TY - JOUR
T1 - Jumping droplets electronics cooling
T2 - Promise versus reality
AU - Foulkes, Thomas
AU - Oh, Junho
AU - Sokalski, Peter
AU - Li, Longnan
AU - Sett, Soumyadip
AU - Sotelo, Jesus
AU - Yan, Xiao
AU - Pilawa Podgurski, Robert Carl Nikolai
AU - Castaneda, Adam
AU - Steinlauf, Matthew
AU - Miljkovic, Nenad
N1 - Funding Information:
The authors gratefully acknowledge funding from the Power Optimization of Electro-Thermal Systems (POETS) National Science Foundation Engineering Research Center with Cooperative Agreement No. EEC-1449548. T.F. gratefully acknowledges funding support from the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1144245. N.M. acknowledges funding from the International Institute for Carbon Neutral Energy Research (No. WPI-I2CNER), sponsored by the Japanese Ministry of Education, Culture, Sports, Science and Technology. Field emission scanning electron microscopy was carried out in the Materials Research Laboratory Central Facilities and Beckman Institute Microscopy Suite, University of Illinois.
PY - 2020/5/18
Y1 - 2020/5/18
N2 - Electrifying both stationary and mobile systems requires ultra-compact, lightweight power electronics and electric machines. Increasing the volumetric and gravimetric density of these systems is constrained, however, by the capacity to remove heat from these assemblies. A promising method for extracting heat is jumping droplet condensation, which can address both spatially and temporally changing hotspots. Yet, disagreement exists in the literature about the maximum attainable heat flux for water-based, droplet jumping devices such as vapor chambers, with values ranging from 5 to 500 W/cm2. Here, using thermal measurements and optical imaging in pure vapor conditions, we directly observe the hydrodynamics occurring inside of a jumping droplet vapor chamber. Our experiments show that flooding is the key obstacle limiting jumping droplet mass flux to hot spots, limiting heat transfer to less than 15 W/cm2. These results indicate that past works reporting high heat fluxes benefited from other hot spot cooling pathways such as previously observed liquid bridges formed due to flooding. To test our hypothesis, we characterize progressive flooding on a variety of structured surfaces ranging in length-scale from 100 nm to 10 μm. Progressive flooding was delayed by decreasing the length-scale of the surface structures, which supports recent observations in the literature. Our work not only helps to understand the wide variability of past results quantifying droplet jumping heat transfer, but also provides design guidelines for the development of surfaces that are capable of maintaining enhanced jumping droplet condensation.
AB - Electrifying both stationary and mobile systems requires ultra-compact, lightweight power electronics and electric machines. Increasing the volumetric and gravimetric density of these systems is constrained, however, by the capacity to remove heat from these assemblies. A promising method for extracting heat is jumping droplet condensation, which can address both spatially and temporally changing hotspots. Yet, disagreement exists in the literature about the maximum attainable heat flux for water-based, droplet jumping devices such as vapor chambers, with values ranging from 5 to 500 W/cm2. Here, using thermal measurements and optical imaging in pure vapor conditions, we directly observe the hydrodynamics occurring inside of a jumping droplet vapor chamber. Our experiments show that flooding is the key obstacle limiting jumping droplet mass flux to hot spots, limiting heat transfer to less than 15 W/cm2. These results indicate that past works reporting high heat fluxes benefited from other hot spot cooling pathways such as previously observed liquid bridges formed due to flooding. To test our hypothesis, we characterize progressive flooding on a variety of structured surfaces ranging in length-scale from 100 nm to 10 μm. Progressive flooding was delayed by decreasing the length-scale of the surface structures, which supports recent observations in the literature. Our work not only helps to understand the wide variability of past results quantifying droplet jumping heat transfer, but also provides design guidelines for the development of surfaces that are capable of maintaining enhanced jumping droplet condensation.
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U2 - 10.1063/5.0002537
DO - 10.1063/5.0002537
M3 - Article
AN - SCOPUS:85090501237
VL - 116
JO - Applied Physics Letters
JF - Applied Physics Letters
SN - 0003-6951
IS - 20
M1 - 203701
ER -