Robin A. Steinbrecher

A Field Investigation Into the Limits of High-Density Air-Cooling

In this paper we report on a field investigation into airflow management challenges in high density data centers. This field investigation has also served to validate laboratory investigations into high density air cooling issues. In data centers with significant power consumption, and consequently high cooling loads per rack, high volumes of room airflow are required to meet server cooling airflow requirements. These volumes of air can be difficult to deliver in raised floor hot aisle / cold aisle layouts. The velocity of the airflow is such that it creates a negative pressure near the bottom of the rack. This negative pressure entrains air from under and behind the rack, causing recirculation and warmer air being provided to the servers at the base of the rack. This can cause operational problems and server performance impacts. This phenomenon has been demonstrated in previous papers reporting on test data using particle imaging velocimetry (PIV) techniques. The current work validates those studies by looking at airflow, infrared thermography, and actual IT performance while the under rack recirculation flows are occurring. Additionally, we demonstrate significant improvement by employing rigorous airflow management practices. We also discuss the limitations of current CFD modeling, the majority of which does not have sufficient grid-wise resolution to capture the problem. Further we discuss typical operational conditions that have suppressed the problem (or perhaps the awareness of) to date. Finally, the paper recommends best practices to mitigate the problem in high density data centers.Copyright

Compact liquid enhanced air cooling thermal solution for high power processors in existing air-cooled platforms

Demand for compute capability continues to drive increased power consumption at both the system and processor level. On the processor side, the power for the CPU die continues to increase due to greater core counts and higher frequency and the capability for applications to use these enhanced resources. Integration of hardware features on the processor package such as separate memory and fabric dies is also driving power increases while enabling increased throughput of the processors. In addition, reducing junction temperature enables some of that frequency increase. All these factors pose challenges for the cooling solution. In this paper, a unique compact form factor thermal solution using pumped-liquid-multiphase cooling (PLMC) is presented to cool higher power processors with the same air-cooled data center server chassis boundary conditions. The experimental study illustrates the comparison between pumped single- and two-phase liquid cooled solutions as well in a 1U chassis.