Nusselt number (Nu) correlations associated with constant property fluids have been deemed to be invalid when quantifying heat transfer rates to supercritical CO₂ (sCO₂) in the vicinity of its pseudocritical temperature (T_PC). For laminar sCO₂ flow, under constant heat flux conditions, previous studies have demonstrated a sudden deterioration in heat transfer near T_PC, followed by a recovery phase where Nu approaches a value greater than 4.36 (associated with fully developed flow conditions for constant property fluids). Through numerical simulations of sCO₂ heat transfer in horizontal circular tubes of diameters (D) from 0.2 mm to 2 mm, subject to constant wall heat fluxes (Q) in the range 0.25 – 25 kW/m² and for inlet Reynolds (Re) numbers of 40, 100 and 400, this study demonstrates for the first time that the extent of the heat transfer deterioration and its subsequent recovery is critically dependent on the magnitude of the imposed heat flux. However, the Nu variations were independent of inlet Re across the different simulation scenarios as long as the product QD was held constant. Therefore, a modified Nu correlation in terms of thermophysical properties evaluated at both the bulk (T_BULK) and wall temperatures (T_WALL) is proposed to represent the observed variations.

当量化到其伪临界温度（T _PC）附近的超临界CO ₂（sCO ₂）的传热速率时，与恒定特性流体相关的Nusselt数（Nu）相关性已被认为是无效的。对于层流sCO ₂流量，在恒定热通量条件下，先前的研究表明，在T _PC附近传热突然恶化，随后是恢复阶段，其中Nu的值大于4.36（与恒定特性流体的充分发展的流动条件有关） ）。通过sCO _2的数值模拟直径（D）从0.2毫米到2毫米的水平圆形管中的热传递，在恒定壁热通量（Q）范围为0.25 – 25 kW / m ^{2的情况下}，进口雷诺数（Re）为40、100和400，这项研究首次证明了传热恶化的程度及其随后的恢复严重取决于所施加的热通量。但是，只要产品QD保持恒定，Nu的变化在不同的模拟情况下都与入口Re无关。因此，在热（T _BULK）和壁温（T _WALL）的热物理性质方面评估了修正的Nu相关性建议使用来代表观察到的变化。