An improved and simplified dnb model based on mass, energy, and momentum balance equations

摘要

Several analytical models for the departure from nucleate boiling (DNB) phenomenon have been developed mainly based on the two DNB mechanisms, i.e., bubble crowding and liquid sublayer dryout mechanisms. Among these models. Chang & Lee's model based on bubble crowding mechanism was remarkable in the fundamental derivation of the DNB formula based on the mass, energy, and momentum balance equations at the DNB conditions. Howeve,r the complexity of the DNB formula and some mistakes in the manipulation of interfacial momentum transfer between the core and bubbly layer regions have been pointed out. Based on these remarks, Chang & Lee's model has been improved and simplified by revising momentum balance equations and removing spurious assumptions as well as negligible terms in the DNB formula. moreover, several new modelling features such as a new skin friction factor model, a theoretically determined bubbly layer thickness, and consideration of DNB before bubble detachment are included in the present DNB model. This model predicts well the extensive DNB data of water in uniformly heated tubes and shows an enhanced prediction capability compared with the original modle.