Overview
This lecture explains the four mechanisms of heat transfer in humans: conduction, convection, radiation, and evaporation, emphasizing their roles in body temperature regulation.
Mechanisms of Heat Transfer
Conduction
- Conduction is heat transfer between objects in direct contact.
- Example: Holding a warm mug heats your hand; sitting on a cold seat chills you.
- Conduction accounts for about 3% of heat transfer in humans.
Convection
- Convection is heat transfer through the movement of air or liquid around the body.
- Wind removes the layer of warm air next to the skin, increasing heat loss (wind chill effect).
- Convection is responsible for about 15% of human heat loss.
Radiation
- Radiation is heat transfer via infrared rays without direct contact.
- The body radiates heat to the environment, like the Sun warming you outdoors.
- Radiation is the primary method of heat loss from the human body.
Evaporation
- Evaporation is the loss of heat as sweat turns into vapor, removing energy from the body.
- About 20% of body heat is lost through evaporation under normal conditions.
- Evaporation (especially sweat evaporation) is the main way to cool down when overheated or exercising.
- The efficiency of evaporation decreases in high humidity, increasing risk of dehydration.
- High humidity causes increased but less effective sweating, raising the risk of heatstroke if sweating stops.
Key Terms & Definitions
- Conduction — Transfer of heat between objects in direct contact.
- Convection — Transfer of heat through fluid or air movement around the body.
- Radiation — Loss of heat through infrared energy emitted from the body.
- Evaporation — Heat loss as liquid (sweat) changes to vapor, cooling the body.
- Humidity — The amount of moisture in the air, affecting evaporation efficiency.
Action Items / Next Steps
- Review the four heat transfer mechanisms and their relative contributions.
- Understand how humidity impacts evaporation and body cooling.
- Prepare to apply these concepts to scenarios involving body temperature regulation.