An analytical investigation of role of expansion tank in semi-closed two-phase natural circulation loop

Role of the expansion tank in a semi-closed two-phase natural circulation loop was examined analytically with the emphasis placed on the flow instability. Loopwise steady circulation rate was obtained, and conditions for flow instability were examined by using the method of the linear stability analysis with perturbations. The homogeneous two-phase model was adopted for the analysis. As well as the pressure at the expansion tank, the length and the cross-sectional area of the tube connected to the expansion tank appeared to be the important parameters determining the flow instability. The system was predicted to be stable with the longer length and the smaller cross-sectional area of the expansion-tank line and also with the higher expansion-tank pressure.