Transient and local two-phase heat transport at macro-scales to nano-scales

Abstract

Two-phase cooling has become a promising method for improving the sustainability and efficiency of high energy-density and power-density devices. Fundamentally, however, two-phase thermal transport is not well understood for local, transient processes, especially at critical to near-critical heat fluxes at the macro, micro, and nano-scales. Here we report spatiotemporal characterization of the single-bubble ebullition cycle in a hot-spot heating configuration with heat fluxes approaching 3 kW cm −2 . In particular, we experimentally reconstruct the spatiotemporal heat transfer coefficient in terms of its proportionality at both the macro-scale (l >> 1 μm) and the micro-to-nanoscale (l < 1 μm). We show that the maximum rates of heat transfer occur during the microlayer evaporation stage of the ebullition cycle, corresponding to critical maxima in the heat transfer coefficient of~160 ± 40 kW m −2 K −1 and~5300 ± 300 kW m −2 K −1 at the macro-scale and micro-to-nanoscale, respectively.

Tutorial: Time-domain thermoreflectance (TDTR) for thermal property characterization of bulk and thin film materials

“…For example, TDTR can also be applied to characterize thermal properties of liquids and fluids, such as the thermal conductivity/heat capacity of liquids, 103 thermal conductance of solid/liquid interfaces, 80,233,234 the heat transfer coefficient of fluids during evaporation, 235,236 condensation, 237 microchannel cooling, 238 and flow boiling. 239 TDTR can also be easily adapted to transient absorption and be exploited to study thermophysical phenomena in nanoparticle solutions, such as the heat diffusion…”

Ultrahigh evaporative heat transfer measured locally in submicron water films

“…Time-domain thermoreflectance was used by Mehrvand and Putnam to study microlayer evaporation in single bubbles during flow boiling of water. 4 More recently, Che et al combined time-domain thermoreflectance and numerical analysis to study the evaporation of an octane liquid film 31 . They report the variation of the overall heat transfer coefficient along the meniscus, obtaining a maximum value of 0.44 MW/ -K. This value includes the conductive thermal resistance of the liquid.…”

“…This ultrahigh h evap value is two orders of magnitude larger than the heat transfer coefficient for single-phase forced convection or evaporation from a bulk liquid. Under the assumption of constant wall temperature, our profiles of h evap and meniscus thickness suggest that 62% of the heat transfer comes from the region lying 0.1-1 μm from the meniscus edge, whereas just 29% comes from the next 100 μm.Spatial resolution of amplified evaporation rates in nanometer-and micrometer-thick liquid films, as are found in menisci, is a long-standing challenge [1][2][3][4] . Accurate measurements require submicron lateral precision and a modeling framework to interpret the results.…”

“…Spatial resolution of amplified evaporation rates in nanometer-and micrometer-thick liquid films, as are found in menisci, is a long-standing challenge [1][2][3][4] . Accurate measurements require submicron lateral precision and a modeling framework to interpret the results.…”

Investigation of flow boiling heat transfer and boiling crisis on a rough surface using infrared thermometry

“…Importantly, we can detect bubble footprints. A crucial advantage of infrared thermometry compared to other thermometry techniques with even higher temporal resolution (e.g., MEMS [5][6][7] or time-domain thermo-reflectance [8]) is that it allows capturing the bubble dynamics over a relatively large area. It enables visualizing the interaction of the bubble footprints on the heated surface, which ultimately leads to the formation of irreversible dry spots.…”