Flow boiling of ethylene glycol/water mixtures in counter-current flow diverging microchannel heat sink for IGBT cooling

The thermal management of insulated-gate bipolar transistor (IGBT) modules in electric vehicles has become increasingly demanding as power levels increase. The present study explores convective boiling heat transfer of ethylene glycol/water (EGW) mixtures in a Counter Current Flow Diverging Micro-channel (CFDM) heat sink for cooling IGBT modules. This work investigates the concentration effects of EGW mixtures at volumetric concentrations of 0% (i.e., deionized water), 10% 30%, and 50% ethylene glycol, which has been commonly employed as the anti-freeze coolant for electric vehicles, on convective boiling heat transfer in CFDM heat sinks with microstructures. The research reveals that the onset of nucleate boiling heat flux decreases and the corresponding wall superheat increases with increasing ethylene glycol concentration, and that this behavior may be fairly well predicted by the classical theory. Increasing the ethylene glycol concentration significantly deteriorates boiling heat transfer due to the mass diffusion of water toward the liquid-vapor interface and the reduced thermal conductivity of the mixture at higher ethylene glycol concentrations. The maximum heat flux achieved for wall temperature below 170 °C with the 50% EGW mixture for the heat sink with cavity arrays only is approximately 249 W/cm² and it reaches 407 W/cm² for the heat sink with both microgrooves and cavity arrays. Compared with the data reported in the literature for a 50% EGW mixture, the present CFDM heat sinks with cavity arrays or microgrooves and cavities demonstrate superior heat transfer performance. The CFDM heat sink also demonstrates two-phase flow pressure drop close to that for single-phase flow with the same mass flux. © 2026 The Authors.