Chemical Engineering - MCQ Practice Questions

For a long thin fin with adiabatic tip condition, the fin efficiency is given by:

In a parallel plate channel with constant heat flux q'' on both walls, what is the thermal entrance length relationship with hydrodynamic entrance length?

The Graetz number in laminar heat transfer represents:

Which statement best describes radiation heat transfer in participating media?

For a microfin tube (enhanced surface), the heat transfer improvement comes primarily from:

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:

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:

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

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:

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:

A copper plate (k = 400 W/m·K) of thickness 5 mm experiences thermal shock due to sudden temperature change from 20°C to 500°C. Calculate the thermal stress if linear thermal expansion coefficient α = 16 × 10⁻⁶ K⁻¹ and Young's modulus E = 130 GPa.

Which of the following statements about the thermal boundary layer in forced convection is incorrect?

In a gas turbine blade cooling system, film cooling effectiveness is defined as η = (T_g - T_surface)/(T_g - T_coolant). If T_g = 1200 K, T_coolant = 600 K, and measured T_surface = 900 K, calculate the cooling effectiveness.

In turbulent forced convection over a flat plate, the local Nusselt number varies as Nu_x ∝ x^n. What is the typical exponent 'n'?

In the design of a steam generator, the pinch point is the minimum temperature approach between steam and feedwater. What is its practical significance?

A cryogenic heat exchanger operates with liquid nitrogen at 77 K on one side. The convective heat transfer coefficient on the nitrogen side is 800 W/(m²·K). The copper tubing has an inner diameter of 12 mm and outer diameter of 14 mm. Assuming the thermal conductivity of copper is 400 W/(m·K), what is the approximate overall heat transfer coefficient (considering only internal convection and conduction through copper wall)?

In the analysis of thermal stability of a convective system, the Richardson number (Ri) is used to compare natural and forced convection. Ri = Gr/Re². When Ri >> 1, what flow regime dominates?

For a finned surface used in air-cooled heat exchangers, the fin efficiency is given by η_f = tanh(mL)/(mL), where m = √(hP/(kA_c)). As the fin length L increases, what happens to the fin efficiency?

In a regenerative heat exchanger (rotary wheel type), the effectiveness depends on the capacity rate ratio and heat capacity of the wheel material. If the wheel rotates slowly (high residence time), what effect does this have on effectiveness?