CIESC Journal ›› 2021, Vol. 72 ›› Issue (5): 2547-2559.DOI: 10.11949/0438-1157.20201220

• Fluid dynamics and transport phenomena • Previous Articles     Next Articles

Impact of thermal dispersion on full-scale heat transfer of borehole heat exchangers

LI Xiaoyu(),XU Hongyang,DAI Min,CAI Shanshan()   

  1. School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
  • Received:2020-08-26 Revised:2020-12-28 Online:2021-05-05 Published:2021-05-05
  • Contact: CAI Shanshan

热弥散对地埋管换热器全尺度传热的影响

李晓宇(),徐宏阳,代敏,蔡姗姗()   

  1. 华中科技大学能源与动力工程学院,湖北 武汉 430074
  • 通讯作者: 蔡姗姗
  • 作者简介:李晓宇(1992—),女,硕士研究生,958561492@qq.com
  • 基金资助:
    国家自然科学基金项目(51706078);湖北省自然科学基金项目(2017CFB131)

Abstract:

Research on the heat transfer of borehole heat exchanger (BHE) is the key to enhance the heat transfer efficiency of the ground source heat pump(GSHP) system. Most of the BHE models proposed in the current literature ignore the influence of thermal dispersion, which is caused by spatial heterogeneity of underground aquifer. In order to consider thermal dispersion effect, an improved full-scale heat transfer model is developed by including thermal dispersion coefficient. The main findings are summarized as follows. The appropriate range of seepage velocity applied in the model is from 1×10-8 m/s to 1×10-6 m/s. The thermal dispersion effect is mainly reflected in the medium and long time scale. Seepage velocity, thermal dispersivity and porosity are the main factors affecting the heat transfer process. High values of the seepage velocity and thermal dispersivity of groundwater, as well as low values of the porosity, may lead to strong thermal dispersion effect. Seepage velocity has the strongest impact on the overall heat transfer around boreholes, followed by the thermal dispersivity, and the porosity has the weakest effect. As far as the borehole group is concerned, thermal dispersion has the greatest impact on the heat transfer process of the upstream borehole, followed by the middle reaches, and the downstream is the least. Within the parameters studied in this paper, thermal dispersion can increase the steady-state heat transfer capacity of the borehole by 5.52% to 49.93%.

Key words: ground source heat pump, borehole heat exchangers, groundwater seepage, full-time scale heat transfer, thermal dispersion

摘要:

开展地埋管换热器的传热研究是增强其传热性能以及提高热泵系统能效比的关键,现有的地埋管换热器传热模型多忽略了由地下含水层空间非均质性而产生的热弥散传热。因此,基于渗流影响下的全尺度模型和求解热弥散系数的速度一次方模型,提出了考虑热弥散影响的地埋管换热器全尺度传热模型。研究表明此模型所适用的地下水渗流速度范围为1×10-8~1×10-6 m/s;热弥散效应主要在中长时间尺度下体现,渗流速度、热弥散度以及孔隙率是影响传热过程的主要因素。地下水渗流速度和热弥散度越大,孔隙率越小,热弥散效应越强。综合考虑三类影响因素,渗流速度对钻孔传热的影响最大,热弥散度次之,孔隙率的影响最弱;对钻孔群而言,热弥散对上游钻孔传热过程的影响最大,中游次之,下游最小;在所研究的参数范围内,热弥散可使钻孔稳态传热能力提升5.52%~49.93%。

关键词: 地源热泵, 地埋管换热器, 地下水渗流, 全尺度传热, 热弥散

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