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Critical heat flux (CHF) characteristics in submerged jet impingement boiling of water on a heated copper surface are investigated at subatmospheric conditions. Data are reported at a fixed surface-to-nozzle diameter ratio of 23.8 and a fixed surface-to-nozzle height of 6 nozzle diameters. Three subatmospheric pressures of 0.176 bars, 0.276 bars, and 0.477 bars are considered, corresponding to fluid saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C and liquid-to-vapor density ratios of 8502, 5544, and 3295, respectively. At each pressure, CHF for varying jet Reynolds numbers (Re) in the range 0–14,000 are compared for two different surface finishes of roughness average values of 123 nm and 33 nm. The CHF enhancement observed with increasing Re is depicted in a nondimensional CHF map. Existing correlations available in the literature, which are out of range of the current experimental conditions, are found to poorly predict the obtained CHF data. A CHF correlation that captures the entire experimental data set within an average error of ±3% and a maximum error of ±13% is developed. The effect of fluid subcooling on submerged jet CHF is studied at the lowest pressure of 0.176 bars. Subcooled jet CHF is found to be well predicted from saturated jet CHF by using a typical subcooled pool boiling CHF correction factor.

An experimental study of mini-jet impingement boiling is presented for saturated conditions. Unique to this study is documentation of boiling characteristics of a submerged water jet under sub-atmospheric conditions. Data are reported at a fixed nozzle-to-surface distance that corresponds to a monotonic decrease in heat transfer coefficient for single-phase jet impingement. A mini nozzle is used in the present study with an internal diameter of 1.16 mm. Experiments are performed at three sub-atmospheric pool pressures of 0.2 bar, 0.3 bar and 0.5 bar. At each pressure, jet impingement boiling at four Reynolds numbers are characterized and compared with the pool boiling heat transfer. Enhancements in critical heat flux with increasing Re are observed for all pressures.