Towards Development of a Passive Datacenter Cooling Technology: On-Server Thermosyphon Cooling Loop under Dynamic Workload

摘要

Despite many advances in electronics liquid cooling, air still remains one of the main means of cooling of high heat flux servers of datacenters. Regardless their long history of use, air-cooled blade servers continue to introduce strong nuisances that need to be considered during their implementation and operation, for instance: large energy consumption, difficult to manage the flow of air mastered by fans, and thus non-optimal spatial layout of components within a blade, high cost of air flow equipment, acoustical noise limitations, dust, etc. To overcome such problems, a new essential datacenter infrastructure is required. Replacing air with another coolant, e.g. water in the AQUASAR computer with copper cooling elements designed by the Heat and Mass Transfer Laboratory (LTCM), has been proven to be very beneficial. However, taking the example above, bringing water to a microchannel cold plate placed over a processing unit requires a driving force to be externally supplied (for example by a liquid pump), and thus it still has a relatively high system energy consumption due to the high pumping power and consequently a high system cost. Also, several other problems can be listed when using water, i.e. corrosion, erosion, high risk of electronic damage in case of leakage, no local control of the water flow rate to inactive servers, etc. A promising alternative is a passive two-phase dielectric fluid cooling system, i.e. a thermosyphon loop, for which the height difference between an evaporator and a condenser defines its driving force and provides noticeable advantages: a compact design, no noise, no power consumption (since the thermosyphon is a pump-less cooling system), a compelling operational cost savings, improved reliability (no moving parts), etc. The present study proposes a thermosyphon cooling loop designed for high heat flux servers and simulated using new in-house code for its thermo-hydrodynamic performance during steady-state and dynamic workload. Aspects such as server temperature, thermosyphon height and working fluid effects on the cooling capacity and critical heat flux, transient effects when considering uniform heat flux and hot spots are evaluated, showing the benefits and reliability of the thermosyphon cooling loop when compared with active cooling systems.