新型平底型相变蓄热器蓄热性能的数值模拟

doi:10.19799/j.cnki.2095-4239.2022.0366

摘要/Abstract

摘要：

为了解决相变材料低热导率所引起的换热效果差的问题，向相变材料中添加高导热的金属泡沫材料以加速固液相变过程、提升整体蓄热效率。然而，浮升力导致高温流体堆积在蓄热单元顶部，蓄热单元底部的相变材料较难熔化。为了改善底部难熔的现象，本工作在控制相变材料容积不变的前提下，以一定的比例切除蓄热单元底部，形成新型平底型相变蓄热器。通过数值模拟的方法，对蓄热单元熔化过程中的熔化率、蓄热量、熔化相界面、速度分布和温度分布进行分析。结果表明，新型平底型相变蓄热器能够有效减少底部难熔区域，从而提高蓄热器整体的蓄热效率。其中底部横切比为0.7时，完全熔化时间最短，比圆管缩短了18.12%。通过模拟结果的对比分析可以发现，去除底部相变材料减小了热源到蓄热器底部(难熔区)的距离，增强了熔化末期底部难熔区域的换热。在熔化末期，横切比为0.7的蓄热单元，在相界面处的流速比圆管的提高了2.10倍。说明底部横切强化了熔化末期蓄热单元底部的传热，减小了蓄热单元底部的低温区域，从而推动了整体的熔化进程。

关键词: 金属泡沫, 蓄热器, 相变材料, 平底形状, 数值模拟

Abstract:

This research was conducted to solve the problem of poor heat-transfer efficiency caused by the low thermal conductivity of phase change materials (PCMs). First, metal foams with high thermal conductivity were added to PCMs to accelerate the solid-liquid phase change process, favoring an improvement of the overall heat storage efficiency. Since the buoyancy force caused an accumulation of high-temperature fluid on top of the heat storage unit, PCMs at the bottom were quite difficult to melt. Hence, the bottom of the heat storage unit was cut off at a certain proportion to improve the refractory phenomenon at the bottom under the precise control of the PCM volume. Then, numerical models were established, and simulations were carried out to evaluate melting rate, heat storage, melting phase interface, velocity distribution, and temperature distribution during the melting process. The results demonstrated that cutting off the bottom of the heat storage unit effectively solved the refractory problem at the bottom, improving the overall heat storage efficiency. Notably, when the bottom cross-cut ratio was 0.7, the complete melting time was the shortest, 18.12% shorter than that of the original round tube. However, after managing the bottom cut, the refractory zone was transferred from the bottom to the cutting edge. This transfer reduced the distance between the heat source and the bottom of the regenerator (refractory zone), shortening the overall phase-change heat-storage time. At the end of melting, the flow rate of the melting phase interface with a cross-cut ratio of 0.7 was 2.10 times higher than that of the circular tube. Therefore, these results show that the bottom cross-cut strengthened the heat transfer at the bottom of the heat storage unit, reduced the low-temperature area at the bottom, and promoted the overall melting process.

Key words: metal foam, heat storage tank, phase change materials, flat-bottom shape, numerical simulation

中图分类号:

TK 513

薛洁, 张军, 杜昭, 胡汝坤, 杨肖虎. 新型平底型相变蓄热器蓄热性能的数值模拟[J]. 储能科学与技术, 2022, 11(12): 3855-3861.

Jie XUE, Jun ZHANG, Zhao DU, Rukun HU, Xiaohu YANG. A numerical simulation study on the heat-storage performance of a flat-bottom heat storage tank[J]. Energy Storage Science and Technology, 2022, 11(12): 3855-3861.

图/表 11

图 1

表1

表2

石蜡和铜泡沫的物理性质"

物理性质	石蜡	铜泡沫
$ρ$ /(kg/m³)	800	8920
$c p$ /[J/kg·K]	2000	380
$λ$ /[W/(m·K)]	0.1～0.2	144
$T m$ /K	326～327	—
$L$ /(kJ/kg)	200	—
$γ$ /K^-1	75	—
$μ$ /[kg/(m·s)]	2.508×10^-3	—

表2

图 2

表 3

图 3

图 4

图 5

图 6

图 7

图 8

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案例	h/R	h/mm	R/mm
1	0.5	16.72	33.45
2	0.6	19.44	32.39
3	0.7	22.06	31.52
4	0.8	24.65	30.81
5	0.9	27.26	30.28
6	1.0	30.00	30.00

网格数	时间步长	200 s时P₁点温度/℃	400 s时P₁点温度/℃	600 s时P₁点温度/℃
54510	0.05	53.47	57.915	58.539
107910	0.05	53.438	57.896	58.525
153510	0.05	53.422	57.891	58.523
107910	0.01	53.438	57.897	58.525
107910	0.1	53.438	57.896	58.525

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