Heat transfer characteristics of turbulent flow of supercritical carbon dioxide (sCO2) in a short-heated microchannel

Abstract

A numerical study, validated by experimental results, of convective heat transfer of supercritical carbon dioxide (sCO2) in a short-heated microchannel is reported here. RANS equations were used to predict heat transfer and fluid flow characteristics, such as heat transfer coefficient, Nusselt number, pressure drop, and flow acceleration. This CFD steady state analysis used a microchannel of hydraulic diameter 300 μm, and simulations were performed using Starccm + for five different heat fluxes. Comparisons to available correlations, such as the Gnielinski, Bringer & Smith, Shitsman and Ornatsky, were conducted. It was observed that the Gnielinski correlation predicted the Nusselt number well with CFD simulations at lower heat fluxes but overpredicted the Nusselt number at higher heat fluxes. Overall, Shitsman correlation was able to predict the Nusselt number well compared to other correlations, but it didn't predict the correct trend at high heat fluxes. Key findings include quantification of the effect of flow acceleration on heat transfer using primitive variables and the benefits of operating at higher pressures. A uniform acceleration was observed over most of the length of the heater, and a 75% increase in the flow acceleration resulted in a 22.22% reduction in the Nusselt number. It was also observed that a 36% increase in the operating pressure can result in more than 50% reduction in the required mass flow rate for the same temperature drop of the heater.