A v²-f model assessment for mixed convection in water-cooled SMR configuration

In vertical upward heating flow which is typical orientation in a reactor core (especially PWR), the turbulent heat transfer can be deteriorated if it goes from forced to mixed convection regime or also known as the deteriorated turbulent heat transfer (DTHT) regime. While nuclear energy plays an important role for addressing global energy issues, more attention is given to the development of Small Modular Reactor (SMR) with passive cooling features. Previous research effort has been focused on the investigation of the effect of size reduction and passive system implementation to operating heat transfer regime of a water cooled system. It has been found that the PWR has a tendency to fall to DTHT regime as the size is reduced from a large size reactor to SMR scale. Furthermore, the tendency will increase as passive operation mode is more incorporated to the system. A suitable mixed convection heat transfer correlation is therefore needed so that we will not overestimate the reactor heat transfer capability under the DTHT regime. Several previous works have been done in finding mixed convection heat transfer correlation for a water system but there is still a big experimental gap to find out the best mixed convection heat transfer correlation in a water system, especially in nuclear system. This paper will first discuss several mixed convection heat transfer correlations for a water system and their experimental limitation. The comparison of the selected correlation is done by performing computational fluid dynamics (CFD) analysis. The problem domain for the CFD analysis is set to represent SMR geometry since the tendency to fall to the DTHT regime is higher in SMR than in a large nuclear reactor. The ν²-f model is chosen as the turbulence model for this case because this model has been proven to perform well for mixed convection case. Through the numerical analysis, the mixed convection heat transfer correlation for a water system which can be used in SMR geometry can be found. This numerical work can give an insight to understand mixed convection phenomenon in PWR and set a basis for experimental verification.