阶梯形肋片对套管式相变蓄热器蓄热性能影响的数值研究
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摘要
在传统等高直肋的基础上,针对套管式相变蓄热器实施非等高的阶梯形肋片以实现其热性能进一步优化。通过焓法模型,首先明确等高直肋的强化传热效果,并在此基础上分析肋高不均性及热源温度的影响。结果显示,与光管蓄热器相比,导热-对流共同作用的相变蓄热过程,等高直肋虽实现强化传热,但蓄热过程材料的融化仍存在竖向不均匀性,蓄热后期装置底部出现传热及融化死角。添加非等高阶梯形肋片的装置,蓄热过程各点融化速率趋于均匀。随肋高不均匀性的增加,其强化传热效果先增强而后趋于稳定,最高可达27.7%。热源温度越高,阶梯形肋片的强化传热效果也越显著。阶梯形肋片可较好地提高装置的热性能,所得结论可为套管式相变蓄热器的优化设计提供参考。
Stepped-fins with variable heights were used in sleeve-tube thermal energy storage units based on equal height rectangular fins to further enhance melting heat transfer. Effects of equal height rectangular fins were analyzed, and effects of non-uniformity of stepped-fin heights as well as heat source temperature were numerically studied by enthalpy model. The results show that iso-height rectangular fins improve melting heat transfer conducted by conduction and nature convection. Solid-liquid interface during melting was distributed asymmetrically along height of the unit. At later stage of the melting process, both melting "dead space" and heat transfer appeared in lower part of the unit. However, the stepped-fins could greatly improve such phenomenon and the melting rate of the whole unit trended to be synchronized. Moreover, increase of non-uniformity shows significant effects on heat transfer enhancement. The maximum thermal storage time reduced is up to 27.7%. In addition, the heat transfer enhancement increases with the increase of heat source temperature. Thermal performance of the unit could be well improved by stepped-fins, which is helpful to the optimal design of sleeve-tube thermal storage units.
Stepped-fins with variable heights were used in sleeve-tube thermal energy storage units based on equal height rectangular fins to further enhance melting heat transfer. Effects of equal height rectangular fins were analyzed, and effects of non-uniformity of stepped-fin heights as well as heat source temperature were numerically studied by enthalpy model. The results show that iso-height rectangular fins improve melting heat transfer conducted by conduction and nature convection. Solid-liquid interface during melting was distributed asymmetrically along height of the unit. At later stage of the melting process, both melting "dead space" and heat transfer appeared in lower part of the unit. However, the stepped-fins could greatly improve such phenomenon and the melting rate of the whole unit trended to be synchronized. Moreover, increase of non-uniformity shows significant effects on heat transfer enhancement. The maximum thermal storage time reduced is up to 27.7%. In addition, the heat transfer enhancement increases with the increase of heat source temperature. Thermal performance of the unit could be well improved by stepped-fins, which is helpful to the optimal design of sleeve-tube thermal storage units.
引文
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[16]Shokouhmand H,Kamkari B.Experimental investigation on melting heat transfer characteristics of lauric acid in a rectangular thermal storage unit[J].Experimental Thermal and Fluid Science,2013,50:201-212.
[2]Nomura T,Akiyama T.High-temperature latent heat storage technology to utilize energy of solar heat and industrial exhaust heat[J].International Journal of Energy Research,2017,41(2):240-251.
[3]YIN Hui-bin(尹辉斌),GAO Xue-nong(高学农),ZHANG Zheng-guo(张正国).Application of phase-change thermal control in heat shock resistance of electronic devices(相变温控应用于电子设备的抗热冲击性能研究)[J].Journal of Chemical Engineering of Chinese Universities(高校化学工程学报),2017,31(3):554-560.
[4]Jegadheeswaran S,Pohekar S D.Performance enhancement in latent heat thermal storage system:a review[J].Renewable&Sustainable Energy Reviews,2009,13(9):2225-2244.
[5]Liu Z,Sun X,Ma C.Experimental investigations on the characteristics of melting processes of stearic acid in an annulus and its thermal conductivity enhancement by fins[J].Energy Conversion&Management,2005,46(6):959-969.
[6]Hosseini S M J.A parametric investigation of a PCM-based pin fin heat sink[J].Mechanical Sciences,2015,6(1):65-73.
[7]Agyenim F,Eames P,Smyth M.A comparison of heat transfer enhancement in a medium temperature thermal energy storage heat exchanger using fins[J].Solar Energy,2009,83(9):1509-1520.
[8]Wang P,Yao H,Lan Z,et al.Numerical investigation of PCM melting process in sleeve tube with internal fins[J].Energy Conversion&Management,2016,110(FEB):428-435.
[9]Lacroix M.Study of the heat transfer behavior of a latent heat thermal energy storage unit with a finned tube[J].International Journal of Heat&Mass Transfer,1993,36(8):2083-2092.
[10]Maryam G,Sezai I.Enhancement of heat transfer in latent heat storage nodules with internal fins[J].Numerical Heat Transfer Part A Applications,2007,53(7):749-765.
[11]Li Z,Wu Z G.Analysis of HTFs,PCMs and fins effects on the thermal performance of shell–tube thermal energy storage units[J].Solar Energy,2015,122(2):382-395.
[12]YANG Xiu(杨秀),CHEN Zhen-qian(陈振乾).Numerical simulation on melting phase change heat transfer in ice storage ball filled with aluminum foam(蓄冰球中填充泡沫铝的融化相变传热过程的数值模拟)[J].Journal of Chemical Industry and Engineering(China)(化工学报),2008,59(s2):139-142.
[13]Cao X,Yuan Y,Xiang B,et al.Numerical investigation on optimal number of longitudinal fins in horizontal annular phase change unit at different wall temperatures[J].Energy&Buildings,2018,158:348-392.
[14]Hu Z,Li A,Gao R,et al.Effect of the length ratio on thermal energy storage in wedge-shaped enclosures[J].Journal of Thermal Analysis&Calorimetry,2014,117(2):807-816.
[15]Hosseini M J,Ranjbar A A,Rahimi M,et al.Experimental and numerical evaluation of longitudinally finned latent heat thermal storage systems[J].Energy&Buildings,2015,99:263-272.
[16]Shokouhmand H,Kamkari B.Experimental investigation on melting heat transfer characteristics of lauric acid in a rectangular thermal storage unit[J].Experimental Thermal and Fluid Science,2013,50:201-212.