Colloquia

Summary

Recent studies projected that the rapid growth of digital society combined with the increasing power density of electronic components leads to major challenges in the sustainability of data centers.  Traditional IT cooling systems, such as air cooling and single-phase liquid cooling, have limited capacity to migrate and re-use the increasing heat loads generated by the CPUs. This research numerically and experimentally investigated the ability and enhancement of new-generation two-phase passive cooling systems based on the additive manufacturing technique. The study evaluates to what extent a 3D-printed surface microstructure dictates the performance of a loop heat pipe system and a two-phase immersion cooling system. 

In order to investigate the performance of a loop heat pipe, a new improved steady-state numerical model is developed that predicts the operation behavior in good agreement with experimental data from the literature. The newly developed model is capable of predicting the loop heat pipe performance by varying several geometry parameters, which was used to find an optimal geometry that minimizes the overall thermal resistance. Furthermore, the numerical model observe that a wick structure based on a selective laser modeled Stainless Steel octahedral unit cell leads to a performance enhancement of 32% compared to a sintered Nickel biporous wick. 

In addition to the numerical model, a 3D-printed evaporator was fabricated that has the ability to transfer 8.6 W/cm2 heat to the back of a server design. On top of that, a test setup was built to test the prototype in practical (using a server design with CPU) and experimental applications (using a heat source). The research includes an extensive approach that describes the limitations and recommendations of this test setup, since the experiments failed to accomplish, related to pressure leakage in the system.

Finally, the 3D-printed evaporator including the wick (lattice structure) and grooves (microchannels) and a prototype that only includes grooves (microchannels) was tested on heat transfer behavior for two-phase immersion cooling applications by doing a pool boiling test for low heat fluxes (8 W/cm2). The experimental results observe that the initial heat transfer coefficient of both structures is higher than the tested performance of plain copper and a lattice structure in literature.

Overall, additive-manufactured two-phase cooling systems appear to be a significant performance enhancement compared to actual two-phase cooling systems and could play a key role in achieving worldwide sustainability goals.