The heat of vaporization of water is 40.66 kJ/mol at 373 K. The entropy of vaporization is approximately:

The correct answer is C: 109 J/mol·K. ΔS_vap = ΔH_vap/T = 40660 J/mol / 373 K ≈ 109 J/mol·K. This follows Trouton's rule (~85-105 J/mol·K for most liquids).

For a polymerization reaction in a batch reactor, the polydispersity index (PDI) and average molecular weight depend on:

The correct answer is B: The ratio of propagation to termination rate constants and conversion. PDI and molecular weight distribution in batch polymerization depend on the relative magnitudes of propagation and termination reactions and the degree of conversion achieved.

The Sherwood number (Sh) correlates with Reynolds (Re) and Schmidt (Sc) numbers. For flow over a flat plate in laminar regime, which expression is approximately correct?

The correct answer is A: Sh = 0.664 Re^(0.5) Sc^(1/3). For laminar flow over a flat plate, the Chilton-Colburn analogy gives Sh = 0.664 Re^0.5 Sc^(1/3), analogous to the Nusselt number in heat transfer.

For a countercurrent liquid-liquid extraction process, the Kremser equation is used. What is the minimum number of stages required if the separation factor is 2.0 and the extraction factor is 1.5?

The correct answer is D: Cannot be determined without additional information. The Kremser equation requires initial and final solute concentrations or minimum separation requirements, which are not provided in the question.

In a CSTR operating at steady state with a first-order irreversible reaction A → B, if the volumetric flow rate is doubled while keeping reactor volume constant, how does the conversion of reactant A change?

The correct answer is B: Conversion decreases because residence time decreases. In a CSTR, conversion depends on residence time (τ = V/Q). When volumetric flow rate Q doubles while V remains constant, residence time τ decreases by half. Since conversion X_A = kτ/(1+kτ) for first-order reaction, decreased τ leads to decreased conversion. This is a fundamental principle in reacto

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Chemical Engineering
Heat Transfer

Process design, thermodynamics, reactions

49 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 49

Topics in Chemical Engineering

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

Q.1 Medium Heat Transfer

In a multipass heat exchanger design, increasing the number of shell passes from 1 to 2 will predominantly affect which parameter?

A Increases the heat transfer coefficient h

B Increases the correction factor F closer to 1

C Decreases required heat exchanger area

D All of the above

Correct Answer: B. Increases the correction factor F closer to 1

EXPLANATION

Adding shell passes (1-2 or 2-4 configuration) brings the temperature distribution closer to counterflow arrangement, increasing the correction factor F (reducing mismatch with LMTD). This increases effective heat transfer driving force without changing h significantly.

Test

Q.2 Medium Heat Transfer

The Prandtl number (Pr = Cp·μ/k) represents the ratio of which two transport properties?

A Momentum diffusivity to thermal diffusivity

B Thermal conductivity to viscosity

C Kinematic viscosity to thermal diffusivity

D Heat capacity to thermal conductivity

Correct Answer: A. Momentum diffusivity to thermal diffusivity

EXPLANATION

Prandtl number = ν/α where ν = μ/ρ (momentum diffusivity) and α = k/(ρCp) (thermal diffusivity). Pr << 1 means heat diffuses faster than momentum; Pr >> 1 means momentum diffuses faster.

Test

Q.3 Medium Heat Transfer

In pool boiling, the critical heat flux (CHF) occurs at which point on the boiling curve?

A Onset of nucleate boiling (ONB)

B Peak of nucleate boiling curve before transition to film boiling

C At transition from nucleate to film boiling

D During saturated liquid heating

Correct Answer: B. Peak of nucleate boiling curve before transition to film boiling

EXPLANATION

Critical heat flux (CHF) is the maximum heat flux in nucleate boiling. Beyond this point, further heat input causes transition to film boiling with lower heat transfer coefficient, leading to surface temperature rise (burnout).

Test

Q.4 Medium Heat Transfer

The overall heat transfer coefficient U in a composite system (series resistances) is determined by which method?

