Numerical Simulation Of Pumping-injection Wells Spacing Of Groundwater Source Heat Pump In Gravel Aquifer

The technology of groundwater source heat pump has been widely used for its sustainable development and utilization of geothermal energy, and has a high operating efficiency, and is friendly to environment. In order to ensure the efficiency and energy-saving features of groundwater source heat pump, the key factor is to maintain that a constant temperature of the pumping well. Since there are some differences between the temperature of injection water and the initial temperature of the underground aquifer, this can lead to the changes in the ambient temperature of the injection wells. Whether the changes can affect the water temperature of the pumping well, and the degree of the influence, these depend on the distance between the pumping and injection wells.The basis of determining the appropriate pumping-injection wells spacing is researching the changes of the underground aquifer temperature field which been led to by the pumping irrigation behavior. This article established a three-dimensional numerical model on the basis of groundwater seepage-heat transfer theory, and used the finite difference software Flowheatl.0to simulate and analyze the influence of the aquifer thickness, pumping capacity, natural groundwater hydraulic gradient and the distance between the injection wells on the pumping-injection wells spacing. This will provide foundation for determining the appropriate distance between the pumping-injection wells spacing.Firstly, the article researched the effect of aquifer thickness on the designed spacing of pumping-injection wells without considering the groundwater hydraulic gradient. The results show that, under the same conditions, the thicker aquifer thickness, the smaller the magnitude of the temperature of the pumping well, but there may be phenomenon that different aquifer thicknesses with the same well spacing; under the same pumping-injection conditions, the designed spacing of pumping-injection wells in the gravel aquifer should be more than the distance in the coarse sand aquifer.Secondly, the impact of the pumping capacity on the designed pumping-injection wells is analyzed. The results show that, with the same conditions, the greater the amount of pumping-injection flow, the bigger the area of influenced by water head and temperature of injection water; within a certain temperature difference between pumping water and injection water, no mater in the coarse sand aquifer or gravel aquifer, greater the pumping flow, the designed spacing of pumping-injection wells should also be greater; When extracting the same heat from groundwater, the designed spacing of pumping-injection wells of "large flow and small temperature difference" should be greater than that of "small flow and large temperature difference".Then, through the study of the natural hydraulic gradient, the results show that, if the natural underground aquifer hydraulic gradient can not be ignored, the pumping well located in the runoff upstream and the injection wells located in the runoff downstream, this well distribution is the most beneficial to mitigate the effect of heat transfixion; using this well layout, the greater the natural hydraulic gradient of the aquifer, the smaller the designed spacing of pumping-injection wells can be; in the same condition of pumping-injection flow, the designed spacing of pumping-injection wells in gravel aquifer can be less than that in coarse sand aquifer, and the effect of the natural hydraulic gradient on the designed spacing of pumping-injection in gravel aquifer is more obvious.Finally, analyzed the influence of the distance between injection wells on the designed spacing of pumping-injection wells, the results suggest that, the effect on determining the spacing of pumping-injection wells is not obvious.