【作者】 郭涛；

【导师】 刘方；

【作者基本信息】 重庆大学 ， 供热、供燃气、通风及空调工程， 2008， 硕士

【摘要】 节能减排是当今全球关注的焦点之一。地源热泵技术具有显著的节能环保特点,正迅速成为暖通空调行业节能减排的重要手段。在地源热泵系统的研究中,地埋管换热器换热性能的研究是其中的重点与难点。地埋管换热器换热性能的研究是推广地源热泵技术的关键。开展地埋管地下换热器的传热特性以及地埋管换热器换热效率的研究,进而为地源热泵系统的优化设计提供理论和设计依据,本研究有重要的学术和工程应用价值。本论文选取占地面积小、适用范围广、性能稳定、换热效率高等显著优势的垂直U型地埋管换热器的土壤源热泵为研究对象。针对地源热泵工程实际,开展了系列实验、理论分析和数值模拟研究,论文主要工作和结论包括:实测对象为重庆某医院地源热泵系统,实测分冬季、过渡季节(3月和5月)和夏季三个阶段进行。热泵运行期间,在不同季节工况下,地埋管进、回水管在地下1m测点与地下9m测点处的水温值出现突降或突增的过程,地下9m与地下29m、地下29m与地下59m测点间的水温差值呈递减变化,且水温差值维持在2℃以内,这表明地埋管与土壤间的主要换热是与浅层土壤之间进行的,随着深度的增加,地埋管与土壤间的换热开始趋于平缓。在实验测试的基础上,建立了垂直U型地埋管换热器进、回水管内流体传热和流动模型、岩土传热模型。采用PHOENICS程序对就地埋管换热器的换热情况进行了模拟分析,模拟结果和实验结果一致。同时探讨了埋管深度、回填材料、U型埋管支管间距及管内流体流量等因素对地埋管换热器换热能力的影响。对影响地埋管换热器换热性能参数进行研究,结果显示:80m埋管的总换热量要高于60m埋管,应考虑地埋管换热器与土壤间的换热有可能在埋管最深处前就已达到换热饱和状态,因而在地源热泵系统的设计中应选择满足换热器最佳换热要求的最佳埋管深度;增强回填材料的导热性能可增加地埋管换热器换热能力,但支管间热短路效应也随之增加;提高U型埋管支管间距可降低支管间的热短路效应,提高地埋管换热器的换热能力;不同流量下,地埋管换热器的换热量并非随流量的增加而增加,地埋管流量与水泵扬程有关,因此在保证系统正常换热的情况下,必存在一个使地埋管换热器达到最佳换热效果的最佳流量。更多还原

【Abstract】 Along with the policy of the energy-conservation and reduction, ground source heat pump (GSHP) technology has become a hot spot research with the features of energy-efficacy and environmental protection in HVAC industry. Focus and difficulties on GSHP system study is the research for the underground heat exchanger system.Study on the characteristics of the heat transfer for the underground heat exchanger in the GSHP system is the key to popularize GSHP system, which can optimize design of GSHP system. Therefore, it is worth making such research on GSHP system.With the advantages of using small area,stable performance,high efficiency of heat transfer ,vertical U-tube GSHP system has been wide concerned and application. This paper aims at a comprehensive understanding of working condition of vertical U-tube GSHP system by using experimental, theory analyzed and numerical method on actual project.The GSHP system used by hospital in Chongqing city is chosen for experimental object, and three test stages are included. Tests on the underground heat exchanger in different working conditions dictate that temperature at test spots between 1m and 9m below surface of soil rises and down sharply;temperatue at test spots among 9m,29m,and 59m below surface of soil decrease with increasing depth, temperature difference within 2℃.It illustrates that heat exchange between underground heat exchange and soil is mainly done in superficial layer of soil and then becomes to be steady with increasing depth.Vertical U-tube heat exchanger model is established by CAD and CFD technique is used to simulate the actual working condition of GSHP system by using above established heat exchanger model. The result of simulation is good with the experiment, that is to verify the mathematics physical model. The factors, which including the length of U-tube, backfill materials, interval space between 2 branches of U-tube, flow rate in U-tube, are studied to analyze their effect on the performance of the underground heat exchanger.Studying on factors which effect on the performance of underground heat exchanger by using PHOENICS, the results indicate that total heat exchange amount of the U-tube with 80m depth is higher than that of the U-tube with 60m depth; while considering heat exchange between underground heat exchanger and soil doesn’t exist in whole tube ,it illustrates that the length of U-tube should be chosen reasonably to make GSHP running in the best working condition.GSHP system performance is better by enforcing the thermal conductance of backfill materials, which can also aggravate thermal short circuit. The thermal short circuit can be reduced by lengthening the interval space between two branches of U-tube, which can promote the performance of underground heat exchanger. The thermal performance of underground heat exchanger is various with various flow rates, therefore, that are there should be an optimal flow rate which makes underground heat exchanger performance best.更多还原