Dynamic performance of a natural circulation loop with end heat exchangers under different excitations

In the present work the dynamic performance of a natural circulation loop (NCL) has been studied under step, ramp, exponential and sinusoidal excitations. The loop is equipped with two heat exchangers at its lower and upper end for the heating and cooling of the loop fluid. For the analysis, transient one-dimensional conservation equations have been constructed for the loop fluid as well as for the two fluid streams of hot and cold end heat exchangers. The solution of a set of differential equations and one integro-differential equation has been obtained through a finite element method (FEM). For different excitations imposed to the inlet temperature of the hot fluid responses have been studied for the outlet temperature of the two fluid streams and the mass flow rate of the coupling fluid. It has been observed that all these quantities experience some initial transients before reaching the steady state. Time needed for the attainment of steady state varies with the type of excitation. A finite time delay is observed before the cold fluid stream temperature starts responding to the excitation. This delay is related to the time required for the advection of a fluid particle.