Experiments and modeling of a two-phase thermosyphon based thermal management system for rack mounted systems

The advantages of in-rack liquid cooling for thermal management of data center electronics have been increasingly recognized. Pumped single phase water cooling, especially with elevated inlet temperatures, i.e. “hot water cooling” has received significant attention as a promising system solution to data center thermal management for present server thermal loads. The continuing evolution of reliable liquid loop hardware, such as leak free plumbing connectors and small reliable pumps, has eroded many of the technical barriers that have impeded the acceptance of liquid cooling. This paper presents the results of a preliminary experimental investigation of an alternative liquid based thermal management system that takes unique advantage of rack-based server architectures in data centers and addresses some of the remaining reliability issues. The system is based on a pump-less two-phase thermosyphon loop using a refrigerant as working fluid. The coolant absorbs heat at the process package via an advanced two-phase boiler and rejects heat at an air-cooled condenser mounted above the rack. It is shown that the available head in a vertical rack based system is more than sufficient to induce buoyancy induced flow at sufficient levels to absorb in excess of 200 W from a simulated processor package at lid temperatures of 60 C. The models developed to simulate the system compare well the measured data and allow the exploration of optimal designs that balance the required boiler thermal performance with manageable pressure drops.