【作者】 雷海燕；

【导师】 朱能； 吕石磊；

【作者基本信息】 天津大学 ， 供热、供燃气、通风及空调工程， 2011， 博士

【摘要】 地源热泵系统近年来在我国建筑中得到了广泛应用,回填材料对地埋管换热器传热性能的影响至关重要。本课题探索采用相变材料(PCM)作为地埋管换热系统的回填材料,与普通回填材料进行对比理论分析和实验研究,研究成果将对相变回填材料的实际工程应用有重要的理论参考意义。本文对并联双U型和套管式地埋管换热器的传热性能进行了理论分析,选用废动物油和混合酸作为套管式换热器的相变回填材料,与沙土回填进行了对比研究,计算了相变区域内固相和液相的温度分布。结果表明:Ste数越大,相界面的移动速率越快,完全凝固(熔化)的时间越短。流量为180 L/h时,Ste ?0.06时的完全凝固时间为7.73 h,PCM和沙土回填时的热影响半径分别为0.23 m和0.66 m; Ste ?0.15时的完全熔化时间为4.04 h,相应的热影响半径分别为0.18 m和0.50 m。本文建立了地埋管换热器传热性能测试系统,进行了并联双U型埋管换热器的现场测试,得到了不同加热功率下的单井供热量、岩土热导率和热影响半径;建立了天津工业大学新校区A区土壤源热泵土壤温度测量系统,可实时监测钻孔内不同深度处逐日、逐月、逐年的温度曲线。本文建立了套管式换热器的模拟实验系统,该系统与实际套管式换热器在结构上实现了几何相似、在流动中实现了运行相似。采用不同回填材料与流体流量和入口温度的组合,进行了外进内出流动方式下的对比实验。结果表明:流量为250 L/h时,在PCM完全凝固(熔化)时间内,径向距离0.1 m处的土壤温度下降了0.7℃(取热工况)或上升了3.5℃(放热工况),而径向距离0.3 m的土壤温度无明显变化;当回填材料分别为沙土和PCM时,取热工况下流体的进出口温差为0.16℃和0.10℃;放热工况下为0.24℃和0.08℃。本文基于套管式换热器模拟系统的理论分析和实验结果,预测了地埋管换热器采用相变材料回填的工程应用可行性。结果表明地埋管相变回填材料可缩小钻孔间距。若能实现钻孔密封并获得蓄热性能良好且价格低廉的相变材料,地埋管热泵系统采用PCM回填将会有很好的应用前景。更多还原

【Abstract】 Ground Source Heat Pumps (GSHP) are widely used for heating and cooling buildings, backfill material is essential in improving the thermal performance of Borehole Heat Exchangers (BHE). In this thesis, an analytical study of the thermal performance of BHE with both phase change materials (PCM) and soil backfill material is compared to and verified against an experimental study.Thermal performance of BHE’s made of a U tube and a coaxial pipe where waste animal oil and a mixture of capric and lauric acid were used as PCM backfill material based on differential scanning calorimetry (DSC) were studied analytically. Heat transfer in the PCM and soil backfill was analyzed, and the temperature distribution in both solid and liquid phases was calculated.The results indicate that the larger the Stefan number is, the faster the phase interface moves, and the smaller the total solidification (melting) time of the PCM backfill is.When the mass flow is 180 L/h, the total solidification time is 7h44min with a Stefan number of 0.06, the thermal disturbance distances due to the fluid temperature away from the borehole central line are 0.23 m and 0.66 m with PCM and soil backfill materials, respectively. The total melting time is 4h02min with a Stefan number of 0.12, and the corresponding distances are 0.18 m and 0.50 m, respectively.A BHE thermal performance test system was also set up, and an in situ experiment for double U tube carried out, heat output of single borehole, heat conductivity of soil and the thermal disturbance distance under different heating load conditions was measured.A real-time monitoring system of soil temperature for GSHP which monitors the daily, monthly and annual temperature distribution was developed at different depths of the borehole at New Campus of Tianjin Technology University.A concentric annular pipe borehole heat exchanger laboratory setup was made, mimicking industry geometry and kinetic similarities.A combination of different backfills, fluid mass flows and inlet temperatures of fluid was tested, with fluid inflow into the outer pipe and coming out from the inner pipe were studied. The results show that when the mass flow is 250 L/h, during the complete PCM solidification (melting) time, soil temperature at a distance of 0.1 m from pipe central line decreased 0.7 oC ( heat extraction) or increased 3.5 oC ( heat injection), but soil temperature at a distance of 0.3 m from pipe central line did not change. When the backfill materials are soil or PCM respectively, temperature difference of fluid are 0.16 oC /0.10 oC for heat extraction, and 0.24 oC /0.08 oC for heat injection.Feasibility of practical application of PCM as backfill material was examined, based on an analytical experimental study. The results indicate that using PCM could shorten the distance between boreholes. If the borehole can be sealed well, and low price PCM are readily available, the practical application of PCM as backfill material can have a bright future in conjunction with borehole heat exchanger systems.更多还原