Heat transfer characteristics and optimization of fractal fin during phase change
-
摘要:
相变材料的低导热率制约了潜热储热系统的效率,提出了一种新型分形翅片改善潜热储热系统的相变传热特性。建立二维管壳潜热储热系统模型,利用焓-多孔介质法进行瞬态模拟,研究了嵌入分形翅片对系统凝固性能的影响,分形翅片长度比和分支角对凝固过程影响显著,分形翅片加快了相变材料的凝固,使系统温度分布更加均匀。与直翅片相比,分形翅片显著强化了系统的换热性能,采用人工神经网络对数据进行拟合,以液相体积分数为优化目标,通过遗传算法得到优化后的翅片结构:最佳长度比为1.425,两分支角分别为50°和30°;优化后分形翅片系统的凝固时间比直翅片系统减少76.9%。对分形翅片参数进行了敏感度分析,结果表明长度比对系统凝固时间的影响更大,1级分支角次之,更应关注这两个参数的变化对凝固时间的影响。
Abstract:The low efficiency of the latent heat storage system attributed to low thermal conductivity of phase change material. A novel fractal fin to strengthen the solidification property of latent heat storage units was proposed. The enthalpy-porosity technique was utilized to build a transient two-dimensional model of shell and tube latent heat storage system. The results demonstrated that the length ratio and branch angle played an important role in solidification performance. The fractal structure improved the solidification speed and led to uniform temperature. The fractal fin displayed a remarkable heat transfer enhancement compared with a conventional fin. The structure optimization of fractal fin was conducted for solidification enhancement by artificial neural network and genetic algorithm. The optimized fin structure was obtained by genetic algorithm: the optimal fin length ratio was 1.425 and the two branch angles were 50° and 30° respectively, the solidification time of the latent heat storage unit with fractal fin after optimization was 76.9% shorter than the system with conventional fin. The sensitive analysis was applied to explore the effect of the parameters of fractal fin on solidification time. The results indicated that the solidification time of the system was more affected by the length ratio, followed by the first-order branch angle. More attention should be paid to the effect of the changes of these two parameters.
-
表 1 材料的热物理性质
Table 1. Thermophysical properties of materials
参数 月桂酸 铝合金 密度/(kg/m3) 869 2703 比热容/(J/(kg∙K)) 1760 (固)/2150 (液)963 熔点/K 315~317 潜热/(kJ/kg) 178.7 导热系数/(W/(m∙K)) 0.22(固)/0.16(液) 180 黏度/(Pa∙s) 0.001 表 2 翅片参数对凝固时间的一阶灵敏度
Table 2. First order sensitivity of fin parameters to solidification time
翅片参数 主效应指标 总效应指标 长度比 0.185 0.675 9 0级分支角 0.076 4 0.642 9 1级分支角 0.143 1 0.480 6 -
[1] RATHOD M K,BANERJEE J. Thermal performance enhancement of shell and tube latent heat storage unit using longitudinal fins[j]. applied thermal engineering,2015,75: 1084-1092. doi: 10.1016/j.applthermaleng.2014.10.074 [2] 王玮琦,邢玉明,郑文远,等. 环肋翅片管相变传热特性及分形优化[J]. 北京航空航天大学学报,2022,48(12): 2520-2528. WANG Weiqi,XING Yuming,ZHENG Wenyuan,et al. Phase change heat transfer characteristics and fractal optimization of radial plate fin tube[J]. Journal of Beijing University of Aeronautics and Astronautics,2022,48(12): 2520-2528. (in ChineseWANG Weiqi, XING Yuming, ZHENG Wenyuan, et al. Phase change heat transfer characteristics and fractal optimization of radial plate fin tube[J]. Journal of Beijing University of Aeronautics and Astronautics, 2022, 48(12): 2520-2528. (in Chinese) [3] ZHAO Chunrong,OPOLOT M,LIU Ming,et al. Numerical study of melting performance enhancement for PCM in an annular enclosure with internal-external fins and metal foams[J]. International Journal of Heat and Mass Transfer,2020,150: 119348. doi: 10.1016/j.ijheatmasstransfer.2020.119348 [4] 马慧齐. 基于分形理论的相变换热单元的传热性能研究[D]. 