Chemical Engineering - MCQ Practice Questions

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:

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.

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?

A condenser operates with steam at 100°C condensing on a tube bank at 20°C. The saturation temperature drop is negligible. Which phase of condensation provides maximum heat transfer rate?

Which of the following methods is most suitable for measuring the convective heat transfer coefficient in real-time industrial applications?

In a cross-flow heat exchanger where both fluids are unmixed, the effectiveness (ε) is lower than in a counter-flow arrangement. What is the main reason for this?

The Grashof number (Gr) is used to characterize natural convection. For natural convection heat transfer, which of the following correctly describes the Grashof number?

In heat exchanger design for petrochemical plants, fouling resistance (Rf) is critical. For a crude oil preheater, the typical internal fouling resistance is 0.0005 m²·K/W. If the design duty is 5 MW, what is the maximum temperature difference loss due to fouling on a surface area of 100 m²?

The thermal entrance length for laminar flow in a pipe is given by x_th/D ≈ 0.05·Re·Pr. For water flowing in a 25 mm diameter pipe with Reynolds number of 1000 and Prandtl number of 7, what is the thermal entrance length?

In a parallel-flow heat exchanger with hot inlet temperature Th,in = 100°C, cold inlet temperature Tc,in = 30°C, and hot outlet temperature Th,out = 60°C, what is the hot fluid capacity rate ratio if the cold outlet temperature is 50°C?

The Colburn factor (j) for heat transfer is related to the Nusselt number. For turbulent flow over a flat plate, the typical correlation is j ≈ 0.037·Re^(-0.2). What does the Colburn factor represent?

In the design of a heat recovery steam generator (HRSG) for a combined cycle power plant, the approach temperature is 5°C. If the exhaust gas inlet temperature is 450°C and the approach temperature represents the difference between exhaust gas exit and steam outlet temperatures, what is the steam outlet temperature?

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