text: In single-phase heat transfer, convection is often the dominant mechanism of heat transfer. For adiabatic flow where the flow receives heat, the temperature of the coolant changes as it flows. An example of single-phase heat transfer is a gas-cooled reactor and molten-salt reactor.
  The most convenient way for characterizing the single-phase heat transfer is based on an empirical approach, where the temperature difference between the wall and bulk flow can be obtained from the heat transfer coefficient. The heat transfer coefficient depends on several factors: mode of heat transfer (e.g., internal or external flow), type of fluid, geometry of the system, flow regime (e.g., laminar or turbulent flow), boundary condition, etc.
  Examples of heat transfer correlations are Dittus-Boelter correlation (turbulent forced convection), Churchill & Chu (natural convection).