Nucleate boiling heat transfer mechanisms on thin substrates

• Substrate thermophysical properties significantly impact nucleate boiling bubble dynamics and heat transfer mechanisms on thin substrates. • Lateral heat conduction within the substrate is the dominant energy source for microlayer evaporation on the thin substrate. • In the substrate-dominant regime, bubble departure diameter increases sharply, and the heat transfer coefficient decreases sharply with increasing λ s δ s . Nucleate boiling heat transfer on thin substrates plays a pivotal role in thermal management systems for advanced miniaturized electronics. Through high-fidelity numerical simulations of water boiling on silicon and copper substrates with thickness ranging from 25 to 500 µm, we demonstrate that substrate's heat transfer process could significantly influence microlayer evaporation. Through detailed heat balance analysis, we demonstrate that lateral heat conduction within the thin heated substrate serves as the primary energy source for microlayer evaporation. Augmenting the substrate thickness or thermal conductivity improves lateral conduction, which intensifies microlayer evaporation and consequently modulates the overall boiling heat transfer performance and bubble dynamics. Furthermore, we define a thermophysical parameter, λ s δ s (the product of substrate thermal conductivity and thickness), to delineate two distinct boiling regimes. In the substrate-dominant regime, lateral heat conduction dictates performance: the bubble departure diameter increases sharply, whereas the spatiotemporal-averaged heat transfer coefficient exhibits a sharp decrease with increasing λ s δ s . Conversely, this influence diminishes in the hydro-dominant regime. These findings sharply contrast with the conventional understanding, which assumes that the influence of the heated substrate side on both bubble departure sizes and heat transfer coefficient is negligible. This study provides fundamental insights into the micro-scale mechanisms of boiling on thin substrates, offering critical guidelines for the thermal design of microelectronic cooling solutions.