Pressure drop of subcooled flow boiling in narrow tube

The pressure drop of subcooled flow boiling in a narrow tube was investigated experimentally using water as a coolant. Experiments were conducted at nearly ambient pressure under the conditions: tube inside diameter: 1 and 3mm, tube length: 10∼100mm, and water mass velocity: 7000∼20000kg/m2s. The friction pressure drop ratio of subcooled flow boiling to non-heating water flow was examined by increasing the heat flux. The ratio begins to increase at the heat flux proposed by the Saha-Zuber correlation that the bubble begins to detach for 3mm inside diameter tube, though the heat flux is higher than the Saha-Zuber heat flux for 1mm tube. The ratio was further compared with the Bergles-Dormer correlation. The two phase friction multiplier of subcooled flow boiling was examined assuming the Ahmad void fraction and applied to the Lockhart-Martinelli (L-M) correlation. The abnormarity of the subcooled flow boiling in the case of 1mm inside diameter tube was confirmed in these discussions. (author)