Study on Reverse Flow in U-Tube Steam Generator under Natural Circulations

Some U-tubes are with flow in the reverse direction under natural circulations, which increases the equivalent local resistance of steam generator and decreases the flow of loop compared to the prediction without considering reverse flow. The stability of flow in a U-tube is discussed based on one-dimension momentum equation in this paper. On this basis, the range of the fraction of U-tubes with reverse flow can be derived from the conservation equations. The effect of loop resistance coefficient and numbers of U-tubes on the fraction of U-tubes with reverse flow is also discussed in this paper. The results show that the decreasing of the loop resistance coefficient and number of U-tubes contributes to decrease the fraction of U-tubes with reverse flow.