CFD Analysis of the Flow Into a Preheater

University essay from KTH/Teknisk mekanik

Abstract: This project has investigated and formed a basis for the thermal- and flow-induceddynamic loads in the lower parts of a preheater situated in a nuclear power plant.Special attention has been given to the bottom plate that separates the heated andnon-heated secondary steam. Using computational fluid dynamics (CFD), steady RANSsimulations were first used to investigate how the flow into the preheater was affectedby the inlet boundary conditions. From there a steady RANS conjugate heat transfer(CHT) analysis was conducted as to obtain the temperature field within the preheaterand its solid components. This also investigated different approaches in modelling theheat transfer between the primary and secondary steam. Lastly, a scale-resolving LESwas conducted as to obtain the flow-induced dynamic loads on the bottom plate. The results show that the modelling used in previous works gives a less uniformtemperature distribution as compared to when appropriate heat transfer coefficient(HTC) correlations are applied. Regardless of how the heat source is modelled, hot spotswith significantly larger temperatures are present in the bottom plate near the outletsof the bottom tube sections. The root mean square value, amplitude and frequencycontent of the fluctuating force acting on the bottom plate have also been obtained.The results of the analysis provide a good starting point for future work examining ifthe loads on their own or in combination may risk damaging the structure.

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