Improved gas heaters for supercritical CO2 Rankine cycles: Considerations on forced and mixed convection heat transfer enhancement

摘要: Abstract To improve heat transfer performance of the gas heater in supercritical CO 2 Rankine cycle, characteristics heated Internally Ribbed Tubes (IRT) was experimentally and numerically investigated over a wide range buoyancy effect. Experiments reveal that for IRT with geometric parameter β  = 109, serious local deterioration did not occur consistently improved transfer. showed far superior smooth tubes. Empirical Nusselt correlations were recommended both upward downward flows. A numerical model then developed verified against experimental data from different geometries. Further studies on 7 demonstrate effect relates closely to rib For  = 0.48–4, flow impaired when Bo is around 10 −4 , though impairment became weaker as increased. When reached 16, buoyancy-induced disappeared number increased gradually stronger. increase up 109 didn’t lead obvious enhancement indicating geometries play smaller role than  > 16. Finally, design strategy provided optimization heaters.