This study experimentally investigated the fluid flow and heat transfer characteristics of the pin-fin heat sink fully filled with packed brass beads under a vertical oncoming airflow. The dimensions of the pin-fin heat sink were fixed. A constant heat flux was applied on the bottom of the heat sink. The pin-fin heat sinks of various pin-fin side lengths and pin-fin interval spaces filled with brass beads of various diameters would result in different porous properties, leading the corresponding changes in the behaviors of the fluid flow and heat transfer. The results indicated that, for the same Reynolds number (Re) of oncoming flow, the pin-fin heat sinks with packed brass beads (Group 3) have significant heat transfer gains (17.0-78.4% and 95.8-311.2% at Re = 10,000, respectively) by comparing with the corresponding pure pin-fin heat sinks (Group 1) and pure packed-brass-beads heat sinks (Group 2). The Nusselt-number empirical formula of the Group 3 heat sink was provided in some superposition form of the Group I heat sink and Group 2 heat sink. The heat-transfer superposition effect fell remarkably when the porosity of the Group 3 heat sink was notably lower than those of the corresponding Group 1 heat sink and Group 2 heat sink. Besides, based on the same dimensionless pumping power, the Group 3 heat sink generally has higher heat transfer performance than the corresponding Group 1 heat sink and Group 2 heat sink, except a few exceptions at smaller dimensionless pumping power. (C) 2015 Elsevier Ltd. All rights reserved.