Performance investigation of sleeve tube heat exchanger filled with multi-layer phase change materials

doi:10.11949/0438-1157.20190609

Abstract

Abstract:

A horizontal sleeve tube heat exchanger filled with three-layer phase change materials is proposed, and a comprehensive storage density evaluation criterion of the heat storage device is established. Based on the criterion, the effects of separated walls, fin arrangements and direction are numerically predicted and investigated. The results show that the natural convection of PCM (phase change material) is significantly suppressed by separated walls, and the higher the phase change temperature, the more significant the suppression effect. Compared with the sleeve tube heat exchanger without fins, the comprehensive thermal storage efficiency for the exchanger with fins in each layer PCM is improved by 2.27 times. The variations of PCM liquid fraction can be divided into two different stages under various fin arrangement directions, and the evenly arranged fin structure (Case2) has superior thermal storage performance. The non-uniformity of the PCM melting rate in each layer is a key factor that restricts the overall system performance of the thermal storage characteristics. Compared with Case2, the uniformity of the melting rate between different-layer PCMs can be significantly improved by Case5, and the comprehensive thermal storage efficiency is improved by 28.30%.

Key words: solar energy, heat transfer, phase change material, fins optimization, numerical simulation

摘要：

提出一种填充三级相变材料的水平套管式储热器，并建立该储热器的综合性能评价指标，基于该指标数值预测和研究了分隔壁面、翅片布置和方向等参数对系统综合性能的影响。结果表明：分隔壁面对PCM的自然对流有明显的抑制作用，且相变温度越高，抑制效果越显著；相对于无翅片结构，在各级PCM中布置翅片的储热器的综合储热效率提高了约2.27倍；不同翅片布置方向下PCM液相率的变化可分为两个不同阶段，且均匀布置的翅片结构（Case2）具有较优的综合性能；各级PCM间熔化速率的不均匀性是制约系统整体储热性能的关键因素；Case5的翅片布置方式使各级PCM间熔化速率的均匀性明显改善，与Case2相比，其综合储热效率提高了28.30%。

关键词: 太阳能, 传热, 相变材料, 翅片优化, 数值模拟

CLC Number:

TK 512

Ning WANG, Chenyu ZHANG, Hongtao XU, Jianfei ZHANG. Performance investigation of sleeve tube heat exchanger filled with multi-layer phase change materials[J]. CIESC Journal, 2019, 70(S2): 191-200.

王宁, 张晨宇, 徐洪涛, 张剑飞. 填充多级相变材料的套管式储热器性能研究[J]. 化工学报, 2019, 70(S2): 191-200.

Figures/Tables 17

Fig.1 Schematic diagram of horizontal sleeve tube heat exchanger filled with three-layer PCMs

Fig.2 2D model diagram

Table 1 Geometric parameters

R_i/mm	R₁/mm	R₂/mm	R₃/mm	R_o/mm	管壁及翅片厚度/mm
20	60	100	140	160	1

Fig.3 Schematic diagram of fin arrangement

Table 2 Thermal property parameters

材料	熔化温度/℃	密度/(kg·m^-3)	比热容/(J·kg^-1·K^-1)	热导率/(W·m^-1·K^-1)	相变潜热/(J·kg^-1)	动力黏度/(Pa·s)
RT42^[26]	42	760	2000	0.2	165000	0.0235
RT50^[27]	50	760	2000	0.2	160000	0.0275
RT60^[28]	60	770	2000	0.2	160000	0.02853
铜	—	8978	381	387.6	—	—

Fig.4 Computational domain and boundary conditions

Fig.5 Validation of mesh independency

Fig.6 Validation of time step independency

Fig.7 Model validation

Fig. 8 Effect of separated walls on liquid fraction of PCMs

Fig. 9 Temperature and liquid fraction contours of PCM (RT60) with or without separated walls

Fig.10 Temperature and liquid fraction contours of PCM with or without fins

Fig.11 Effect of fins on liquid fraction

Fig.12 Effect of fins on liquid fraction of each-layer PCMs

Fig.13 Effect of fin direction on liquid fraction

Fig.14 Melting time of each-layer PCMs at different fin angles

Fig.15 Variation of liquid fraction of each PCMs in Case2 and Case5

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