Numerical analysis of local flow and heat transfer of FCC domain in pebble bed reactor

doi:10.11949/0438-1157.20190622

Abstract

Abstract:

The existence of hot spots on the surface of pebbles in pebble reactors affects the safety of the reactor and its formation is closely related to the local flow of coolant at the pebble scale. In order to ensure the accuracy and physical reality of the solution, the large eddy simulation (LES) method and the fully structured grid are applied to conduct the numerical analysis of the local flow and heat transfer of the face-centered cubic (FCC) unit in the area contact arrangement mode. The characteristics of unsteady flow and its effect on convective heat transfer are analyzed. The time-averaged temperature distribution indicates that there are stable hot spots on the surface of pebbles, and it is also found that the instantaneous temperature fluctuation on the surface of pebble is large, and there are also instantaneous hot spots where the temperature is significantly higher than the time-averaged temperature.

Key words: fixed-bed, convection, face-centered cubic, LES, structured grid, area contact, numerical analysis

摘要：

球床反应堆燃料球表面局部热点的存在影响到反应堆的安全，其形成与燃料球尺度的冷却剂局部流动密切相关。为保证计算结果的准确性和物理真实性，采用大涡模拟(LES)方法和全结构网格对面心立方(FCC)单元面接触排列方式的局部流动和传热进行了数值分析。研究分析了非定常流动的特点及其对对流换热的影响。燃料球表面的时均温度分布表明燃料球表面存在稳定的热点或热斑，也发现瞬时温度波动较大，存在明显高于时均值的瞬时热点。

关键词: 固定床, 对流, 面心立方, 大涡模拟, 结构网格, 面接触, 数值分析

CLC Number:

TK 11⁺2

Qiang YAO, Xueyan GUO, Fan YANG, Zhiyuan WANG. Numerical analysis of local flow and heat transfer of FCC domain in pebble bed reactor[J]. CIESC Journal, 2019, 70(S2): 161-168.

姚强, 郭雪岩, 杨帆, 王志远. 球床反应堆面心立方单元局部流动与传热的数值分析[J]. 化工学报, 2019, 70(S2): 161-168.

Figures/Tables 16

Fig.1 Pebble bed packing methods (a) and contact modes between pebbles (b)

Fig.2 Calculation model

Table 1 Physical property parameters[14]

参数	氦气	石墨
密度/(kg/m³)	5.36	1750
动力黏度/(N·s/m²)	3.69e^-5	—
热导率/(W/(m·K))	0.3047	25
比热容/(J/(kg·K))	5441.6	1690

Fig.3 FCC cell grid with area contact

Fig.4 Grid applicability verification

Fig.5 Slice positions

Fig.6 Stagnation and wake region of spherical central region

Fig.7 Instantaneous velocity and temperature distributions

Fig.8 Time-averaged velocity and temperature distributions

Fig.9 Instantaneous streamline charts of section areas

Fig.10 Three area contact positions

Fig.11 Instantaneous temperature distributions on surface of central pebble and instantaneous velocity distributions

Fig.12 Time-averaged temperature distributions on surface of central pebble and time-averaged velocity distributions at 0.5 mm away from sphere

Fig.13 Time-mean distributions of angle between velocity and temperature gradient in flow field at 0.5 mm away from fuel sphere

Fig.14 Positions of extracted lines

Fig.15 Instantaneous and time-mean temperature distributions on lines

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