شبیه‌سازی دوبُعدی جوشش هسته‌ای استخری و بررسی مکانیزم تغییر فاز در شارهای حرارتی پایین

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده‌ی مهندسی مکانیک، دانشگاه گیلان، رشت، ایران

2 گیلان*مهندسی مکانیک

چکیده

در پژوهش حاضر، جوشش هسته‌ای استخری مبرد R-245fa در شرایط اشباع روی یک لوله‌ی افقی در فشار kPa 8/123 و دمای °C 20 تحت شارهای حرارتی مختلف (بین kW/m2 18 تا 27) به صورت عددی شبیه‌سازی شده و جزئیات جریان در آن مورد بررسی قرار گرفته است. شبیه‌سازی عددی توسط مدل چندفازی حجم سیال با بازسازی هندسی سطح مشترک، بدون ایجاد هسته‌ی حباب‌های اولیه توسط مدل تغییر فاز لی و مدل کشش سطحی نیروی سطحی پیوسته صورت پذیرفته است. اهمیت این مطالعه و ایجاد این مدل عددی، علاوه بر اهمیت صنعتی جوشش استخری در طراحی رآکتورهای هسته‌ای و اواپراتورهای مغروق در سیال، در اعتبارسنجی مدل عددی در پیش‌بینی سهم جوشش در جریان‌های اجباری فیلم‌ریزان یا بالارونده روی لوله یا دسته‌لوله‌ی افقی است. ضریب انتقال حرارت جابه‌جایی مدل عددی ایجادشده در مقایسه با داده‌های تجربی در دو شار حرارتی kW/m218 و 24، حداکثر 67/6% خطا داشته و در مقایسه با رابطه‌ی جوشش کوپر در شارهای حرارتی kW/m218 تا 27، حداکثر 64/8% متفاوت است. علاوه بر این، در این بررسی، روند حباب‌زایی و کنده‌شدن حباب‌ها از دیواره‌ی لوله و مایع مافوق اشباع کناره‌ی آن، دمای مایع و حباب و نحوه‌ی حرکت جریان تحت اثر حباب‌های ایجادشده در اطراف لوله مورد مطالعه قرار گرفته است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Two-dimensional simulation of nucleation pool boiling and investigation of phase change mechanism at low heat fluxes

نویسندگان [English]

  • Maryam Hassani 1
  • Ramin Kouhi Kamali 2
1 Faculty of Mechanical Engineering/University of Guilan/Rasht/Iran
چکیده [English]

In the present study, nucleation pool boiling of the saturated refrigerant R-245fa on the horizontal tube at a pressure of 123.8 kPa and temperature of 20°C under different heat fluxes (18-27 kW/m2) has been numerically simulated and the details of the flow are investigated. Numerical simulation is carried out based on the volume of fluid model with a piecewise linear interface construction method, without pre-determined bubbles by Lee phase change model and surface tension model of continuum surface force. The importance of this study and the numerical model, in addition to its industrial applications at nuclear reactors and flooded evaporators, is the model validation at predicting boiling portion of forced falling or climbing flows on horizontal tubes or bundle of tubes. The heat transfer coefficient of the present model, in comparison with the experimental data at two heat fluxes of 18 and 24 kW/m2 and the results of pool boiling Cooper correlation at heat fluxes of 18-27 kW/m2 has the maximum error of 6.67% and 8.64%, respectively. In addition, in this study, bubble nucleation and its departure from the tube wall and superheated liquid beside the wall, liquid and bubble temperature and modality of fluid movement due to the generated bubbles around the tube have been studied.

کلیدواژه‌ها [English]

  • Pool boiling
  • Nucleation
  • heat transfer coefficient
  • numerical simulation
  • volume of fluid model
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