Fluid flow and heat transport near the critical point of H₂O

Near-critical extrema in the properties of water may influence flow patterns in hydrothermal systems, but singularities in equations of state for H₂O at its critical point have inhibited quantitative modeling. Posing governing equations in terms of pressure (P) and enthalpy (H) avoids these singularities and facilitates computation. Numerical simulations with a P-H based model show little near-critical enhancement in heat transfer for systems in which flow is driven by fixed pressure drops. However, in density-driven systems, near-critical variations in fluid properties can enhance convective heat transfer by a factor of 10² or more (“superconvection”) if permeability is sufficiently high. Near-critical two-phase processes (“heat pipes”) are at least equally effective at dissipating thermal energy. The restriction to high-permeability environments within a fairly narrow P-H window suggests that superconvection may be quite rare in natural systems