Research on start-up characteristics of super-long gravity heat pipe-heat pump heating system

doi:10.11949/0438-1157.20250405

CIESC Journal ›› 2025, Vol. 76 ›› Issue (10): 5035-5046.DOI: 10.11949/0438-1157.20250405

• Fluid dynamics and transport phenomena • Previous Articles Next Articles

Research on start-up characteristics of super-long gravity heat pipe-heat pump heating system

Bin WANG¹^,²^,³^,⁴(), Zihao LI¹^,²^,³^,⁴, Wenbo HUANG¹^,²^,³, Juanwen CHEN¹^,²^,³(), Ang LI¹^,²^,³^,⁵, Pengfei DANG⁴, Fangming JIANG¹^,²^,³^,⁵()

^1.Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, China
^2.CAS Key Laboratory of Renewable Energy, Guangzhou 510640, Guangdong, China
^3.Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, Guangdong, China
^4.School of Mechanical and Power Engineering, Shenyang University of Chemical Technology, Shenyang 110142, Liaoning, China
^5.School of Energy Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui, China

Received:2025-04-16 Revised:2025-06-10 Online:2025-11-25 Published:2025-10-25
Contact: Juanwen CHEN, Fangming JIANG

超长重力热管-热泵供暖系统启动特性研究

王宾¹^,²^,³^,⁴(), 李子豪¹^,²^,³^,⁴, 黄文博¹^,²^,³, 陈娟雯¹^,²^,³(), 李昂¹^,²^,³^,⁵, 党鹏飞⁴, 蒋方明¹^,²^,³^,⁵()

^1.中国科学院广州能源研究所，广东广州 510640
^2.中国科学院可再生能源重点实验室，广东广州 510640
^3.广东省新能源和可再生能源研究开发与应用重点实验室，广东广州 510640
^4.沈阳化工大学机械与动力工程学院，辽宁沈阳 110142
^5.中国科学技术大学能源科学与技术学院，安徽合肥 230026

通讯作者: 陈娟雯,蒋方明
作者简介:王宾（1998—），男，硕士，a626954940@163.com
基金资助:
国家重点研发计划项目(2021YFB1507300);国家重点研发计划项目(2021YFB1507301);国家自然科学基金项目(52206126);国家自然科学基金项目(52206287);广州市科技计划项目(SL2023A04J01976)

Abstract

Abstract:

Super-long gravity heat pipe (SLGHP) has shown broad application prospects in the field of geothermal energy development due to its excellent heat transfer capacity and pump-free drive characteristics. However, in practical applications, the start-up process of SLGHP involves complex phase change and heat transfer mechanisms, especially regarding the temperature response and thermal equilibrium following working fluid injection, which remain inadequately understood. This study investigates the liquid-injection start-up process, heat extraction start-up characteristics, and the influence of heat pump start-up modes on the operational performance of the SLGHP-heat pump heating system through combined experimental measurements and numerical simulations. Fiber optic temperature sensing was employed to monitor the dynamic evolution of wall temperature during the injection process. The results indicate that the temperature inflection point formed during the downward wetting of ammonia correlates strongly with the injection depth and can serve as a dynamic indicator of fluid distribution. Upon completion of injection, the axial temperature gradient of the heat pipe decreases from 18.4℃/km to 2℃/km, significantly improving thermal uniformity. The numerical model exhibits less than 3% deviation from experimental data, validating the predictive accuracy of working fluid distribution and temperature field evolution. Moreover, an engineering criterion based on the temperature deviation between wellhead vapor and formation average temperature after 12 h of injection is proposed, enabling assessment of the start-up completion without the need for external temperature sensors. Further analysis reveals that during cold start-up, the discharge pressure of the heat pump increases from 0.55 MPa to 1.06 MPa, with heating output reaching 900 kW within 1 h and a COP stabilizing at 6.5. In contrast, during thermal start-up, the presence of residual thermal energy in the system shortens the time required to reach a relatively stable state by 28%. This study elucidates the heat transfer mechanism during the start-up phase of the SLGHP-heat pump system, providing valuable insights for the optimized design and stable operation of SLGHP geothermal systems.

