含水层热弥散效应对地埋管换热器井群传热性能的影响

Effects of heat dispersion on heat transfer characteristic of borehole heat exchangers

根据含水层渗流和传热理论以及地埋管换热器传热模型,建立地埋管井群所在含水层的三维非稳态对流-热弥散型传热模型。利用数值模拟方法,探究含水层热弥散效应对地埋管井群传热性能的影响。研究结果表明:随着含水层热弥散度的提高,地埋管井群的热影响范围以该井群为中心并呈现出对称扩散的传热特征,这样可以有效增强地埋管的换热效率;在地下水达西流速为2.5×10^(-7)m/s条件下,与忽略含水层热弥散效应的工况相比,当含水层纵向热弥散度为5 m时,地埋管井群平均出水温度的均方根误差RMSE为0.4℃,能效系数提高了4.5%。

Based upon the heat transfer and gr oundwater seepage theory in aquifers and the heat transfer model for the borehole heat exchanger（BHE） with 2 U-tube, an unsteady state numerical model combining convective heat transfer and heat dispersion was established in the aquifer outside BHEs. Effects of the heat dispersion in the aquifer on the long-term heat transfer performance of BHEs were studied by the numerical simulation method. The results show that temperature plumes around BHEs appears the symmetrical diffusion characteristic with the thermal dispersivity increasing, meanwhile the heat exchange performance of BHEs enhances obviously. When the Darcy velocity of groundwater is 2.5 ×10^-7 m/s, comparing to ignoring the heat dispersion condition, the computed root mean square error（RMSE） of the average outlet fluid temperature of BHEs is 0.4 ℃and the energy efficiency coefficient increases 4.5% while the longitudinal dispersivity is set to 5 m.