Moving a megawatt: air vs liquid, by the numbers

Every single-phase cooling loop obeys the same bookkeeping: Q = ρ·V̇·c_p·ΔT. Set the heat load and the allowed coolant temperature rise, and compare the volume flow each medium needs. The gap is not engineering preference — it is the volumetric heat capacity ρc_p, and it is why liquid becomes increasingly necessary at the highest rack densities.

Model: steady sensible-heat balance Q = ρ·V̇·cₚ·ΔT with room-temperature properties (air ρ≈1.18 kg/m³, cₚ≈1006 J/kg·K; water ρ≈997, cₚ≈4180; a representative single-phase dielectric ρ≈1600, cₚ≈1100). It compares transport capacity only — fan/pump power, pressure drop, heat-exchanger area and two-phase latent heat are outside this simplified model, and two-phase operation requires a different model that includes latent heat, wall superheat, critical heat flux and dryout.