PREDICTING FLOW BOILING HEAT-TRANSFER OF REFRIGERANTS IN MICROFIN TUBES

Microfin tubes are used in evaporators and condensers of refrigeration systems. The performance of different microfin tubes has been experim entally determined by a number of investigators, and the data are avai lable in literature, In order to use this information in the design of equipment, it is necessary to correlate this data into a readily usab le form. It is desirable that the correlation not only fit the availab le data well, but also reflect the parametric trends correctly. Kandli kar (1991a) presented a correlation scheme to correlate flow boiling d ata for augmented tubes and compact evaporators. This correlation was based on the original correlation by Kandlikar (1990) for smooth tubes which accurately represented various trends in heat transfer coeffici ent with important system parameters, In the present work, the Kandlik ar (1991a) correlation is modified to correctly account for the Reynol ds number exponent in the single-phase flow. Also the missing(k/D) rat io is introduced in the single-phase heat transfer correlation. The au gmented tube correlation scheme is applied to five sets of microfin tu be flow boiling data available in literature, A single set of constant s is found to correlate different refrigerant data sets obtained with the same microfin tube geometry. Parametric trends in heat transfer co efficient for microfin tubes obtained from the correlation are present ed. It has been found that the enhancements in the nucleate boiling an d the convective boiling contributions in the microfin tubes are influ enced by the microfin geometry, To further improve the correlation cap ability for microfin tubes, it is recommended that single-phase heat t ransfer data should be obtained for that tube over a wide range of Rey nolds number.