Enhanced Heat Transfer Study Of Phase Change Energy Storage Device Based On Waste Heat Utilization Of Ship Main Engine Cooling Water

In this thesis,phase change energy storage was adopted to recover the waste heat of ship main engine cooling water to improve the energy utilization rate of ship,effectively reduce the waste heat of ship,solve the contradiction of energy supply and demand in time and space,and improve the energy utilization efficiency of ship.Firstly,paraffin wax is selected as the phase change material in the process of phase change energy storage and waste heat recovery of ship’s main engine cooling water according to the temperature of the main engine cooling water and the physical and chemical properties of the phase change material(PCM).Due to the low thermal conductivity of paraffin wax,the study of how to enhance the heat transfer efficiency of the phase change energy storage system became the main research content of this thesis.In this thesis,an integrated phase change energy storage unit composed of a horizontally placed shell and tube phase change energy storage structure is selected as the research object,and the two-dimensional phase change heat transfer process of the shell and tube phase change energy storage structure is studied for reasonable and simplified calculation.A mathematical model and a physical model are established,and the independence of the established model is verified,and the reliability of the established model is demonstrated by comparing it with the experimental process of the previously published article.The variation of the structure,heat transfer fluid(HTF)conditions and fin material of the casing and tube energy storage system also affects the phase change heat transfer process.The simulation calculation of different structures by Fluent shows that the three-casing energy storage system increases the heat transfer area and the efficiency of melting process and solidification process is significantly enhanced compared to the two-casing energy storage system.A new type of double Y-shaped fins is proposed,and the melting time decreases by 26.15% and the heat storage increases by 3.07% when the fins are evenly arranged around the outer wall of the middle pipe;the solidification time decreases by 36.56% and the heat release increases by 0.46%.the HTF temperature variation has a greater effect on the heat transfer characteristics of the phase change energy storage system,and the HTF temperature of the melting process increases from 353 K to 373 K,and the melting time decreased by 42.40%.The solidification time decreases by 64.62% when the HTF temperature is 283 K compared to 313 K for the solidification process.The best heat transfer efficiency is achieved when the fin material is copper,which reduces the melting time by 78.20% and the solidification time by 5.13% compared to the fin material of iron.Therefore,the fins should be selected as double Y-shaped fins evenly arranged along the outer wall surface of the pipe,and the fin material is copper for the three-casing phase change energy storage system to enhance the phase change heat transfer efficiency.A new type of double Y-shaped fins is used to increase the heat transfer efficiency and to study the heat transfer process of PCM with different fin structure parameters.The melting process of natural convection affects the phase change process of PCM,and the solidification process is dominated by heat conduction,and the same fin structure has different effects on the melting and solidification processes of PCM.The change of fin structure affects the quality of PCM,and it is necessary to calculate the heat storage and heat release as evaluation parameters.When the fin angle is 60°,the PCM has the best heat storage performance,the most heat storage,and the melting time is small compared to other angles.The solidification process has the most heat release at a fin angle of 60° and the shortest solidification time at 70°.The best melting performance is achieved when the fin branch lengths are 8 mm and 6 mm respectively;however,the longer the branch fin lengths are during solidification,the less the solidification time is,but the heat storage is also minimal.The effect of width variation on the melting and solidification process is different,with the best heat storage when the fin width is 0.5mm,while its melting time is 21.70%more than the minimum melting time,and the shortest melting time but the least heat storage when the fin width is 1.5mm.Longer width will reduce the solidification time and heat release.In order to have good heat transfer performance,the fin width is taken as 0.5mm.when the fin angle is 60°,the fin width is 0.5 mm,and the fin branch length is 8 mm and 6 mm,it is more beneficial to the heat transfer efficiency of the energy storage system.