Proposed use of a novel server-actuated flow-boiling approach for heat removal at “Chip → Server → Rack → Data Center” levels – together with new thermal system designs incorporating a dedicated power supply approach for data centers – is shown to enable, respectively, high cooling rates for next generation chips and significant waste heat recovery (as electricity). Since large number of data centers continue to appear at increasingly large power consumption ( ~ 1 – 10 MWe) levels, the proposed waste heat recovery approaches have significant societal value.

 

For dedicated power supply, one option is to utilize miniaturized Combined Cycle Power Plants (mini-CCPP1) that combine mini/micro-turbines (MGTs) and Organic Rankine Cycles (ORCs). The hot air exhaust from a commercially available MGT is used as a heat-source for the ORC – and it should be noted that relevant Organic Rankine Cycle (ORC) technologies2 are now commercially available. For data centers requiring less than 1 MWe power, there are other economically competitive power-supply options – such as use of lithium-ion battery stacks that are recharged by power generation from ORC and solar panels.

 

 Mini/micro-channel flow-boiling based heat-sinks for server/chip cooling at high heat-fluxes (5 – 500 W/cm2) – as sought earlier over the last decade – did not see much translation of the science into actual technology (except for limited use of immersion cooling3). This was due to precipitous drop in efficiency of micro-channels (ratio of heat removed to pressure-drops) resulting from large pressure-drops as well as difficulties associated with presence of plug/slug regimes and related instabilities – both of which come into play at desired high levels of mass-flux associated with high heat-flux values (25-500 W/cm2). This talk highlights a new approach (supported by results from new experiments) that leads to increased heat-flux values – all else being the same, including the same representative temperature-difference (between the wall and a representative saturation temperature). Since micro-structuring of boiling-surface is known4 to significantly enhance flow-boiling performance, the reported experiments employ a specific layering of micro-meshes and diffusion-bonding based inexpensive approach to micro-structuring of the boiling-surface (leading to 40 – 60 % improvements in heat-flux over plane unstructured copper-surface). This approach is then made much more efficient – with the help of our new patent5 that targets electronic cooling applications – by suitable active energization of the meshed boiling-surface. This energization is by introduction of suitable shear mode acoustic waves (of controllable amplitude and frequencies) and associated shear stresses in the micro-layers of the nucleating bubbles. For this acoustic energization, electronically controlled Piezoelectric-transducers are used – and at this time – we report additional 20-30% improvements. Even better performances (an additional 30 – 60% over meshed-surface) are possible. These two enhancement mechanisms (mesh-based micro structuring and Piezos-based energization techniques) for flow boiling – in conjunction with the proposed thermal systems – promote new energy efficient and environment friendly approaches for cooling at “Chip → Server → Rack → Data Center” levels.