High pressure saturated flow boiling of CO2 at the micro scale

Abstract

Saturated flow boiling heat transfer of carbon dioxide (CO2) at the microscale was studied with pressures ranging from 2.4 MPa to 6 MPa (i.e., reduced pressure ranging from 0.3 to 0.81, respectively), mass fluxes ranging from 1199 kg/m2s to 2428 kg/m2s, mass qualities up to 0.94, heat fluxes up to 270 W/cm2, and ΔTsat up to 150 K. A maximum heat transfer coefficient (HTC) of about 150 kW/m2K, and a maximum critical heat flux (CHF) of about 200 W/cm2 was recorded. Comparison to established correlations were made and discussed based on a flow map of saturated flow boiling of carbon dioxide by Cheng et al. The map classified the flow into different patterns (i.e., bubbly, annular, dry-out, and mist flows), and provided insight about the observed HTC trends based on the mass quality. The Shah and the Cheng et al. correlations predicted the HTC reasonably well for mass qualities of up to 0.45 with mean average errors of about 23%, but for a mass quality of 0.94, the Kandlikar, the Shah, and the Cheng et al. correlations underpredicted experiments with mean average errors of 80%, 24%, and 98%, respectively. The critical heat flux condition was predicted well with different models, and the Katto et al. correlation provided the lowest mean average error of 23.0%.