Key words: super-long gravity heat pipe, geothermal energy, start-up characteristics, phase-change heat transfer, cold and thermal start-up of heat pump

摘要：

超长重力热管（SLGHP）因其优异的热传输能力和无泵驱动的特点，在地热能开发领域展现出广阔的应用前景。然而，在实际应用中，SLGHP的启动过程涉及复杂的气液相变与传热机制，尤其是工质注入后的温度响应及热力平衡过程尚不明确。结合实验测量与数值模拟，研究了SLGHP-热泵供暖系统的注液启动过程、取热启动特性及热泵启动方式对系统运行性能的影响。实验采用光纤测温技术实时监测注液过程中管壁温度的动态演变，发现氨工质自上而下润湿过程中形成的温度转折点与工质注入深度高度关联，可作为工质分布的动态指示参数。注液完成后，热管轴向温度梯度由初始的18.4℃/km降至2℃/km，均温性显著提升。数值模型与实验结果误差小于3%，验证了工质分布与温度场演化预测的可靠性。此外，提出了基于注液完成12 h后井口蒸汽温度与地层平均温度偏差的工程判据，无须额外布设管外测温装置即可评估注液启动阶段完成状态。进一步分析表明，热泵冷启动时，排气压力由0.55 MPa升至1.06 MPa，供暖量1 h内达900 kW，性能系数（COP）稳定于6.5；而热泵热启动过程由于系统残余热量，系统达到相对稳定所需时间缩短28%。本研究揭示了SLGHP-热泵系统启动阶段的传热机制，为SLGHP地热系统的优化设计与稳定运行提供参考。

关键词: 超长重力热管, 地热能, 启动特性, 相变传热, 热泵冷热启动

CLC Number:

TK 172

Bin WANG, Zihao LI, Wenbo HUANG, Juanwen CHEN, Ang LI, Pengfei DANG, Fangming JIANG. Research on start-up characteristics of super-long gravity heat pipe-heat pump heating system[J]. CIESC Journal, 2025, 76(10): 5035-5046.

王宾, 李子豪, 黄文博, 陈娟雯, 李昂, 党鹏飞, 蒋方明. 超长重力热管-热泵供暖系统启动特性研究[J]. 化工学报, 2025, 76(10): 5035-5046.

Figures/Tables 11

Fig.1 Schematic of SLGHP-heat pump heating system

Fig.2 Fiber optic temperature measurement at different stages of ammonia injection

Fig.3 Comparison of fiber optic temperature measurement and simulated temperature during ammonia injection process

Fig.4 (a) Geometric structure of the model; (b) Model equation

Table 1 Calculation parameters

项目	实验参数	实验范围
热管结构	长度L/m	3000
	直径D/mm	177.8
	粗糙度e/mm	0.1
实验场地条件	地层温度 $T O F$ /(K/m)	根据测井数据设置
	冷凝温度 $T c$ /℃	根据实验数据设置
	地面温度 $T g r$ /℃	15
	地下岩石密度 $ρ$ ^s/(kg/m³)	根据测井数据设置
	岩石比热容 $c p s$ /(J/(kg·K))	根据测井数据设置
	干热岩热导率 $λ e f f$ / (W/m·K))	初始值2.1，然后根据计算结果进行修改
工作流体	物理性质	R717（氨）
	黏度	温度相关（Refprop^①）
	密度	温度相关（Refprop^①）
	潜热	温度相关（Refprop^①）
计算规模	计算域规模	径向：距离热管轴线100 m的半径轴向：从地面到热管底部以下250 m处
	计算时间尺度	0~14 h

Table 1 Calculation parameters

项目	实验参数	实验范围
热管结构	长度L/m	3000
	直径D/mm	177.8
	粗糙度e/mm	0.1
实验场地条件	地层温度 $T O F$ /(K/m)	根据测井数据设置
	冷凝温度 $T c$ /℃	根据实验数据设置
	地面温度 $T g r$ /℃	15
	地下岩石密度 $ρ$ ^s/(kg/m³)	根据测井数据设置
	岩石比热容 $c p s$ /(J/(kg·K))	根据测井数据设置
	干热岩热导率 $λ e f f$ / (W/m·K))	初始值2.1，然后根据计算结果进行修改
工作流体	物理性质	R717（氨）
	黏度	温度相关（Refprop^①）
	密度	温度相关（Refprop^①）
	潜热	温度相关（Refprop^①）
计算规模	计算域规模	径向：距离热管轴线100 m的半径轴向：从地面到热管底部以下250 m处
	计算时间尺度	0~14 h

Fig.5 Changes in heat pipe temperature over time after cold start of heat pump

Fig.6 Changes in heating capacity, compressor power, and COP during cold start of heat pump

Fig.7 Changes in temperature, exhaust pressure, and intake pressure of ammonia refrigerant entering and leaving the evaporator during the cold start process of the heat pump

Fig.8 Changes in exhaust pressure and suction pressure during the hot start process of the heat pump

Fig.9 Temperature changes of ammonia refrigerant entering and leaving the evaporator during the hot start process of the heat pump

Fig.10 Changes in compressor power consumption and COP during heat pump thermal start process

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Research on start-up characteristics of super-long gravity heat pipe-heat pump heating system

超长重力热管-热泵供暖系统启动特性研究

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References 33

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