Effects of viscous shear stress on thermoregulation of electronics. Transient free convection in diode enclosures induced by discrete heat bands under constant heat flux

A. Baïri (1)

1 UPN - Université Paris Nanterre

Thermal and dynamic phenomena that occur in the immediate vicinity of electronic components during operation generate viscous shear stresses due to velocity gradients. When thermocouples used for thermal regulation of these assemblies are installed in this environment, temperature measurements may be erroneous. It is therefore essential to take into account viscous effects in the boundary layer when dealing with thermal control of electronics subjected to natural convection. These phenomena are particularly pronounced and complex when generation of heat at the active wall is not uniform. That is the case for the real device treated in this work. The natural convective flow is generated by a vertical wall composed by alternated adiabatic and heated bands under constant heat flux, representing a working electronic equipment. The 2D transient boundary layer near the vertical active hot wall of parallelogram-shaped enclosures is treated in order to determine the viscous shear stress. Results are obtained by numerical approach using the finite volume method. Many geometrical configurations are treated while varying the inclination angle of the top and bottom passive adiabatic walls. The very different local distributions of viscous shear stresses and vertical thermal gradients confirm the necessity to take them into account to properly install the sensors used for thermoregulation.

Mots clés: Heat transfer; thermal shear viscous stresses; electronic equipment; transient natural convection; diode cavities

Domaines: Thermique [physics.class-ph]; Thermique [physics.class-ph]

A. Baïri. Effects of viscous shear stress on thermoregulation of electronics. Transient free convection in diode enclosures induced by discrete heat bands under constant heat flux. Applied Thermal Engineering, 2011, 31 (16), pp.3308. ⟨10.1016/j.applthermaleng.2011.06.009⟩. ⟨hal-00789869⟩