Effect of heat loss to ambient on steady-state behaviour of a single-phase natural circulation loop

This study aims at modelling of a single-phase rectangular natural circulation loop as a conjugate problem to investigate the influence of ambient temperature on the steady-state temperature profile for the loop fluid and wall temperature. Finite volume technique has been employed for the solution of non-dimensional governing equations. Numerically predicted values have been compared with available test data from literature. Natural convection heat loss to the ambient is found to cause significant changes in the loop fluid and wall material temperature along the bare sections. Warmer ambient conditions increase the fraction of input power transferred to the cooling stream and hence cause a rise in coolant temperature across the cooler. Increase in ambient temperature results in higher coolant outlet temperature and thus higher heat exchange effectiveness for the system. The loop temperature profiles gradually approach the ideal condition of perfect insulation with increase in ambient temperature. The combined effect of change in power input and ambient temperature predicts a particular ambient condition, when the system produces a constant effectiveness regardless of the power input.