LDV measurements and heat transfer experiments for nucleate pool boiling from two horizontal enhanced tubes with porous copper on copper surfaces immersed in saturated R-134a were conducted. The influence of tube position (alignment) and tube pitch on bubble dynamics and boiling characteristics were studied. Photographs indicate that the average number of bubbles increases with heat fluxes, which is the same as those in previous studies of single tube. However, the bubble departure diameters of the upper tube show an opposite trend with an increase as compared to previous single-tube studies. LDV measurements show that the present tube arrangement has significant influence on local velocity in both magnitude and trend. The heat transfer mechanism and modeling for the upper tube were studied and developed. (C) 2003 Elsevier Ltd. All rights reserved.