| With the development of utilization of shallow geothermal technology,ground souce heat pump(GSHP)has appealed more and more attention of people.Compared to air souce heat pump,GSHP has a superior ability of sustain temperature and heat storage,the main utilization form of GSHP was bore-hole heat exchanger(BHE).BHE is used to contact the underground environment directly,the risk of underground pollution have been increased greatly due to reaching the life span of the tube material and leakaging of the working fluid appendix,now,and there is rare research on this problem.Considering the large potential of underground contamination caused by the considerable utilization scale of the BHE,a simulation of the migration of BHE leakage contaminant under the the actual working condition in porous medium has been done by using LBM.In this work,according to the geometry character of the BHE and the real working condition,a physical model of migration of leakage contaminant of BHE has been built and simplified it by an axisymmetric LBM model,a computer programe was designed to calculate the result.The concentration distribution of contaminant was simulated under the condition of no underground flow and alternating hot and cold periodic temperature boundary conditions.Analogous to actual operating condition,make the whole process into four parts heat injection,heat recovery,heat extraction and heat recovery,analised the impact of temperature Raley number(Ra_t),concentration Raley number(Ra_c),Leuis number(Le),the character of porous medium like Darcy number(Da)and porosity(?)and the different order of working condition.According to the result:(1)the underground flow has a significant impact on the distribution of contaminant.There exists a relative coefficient of the impact caused by temperature and concentration change which isψ=|(Ra_t/Ra_c)Le|,when there have two factors as the driving force of the fluid,temperature and concentration,in a physical process.According to this coefficient the direction of flow can be recognized and know the distribution of the contaminant.Whileψ<1,the gravity change mainly comes from the concentration change,in the whole process the fluid flow in the same direction,under the impact of the movement of the liquid,the contaminant goes down over time,as a result,the scale of the concentration field keep expand;whileψ>1,the majority of tha gravity change is caused by the temperature change,in the heat injection and the followed recovery parts the concentration field shows a go up trend,and in the heat extraction and the followed recovery parts the trend of concentration goes down.Compared withψ<1,this condition has a smaller scale of the concentration field;whileψ=1,the change in gravity caused by the change in temperature and concentration is equivalent,the scale of concentration field is the smallest between the different simulated conditions but it also shows a considerable go down trend.(2)The concentration distribution will be changed by changing the porous medium,decreasing Da can contribute a positive effect on sustaining the contaminant in a relative stable scale especially in vertical direction.Compared to reduce Da,lower porosity medium can also reduce the migration of the pollutant slightly. |
