Effects of heater surface orientation on the critical heat flux .2. A model for pool and forced convection subcooled boiling

A model for the critical heat flux (CHF) in pool and low-velocity forced convection boiling is proposed for heater surfaces relatively short in the flow direction, which utilizes an experimentally-observed relationship between the CHF and the bubble residence time for closure of the momentum and energy equations. The model is primarily concerned with describing the combined effects of healer surface orientation and flow on the CHF. Furthermore, it incorporates a convenient analytical means for including various other parametric influences, such as the bulk liquid subcooling and fluid property variations. A comparison of the model predictions with experimental results is given, showing reasonable agreement with the measured CHF for bulk liquid subcoolings ranging from 2.8 to 22.2 K, bulk flow velocities from 0.04 to 0.55 m s(-1) and heater orientations from zero to 360 degrees. The present model represents an improvement over existing models for the effects of orientation in forced convection, and approaches the result of an earlier model for pool boiling. (C) 1997 Elsevier Science Ltd.