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Phy100: Heat transport

Phy100: Heat transport. Three basic forms of thermal heat transport i) Conduction; ii) Convection; iii) Radiation. Heat conduction. Conduction is heat transfer, or transfer of thermal energy within a substance or between different substances without motion of materials.

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Phy100: Heat transport

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  1. Phy100: Heat transport Three basic forms of thermal heat transport i) Conduction; ii) Convection; iii) Radiation.

  2. Heat conduction Conduction is heat transfer, or transfer of thermal energy within a substance or between different substances without motion of materials. It occurs when there is a temperature gradient within a substance or temperature differences between substances.

  3. Examples of heat conduction

  4. Conduction and collisions Microscopically, heat conduction occurs by means of collisions between molecules or atoms in crystals or diffusions of electrons in metals. The following pictures Illustrate such processes.

  5. Heat conduction rate or power = heat transferred intime t = thermal conductivity of thebarrier A=Cross section area T=temperature d

  6. SI units Q/t: J/s or Watts A: m^2 d: m T: Kelvin k: W m/K

  7. Thermal conductivity table Copper 385 (in units of W/m K) Gold 314 Iron 79.5 Steel 50.2 Glass 0.8 Concrete 0.8 Brick, insulating 0.15 Brick, red 0.6 Wood 0.12-0.04 Fiberglass 0.04 Styrofoam 0.033 Polyurethane 0.02 Air (0c) 0.024

  8. Q1 Which of the following does not reduce heat conduction between the hot and cold objects A) decrease the cross section A; B) increase the length L; C) use materials with lower thermal conductivity; D) increase the temperature of the hot object.

  9. Q2 The heat conduction rate is doubled if A) The length L is doubled; B) The “hot” temperature is doubled ; C) The cross section area A is doubled; D) None of above.

  10. R value • This is a quantity usually usedto specify house insulation properties in construction bussiness. • R = d /k Q/t = A (T2 - T1)/R • R is defined in US units: (ft2·°F·hr/BTU) • BTU A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F. • I BTU=1055 Joules • 1 R = 0.093 m2∙0.55 °C∙3600s/1055J = 0.17 m2∙°K ∙s/J

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