Chemical Engineering - MCQ Practice Questions

In steady-state heat conduction through a composite wall with three layers in series, if the thermal conductivities are k₁ > k₂ > k₃, which layer will have the maximum temperature drop?

The Biot number (Bi) is defined as the ratio of which resistances in transient heat conduction?

For a circular fin of diameter d and length L attached to a surface at temperature T₀, the fin effectiveness approaches zero when:

In forced convection heat transfer, the Colburn factor (j_H) is related to which dimensionless numbers?

The Fourier number (Fo = αt/L²) in unsteady-state conduction represents the ratio of:

In a counter-flow double pipe heat exchanger, the outlet temperature of hot fluid becomes lower than the outlet temperature of cold fluid. This is:

The Stefan-Boltzmann constant (σ) has SI units of:

In laminar flow through a circular tube with constant wall temperature, the Nusselt number is constant at Nu ≈ 3.66. This means:

For radiation heat exchange between two parallel plates at temperatures T₁ and T₂ with emissivities ε₁ and ε₂, the radiation heat transfer is reduced by factor:

The Rayleigh number (Ra) in natural convection is defined as Ra = Gr·Pr. When Ra < 10⁹ for vertical surfaces, the heat transfer is primarily:

In a recuperative heat exchanger, the effectiveness (ε) is defined as the ratio of actual heat transfer to:

The Peclet number (Pe = Re·Pr) in convective heat transfer indicates that:

For boiling heat transfer, the critical heat flux (CHF) depends on which property most strongly?

The mean free path (λ) in gas kinetic theory at standard conditions is approximately 60 nm. This implies that at atmospheric pressure, heat conduction in gases is primarily through:

In turbulent flow heat transfer for gases (Pr ≈ 0.7), the viscous sublayer thickness δ_v relates to thermal boundary layer thickness δ_t as:

In a once-through steam generator (OTSG) for heat recovery, the effectiveness-NTU relation for counterflow is ε = 1 - exp(-NTU(1-C_r))/(1-C_r·exp(-NTU(1-C_r))) where C_r = C_min/C_max. When C_r = 1, this simplifies to:

The convective heat transfer coefficient 'h' for natural convection from a vertical surface at constant temperature increases with height due to:

In radiation view factor calculations, the reciprocity relation F₁₂·A₁ = F₂₁·A₂ ensures:

For condensation of saturated steam on a vertical cold surface, the local heat transfer coefficient h_x at height x is given by Nusselt equation: h_x = 0.943[ρ_l(ρ_l-ρ_v)gk_l³h_fg/(μ_l·ΔT·x)]^($\frac{1}{4}$). When condensate film thickness increases:

The dimensionless Stanton number (St = h/(ρ·v·c_p)) in heat transfer represents: