Energy Transport And Heat Transfer On Ground-water Motion Of Pumping And Injecting Well Group

Ground water heat pump (GWHP) is a branch of ground source heat pump (GSHP),which is an emerging and sustainable development mode of shallow layer geothermal energy.It takes groundwater as heat source and water temperature is not affect by four seasonstemperature, meanwhile, specific heat is big and heat transfer performance is good of thewater, in addition, this system runs stably, energy saving and environmental protection.Therefore, GWHP gets a very rapid development in China, and application scope is moreand more widely in recent years.Temperature field change of the aquifer is an important factor to decide the efficacy ofheat pump units, and heat transport rule study of the aquifer is the basic prerequisite for thesustainable running and engineering appraisal. Now, more and more scholars at home andabroad began to pay attention to this research, and the related research work of GWHPsystem develop rapidly in recent years, especially in model analysis and numerical research.However, these simulation researches are mostly focus on the groundwater heat pump withpumping&recharging in the same well or doublet well system, and less on pumping andinjecting well groups, and the related basic scientific research is still far behind the practicalapplication. For pumping and injecting well groups system, heat transport and hydrodynamiccirculation are more active and thermorheologic of the aquifer is more complicated, whichneed to carry out more in-depth research. In addition, limited to the difficulty andvisualization problem of the underground experiments, systematic test study especially thekey mechanism characteristic experiment develop lag, and field experiment and laboratorytests of the water-heat transportation of the aquifer are rare, lack of relevant experimentaldata. Therefore, the basic heat transfer, process evolution and time-varying regularity, etc.are eager to carry out, to solve the blindness of numerical simulation and lack of a broaderconfirmation. This study integrates the National Natural Science Fund, and focuses on the energytransport and heat transfer on the groundwater motion of pumping and injecting well group.Through the experimental research and numerical simulation, to study the effect of variousinfluencing factors to the aquifer temperature field, water level field and velocity field inpumping and injecting well group area, to reveal the development, evolution and actionmechanism of heat flow field in long term running process of the GWHP, and also to expandthe energy transport and heat transfer control theory of the groundwater motion of pumpingand injecting well group, provide the theoretical guidance for further application.The main research works included in this paper are as follows:Establish the experimental system of sand tank seepage based on the principles ofsimilarity theory, to reproduce the aquifer seepage dynamic and process of the pumping andinjecting well group. The paper studied the development and evolution of heat flow field ofpumping and injecting well group under conditions of different aquifer structure, totalamount of pumping and injection. In addition, a contrastive analysis of hydraulic gradientdistribution and seepage velocity change are made, and according to this to explore theactive control mechanism and the pattern of aquifer heat flow field, achieve a controlledground heat transfer process and maximum avoid and alleviate the thermal breakthrough andthermal interaction.Nature cross flow is the main cause to produce the feature difference of aquifer heattransfer, and also the key of thermal breakthrough. The study established the experimentalsystem of sand tank seepage, which can simulate the nature cross flow, and studied thedirection change and energy transport properties of the heat-flow field under different naturecross flow conditions. In addition, this dissertation mainly analyzed the pumping watertemperature, aquifer temperature field, water-level field, thermal breakthrough and thermalinteraction, which can provide a basis for the design of pumping and injecting well groupsystem.It exists two-part cyclical process of water and heat between air conditioning system ofheat pump on the ground and underground aquifers, which form two field coupling problems of the seepage field and thermal potential field. This study analyzed the groundwater motionand its main heat transfer process, and established the model of aquifer heat flow by usingthe computational fluid dynamics (CFD) commercial software FLUENT, meanwhile,geometrical model, boundary conditions, grid division and basic parameters setting areintroduced in details. In addition, verified the model according to the heat flow variableexperiment, which include pumping water temperature validation and aquifer temperaturefield validation. Analysis indicated that this model can be used to analyze and predict theaquifer temperature change of the actual project, which can provide accurate simulation data.The paper carry out the simulation research for multicycle, long time running ofpumping and injecting well group under practical application structure scale condition, tobreak through the limitations of laboratory conditions. The study from running mode, wellgroup arrangement and variable condition control three factors to analyze the water heattransport process of the aquifer in well group area, and according to the pumping watertemperature, thermal breakthrough and thermal interaction to evaluate the work efficiency ofheat pump system. Meanwhile, put forward reasonable layout of well group and systemrunning mode, which can provide the theoretical guidance for further establish and perfectthe heat transfer control mechanism of underground energy mining systems.For nature cross flow aquifer, the paper studied the effect of water direction andvelocity to the temperature field and velocity field of the aquifer, and comprehensivelyelaborated the characteristics of thermal diffusion promote, inhibit and offset under differentwater direction and velocity conditions, to reveal the development, evolution and actionmechanism of heat flow field of the aquifer in long term running process, which can providetheoretical reference and a basis for the practical engineering applications.