Two-phase flow through complex micro-geometries is acknowledged as one of the most efficient cooling solutions for high power density applications. Micro-pin heat evaporators are emerging as a potential alternative to traditional multi-microchannel evaporators as the pin fins enhance fluid mixing and mitigate hydrodynamic instabilities. However, detailed studies of the evolution of the two-phase flow dynamics across pin fin arrays are still missing in literature, as the existing studies have mostly been dedicated to characterising the overall thermal performances of the heat sinks. We present the results of systematic investigations of flow boiling within micro-pin heat evaporators. Direct numerical simulations of the two-phase flows are performed using the open-source finite-volume solver OpenFOAM v.2106, where the Volume of Fluid (VOF) method is adopted to capture the interface dynamics. The study is performed by emulating related experimental works using refrigerant R236fa. A micro-evaporator with cylindrical pin fins of diameter of 50µm is modelled, where single or multiple bubbles are generated where the fins meet the base surface of the evaporator. The bubbles grow due to evaporation and flow downstream propagating through the pin fins owing to a flow rate of liquid set at the domain inlet. We study the flow boiling when the evaporator is heated from the bottom surface with heat fluxes in the range of q = 20−200kW/m². The simulations emphasise that the heat transfer efficiency is strongly linked to the thickness and morphology of the lubricating film surrounding the bubbles.