南京: 南京师范大学,2020. MA Huiqi. Study on heat transfer performance of phase change heat exchange unit based on fractal theory[D]. Nanjing: Nanjing Normal University,2020. (in ChineseMA Huiqi. Study on heat transfer performance of phase change heat exchange unit based on fractal theory[D]. Nanjing: Nanjing Normal University, 2020. (in Chinese) [5] SCIACOVELLI A,GAGLIARDI F,VERDA V. Maximization of performance of a PCM latent heat storage system with innovative fins[J]. Applied Energy,2015,137: 707-715. doi: 10.1016/j.apenergy.2014.07.015 [6] DENG Zilong,WU Suchen,XU Hao,et al. Melting heat transfer enhancement of a horizontal latent heat storage unit by fern-fractal fins[J]. Chinese Journal of Chemical Engineering,2020,28(11): 2857-2871. doi: 10.1016/j.cjche.2020.08.022 [7] SHEIKHOLESLAMI M,LOHRASBI S,GANJI D D. Numerical analysis of discharging process acceleration in LHTESS by immersing innovative fin configuration using finite element method[J]. Applied Thermal Engineering,2016,107: 154-166. doi: 10.1016/j.applthermaleng.2016.06.158 [8] YU Cheng,WU Suchen,HUANG Yongping,et al. Charging performance optimization of a latent heat storage unit with fractal tree-like fins[J]. Journal of Energy Storage,2020,30: 101498. doi: 10.1016/j.est.2020.101498 [9] ZHANG C,LI J,CHEN Y. Improving the energy discharging performance of a latent heat storage (LHS) unit using fractal-tree-shaped fins[J]. Applied Energy,2020,259(2): 114102.1-114102.15. [10] MOTAHAR S. Experimental study and ANN-based prediction of melting heat transfer in a uniform heat flux PCM enclosure[J]. Journal of Energy Storage,2020,30: 101535. doi: 10.1016/j.est.2020.101535 [11] BABY R,BALAJI C. Thermal optimization of PCM based pin fin heat sinks: an experimental study[J]. Applied Thermal Engineering,2013,54(1): 65-77. doi: 10.1016/j.applthermaleng.2012.10.056 [12] 冯鸿渔,王健,冯佰威. 双尾船尾型参数对阻力和伴流的敏感度分析[J]. 武汉理工大学学报(交通科学与工程版),2023,47(04): 654-658. FENG Hongyu,WANG Jian,FENG Baiwei. Sensitivity analysis of parameters of twin-skeg ship’s stern to resistance and wake[J]. Journal of Wuhan University of Technology (Transportation Science and Engineering Edition): 1-13. (in ChineseFENG Hongyu, WANG Jian, FENG Baiwei. Sensitivity analysis of parameters of twin-skeg ship’s stern to resistance and wake[J]. Journal of Wuhan University of Technology (Transportation Science and Engineering Edition): 1-13. (in Chinese) [13] AL-ABIDI A A,MAT S,SOPIAN K,et al. Numerical study of PCM solidification in a triplex tube heat exchanger with internal and external fins[J]. International Journal of Heat and Mass Transfer,2013,61: 684-695. doi: 10.1016/j.ijheatmasstransfer.2013.02.030 [14] BELÉN Z,JOSÉ M M,CABEZA L F,et al. Review on thermal energy storage with phase change: materials,heat transfer analysis and applications[J]. Applied Thermal Engineering,2003,23(3): 251-283. [15] SWAMINATHAN C R,VOLLER V R. A general enthalpy method for modeling solidification processes[J]. Metallurgical Transactions B,1992,23(5): 651-664. doi: 10.1007/BF02649725 [16] ISMAIL K A R,ALVES C L F,MODESTO M S. Numerical and experimental study on the solidification of PCM around a vertical axially finned isothermal cylinder[J]. Applied Thermal Engineering,2001,21(1): 53-77. doi: 10.1016/S1359-4311(00)00002-8 [17] HOLLAND J H. Adaptation in natural and artificial systems: an introductory analysis with applications to biology,control,and artificial intelligence[M]. Michigan: The MIT Press,1992. [18] SOBOLÁ I M. Global sensitivity indices for nonlinear mathematical models and their Monte Carlo estimates[J]. Mathematics and Computers in Simulation,2001,55(1/2/3): 271-280. -