Overview
Thermodynamics tells you how much heat moves. Heat transfer tells you how fast it moves. This is critical for keeping computers cool and houses warm.
Core Idea
Modes of Heat Transfer:
- Conduction: Direct contact (touching a hot stove).
- Convection: Fluid motion (hot air rising, wind chill).
- Radiation: Electromagnetic waves (sunlight, feeling heat from a fire).
Formal Definition (if applicable)
Fourier’s Law of Conduction: Heat flux is proportional to the temperature gradient. Heat flows from hot to cold.
Intuition
- Insulation: Slowing down heat transfer (a winter coat traps air, which is a bad conductor).
- Heat Sink: Increasing surface area to speed up heat transfer (fins on a computer chip).
Examples
- Double-Pane Windows: Trapping air between glass to insulate.
- Car Radiator: Using air flow to cool the coolant.
- Thermos: Using a vacuum (no matter) to stop conduction and convection.
Common Misconceptions
- “Cold flows in.” (There is no such thing as “cold energy.” Cold is just the absence of heat. Heat flows out.)
- “Fans cool the room.” (Fans cool you by evaporation/convection, but the motor actually adds heat to the room.)
Related Concepts
- Thermal Conductivity ($k$): How well a material conducts heat (Copper = High, Styrofoam = Low).
- Black Body Radiation: An idealized object that absorbs all radiation.
- Heat Exchanger: A device to transfer heat between two fluids without mixing them.
Applications
- Electronics Cooling: Preventing CPUs from melting.
- Building Design: Energy efficiency.
- Cooking: Baking (convection) vs. Broiling (radiation).
Criticism / Limitations
Predicting convection is difficult because it depends on fluid flow (turbulence).
Further Reading
- Incropera & DeWitt, Fundamentals of Heat and Mass Transfer