Pool boiling characteristics of pyramidal shaped re-entrant cavities (characteristic size 40 mu m) etched in silicon were evaluated in this study. A test surface was fabricated to totally eliminate back heat loss and minimize spreading in the substrate. The effect of inter-cavity spacing and convection plumes from a heat source located below the test surface on nucleate boiling parameters is documented. High speed photography was used to record and quantify the bubble departure frequency, the departure diameter, the active site density and to observe the effect of interaction between neighboring nucleation sites. Experiments were conducted in saturated FC 72 at atmospheric pressure. (c) 2006 Elsevier Ltd. All rights reserved.