Study on whole process characteristic of heat transfer in solar heating system with heat storage

doi:10.11949/0438-1157.20210480

Abstract

Abstract:

The heat storage type solar heating system based on low temperature radiation heat dissipation is studied. The heat collection characteristics and the heat absorption/exothermic characteristics of phase change heat storage material of the system were analyzed. Variation of temperature field inhomogeneity in phase change heat storage unit was revealed. At the same time, the heat transfer rate of the phase change heat storage unit and the comprehensive utilization ability of solar energy of the system were measured. The operation condition of capillary network was optimized and the system economy was discussed. The results show that in the heat collection and storage stage, the temperature field inhomogeneity of the phase change heat storage unit increases linearly from 0.0265 to the peak value of 0.11 in the heat storage and heating range from 38℃ to 47.7℃. In the range of 47.7℃ to 53.9℃ for heat storage, the temperature field unevenness of the phase change heat storage unit decreases from the peak value of 0.11 to the turning point of 0.0603 with a nearly linear regularity. And the turning point is near the melting point (freezing point). After melting point (freezing point), the unevenness of temperature field tends to stable state distribution. In the stage of heat release and heat dissipation, the internal temperature field of phase change heat storage unit maintains the minimum steady-state uniformity (around 0.020) in the range of 57.9℃ to 55℃. After melting (solidification) temperature point, in the exothermic cooling range of 55℃ to 47.3℃, the temperature field uniformity increases from 0.0238 in a nearly linear pattern to the peak value of 0.0952, and the peak value is near the exothermic solidification peak. After the peak value, the unevenness of temperature field decreases with the heat release time. The effective heat storage of the phase change heat storage unit is 5.0911 MJ, and the heat storage density is 181.51 J/g. The average heat storage rate and average heat release rate are basically the same, which are 1.829 MJ/h and 1.803 MJ/h respectively. In the solar heating system, the efficiency of heat collection and heat storage is 0.3648, the heat release and heat dissipation efficiency is 0.5843, and the comprehensive utilization capacity of solar energy is 0.2132. When the inlet temperature of capillary network is higher than 40℃, the heat dissipation power increases linearly with the inlet temperature, and when the inlet temperature is higher than 52℃, the heat dissipation power stabilizes around 410 W. When the inlet temperature of the capillary network is less than 40℃, the heat dissipation power increases linearly with the inlet temperature, and there is a single peak value of 262 W. When the inlet temperature and heat dissipation temperature difference of the capillary network are 36℃ and 8℃ respectively, the maximum heat dissipation capacity of the capillary network is 65.5 W/m². In heat storage type solar heating system, the optimal ratio of effective heat collection area to heating area is 0.4, the optimal ratio of phase change material mass to effective heat collection area is 15 kg/m², the optimal ratio of heat dissipation area and heating area is 0.35, the initial investment per unit heating area is 225.8 CNY/m², the operation and maintenance cost per unit area is 4.28 CNY/m², and the static investment payback period of the system is 8.7 years. The research has important guiding significance to improve the reliability of heat storage type solar heating system.

Key words: phase change, heat storage, solar energy, heating system, heat transport, characteristics, optimization

摘要：

研究了基于低温辐射散热的储热型太阳能供暖系统。分析了平板热管型太阳能集热器的集热特性和相变储热材料的吸/放热特性，揭示了相变储热单元温度场不均匀度的变化规律，测定了相变储热单元的热传输速率及系统的太阳能综合利用能力，优化了毛细管网运行条件，讨论了系统经济性。结果表明：平板热管型太阳能集热器热损系数为5.5447 W/（m²·K），截距效率为86%；相变储热材料熔点及相变焓分别为55.69℃、163.09 J/g；相变储热单元温度场不均匀度在储热/放热阶段的变化趋势基本一致，平均储热速率和放热速率分别为1.829、1.803 MJ/h；系统的太阳能综合利用能力为0.2132；毛细管网的最佳进口温度和散热温差分别为36、8℃；系统初投资和运维成本分别为225.8、4.28元/m²，静态投资回收期为8.7年。

关键词: 相变, 储热, 太阳能, 供暖系统, 热输送, 特性, 优化

CLC Number:

TK 512

Xiao GUO,Yunfeng QIU,Zhiguo SHI,Yahui WANG,Li SONG,Rui TIAN. Study on whole process characteristic of heat transfer in solar heating system with heat storage[J]. CIESC Journal, 2021, 72(10): 5384-5395.

郭枭,邱云峰,史志国,王亚辉,宋力,田瑞. 储热型太阳能供暖系统热输送全过程特性研究[J]. 化工学报, 2021, 72(10): 5384-5395.

Figures/Tables 14

Fig.1 Test schematic diagram

Table 1 Type and specification of key unit

名称	型号规格
平板热管型太阳能集热器	100 L(2 m²)
毛细管网	U20(4 m²)
循环泵	12 WZR-8

Fig.2 Meshing heat exchanger

Fig.3 Layout of temperature measuring points

Table 2 Type and main technical parameters of instruments and meters

名称	型号	量程/采样频率	精度/最小分度值
一等标准水银温度计	WLB	0~75℃	±0.05℃
电子天平	JA31002	0~3.1 kg	0.01 g
分析天平	ES1035B	0~31 g	0.01 mg
玻璃浮子流量计	LZB-15	40~400 L/h	±1.5%
太阳总辐射表	LI-200X	0~2000 W/m²	±3%
环境温度传感器	CS215	-40~70℃	±0.3℃
风速仪	#40	0~60 m/s	±2%
风向标	#200P	0~360°	±5°
数据采集器	TP700/CR3000	10 s/次	±0.2%
温度传感器	K型	0~150℃	±0.1℃
差示扫描量热仪	DCS250	-180~725℃	±1%/±0.01℃

Fig.4 The change curve of instantaneous heat collection efficiency with normalized temperature difference

Fig.5 Heat flow curves of phase change heat storage material (upward heat release,downward heat absorption)

Fig.6 The change curves of temperature field unevenness of heat storage unit

Fig.7 Transition diagram of solid phase interface in heat storage grid (heat release stage)

Fig.8 The change trend of heat storage power and heat release power change with test time

Fig.9 The change curve of total solar irradiance of inclined plane change with test time

Fig.10 The change curve of temperature at the upper 1.5 m of capillary net with test time

Fig.11 The change curve of heat dissipation power change with inlet temperature of capillary network

Table 3 Material schedule

名称	型号规格	单价/元	数量	总价/元
总计/元	17162
平板热管型太阳能集热器	2 m²	520	16	8320
相变储热单元	0.0651 m³	580	10	5800
毛细管网	4 m²	128	7	896
循环泵	MP-100RM	515	1	515
Y型过滤器	1寸	62	1	62
缓冲水箱	100 L	300	1	300
球阀	1寸	12	8	96
电动三通阀	DN32	375	2	750
智能温控器	TC-05B	255	1	255
预装PPR保温管	1寸	8.4	20	168

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