Numerical studies on heat transfer characteristics of pile heat exchanger with double spiral pipes buried in parallel

doi:10.11949/j.issn.0438-1157.20161741

Abstract

Abstract:

It is critical to understand the heat transfer characteristics of pile heat exchanger (PHE) with double spiral pipes buried in parallel so that it can be designed feasibly and operated efficiently. Therefore, a 3-D dynamic simulation model as established to study the heat transfer processes of a pile heat exchanger in which double spiral pipes and the return risers were buried in parallel. And the numerical simulation results were validated by the data obtained in an in-situ test and analytical solution of the solid cylindrical heat source model. The temperature distributions along the pipes, in the pile body and soil surrounding are illustrated and analyzed. A continuous and three intermittent heat transfer processes of this PHE were simulated dynamically. Such parameters as the dynamic outlet water temperatures of the buried parallel double spiral pipes and the heat transfer rate per unit pipe length are revealed. The temperature variations at different locations on the pile wall and in the soil surrounding along the pile depth and in radial directions are analyzed. The index of pile wall temperature recovery percentage is proposed to quantify the temperature recovery degree under different intermittent operational modes. It is found that the smaller the on-off ratio, the more significantly the temperature recovery degree along the pile wall can be achieved. But the recovery degree in each intermittent period tends to decrease as the operational cyclic increases.

Key words: computational fluid dynamics, heat conduction, heat transfer, pile heat exchanger with double spiral pipes buried in parallel, experimental validation, numerical simulation, intermittent mode

摘要：

摸清桩基并联双螺旋型埋管换热器的传热特性是进行合理设计、确保其高效运行的前提。建立了包含回水立管在内的桩基并联双螺旋型埋管换热器三维动态传热的仿真模型，利用其对现场实验的仿真复现及实心圆柱源热源模型解析解的对比验证了模拟结果的正确性。对桩身和土壤温度的模拟结果进行了分析，给出了沿管程、桩基内部以及周围土壤的温度分布。对连续和3种间歇运行模式下桩基并联双螺旋型埋管换热器的运行情况进行了仿真，揭示了其出口水温和单位管长放热量等性能参数的动态变化规律以及桩壁和周围土壤温度沿桩深和桩径方向的分布特征，提出了桩壁温度恢复百分比指标，定量评价了其在间歇运行模式下的温度恢复程度。表明了运停比越小，桩壁温度恢复程度越显著，但随着间歇运行周期的增加，每一间歇期的温度恢复程度呈现下降趋势。

关键词: 计算流体力学, 热传导, 传热, 桩基并联双螺旋型埋管换热器, 实验验证, 数值模拟, 间歇运行

CLC Number:

TK521

ZHU Shuiping, ZHAO Lei, YANG Liu, WANG Zhenyu. Numerical studies on heat transfer characteristics of pile heat exchanger with double spiral pipes buried in parallel[J]. CIESC Journal, 2017, 68(7): 2730-2738.

朱税平, 赵蕾, 杨柳, 王振宇. 桩基并联双螺旋型埋管换热器传热特性的数值仿真[J]. 化工学报, 2017, 68(7): 2730-2738.

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