Cavitation dynamics in Venturi-type microchannels: Experimental observations and numerical modeling

Cavitation in fluids can severely hinder the efficiency of the associated flows. This undesired phenomenon is strongly influenced by local flow conditions, flow orientation, proximity to boundaries, and liquid/gas properties at saturation. When liquid flow is severely constricted and cavitation occurs, diverging microchannels can suppress vapor formation through effective pressure recovery; however, the behavior of such microchannels under different geometric and operating conditions remains unclear. This work combines experimental data and computational modeling to elucidate the intricate flow dynamics of cavitation-induced phase change of refrigerant (R134a) flow in a Venturi-type microchannel. Full-field numerical simulations are carried out using the interPhaseChangeFoam solver in OpenFOAM®, with the model coefficients being validated against experimental data obtained with an identical system. The effects of flow rate, channel opening angle, and inlet cross-sectional geometry are explored with a focus on pressure drop, velocity distribution, and cavitation characteristics, including vapor fraction. The results highlight the roles of flow velocity, orifice-to-channel width ratio, orifice size, and channel divergence angle on overall pressure drop. A channel opening angle of 12° minimizes pressure drop, in contrast with conventional single-phase Venturi geometries where the optimal opening angle typically lies between 5° and 7°. The study underscores that the cavitation number, including its sign, serves as a critical quantitative indicator of cavitation severity—where increasingly negative values correspond to intensified vapor generation in microscale constrictions. By identifying the relationships between operating conditions and cavitation phenomena, this work provides a framework for understanding and optimizing microchannel designs under conditions prone to cavitation.