A contribution to the hydrodynamics of boiling crisis in a forced flow of water

Abstract A physical approach is presented for defining the mechanisms responsible for the ‘departure from nucleate boiling’, DNB, in cooling water under forced convection. Based on experimental observations, a hydrodynamic model is proposed. It considers the flow of vapour bubbles away from the heated surface and the counter-current of liquid coolant streaming towards it. The general DNB correlation derived from this model is compared with numerous experimental results reported in literature and with well-known empirical DNB equations. The application to critical heat flux in uniformly heated round tubes and annuli; as well as to non-uniform heat flux profiles, is examined. Due to the scatter inherent at the onset of the boiling crisis, the proposed correlation has been set to fit the lower conservative limit of heat flux density, where DNB is observed rather than to a most probable mean value.