تخمین آزمایشگاهی ضرایب پراکندگی طولی و عرضی رسوبات ماسه ای در حالت اشباع

نوع مقاله: پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد / دانشگاه تهران

2 استاد / دانشگاه تهران

3 دانشیار / دانشگاه تهران

چکیده

در مقاله حاضر با طراحی و ساخت یک مدل آزمایشگاهی از محیط متخلخل اشباع و همگن انتقال آلاینده شبیه‌سازی ‌شد. هدف اصلی ردیابی پراکندگی آلودگی در مقیاس آزمایشگاهی و تدقیق ضرایب پراکندگی طولی و عرضی آلودگی بود. از ماسه یکنواخت با قطر 5/2-1 میلی متر و از نمک طعام با سه غلظت 5، 7.5 و 10 گرم در لیتر به عنوان ردیاب استفاده شد. از دستگاه EC متر جهت داده برداری استفاده و پس از آن مقادیر غلظت متناظر با هر EC محاسبه شد. مقادیر غلظت در هر گام زمانی با مقدار غلظت که از حل تحلیلی قانون دوم فیک مقایسه شدند و با استفاده از ریشه میانگین مربعات خطا ضرایب پراکندگی بهینه به دست آمدند. در نهایت مقادیر ضرایب پراکندگی طولی ردیاب برای شرایط مطالعه شده به ترتیب برابر3.08e-6 ،3.36e-6 و 3.52e-6 و مقادیر ضرایب پراکندگی عرضی برابر 6.49e-7، 6.58e-7 و 6.79e-7 متر مربع بر ثانیه به دست آمد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Estimation of the longitudinal and transverse dispersion coefficients of sand sediments in saturated state

نویسندگان [English]

  • Mohammad-Reza Nazem 1
  • Kumars Ebrahimi 2
  • Abdolmajid Liaghat 2
  • Shahab Araghinejad 3
1 MSc Student / University of Tehran
2 Associate Professor / University of Tehran
3 Associate Professor / University of Tehran
چکیده [English]

Groundwater resources play an essential role in water supply for drink, agriculture and industry sectors. Now todays, as a result of various reasons, such as urban and population growth, indiscriminate use of fertilizers and chemical poisons, groundwater resources have been populated. Therefore, studying of the pollutions, their fate and preventing groundwater resources from the pollutants, is necessary. In this research study, a laboratory physical model has been designed and performed in order to obtain enough data of pollution movement in a homogeneous porous media. In other words, the main aim of this paper has been tracking the distribution of a conservative tracer in porous media in a laboratory scale model, to estimate the longitudinal and transverse dispersion coefficients. In this study non-cohesive sands were used to create the porous media body in the laboratory model and the grain diameter of the sand was 1-2.5 mm. Salt with concentrations of 5, 7.5 and 10 gr/l was used as a tracer. The porosity of the sand was measured equal to 39% and the hydraulic conductivity of that was measured equal to 172.26 cm/hr using the constant load test. In order to control changes of flow velocity, to minimize test errors, a constant head of water was created over the entrance of the sand body. The flow velocity was also measured equal to 1.21 mm/sec. An EC-meter apparatus was used to measure the EC values of the tracer inside model and then these data were used to calculate the concentration of tracer in different points over time, during each test. Then, the values of the concentration were compared with values of concentration which were obtained from the analytical solution of Fick's second law. Root Mean Square Error criterion (RMSE) was used to compare the measured and calculated mentioned data. According to the results, the values of the longitudinal coefficient tracer for the studied conditions, concentrations of 5, 7.5 and 10 gr/l ,obtained 3.36e-6, 3.08e-6 and 3.52e-6 and for the transverse coefficient 6.58e-7, 6.49e-7 and 6.79e-7 m2/s, respectively.

کلیدواژه‌ها [English]

  • Groundwater pollution
  • tracer
  • analytical solutions
  • Physical Model
  • longitudinal and transverse dispersion coefficients