Study On The Performance Of The Staggered Tube-bundle Seawater Heat Exchanger In Oscillating Flow

Owing to the global urgent need for renewable energy,ocean thermal energy is attracting increasing attention for the large amount of clean energy resources storing in the seawater.Seawater source heat pump is one of the key ways to utilize ocean thermal energy.Particularly,seawater heat exchanger is a key component of closed-loop seawater source heat pump which can maintain indirect contact between the unit and the seawater to avoid the problems of corrosion,blockage and icing.In this study,the investigation of the staggered tube-bundle seawater heat exchanger was conducted,the findings could provide the basic data and theoretical reference for the design of the seawater heat exchanger in the seawater source heat pump system.The main findings were summarized as follows:(i)To obtain the criterion correlation between Nusselt number and Reynolds number required in the heat transfer model,an experimental system was built in the wave-inducing pool to investigate the thermal and hydraulic characteristic of the staggered tube-bundle heat exchanger immersed in the oscillating flow.Based on the wave theory and experimental data,a dimensionless correlation was proposed to calculate the external convective heat transfer coefficient,and the relationship between the seawater velocity and wave amplitude,wave period,water depth and sinking depth of heat exchanger were established.(ii)A heat transfer mathematical model was firstly developed to describe the heat transfer of staggered tube-bundle seawater heat exchanger under non-icing and icing conditions.Additionally,a thermal performance system under actual ocean conditions was conducted to vertify the heat transfer model.The average deviation between the experimental results and simulated results of the heat transfer rate under non-icing and icing conditions was 1.30% and 5.84%,respectively.(iii)The effects of wave parameters,structural parameters and operating parameters on the heat transfer performance of seawater heat exchangers under nonicing conditions and on the ice thickness under icing conditions were investigated by adopting the heat transfer mathematical model.(iv)For improving the performance of seawater heat exchanger,a design method on staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement was developed.The overall heat transfer coefficient and thermal efficiency of the staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement were approximately 35% and 30% higher than those with equally-pitch arrangement,respectively.Moreover,the pressure drop of the heat exchanger with unequally-pitch arrangement was approximately 15% lower than that with equally-pitch arrangement at the same heat transfer medium flow rate.