Simulation studies on heat transfer characteristics of PCM micro-encapsulated fluids based on discrete phase model

doi:10.11949/0438-1157.20190964

Abstract

Abstract:

Micro-encapsulated phase change material slurry is a new type of heat transfer media which consists of microencapsulated phase change particles and a single-phase heat fluid. Due to the advantages of high coefficient of heat transfer, integration of heat transfer and energy storage, the new media has great development potential. In this paper, we used discrete phase model to numerically analyze the heat transfer characteristics of micro-encapsulated slurry in horizontal circular tube under constant heat flux. The model is verified by comparing with the experimental results. The effects of particle size, mass fraction, phase change latent heat, especially particle distribution on heat transfer were quantitatively analyzed. The results show that as the mass fraction of microcapsules increases, particle size decreases, latent heat of phase change increases, the heat transfer at wall is better. Moreover, the effect of latent heat on wall temperature control and heat transfer is greater than that of particle mass fraction and particle size. The calculation results of the discrete phase model and the commonly used single-phase flow model are compared. It is found that the higher the mass fraction, the higher the degree of particle aggregation, and the greater the deviation of the single-phase flow model.

Key words: CFD, phase change, microcapsule, particle size distribution, convective, heat transfer

摘要：

相变材料微胶囊悬浮液是将相变微胶囊颗粒添加至单相流体中形成的一种新型传热介质，由于传热系数高、传热储能一体化等优势，具备很大的发展潜力。采用离散相两相流模型，对恒热流水平圆管中相变微胶囊流体的传热特性进行了模拟计算，通过对比实验数据验证了模型的可靠性，进而定量分析了颗粒尺寸、质量分数、相变潜热，特别是颗粒分布对传热的影响。结果表明随着微胶囊颗粒质量分数增加，颗粒粒径减小，相变潜热增大，壁面传热效果越好，且相变潜热大小对壁温控制和壁面传热的影响大于颗粒质量分数和颗粒尺寸的影响。比较了离散相模型与常用的单相流模型的计算结果，发现质量分数越高，颗粒集聚程度越高，单相流模型计算的偏差越大。

关键词: 计算流体力学, 相变, 微胶囊, 粒度分布, 对流, 传热

CLC Number:

TK 01⁺8

Xinghui WU, Zhen YANG, Ying CHEN, Yuanyuan DUAN. Simulation studies on heat transfer characteristics of PCM micro-encapsulated fluids based on discrete phase model[J]. CIESC Journal, 2020, 71(4): 1491-1501.

吴兴辉, 杨震, 陈颖, 段远源. 基于离散相模型的相变微胶囊流体传热特性数值模拟[J]. 化工学报, 2020, 71(4): 1491-1501.

Figures/Tables 15

Fig.1 Schematic diagram of MPCS

Fig.2 Mathematical domain

Table 1 Physical properties of PMMA and paraffin

材料	ρ/(kg/m³)	c_p /(J/(kg·K))	k/(W/(m·K))	?H/(kJ/kg)
PMMA	1,190	1,470	0.21
石蜡	931.4	2,136	0.2	190

Fig.3 Schematic diagram of equivalent specific heat method

Fig.4 Comparisons between numerical results and experimental results: temperature of MPCS along pipe

Fig.5 Numerical results when Re = 900, mass fraction = 5%, particle size = 10 μm

Fig.6 Wall temperature and Nusselt number distribution under different particle mass fraction

Table 2 Comparison of microcapsules with different mass fraction

质量分数ω/%	?T/K	?T减小/%	Nu	提升/%
2	3.69	—	9.83	—
5	3.18	13.8	10.1	2.44
8	2.9	21.4	10.2	3.76

Fig.7 Wall temperature and Nu distribution under different particle size

Table 3 Comparison of microcapsules with different particle size

粒径大小/μm	?T/K	?T减小/%	Nu	提升/%
100	4	—	9.69	—
50	3.84	4	9.76	0.72
10	3.18	20.5	10.1	3.92

Fig.8 Wall temperature and Nu distribution under different latent heat

Table 4 Comparison of microcapsules with different latent heat

微胶囊	?T/K	?T减小/%	Nu	提升/%
不发生相变的微胶囊	3.9	—	9.74	—
常规相变的微胶囊	3.18	18.5	10.1	3.39
相变潜热为正常值两倍时的相变微胶囊	2.98	23.6	10.2	4.31

Fig.9 Comparison of two models under different mass fractions

Table 5 Comparison between discrete phase model and single phase model

模型	离散相	单相流	相对偏差/%
2%出流面?T/K	3.69	4.21	14.1
2%壁面Nu	9.83	9.60	-2.34
5%出流面?T/K	3.18	3.70	16.4
5%壁面Nu	10.1	9.83	-2.38
8%出流面?T/K	2.90	3.40	17.2
8%壁面Nu	10.2	9.96	-2.35

Fig.10 Concentration and temperature distribution of middle stream surface under different mass fraction

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