A review of on-chip micro-evaporation: Experimental evaluation of liquid pumping and vapor compression driven cooling systems and control

Thermal designers of data centers and server manufacturers are showing a greater concern regarding the cooling of the new generation data centers, which consume considerably more electricity and dissipate much more waste heat, a situation that is creating a re-thinking about the most effective cooling systems for the future beyond conventional air cooling of the chips/servers. A potential significantly better solution is to make use of on-chip two-phase cooling, which, besides improving the cooling performance at the chip level, also adds the capability to reuse the waste heat in a convenient manner, since higher evaporating and condensing temperatures of the two-phase cooling system (from 60 to 95 °C) are possible with such a new “green” cooling technology. In the present project, two such two-phase cooling cycles using micro-evaporation technology were experimentally evaluated with specific attention being paid to (i) controllability of the two-phase cooling system, (ii) energy consumption and (iii) overall exergetic efficiency. The controllers were evaluated by tracking and disturbance rejection tests, which were shown to be efficient and effective. The average temperatures of the chips were maintained below the limit of 85 °C for all tests evaluated in steady state and transient conditions. In general, simple SISO strategies were sufficient to attain the requirements of control. Regarding energy and exergy analyses, the experimental results showed that both systems can be thermodynamically improved since only about 10% of the exergy supplied is in fact recovered in the condenser in the present setup.