Effect of Liquid Volume on Thermosiphon Loop Performance Using Open Microchannels Manifold for CPU Cooling in Data Center

The efficient cooling of servers in data center offers unique challenge to reduce the worldwide energy consumption and fluid inventory. The presented work addresses the great potential of a thermosiphon system using two-phase heat transfer process which improves the efficiency of the system by significantly improving the heat dissipation ability. The latent heat transfer is more effective than sensible heat. However, the system performance is limited by Critical Heat Flux (CHF) and Heat Transfer Coefficients (HTC). An increase in CHF offers wide temperature operating range while HTC defines the efficiency of the process. In the current design of the cooling solution, a manifold with a taper is employed over the heater surface to guide vapor away from the surface along the flow length. The incoming liquid flows over the heating surface unobstructed developing separate liquid-vapor pathways. A 6° taper manifold is analyzed with HFE7000 as the working fluid. The performance of thermosiphon loop is evaluated for three different liquid volumes resulting in three different liquid heads available in the thermosiphon loop. The respective heat flux and HTC are compared. The maximum heat dissipation was observed for 325ml liquid with a microchannel chip resulting in a CHF of 42.1W/cm² at a wall superheat of 17.8°C. The observed performance data shows that thermosiphon loop is an eligible replacement for conventional single-phase cooling techniques used for CPU cooling in data centers.