Laboratory Test On The Effect Of Temperature On Particle Transport In Porous Media

The transport of suspended particles in porous media is a hot study topic in the field of geotechnical engineering in recent years. It has important significance in sewage treatment, artificial recharge of ground water, heavy metal pollutant treatment, biofilm bacteria purification and nuclear waste disposal.It has found in recent studies that the temperature will also affect the migration and deposition of suspended particles.Through laboratory experiments and theoretical analysis, the transport process of suspended particles in porous media under different thermal has been studied.Other influence factors which are combined with flow velocity、 particle concentration、 tracer、 injection time and suspended particle size have been compared, the effect of temperature on the transport of the suspended particles in saturated porous media has also been revealed. Then, the transport parameters in convection-diffusion equation have been theoretically solved,and breakthrough curves have been fitted.The main contents are as follows:(1) To study the effects of temperature and other physical factors on the transport of suspended particles in saturated porous media, soil column seepage tests have been carried out under three different temperatures、 three different flow velocities and six different particle sizes. The results show, for the same size particle under the same flow velocity, the peak concentration of breakthrough curves decreases and its pore volume increases with the increasing temperature.(2) To compare the differences between suspended particles and tracer (fluores-cein sodium) transport processes, soil column seepage tests with tracer have been carried out under three different temperatures、 three different flow velocities and two different particle sizes. The results show, under the same flow velocity, the pore volume of the peak concentration of silicon particles is smaller than the pore volume of the peak fluorescence value of fluorescein sodium.The peak concentration of silicon particles decreases significantly with the increasing temperature, while the peak fluorescence value of fluorescein sodium increases slightly.(3) To study the effects of measurement conditions on turbidity and fluorescence value, soil column seepage tests with tracer have been carried out under three different temperatures、 three different flow velocities and two different particle sizes. The related datas of effluent have been measured under three different conditions: turbidity and fluorescence value measured immediately, turbidity and fluorescence value measured when the effluent cools to room temperature, and fluorescence value measured in supernatant after 24h. The results show, different measurement conditions (temperature, time of repose) almost have no effect on the turbidity of silicon particles and fluorescence values of fluorescein sodium.(4) To study the effect of the duration of injection time on the transport of suspended particles, soil column seepage tests with one particle size have been carried out under two different temperatures、 two different flow velocities、 and three different injection time. The results show, under the constant flow velocity and temperature, the maximum concentration of the breakthrough curve decreases and its pore volume increases with the increasing injection time. Under higher flow velocity, with the increasing injection time, the maximum concentration occurs at a certain point becomes persistant near a pore volume, and even there is a concentration platform on which the concentration is close to the maximum concentration and fluctuates slightly around the maximum concentration.(5) The transport parameters (diffusion coefficient DL、deposition rate Kdep、 average particle velocity u) have been determined by theoretical formula (advection diffusion equation with deposition coefficient) and breakthrough curves have been fitted. Under the constant flow velocity, the particle diffusion coefficient decreases and the particle deposition rate increases with the increasing temperature, while the average particle velocity changes little. Under the constant temperature, particle diffusion coefficient、particle deposition rate and the average particle velocity all increase with the increasing flow velocity.