Heat Transfer & Thermal Resistance Concept

Heat Transfer and Thermal Resistance

  • Heat Transfer

    • Stopping heat transfer involves adding extra resistance with low thermal conductivity.
    • Material Examples
      • Low Thermal Conductivity Material: Glass
      • High Thermal Conductivity Materials: Copper and Aluminum
    • Goal: Minimize resistance to enhance heat transfer efficiency.

  • Contact Resistance

    • Definition: The resistance occurring at the interface where two different materials meet, affecting overall heat transfer despite individual thermal conductivities.
    • Factors Contributing to Contact Resistance:
      • Roughness of surfaces that can trap air and create resistance.
      • Presence of contaminants between surfaces.
    • Methods to Minimize Contact Resistance:
      • Introducing fluids to fill gaps between surfaces.
      • Smoothing surfaces to enhance contact.
    • Importance: High thermal conductivity materials like graphene or carbon nanotubes can still perform poorly in heat transfer due to contact resistance.

  • Measuring and Quantifying Contact Resistance

    • Notable Example:
      • Interface of aluminum with another aluminum piece can have a thermal resistance of 0.07.
      • Between silicon chip and aluminum: Up to 0.32 - 0.36.
    • Impact of Pressure on Resistance:
      • Example: Natural contact resistance of stainless steel can vary from 6 to 25 in units of thermal resistance (m²·K/W).
      • By applying pressure (from 100 kPa to 10,000 kPa), resistance can be reduced significantly (to about one-tenth).

  • Design Considerations in Heat Management

    • Importance of preventing air gaps:
      • Design implementations should avoid vacuum or unnecessary air presence that enhances thermal resistance.

  • Practice and Application

    • Current Activity: Activity Number Eight
      • Five longer examples aimed at helping students calculate and understand heat transfer dynamics better.
    • Example 3: Initial calculations involving basic resistance concepts.
    • Essential for students to engage with hands-on examples, demonstrating theoretical knowledge through practical applications.

  • Discussion Points

    • Clarification of terminology and concepts:
      • "l" represents the actual thickness in problems regarding resistance.
      • Review of thermal conductivity and how it influences heat transfer based on surface area and thickness.
    • Key takeaways regarding conduction and convection heat transfer methods and their mathematical relationships.

  • Feedback and Engagement During Class

    • Emphasis on peer understanding:
      • Encourage questions, ensuring that every student comprehends the examples and problems discussed during the lecture.
    • Strategies for tackling complex problems involving contact resistance and different thermal interactions.

  • Concluding Note

    • Takeaways from today's discussion should lead to further contemplation on designs that incorporate low thermal resistance strategies.
    • Reminder for students to submit relevant drawings and slides that encapsulate their understanding for feedback.

  • Thermal Power Consideration

    • Reference to the thermal power equation:
      P=AimesximestP = A imes x imes t
    • Important to integrate this understanding into problem-solving strategies for designs and thermal evaluations.