The rapid growth of the global network infrastructure has resulted in a sharp increase in the number and size of data center facilities. Total data center power consumption now represents a significant fraction of global electricity production. To conserve natural resources, and to satisfy the cooling demands of compact, powerful electronics, thermal management strategies with high heat transfer coefficients must be employed. Two-phase liquid immersion cooling is one such strategy that has been gaining momentum in commercial cooling applications over recent years. The work discussed in this paper provides information on two different flow boiling investigations performed on vertically oriented surfaces in a small form factor server model. Two different types of surfaces — bare silicon, and silicon surfaces attached with microfinned heat sinks were tested in this study. Novec 649 dielectric fluid was used as the primary working fluid. The first investigation compares the thermal performance of parallel and impinging flow distribution systems, for different subcooling and flow rate conditions. The second investigation is on nucleation suppression in flow boiling for the parallel and impinging flow distribution systems. In this study, flow rates ranging from 0 ml/min to 1650 ml/min were tested and high-speed imaging was performed to capture the change in bubble characteristics. The resulting observations, including highest heat flux values supported without nucleation activity, are reported and discussed.

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