Two-phase pressure drop with non uniform distribution.

Zusammenfassung

The use of multiport micro- and mini-channels in heat exchangers has increased in recent decades. They contribute to increasing efficiency and to reducing the refrigerant charge and compactness of heat exchangers. In this study we have considered a multiport tube with ten ports, 1.27 metres length and a hydraulic diameter of 1.17 mm. During condensation of an uniform flow, the refrigerant condenses equally in each port but it is possible to have a non-uniform distribution in all ports, thus, the condensation process depends heavily on the quality and mass flow of each port. The aim of this study is to numerically determine how non-uniform distribution in multiport mini-channel tube affects the two-phase pressure drop, several assumptions being made to simplify the model. Some hypotheses simplify the calculus, such as considering pressure drop in condensation and absence of transversal heat transfer between mini-channels. This study has been done with several values of saturation pressure, mass flux, vapour quality and heat flux. A single port with uniform distribution is compared with a double port with non-uniform distribution and a multiport tube with ten ports, all of them with the same hydraulic diameter. With this comparison it can be observed how non-uniform distribution affects pressure drop. To get valid solutions, possible data pairs of quality and mass flux are computed to achieve the same pressure drop, and after that, two-phase pressure drop evolution for a two ports tube is calculated and finally several combinations are calculated for a real ten port tube.