Flow boiling of carbon dioxide with a micro impinging jet

Abstract

Flow boiling of carbon dioxide with a micro impinging jet was experimentally studied. The flow was issued from a 206 µm diameter nozzle onto a fused silica substrate that held a serpentine heater and three concentrically distributed resistance temperature detectors (RTDs). The effects of heat flux, radial position, mass flux, and pressure were experimentally studied. Heat fluxes up to 140 W/cm2, mass fluxes from 0.7 to 2.4 kg/cm2s, and saturation temperatures from 16.5 to 26.7 °C, corresponding to pressures of ∼ 5.3 to 6.7 MPa, respectively, were studied. To reveal the heat flux, radial position, and mass flux effects, the fluid entered at a temperature of 21.2 °C and a pressure of 5.9 MPa, which was around the saturation conditions of CO2, resulting in a rapid onset of nucleate boiling in most of the experiments. Results showed an increase in the heat transfer coefficient with heat flux, mass flux, and pressure up until the critical heat flux condition. In contrast, the heat transfer coefficient declined with radial position characterized by a pronounced influence of the jet hydrodynamics. Finally, comparisons with available correlations showed discrepancies, resulting in the proposal of a new correlation.