钻孔埋管换热器用于寒区隧道消防管网加热保温的理论研究

Theoretical research on application of borehole heat exchangers to heating fire pipes in cold region tunnels

为解决寒区隧道消防管冻结失效问题,提出一种基于钻孔埋管换热器的新型加热保温系统;基于非等温管道流模型,联立消防管段加热过程和埋管换热器换热理论,得到系统运行过程中流体温度分布的解析解。以林场隧道工程为背景,对加热段水温、换热器换热效率等的变化规律进行理论分析与数值验证。研究结果表明:进、出口水温先降低后快速上升再缓慢下降,10 h时达到峰值;加热初期,轴向水温分布为“进口温度高、出口温度低、段中温度突变”,之后在4~5℃范围内近似呈均匀分布;随着系统的运行,换热器平均换热效率稳定在约15 W/m。系统连续运行对地温的影响范围不断扩大,钻孔附近地温不断降低。系统间歇运行模式由设定高限和低限控制,在间歇期内,围岩地温可得到一定程度的恢复,且换热器换热效率较连续运行工况下的高。水温、换热器换热效率等的理论计算结果与数值模拟结果吻合度较高,本文所提出的寒区隧道消防管网钻孔埋管换热保温系统可使消防管段水温维持在设定低限温度以上,节能高效,有一定的应用价值。

A new heating and insulation system using borehole heat exchangers was proposed to solve the freezing problem of fire pipes in cold region tunnels.Using the non-isothermal pipe flow model and combing heating process of fire pipes with heat transfer theory of heat exchangers,the analytical solution to the fluid temperature distribution was established.Further theoretical analysis and numerical verification of water temperature and the capacity of the heat exchanger were conducted based on the background of Linchang tunnel.The results show that the water temperatures of inlet and outlet of fire pipe first decrease,then increase rapidly and then slowly decrease again.The peak of water temperature is observed at 10 h.The axial distribution of water temperature at the beginning of heating process is"high at the inlet,low at the outlet,and a sudden drop at the connection",and then the water temperature is evenly distributed at the range of 4−5℃.The average specific energy output capacity of heat exchangers stabilizes at around 15 W/m with the operation of the system.The soil temperature is disturbed and continues to decrease near the borehole.Discontinuous operation of the system controlled by the default upper and lower limit is good for the recovery of soil temperature around the heat exchangers and has a bigger capacity of specific energy output than continuous operation.The theoretical and numerical results of water temperature and capacity of heat exchangers show great consistency.The proposed heating system with borehole heat exchangers can maintain a higher temperature than the default lower limit of water in fire pipes efficiently and is of relatively high application value in cold region tunnels.