Exploring water-in-oil emulsions for immersion cooling: thermophysical properties, electrical insulation, and chip-level performance

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.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Yang, Haoshen

Contributors dc:contributor

• Miljkovic, Nenad

• water-in-oil emulsion
• immersion cooling
• natural convection
• dielectric coolant
• power electronics
• subcooled boiling

Statement dc:rights

• Copyright 2025 Haoshen Yang

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132702

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132702