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Thermal-hydraulic and particle deposition analysis of supercritical CO2 in different tubes

Mao, S.; Zhou, T.; Liao, Y.; Tang, J.; Liu, X.

To compare the thermo-hydraulic and particle deposition characteristics of supercritical CO2 (SCO2) in different tubes, the SCO2 thermal-hydraulic performance and particle deposition characteristics were numerically investigated. Three different tube types, including circular tubes, semi-circular tubes and square tubes, were created. The effects of cross sections on heat transfer and particle type, mass flux and heat flux on particle deposition were investigated and discussed. The results indicated that the heat transfer coefficients (h) reach the peaks when the bulk temperature (Tb) is just below pseudo-critical temperature (Tpc) among three tubes. The h peaks are 4.8 kW/(m2·K), 8.4 kW/(m2·K) and 7.9 kW/(m2·K) for circular, semi-circular and square tubes, respectively. The semi-circular tube has the best heat transfer performance and it could alleviate the buoyancy effect efficiently. Moreover, the corners of the semicircular and square tubes should be further optimized to avoid excessive temperatures. The particle deposition efficiency (η) is 79.6%, 76.1% and 84.4% for circular, semicircular and square tubes, respectively, at dp=1 μm. Therefore, the semi-circular tube has a certain anti-deposition. The η for steel and graphite overlaps at dp<1 μm and steel is obvious higher than graphite at dp≥1 μm. Furthermore, small particles are impacted by mass and heat fluxes, whereas large particles are hardly affected. The η of small particles (dp<10 μm) increase with increasing mass flux. However, the η of small particles (dp<1 μm) decrease with increasing heat flux. It would be desirable that the flow channels can be further optimized to obtain the high thermal performance and anti-deposition for heat exchangers using SCO2 as working fluid.

Keywords: Supercritical carbon dioxide (SCO2); Thermal-hydraulic performance; Particle deposition; Different channels

Publ.-Id: 35429