مطالعه‌ي تجربي بهبود انتقال حرارت ترموسيفون دوفازي بسته تحت ميدان الكتريكي با نانوسيال آب/آلومينا

Experimental Investigation of Heat Transfer Performance of Two-Phase Closed Thermosyphon under Electrical Field Effect and Al2O3/Water Nanofluid

سيستم اصلي اين پژوهش يك ترموسيفون دوفازي بسته است. براي بهبود عملكرد حرارتي اين دستگاه، از دو عامل فعال و كنش‌پذير اعمال ميدان الكتريكي و تزريق نانو سيال آب/آلومينا استفاده شده است. بدين‌منظور نانوسيال آب/آلومينا با غلظت‌هاي مختلف تهيه و در ترموسيفون تزريق ‌شد. سپس ميدان الكتريكي با ولتاژهاي مختلف به سيستم اعمال، و تغييرات بازده حرارتي و مقاومت حرارتي با تغيير پارامترهاي متفاوت تعيين ‌شد. همچنين عدد ناسلت تعريفي ترموسيفون در حالت‌هاي مختلف محاسبه ‌شد. نتايج تجربي بيان‌گر آن است كه بازده حرارتي و عدد ناسلت ترموسيفون با اعمال ميدان الكتريكي و افزايش غلظت نانوسيال افزايش يافته ولي مقاومت حرارتي كاهش مي‌يابد. البته ميزان تغييرات در اثر تزريق نانوسيال بيشتر از تاثير ميدان الكتريكي است به‌طوري كه بيشترين افزايش نسبت عدد ناسلت و بازده حرارتي در حضور ميدان الكتريكي در بالاترين غلظت نانوسيال به‌ترتيب 36‌درصد و 38‌درصد است.

A two-phase closed thermosyphon (TPCT) was used as the main experimental system. Thermosyphon consists of three sections: Condenser, adiabatic and evaporator. 40% volume of evaporator is filled with nanofluid with different concentrations. Water is used as coolant fluid around the condenser. The flow rate of the coolant water was 200 ml/min. The condenser and evaporator are the electrodes of the electrical field. These two electrodes are attached to an AC electrical source. In each investigation, four parameters were measured after the stable state: Inlet and outlet temperature, flow rate of cooling water, evaporator and condenser temperatures. In this study, in order to improve the heat transfer performance of thermosyphon, two different passive and active techniques (applying electrical field and nanofluid injection) were used. Al2O3/water nanofluid with different concentration is prepared and injected to the evaporator section of the thermosyphon. Also, an electrical field with different voltage density was applied to the system, and the variations of thermal efficiency and resistance versus different parameters, such as nanofluid concentration, evaporator heat load and electrical voltage, were determined. During the present study, the defined Nusselt number for a two-phase closed thermosyphon, calculated for different conditions, and the ratio of Nu in the presence of an electrical field to Nu in the absence of an electrical field, in order to evaluate the effect of electrical field density on the heat transfer enhancement of a two-phase closed thermosyphon, were presented. The experimental results indicated that thermal efficiency and Nu were increased with nanofluid concentration and voltage increase, but the thermosyphon resistance decreased with these parameters. The variation of thermal properties through nanofluid injection was higher than through electrical field application. So, the maximum increment in Nusselt number ratio (Nusselt number in the presence of electrical field to Nusselt number in the absence of electrical field) and thermal efficiency at the maximum concentration of the present study, along with electrical field application, were 36% and 38%, respectively.