SCALING OF THERMALLY DIFFERENTIATED FLOWS IN PRIMARY SYSTEM FLOW GEOMETRIES

摘要

An experimental program has been conducted at the U. of Md. 2×4 thermal hydraulic facility investigating the degree of mixing which occurs when flow is initiated in a previously stagnant primary system and segregated fluid volumes (volumes which differ in salt content and/or temperature) are moved towards the core region. The program was preceded by a scaling effort which strove to create consistently scaled flow conditions for all of the principal system components through which the segregated fluid volumes move before reaching the core. This resulted in the modification of the RPV (Reactor Pressure Vessel) downcomer and lower plenum regions. The tests cover a broad range of primary system flow conditions, and a broad range of segregated slug volumes and slug-to-ambient density differences. This includes the transport of segregated water plugs which are either negatively or positively buoyant with respect to the bulk coolant of the system. Judicious use of temperature difference and salt concentration makes it possible to create conditions for which the segregated plug is neutrally buoyant.rnThe experimental data which has been generated has provided additional insight into the principal phenomena which determine the mixing of moving fluid volumes in complicated flow geometries. The newly obtained information is used to reexamine and broaden the previously used scaling approach. This study presents a fundamental derivation of scaling criteria based on the Navier-Stokes equations. The derived relationships are tested against the measured experimental data. The comparisons show that in order to apply them to actual flow systems it is necessary to take into account the effect of turbulence on the fluid diffusivity and viscosity. Concepts used in the chemical industry to determine the dispersion characteristics of vessels are applied to derive arnrelationship between the diffiisivity of the flow path and fluid velocity.