| Due to the energy crisis and environmental problems,sustainable energy sources such as solar,wind and tidal power are considered the most promising alternative to fossil energy because of their abundance and low pollution.In the large-scale application of sustainable energy,the inherent discontinuity and instability are the main challenges facing the research institute.In this context,latent heat thermal energy storage technology using organic phase change material provides an effective means to improve energy supply and demand matching.There are three main heat storage methods for thermal energy storage system: sensible heat thermal energy storage,latent heat thermal energy storage and thermochemical energy storage.Among them,latent heat energy storage using phase change materials is the most attractive form of energy storage because of its high energy storage density,small temperature change during phase change,stable chemical properties and non-corrosive characteristics.However,the low thermal conductivity of phase change materials limits the energy storage/release rate,resulting in uneven melting/solidification interface evolution.At the same time,there are also the phenomena of supercooling and phase separation,which will reduce the thermal performance of the energy storage unit in the process of energy storage and discharge.In recent years,researchers have carried out comprehensive research on the heat transfer enhancement characteristics of phase change materials,such as heat pipe,metal foam or nanoparticles to enhance the melting performance of phase change material;fin structure is used to expand the heat transfer surface and so on.Among them,the fin not only has the characteristics of easy installation and use,but also the thermal conductivity is much higher than the phase change material,which helps to improve the heat transfer rate between the heat transfer fluid and the phase change material,and enhance the overall performance of the energy storage system in terms of heat storage and release rate.Therefore,this paper mainly studies the enhanced heat transfer characteristics of phase change material with fins in shell and tube energy storage unit.According to the structure of shell and tube energy storage unit,the arc-shaped fractal fin is innovatively designed,and the heat storage and release process is compared with the baseline condition without fins and the flat fin condition.The effects of fin parameters such as length curvature and adjacent angle on thermal performance during heat storage and release are discussed.The length of the fins has a positive effect on the thermal performance of the energy storage unit.The main fins can effectively enhance the thermal permeability,and the branch fins can effectively enhance the thermal uniformity,which can shorten the melting process by up to76.3% and the solidification process by 84.1%.Compared with the common long and straight fractal fins,the arc-shaped fractal fin configuration makes the temperature field in the energy storage unit more uniform and has less hindering effect on natural convection.Moreover,the fin configuration that extends the thermal penetration depth vertically downward and makes the phase transition region more uniform are the best fin configuration choices for enhancing the thermal performance of the energy storage unit.In addition,for shell and tube energy storage units,this paper also innovatively adopts the three-pipe structure to optimize different energy storage processes,and focuses on discussing the evaluation indexes such as temperature field,velocity field change and entropy generation inside the energy storage unit.Through the setting of different source walls,it is concluded that the cooling of the outer wall and the heating of the inner wall are the most reasonable source wall settings for the dual-source energy storage unit without fins.On this basis,the inner wall surface is vertically arranged in a cross,the outer wall surface is arranged in a cross shape,and the fin configuration of the concentric branch fins has the best effect on the thermal performance of the energy storage unit.Compared with the condition without fins,this The total time for the working condition to reach the equilibrium moment is shortened by 36.17%.Based on the basic theory of phase change energy storage,the results of this paper have certain reference value for the design of fractal fin and the optimization of shell and tube phase change energy storage unit. |
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