Thermal Boundary Layers with Coupling of the Velocity Field to the Temperature Field
In the treatment of thermal boundary layers until now, we assumed constant physical properties and so the velocity field was independent of the temperature field. In this chapter we will investigate the effect of variable physical properties. These properties are the density ρ, the viscosity μ, the isobaric specific heat capacity c p and the thermal conductivity λ. In the most general case, the properties can depend on the temperature and the pressure. A consequence of the dependence of the density and the viscosity on the temperature is that there is a coupling of the velocity field to the temperature field. In addition, the temperature dependence of the density means that buoyancy forces in the gravity field appear in the momentum equation. These buoyancy forces alone can produce flows called natural convection (or free convection). If buoyancy forces due to gravity also occur alongside the forced convection discussed in the last chapter, we speak of mixed convection.
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