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• A novel heat exchanger with unequally-pitch arrangement is proposed. • The thermal, hydraulic and thermal-hydraulic performance are analyzed. • The novel heat exchanger is superior to that with equally-pitch arrangement. A novel staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement, which the transversal and longitudinal tube pitches are inhomogeneous, is firstly proposed and applied in the closed-loop seawater source heat pump system. An experimental system that can induce the regular wave to simulate the seawater flow is established to investigate the thermal resistance ratio, overall heat transfer coefficient, thermal efficiency of heat exchanger under various wave parameters. The thermal performance, hydraulic performance, and comprehensive thermal-hydraulic performance of heat exchangers with unequally-pitch arrangement and equally-pitch arrangement are compared. The results indicate that the unequally-pitch arrangement of tube-bundle heat exchanger can significantly enhance the overall heat transfer coefficient and thermal efficiency, meanwhile decrease the pressure drop, and consequently improve the comprehensive performance. The present study is conducive to improve the performance potential of staggered tube-bundle seawater heat exchanger and promote the exploitation of ocean thermal energy. [ABSTRACT FROM AUTHOR]

• The effects of the oscillating flow on the thermal performance were studied. • An empirical correlation with acceptable accuracy was proposed. • Comparisons of various correlations and experimental results were conducted. Owing to the growing demands to develop sustainable energy, ocean energy is attracting increasing attention for the large amount of renewable, available, and potential energy resources stored in the ocean. An experimental system was constructed to study the heat transfer characteristics of staggered tube bundle heat exchanger immersed in oscillating flow. The results revealed that the instantaneous horizontal and vertical velocities of the oscillating flow exhibited a periodic fluctuation trend. Moreover, the cycle-averaged velocity and the external heat transfer coefficients were clearly affected by the wave height, whereas the wave period had little effect. To quantitatively describe the heat convection of staggered tube bundle heat exchanger in oscillating flow, a correlation of the Nusselt number that accounted for the combined effects of the wave parameters (including the wave height and wave period), water depth, and location depth of the submersed tube bundles was proposed. Comparisons with various correlations revealed that previous correlations could not describe the external heat convection in oscillating flow accurately. The newly proposed correlation was proven to predict the external Nusselt number with an acceptable accuracy under various testing conditions, which benefitted the design of the seawater heat exchanger. [ABSTRACT FROM AUTHOR]