Abstract
Flow oscillations in natural circulation loop were studied experimentally, with a small-scale test loop consisting of upper and lower drums, an electrically heated evaporator, an unheated riser and a downcomer. Inlet velocity of evaporator was monitored with an electro-magnetic flow meter and, in some experiments, flow patterns at the exit of the evaporator were observed through a pyrex grass tube. The obtained stability map was compared with the analytical result of a homogeneous flow model, and examined in relation to estimated or observed flow patterns at the exit of the evaporator. It was suggested that the flow pattern transitions in the evaporator were not causes of flow oscillations.