An Open Loop Pulsating Heat Pipe for Integrated Electronic Cooling Applications

Increasing trends towards integrated power electronic systems demand advancements in novel, efficient thermal management solutions to cope with the increasing the power density. This paper investigates the performance of a novel open loop pulsating heat pipe embedded in an FR4 organic substrate. The heat pipe and is comprised of 26 parallel minichannels with 13 turns, an average hydraulic diameter of 1.9mm and maximum surface roughness of 2.5μm. The bulk thermal performance of three saturated working fluids — Novec 649, Novec 7200 and Ethanol (99.8%) — is investigated in terms of fill ratio, three angles of orientation, and applied heat fluxes ranging from 0.4 to 2.5W/cm² at sub-ambient pressures. Novec 649 achieved quasi-stable pulsations at lower heat fluxes due to lower (dp/dT)_sat. In addition, the dielectric Novec 649 fluid showed significant potential for integrated heat spreading applications demonstrating heat transfer of up to 176W and thermal resistances as low as 0.25°C/W for a filling ratio of 30% — a 16× improvement to that of a standard dry FR4 substrate.