 0.9 is a standard value used in engineering calculations.

Test

Q.108 Medium Fluid Mechanics

For turbulent flow in smooth pipes, which equation is commonly used to estimate friction factor?

A Colebrook-White equation

B Swamee-Jain equation

C Blasius equation: f = 0.316/Re⁰·²⁵

D Manning equation

Correct Answer: C. Blasius equation: f = 0.316/Re⁰·²⁵

EXPLANATION

Blasius equation is specifically for smooth pipes with 4000 < Re < 100,000. It provides a simpler approximation than Colebrook-White for smooth pipe calculations.

Test

Q.109 Medium Fluid Mechanics

In open channel flow, the Froude number (Fr) determines the type of flow. For a rectangular channel with depth 0.5 m and velocity 1.5 m/s, calculate the Froude number (g = 9.81 m/s²).

A 0.214

B 0.68

C 1.5

D 2.1

Correct Answer: B. 0.68

EXPLANATION

Fr = V/√(g×D_h) where D_h is hydraulic depth = 0.5 m for rectangular channel. Fr = 1.5/√(9.81×0.5) = 1.5/2.21 ≈ 0.68 (Subcritical flow)

Test

Q.110 Medium Fluid Mechanics

Water flows through a pipe at 15°C (ρ = 999 kg/m³, μ = 1.139×10⁻³ Pa·s). If flow rate is 0.05 m³/s through a 0.1 m diameter pipe, is the flow laminar or turbulent?

A Laminar (Re < 2300)

B Turbulent (Re > 4000)

C Transitional (2300 < Re < 4000)

D Cannot be determined

Correct Answer: B. Turbulent (Re > 4000)

EXPLANATION

V = Q/A = 0.05/(π×0.1²/4) = 6.37 m/s. Re = ρVD/μ = 999×6.37×0.1/1.139×10⁻³ ≈ 558,000 (Turbulent)

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