Numerical Simulation Of Water-Thermal Coupling Temperature Field For In-situ Heat Conduction Remediation Of Groundwater

In-situ heat conduction remediation of groundwater can directly introduce thermal energy into the aquifer,providing a suitable temperature zone to influence the physical/chemical properties of the pollutant/remediation agent and speed up the reaction rate of the subsurface pollutant.The technology with its high heat transfer efficiency,not limited by the underground heterogeneity of the advantages,coupled with the continuous reduction of heating energy consumption,can meet the purpose of shortening the engineering remediation cycle,cost saving.In recent years,in-situ heating technology has been more frequently combined with other remediation methods.How to increase the temperature of groundwater economically and effectively to improve the removal rate of pollutants and achieve the purpose of rapid remediation has attracted widespread attention.Based on the heat transfer law summarized in the indoor heat conduction technology heating aquifer experiment,this paper uses Fluent solution software based on finite volume method and adopts porous media heat transfer model as the mathematical model of in-situ heat conduction remediation of groundwater to analyze the variation law of different factors on groundwater heat transfer.From the perspective of remediation engineering application,the heating method of the heating rod is changed by Fluent udf,the transient numerical calculation is carried out for the temperature field change under different working conditions during the heating process,and the optimization design is carried out for the energy consumption problem in the project.The research conclusions are as follows:（1）The thermal and physical properties of aquifer medium change the efficiency of heat conduction,thus affecting the process of groundwater heat transfer.When the specific heat capacity of aquifer medium doubles,the temperature diffusion distance at each moment is about 1/3 smaller than that of the former,and the time for each monitoring point to reach the effective remediation temperature is also doubled.The increase of thermal conductivity of aquifer medium has little influence on the diffusion distance of effective remediation temperature during heating,and the diffusion distance decreases significantly after heating is stopped.（2）Hydrogeological parameters change the basic way of groundwater heat transfer,thus affecting the process of groundwater heat transfer.The increase of groundwater flow rate leads to the enhancement of thermal convection,which makes the monitoring points downstream of the heating rod reach the effective repair temperature earlier,but this law is significant only when the groundwater flow rate is greater than 1 m/d.The larger the porosity is,the more active the groundwater flow and the more significant the thermal convection,which plays a leading role in the distribution of regional temperature field.（3）The variation characteristics of temperature field in coarse sand,medium sand,fine sand and silty sand media under five heating powers were considered respectively.Under the condition of increasing the same power,the relationship between the heating effect of medium is as follows: coarse sand < Medium sand < Fine sand < Silt;The farther the distance from the heating rod is,the smaller the temperature increase is.The difference between the increase value of the monitoring point 2 m away from the heating rod and 2.5 m away from the heating rod is less than 2℃,and the effective thermal conductivity radius of the heating rod is 2 m.For the heating rod with a length of 2 m,the temperature of 1000 W rises gently in all types of aquifers,which can be used as a stable power to maintain the temperature of aquifers.The effective remediation radius of 4000 W can reach 2 m,and the spacing of heating rod can reach more than 4 m,which can meet the needs of the project.（4）Two heating rod operation schemes were designed for different aquifer media.The results show that when the length of the heating rod is 5 m and the space between the heating rod is 4 m,the time available for the remediation work is more than 300 h after the heating area reaches the effective remediation temperature,and the remediation work time is sufficient.The heating scheme takes energy consumption as the priority.For each scheme with an interval of 5 m,it is necessary to ensure that the aquifer is stabilized in the effective remediation temperature range as soon as possible within the remediation cycle,and the heating scheme takes efficiency as the priority.This paper has important academic significance and application value to study the heat transfer law of groundwater in-situ heat conduction restoration technology,and has important guiding significance to practical production work.The research results and numerical simulation technology can be extended to other similar areas of scientific research and production work.