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This study is part of the preliminary experimental investigations designed to assess the feasibility of using supercritical carbon dioxide (sCO2) in the vicinity of its critical point for thermal management applications. In the present study, sCO2 was used as a working fluid in a diffusion bonded 316/316L stainless steel test section having staggered micro pin fin array flow passages of hydraulic diameter 679 µm (0.679 mm). The test section was subjected to a single wall non-uniform heat flux boundary condition and was operated in a horizontal orientation. The primary objective was to characterize the heat transfer performance of sCO2 as it flows through the staggered pin fin array for experimental conditions that span its critical and pseudocritical point. Data analysis methods employing 2-D and 3-D heat transfer models of the test section were used to calculate the average heat transfer coefficients for a given set of experimental conditions. Experiments were conducted by varying the inlet temperature (18 ≤ T_in ≤ 50 °C) and for fixed mass flux (300 kg m-2 s-1), heat flux (40 W cm-2), and reduced pressure (1.1). Experimental data were also compared against the predictions of a correlation proposed for single phase flows in microchannel staggered diamond pin arrays. The correlation predicted the data within 4.3 % when the ratio, T_Bulk/T_PC exceeded 1. It was also found that the enhancement in the heat transfer, a result of employing staggered pin array flow geometry instead of microchannels, carries a commensurate penalty in pressure drop.
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LES Simulation of turbulent supercritical CO2 heat transfer in microchannels
Although supercritical CO2 (sCO2) heat transfer has been employed in industrial process since the 1960s, the underlying transport phenomenon in high-flux microscale geometries, as could be employed in concentrating solar receivers, is poorly understood. To date, nearly all experimental studies and simulations of supercritical convective heat transfer have focused on large diameter vertical channel and tube bundle flows, which may differ dramatically from microscale supercritical convection. Computational studies have primarily employed Reynolds averaged (RANS) turbulence modeling approaches, which may not capture effects from the sharply varying property trends of supercritical fluids. In this study, large eddy simulation (LES) turbulence modeling techniques are employed to study heat transfer characteristics of sCO2 in microscale heat exchangers. The simulation geometry consists of a microchannel of 750×737 μm cross-section and 5 mm length, heated from all four sides. Simulation cases are evaluated at reduced pressure P_r = 1.1, mass flux G = 1000 kg/m^2-s, heat flux q'' = 1.7 − 8.9 W/cm^2 , and varying inlet temperature: 20 − 100℃. Computational results reveal thermal transport mechanisms specific to microscale sCO2 flows. Results have been compared with available supercritical convection correlations to identify the most applicable heat transfer models for engineering of microchannel sCO2 heat exchangers.
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- Award ID(s):
- 1604538
- PAR ID:
- 10074126
- Date Published:
- Journal Name:
- 6th International Supercritical CO2 Power Cycles Symposium
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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