  This paper presents the latest progress on characterization of our membrane
assisted phase-change heat sink (MHS) at conditions suitable for implementation
in data centers (DCs). Experiments are conducted using water as the working
fluid at a vapor space pressure ($P_{vapor}$) of 16 kPa, corresponding to a
saturation temperature of $\sim$ 55$^{\circ}$C. This temperature is
sufficiently lower than the silicon junction temperature of ~80$^{\circ}$C. As
anticipated, the overall performance of MHS at sub-atmospheric pressure is
lower compared to analogous tests at atmospheric pressure. In agreement with
previous studies on MHS, the critical heat flux limit (CHF) increases with
enhancement of the heat transfer area ratio ($A_r$) and liquid space pressure
($P_{pool}$). We report a maximum CHF of 670 W/cm$^2$ on a surface with an
enhanced area ratio of 3.45, multiple times greater than the CHF reported
hitherto by a comparable two-phase heat sink in literature. Heat transfer
coefficients (HTC) as high as $\sim$ 1 MW/m$^2$-K are obtained. These record
performance data along with unique characteristics of the MHS promise to
greatly benefit next generation highly energy efficient DCs.