A U = 1/(R_total) where R_total = R_conv,1 + R_cond + R_conv,2

B U = h₁ + h₂ + (k/L)

C U is constant regardless of resistance arrangement

D U must be measured experimentally

Correct Answer: A. U = 1/(R_total) where R_total = R_conv,1 + R_cond + R_conv,2

EXPLANATION

Overall heat transfer coefficient is the reciprocal of total thermal resistance: 1/U = 1/(h₁A) + L/(kA) + 1/(h₂A). This accounts for series arrangement of convection and conduction resistances.

Test

Q.5 Medium Heat Transfer

For radiation heat transfer between two surfaces, increasing the absolute temperature of the hot surface by 10% will increase radiative heat transfer by approximately what percentage?

A 10%

B 21%

C 40%

D 46%

Correct Answer: D. 46%

EXPLANATION

Radiative heat transfer follows Stefan-Boltzmann law: Q ∝ T⁴. If T increases by 10%, new flux = (1.1T)⁴ = 1.464T⁴ ≈ 46.4% increase.

Test

Q.6 Medium Heat Transfer

In convective heat transfer, which dimensionless number represents the ratio of buoyant to viscous forces?

A Rayleigh number (Ra)

B Grashof number (Gr)

C Richardson number (Ri)

D Both A and B

Correct Answer: D. Both A and B

EXPLANATION

Grashof number (Gr = gβΔT L³/ν²) directly represents buoyancy to viscous force ratio. Rayleigh number (Ra = Gr·Pr) combines Grashof and Prandtl numbers for natural convection.

Test

Q.7 Medium Heat Transfer

A shell-and-tube heat exchanger with one shell pass and two tube passes (1-2 STHE) has a correction factor F. What is the typical range of F values?

A 0.5 to 0.9

B 0.9 to 1.0

C 1.0 to 1.2

D 0.2 to 0.8

Correct Answer: A. 0.5 to 0.9

EXPLANATION

The correction factor F (applied to LMTD) for 1-2 STHE typically ranges from 0.5 to 0.9 depending on temperature ratios and heat capacity ratios. F is always ≤ 1.

Test

Q.8 Medium Heat Transfer

The Peclet number (Pe = Re·Pr) is used to determine the relative importance of convection to conduction. For Pe

A Convection is dominant

B Conduction is dominant

C Both are equally important

D Neither is significant

Correct Answer: B. Conduction is dominant

EXPLANATION

The Peclet number Pe = Re·Pr = (velocity × characteristic length × ρ·cp)/k represents the ratio of convection to conduction. When Pe << 1, conduction dominates over convection because advective transport is very slow compared to thermal diffusion.

Test

Q.9 Medium Heat Transfer

For turbulent flow in a rough pipe, the friction factor is determined by both Reynolds number and relative roughness (ε/D). According to the Moody chart, in the complete turbulence zone, the friction factor becomes independent of:

A Reynolds number

B Relative roughness

C Pipe diameter

D Fluid viscosity

Correct Answer: A. Reynolds number

EXPLANATION

In the complete turbulence zone (very high Reynolds numbers), the friction factor depends only on the relative roughness (ε/D) and becomes independent of Reynolds number. This is because inertial forces completely dominate over viscous forces.

Test

Q.10 Medium Heat Transfer

The effectiveness-NTU (Number of Transfer Units) method is preferred over LMTD method when designing heat exchangers because:

A It requires less computational effort

B LMTD method cannot handle cases where outlet temperatures are unknown (design problems)

C NTU method is always more accurate than LMTD

D NTU method eliminates the need for correction factors

Correct Answer: B. LMTD method cannot handle cases where outlet temperatures are unknown (design problems)

EXPLANATION

In heat exchanger design, outlet temperatures are unknown, making the LMTD method iterative and cumbersome. The NTU method (ε-NTU) directly uses inlet temperatures and known parameters to find the outlet temperatures without iteration, making it ideal for design problems.

Test

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