ABSTRACT
The regimes of heat transfer in a flowing system depend on a number of variables: mass flow rate, fluids employed, wall materials, geometry of the system, heat flux magnitude, and distribution. In nuclear applications, the two basic boundary conditions are the surface heat flux condition on the fuel elements surrounding the flow channel and the primary coolant side surface temperature condition on a steam generator tube or the surface temperature of other heat exchange equipment. For the fuel element, the axial heat flux distribution while ideally cosine shaped is altered significantly in LWRs, particularly BWRs, due to neutronic-thermal hydraulic interactions. For steam generators the once-through versus the U-tube design achieves a limited degree of secondary coolant superheat.
