| Summary: | 碩士 === 國立高雄應用科技大學 === 機械工程系 === 106 === In this study, the experimental test on the pulsating heat pipe heat exchanger filled with either water or HFE-7000 under various testing conditions was conducted. The filling ratio of the pulsating heat pipe was 35%, 50%, 65% tested with frontal air velocity between 0.5 m/s and 2 m/s at operating temperature between 60C and 120C. The heat transfer capability, the effectiveness, and the heat transfer coefficient of the heat exchanger were estimated to investigate the thermal performance of the pulsating heat pipe heat exchanger. The pulsating heat pipe was installed in the plate-fin array, which consists of 124 plates with fin pitch of 1.6 mm, with staggered arrangement in three rows. The overall size of the heat exchanger is 132 mm in length, 44 mm in width and 200 mm in height. Both the evaporator section and the condenser section of the heat exchanger were installed in individual air ducts to achieve heat exchange between hot airflow and cold airflow.
The results showed that as the operating temperature was between 60C and 120C with frontal air velocity of 0.5 m/s, the effectiveness of the pulsating heat pipe heat exchanger filled with 35% water was 35.7%, 43.98%, 46.43%, 47.36%, while that of the pulsating heat pipe heat exchanger filled with 35% HFE-7000 was 42.96%, 45.71%, 46.14%, 46.80%. Besides, it was found that the effectiveness of the heat exchanger filled with HFE-7000 was higher than that filled with water at low operating temperature. This is likely because HFE-7000 has a lower saturation temperature and a higher slope of saturation pressure versus temperature than those of water, resulting in easier start-up of the pulsating heat pipe. However, the pulsating heat pipe filled with water in filling ratio of 50% and 65% operated at low temperature was not able to start-up of the pulsating motion, causing a low heat transfer capability. As the operating temperature increased, the pressure difference between the evaporation section and the condensation section could be established, so that the pulsating heat pipe was able to function.
In order to enhance the maximum possible heat transfer capability, two pulsating heat pipe heat exchangers arranged in series with the water-filled pulsating heat pipe heat exchanger at vacuum condition being placed ahead of the HFE-7000-filled pulsating heat pipe heat exchanger at vacuum condition. The results showed that such arrangement with filling ratio of 35% could reach a heat transfer capability of 186 W, at frontal velocity of 2 m/s at higher temperature, which is an increase of 32% compared to the heat exchanger with a single heat exchanger.
|
|---|
