Chemical Engineering - MCQ Practice Questions

In a parallel flow heat exchanger, hot fluid enters at 80°C and exits at 50°C while cold fluid enters at 20°C and exits at 40°C. Calculate the Log Mean Temperature Difference (LMTD).

Which of the following dimensionless numbers is used to predict the transition from laminar to turbulent flow in forced convection?

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.

In the context of thermal radiation, the Stefan-Boltzmann constant has a value of:

A horizontal cylindrical pipe carries hot water at 80°C through ambient air at 20°C. The convective heat transfer coefficient is 25 W/m²·K and pipe diameter is 50 mm. Calculate heat loss per unit length if the pipe is not insulated.

Which heat exchanger type provides the maximum temperature effectiveness under the same flow conditions?

A surface at 300 K with emissivity 0.8 radiates heat to surroundings at 250 K. Calculate the net radiative heat transfer per m² (σ = 5.67 × 10⁻⁸ W/m²·K⁴).

In transient heat conduction, the Fourier number (Fo = α·t/L²) represents:

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.

For natural convection over a vertical flat plate, the Nusselt number correlation is typically given by Nu = C·Ra^n. What is the typical value of exponent 'n'?

In a shell and tube heat exchanger, which configuration reduces the pressure drop while maintaining adequate heat transfer?

A spherical tank of diameter 1 m containing hot liquid at 90°C is placed in ambient air at 15°C. If h = 8 W/m²·K and k_insulation = 0.05 W/m·K with 50 mm insulation thickness, calculate the heat loss rate.

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

In a finned tube heat exchanger, the overall surface effectiveness is 0.75. This means:

A composite wall consists of three layers: Layer 1 (k₁ = 50 W/m·K, L₁ = 10 mm), Layer 2 (k₂ = 2 W/m·K, L₂ = 20 mm), Layer 3 (k₃ = 30 W/m·K, L₃ = 15 mm). The inner surface is at 100°C and outer at 25°C. Calculate thermal resistance per unit area.

In a double-pipe heat exchanger with counter-flow arrangement, the LMTD correction factor F = 0.95. What does this indicate?

A heat pipe is used to transfer heat from an electronic component at 80°C to ambient air at 25°C through evaporation and condensation. What is the primary advantage of a heat pipe over conventional conduction cooling?

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.

Which of the following materials would be most suitable for a heat sink application requiring high thermal conductivity and low cost?

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