Experimental study on thermal stratification characteristics of C-shaped heat exchanger under stationary and rolling conditions

• A scaled experimental facility of the secondary side PRHRS was designed and built. • Rolling motion enhances initial heat removal by promoting fluid mixing and natural circulation in the C-shaped heat exchanger. • Larger rolling amplitudes reduce the heat exchanger outlet temperature, while longer rolling periods lower system pressure. • Rolling motion weakens thermal stratification intensity but prolongs its persistence due to enhanced fluid agitation. This study investigates the thermal stratification characteristics and operating performance of a C-shaped heat exchanger in the secondary passive residual heat removal system (PRHRS) under stationary and rolling conditions, relevant to Offshore Floating Nuclear Power Plants (OFNPs). A scaled-down experimental facility was designed to simulate the PRHRS, incorporating a swaying platform to replicate marine rolling motions. Experiments were conducted under varying rolling amplitudes (15°, 24°) and periods (8 s, 14 s), with heating powers of 34 kW and 31 kW, to analyze the effects of dynamic conditions on heat removal capacity, system stability, and thermal stratification. Key findings reveal that rolling motion enhances heat removal during the initial operational phase by promoting fluid mixing and natural circulation. However, under quasi-steady states, rolling conditions induced periodic oscillations in system pressure, mass flow rate, and heat removal power, synchronized with the imposed rolling period. Thermal stratification was weakened under rolling motion due to enhanced fluid mixing, though the duration of stratification persistence increased. Notably, larger rolling amplitudes reduced the heat exchanger outlet temperature, while longer periods lowered system pressure. These results provide critical insights into optimizing PRHRS design for OFNPs operating in dynamic marine environments.