ABSTRACT
The augmentation of subcooled flow boiling can be accomplished in two ways. In the partial boiling region, the single phase contribution to heat transfer can be increased by the use of fins, twisted tapes, and similar devices used in augmenting heat transfer in single phase flow. Another way is by increasing the nucleate boiling contribution, which is beneficial in partial as well as fully developed boiling regions. Augmentation devices used for flow inside tubes can be broadly categorized into two types, depending on whether the nucleate boiling mechanism or the convective mechanism is augmented. Microfin or grooved tubes represent the fastest growing augmentation technique for in-tube evaporator application in refrigeration industry. Fujie et al. of Hitachi Cable Ltd. are attributed with the development of the first microfin tube. The basic geometry has multi-start spiral grooves of approximately 0.2 mm height and 19° spiral angle.
