Heat Transfer Enhancement of a Cascaded Latent Heat Thermal Energy Storage System by Fins With Different Uneven Layouts

doi:10.12096/j.2096-4528.pgt.20114

Abstract

Abstract:

The cascaded latent heat thermal energy storage (CLH-TES) is a kind of thermal energy storage technology with promising commercial prospects. The heat transfer enhancement of CLH-TES system by adding uneven number/height of fins for different phase change material (PCM) layers (uneven number/height layout) was numerically investigated. Firstly, for the system adding same number/height of fins for all the PCM layers (even number/height layout), the influences of number and height of fins on the charging and discharging performance were compared. Then, the charging and discharging performances of the systems with uneven number/height layout of fins were calculated. The results show, comparing to the even number layout,the system with uneven number layout can shorten the total time for the melting and solidification processes by 5.2% and increase the average charging rate by 12.6%. Besides, comparing to the even height layout, the system with uneven height layout can slightly decrease the total time for the melting and solidification processes but hardly affect the average charging and discharging rate. The findings can guidance the design of heat transfer enhancement to the CLH-TES with fins.

Key words: solar thermal power generation, cascaded latent heat thermal energy storage (CLH-TES), phase change material (PCM), heat transfer enhancement, uneven fins, numerical simulation

CLC Number:

TK 512⁺.4

Zhirong LIAO, Pengda LI, Ziqian TIAN, Chao XU, Gaosheng WEI. Heat Transfer Enhancement of a Cascaded Latent Heat Thermal Energy Storage System by Fins With Different Uneven Layouts[J]. Power Generation Technology, 2022, 43(1): 83-91.

Figures/Tables 16

Fig. 1 CLH-TES system with three PCMs

Tab. 1 Geometric dimensions of phase change heat storage module in heat storage system

参数	数值
壳内径/长度/厚度	60/400/5
管内径/厚度	12.5/1.5
翅片高度/厚度	12/2

Fig. 2 Physical model of CLH-TES system with three PCMs

Tab. 2 Thermophysical properties of three PCMs

热物性	PCM1	PCM2	PCM3
固相线温度/K	494.15	463.75	415.59
液相线温度/K	509.15	475.85	423.25
潜热值/(J·g^-1)	102.10	250.10	51.63
导热系数/ (W·m^-1·K^-1)	0.76(固相)	0.74(固相)	0.99(固相)
导热系数/ (W·m^-1·K^-1)	0.45(液相)	0.48(液相)	0.56(液相)
比热容/ (J·kg^-1·K^-1)	399.33+ 2.193 4T	890.323 4+1.564T(固相)	291.33+ 2.661 8T
比热容/ (J·kg^-1·K^-1)	399.33+ 2.193 4T	-14 195.743+60.478T- 0.055 79T²(液相)	291.33+ 2.661 8T
密度/(kg·m^-3)	2 074	1 994	2 061

Tab. 3 Thermophysical properties of thermal oil, air, stainless steel, and glass wool

热物性	导热油		空气	不锈钢	玻璃棉
热物性	553 K	353 K	空气	不锈钢	玻璃棉
导热系数/(W·m^-1·K^-1)	0.100 6	0.114 6	0.024 2	18.000 0	0.043 0
比热容/(J·kg^-1·K^-1)	2 380.0	1 780.0	1 006.4	502.0	750.0
密度/(kg·m^-3)	849.000	966.500	0.854	7 930.000	30.000

Fig. 3 Change curves of PCM3 liquid volume fraction during charging processes under different conditions

Fig. 4 Temperature comparison of monitoring points between experiment and numerical model

Fig. 5 Curves of total time required for complete melting and solidification of PCMs with fin number and fin height

Tab. 4 Three conditions of even and uneven fin number

工况	翅片高度/mm	翅片数量/个
工况	翅片高度/mm	PCM1	PCM2	PCM3
1	12	4	4	4
2	12	4	8	0
3	12	2	10	0

Fig. 6 Liquid volume fraction distribution of cases 1, 2, 3 and velocity distribution of case 2

Fig. 7 Total time for complete melting and solidification of PCMs under cases 1, 2, 3

Fig. 8 Average power of system charging/discharging processes under cases 1, 2, 3

Tab. 5 Three cases of even and uneven fin height

工况	翅片数量/个	翅片高度/mm
工况	翅片数量/个	PCM1	PCM2	PCM3
1	4	12	12	12
4	4	12	14	10
5	4	12	16	8

Fig. 9 Liquid volume fraction distribution of PCMs under cases 4, 5

Fig. 10 Total time for complete melting and solidification of PCMs under cases 1, 4, 5

Fig. 11 Average power of system charging/discharging processes under cases 1, 4, 5

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