•Performed experiments of pool boiling of PF-dielectric liquid on dimpled Cu surfaces.•Investigated and correlated effects of inclination angle and liquid subcooling on nucleate boiling and critical heat flux.•Dimpled Cu surfaces enhance both nucleate boiling and the critical heat flux.•Critical heat flux increases linearly with liquid subcooling. This paper investigated natural convection and nucleate boiling of PF-5060 dielectric liquid on 10×10mm 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 500μm in diameter and 200μm deep, have a triangular lattice with a pitch-to-diameter ratio of 2.0. The total number of dimples on the 10×10mm 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, hNB, and the critical heat flux (CHF). The inclination angle varied from 0° (upward facing) to 180° (downward facing) in increments of 30°, and the liquid subcooling includes 0K (saturation), 10K, 20K and 30K. In the upward facing orientation, the Cu surface with 400μm dimples gives the highest hMNB (∼1.06W/cm2K) and CHF (∼19.3W/cm2). The values for the surface with 500μm dimples are ∼1.0W/cm2K and ∼18.7W/cm2, respectively, and ∼0.7W/cm2K and ∼18W/cm2 on the surface with 300μm 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 ∼36% and ∼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.