Heat Transfer Questions

• 1D conduction through insulation: An insulating wall has thermal conductivity K = 0.04 W/m·K and thickness L = 0.16 m. The steady heat flux from outside to inside is 10 W/m^2, and the inside surface is at −5 °C. What is the outside surface temperature?
• Counter-current heat exchanger LMTD: Hot water (0.01 m^3/min) cools from 80 °C to 50 °C in the tube side of a counter-current shell-and-tube exchanger. Cold oil (0.05 m^3/min, density 800 kg/m^3, cp = 2 kJ/kg·K) enters at 20 °C. What is the approximate log-mean temperature difference (LMTD) in °C?
• Vertical-tube evaporators and liquor level: In a vertical tube evaporator, how does increasing the liquor level generally affect the overall heat-transfer coefficient U?
• Evaporator performance metric: The number of kilograms of solvent vaporized per kilogram of steam supplied to an evaporator is called the ________ of the evaporator.
• Radiation properties of an ideal black body: Which statement correctly characterizes an ideal black body in terms of basic radiative properties?
• Shell-and-tube heat exchangers — Why is a floating head provided in certain designs? (Choose the primary engineering reason for incorporating a floating head construction.)
• Boiling regimes — When vaporization initiates directly at the heating surface with discrete bubbles forming on nucleation sites, the phenomenon is called:
• Steam-jet devices — A steam ejector (steam-jet ejector) is primarily used to:
• Overall heat transfer — In the relation Q = U * A * Δt, the appropriate mean temperature difference Δt for steady-state heat exchangers is:
• Critical radius of insulation (cylindrical) — A 10 cm outside-diameter steam pipe at 180°C is insulated with a material of k = 0.6 W/m·°C. Ambient air is at 30°C, and the external convective coefficient is h = 0.8 W/m²·°C. Neglect pipe-wall and steam-side resistances. If 2 cm of insulation is added, the rate of heat loss from the pipe will be:
• Joule’s paddle-wheel experiment (energy balance) — An insulated container holds 20 kg of water at 25°C. An agitator is driven by a 40 kg mass falling through 4 m, and this is repeated 500 times. Take g = 9.8 m/s² and neglect agitator heat capacity. The final water temperature (°C) will be:
• Design allowances — In heat-exchanger calculations, the fouling factor is introduced to:
• Thermal conductivity trends — With increase in temperature, the thermal conductivity of non-metallic amorphous solids generally:
• Heat–mass transfer analogy — Which of the following is explicitly concerned with both heat and mass transfer by relating their coefficients?
• Choosing flow arrangement — A dilute aqueous process stream (10 kg/s) must be heated using available steam condensate at 95°C (also 10 kg/s) in a 1–1 shell-and-tube exchanger. Which arrangement typically maximizes the thermal driving force and controllability?
• Thermal conductivity vs. porosity — As the porosity of a solid increases (more voids/air pockets within the solid matrix), how does the effective thermal conductivity of the solid change?
• Thermal radiation (heat waves) — Which statements correctly describe the propagation and reflection behavior of thermal radiation?
• Condensation with non-condensable gas — What is the effect of a non-condensing gas mixed with a condensing vapor on the condensation process?
• High-temperature heating media — Which of the following is NOT commonly used as a circulating heat-transfer medium for high-temperature service in process plants?
• Internal convection in tubes — The convective heat-transfer coefficient becomes essentially independent of the tube length-to-diameter (L/D) ratio when the flow is in which regime?