Thermodynamics, Heat Transfer, and Applied Mechanics
Domain focus
The exam tests first and second laws, steam tables, heat transfer modes, and simple stress/strain and beam behavior. Expect unit conversions and absolute-temperature calculations.
Core rules
- First law: energy in = energy out + change in stored energy. For steady flow, enthalpy and kinetic/potential terms matter.
- Second law sets the maximum cycle efficiency; Rankine efficiency is below Carnot because of irreversibilities and finite temperature differences.
- Conduction: Q = kAΔT/L. Convection depends on fluid velocity and surface area; radiation depends on absolute temperature to the fourth power.
- Sensible heat changes temperature; latent heat changes phase at constant temperature.
- Stress = force/area; strain = deformation/original length; thermal expansion causes stress when restrained.
Worked example
A 0.1 m thick wall has k = 25 W/(m·K), area 10 m², and a 100 K temperature difference. Q = kAΔT/L = 25 × 10 × 100/0.1 = 250,000 W = 250 kW. The reasoning: thicker wall reduces heat flow; larger area and higher conductivity increase it. Fouling adds resistance in series, so Q falls unless ΔT rises.
Traps
Using gauge pressure in gas laws; mixing Btu/lb with Btu/lb·°F; forgetting absolute temperature in radiation; and treating heat transfer coefficient as a material property. Check units before calculating.