Heat Transfer Lecture Notes

Introduction

• Instructor: Dr. Cody Powell
• Course Overview: Introduction to basic definitions and concepts in heat transfer.

What is Heat Transfer?

• Definition: Transportation of thermal energy (heat) through matter.
• Objective: Understand how heat moves and quantify the rate of heat movement.
• Energy Balances: Used to determine how the temperature of materials changes over time.

Key Concepts

Thermal Energy

• Definition: Energy due to the movement of atoms and molecules in matter.
• Measurement: Temperature as an indirect measure of thermal energy.
  • Units: Joules (J) or Joules per kilogram (J/kg)
  • Symbols:
    • Total Thermal Energy: U (Joules)
    • Thermal Energy per Unit Mass: u (J/kg)

Temperature

• Measurement: Kelvin (K) or Degrees Celsius (°C)
• Unit Systems: Primarily SI units (Kelvin, Celsius), with a note on English units (Fahrenheit, Rankine).

Heat Transfer Mechanisms

• Driving Force: Temperature difference or gradient between materials.
• Flow: Natural from higher temperature material to lower temperature material.

Terms and Units

• Heat Transfer: Transport of thermal energy due to a temperature gradient.

  • Heat (Q): Total thermal energy moved over time, measured in Joules.
  • Heat Rate (q): Thermal energy transfer per unit time, measured in Watts (W).

• Specific Terms:

  • Heat Rate per Unit Length (q'): Watts per meter (W/m)
  • Heat Flux (q"): Watts per meter squared (W/m²)
  • Heat Generation (q·): Watts per cubic meter (W/m³)

Modes of Heat Transfer

1. Conduction

   • Occurs in solids or stationary fluids.
   • Heat is transferred through molecular activity without bulk movement.

2. Convection

   • Involves moving fluid over a surface.
   • Combines bulk motion and random molecular motion.

3. Radiation

   • Transfer of energy via electromagnetic waves or photons.
   • Can occur in a vacuum without a material medium.

Examples and Discussion

Sun to Earth

• Mode: Radiation
• Explanation: Heat transfer across a vacuum without a material medium.

Boiling Water on a Stove

• Modes: Convection, Radiation, and Conduction
• Explanation:
  • Convection: Fluid motion in water.
  • Radiation: Energy from the flame to the pan.
  • Conduction: Heat transfer through the pan and handle.

Next Steps

• Future Lectures:
  • Relation of heat transfer to thermodynamics.
  • Detailed analysis of thermal energy transport rates.

Study Tips

• Develop a mental model to understand concepts.
• Avoid rote memorization of equations—focus on conceptual understanding.