Onset of Nucleate Boiling in Natural Circulation Systems Predicted Using the Second Stir Theory

Experimental data and calculated results for the onset of nucleate boiling (ONB) in natural circulationsystems show that for the same operating conditions, the equilibrium vapor quality for ONB in naturalcirculation is lower than for forced convections. The differences can be explained using second stir theory.The weak vortices and small stir energy in natural circulation systems result in nucleate boiling occurring earlier than in forced convection systems. In natural circulation systems high mass flow rates are accompanied by large kinetic energies and large stir energies, which enables changes in the directions of flow eddies and energy transport. The equilibrium vapor qualities at ONB are then higher at higher mass flow rates. The influence of other flow parameters on ONB can be evaluated by the relationships between these flow parameters and the mass flow rate. The same values can lead to different results due to different eddy directions. This indicates that the quantitative comparability in mathematics cannot be considered as only scientific standard. The second stir theory offers a new visual angle for researches on natural circulation.