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Fabricating micro and nanosized structures to induce hemiwicking on a heated surface has risen in popularity due to the higher heat flux the surface can experience. Recent studies have focused on the effects on the pillar geometry and spacing on the wicking velocity and the critical heat flux. As a result, a majority of the models that have been derived focus on the fluid properties and the wicking structure geometry and spacing. This study presents changes to the wicking performance when the stiffness of a soft material is taken into effect. Multiple similar wicking structures were fabricated using a negative mold method utilizing an in-house stamping apparatus. Using the mold, multiple polydimethylsiloxane (PDMS) samples were created, where the stiffness of the samples was varied by altering the mixing ratio and the curing time. The wicking velocity of ethanol, isopropyl alcohol, and isooctane did not vary for the samples that had a Young's Modulus greater than 1 MPa, but a notable decrease in the wicking velocity for all three fluids were observed for samples with a Young's Modulus less than 1 MPa. This study provides insight to the importance of the stiffness of the material is for hemiwicking on soft materials and that deformation effects have to be taken into account for Young's Moduli less than 1 MPa.
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Spatiotemporal wicking dynamics: The effects of pillar height, density, and anisotropic geometries
Asymmetric microstructures are of particular interest to many technical fields. Such structures can produce anisotropic flow-fields, which, for example, can be used to control heat and mass transport processes. Anisotropic wicking structures can now be systematically engineered with unique micro-pillar geometries and spatial pillar-placement distributions. Such asymmetric wicking structure designs are of particular interest to the thermal management community due to need to cool heterogeneous materials with specific heat load configurations. In this study, asymmetric half-conical micropillars have been fabricated utilizing two-photon polymerization. Macroscopic characterization of anisotropic flow-field velocities is performed via high-speed videography. High-speed thin-film interferometry and microscopic side-angle videography are also used to characterize the microscale evolution of meniscus curvature during inter-pillar wicking. The wicking velocity is observed to be directly proportional to both the meniscus curvature and the cross-sectional area of the micro-pillars (normal to the flow). An anisotropic hemiwicking model is also described with comparisons to experimental data. The hemiwicking model predicts the macroscopic wicking behavior (within 20% or less) for the relatively broad range of pillar geometries and pillar spacing configurations. These anisotropic flow-field predictions can help engineers design the next-generation of micro-structured heat sinks, fluid-based sensors and chemical harvesting systems.
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- Award ID(s):
- 1653396
- PAR ID:
- 10232097
- Date Published:
- Journal Name:
- ITherm 2021 The Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems June 1 - June 4, 2021
- Page Range / eLocation ID:
- 277
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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