Comparative Evaluation of Subcooled Pool Boiling Performance Using Novec 7000 and Water in a Taper Microgap Boiling Chamber

Abstract

A comparative experimental investigation of subcooled pool boiling heat transfer performance was conducted using 3M Novec 7000 (HFE-7000) near atmospheric pressure (1 atm, Tsat = 34°C) and deionized water at subatmospheric pressure (12 kPa, Tsat ≈ = 49°C) in a compact boiling chamber with submerged condensation. The chamber incorporates an enhanced finned-tube condenser and dual taper microgap manifolds over microchannel-enhanced copper substrates. Four open microchannels were tested. For Novec 7000, the highest critical heat flux (CHF) of 51.4 W/cm2 was achieved for the 762 μm channel and taper microgap at 20°C coolant, indicating a 38% enhancement over the no-taper baseline. At a coolant inlet temperature of 40°C, the same configuration reached approximately 66 W/cm2, the highest value reported for HFE-7000 on any surface area above 1 cm2. At 12 kPa, the 381 μm microchannel without taper achieved 185.3 W/cm2. Increasing the coolant inlet temperature from 20°C to 45°C in the 381 μm taper configuration raised water CHF to 195.3 W/cm2, a 56% increase. The water-to-Novec CHF ratio ranged from 3.6× to 5.0× across configurations.