This paper investigated natural convection and nucleate boiling of PF-5060 dielectric liquid on 10 x 10 mm uniformly heated copper (Cu) surfaces with different diameter dimples, for potential application to immersion cooling of high power computer chips. The circular dimples, 300, 400, and 500 mu m in diameter and 200 mu m deep, have a triangular lattice with a pitch-to-diameter ratio of 2.0. The total number of dimples on the 10 x 10 mm surfaces increases with decreasing the dimple diameter. In addition to the dimple diameter, the performed experiments quantified the effects of the surface inclination angle and the liquid subcooling on the nucleate boiling heat transfer coefficient, h(NB), and the critical heat flux (CHF). The inclination angle varied from 0 degrees (upward facing) to 180 degrees (downward facing) in increments of 30 degrees, and the liquid subcooling includes 0 K (saturation), 10 K, 20 K and 30 K. In the upward facing orientation, the Cu surface with 400 mu m dimples gives the highest h(MNB) (similar to 1.06 W/cm(2) K) and CHF (similar to 19.3 W/cm(2)). The values for the surface with 500 mu m dimples are similar to 1.0 W/cm(2) K and 18.7 W/cm(2), respectively, and similar to 0.7 W/cm2 K and 18 W/cm(2) on the surface with 300 gm dimples. The CHF and hMNB on all dimpled Cu surfaces decrease with increased inclination angle to the lowest values in the downward facing orientation. These values are similar to 36% and similar to 33% of those in the upward facing orientation, respectively. In addition, the CHF in the upward facing orientation, increases linearly with increased liquid subcooling at a rate of 1.8%/K. (C) 2015 Elsevier Ltd. All rights reserved.