Thermodynamics, Heat Transfer, and Applied Calculations
Domain 6: Thermodynamics, Heat Transfer, and Applied Calculations
This domain tests energy balances, steam properties, Rankine cycle basics, and the three heat-transfer modes in plant equipment.
Core rules
- First law for a steady-flow device: heat added minus work done equals enthalpy change, plus kinetic and potential changes when significant.
- Sensible heat changes temperature; latent heat changes phase at constant temperature. Superheated steam tables are required above saturation.
- Conduction: q = kA deltaT/L. Convection depends on film coefficient and area. Radiation varies with absolute temperature to the fourth power.
- Heat-exchanger duty uses Q = U A LMTD, with LMTD built from the two terminal temperature differences.
- Boiler efficiency compares heat output to fuel heat input; stack loss and excess air are major variables.
Worked example
Heat 1,000 lb of water from 60 F to 200 F. Q = m cp deltaT = 1,000 x 1.0 x 140 = 140,000 Btu. If the heater is 80% efficient, fuel energy required = 140,000 / 0.80 = 175,000 Btu. The reasoning: calculate useful heat first, then divide by efficiency to account for losses. Do not add latent heat because the water remains liquid.
Traps
Using cp = 1.0 across a phase change; mixing gauge and absolute pressure; computing LMTD with same-end temperatures; and treating radiation as linear in temperature.