Below we describe the conservation equations, the flow rate model, the correlations utilized for determining the onset of nucleate boiling and critical heat flux conditions, and the numerical approach considered in the COTENP code.
The main program controls 5 modules: (I) input parameters; (II) geometrical parameter calculations; (III) thermal-hydraulic calculations (coolant velocity estimation, conservation equations, and temperature distribution estimation); (IV) estimation of critical heat flux and onset of nucleate boiling conditions; and (V) output results.
The onset of nucleate boiling can be found observing the trend of the wall superheat temperature versus heat flux as shown in Figure 11.
The onset of nucleate boiling is strongly determined by local wall temperatures and by the presence of hot spots.
The model, in fact, computes both the heat flux needed for the onset of nucleate boiling, [q.sub.ONB], and the actual heat flux through the engine walls, [q.sub.w].