【作者】 倪龙；

【导师】 马最良；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风及空调工程， 2007， 博士

【摘要】 同井回灌地下水源热泵的源汇井现在有两种型式:抽灌同井和单井循环系统,它们均能在一口井内完成抽水和回灌。对于抽灌同井,其井内通过隔板把井分成三部分,井的下部是低压吸水区,上部是高压回水区,中间为隔断区。潜水泵运行时,地下水从低压吸水区被抽至井口换热器中,与热泵低温水换热,再由同井返回到高压回水区。单井循环系统是土壤耦合热泵套管换热器的一种变形,在强岩层之下取消了套管外管,水直接在井孔内循环与井壁岩土进行热交换。高峰负荷期间,为了满足负荷要求,单井循环系统通过排放一定比例的循环水来引入一定量的地下原水。本文系统地研究了这两种型式源汇井的运行特性,主要研究内容和取得的成果如下:(1)开展了抽灌同井的现场试验研究工作,提供了近两年的测试数据。通过现场试验,将热贯通分为瞬变热贯通和缓变热贯通。系统存在瞬变热贯通时,会使抽水温度随着回水温度变化。为了缓解抽水温度的变化和减轻回灌压力,将排放引入到抽灌同井系统中,组成单、双井混合系统。同时测试结果也表明抽灌同井冬夏均运行时,季节性储能是抽灌同井低位热量来源的一个重要组成部分。(2)受测试结果的启发,根据源汇井的建造工艺,将抽灌同井分为无回填抽灌同井和砾石回填抽灌同井。分别建立了无回填抽灌同井、砾石回填抽灌同井和单井循环系统的地下水流动和换热数学模型,并给出了数值求解方法。通过收集到的丹麦技术大学无回填抽灌同井的试验数据、美国宾夕法尼亚州立大学无排放单井循环系统的试验数据以及笔者开展的北京某砾石回填抽灌同井的现场试验数据,较全面地验证了本文建立的数学模型。(3)在Hantush非完整井抽水降深理论解的基础上,利用叠加原理推导了单一介质承压含水层中无回填抽灌同井的地下水降深理论解,并得出了稳态降深方程、稳态渗流速度方程、准稳态时间方程和理想井间距方程。源汇井特性分析表明,抽灌同井运行时会发生热贯通现象,但由于热影响范围较大,能承担较大的负荷。砾石回填抽灌同井较无回填抽灌同井能够减小抽水和回灌的压力,热贯通也更严重。对于单井循环系统,原水交换承担了很大一部分负荷,使得单井循环系统较套管换热器能够承担更大的负荷;同时由于含水层中地下水流速小,热影响范围小,其承担负荷的能力又比抽灌同井小。此外还对热贯通现象进行了定量研究。(4)进行了参数研究。研究结果表明,对抽灌同井,渗透系数是抽水和回灌难易程度的关键;渗透系数比是抽水温度变化的关键影响因素;小流量、大温差对于抽灌同井是可行的。对于单井循环系统,其没有回灌困难的问题。渗透系数亦是一个关键性参数;渗透性能较好的含水层极大地提高了系统承担负荷的能力;增加孔深是提高系统承担负荷的能力的有效方法。排放减轻和延缓了抽水温度的变化,但排放的比例和起到的效果并不对等,因而排放应该作为一种紧急措施,来缓解回灌压力和抽水温度的急剧变化。(5)在同井回灌地下水源热泵常年运行工况分析的基础上,对运行过程中的季节性储能现象进行了定量地研究。计算表明,抽灌同井常年运行时,出现了明显的季节性储能现象,季节性储能提供了很大一部分热源或热汇。当累积负荷不平衡时,长期运行抽灌同井的抽水温度会出现明显地年度升高或降低,严重时使源汇井失效。然而单井循环系统并没有出现明显的季节性储能现象,储能比近似等于0。单井循环系统前期的运行对后期的抽水温度基本没有影响,因而对于单井循环系统不用考虑负荷不平衡的问题。本文的研究工作对深入认识同井回灌地下水源热泵的源汇井提供了理论参考,为辨析抽灌同井和单井循环系统的混淆提供了依据。更多还原

