Research On Hydraulics Of Groundwater Source Heat Pump System And Its Influence On Temperature Field

Aquifer thermal energy storage technology for Groundwater source heat pump (GSHP),which emerged in 1970s and was widely used in 1990s in those of western countries,is a new sustainable development use type of geothermal energy.GSHP uses groundwater as its heat source.Aquifers have pores,fissures and caverns and other storage structures in them,and groundwater inside aquifers flows slowly,and also its temperature never changes sharply.These are the characteristics of aquifers. Generally we recharge the wells with some hot water or cold water.The new water pushes the original groundwater away because of the pressure of its own,and then it stays inside aquifers around the wells.The aquifer as storage layer has become a new technology,linked closely with the heat pump technology development.It can predict flow and temperature distribution in the aquifer surrounding the storage well,showing a significant utilization of energy in storage well.And the state of the aquifer around the storage well is affected by two kinds of physical fields,the groundwater flow and the temperature field,which is the result of the coupling of flow velocity and heat transferring in the medium of groundwater.It is essential that the law of the nature of groundwater hydraulics and temperature changes is studied,and then it offers a reliable basis to the projects' design in the underground aquifer.Thesis which combined with the National Science Fund Project "Heat Transform Pile -Hydro-Soil system's THM Coupling effect Mechanism Research (No.40472134)",and used the groundwater flow numerical simulation software of MODFLOW and COMSOL Multiphysics finite element software,researches hydraulic mechanism and hydro-thermal coupling which are GWHP's thermal energy storage of aquifer.Paper discusses four aspects:1.Hydraulic mechanism analysis on thermal energy storage of aquifer;2.Analysis on seepage flow field of the groundwater source heat pump system and its influence on the temperature field;3. Test of model validation in Shenyang;4.Study on model of Simulation,prediction and Analysis.Part one:firstly proposes the concepts relating to the underground storage aquifer hydraulics,then establishes the pumping,irrigation hydrodynamic numerical model combining the features of the well pumping,well irrigation,and gives the numerical solution of the model and simulation of the numerical software,and analyses the general characteristic of the groundwater flow field during the operation process of wells pumping and wells irrigation,convects through the preliminary. Propose the defects of the flow transfixion,in the actual project the heat transfixion is not conducive to the use of energy,in order to reduce the heat proliferating to the affected area of the pumping well,can reduce the pumping capacity,and in the permited conditions to increase the spacing between the pumping well and injection well,when the pumping,irrigation well run a cycle adjust the position of the pumping,irrigation well so as to reduce the affected area of the heat proliferating.Part two:First of all,give a brief elaboration about various types of thermal conductivity mechanism,analyze the thermal conductivity mechanism in the underground energy storage layer,based on the analysis propose model assumptions and limiting conditions,and establish numerical models about the thermal conductivity in the underground energy storage layer;analyze the relations between the seepage field and temperature field in the energy storage layer,establish the water -hot-coupling model;then raise the concept of heat breakthrough,that is heat transfixion which plays a direct impact on the efficiency of work in the underground water-source heat pump mining project.At last conclude the impact from underground seepage field to the heat transfixion,put forward that in the practical engineering application about the underground water-source heat pump mining,the pumping wells(above) is relatively near to the recharge wells(above),the temperature about the exploitation wells(above) is usually impacted by the recharge water,the occurrence of the potential phenomenon and its impact on the exploitation wells temperature will directly affect the effectiveness of the heat pump system and the economic benefits of the project.Therefore,in the design work about the underground water-source heat pump mining project,it needs a specific study about the temperature field of the mining wells and the time of occurrence of the heat transfixion according to the actual geological conditions and the strength of the mining. Part three:carry out field trials about the underground water-source heat pump project which use the pumping irrigation to wells in Shenyang,establish a test model and verify the correctness of the model.Firstly give a brief introduction about the scene of the pumping irrigation to wells,although not perfect in many respects,but as a useful attempt,there is much benefits about the research about the operating characteristics of the pumping irrigation wells in different and the characteristics of the temperature change of the aquifer from the point of view of the practice;Secondly, establish the model for the test site area,from the generalization about the hydro-geological conditions in the area of the test site,establish numerical simulation model about the groundwater flow in the study area,the model identification results show that the model established can characterize the hydro-geological conditions and the rock characteristics of the rock layer dielectric properties in the study area well,the evolution of the Seepage field in the future under the mining system operation conditions will be predicted on the model is adopted;at last according to temperature in this test,couple the underground seepage field and ground temperature field,establish the water-thermal coupling model,and verify the correctness of the model,the results show that the water-thermal coupling model established can accurately portray the characteristics of the groundwater and the temperature field in the study area,and this model can be adopted to predict the evolution of temperature field in the future under the mining system is operating.Part four:combining the numerical model proposed in the third part,this part calculates,simulates and predicts about the layer flow field and temperature field of the double- wells pumping and irrigation underground energy storage,there arises a series of conclusions.In the calculation of the prediction about the Hydro-geological model,predict and simulate the changes of the groundwater flow field when the groundwater source heat pump runs a cycle,give a general characteristics of the groundwater flow field under a running cycle;according to the feature that the hydraulic gradient tends to zero after the pumping,irrigation test runs a certain time, this paper proposes the concept of the flow transfixion,while,in the past literatures it mainly referred the heat transfixion,which is unique in this field;Analyze the impact from the changes of the pumping,irrigation volumes to the flow transfixion based on the above conclusion,and found that the occurrence time of the flow transfixion is shorten with the increasing of the pumping,irrigation volumes,that is unfavorable for mining in the underground water-source heat pump energy mining project,therefore it should to use the small water pumping and irrigation when the underground water-source heat pump is running so as to reduce the occurrence of flow transfixion and avoiding heat transfixion.Through forecasting,simulating and analyzing about the water-heat coupled model,it shows that under the underground water- source heat pump is running,the difference of the pumping irrigation rate will directly affect the change and the distribution of the temperature field;With the increasing of the recharge water temperature,the affected area of the underground temperature field will expand correspondingly;from studying about the different recharge quantity,we can find that the affected area of the recharge quantity will be large when the recharge quantity is large.Therefore,in practical engineering designing,it is important to consider Comprehensive the use of the information from the change data determined in the temperature changes of the hot water pumping,irrigation test and the actual engineering operation,design the optimal rate of pumping irrigation,recharge temperature and recharge quantity suitable to the practical engineering,and then use the energy effectively.