An Extended Analysis for Flow Splitting in Multiple, Parallel-Boiling Channels Systems

Abstract

Previous results are generalized to consider multiple boiling channels systems. The analysis is consistent with the approximations usually adopted in the use of systems codes (like RELAP5 and TRACE5) commonly applied to perform safety analyses of nuclear power plants. The problem is related to multiple, identical, parallel boiling channels, connected through common plena. Flow splitting without reversal was computationally found and to explain this behavior a theoretical model limited in scope was developed. The unified analysis performed and the confirmatory computational results found are summarized in this paper. New maps showing the zones where this behavior is predicted are shown considering again twin pipes. Multiple pipe systems have been found not easily amenable for analytical analysis when dealing with more than three parallel pipes. However, the particular splitting found (flow dividing in 1 standalone pipe flow plus N-1 identical pipe flows) has been verified up to twelve pipes, involving calculations in systems with even and odd number of pipes using the RELAP5 systems thermal-hydraulic codes. Although not shown in this paper, results have been also generalized to consider the flow in systems of identical, parallel, condensing, inverted U-tubes.