  A Coupled Natural Circulation Loop (CNCL) consists of two Natural Circulation
Loops (NCL) coupled thermally via a common heat exchanger. The transient
modelling of such systems that have practical relevance has not been reported
in the literature to the best of the author's knowledge. The present work aims
to bridge this gap and investigate the dynamic characteristics of a CNCL system
using a 1-D mathematical model. The validation of the model is accomplished by
comparison of the results obtained via 3-D CFD simulation. Both horizontal and
vertical CNCL systems have been considered for this study and behaviour of the
system for parallel and counter flow configurations in the heat exchanger
section is elaborated. Transient and steady state CFD analysis has been
conducted to analyse CNCL system for different heater and cooler orientations
and flow initialisation. The behaviour of the CNCL system is then examined by
carrying a thorough parametric study employing the validated 1-D single phase
CNCL model with liquid sodium as the operating fluid. The CNCL orientation
(vertical or horizontal) coupled with the heater and cooler configuration
determines the system dynamics and behaviour. The CNCL system also exhibits
chaotic flow oscillations at high heat loads.
