Investigation of heat transfer enhancement mechanism and performance of phase change materials using expanded graphite in double helical coils

doi:10.19799/j.cnki.2095-4239.2023.0717

Abstract

Abstract:

This paper presents a novel structure for a phase change heat storage system incorporating double spiral coils and expanding graphite to enhance heat transfer. A model of the double spiral coil phase change heat storage system is established to simulate the impact of coil pitch and thermal properties of materials on heat storage and release performance. The study delves into the influence of natural convection of phase change materials and the enhancement of material thermal conductivity on heat transfer in confined spaces. Results indicate that reducing the pitch and increasing the number of spiral coils within limited pitch conditions can enhance the heat release performance of the heat storage system. Incorporating expanded graphite boosts the thermal conductivity of phase change materials, albeit with an increase in material viscosity. Consequently, adding the expanded graphite improves the heat transfer and exchange efficiency of the heat storage system, albeit at the cost of suppressing natural convection heat transfer. Comparative analysis reveals that, under confined space conditions, the enhanced heat transfer resulting from material thermal conductivity enhancement compensates for the heat loss attributed to inadequate natural convection heat transfer. This study underscores that the key to controlling heat transfer enhancement in phase change heat storage systems lies in the thermal conductivity enhancement of materials. Drawing on experimental and simulation approaches, this article presents a designed heat storage system structure for heating domestic hot water. The proposed system exhibits excellent heat release performance across a broad range of inlet temperatures and flow rates. When combined with an electric heater, this heat storage system achieves a heating power exceeding 3500 W with electric power consumption below 2200 W, surpassing the power limitations of typical household electric heating equipment.

Key words: double spiral coil tube, phase change heat storage exchanger, numerical simulation, enhanced thermal conductivity, natural convection

CLC Number:

TK 02

Yanqin GUO, Zhen ZENG, Hongguang ZHANG, Ziye LING, Zhengguo ZHANG, Xiaoming FANG. Investigation of heat transfer enhancement mechanism and performance of phase change materials using expanded graphite in double helical coils[J]. Energy Storage Science and Technology, 2023, 12(12): 3678-3689.

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仪器名称	型号	主要参数	生产厂家
液体涡轮流量计	RZ-LD15	流量范围：0～50 L/h 精度：0.5%	淮安润中仪表科技有限公司
电热恒温鼓风干燥箱	DHG-9070A	控温精度：±1℃	上海齐欣科学仪器有限公司
恒温槽	CK-4007GD	控温精度：±1℃	宁波新芝生物科技股份有限公司
水泵	15WZ10-15	—	玉环市楚门金龙水泵厂
数据采集仪	34970A	热电偶精度：±0.1℃	安捷伦科技有限公司
电源	HY3003E	电压和电流范围：30 V，3 A 电压精度：0.1%	杭州华谊电子实业有限公司

螺旋数/圈	螺距/mm	换热面积/cm²	复合相变材料填充质量/g
5	16	379.2	393.4
6	13.3	448	384.6
7	11.4	521.6	374
8	10	592	363.7
9	8.8	662.4	352.7
10	8	732.8	342.6

物理性质	石蜡	不锈钢
ρ /(kg/m³)	850	8030
c_p /[J/(kg · K)]	1600	502
λ /[W/(m · K)]	0.2～0.24	16
T_m/K	351～354	—
μ/cP	17	—

CPCM种类	EG质量分数/%	热导率 /[W/(m·K)]	相变焓 /(J/g)	黏度 /mPa·s
0	0	0.23	264.90	17.00
1	1	0.50	262.25	52.23
2	2	0.65	259.60	585.57
3	3	0.86	256.95	1708.20
4	4	1.30	254.30	4166.89
5	5	1.70	251.65	固体

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