Moving Boundary (MB) dynamic model is an appealing approach for investigation of advanced control schemes for two-phase flow heat exchanger. For the confusion of relative velocities between boundaries and fluid existing in the previous MB model, this paper presents a modified moving boundary model. The dynamic model incorporated with the relative velocities is derived from physical principles of mass and energy conservation. And the model is then implemented in a novel underwater HYDROX system to predict cyclic performance. The simulation results from discretized model using MATLAB language show that the oscillations which is known as "Chattering" have been suppressed. (C) 2015 Elsevier Ltd. All rights reserved.