Chemical Engineering - MCQ Practice Questions

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?

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

In a shell-and-tube heat exchanger, what is the primary advantage of using baffles?

The Nusselt number (Nu) relationship for laminar flow in a circular pipe is given by Nu = 3.66. What does this value represent?

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

In radiation heat transfer, the Stefan-Boltzmann constant σ has a value of 5.67 × 10⁻⁸ W/(m²·K⁴). A black body at 500 K radiates heat. If the temperature is doubled to 1000 K, by what factor does the radiated heat increase?

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?

A flat-plate solar collector has a black absorber plate maintained at 80°C. The ambient temperature is 20°C and the heat loss coefficient (overall U value including radiation and convection) is 8 W/(m²·K). For a collector area of 4 m², what is the heat loss rate to the surroundings?

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:

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 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?