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E140 — Heat Transfer, Specific Heat & Thermal Efficiency — Conduction, Convection, Radiation, BTU Relationships, Fuel Heat & Heat-Sink Effects
Frozen parent: ENGINE.THERMO · 33 unique source families · 48 source occurrences · 10 verified teaching facts
Trace how heat moves, quantify sensible heating, and connect temperature levels to practical efficiency.
✓ H1 Heat flows spontaneously from higher temperature toward lower temperature; temperature difference is the driving force and strongly affects heat-transfer rate.
Three modes of heat transfer
✓ H2 Conduction transfers thermal energy through matter by microscopic interactions and is the principal mode through a solid wall.
Conduction through a wall
✓ H3 Convection transfers heat by the bulk motion of a fluid; combustion gas moving through boiler gas passes is a marine example.
Convection loop
✓ H4 Thermal radiation transfers energy by electromagnetic waves and does not require physical contact or a material medium.
Sensible heating
✓ H5 Specific heat capacity is the heat required per unit mass for a one-degree temperature rise. For exam approximations, liquid water is about 1 Btu/(lb·°F).
Heat-engine temperature levels
✓ H6 Sensible heating follows Q = m·cₚ·ΔT when specific heat is treated as constant over the range.
✓ H7 Useful energy equivalences: 1 Btu ≈ 252.16 cal and ≈ 778.17 ft·lbf. Thus 10 Btu is about 2,522 cal.
✓ H8 Fuel heating value is the heat released by combustion per unit quantity of fuel; nitrogen and excess gas carried through the exhaust can transport otherwise useful heat out of the process.
✓ H9 For a heat engine, raising the heat-sink or condenser temperature reduces the available temperature difference and generally reduces thermal efficiency.
✓ H10 Energy-conservation features should reduce avoidable heat rejection, pressure loss, leakage, friction, and unnecessary temperature lift rather than merely moving waste heat elsewhere.
MEMORY: identify the state → identify the energy transfer → apply the correct property relationship → check whether the result is physically reasonable.
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