蓄取热工况下同轴套管式地埋管换热器周围土壤温度变化规律

Study on soil temperature variation around coaxial casing ground heat exchanger under heat and release storage condition

为研究不同因素对同轴套管式地埋管周围土壤温度的影响,建立三维同轴套管式地埋管换热器非稳态传热数理模型,利用自建实验台开展试验对数理模型进行试验验证。在此基础上,对蓄取热工况下同轴套管式地埋管的非稳态传热过程进行数值模拟研究,分析了管径、回填材料、土壤初始温度等因素对同轴套管式地埋管周围土壤温度的影响,获得了不同因素对套管式地埋管换热器周围温度场的影响规律。研究结果表明:外管径相同时,内管径的变化对周围土壤温度场影响较小;径向距离0.4 m处,土壤初始温度为14℃时地埋管周围土壤温度最高为17.803℃;循环介质选用氯化钙比选用水换热量提高约23%。试验验证表明,所建模型最大相对误差为12.5%,具有合理性。研究结果显示蓄热时土壤初始温度越高的地区越有利于地埋管周围土壤储存热量,取热时循环介质选择氯化钙溶液可使系统高效运行。

In order to study the influence of different factors on the soil temperature around the coaxial casing buried pipeline,the unsteady heat transfer mathematical model of three-dimensional coaxial casing buried pipeline was established.The mathematical model was verified experimentally using the self-built experimental bench.On this basis,the unsteady heat transfer process of coaxial casing buried pipeline under heat storage and release condition was studied by numerical simulation.The effects of pipe diameter,backfill material and soil initial temperature on soil temperature around the coaxial casing buried pipe was analyzed and obtained.The results indicate that when the outer diameters are the same,the change of inner diameter has little effect on the surrounding soil temperature field.At the radial distance of 0.4 m,the maximum soil temperature around the buried pipe is 17.803℃when the initial soil temperature is 14℃.The heat transfer of calcium chloride as a circulating medium is about 23%higher than that of water as a circulating medium.The experimental validation shows that the established model is reasonable and the maximum relative error is 12.5%.The results show that higher initial soil temperature is beneficial to soil heat storage around the buried pipe during heat storage.Calcium chloride solution can be selected as the circulating medium to make the system run efficiently during heat release.