【Abstract】 The heat source / sink wells (HSSW) of groundwater heat pump with pumping and recharging in the same well (GWHPPRSW) have two types now, one is pumping & recharging well (PRW), the other is standing column well (SCW). They both can finish the operations of pumping and recharging in only one well. For PRW, the well is divided into three parts by clapboards: low pressure (production) space in the low part of the well, seal section in the middle part and high pressure (injection) space in the top part. When the submersible pump is running, groundwater is sent to heat exchanger at the wellhead, where it releases heat, and then is sent back to the injection space through the same well. SCW can be regarded as a transfiguration of the coaxial heat exchanger of ground-coupled heat pump (GCHP). It cuts down the outside pipe of the coaxial pipe in competent bedrock, and lets fluid circulate directly in the borehole to exchange heat with rock of the borehole. During peak load periods, SCW can bleed some circulation water from the borehole to induce original groundwater flow.In this work, the operation performance of these two types of HSSW was studied in detail and systematically. The main works and results of this dissertation are listed as following:(1) The in-situ experiment of PRW was performed, and nearly two years’experimental data were obtained. Based on in-situ test, the phenomenon of thermal transfixion was delimited as the slow-response thermal transfixion and the fast-response thermal transfixion. When the fast-response thermal transfixion was existence in the system, the pumping temperature would vary along with the recharging temperature. The bleed tragedy was introduced to PRW, and the HSSW was called single-double wells mixed GWHP system. At the same time, the test results showed that for full-year-operation PRW the seasonal thermal energy storage (STES) played an important role in the heat source for PRW.(2) The PRW were sorted as non-backfill PRW and gravel-backfill PRW according to the technology of well construction and the instruction of the in-situ test results. The models of groundwater flow and heat transfer for non-backfill PRW, gravel-backfill PRW and SCW were established, respectively. The methods of numerical solution were provided. The mathematic models were validated more completely through the experimental data collected from Technical University of Denmark for non-backfill PRW and from Pennsylvania State University for SCW as well as conducted by us for gravel-backfill PRW.(3) The analytic drawdown equation for non-backfill PRW in a unitary homogenous confined aquifer was acquired through the principle of superposition based on the analytic drawdown equation for partially penetrating well presented by Hantush. Equations of steady drawdown, seepage velocity, quasi steady time and ideal well distance were gained through the analytic drawdown equation. The characteristic analyses results showed that the phenomena of thermal transfixion would happen when PRW kept running. Even though the existence of thermal transfixion the PRW could burden big load because of the large thermal effective radius. Compared with the non-backfill PRW, the gravel-backfill PRW could reduce the pressure of pumping and recharging and had more serious thermal transfixion, too. For SCW, the original groundwater exchange burdened much large part of load, which made SCW can undertake larger load than the coaxial heat exchanger. Meanwhile, the load ability of SCW was smaller than that of PRW for the smallness of groundwater velocity in aquifer and the thermal effective radius. In addition, the phenomena of thermal transfixion were studied quantitatively.(4) The parametric study was presented. For PRW, the results showed that the coefficient of permeability was critical for pumping and recharging and the ratio of permeability coefficient (horizontal / vertical) was the key factor for the variation of pumping temperature. The operation strategy of small flow rate and large temperature difference was feasible to PRW. SCW didn’t have the trouble of recharging. The coefficient of permeability was also the key parameter to SCW. The load ability of SCW could be promoted greatly if SCW was in the aquifer with good permeability. The increase of borehole length was an effective method for SCW to enhance the ability of load. The bleed strategy could alleviate and postpone the change of pumping temperature. But there was unbalance between the rate of bleed and its impact. Therefore, the bleed strategy should be adopted as an emergency method to delay the sharp change of recharging pressure and pumping temperature.(5) The phenomena of seasonal thermal energy storage (STES) in the operation period were discussed on the basis of the analyses of perennial behavior of GWHPPRSW. The calculation results showed that when PRW ran perennially the phenomena of STES appeared apparently and the STES provided much large part of heat source or sink to PRW. When the accumulated load kept unbalance, for perennial-operation PRW the pumping temperature could increase or reduce much annually, which even made PRW not work. However, for SCW the phenomena of STES didn’t occur and the thermal energy storage ratio was nearly zero. There was little effect to the later pumping temperature of SCW due to its previous operation. Thus, the problem of load unbalance didn’t need to be considered at all for SCW.The works of this dissertation provided the theroical references to comprehensively understand the HSSW of GWHPPRSW and offered the evidences to distinguish the confusion of PRW with SCW.更多还原