Simulated optimization of eccentricity and fin structure of a horizontal double-tube latent heat storage unit

doi:10.19799/j.cnki.2095-4239.2023.0758

Abstract

Abstract:

Enhancing natural convection inside a phase change material (PCM) improves the performance of latent heat storage (LHS) systems. To investigate the impact of eccentric arrangement in detail, a three-dimensional numerical model was established for the horizontal double-pipe LHS unit based on the enthalpy-void fraction method, and the melting process of the PCM in annular space was simulated using Fluent software. Analyses of the flow field, temperature, and liquid fraction contours during the melting process lead to the melting process being divided into three stages: the initial stage in which heat conduction predominates, followed by the concurrent action of natural convection and heat conduction, and the final stage in which heat conduction dominates again. The corresponding annular space of PCM can be divided into two regions, and a new evaluation parameter called the "eccentric area ratio" is proposed accordingly. The results showed that the optimal eccentric area ratio is approximately 16∶1 for the PCM stearic acid. The melting time decreases by 45.8% compared with that of the concentric structure, whereas the energy efficiency of the LHS unit decreases slightly. The optimal eccentric area ratio for other materials should be directly related to the ratio of the natural convection intensity to the heat conduction of the material. Combining the eccentric structure with fins further enhances heat transfer. The results show that the X-shaped fins perform best; the melting time decreases by 36.7%, 20.3%, and 7.1% compared with that of the smooth structure, helical fins, and cross-shaped fins, respectively.

Key words: latent heat storage, eccentric area ratio, fin, heat transfer enhancement, exergy efficiency

CLC Number:

TK 02

Ludi ZHANG, Guobing ZHOU. Simulated optimization of eccentricity and fin structure of a horizontal double-tube latent heat storage unit[J]. Energy Storage Science and Technology, 2024, 13(3): 1019-1029.

Figures/Tables 14

Fig. 1

Table 1

Fig. 2

Fig. 3

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Table 2

Eccentric distance y corresponding to each eccentric area ratio"

偏心面积比 $ε$	偏心距离y/mm
同心布置	0
4∶1	4.49
8∶1	7.69
16∶1	9.92
24∶1	10.86

Table 2

Fig. 7

Fig. 8

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物性参数	硬脂酸	水	铜
固体密度，ρ_S/(kg/m³)	965	—	8798
液体密度，ρ_L/(kg/m³)	862	998.2	—
导热系数，k/[W/(m/K)]	0.162	0.670	387.6
相变潜热，L_PCM/(kJ/kg)	220.8	—	—
固相线温度，T_S/K	340.13	—	—
液相线温度，T_L/K	344.05	—	—
固态定压比热容，C_p_S/[kJ/(kg/K)]	2.27	—	0.381
液态定压比热容，C_p_L/[kJ/(kg/K)]	1.76	4.197	—
黏度，μ/[kg/(m/s)]	0.00631	0.0003543	—
热膨胀系数，β/K^-1	0.00005	—	—

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