The design of a buoyancy valve for a renewable energy thermal storage tank led us to this interesting CFD problem. The purpose of the valve is to allow water to circulate within the system when the temperature of the water rises above a critical value. From Archimedes principle, a buoyancy oat made from a given material will rise (providing a closed state for the valve) when below a critical temperature and sink (providing an open state for the valve) when above a critical temperature. However, the precise valve response depends on internal temperature and mass-
ow dynamics. In this paper, we present a CFD investigation of the valve's behaviour under specic conditions.