Numerical investigation on heat transfer of supercritical CO2 in heated helically coiled tubes

Computational investigations on heat transfer of turbulent supercritical CO2 in large tubes using RANS modelling

“…We observe an apparent reduction in heat transfer coefficient. This is different from the results observed in small tubes [108,110,121]. Based on the analysis for turbulent sCO2 flow characteristics under high heat load densities, as described in Section 3.4.2, we are able to explain this difference.…”

“…The higher rate of increase is due to the drastically growing specific heat. At = 10 kW/m 2 , when value is lower than 0.1, the buoyancy has almost no impact on heat transfer coefficient, indicating the appropriateness in using the limit value 0.1 for as the criterion to assess the buoyancy effect on sCO2 heat transfer coefficient in large horizontal tubes; As the buoyancy effects intensify ( > 0.1) near the critical region caused by the considerable density variations, some slight increases in heat transfer coefficients appear, as those observed in literatures for small diameter tubes [108,110,121,181]. This is mainly attributed to the fact that the circulation induced by the free convection intensifies the turbulence mixing for sCO2 flows, in particular for the near-wall fluids.…”

“…Similar conclusions were also arrived by Zhao and Che [21] where turbulent As the tube diameter goes up, the buoyancy effect becomes more significant [45,110,180]. However, most of the previous studies on buoyancy influencing turbulent sCO2 heat transfer were focused on vertical flows, despite some within large vertical tubes ( ≈ 20 mm) at early stage [133,[167][168][169] are also included, no detailed investigation has been performed to reveal the mechanism of buoyancy effect and discuss its influence within large-tube horizontal sCO2 flows, even though the mixed convection has already been observed in small horizontal pipes [44,108,110,121,181]. Adebiyi and Hall [114] measured the wall temperature distributions of horizontal sCO2 flows in a large tube, and found that the buoyancy effect generates considerably different heat transfer behaviour from that for large vertical tubes, but the datasets for heat transfer and turbulent flowfields were still pretty limited.…”

Review of carbon dioxide (CO 2 ) based heating and cooling technologies: Past, present, and future outlook

“…Thermosiphon driven supercritical systems are under development due to high pressure and reverse heat flow problem during the night may be solved using nonreturn valves which are choked by dry ice. Researchers are testing vertical, horizontal, circular, helical, and angled tubes configurations to improve supercritical heating and cooling systems . Impact of tube curvature on buoyancy, natural circulation, pressure drops, charge reduction and fins or foam inside tubes on performance of supercritical CO 2 heat transfer systems .…”

“…Researchers are testing vertical, horizontal, circular, helical, and angled tubes configurations to improve supercritical heating and cooling systems. [247][248][249][250][251][252][253][254][255] Impact of tube curvature on buoyancy, natural circulation, pressure drops, charge reduction and fins or foam inside tubes on performance of supercritical CO 2 heat transfer systems. [256][257][258][259][260] The integration of gas coolers, ejectors, and boosters is under extensive research to increase performance of subcritical, transcritical, and supercritical CO 2 systems for residential, commercial, and industrial applications.…”