نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده عمران، آب و محیط زیست، دانشگاه شهید بهشتی، تهران، ایران

چکیده

سابقه و هدف:
نشت در شبکه‌های آبرسانی سبب از دست رفتن منابع آب و انرژی زیادی می‌شود. پیش‌بینی میزان نشت و تصمیم‌گیری بهینه در مورد استراتژی‌های کنترل نشت، به درک عمیقی در مورد رابطه نشت-فشار نیاز دارد. لوله‌های پلی‌اتیلن چگالی بالا (HDPE) به صورت گسترده در شبکه‌های توزیع آب در دهه‌های اخیر استفاده می‌شود و رفتار نشت در این نوع لوله‌ها هنوز کاملا مشخص نیست. هدف از انجام این مطالعه شناخت رفتار نشت از شکاف طولی برای لوله‌های پلی‌اتیلن و پارامترهای موثر برای رفتار الاستیک می‌باشد.
مواد و روش ها:
برای نیل به اهداف این پژوهش، مدل نیمه صنعتی آزمایشگاهی ساخته شد. براساس بررسی های اولیه و مطالعات کتابخانه ای، پارامترهای موثر استخراج شده و سپس با در نظر گرفتن پارامترهای قطر و ضخامت لوله، ابعاد ترک و دما، 10 نمونه آزمایشگاهی تهیه شد. سپس نمونه ها توسط پمپ فشار قوی تحت فشار قرار داده شدند و با تنظیم فشار میزان دبی خروجی از ترک طولی و دمای محیط در طول آزمایش برای هر فشار اندازه‌گیری گردید. سپس با استفاده از روش آنالیز ابعادی، نتایج حاصل آزمایشگاهی تحلیل گردید.
نتایج و بحث:
در شکاف‌های طولی لوله‌های پلی‌اتیلن مقدار دبی نشت تابعی از تغییرات مساحت موضع نشت است. نتایج آزمایش‌ها نشان داد که میزان تغییر در مساحت موثر موضع نشت با فشار در حالت الاستیک رابطه تقریبا خطی دارد. همچنین شیب تغییرات مساحت موثر نسبت تغییرات فشار بستگی به پارامترهایی نظیر ابعاد ترک، قطر و ضخامت لوله و دمای محیط دارد. از میان این پارامترها تاثیر طول ترک و دمای محیط به نسبت دیگر پارامترها برجسته بوده و تاثیر بیشتری بر میزان نشت در ترک طولی داشته است. با استفاده از نتایج آزمایشگاهی و استفاده از تحلیل ابعادی، رابطه‌ای برای تخمین تغییر مساحت موثر موضع نشت در ترک طولی لوله پلی‌اتیلن ارائه شده است. با استفاده از این رابطه دبی نشت در فشارهای مختلف قابل محاسبه است. در مطالعه حاضر توان نشت برای ترک های طولی لوله پلی‌اتیلن در محدوده 0.44 تا 1.44 محاسبه شده است و با رابطه ارائه شده همخوانی دارد. در صورتی که هر کدام از پارامترهای موثر مانند طول ترک و یا فشار افزایش یابد، در حالت الاستیک توان نشت به 1.5 نزدیک می‌گردد. با توجه به وجود عدم قطعیت در مورد ابعاد ترک ها در شبکه های توزیع آب نمی توان یک عدد را برای توان نشت ارائه کرد اما میانگین توان نشت در آزمایشات صورت گرفته معادل 1 می باشد. همچنین در آزمایش دیگری اثر دما بر میزان نشت به طور مستقل در فشار 5 بار بررسی شد و نشان داد افزایش دما می‌تواند سبب افزایش نشت در لوله‌های پلی‌اتیلن گردد. همچنین در فشار 40 درجه سانتی‌گراد از حالت الاستیک خارج شده و شیب تغییرات به شدت افزایش می یابد.
نتیجه‌گیری:
براساس نتایج این تحقیق می‌توان گفت برای کنترل نشت در شبکه های توزیع آب شهری که لوله های پلی‌اتیلن به کار رفته است بایستی به کنترل و مدیریت فشار توجه بیشتری نمود. همچنین علاوه بر پارامترهای مرسوم بایستی به دمای محیط توجه کرد. در مناطق گرمسیر برای تخمین میزان نشت لوله‌های پلی‌اتیلن و انتخاب استراتژی مناسب جهت کاهش میزان نشت از رابطه توسعه یافته ارائه شده استفاده کرد.

