For the densest sovereign compute, the accelerators live in the coolant. Submerging the hardware removes air from the thermal path entirely and lets an owner pack extreme density into a small, controlled footprint.
Immersion places whole servers in a dielectric fluid, so heat leaves every surface into liquid instead of a handful of cold plates plus air.
The server sits fully in dielectric fluid, so the accelerator die, memory, regulators, and NICs all reject heat into the same liquid. There is no fan wall and no hot-spot component left to air, which is what enables the highest sustained densities.
The fluid is electrically non-conductive and chemically compatible with board materials, so live hardware operates while submerged. Fluid selection weighs dielectric strength, material compatibility, viscosity, and long-term stability, not just thermal performance.
Removing air removes fan power, fan failures, and airborne contamination from the compute. It also removes acoustic and vibration paths, and it lets hardware run in a sealed medium that is easier to keep clean than a raised-floor air plenum.
Immersion targets the deployments where an owner wants maximum compute in minimum secured floor space. Fewer square meters under physical control is a direct advantage when the perimeter is part of the sovereignty guarantee.
Single-phase is the more established path: the coolant never boils, and heat is carried away by circulation.
Pumps move warmed dielectric fluid from the tank through a liquid-to-liquid heat exchanger and back, transferring heat to the facility water loop. The fluid stays in the liquid phase throughout, so there is no vapor to manage or recover.
Servers mount vertically in an open-top tank filled with fluid, accessible for service by lifting a sled and letting it drain. Operationally it resembles a fluid-filled rack lying on its back, with defined lift and drip-drain procedures.
Because nothing boils, the tank runs near atmospheric pressure and the fluid loss mechanism is spillage and evaporation, both slow and manageable. This makes single-phase the lower-complexity choice for many sovereign sites.
Fluids are matched to gaskets, thermal interface materials, and cable jackets, since prolonged immersion can attack incompatible plastics and elastomers. Boards and components are qualified for immersion rather than assumed compatible.
Two-phase uses the latent heat of boiling to move enormous heat flux from the densest parts, at the cost of a sealed, regulated system.
An engineered fluid with a low boiling point vaporizes directly on the hottest surfaces, absorbing large heat flux as latent heat. Phase change pins surface temperature near the boiling point, which is what makes two-phase suited to the most extreme accelerator densities.
Vapor rises to a condenser coil at the top of a sealed tank, gives up its heat to the facility loop, and drips back as liquid in a closed cycle. The system is a sealed vapor space, not an open bath, and must hold that seal to retain fluid.
Two-phase fluids are costly and regulated, so vapor loss, fluid selection, and end-of-life handling are governed deliberately. The design minimizes vapor escape at every seal because lost fluid is both an operating cost and an environmental obligation.
Because the tank operates as a pressure-and-vapor-managed vessel, service requires controlled opening and fluid recovery. The complexity is real; two-phase is chosen where the density demand justifies the added operational rigor.
Committing to immersion is a facility-level decision that touches structure, handling, fluid logistics, and staff training.
Filled tanks are heavy and horizontal, so floor loading, tank layout, and lift equipment are engineered up front. Immersion halls look different from air-cooled data halls and are planned as such under EPC.
Pulling a server means lifting it from fluid, letting it drain, and servicing it wet or after draining, with defined handling for the fluid that comes with it. Staff are trained on immersion-specific procedures rather than air-cooled habits.
Dielectric fluid is a tracked, replenished consumable with its own procurement, storage, and disposal chain. Fluid inventory and losses are logged as part of running the facility, especially for regulated two-phase fluids.
Immersion is offered where an owner needs the tightest possible footprint for sovereign training and settlement compute inside a controlled perimeter. The choice between single- and two-phase is made against the owner's density, complexity tolerance, and residency constraints.