مطالعه عددی تأثیر سطوح گسترش‌یافته بر عملکرد مبدل حرارتی زمین‌گرمایی هم‌محور

نوع مقاله : مقاله مکانیک

نویسندگان

1 دانشجوی کارشناسی ارشد، دانشکده انرژی، پردیس علوم و فن‌آوری‌های نوین، دانشگاه سمنان

2 استادیار، دانشکده انرژی، پردیس علوم و فن‌آوری‌های نوین، دانشگاه سمنان

3 دانشکده مهندسی مکانیک، دانشگاه سمنان

چکیده

در این مطالعه، تأثیر سطوح گسترش‌یافته بر عملکرد یک مبدل حرارتی زمین‌گرمایی هم‌محور عمودی بررسی شده است. سیال (آب) با دمای اولیه ۵/۳ درجه سلسیوس و با دبی حجمی ۰۰۰۸/۰ متر مکعب بر ثانیه از ناحیه حلقوی وارد و از لوله میانی خارج می‌شود. شبیه‌سازی برای حالت جذب حرارت انجام شده است. مدل آشفتگی SST k-ω برای جریان آشفته به کار گرفته شده است. با قرار دادن دندانه و گودی با چند هندسه مختلف بر روی سطح لوله خارجی، عملکرد حرارتی مبدل بهبود یافته است. سطوح مثلثی شکل نسبت به سایر هندسه‌ها خروجی دمایی بهتری از خود نشان دادند. اختلاف دمای ورودی و خروجی سیال در مبدل دارای گودی و دندانه مثلثی با عمق گودی 5 میلی‌متر، 5/6 درصد افزایش یافته است. بیشترین افت فشار در میان انواع مبدل نیز مربوط به مبدل با گودی و دندانه مثلثی با عمق گودی 5 میلی‌متر است که مقدار آن 9/10 کیلوپاسکال می‌باشد. مقادیر مختلف عدد ناسلت محلی در ناحیه حلقوی مبدل به ازای عمق‌های مختلف محاسبه شده است. مبدل ساده بالاترین مقدار ناسلت متوسط در محدوده مورد مطالعه مبدل را دارد و مقدار عدد ناسلت متوسط برای این نوع مبدل حرارتی برابر با 15/57 است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical study on the effects of extended surfaces on the performance of a coaxial geothermal heat exchanger

نویسندگان [English]

  • Naser Bakhshi 1
  • Saman Rashidi 2
  • Roohollah Rafee 3
1 Department of Energy, Faculty of New Sciences and Technologies, Semnan University, Semnan, Iran
2 Department of Energy, Faculty of New Sciences and Technologies, Semnan University, Semnan, Iran
3 Faculty of Mechanical Engineering, Semnan University, Semnan, Iran
چکیده [English]

In this study, the effect of expanded surfaces on the performance of a vertical coaxial geothermal heat exchanger has been investigated. The fluid (water) with an initial temperature of 3.5 ºC and a volumetric flow rate of 0.0008 m3/s enters from the annular area and exits from the middle pipe. The simulation is done for the heat absorption mode. The SST k-ω turbulence model is used for simulation of the turbulent flow. The thermal performance of the heat exchanger has been improved by placing ribs and dimples with several different geometries on the surface of the outer tube. Triangular surfaces showed better temperature output than other geometries. The temperature difference between the inlet and outlet of the fluid in the heat exchanger with a dimple and a triangular rib with a dimple depth of 5 mm has increased by 6.5%. The highest pressure drop is related to the heat exchanger with a dimple and a triangular tooth with a dimple depth of 5 mm, the value of which is 10.9 kPa. Different values of the local Nusselt number in the annular region of the heat exchanger have been calculated for different depths. The simple heat exchanger has the highest average Nusselt number in the studied range, and the average Nusselt number for this type of heat exchanger is 57.15.

کلیدواژه‌ها [English]

  • Geothermal heat exchanger
  • Convective heat transfer
  • Numerical solution
  • Extended surfaces
  • Pressure drop
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