This topic covers the fundamental concepts of heat transfer, including the three main modes of heat transfer (conduction, convection, and radiation) and the basic principles that govern heat transfer processes.
Introduction to Heat Transfer
Fundamentals, mechanisms, and key concepts for engineering and science students
| Definition | Explanation |
|---|---|
| Heat transfer | The movement of thermal energy from a region of higher temperature to a region of lower temperature. |
| System boundary | The surface (real or imagined) that separates the system (where we track energy) from its surroundings. |
| Driving force | Temperature difference (ΔT) between two points. |
Key point: Heat transfer does not create or destroy energy; it merely relocates it. The total energy of an isolated system remains constant (first law of thermodynamics).
| Mode | Physical Mechanism | Governing Law | Typical Applications |
|---|---|---|---|
| Conduction | Molecular/atomic vibration and electron motion in solids and stationary fluids. | Fourier’s Law: q = -k ∇T (heat flux q, thermal conductivity k, temperature gradient ∇T) | Heat exchangers, building walls, electronic components. |
| Convection | Bulk fluid motion carries heat; includes both forced (pump/fan) and natural (buoyancy) flow. | Newton’s Law of Cooling: q = h A (T_s – T_∞) (heat transfer coefficient h, area A, surface temperature T_s, fluid temperature T_∞) | HVAC systems, cooling of turbines, oceanic/atmospheric circulation. |
| Radiation | Emission of electromagnetic waves (infrared) from any body with temperature > 0 K. | Stefan‑Boltzmann Law: q = εσA(T⁴ – T_surr⁴) (emissivity ε, Stefan‑Boltzmann constant σ = 5.67×10⁻⁸ W/m²K⁴) | Solar heating, furnace walls, spacecraft thermal control. |
All three modes can act simultaneously; the dominant mode depends on geometry, material, and operating conditions.
| Number | Physical Meaning | Typical Form |
|---|---|---|
| Re (Reynolds) | Ratio of inertial to viscous forces (flow regime) | **Re = ρ V |