Thermal Energy Transfer Concepts

  • U-Value

    • Definition: A measure of heat conduction for building materials
    • Specifically refers to the heat energy conducted per second through 1 m² when there is a temperature difference of 1 °C (1 K)
    • Unit: ext{W m}^{-2} ext{K}^{-1}
    • High U-value indicates a poor insulator (good conductor)
    • Low U-value indicates a good insulator
    • Insulation improvements result in reduced U-values

  • Radiation

    • Defined as the transfer of heat energy through electromagnetic waves
    • Electrons at the surface vibrate thermally, emitting waves
    • Higher temperatures lead to shorter wavelengths emitted
    • Speed of light: 3 imes 10^{8} ext{ms}^{-1}
    • Darker objects radiate and absorb heat better than lighter-colored objects
    • Example: Black can versus shiny metallic can; black can loses heat faster and absorbs heat radiation better

  • Solar Constant (Solar Irradiance)

    • Definition: The average solar energy falling per second on 1 m² of Earth's atmosphere
    • Value: Approximately 1.35 ext{ kW m}^{-2}

  • Solar Heating

    • Defined as using solar energy to heat substances
    • Example: Water heated in black pipes under glass
    • Phococells in solar panels convert solar energy into electrical energy

  • Convection

    • Defined as heat transfer in fluids due to circulating currents
    • Process: Heating causes fluid to expand, decrease in density, and rise
    • Causes convection currents, observable in liquids and gases
    • Example: Hot water rises in a tank, leading to hot water at the outlet
    • Notable that convection is gravity-dependent and does not occur in orbit

  • Key Formulas

    • Heat transfer: Q = CA heta_0
    • Specific heat transfer: Q = mc heta_0
    • Latent heat: Q = ml

  • Definitions and Units

    • Heat Capacity: Amount of heat required to change the temperature of a unit mass by 1 °C
    • Specific Heat Capacity: Heat required to change the temperature of 1 kg by 1 °C
    • Latent Heat: Heat absorbed or released during a phase change
    • Specific Latent Heat of Fusion: Heat required to convert 1 kg of a solid into liquid without temperature change
    • Specific Latent Heat of Vaporisation: Heat required to convert 1 kg of liquid into gas without temperature change
    • Specific Latent Heat of Fusion Unit: ext{J kg}^{-1}
    • Solar Constant Unit: ext{W m}^{-2}
    • U-Value Unit: ext{W m}^{-2} ext{K}^{-1}

  • Experiments

    • Measure specific heat capacity of water
    • Measure specific latent heat of fusion of ice
    • Measure specific latent heat of vaporisation of water
    • Compare conduction rates through solids
    • Show convection through experiments