Liquid film–induced critical heat flux enhancement on structured surfaces

Abstract

Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.

Computer vision-assisted investigation of boiling heat transfer on segmented nanowires with vertical wettability

“…Here, the autonomous curation of massive in situ bubble datasets enabled by our framework stands to compliment recent advances in imaging techniques, that exclusively study top- and bottom-view bubble statistics to identify the fundamental physics governing pool boiling. 58,59,66,67 The datasets acquired at the ONB confirmed the correlations between bubble statistics and heat transfer performances. Due to the multidimensionality of the problem, innate structural heterogeneity of the hybrid NWs, and intrinsic variability of pool boiling experiments, still it is challenging to precisely predict overall HTC and CHF.…”

Pool Boiling Performance of Multilayer Micromeshes for Commercial High-Power Cooling

“…Rishi et al [26] utilized a combination of ball milling, salt templating, and sintering techniques to achieve a porous coating. This sample exhibited a CHF of 289 W/cm 2 at a wall superheat of only 2.2 • C. Nanoflower structures fabricated by chemical etching presented a high CHF of 299.7 W/cm 2 [27]. The CHF of MCM-5 is 210 W/cm 2 , lower than the micro-nanostructures proposed in Refs.…”

“…This sample exhibited a CHF of 289 W/cm 2 at a wall superheat of only 2.2 °C. Nanoflower structures fabricated by chemical etching presented a high CHF of 299.7 W/cm 2 [ 27 ]. The CHF of MCM-5 is 210 W/cm 2 , lower than the micro-nanostructures proposed in Refs.…”

Scalable and Resilient Etched Metallic Micro- and Nanostructured Surfaces for Enhanced Flow Boiling

“…Flow patterns have previously been shown to affect heat transfer coefficient values, and numerous flow regime maps exist to identify local regimes and threshold criteria for transition between flow regimes. , As shown in Figure D, an appropriate flow regime map (see Section S9) was chosen to identify the regime near the entrance of the test section. , Nucleation and the resulting bubbles formed drive the thermal performance in this region of high heat transfer enhancement at low vapor qualities ( x < 0.1). Concentrating on the bubble characteristics (Figure E), an increase in the rate at which bubbles depart from the surface, known as the bubble departure frequency ( f ), contributes to an increase in heat transfer during nucleate boiling. The duration of bubble growth is dependent on the time required for the bubble to reach departure diameter size, and therefore, the departure frequency is inversely proportional to bubble departure diameter ( D d ).…”

“…52,53 Nucleation and the resulting bubbles formed drive the thermal performance in this region of high heat transfer enhancement at low vapor qualities (x < 0.1). Concentrating on the bubble characteristics (Figure 4E), an increase in the rate at which bubbles depart from the surface, known as the bubble departure frequency (f), 54 contributes to an increase in heat transfer during nucleate boiling. The duration of bubble growth is dependent on the time required for the bubble to reach departure diameter size, and therefore, the departure frequency is inversely proportional to bubble departure diameter (D d ).…”