The Case for Water-Immersion Computer Boards

Abstract

A key concern for a high-power processor is heat dissipation, which limits the power, and thus the operating frequencies, of chips so as not to exceed some temperature threshold. In particular, 3-D chip integration will further increase power density, thus requiring more efficient cooling technology. While air, fluorinert and mineral oil have been traditionally used as coolants, in this study, we propose to directly use tap or natural water due to its superior thermal conductivity. We have developed the "in-water computer" prototypes that rely on a parylene film insulation coating. Our prototypes can support direct water-immersion cooling by taking and draining natural water, while existing cooling requires the secondary coolant (e.g. outside air in cold climates) for cooling the primary coolants that contact chips. Our prototypes successfully reduce by 20 degrees the chip temperature of commodity processor chips. Our analysis results show that the in-water cooling increases the acceptable amount of power density of chips, thus achieving higher operating frequencies of chips. Through a full-system simulation, our results show that the water-immersion chip multiprocessors outperform the counterpart water-pipe cooled and oil-immersion chips by up to 14% and 4.5%, respectively, in terms of execution times of NAS Parallel Benchmarks.