Numerical study of transient heat transfer performance for molten salt receiver tube

doi:10.11949/0438-1157.20200221

Abstract

Abstract:

The heat transfer experimental system and mathematical model of receiver tube are established to analyze the transient heat transfer performance of molten salt with heat flux of outer wall sudden change, molten salt velocity sharp reduction, heat flux of outer wall and molten salt velocity sharp reduction at the same time. The results show that when the heat flow on the outer wall of the tube changes suddenly (sudden increase or decrease), the temperature of the molten salt in the center of the tube at the inlet section of the heat absorption tube changes less, but the temperature of the tube wall changes faster. When the molten salt velocity sharp reduction, the outlet temperature of molten salt and the outer wall temperature increase with time, but the difference of outer wall and inner wall temperature decreases at first and then increases, when t≥16.0 s, each temperature and temperature difference reach steady state. When the heat flux on the outer wall of the heat absorption tube and the molten salt flow rate in the tube are halved at the same time, the temperature of the molten salt in the center and the outlet of the tube rises first and then decreases with the passage of time. After the steady state, the two molten salt temperatures maintain a constant value and are compared with the transient state. The corresponding molten salt temperature is close to initial starting temperature. The difference of outer wall and inner wall temperature after transient stability is proportional to the heat flux of outer wall, but which is independent of molten salt velocity. The outlet temperature equation of molten salt in receiver tube after transient stability is obtained, which provides a theoretical basis for the outlet temperature control of molten salt in receiver during the transient heat transfer process.

Key words: molten salt, receiver tube, heat transfer, solar energy, numerical simulation

摘要：

建立熔盐吸热管瞬态传热的实验台和数值计算模型，分析管外壁热通量突变、熔盐流速突减、外壁热通量和熔盐流速同时突减对吸热管瞬态传热特性的影响规律，结果表明：管外壁热通量突变（突增或突减）时，吸热管入口段的管中心熔盐温度变化较小，但其管壁温度变化较快。管内熔盐流速突减时，熔盐出口温度和管外壁温度均随时间的推移逐渐增大，而管外壁与管内壁温差随时间的推移先降低后升高，t≥16.0 s，各温度和温差基本稳定。吸热管外壁热通量和管内熔盐流速同时减半时，管中心及出口熔盐温度均随时间的推移先升高后降低，稳态后两处熔盐温度保持定值且与瞬态开始前对应熔盐温度接近。吸热管瞬态稳定后的管外壁与管内壁温差和管外壁热通量变化呈正比，与熔盐流速变化无关。得到瞬态稳定后吸热管熔盐出口温度表达式，为瞬态传热过程中吸热器熔盐出口温度控制提供理论依据。

关键词: 熔盐, 吸热管, 传热, 太阳能, 数值模拟

CLC Number:

TK 124

Xiangyang SHEN,Jing DING,Jianfeng LU. Numerical study of transient heat transfer performance for molten salt receiver tube[J]. CIESC Journal, 2020, 71(11): 5140-5149.

沈向阳,丁静,陆建峰. 熔盐吸热管瞬态传热特性的数值研究[J]. 化工学报, 2020, 71(11): 5140-5149.

Figures/Tables 12

Fig.1 Physical model of receiver tube with transient heat transfer

Fig.2 Experimental system

Fig.3 Outlet temperature of molten salt with simulation and experiment

Fig.4 Temperature responses of wall and molten salt at outlet (qtran=0→201.8 kW/m2)

Fig.5 Temperature responses of tube center and wall (qtran=0→201.8 kW/m2)

Fig.6 Temperature responses of Tout and Tow, Tow-Tw, Tw-Tf0 at x=0.65 m (qtran=0→201.8 kW/m2)

Fig.7 Temperature responses of tube center and wall (qtran=201.8→100.9 kW/m2)

Fig.8 Temperature responses of Tout and Tow, Tow-Tw, Tw-Tf0 at x=0.65 m (qtran=201.8→100.9 kW/m2)

Fig.9 Temperature responses of tube center (uin=2.98→1.49 m/s)

Fig.10 Temperature responses of Tout and Tow, Tow-Tw, Tw-Tf0 at x=0.65 m (uin=2.98→1.49 m/s)

Fig.11 Temperature responses of tube center (qtran=201.8→100.9 kW/m2，uin=2.98→1.49 m/s)

Fig.12 Temperature responses of Tout and Tow, Tow-Tw, Tw-Tf0 at x=0.65 m (qtran=201.8→100.9 kW/m2，uin=2.98→1.49 m/s)

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