Research on natural convection heat transfer of molten salts on vertical cylinder surface during heat storage

doi:10.3969/j.issn.1674-1951.2021.07.009

Abstract

Abstract:

In order to obtain the natural convection heat transfer law by of molten salts on the surface of vertical cylinders during heat charging,a numerical simulation was made on the natural convection heat transfer around a cylinder array with 2 to 8 vertical pillars whose cylindrical spacing （ S/D）=5~10 （S is the distance between two adjacent cylinders,D is the diameter of the cylinder）.The results show that the natural convection heat transfer on each cylinder surface is related to the position of the cylinder in the row and the its S/D.The average Nu（Nu_a）of the natural convection heat transfer made by molten salt around the whole cylinder array is determined by the S/D,the number of cylinders（N） and Ra.When S/D is small（S/D=5）,the Nu_a of natural convection heat transfer of molten salt on the cylinders' surface will decrease with the number of cylinders in the row.When S/D is large（S/D=10）,the Nu_a of natural convection heat transfer on the cylinders' surface will augment with the number of cylinders in the row.The research results can provide theoretical basis for the design of molten salt heat storage device.

Key words: natural convection, molten salt, cylinder array, cylindrical spacing, Nu, Ra, heat transfer law, carbon neutrality

CLC Number:

TK124

YU Qiang, HE Cong, ZHI Ruiping, LU Yuanwei, WU Yuting, YANG Guichun. Research on natural convection heat transfer of molten salts on vertical cylinder surface during heat storage[J]. Huadian Technology, 2021, 43(7): 54-61.

