耦合抽-灌井式埋地换热系统咸水层传热过程研究

基于多孔介质传热、传质控制方程与线热源理论,以耦合抽-灌井式埋管换热系统为研究对象,建立埋地换热器及咸水层水-热-盐运移耦合数学模型。选用有限元计算软件FEFLOW6.1针对不同运行模式下咸水层温度场演变规律与传热过程开展模拟研究。计算结果得到,单独使用埋管换热系统,运行8年后观测井2所在咸水层温度上升1.4℃;采用耦合式系统,相同观测点未出现升温趋势,有效避免"热堆积"发生。在抽-灌水量不变条件下,采用去离子水回灌时观测井1所在中粉砂咸水层达西流速高于原水回灌工况54%。研究表明,回灌溶液盐度降低是诱导地下水渗流速度上升,对流换热与热弥散效应增强的主要作用机制。

Researches of the Heat Transfer Process in Brackish Aquifers upon the Coupling Pumping and Injection Wells with Underground Heat Exchangers System

A three-dimensional mathematical model coupling of heat transferring of ground heat exchangers and groundwater flow and thermal transferring and solute movement in brackish aquifers is established based upon the control equation of the thermal and mass transferring in porous media and the line heat source theory. The calibrated numerical model is used to probe into the variation regularity of the geo-temperature field and the thermal transfer characteristics in different operating modes adoption of finite element calculation software FEFLOW6. 1,which the coupling pumping- injection wells and multi-borehole heat exchangers system is taken as the research object. The simulated calculation indicates that the temperature of the 2ndobservation well increases 1. 4℃ at the end of the 8thoperation period in the medium silt aquifer when the ground heat exchangers are operated individually. However,the temperature of the same observation point is no rising trend during the couple system operating,which the hot stack can be avoided effectively. Meanwhile,the comparison demonstrates that the rate of improvement in Darcy velocity in the condition of recharging the deionization solution is 54% more than recharging the original brackish solution when the pumping and recharge water remains the same. The results show that the seepage velocity of groundwater can be increased while the recharge solution salinity is decreased,which heat convection and thermodispersion are intensified and then the influence scope and range of the recharge solution temperature field are increased.