Supplemental material for the Research paper titled "Integration of an open natural circulation system to single-phase immersion cooling of data center: An experimental approach for proof of concept"

Cooling systems are the second-largest energy consumers in data centers, ensuring safe operating temperatures for high-heat-flux electronics. Among various thermal management techniques, immersion cooling is highly efficient but requires significant infrastructure investment due to its active cooling mode. To address this limitation, a proof of concept is demonstrated, integrating an open-loop natural circulation system with single-phase immersion cooling. Novel concepts are introduced based on data center load patterns, achieving a power usage effectiveness close to unity. While data centers are often connected to waste heat recovery systems, this experimental study (using simulated heating) validates the efficiency of a completely sustainable and maintenance-free mechanism. However, the proposed concept can also be integrated with external heat recovery systems. Without active heat removal, immersion cooling alone allowed the heater surface temperature to rise from approximately 35 ℃ to 70 ℃ within 54, 43, and 22 minutes for heat loads of 500 W, 750 W, and 1000 W respectively. With the proposed system, the temperatures remained below 60 ℃, 65 ℃, and 70 ℃, even after 120 minutes. Additionally, the introduction of novel floating fins resulted in temperature drops of 4°C, 5°C, and 8°C for the respective wattages compared to the base models. At a later stage, transitioning from a fully passive mechanism to a hybrid approach yielded notable results, particularly at lower heat loads, as air injection into hot legs enhanced the natural circulation flow rate due to void buoyancy. Since the simulated heater (immersion heater) model differs from an actual server, the proposed thermal management outcome is noteworthy. Hence, future studies can implement this proof of concept in a realistic model for further validation.