Convective heat transfer in liquid microchannels with hydrophobic and hydrophilic surfaces

Experiments were performed to study the heat transfer characteristics of channel flows of deionized (DI) water, methanol, 50 wt% DI water/50 wt% methanol mixture, and ethanol solution in asymmetrically (one sided heating) heated rectangular microchannels with an aspect ratio (H/W) of 0.56 and the corresponding hydraulic diameters (D) of 129 μm at 5 ⩽ Re ⩽ 240. Local heat transfer coefficients distribution were recorded with both isothermal (273 K) and isoflux (12.6, 18.1, 32.3, 50.5 mW/mm2) heating. The influences of test liquid mass flow rates, test fluids, heating condition (isothermal vs isoflux), and surface condition (hydrophilic vs hydrophobic) on heat transfer behavior were examined. Thermal entrance length were also found and correlated in terms of the relevant parameters.