Meaning
Multi-phase fluid dynamics and high-rate heat transfer processes often feature situations where the different phases do not share a single temperature. This physical state, referred to as thermal non equilibrium, occurs during rapid pressure changes or fast transient boiling where the liquid and vapor phases have distinct local temperatures. This condition is particularly important in cryogenic fuel systems and steam turbines where rapid expansion causes sudden phase changes.
It ceases to exist when the phases are given sufficient residence time to reach a uniform temperature.
Interphase Heat Transfer
Rate-limiting thermal transport across the interface between phases governs the speed of temperature equalization. In high-pressure steam systems, rapid depressurization causes the liquid phase to become superheated while the vapor remains at saturation. This temperature difference drives the evaporation rate.
System Modeling
Simulation tools must use multi-fluid models with separate energy equations for each phase to accurately predict this state. Assuming a single mixture temperature in these cases would lead to incorrect predictions of pressure drops and phase change rates. This modeling approach is critical for safety analyses of nuclear reactors and boilers.
Transient Response
Fast thermal transients in industrial chemical reactors often create localized regions of varying temperatures. These variations can trigger unexpected chemical reactions or localized material stresses in the vessel walls. Monitoring these transient states helps prevent equipment failure.
