Direct liquid jet-impingement cooling with micron-sized nozzle array and distributed return architecture

We demonstrate submerged single-phase direct liquid-jet-impingement cold plates that use arrays of jets with diameters in the range of 31 to 126 pm and cell pitches from 100 to 500 pin for high power-density microprocessor cooling applications. Using parallel inlet and outlet manifolds, a distributed return concept for easy scaling to 40,000 cells on an area of 4 cm 2 was implemented. Pressure drops < 0.1 bar at 2.5 l/min flow rate have been reached with a hierarchical tree-like double-branching manifold. Experiments were carried out with water jets having Reynolds numbers smaller than 900 at nozzle to heater gaps ranging between 3 to 300 pm. We identified four flow regimes, namely, pinch-off, transition, impingement, and separation, with different influences on heat-removal and pressure-drop characteristics. Parametric analysis resulted in an optimal heat-removal rate of 420 W/cm(2) using water as a coolant. For a near optimal design with a gap to inlet diameter ratio of 1.2. we measured a heat-transfer coefficient of 8.7 W/cm(2) K and a junction to inlet fluid unit thermal resistance of 0.17 Kcm(2)/W (720 mu m chip), which is equivalent to a 370 W/cm(2) cooling performance at a junction to inlet fluid temperature rise of 63 degrees C, a pressure drop of 0.35 bar, and a flow rate of 2.5 l/min.