Comparison of the thermal and hydraulic performance of single U-tube, double U-tube and coaxial medium-to-deep borehole heat exchangers
Comparison of the thermal and hydraulic performance of single U-tube, double U-tube and coaxial medium-to-deep borehole heat exchangers
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DOI：
10.1016/j.geothermics.2023.102888
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发表时间：
2024-02
期刊：
影响因子：
3.9
通讯作者：
C. Brown;I. Kolo;D. Banks;G. Falcone
中科院分区：
文献类型：
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作者：
C. Brown;I. Kolo;D. Banks;G. Falcone
热量脱碳对于抑制二氧化碳排放至关重要，可以通过使用地热系统来实现。最近，单井，闭环，深埋管换热器，使用同轴设计，已成为关注的焦点，部分原因是重新利用现有的基础设施（如石油和天然气威尔斯）的潜力;然而，很少有研究其他类型的热交换器的潜力，中深地热系统。为此，采用OpenGeoSys软件对同轴、单U型管和双U型管中深埋管换热器（MDBHEs）的热工水力性能进行了全面的数值分析。本文的目的是测试每种管道配置的最大作业深度，因为很少有威尔斯井使用单/双U形管配置完成深度超过500 m。性能最佳的MDBHE应最大限度地减少寄生和水力损失，同时最大限度地提高热输出。此外，地源热泵需要电力;因此，在电价高的时候（钻井成本可以最小化），利用MDBHEs遇到更高的温度可能更有利。结果表明，同轴MDBHEs在比热提取和最低的压力/寄生损失方面提供最佳性能。双U形管MDBHE可以提供与同轴设计相似的热性能，但是在所有模拟中具有显著更大的液压损失，这转化为更大的寄生泵送功率成本。单U形管MDBHE在热提取和压力损失方面表现出最差的性能。在800 m MDBHE、同轴、U形管和双U形管配置的25年基本情景结束时，流体循环速率均为5 L/s，提供的比热提取率分别为39.1 W/m、32.8 W/m和36.0 W/m，流体入口温度设定为5 °C。对于这些模拟，压力损失估计为85 kPa（同轴）、1.46 MPa（单U形管）和423 kPa（双U形管）-单U形管值接近SDR 11高密度聚乙烯管的标称16 bar（1.6 Mpa）压力等级。还进行了进一步的参数分析，调查深度，流速，岩石热导率，管道直径和柄间距。
Decarbonisation of heat is essential in curbing carbon dioxide emissions and can be achieved through the use of geothermal systems. Recently, single-well, closed-loop, deep borehole heat exchangers, using a coaxial design, have become the focus of attention, partly due to the potential to repurpose existing infrastructure (such as oil and gas wells); however, few have investigated the potential for other types of heat exchanger for middle-deep geothermal systems. Therefore, in this study, a comprehensive numerical analysis was undertaken using OpenGeoSys software to investigate the thermal and hydraulic performance of coaxial, single U-tube and double U-tube middle-deep borehole heat exchangers (MDBHEs). The purpose of this paper is to test the maximum operational depth for each type of pipe configuration as few wells have been completed to depths exceeding 500 m using single/double U-tube configurations. The best performing MDBHEs should minimise parasitic and hydraulic losses, whilst maximising thermal output. Furthermore, ground sourced heat pumps require electricity; therefore, at times where electricity prices are high (and drilling costs can be minimised) it may be more beneficial to utilise MDBHEs to encounter greater temperatures.Results indicate that coaxial MDBHEs provide the best performance in terms of specific heat extraction and lowest pressure/parasitic losses. Double U-tube MDBHEs can provide a similar thermal performance to the coaxial design, but have significantly greater hydraulic pressure losses across all simulations, which translates to greater parasitic pumping power costs. Single U-tube MDBHEs demonstrate the poorest performance in terms of heat extraction and pressure losses. At the end of the 25-year base case scenario for a 800 m MDBHE, coaxial, U-tube and double U-tube configurations, all with a fluid circulation rate of 5 L/s, provided specific heat extraction rates of 39.1 W/m, 32.8 W/m, and 36.0 W/m, respectively, with the fluid inlet temperature set as a constant of 5 °C. For these simulations, pressure losses were estimated as 85 kPa (coaxial), 1.46 MPa (single U-tube) and 423 kPa (double U-tube)—the single U-tube value being close to the nominal 16 bar (1.6 Mpa) pressure rating of SDR11 high density polyethylene pipe. Further parametric analysis was also undertaken, investigating depth, flow rate, rock thermal conductivity, pipe diameter and shank spacing.