Theoretical and experimental analyses of two-phase flow condensation heat transfer inside the horizontal micro-fin tube

Abstract

On the basis of previous experimental studies of two-phase flow condensation heat transfer for R134a inside the horizontal micro-fin tubes, a theoretically analysis of heat transfer characteristic combining both heat transfer mechanism and flow mechanism is discussed by the experimental data of heat transfer coefficient and pressure drop, to further clarify the influence of experimental condition and tube structure on heat transfer characteristics under the special working condition. Two performance factors, enhancement factor (EF) and penalty factor (PF), are introduced to quantitatively compare the effect of micro-fin on the heat transfer coefficient and the pressure drop between enhance tube and smooth tube. Meanwhile, the comprehensive factor, CHF, is applied to evaluate the comprehensive performance of heat transfer tube. It was found that enhancement factor (EF) and penalty factor (PF) both increase with increasing mass flux and fin helical angle, and decreasing saturation temperature, the comprehensive factor, CHF, is always greater than one and increases with increasing fin helical angle and mass flux, and decreasing saturation temperature. Moreover, based on the comparative analysis findings that some existing correlations of heat transfer characteristics underestimate most of the experimental data, and the experimental variable has great influences on the correlation prediction accuracy, such as mass flux, which is proportionate to the prediction deviation of correlation. Therefore, a new correlation was developed through analyzing quantitatively influencing mechanism of the experimental variable on the heat transfer characteristics, in a way that a two-phase frictional multiplier is defined firstly from the experimental data and then the forced convection heat transfer mechanism is redefined based on the comprehensive effect of various experimental variables. By the experimental data verification, the new correlation shows good prediction effect with the mean deviation of less than 5%.