流速对桩-筏基础中能量桩换热效率与热力耦合特性影响研究

Study on influence of flow velocity on heat transfer efficiency and thermalcoupling characteristics of energy piles in pile-raft foundation

能量桩是一种承担上部建筑荷载并传递浅层地温能的新型桩基技术,其换热效率和附加温度应力是该技术的两个关键性科学问题。已有的研究主要针对单根能量桩的热力耦合特性,对于桩-筏基础中能量桩的研究相对较少。基于桩-筏基础,开展不同换热液流速下单根3U型埋管能量桩换热效率和热力耦合特性现场试验,在实测制冷工况下研究能量桩桩体温度与应力、筏板温度与变形的变化规律,探讨入口流速的影响规律。研究结果表明,文中试验条件和制冷工况下能量桩在0.8、0.4、0.2 m/s三种流速下的换热效率分别为75.0、82.5、63.8 W/m;能量桩受筏板约束影响,在桩顶处产生最大约束拉应力,约为38.9 kPa,筏板下侧产生的最大约束拉应力约为47.2 kPa;随着流速逐渐降低,桩体温度小幅回升,桩身约束拉应力值减小;短期制冷工况对筏板温度的影响可忽略不计。

Energy pile is a new type of pile foundation technology that bears the load of the upper building and transmits the shallow geothermal energy.Heat transfer efficiency and thermal induced stress are two key problems must be solved before energy pile can be widely applied.Present studies mainly focus on the thermo-mechanical coupling characteristics of single pile,while the researches on the thermo-mechanical characteristics of pile-raft foundation are relatively limited.Based on the pile-raft foundation,field tests on heat transfer efficiency and thermo-mechanical characteristics under different velocities were carried out.The temperature and stress changes of both energy pile and raft under cooling condition were measured and analysed.The influence caused by different velocities was also discussed.The results show that when the energy pile is running at the velocities of 0.8,0.4,0.2 m/s,the corresponding heat transfer efficiency are around 75.0,82.5,63.8 W/m.Under the influence of raft restraint,the maximum constrained tensile stress of pile is about 38.9 kPa,which is generated in the top of the pile;and the maximum constrained tensile stress of raft is about 47.2 kPa,which is in the bottom side of the raft.As the velocity of flow decreases,the temperature of pile rises slightly is increased and the value of tensile stress decreases.The influence of short-term cooling condition on the temperature of the raft is negligible.