text: The Sieder–Tate correlation for turbulent flow is an implicit function, as it analyzes the system as a nonlinear boundary value problem. The Sieder–Tate result can be more accurate as it takes into account the change in viscosity ( and ) due to temperature change between the bulk fluid average temperature and the heat transfer surface temperature, respectively. The Sieder–Tate correlation is normally solved by an iterative process, as the viscosity factor will change as the Nusselt number changes.
  where:
  : is the fluid viscosity at the bulk fluid temperature
  : is the fluid viscosity at the heat-transfer boundary surface temperature
  The Sieder–Tate correlation is valid for