Supercritical carbon dioxide in an array of micro impinging jets

Abstract

Heat transfer of micro multi-jet with supercritical carbon dioxide is experimentally studied. A thermal micro specimen chip constituting of a concentric distribution of three resistance temperature detectors (RTDs) on a serpentine heater, which was mechanically supported by a 500 µm thick fused silica substrate, was microfabricated and used to obtain the heat transfer coefficient under a range of operating conditions. The jets issued from a concentric array of thirteen micro jets with an interject spacing (S/d) of ∼ 1.5, each measuring ∅205 µm, which were perpendicularly positioned over the temperature sensors with a relative standoff, L/d, of 7.3. The effect of radial position, heat flux, mass flux and inlet pressure on the heat transfer were studied at an inlet temperature of 21.7 °C.Results showed a uniform heat transfer coefficient over the heater with optimum values recorded mostly around the pseudocritical condition. In addition, the heat transfer coefficient increased with pressure above the critical condition, which was tied to a corresponding increase in the pseudocritical temperature. Furthermore, the observed heat transfer characteristics of the micro jet impingement cooling using multi-jet were compared to single jet under the same working conditions. This comparison showed that although the multi-jet ensued a more uniform temperature distribution over the heater, the single jet performed better due to an undermined heat transfer process in the multi-jet — a consequence of the jet-to-jet interaction.