Two-phase refrigerant flow distribution in a multipass evaporator with vertical upward main tube (3rd report: prediction model of the flow distribution)

摘要

In this article, a calculation model that enables to predict two-phase flow distribution in a multipass evaporator is proposed. The model considers the multipass evaporator as the combination of simple elements, i.e. straight pipes and T-junctions, and utilizes the correlations to predict the pressure drop at the elements. For the T-junction, however, we have so little knowledge, especially for the small diameter T-junction, that we make some experiments to evaluate the existing correlations for the junction pressure drop. We also do not have reliable model for predicting the phase separation characteristics, so that we used the empirical equations for liquid division ratio derived in our previous papers. By this model, gas phase flow distribution to each pass is determined as it makes the pressure at the outlet of each pass equal. Calculation results well predict the previously presented experimental data that were obtained under the condition of larger quality at the header inlet. The suitableness of this model suggests that the complexity of the two-phase flow distribution in multipass tube attributes to the phase separation phenomena in dividing two-phase flow at a T-junction.