电热水器内部结构优化及储能特性研究

doi:10.12034/j.issn.1009-606X.220206

摘要/Abstract

摘要：

将相变储能技术应用于电热水器，并通过添加石墨纳米颗粒改善相变材料的导热特性，对其储能过程进行调节，可以起到“移峰填谷”的作用。建立了四种不同结构的电热水器三维模型，模拟了电热水器内部速度场与温度场分布特性。考察了进出口水管结构、电加热管布置方式、保温层结构等因素对热水器内部流场及传热特性的影响，研究了不同储能层厚度对电热水器储能的影响。结果表明，水平加热管与垂直加热管相比，加热过程中加热效率提高了2.2%；进水管管径增大1.5倍，热水输出率提升了17.9%；加入相变材料可在相同保温时间内(36 h)使水温最大提高10.6%。

关键词: 电热水器, 相变材料储能技术, 数值模拟, 移峰填谷

Abstract:

The energy consumption of electric water heater in China has a large proportion of total energy consumption. Therefore, it is of great significance to optimize the energy consumption process of electric water heater. The phase change materials (PCM) have the characteristics of high energy storage density and approximately constant temperature in the process of phase transition. In addition, the thermal conductivity of phase change materials can be enhanced by adding nanometer materials such as graphite. Therefore, it has obvious advantages in heat energy storage and utilization of phase change materials. So, the phase change energy storage technology can be applied to electric water heater to adjust the energy storage process and the goal of "peak shifting" also can be achieved. In this work, the energy storage characteristic of energy storage water heater with phase change material were researched employing numerical simulation method. Four different structural models were established and the influent of inlet and outlet piping construction, electric heating tube arrangement, insulation structure on flow and heat transfer characteristics of water in water heater were discussed. And the influence of energy storage layer thickness on energy storage of electric water heater were researched. The results showed that, compared with the vertical heating tube, the water temperature distribution of horizontal heating tube was more uniform during heating process, and the heating efficiency was improved by about 2.2%. When the inlet tube diameter increased to 1.5 times, the output status of hot water can be excellent improved, and the hot water output efficiency can be increased 17.9%. The addition of phase change materials can increase the water temperature by 10.6% under the condition of same heat preservation time (36 h). The results of this study can provide data support for structural optimization of electric water heater and application of phase change energy storage technology.

Key words: electric water heater, phase-change thermal energy storage technology, numerical simulation, peak load shifting

中图分类号:

TB34

吴丽, 何杰, 鲁进利, 韩亚芳, 洪泽. 电热水器内部结构优化及储能特性研究[J]. 过程工程学报, 2021, 21(7): 786-793.

Li WU, Jie HE, Jinli LU, Yafang HAN, Ze HONG. Research on internal structure optimization and energy storage characteristics of electric water heater[J]. The Chinese Journal of Process Engineering, 2021, 21(7): 786-793.

图/表 13

图1 电热水器内部结构示意图

Fig.1 Schematic diagram of internal structure of electric water heater

表1 不同结构电热水器

Table 1 Different structure electric water heaters

Case	Structure
1	Vertical heating tube+normal inlet pipe diameter
2	Horizontal heating tube+normal inlet pipe diameter
3	Vertical heating tube+1.5 times diameter of the inlet pipe
4	Horizontal heating tube+1.5 times diameter of the inlet pipe

图2 含PCM的电热水器保温层示意图

Fig.2 Schematic diagram of insulation layer of electric water heater with PCM

表2 保温材料的物性参数

Table 2 Physical properties of thermal insulation materials

Material

Phase change temperature/℃

Latent heat/(kJ/kg)

Specific heat/

[J/(kg·K)]

Heat conductivity coefficient/[W/(m·K)]

Paraffine+10wt% Graphite^[18]

图3 不同加热功率对加热时间的影响

Fig.3 The effect of different heating powers on heating time

图4 加热完成后热水温度分布(单位：℃)

Fig.4 Temperature distribution of hot water after heating (Unit: ℃)

图5 加热完成时温度沿高度的分布

Fig.5 Temperature distribution along height when heating completed

图6 进水30 s时电热水器内水流速度矢量图

Fig.6 Velocity vector diagrams in the electric water heater for 30 s water intake

图7 进水60 s时电热水器内温度分布

Fig.7 Temperature distributions in the electric water heater for 60 s water intake

图8 热水器出口温度随时间变化

Fig.8 Variation of outlet temperature of electric water heater with heating time

表3 不同方案热水输出率

Table 3 The hot water output rate under different schemes

Parameter	Case 1	Case 2	Case 3	Case 4
Maximum temperature/℃	68.72	68.56	68.86	68.28
Minimum temperature/℃	48.02	47.99	48.47	48.45
Time/s	370	390	430	460
Water quality/kg	30.25	31.89	35.16	37.62
Water temperature/℃	63.53	63.49	63.82	63.50
Shutdown temperature/℃	63.27	63.35	63.27	63.35
Hot water output rate/%	62.00	65.20	72.48	76.90

图9 不同相变材料熔化过程液相率变化曲线

Fig.9 Variation curve of liquid phase ratio during melting of different phase change materials

图10 不同相变层厚度对保温过程中热水器平均水温的影响

Fig.10 The influence of different thicknesses of PCM on the average water temperature of electric water heater during heat preservation process

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