Visualization and measurement of reverse flow in an actual channel of a microchannel evaporator

Two leading edge channels of a microchannel evaporator are made transparent to visualize the flow regimes inside. The evaporator is operated in an automotive air conditioning system under both two-phase refrigerant feeding and liquid refrigerant feeding modes. The flow regimes in the microchannels are different in these two operation modes. In two-phase feeding mode: churn, bubbly/slug, and annular flows occur alternatively, but the period of each flow regime is not constant. Flow reversal is only witnessed occasionally in bubbly/slug flow regime. In liquid feeding mode, only liquid and bubbly/slug flows are observed. Reverse flow occurs periodically. The duration of flow reversal is shorter in two-phase feeding mode than in liquid feeding mode. Most likely it is due to higher upstream resistance caused by two-phase refrigerant feeding.