The mass flow characteristics of flashing Refrigerant-22 from a small vessel were investigated. A flash boiling apparatus was designed and built. It was modeled after the flashing process encountered by the accumulator of air-source heat pump systems. Three small pyrex glass vessels were used to hold the refrigerant and allow for visualization studies of the flashing process. Baseline experiments were run varying initial pressure, initial refrigerant amount, orifice diameter, and vessel geometry. Three sets of experiments were run using two passive enhancement methods (the addition of steel balls and the addition of small amounts of oil) and one active enhancement method (the addition of an immersion heater). Furthermore, a lumped-parameter analytical model was developed from basic thermodynamic principles that predicted the rate of depressurization for the flashing refrigerant. The study showed that the initial refrigerant amount and the orifice size had the greatest influence on the mass flow and pressure characteristics during each sixty second test. The initial pressure and vessel volume had less of an impact under the conditions tested. Two of the enhancement methods consistently increased the amount of refrigerant flashed during the tests as compared to the baseline data for the same initial conditions. The addition a 1 cm layer of 3.6 mm steel balls to the base of the vessel increased the amount flashed from 21% to 81% and the addition of the 215-watt flat-spiral immersion heater the increased the amount flashed from 47% to 111 %. Foaming at the vapor-liquid interface was observed with the refrigerant-oil mixture experiments as two of the eight test conditions averaged an increase while six averaged a decrease, ranging from a 21% increase to a 27% decrease. The analytical depressurization model predicted general pressure and mass flux trends, and revisions to the model improved pressure predictions to within ±11%
