two-phase flow, flow distribution, phase separation, microchannel condenser, modeling
The experimental study of an automotive microchannel condenser with separation circuiting was presented in the past by the same authors demonstrating the potential for performance improvement (lower refrigerant exit temperature or higher condensate flow rate). The condenser has an inlet in the middle of the height and vapor is expected to separate from liquid in the second header after de-superheating in the first pass. Upper path (for vapor) and lower path (for liquid) recombine upstream the exit of the condenser. This paper presents a mechanistic model developed to predict the phase separation efficiency in the second header that is incorporated into the condenser model. At the outlet of the second header refrigerant flows to the upper (vapor) exit and to the lower (liquid) exit. These are the inlets for its downstream passes in the condenser. Thus, other than the in-header mechanisms for two phase interactions, the downstream flow resistance (a function of cross-sectional area and heat flux) also influences the separation results in the second header by setting up the boundary pressures, based on equal pressure drop in the upper path and lower path. The condenser model is validated by condenser test results in which R-134a is used as the refrigerant. Its mass flux through the first pass is in the range of 145 - 330 kg/(m2s). The difference between measurement and modeling results is ±5% for capacity and ±20% for pressure drop. The model could work as a guidance for the design of phase separation condenser.