Physics of ultrasound-assisted augmentation of saturated nucleate boiling through the interaction of multiphase fluid flow is revealed in the present work. Different regimes of influence of ultrasound, ranging from augmentation to deterioration and even no effect, as reported in literature in a contradictory fashion, have been observed. However unlike the previous studies, here it has been clearly demonstrated that this apparent anomaly lies in the different natures of interactions between the influencing parameters like heat flux, ultrasonic frequency, and pressure amplitude. The present results clearly bring out an interactive effect of these operating parameters with surface parameter like surface roughness. A mechanistic model unifying all these parameters has been presented to explain quantitatively the physics of the interaction. The model-based predictions match experimental results quite well suggesting the validity of the hypothesis on liquid–vapor-surface interaction through the process of nucleation and its site density, on which the model is built, and thus revealing the underlying physics.