کلیدواژه‌ها

عنوان مقاله [English]

An experimental investigation of leakage from the longitudinal slits of the HDPE high density polyethylene pipes

نویسندگان [English]

  • Seyed Ali Sadr-Al-Sadati
  • Mohammadreza Jalili Ghazizadeh

Department of Water and Wastewater, Faculty of Civil, Water and Environmental Sciences, Shahid Beheshti University, Tehran, Iran

چکیده [English]

Introduction:
Leakage in water supply networks causes loss of water and energy resources (Xu et al. 2014). Leakage prediction and optimal decision making on leakage control strategies require a deep understanding of the leakage-pressure relationship. High-density polyethylene pipes (HDPE) have been used extensively in water distribution networks in recent decades (Kim and Lee, 2015), and leakage behavior in this material is still debatable. The purpose of this study is to identify the leakage behavior of the longitudinal slits for high-density polyethylene pipes and the effective parameters in elastic faze.
Materials and methods:
To achieve the objectives of this research, a semi-industrial laboratory model was developed. Based on the preliminary studies and literature review, effective parameters were extracted and then 10 samples were prepared by considering the parameters of diameter and thickness of pipes, dimensions of slits and temperature. Then, the samples were pressurized by a high-pressure pump and, by setting the pressure, the leakage discharge of the longitudinal slits and temperature was measured during the test for each pressure. Using the dimensional analysis method, the experimental results were analyzed.
Results and discussion:
In the longitudinal slit of HDPE pipes, the leakage flow is a function of changes in the area of the leak. The results of the experimental investigation showed that the change in the effective area of the leak position with the pressure in the elastic state is relatively linear (Cassa, et al, 2010). Also, the slope of the effective area change due to the pressure variation depends on the parameters such as dimensions of slits, pipe diameter and thickness, and temperature. Among these parameters, the effect of the slits length and temperature had a greater effect on the amount of leakage in longitudinal slits. Using experimental results and using dimensional analysis, a relationship has been developed to estimate the effective area change of the leak in the longitudinal slits in the HDPE pipes. Using this relationship, leakage can be calculated at different pressures. In the present study, the leakage exponent for longitudinal slits in the HDPE pipe is calculated in the range of 0.44 to 1.44 and is consistent with the proposed relationship. If any of the effective parameters such as cracking length or pressure increase, in the elastic state, the leakage power is approaching 1.5 (Van Zyl and Cassa, 2013). Given the uncertainty about the size of the slits in the water distribution networks, one cannot provide a number for leakage power, but the average leakage power in the experiments is equal to 1. In another experiment, the effect of temperature on leakage was investigated independently at a pressure of 5 bar and showed that increasing the temperature could increase leakage in HDPE pipes. Also, at 40 ° C, it exits from the elastic state, and the slope of the changes increases significantly.
Conclusion:
Based on the results of this research, it should be noted that the leakage control and pressure management should be considered more in urban water distribution networks with HDPE pipes. In addition to conventional parameters, the temperature should be taken into account. In the tropics area, the developed relationship was suggested to estimate the leakage of HDPE pipes and to select the appropriate strategy to reduce leakage.

کلیدواژه‌ها [English]

  • Water distribution network (WDN)
  • leakage-pressure relation
  • high-density polyethylene (HDPE) pipe
  • longitudinal slit
  • Temperature
  • elastic behavior

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