The multi-hole steam ejection system is widely applied in practical engineering applications, whereas the heat transfer mechanisms in unstable condensation conditions are not very clear yet. In this study, the separate-effect mechanism tests of single/double-hole sparger, and 88-hole scaled ADS sparger tests are carried out to investigate the unstable steam spraying condensation performances. The experimental results indicate that for the multi-hole steam unstable condensation process, the plumes expand and contract in high frequency, and the instantaneous heat transfer coefficients are estimated quantitatively. The multi-hole steam condensation regimes are significantly determined by the steam mass flow flux and water sub-cooling degree, then the double-hole condensation regimes map is proposed based on the key inputting parameters. Moreover, the simplified lumped condensation model for the multi-hole condensation process is developed, in which the upper and lower heat transfer coefficient values limitations are evaluated to be 4.3-5.9 MW/(m(2) degrees C) and 0.89-0.94 MW/(m(2) degrees C), respectively. The ADS 1-3 scaled 88-hole steam condensation results further validate the appropriation of the lumped condensation model, with the heat transfer coefficients estimated as 0.17-2.9 MW/(m(2) degrees C). (C) 2019 Elsevier Ltd. All rights reserved.