用于冬季葡萄根系土壤增温的混合重力热管温度响应及热性能分析

    Analysis of temperature response and thermal performance of hybrid gravity heat pipes for winter soil warming of grapevine root systems

    • 摘要: 重力热管是一种高效的传热设备,在浅层地热能的开发方面具有巨大潜力。为提高冬季葡萄根系土壤的温度,该研究设计并测试了一种混合重力热管(hybrid gravity heat pipe,HGHP)。HGHP由铜和聚丙烯无规共聚物(polypropylene random,PPR)材料组成,其中铜用于蒸发段和冷凝段,PPR用于绝热段。通过大地试验研究比较了HGHP与传统铜重力热管(copper gravity heat pipe,CGHP)的热力学性能。结果显示,与对照组相比,CGHP和HGHP分别使土壤温度提高了4.94 和3.08 ℃,增温效果显著;两种热管均表现出良好的等温特性。由于使用了低成本的PPR材料替代昂贵的铜材料,HGHP成本较CGHP降低48.39%,降幅明显。尽管HGHP的热传递性能略低于CGHP,其经济性和可行性使其在地热能开发中具有应用潜力。该研究为降低地热能开发成本提供了可行的解决方案,并为重力热管在农业领域的应用提供了理论依据和实践指导。

       

      Abstract: A hybrid gravity heat pipe (HGHP) can greatly contribute to the soil warming of the grapevine root systems in cold agricultural regions in winter. According to the shallow geothermal energy, HGHP technology can provide an efficient yet economically feasible solution to sustain the root temperatures for plant growth during cold seasons. Among them, copper is used in the evaporative and condensative sections, while the polypropylene random copolymer (PPR) is in the adiabatic section, indicating a cost-efficient alternative to traditional all-copper heat pipes. This research aims to investigate the thermal response and performance of the HGHP. A series of tests were conducted in a vineyard region in Ningxia in northwest China. Particularly, the harsh winter temperatures shared a significant impact on grapevine productivity and survival. The efficacy of the HGHP was also evaluated on the soil temperatures at grapevine root zones. A comparison was then made on the thermal efficiency and economic benefits against the conventional copper gravity heat pipe (CGHP). The feasibility of HGHP was verified to evaluate the performance under varying environmental conditions. A stable thermal environment was also maintained on the grapevine growth. A field experiment was conducted at a vineyard in the Helan Mountain area of Ningxia, particularly with both HGHP and CGHP installed under similar conditions. Both systems shared the identical configuration, except for the materials in the adiabatic sections. Each evaporator of pipe was positioned in groundwater to absorb the heat. While the adiabatic sections were embedded in soil with insulative covering to minimize the external thermal influence. Temperature sensors were placed along each evaporative of heat pipe, adiabatic, and condensative sections, as well as in surrounding soil, in order to capture the temperature fluctuations. Observations were conducted across 121 days, thus covering the distinct meteorological conditions, including cloudy, snowy, extremely low-temperature, typical winter, and high-temperature scenarios. A systematic analysis was implemented on the thermal response, heat transfer efficiency, and stability of both HGHP and CGHP under real field conditions. The results indicate that both HGHP and CGHP effectively enhanced the soil temperatures for the grapevine root systems, compared with the control group without heat pipes. The HGHP raised the soil temperature by an average of 3.08℃, whereas the CGHP was achieved in the more substantial increase of 4.94℃. Thermal profiles demonstrated that the HGHP retained isothermal performance in the adiabatic section. Notably, the heat transfer capacity of CGHP outperformed that of the HGHP, due mainly to the superior thermal conductivity of copper. The CGHP condenser section shared an average temperature increase of 1.21℃ over that of the HGHP. However, the performance of the HGHP declined at high temperatures. The condenser section reached the equilibrium with the evaporator, indicating the cessation of heat transfer. Economically, the HGHP reduced the costs by 48.39%, compared with the CGHP. This substantial cost advantage was attributed to the replacement of copper with PPR in the adiabatic section, which significantly lowered material and manufacturing expenses without severely compromising thermal efficiency. Therefore, the HGHP can offer a cost-effective and operationally viable alternative to CGHP for agricultural soil warming applications, particularly for low-temperature settings. The cost benefits of PPR greatly contributed to the functional heat transfer suitable for geothermal applications. Although the thermal performance of HGHP was marginally lower than that of CGHP, significant cost savings can be expected for the promising scalable solution for sustainable agriculture. Furthermore, the adiabatic section of the HGHP system can be expected to improve thermal stability across a broader range of weather conditions. The HGHP can also be extended in fields of geothermal energy beyond agriculture.

       

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