NATURAL CIRCULATION LOOPS WITH PARALLEL CHANNELS TRANSIENT-BEHAVIOR

A theoretical modeling method is presented for describing the transient flow and heat transfer in natural circulation loops. The system under consideration includes a common heat source and a general number of parallel branches having a heat sink (heat exchanger). The conservation continuity, momentum and energy equations are written, based on a one dimensional approach. The momentum equation is integrated around every closed loop such that the pressure terms are eliminated and the energy equation is integrated separately for every component. This procedure leads to a set of simultaneous ordinary differential equation for the time dependent flow rates and average component temperatures. The equations are solved numerically using a combination of explicit and implicit techniques. The method has been applied to a small scale 4-loop system relevant to a PWR.