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\u201cFacility water loops sometimes have good water quality, sometimes bad,\u201d says My Troung, CTO at ZutaCore<\/a>, a liquid cooling company. \u201cSometimes you have organics you don\u2019t want to have inside the technical loop.\u201d<\/p>\n So there\u2019s one set of pipes that goes around the data center, collecting the heat from the server racks, and another set of smaller pipes that lives inside individual racks or servers. \u201cThat inner loop is some sort of technical fluid, and the two loops exchange heat across a heat exchanger<\/a>,\u201d says Troung.<\/p>\n The most common approach today, he says, is to use a single-phase liquid \u2014 one that stays in liquid form and never evaporates into a gas \u2014 such as water or propylene glycol. But it\u2019s not the most efficient option.<\/p>\n Evaporation is a great way to dissipate heat. That\u2019s what our bodies do when we sweat. When water goes from a liquid to a gas it\u2019s called a phase change, and it uses up energy and makes everything around it slightly cooler.<\/p>\n Of course, few servers run hot enough to boil water \u2014 but they can boil other liquids. \u201cTwo phase is the most efficient cooling technology,\u201d says Xianming (Simon) Dai, a professor at University of Texas at Dallas.<\/p>\n And it might be here sooner than you think. In a keynote address<\/a> in March at Nvidia GTC, Nvidia CEO Jensen Huang unveiled the Rubin Ultra NVL576<\/a>, due in the second half of 2027 \u2014 with 600 kilowatts per rack.<\/p>\n \u201cWith the 600 kilowatt racks that Nvidia is announcing, the industry will have to shift very soon from single-phase approaches to two-phase,\u201d says ZutaCore\u2019s Troung.<\/p>\n Another highly-efficient cooling approach is immersion cooling.<\/p>\n