Thermofluid-dynamics in pool heat exchangers.

Natural circulation has many engineering application and one of them is the decay heat removal from the core of a nuclear power plant. Passive safety systems based on natural circulation are used to accomplish safety function without requiring any active power source or moving mechanical parts. There are two main components in these kind of systems: a large pool (the heat sink) and an heat exchanger (the heat source). The heat removal process involves a complex interaction of mass and heat transfer, characterized by single and two-phase flow. Density gradient induces the fluid's motion inside the pool, where a non uniform temperature distribution can be detected, as a consequence of the thermal stratification. Thermal stratification lasts until the saturation temperature is reached inside the pool, then mixing phenomena dominate the heat transfer process. The goal of this work is to collect the results obtained by experimental and numerical studies focused on the thermofluid-dynamics in pool heat exchangers and then try to provide a simplified model capable to predict and describe the heat transfer phenomena involved in an experimental tEst-facility. The test-facility is a characterized by a small cylindrical pool (height 1000 mm, outer diameter 600 mm) with a single tube (height 1000 m, outer diameter 33.4 mm) where saturated steam flows. In order to verify the results obtained by the simplified model empirical studies need to be performed.