螺旋叶片强化中深层地热同轴换热器换热性能数值模拟

Numerical simulation of heat transfer performance of spiral vane reinforced medium and deep geothermal coaxial heat exchanger

为强化同轴换热器在中深层地热开发中的传热效果,提出一种螺旋叶片形式新型地热同轴换热器。通过建立内插不同间距(d=200、150、100 mm)螺旋叶片的换热器数值模型,模拟套管中换热流体特性。结果表明:在Re=4500~11500的湍流状态下,螺旋叶片作为扰流元件,通过改变流体的流动形态和热边界层厚度,可以有效强化换热器的单相对流换热效果,提高开采岩土体热量的能力。随着间距减小,强化换热效果进一步增强,努赛尔数(Nu)增大。当间距d=100 mm时,强化传热效果最好,综合换热能力最强,较光滑管的Nu提高了41.05%~44.18%,传热增强因子TEF为1.16,该工作为同轴套管换热器的优化设计提供了理论基础。

To enhance the heat transfer effect of coaxial heat exchanger in medium and deep geothermal development,a new geothermal coaxial heat exchanger in the form of spiral vane is proposed.By establishing a numerical model of the heat exchanger with interpolated spiral blades of different spacing(d=200,150,100 mm),the heat transfer fluid characteristics in the casing are simulated.The results show that under the turbulent flow state of Re=4500-11500,the spiral blades as a disturbing element can effectively strengthen the single-phase convective heat transfer effect of the heat exchanger and improve the ability to extract heat from the rock and soil body by changing the flow pattern of the fluid and the thickness of the thermal boundary layer.As the spacing d decreases,the enhanced heat exchange effect is further enhanced and the Nusser number(Nu)increases.When the spacing d is 100 mm,the enhanced heat transfer effect is the best and the comprehensive heat transfer capacity is the strongest,with Nu increased by 41.05%-44.18%compared with that of smooth tube,and the heat transfer enhancement factor TEF is 1.16.This work provides a theoretical basis for the optimal design of coaxial casing heat exchanger.