  The study of heat exchangers with both the hot and cold fluid sides driven by
buoyancy forces is an area of considerable interest due to their inherent
passivity and non-existence of moving parts. The current study aims to study
such heat exchange devices employing the basic Coupled Natural Circulation Loop
(CNCL) systems. A 1-D Fourier series based semi-analytical model of the basic
CNCL system is proposed. A 3-D CFD validation is performed to validate the
developed 1-D model. The non-dimensional numbers such as Grashof number,
Fourier number, Stanton number and Reynolds number, which determine the system
behavior are identified and a detailed parametric study is performed. Both
vertical and horizontal CNCL systems are considered along with the parallel and
counter flow configurations. The heater-cooler location greatly influences the
behavior of CNCL system. The vertical CNCL always exhibits counter flow
configuration whereas the horizontal CNCL system may exhibit parallel or
counter flow arrangement depending on the heater-cooler location and initial
flow conditions.
