Abstract
The influence of radiative heat transfer in a CO<sub>2</sub> pipe flow is numerically investigated at different pressures.Coupled heat and mass transfer, including radiation transport, are modeled. The physical models and the high temperature and high pressure radiative properties method of computation are presented. Simulations are conducted for pure CO<sub>2</sub> flows in a high temperature pipe at 1100 K (with radius 2 cm) with a fixed velocity (1 m·s<sup>-1</sup>) and for di erent operating pressures, 0:1, 1, 5 and 20 MPa (supercritical CO<sub>2</sub>). The coupling between the temperature and velocity fields is discussed and it is found that the in uence of radiation absorption is important at low pressure and as the operating pressure increases above 5 MPa the influence of radiation becomes weaker due to an increase of CO<sub>2</sub> optical thickness.
Highlights
Current heat transfer fluids (HTF) for solar concentrating systems are: synthetic oil, steam, molten salt and air
The CO2 supercritical state (s-CO2) is observed at 73.8 b and 304.5 K favorable heat transfer and viscous supercritical properties may be built on designing innovative conversion systems
Solar-driven carbon dioxide transcritical power system using evacuated tube type solar collectors was studied in [2] whereas supercritical Rankine cycle was examined in [3] and demonstrated in [4]. In this latter paper evacuated CO2-based solar collectors showed 65-70% solar heat collection efficiency and the measured power conversion efficiency was in the range 8.78-9.45%. It was pointed out in [5] that s-CO2 recompression Brayton cycle can be as efficient as helium Brayton cycle with lower inlet turbine temperature (550 ◦C for s-CO2 vs. 850 ◦C for He) but higher inlet pressure (20 MPa for s-CO2 vs 8 MPa for He)
Summary
Current heat transfer fluids (HTF) for solar concentrating systems are: synthetic oil, steam, molten salt and air. Solar-driven carbon dioxide transcritical power system using evacuated tube type solar collectors was studied in [2] whereas supercritical Rankine cycle was examined in [3] and demonstrated in [4]. In this latter paper evacuated CO2-based solar collectors showed 65-70% solar heat collection efficiency and the measured power conversion efficiency was in the range 8.78-9.45%. A molten salt solar tower using s-CO2 Brayton cycle to produce electricity was described in [8] and the integration of heat storage to a supercritical
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