This experimental study investigated the geometric parameter of enhanced boiling surfaces having cross grooves. Boiling performance of various surfaces were tested in a rectangular boiling container, in which the gap between the boiling surface and the opposing wall of the container was variable. Fixed gap width of 0.5, 1.0 mm were tested and compared with the results of an unconfined container. The HFC4310 were tested at 75.5°C saturation temperature. The surface geometric parameters of the cross-grooved surface were varied and tested with various sizes of boiling space. We found that the boiling performance was enhanced as the gap reduced from 2.0 mm to 0.5mm, but the critical heat flux reduced as decreasing gap size. We found two non-dimensional geometric parameters, D{sup}* and O{sup}*, were the key parameters that affected the boiling performance. The best boiling performance having D{sup}* = 0.226 and O{sup}* = 0.0517 yielded the best performance. It enhanced the boiling performance by 2.5 folds as compared with the smooth surface. A predictive correlation of the critical heat flux was developed for the enhanced surfaces in a vessel of 0.5 mm gap. This correlation predicted the data of the present enhanced surface within ±13%.
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