12. Contact Resistance

  • When two such surfaces are pressed against each other, the peaks form good material contact but the valleys form voids filled with air. These numerous air gaps of varying sizes act as insulation because of the low thermal conductivity of air. Thus, an interface offers some resistance to heat transfer, and this resistance per unit interface area is called the thermal contact resistance, RC.
  • The value of thermal contact resistance depends on: surface roughness, material properties, temperature and pressure at the interface type of fluid trapped at the interface.
  • Thermal contact resistance is significant and can even dominate the heat transfer for good heat conductors such as metals, but can be disregarded for poor heat conductors such as insulations.