Measurement of liquid-vapor phase distribution on nano- and microstructured boiling surfaces

Many studies have reported that the boiling heat transfer coefficient (HTC) and critical heat flux (CHF) are significantly enhanced by nano- and microstructures on a boiling surface, which may effectively change the nucleation characteristics of bubbles and the micro-hydrodynamics of liquid layers underneath growing bubbles. However, there has been no direct observation of how these surface structures alter such physical phenomena at the bubble scale. Here, we report the first direct observations of the distribution and dynamics of the liquid and vapor phases and triple contact line on nano- and microstructured surfaces during boiling of saturated water using an infrared-based detection technique, DEtection of Phase by Infrared Thermometry (DEPIcT). Fundamental boiling parameters at the level of individual bubbles, such as nucleation site density and frequency, dry area fraction, triple contact line density, and bubble base diameter, were measured from the observed results. Finally, the changes in the HTC and CHF values on the structured surfaces were interpreted using quantified boiling parameter data.