Effect of bending angle on heat transfer performance of flat heat pipe

doi:10.19799/j.cnki.2095-4239.2019.0228

Abstract

Abstract:

Heat transfer was experimentally investigated in a sintered flat heat pipe. The shell of the heat pipe was fabricated from oxygen-free copper, and the working medium was a mixture of water and ethanol. The wick of the heat pipe was a sintered copper ball. The sintered flat heat pipe was 3.2 mm thick, 8 mm wide, and 400 mm long. Its bending radius was 20 mm, and its bending angle was varied as 30°, 50°, 70°, and 90°. The heat transfer performance of the pipe was evaluated for heat sources of different temperatures (50 ℃, 60 ℃, 70 ℃, and 80 ℃), generated by heating quantitative cold water. In a preliminary test, the temperature difference in each part of the heat pipe was not significantly affected by the bending angle. Even the pipe bent at 90° showed good isothermal properties. In a further study, the thermal resistance of the heat pipe was reduced by increasing the source temperature and reducing the bending angle. The heat resistance performance of the heat pipe mainly depended on the bending angle. When the bending angle increased from 30° to 90°, the thermal resistance increased by more than 60% because the bend crushed the liquid core and deformed the flow of the absorption liquid working medium. Consequently, the fluid flow was hindered and the heat transfer performance declined. Moreover, changing the temperature of the heat source altered the heat transfer capacity in the evaporation section of the heat pipe. As the source temperature increased, the heat resistance of the heat pipe decreased. Finally, sensitive heat storage was investigated in a bent flat heat pipe. At higher source temperatures and lower bending angles of the heat pipe, the time of the sensible heat storage was lowered and the rate of sensible heat storage increased.

Key words: heat pipe, bending, thermal resistance, the heat transfer performance

CLC Number:

TK 124

LI Xinyu, LI Peng, HAN Zhongxian, LIU Tao, WANG Lei, CHEN Lin. Effect of bending angle on heat transfer performance of flat heat pipe[J]. Energy Storage Science and Technology, 2020, 9(3): 840-847.

Figures/Tables 11

Fig.1

Fig.2

Table 1

Fig.3

Fig.4

Fig.5

Fig.6

Fig.7

Table 2

Fig.8

A _v ，A _w	—	气态工质流道，吸液芯的截面面积，m²
$c H 2 O$	—	标准状况下冷水的定压比热，J/(kg·℃)
f _v ，f _l	—	气态，液态工质的摩擦系数
h _fg	—	气态工质的潜热，kJ/kg
k	—	吸液芯的渗透率
L _e ，L _a ，L _c	—	热管蒸发段，绝热段，冷凝段长度，mm
l _eff	—	热管的有效长度，mm
m	—	液体工质的质量流量，kg/s
$m H 2 O$	—	热管冷凝段加热冷水的质量，kg
Q	—	热管输入的热流，W
r _e	—	吸液芯的水力学半径，mm
R _v	—	蒸气流道截面半径，mm
t	—	冷水被加热到指定温度用的时间，min
T _r ，T _l ，T _lp	—	热源的温度，冷源的温度，冷水的平均温度，℃
v _v ，v _l	—	气态，液态工质的流速，m/s
σ	—	吸液芯的表面张力，N/m
ρ _v ，ρ _l	—	气态，液态工质的密度，kg/m3
δ	—	热管轴线与重力方向的夹角，(°)
ΔT	—	热源与冷源之间的温差，℃
$? T H 2 O$	—	热管冷凝段加热冷水的温度变化，℃

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参数	数值
壳体材料	无氧铜
吸液芯	烧结铜
工质	水，乙醇混合物
厚度	3.2 mm
宽度	8 mm
长度	400 mm
弯曲角度	30°，50°，70°，90°
弯曲半径	20 mm
蒸发段长度L _e	80 mm
绝热段长度L _a	240 mm
冷凝段长度L _c	80 mm

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