Bitcoin, the world’s largest cryptocurrency, currently consumes an estimated 150 terawatt-hours of electricity annually. Most cryptocurrency miners have dissipated the thermal energy from mining chips to the ambient by air cooling circulation. To recover the thermal energy from cryptocurrency mining, an advanced heat recovery system has been developed, prototyped, and tested. The cryptocurrency miners in an enclosure are cooled by spraying dielectric coolant, then the coolant heated by the mining chips is collected and driven through the spiral heating coil immersed in a 190 L hot water tank. High efficient liquid spray cooling mechanism is the core of this design, by which maximum coolant temperature can reach 70°C in the field trail within the safe temperature limits of mining chips. In practice, this record temperature not only meets the minimum legionellosis risk management requirements for building water systems defined by ANSI/ASHRAE Standard 188-2018 but also provides high-grade energy input to the building, district heating system, or booster heat pump/boiler if needed. In theory, the conventional concept of PUE based on energy has been redefined by the PUE based on exergy. The energy-based PUE is 1.03 and the exergy-based PUE is 0.95 in this case, which can truly reflect the useful energy flow, exergy, in the heat reclaim system.

Data centers’ electricity energy consumption accounts for 1% of global electricity demand and 0.3% of all global CO2 emissions. Energy reuse as a core of a net zero carbon data center, as a macro goal benefiting to mankind, needs micro innovations from thermal engineers to reclaim the distributed and low-grade thermal energy from diversified electronic equipment. This article presents the attempt to combine the advantages of high-density heat transferring technology by two-phase microchannels and the agility of Additive Manufacturing (A.M.) technology into a heat sink by which thermal energy can be collected in premium quantity and quality. The heat sink prototype adopted the two-layer microchannel design by leveraging the unique capability of A.M. technology to form complicated spatial geometric features, such as the functional channel profiles with diverged cross-sections along the flow direction, intermittent channels, and curved channels. It was fabricated at one-time processing by AlSi10Mg powder SLS/SLM, had an exterior base area of 25 cm2, and interior micro-fins with a minimal thickness of 0.2 mm and fin pitch of 0.38 mm. A test rig had been built to validate the thermal dynamic and hydraulic performance of this microchannel heat exchanger working with HFE 7100 as the coolant. The heat flux under certain wall superheat and pressure drop catches the equivalent grade of microchannels made by conventional micro-cutting approaches on copper or aluminum. The maximum inlet coolant temperature could be elevated up to 60.0 °C with less than 90.0 °C CPU case temperature, which provides the feasibility of high-grade heat recovery. The test results present the promising prospects of this design and A.M. technology in the field of two-phase microchannel heat exchanging, by which the electronic devices in megawatt hyperscale data center can be changed from energy consumers to energy generators for the greenhouse, district heating, and hot water system.