نوع مقاله : مقاله پژوهشی
نویسندگان
1 پردیس دانشکده های فنی- دانشگاه تهران
2 پردیس دانشکده های های فنی - دانشگاه تهران
3 مرکز تحقیقات ساختمان و مسکن
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
In this study, the heat transfer properties of R-134a under convective boiling conditions in horizontal microfinned flattened tubes were investigated. Microfinned copper tubes with outer diameter of 9.52 mm were flattened into oblong shapes with different internal heights of 6.6, 5.5, 3.8 and 2.8 mm. The experimental set-up used in this investigation was a well instrumented vapor compression refrigeration cycle. It consisted of a test evaporator, on which all experiments were carried out. In addition, there was a pre-evaporator to achieve the required vapor qualities. A post-evaporator was used to superheat the fluid before entering the compressor. The refrigerant which flows inside the tube of evaporators is electrically heated by an electrical coil wrapped around it.The experiments were carried out for mass velocities from 74 to 107 kgm$^2$s$^{-1}$ and vapor qualities from, approximately, 25\% to 95\%. The results show that for a given mass velocity and vapor quality, the heat transfer coefficient increases as the tube profile is flattened. Also, the heat transfer coefficient increases with an increase in mass velocity and vapor quality for the flattened tubes, just similar to the round tubes. A new correlation was developed to predict the flow boiling heat transfer coefficient inside the microfinned flattened tubes.
کلیدواژهها [English]
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