Effect of subcooling, flow rate and surface characteristics on flow boiling performance of high performance liquid cooled immersion server model

The dramatic increase in data center power consumption due to amplified global data traffic, combined with the demand for compact and energy-efficient data centers, have resulted in liquid immersion cooling gaining a prime focus as a thermal management strategy. As the technology finds its way to commercial applications, extensive knowledge on the effect of critical operational and system parameters on thermal performance is more essential than ever. The experimental study discussed in this paper addresses this by investigating the effect of subcooling, mass flow rate and surface enhancement on the flow boiling performance of a small form factor cooling system with vertically-oriented array of heaters that simulate electronic chips on a printed circuit board. Heat flux values up to 20.5 W/cm2 were achieved with a bare silicon surface for the highest subcooling and flow rate used in this study. Experiments were also conducted on two surface enhancements attached to the bare die — a sintered copper microporous heat sink and a heat sink with an array of microscale fins. With microfinned surface heat flux values up to 20.8 W/cm2 were achieved at surface temperatures less than 70°C. For the microporous surface, even higher heat flux values were achieved with increase in subcooling and flow rate.