Abstract




 
   

IJE TRANSACTIONS A: Basics Vol. 32, No. 4 (April 2019) 569-579    Article in Press

PDF URL: http://www.ije.ir/Vol32/No4/A/15-3055.pdf  
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  MODELING OF A SINGLE TURN PULSATING HEAT PIPE BASED ON FLOW BOILING AND CONDENSATION PHENOMENA
 
F. Mobadersani, S. Jafarmadar and A. Rezavand
 
( Received: July 03, 2018 – Accepted: March 07, 2019 )
 
 

Abstract    Demand for high-performance cooling systems is one of the most challenging and virtual issues in the industry and Pulsating heat pipes are effective solutions for this concern. In the present study, the best predictor correlations of flow boiling and condensation are taken into account to model a single turn pulsating heat pipe mathematically. These considerations, result in derivation of more accurate results. The nucleate boiling phenomenon has been considered as the dominant mechanism of the boiling process in the evaporator. However, due to the annular flow assumption, a thin film of liquid is considered in calculation of the mass transfer out of the vapor plugs. All the fundamental relations such as momentum, mass and energy equations are solved implicitly, except the energy equation of liquid slug. The liquid slug displacement results are compared with the previous studies and the comparison indicates increase in both the frequency and the amplitude of the slug displacement. Moreover, the calculated heat flux is verified with the empirical results. The comparison shows an acceptable agreement between the findings, which is better than previous modelings without boiling and condensation. Furthermore, the effect of pipe diameter on the flow and heat transfer mechanisms has been derived. According to the results, by increasing the pipe diameter, despite a frequency decrease, the oscillation amplitude of liquid slug and total heat flux transferred into the pulsating heat pipe increases. Sensible heat contribution in the heat trasnfer mechanism reduces by higher pipe diameter values.

 

Keywords    Pulsating Heat Pipe; Flow Boiling; Flow Condensation; Numerical Modelling

 

چکیده   

سیستم‌های خنک‌کاری با کارآیی بالا یکی از چالشی‌ترین موضوعات در صنعت است و لوله‌های حرارتی ضربانی یکی از راهکارهای موثر در این زمینه می‌باشد. در این مقاله، با استفاده از دقیق‌ترین روابط موجود در زمینه‌ی جوشش و چگالش جریانی برای مدل‌سازی تحلیلی یک لوله‌ی حرارتی ضربانی مورد استفاده قرار گرفته است. استفاده از این روابط موجب شده است که نتایج صحیح‌تری بدست آید. پدیده‌ی جوشش حباب‌زا به عنوان مکانیزم غالب در فرآیند جوشش در ناحیه‌ی اواپراتور در نظر گرفته شده است. با این وجود با فرض جریان دو فازی حلقه‌ای، فیلم نازکی از مایع برای محاسبه‌ی جرم چگالش شده از ستون های بخار در نظر گرفته شده است. تمام روابط اساسی مانند معادلات مومنتوم، جرم و انرژی، به جز معادله بقا انرژی برای ستون مایع، به صورت ضمنی حل شده است. نتایج جابجایی ستون مایع با نتایج گذشته مقایسه شده است که این مقایسه، افزایش فرکانس و دامنه‌ی نوسانات را نشان می‌دهد. علاوه بر این، صحت شار حرارتی محاسبه شده با نتایج تجربی بررسی شده است که صحت قابل قبولی را نشان می‌دهد. همینطور اثرات قطر لوله بر روی جریان و انتقال حرارت مورد بررسی قرار گرفته است. با توجه به این نتایج، با افزایش قطر لوله، بر خلاف فرکانس، دامنه‌ی نوسانات ستون مایع و کل انتقال حرارت منتقل شده به لوله‌ی حرارتی ضربانی افزایش می‌یابد. همچنین سهم انتقال حرارت محسوس در نرخ انتقال حرارت با افزایش قطر لوله کاهش می‌دهد.

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