ABSORPTION MINI-CHANNEL ANNULUS
In order to reduce investment costs and refrigerant charge for heat pump equipment, the design of the required heat exchangers should be optimized. Mini-channels heat exchangers are proposed since they can dissipate a higher heat flux and they can be more compact. An accurate prediction of the two-phase heat transfer coefficient in mini-channels is necessary for the heat exchangers design. Several correlations have been proposed in the literature but they cannot cover the wide ranges of working fluids, operating conditions and different mini-channels dimensions. This paper presents and compares the most suitable correlations available in the literature for mini-channel heat transfer and pressure drop during two-phase flow. Also a new theoretical model is proposed for absorption of ammonia into ammonia-water in mini-channel annuli. The suitability of previously published correlations for prediction of heat transfer coefficients and pressure drop in mini-channels during absorption of ammonia-water mixture is then evaluated. For this purpose, experimental data have been collected in a mini-channel with the hydraulic diameter of 0.4 mm and 0.8 m length, so that the predictions of the correlations can be compared with the values from the experiments. The effect of vapour quality and mass flux on the two-phase heat transfer coefficient is investigated. From the comparison with the experimental data the prediction accuracy of different methods is evaluated.