Figures/Tables 12

Fig.1

Fig.2

Fig.3

Fig.4

Fig.5

Fig.6

Tab.1

Fig.7

Fig.8

Fig.9

Fig.10

Fig.11

References 20

[1]	LIU M, TAY S N H, BELL S, et al. Review on concentrating solar power plants and new developments in high temperature thermal energy storage technologies[J]. Renewable and Sustainable Energy Reviews, 2016, 53:1411-1432. doi: 10.1016/j.rser.2015.09.026
[2]	ACHKARI O, FADAR A E. Latest developments on TES and CSP technologies-energy and environmental issues, applications and research trends[J]. Applied Thermal Engineering, 2020, 167:1359-4311.
[3]	AWAN A B, ZUBAIR M, PRAVEEN R P, et al. Design and comparative analysis of photovoltaic and parabolic trough based CSP plants[J]. Solar Energy, 2019, 183:551-565. doi: 10.1016/j.solener.2019.03.037
[4]	徐其利, 孙杰. 用于太阳能光热发电系统的CaO/Ca(OH)₂化学储热技术综述[J]. 华电技术, 2020, 42(4):1-11.
	XU Qili, SUN Jie. Review of CaO/Ca(OH)₂ chemical heat storage technology for CSP [J]. Huadian Technology, 2020, 42(4):1-11.
[5]	HUANG Z J, ZOU Y K, WEI X L, et al. Mixed convection heat transfer of molten salt outside coiled tube[J]. International Communications in Heat and Mass Transfer, 2021, 120(2).DOI: 10.1016/j.icheatmasstransfer.2020.105004.
[6]	CHEN H, CHEN X, WU Y T, et al. Experimental study on forced convection heat transfer of KNO₃-Ca(NO₃)₂+SiO₂ molten salt nanofluid in circular tube[J]. Solar Energy, 2020, 206:900-906. doi: 10.1016/j.solener.2020.06.061
[7]	韩伟, 崔凯平, 赵晓辉, 等. 光热电站储热系统设计及储罐预热方案研究[J]. 华电技术, 2020, 42(4):42-46.
	HAN Wei, CUI Kaiping, ZHAO Xiaohui, et al. Design for CSP plants' energy storage system and research on preheating strategy with tanks[J]. Huadian Technology, 2020, 42(4):42-46.
[8]	崔凯平, 韩伟, 倪煜, 等. 熔盐储罐热分层混温过程研究[J]. 华电技术, 2020, 42(5):8-13.
	CUI Kaiping, HAN Wei, NI Yu, et al. Research on thermal stratification and control process in molten salt storage tanks[J]. Huadian Technology, 2020, 42(5):8-13.
[9]	LU Y W, ZHANG Y H, ZHANG C C, et al. Experimental study on heat discharging characteristic of single tank with different annular baffle conditions[J]. International Journal of Energy Research, 2020, 44:11434-11442. doi: 10.1002/er.v44.14
[10]	ZHANG C C, SHI S L, LU Y W, et al. Heat discharging and natural convection heat transfer performance of coil heat exchanger in single molten salt tank[J]. Applied Thermal Engineering, 2020, 166.DOI: 10.1016/j.applthermaleng.2019.114689.
[11]	YOUSEFI T, ASHJAEE M. Experimental study of natural convection heat transfer from vertical array of isothermal horizontal elliptic cylinders[J]. Experimental Thermal and Fluid Science, 2007, 32:240-248. doi: 10.1016/j.expthermflusci.2007.04.001
[12]	REYMOND O, MURRAY D B, O'DONOVAN T S. Natural convection heat transfer from two horizontal cylinders[J]. Experimental Thermal and Fluid Science, 2008, 32(8):1702-1709. doi: 10.1016/j.expthermflusci.2008.06.005
[13]	SPARROW E M, NIETHAMMER J E. Effect of vertical separation distance and cylinder-to-cylinder temperature imbalance on natural convection for a pair of horizontal cylinders[J]. Journal of Heat Transfer, 1981, 103:638-644. doi: 10.1115/1.3244520
[14]	ZAHRA R, NENAD S. Natural convection heat transfer from a bundle of heated circular cylinders with staggered arrangement immersed in molten solar salt[J]. International Journal of Heat and Mass Transfer, 2020, 156.DOI: 10.1016/j.ijheatmasstransfer.2019.119032.
[15]	ZAHRA R, NENAD S. Natural convection heat transfer from a bundle of in-line heated circular cylinders immersed in molten solar salt[J]. International Journal of Heat and Mass Transfer, 2020, 148.DOI: 10.1016/j.ijheatmasstransfer.2019.119032.
[16]	LU Y W, YU Q, DU W B, et al. Natural convection heat transfer of molten salts around a vertically aligned horizontal cylinder set[J]. International Communications in Heat & Mass Transfer, 2016, 76:147-155.
[17]	CORCIONE M. Correlating equations for free convection heat transfer from horizontal isothermal cylinders set in a vertical array[J]. International Journal of Heat & Mass Transfer, 2005, 48(17):3660-3673.
[18]	REN N, WU Y T, MA C F, et al. Preparation and thermal properties of quaternary mixed nitrate with low melting point[J]. Solar Energy Materials & Solar Cells, 2014, 127:6-13. doi: 10.1016/j.solmat.2014.03.056
[19]	张晓盼, 鹿院卫, 于强, 等. 超声-微波法制备熔盐纳米复合材料试验研究[J]. 华电技术, 2020, 42(4):12-16.
	ZHANG Xiaopan, LU Yuanwei, YU Qiang, et al. Experimental study on preparation of a molten salt nanocomposite by ultrasonic dispersion and microwave method[J]. Huadian Technology, 2020, 42(4):12-16.
[20]	陈睿哲, 熊亚选, 张慧, 等. 储能供热熔盐换热器设计及运行特性分析[J]. 华电技术, 2020, 42(12):54-59.
	CHEN Ruizhe, XIONG Yaxuan, ZHANG Hui, et al. Design and dynamic performance analysis on a molten salt heat exchanger for energy storage and heating[J]. Huadian Technology, 2020, 42(12):54-59.

项目	底部圆柱表面的局部对流换热系数
项目	h₁	h₂	h₃	h₄	h₅
S/D=5	727.45	768.35	751.76	731.84	713.89
S/D=6	732.84	791.61	782.61	767.12	752.60
S/D=7	726.86	809.26	806.97	796.07	783.46
S/D=8	723.51	823.89	827.47	820.36	810.19
S/D=9	723.55	837.15	845.81	841.75	833.55
S/D=10	723.98	848.55	861.95	860.49	854.53