Numerical simulation of start-up characteristics and heat transfer performance of ultra-thin heat pipe

doi:10.11949/0438-1157.20230429

Abstract

Abstract:

In this paper, a simplified three-dimensional transient model of ultra-thin heat pipe was proposed to simulate the process of heat pipe from start-up to stable operation. Based on the previous work of the team, the accuracy of the model was verified. Heat pipes with different vapor core thicknesses, types of wicks and bending section geometry were studied by numerical simulation. The influence of different parameters on the vapor flow characteristics, temperature distribution and start-up performance is analyzed. Based on the control theory, the thermal response characteristics of heat pipes with different structures are quantitatively analyzed. The maximum RMSE is only 0.385. The results show that the flow resistance and energy loss of vapor will increase if the vapor core thickness is too small. Different structures of wicks mainly affect the steam flow characteristics through the difference in the width of the steam channel. The smaller the vapor core thickness is, the more easily it is affected by the bending radius and bending angle of the bending section. In addition, if the thickness of the flow channel is less than 0.2 mm, it will also affect the temperature uniformity of the heat pipe and limit the vapor-liquid circulation. The total thermal resistance and start-up time of the heat pipe are mainly affected by the heat load.

Key words: ultra-thin heat pipe, numerical simulation, phase change, heat transfer, start-up performance

摘要：

提出了一种简化的超薄热管三维瞬态模型，模拟热管由启动至稳定运行的过程，基于团队前期工作验证了模型的准确性，通过数值模拟研究了不同流道厚度、吸液芯类型及折弯段几何结构的热管，分析了各参数对蒸汽流动特性、温度分布特性及启动性能的影响，基于控制理论对不同结构热管的热响应特性进行了定量分析，最大均方根误差(RMSE)仅为0.385。研究表明：流道厚度过小将增大蒸汽流动阻力和能量损失，不同结构吸液芯主要通过蒸汽通道宽度差异影响蒸汽流动特性，流道厚度越小越易受折弯段折弯半径和折弯角度的影响。此外，流道厚度小于0.2 mm还将影响热管均温性，使气液循环受限，热管总热阻和启动时间主要受热负荷的影响。

关键词: 超薄热管, 数值模拟, 相变, 传热, 启动性能

CLC Number:

TK 172.4

Fangzhe SHI, Yunhua GAN. Numerical simulation of start-up characteristics and heat transfer performance of ultra-thin heat pipe[J]. CIESC Journal, 2023, 74(7): 2814-2823.

史方哲, 甘云华. 超薄热管启动特性和传热性能数值模拟[J]. 化工学报, 2023, 74(7): 2814-2823.

Figures/Tables 14

Fig.1 Geometric model of ultra-thin heat pipe

Table 1 Structural parameters of heat pipe and heating condensation module

参数	数值
热管长度/mm	115
热管宽度/mm	7.7
热管壁厚/mm	0.2
流道厚度/mm	0.1~0.4
加热铜块尺寸/mm×mm	7.7×15
冷却铜块尺寸/mm×mm	7.7×40
冷却水流量/(L·h^-1)	20

Table 2 Structural parameters of wick

名称	每毫米孔数	线径/mm	宽度/mm	孔隙率	渗透率/m²
NSM	6.02	0.04	2.6	0.801	1.709×10^-10
TSM	6.69	0.04	3.0	0.779	1.273×10^-10
ESM	7.36	0.04	3.4	0.757	9.652×10^-11

Fig.2 Grid independence test

Fig.3 Comparison between simulated and experimental values of heat pipe temperature

Fig.4 Relationship between steam pressure drop and heat load with different channel thickness

Fig.5 Effect of different channel thickness and wick structure on the average steam velocity in the bending section

Fig.6 Influence of bending radius of heat pipe on circulating flow rate and average speed of bending section

Fig.7 Influence of different channel thickness, wick structure and bending angle on maximum steam velocity

Fig.8 Temperature distribution of heat pipe with different channel thickness

Fig.9 Influence of heat load on thermal resistance of heat pipe with different channel thickness

Fig.10 Relationship between start-up time and heating power of heat pipe with different channel thickness

Fig.11 Control theory of heat pipe thermal response and numerical simulation of temperature changes

Table 3 Calculation values of control theory parameter for UTHP startup

传递函数	h_w/mm	T_ct/℃	RMSE	k_ct	t_ct/s
$\frac{k_{c t}}{1 + t_{c t} S}$	0.1	55.895	0.385	4.955	27.002
	0.2	48.160	0.376	4.566	31.579
	0.3	46.882	0.196	4.511	34.567

Table 3 Calculation values of control theory parameter for UTHP startup

传递函数	h_w/mm	T_ct/℃	RMSE	k_ct	t_ct/s
$\frac{k_{c t}}{1 + t_{c t} S}$	0.1	55.895	0.385	4.955	27.002
	0.2	48.160	0.376	4.566	31.579
	0.3	46.882	0.196	4.511	34.567

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