Thermal-Hydraulic Characterization of a Thermosyphon Cooling System for Highly Compact Edge MicroDataCenter

In the European project BRAINE, an extremely efficient passive thermosyphon cooling system was developed for a novel type of Edge MicroDataCenter (EMDC) with high heat fluxes to dissipate on individual computer cards and high heat dissipation rate per unit volume in the dense array of these cards. The primary objective was the cooling of 11 nodes (which include central processing units (CPUs), field programmable gate arrays, graphics processing units, and storage) considering one heat sink evaporator per node. This study shows the experimental results obtained with the new environmentally friendly refrigerants R1233zd(E) and R1234ze(E) as well as a validation of the solver used to design the thermosyphon for a first demo EMDC with four slots (i.e., four nodes). The maximal total dissipated power was 950 W, and performance ratios of heat dissipation-to-cooling fan power up to 98-to-1 were obtained. The solver validation was performed by comparing pressure drop of the different components as well as the maximum temperature of heaters mimicking CPUs for 232 simulated datapoints and proved extremely good accuracy without any scaling or empirical factors: 99%, 78%, 53%, and 95% of the datapoints for the evaporator, riser, condenser, and total pressure drop, respectively, were within +/- 30% of the experimental results, which is accuracy comparable to the best two-phase pressure drop correlations in the literature, so a very good validation results. For the temperature validation, 97% of the datapoints were within +/- 5 degrees C of the experimental measurements, highlighting the robustness of the solver.