Numerical Simulation Of Enhanced Heat Transfer In Spiral Tube Phase Change Energy Storage Heat Exchanger With Fins

The intermittency and instability of solar energy make it necessary to configure a heat storage device during its utilization,and often form an energy storage heat exchanger with a heat transfer medium(heat transfer fluid,HTF).The latent heat storage of phase change materials(PCMs)can increase the heat storage density and have the advantages of stable heat output temperature.However,the low thermal conductivity of phase change materials affects the heat storage/discharge rate of phase change energy storage heat exchangers.Therefore,it is of great significance to improve the heat transfer performance of the phase change energy storage heat exchanger.In this paper,taking the spiral tube phase change energy storage heat exchanger as the research object,the influence of fin geometry parameters and HTF operating parameters on the heat storage and discharge performance of the phase change energy storage heat exchanger is studied through numerical simulation.(1)To study the effect of HTF operating parameters(inlet direction,inlet temperature,flow rate)on the melting and solidification process.The results show that for the melting process,the HTF flows upwards,and the higher the inlet temperature,the faster the flow rate and the shorter the melting time;while for the solidification process,the HTF flows downwards,and the lower the inlet temperature,the faster the flow rate,the shorter the solidification time.And the effect of inlet temperature is more obvious.For the melting process,the upward flow,and the greater the inlet temperature,the slower the flow rate and the higher the exergy efficiency.(2)To study the effect of straight fin geometric parameters on the melting and solidification process.The fin angle(angle between fin normal and horizontal plane)and height have a certain degree of influence on the melting process,while the fin thickness has a limited effect.The structure with fin angle of 90° has the best heat transfer effect,shortens the melting time by 24.2%,and increases the exergy efficiency by 3.6%.And the larger the fin height,the shorter the melting time,and the higher the exergy efficiency.The melting time and exergy efficiency of different fin thicknesses are basically the same.During the solidification process,different fin angles have almost no effect on the solidification time.(3)To study the effect of geometric parameters of spiral fins on the melting and solidification process,and to compare with straight fin structures.Compared with the fin thickness and the number of fin spiral turns(degree of deformation of spiral fins),the height has more obvious influence on the melting process.The more fin spiral turns,the greater the fin height,the shorter the melting time,and the greater the exergy efficiency.The melting time was shortened by up to 41.6%,and the exergy efficiency was increased by 7.4%.In the melting process,compared with straight fins with the same fin height and thickness,the spiral fins have larger heat transfer area and higher exergy efficiency,however,their horizontal projected area is relatively smaller and the melting time is longer;while during the solidification process,the effect of fins is negligible.