Comprehensive investigation of a novel multi-segment heat exchanger for PCM/MF based ocean thermal engine: Numerical analysis, model reduction and experimental work

Phase change material/metal foam based exchangers are widely used in thermal energy storage and ocean engineering. In this paper, a novel heat exchanger called multi-segment heat exchanger is proposed for installation on an ocean thermal engine. This heat exchanger has several concentric circular shaped thin slices inside, which divide the interior into several small areas. During the melting process, independent vortices were formed in each segment. Three aspects of research were conducted: (i) in the investigation of heat transfer enhancement mechanisms, by numerically solving the N-S equations, the reason for enhanced heat transfer in the multi-segment heat exchanger was explained using the field synergy principle theory, and the influence of dimensions and environmental parameters on the melting process was analyzed. Results show that the optimal ratio of height to radius (H/R) for each segment is 1 and the total melting time is reduced by 31–38 %; (ii) for model reduction, by simplifying the full order physical equations for conduction dominant and convection dominant processes separately, ordinary differential equations describing multi-segment heat exchangers were obtained, which can be used for rapid prediction in the engineering practice. The calculation time of the reduced order model is within 0.1 s; (iii) in experimental work, an experimental set-up was built to test the original and the multi-segment heat exchangers, respectively. The numerical work and reduced order model were validated, and results showed that the proposed heat exchanger reduced the melting time by 34 %.