Abstract
The characteristics of bubbles of different sizes in fuel assembly are vital to two-phase flow resistance and heat transfer capacity. However, due to the swirl flow caused by the mixing vane, bubbles can crowd at the heated surface, which may anticipate the occurrence of departure from nucleation boiling. In the current work, the adiabatic two-phase flow in a simplified fuel assembly was analyzed by using the Eulerian two-fluid model and the MUSIG (MUltiple SIze Group) model. This computational domain consists of two coolant channels and two sets of vaned spacers, with three sets of periodic boundary conditions at the side faces of the domain. The distributions of vapor phase and bubble diameters were obtained, based on which the effects of mixing vanes on the bubble characteristics were analyzed. Vapor phase crowded at the rod surface in the higher inlet vapor fraction case, but crowded in the channel center in the lower inlet vapor fraction cases. This work can be used as a reference for the design of mixing vanes to avoid the anticipation of departure of nucleation boiling that may be caused by unreasonable design.
Highlights
Two-phase boiling flow has been widely used in power systems because of its high heat transfer performance compared with single-phase convective flow
In a newly designed pressurized water reactor (PWR), such as AP1000 (Westinghouse Co., Pittsburg, PA, USA), subcooled boiling and even saturated boiling is allowed in the core due to increasing confidence in the design and analysis technologies of PWR and the increasing demand on the economy of PWR
The enhancement of the heat transfer ability is limited by the boiling crisis, where the wall heat flux reaches the critical heat flux and the local heat transfer coefficient decreases by one or two orders of magnitude
Summary
Two-phase boiling flow has been widely used in power systems because of its high heat transfer performance compared with single-phase convective flow. Two-phase flow has drawn lots of attention in the past few decades due to its essential role in the safety analysis of reactor systems. It has been studied by experimental and numerical methods. Energies 2018, 11, 256 traditionally, obtaining the basic senses on the two-phase nature and analysis tools such as RELAP-5, which are quite important to the design and safety analysis of nuclear reactor These two traditional methods suffer from some critical defects. The adiabatic liquid-vapor two-phase flow in the fuel channel with spacer grid and mixing vane was simulated by the two-fluid framework coupled with the homogenous. The effects of vaned spacer on the bubble diameter distribution mean bubble diameter and pressure drop were obtained
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