In this work, the external and internal airflow analysis in an urban bus is carried out through computational fluid dynamics. The research addresses the study of the internal flow to estimate the air change rate caused by the opening of windows. Two cases are considered: fully opening and partially opening the windows, and three bus speeds of 20, 40, and 60 km/h are assessed. The quantification of the air flow rate through the windows clearly displays that air enters through the rear windows and exits the bus through the front windows. This effect is explained by the pressure distribution in the outer of the bus, which causes the suction of the indoor air. At low bus speeds, the incoming air flow rate increases linearly with the speed, but the improvement is lower for high speeds. The theoretical air change time at 20 km/h is around 25.7 s, which is 9 times lower than expected by using HVAC systems. On the other hand, the estimation of the real air renewal time by solving a concentration shows that 40 s are needed to exchange 85% of the internal air of the bus. The research also assesses the effect of different levels of occupation inside the bus. Results are conclusive to recommend the circulation with full or partial window opening configurations in order to reduce the risk of airborne disease transmission.
Se aplicó un procedimiento computacional multidominio para modelar el generador de vapor RD-14M. Se utilizó el enfoque Euleriano de dos-fluidos para modelar el flujo de agua y vapor, el método de blending para los términos de fuerzas interfaciales, el modelo de partición de calor de pared (RPI) para la ebullición de pared y el método de transferencia de calor conjugado (CHT) para acoplamiento térmico entre los circuitos primario y secundario. El modelo computacional de todo el generador de vapor se modeló mediante la combinación de una simulación 3D completa del riser y el modelado 0D con condiciones de borde dinámica ad hoc de las regiones del separador/secador, downcomer y precalentador. La implementación se realizó en la plataforma OpenFOAM(R). Se estudió inicialmente la sensibilidad de malla sobre las condiciones nominales de estado estacionario y luego se estudió el evento transitorio parada del reactor. Los resultados se compararon con los modelos RELAP5 y full-3D anteriores y se obtuvo buen acuerdo. El modelo completo demostró ser una herramienta adecuada para comprender el comportamiento termo-hidráulico general de los generadores de vapor, pero también los fenómenos locales alrededor de los tubos y baffles dentro del riser.
The Spent Fuel Pool (SFP) of Angra II, from Brazil, has received standard spent fuel (SF) assemblies of Uranium dioxide (UO2) discharged from Pressurized Water Reactors (PWR) of the Nuclear Power Plants (NPP) of Angra since the beginning of its operation. However, in case of using Mixed Oxide (MOX) or Thorium-based fuels, it would require further thermal studies of wet storage. It includes the determination of the water boiling time (Tb) of the SFP in case of breakdown of its external cooling system (ECS). This work presents studies of Tb of a simulated SFP storing mixed SF discharged from PWRs. The types of mixed SF studied include MOX plus UO2, oxide of thorium/uranium (U-Th)O2 plus UO2, and oxide of Thorium/transuranic (TRU-Th)O2 plus UO2. The simulations were implemented in CFX Ansys considering the top of the SFP as either adiabatic or non-adiabatic wall. Tb is considerably higher when the non-adiabatic boundary condition is used.
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