Assessment of Pump Power Savings at Rack level for Dynamic Direct-to-Chip Liquid Cooling Using a Novel Flow Control Device

TL;DR: In this paper , the authors proposed an active flow control device for direct-to-chip liquid cooling in data centers, which is capable of targeted delivery of coolant to the cold plates based on the instantaneous workload of processing units.

Abstract: A substantial increment in usage of network-based services such as high-performance computing and cloud storage is being matched by developments in high-power-density chips. This also requires more efficient cooling technologies than traditional air cooling due to its heat transfer limitations. Direct-to-chip liquid cooling is one of the most popular techniques for cooling high heat fluxes due to the higher thermal performance of water-based coolants. Typical liquid-cooled data centers provide the servers with a constant and redundant coolant flow rate to the servers irrespective of server workload utilization, leading to excessive pump power consumption. This investigation proposes the implementation of an active flow control device to resolve this problem and quantifies the maximum power savings possible for different power levels in servers in a rack. This device is capable of targeted delivery of coolant to the cold plates based on the instantaneous workloads of processing units. The 3D printed flow control device contains a V-cut ball valve that varies the open area inside the device to regulate the flow rate. Four custom-made thermal test vehicles (TTVs), each representing a server, in a rack were used to mimic workloads. The TTV assembly was placed at four different levels in a standard 19-inch information technology equipment rack in test fixtures mounted with cold plates. The flow regulation to each of the TTVs was varied based on the power dissipated by each TTV. A maximum pump power savings of 88% was achieved for a case where all TTVs operate at idle, with 15% utilization.