Experimental study on heat transfer performance of super long gravity heat pipe

doi:10.11949/0438-1157.20190630

Abstract

Abstract:

There are many problems in the enhanced geothermal system used for dry hot rock thermal energy exploitation, such as high investment, high risk, working medium leakage, equipment corrosion, land subsidence,etc. Using super long gravity heat pipe to mine hot dry rock geothermal energy can effectively avoid these problems. In this paper, an experimental platform for super long gravity heat pipe is built. The suitable liquid filling capacity, stability of operation and heat transfer performance under different cooling water flow rates are studied experimentally. The possible causes are analyzed. The research shows that under the constant power, the suitable liquid filling amount of the heat pipe is about 40% of the total liquid filling amount of the evaporation section. During operation, compared with the conventional short heat pipe, the super long heat pipe exhibits strong oscillation, oscillation frequency and heating power and charging. The amount of liquid is closely related. At a constant heating power, as the flow rate of the cooling water increases, the power of the heat pipe increases first and then gradually becomes gentle. In addition, the heat transfer performance of the heat pipe under the extreme liquid filling amount is especially discussed. The research shows that under the extreme liquid filling amount, the gas column forms a certain height at the bottom of the heat pipe, and the heat cannot be transferred to the top of the heat pipe due to the continuous existence of the gas column. The experimental results preliminarily verify the feasibility about using the super long gravity heat pipe to mine hot dry rock geothermal energy and offer fundamental supports for the future practical applications.

Key words: hot dry rock, super long, gravity heat pipe, evaporation, heat transfer, experimental validation

摘要：

用于干热岩热能开采的增强型地热系统存在投资高、风险大、工质漏损、设备腐蚀、地面沉降等问题，利用超长重力热管进行地热开采可以有效规避这些问题。搭建了超长重力热管实验平台，实验研究了超长重力热管的适宜充液量、运行的稳定性和不同冷却水流量下的传热性能并分析了其可能的原因；研究表明在恒定加热功率下，热管的合适充液量为蒸发容积的40%左右，在运行期间，与传统短热管相比，超长热管展现出了强烈的振荡性，振荡频率与加热功率和充液量息息相关；在恒定加热功率下，随着冷却水流量的增加，热管采出功率先增加后逐渐趋于平缓。此外，特别探讨了热管在极端充液量下的传热性能，研究表明在极端充液量下，热管底部形成一定高度的气柱，由于气柱的持续存在导致热量无法传递到热管顶端。实验结果初步证实了超长重力热管在开采干热岩热能上的可行性，为下一步的实际应用提供了基础支持。

关键词: 干热岩, 超长, 重力热管, 蒸发, 传热, 实验验证

CLC Number:

TK 172

Tingliang LI, Jiwen CEN, Wenbo HUANG, Wenjiong CAO, Fangming JIANG. Experimental study on heat transfer performance of super long gravity heat pipe[J]. CIESC Journal, 2020, 71(3): 997-1008.

李庭樑, 岑继文, 黄文博, 曹文炅, 蒋方明. 超长重力热管传热性能实验研究[J]. 化工学报, 2020, 71(3): 997-1008.

Figures/Tables 15

Fig.1 Physical diagram of super long gravity heat pipe experiment system

Fig.2 Schematic diagram of super long gravity heat pipe experimental system

Fig.3 Heat transfer performance of heat pipes with different liquid filling (cooling water flow rate is 5.5 ml/s)

Fig.4 Heat transfer performance of heat pipes under different liquid filling (heat power is 800 W, cooling water flow rate is 6.0 ml/s )

Table 1 Depth of filling water and production power at different liquid fillings (heating power is 600 W, cooling water flow rate is 5.5 ml/s)

充液量/ml	积液深度/cm	采出功率/W
200	88.2	460.4
300	132.2	474.8
400	176.4	499.8
600	264.5	451.9
800	352.6	446.6
1000	440.9	445.5
1300	573.0	434.9
1600	705.3	418.6
2500	1102.0	286.2
5000	2204.0	0

Fig.5 Depth of filling water and production power under different liquid fillings (heating power is 600 W, cooling water flow rate is 5.5 ml/s)

Table 2 Theoretical and actual evaporation temperature (heating power is 600 W, circulating flow rate is 5.5 ml/s)

充液量/ml	积液深度/cm	静水压/kPa	绝热段温度/℃	绝热段饱和蒸汽压力/kPa	蒸发段总压力/kPa	理论蒸发温度/℃	热管实际蒸发温度/℃
200	88.2	8.8	53.2	14.5	23.3	63.4	68.2
300	132.2	13.2	50.8	12.9	26.1	65.9	66.8
400	176.4	17.6	51.4	13.2	30.9	69.8	71.8
600	264.5	26.5	50.9	12.9	39.3	75.5	74.7
800	352.6	35.3	51.3	13.2	48.5	80.5	81.5
1000	440.9	44.1	61.2	21.1	65.2	88.1	90.1
1300	573.0	57.3	50.4	12.6	69.9	89.9	90.8
1600	705.3	70.5	48.2	11.3	81.8	94.1	95.3
2500	1102	110.2	46.0	10.1	120.3	104.8	102.5

Fig.6 Comparison of theoretical and actual evaporation temperature (heating power is 600 W, circulating flow rate is 5.5 ml/s)

Fig.7 Temperaturevs time curve of each measuring point under different liquid fillings (cooling water flow rate is 5.5 ml/s)

Fig.8 Temperature variation curve of heat pipe under different heating powers (filling water volume is 5000 ml, cooling water flow rate is 5.5 ml/s)

Fig.9 Temperature of heat pipe changes with time when the heating power is 600 W (a) and heating power is stopped (b) (filling water volume is 5000 ml, cooling water flow rate is 5.5 ml/s)

Fig.10 Heat transfer performance of heat pipes under different cooling water flow rates (filling water volume is 400 ml, heating power is 800 W)

Fig.11 Evaporation section temperature and adiabatic section temperature evolution with increasing cooling water flow rate (filling water volume is 400 ml, heating power is 800 W)

Fig.12 Oscillation frequency of heat pipe under different heating powers(filling water volume is 400 ml, cooling water flow rate is 6.0 ml/s)

Fig.13 Oscillation frequency of heat pipe under different heating powers(filling water volume is 1000 ml, cooling water flow rate is 6.0 ml/s)

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