Abstract
Similar to our previous study, the effect of bubble size used in air bubble injection on enhancing heat transfer in a vertically coiled tube heat exchanger was determined experimentally in the present work. Three bubble sizes (0.1, 0.8, and 1.5 mm) were tested under four shell-side flow rates (2, 4, 6, and 8 L min), constant hot fluid flow rate (1 L min), and constant temperature difference (20 °C). The temperature distribution along the height of the heat exchanger was measured with the heat transfer rate. Results indicated that air bubbles’ injection generally led to a significant augmentation of the heat transfer rate in the heat exchanger. This phenomenon was clearly demonstrated by the rise in temperature distribution over the heat exchanger, and accordingly, by the calculated heat transfer rate. Moreover, the results showed that an increase in bubble size further improved the heat transfer rate. However, an optimum bubble size at which the heat exchanger can work with maximum effectiveness exists. The optimum bubble size for the present study was 0.8 mm. Further studies are recommended to gather more evidence for this phenomenon.
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