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This study numerically investigated the heat transfer characteristics of the supercritical CO2 under the non-uniform cooling condition. The non-uniformity of heat flux distribution on a typical air-cooled exchanger is estimated at first and the heat transfer performances of supercritical CO2 under uniform and non-uniform cooling conditions are compared. The results demonstrated that the heat flux of the finned tube exhibited a significantly uneven distribution along the circumferential tube wall, and the unevenness increased with an increase in the wind speed. A clear distinction can be observed between uniform cooling and non-uniform cooling of supercritical CO2. Different from the non-uniformly heated CO2, when the bulk temperature is much higher than the pseudocritical point, the average heat transfer coefficient of non-uniformly cooled supercritical CO2 was 6.84% higher than that of the uniformly cooled supercritical CO2 and the situation is reversed when the bulk temperature was close to the pseudocritical point. The difference between non-uniform cooling and uniform cooling increased with an increase in the unevenness of the heat flux and fluid mass flux. The non-linear change of thermophysical properties and the buoyancy effect of CO2 near the pseudocritical point are the main reasons for the difference between uniform cooling and non-uniform cooling.

The turbulences from the cooling system have a significant impact on the thermal efficiency and safety operation of the power plant. The crosswind effect, which is one of the most frequent turbulence from the natural draft cooling system, is studied using a three-dimensional transient CFD model. Two common unsteady fluctuations: the emergence of the crosswind and the disappearance of the crosswind are simulated with different crosswind speeds. The changing rules of the aerodynamic characteristics and the heat transfer performance of the cooling tower under transients are presented and their mechanisms are discussed. The results show that the characteristic parameters of the cooling tower vary significantly with the turbulence of the crosswind. In terms of the response period, it is easier for the tower to resist the disturbance of the crosswind with lower speed. Due to the difference in the air flow driving force, the dynamic response of the cooling tower to crosswind emergence and disappearance is not mirrored. For the cooling tower experiencing minor crosswind speed changes, the response periods of the wind disappearing cases are longer than that of wind emerging. Whereas for the cooling tower experiencing major crosswind speed changes, the response periods of wind emerging cases are longer.