Flow boiling heat transfer on a heating element restricted by an interference sleeve

The ̄ow boiling phenomenon over a heated tube restricted by an interference sleeve, which is a passive enhancement technique, has been analysed using a semi-empirical approach. The liquid boiled was water ̄owing through an annular cross-section. A model developed earlier for the case of pool boiling over porous surfaces has been adapted after modi®cation to pool boiling with interference surfaces using equivalent geometrical parameters and a modi®ed permeability factor. This was further extended to saturated ̄ow boiling situation using an additive mechanism. The single phase heat transfer coecient required for the additive mechanism is obtained from an experimental correlation developed in the present study. The suppression factors evaluated for the eight sleeve geometries used in the present investigation are expressed in terms of the single phase Reynolds number and the Martinelli parameter. Very good agreement was observed between the model predictions and experimental data validating the mechanisms postulated. Further, a purely empirical correlation based on the present experimental data has been proposed to estimate the two-phase heat transfer coecient. While the empirical correlation shows a better ®t with the experimental data, the additive model has a physical basis. Ó 1998 Elsevier Science Inc. All rights reserved. International Journal of Heat and Fluid Flow 19 (1998) 661±671