LAUSR

Abstract Experimental studies are carried out on a supercritical carbon dioxide based natural circulation loop (NCL) to investigate the loop behaviour under transient conditions. An electrical heater with controlled heat flux is used as the heat source, while an air-cooled fin & tube type heat exchanger with controlled air flow rate and air inlet temperature is used as the heat sink. Start-up and shutdown transients are studied with different heater power levels. Due to the unique properties of CO 2 , especially its critical temperature which is closer to ambient temperature, interesting results are obtained during the transient stages of the loop. It is seen that during shut-down, there is local condensation of CO 2 at cooler outlet as the temperature is less than corresponding saturation temperature. The resulting latent heat of condensation of CO 2 leads to sensible heating of CO 2 at other locations of the loop. It is observed that during fan failure there is sudden temperature and pressure rise, necessitating the need for protection against over temperature and pressure. A complete power failure study shows that there is a rise in pressure and temperature for a short duration followed by a slow cooling through natural convection heat loss to the ambient.