Exploring water-in-oil emulsions for immersion cooling: thermophysical properties, electrical insulation, and chip-level performance
Yang, Haoshen
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https://hdl.handle.net/2142/132702
Description
Title
Exploring water-in-oil emulsions for immersion cooling: thermophysical properties, electrical insulation, and chip-level performance
Author(s)
Yang, Haoshen
Issue Date
2025-12-11
Director of Research (if dissertation) or Advisor (if thesis)
Miljkovic, Nenad
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
water-in-oil emulsion
immersion cooling
natural convection
dielectric coolant
power electronics
subcooled boiling
Abstract
This thesis experimentally evaluates Span 80–stabilized water-in-oil (W/O) emulsions, prepared from Crystal Plus Oil 70T with 2.5–20 vol% water, as immersion coolants for natural-convection cooling of high-power electronics. Conventional dielectric oils provide good insulation but low thermal conductivity, which limits chip-level heat dissipation. A property-based figure of merit for natural convection is derived to assess how density, heat capacity, thermal conductivity, thermal expansion, and viscosity jointly affect performance, and is used to guide emulsion formulation. The fluids are characterized by dynamic light scattering, rheometry, thermal-conductivity measurements, and high-voltage DC leakage tests up to 550 V, followed by chip-level immersion-cooling experiments on an Infineon MOSFET module. For water contents up to 10 vol%, leakage currents remain within the range of commercial dielectric fluids, whereas 20 vol% causes a sharp rise in leakage. Water addition increases thermal conductivity by ~10–30% but also raises viscosity by up to several-fold, making viscosity the dominant constraint. Chip-level results show that 2.5 vol% water reduces minimum thermal resistance from ~6.75 to 5.07 K/W and increases maximum sustainable power from ≈18.3 to ≈24.2 W. Thus, low-water W/O emulsions (≈2.5–5 vol%) are promising immersion coolants that partially relax the trade-off between thermal and electrical performance.
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