The mixed turbulent convection heat-transfer characteristics of supercritical CO₂ (S-CO₂) heated in both vertical and horizontal oriented helically coiled tube (HC-tube) is investigated via experimental and numerical methods. Firstly, the coupled equations of flow direction, buoyancy force and centrifugal force in HC-tube are established. Then, the influence of the three factors on axial and radial heat transfer coefficient (HTC) performance are discussed. In vertical oriented HC-tube, the HTC first increases progressively and then drop swiftly, presenting a peak value at the pseudo-critical point. But, in horizontal oriented HC-tube, due to buoyancy force effects, the HTC oscillates dramatically which indicates the poor heat-transfer stability. Meanwhile, the numerical simulation, corresponding to the experiment condition, is carried out. To capture the flow structures, 6 characteristic lines on each cross-section are selected and the corresponding velocity and the turbulent kinetic energy distributions are comparative analyzed. The results showed that the coupling effects of centrifugal force and buoyancy force mainly affect heat-transfer on the inside of a cross-section. In addition, different from the M-type velocity in straight tube, the salient point of M-type velocity in HC-tube always locate at the outer side of the buffer-layer and the heat-transfer is slightly affected. The local heat-transfer deterioration mainly occurs at inside of a cross section where the velocity is obviously suppressed.

超临界CO ₂（S-CO _2）的混合湍流对流传热特性通过实验和数值方法研究了在垂直和水平方向的螺旋盘管（HC-tube）中加热的温度。首先，建立了HC管中流向，浮力和离心力的耦合方程。然后，讨论了这三个因素对轴向和径向传热系数（HTC）性能的影响。在垂直定向的HC管中，HTC首先逐渐增加，然后迅速下降，在伪临界点出现峰值。但是，在水平取向的HC管中，由于浮力作用，HTC剧烈振荡，这表明传热稳定性很差。同时，进行了与实验条件相对应的数值模拟。要捕获流结构，选择每个横截面上的6条特征线，并比较相应的速度和湍动能分布。结果表明，离心力和浮力的耦合作用主要影响截面内部的传热。此外，与直管中的M型速度不同，HC管中的M型速度的凸点始终位于缓冲层的外侧，并且对传热的影响很小。局部传热恶化主要发生在明显抑制速度的横截面内部。结果表明，离心力和浮力的耦合作用主要影响截面内部的传热。此外，与直管中的M型速度不同，HC管中的M型速度的凸点始终位于缓冲层的外侧，并且对传热的影响很小。局部传热恶化主要发生在明显抑制速度的横截面内部。结果表明，离心力和浮力的耦合作用主要影响截面内部的传热。此外，与直管中的M型速度不同，HC管中的M型速度的凸点始终位于缓冲层的外侧，并且对传热的影响很小。局部传热恶化主要发生在明显抑制速度的横截面内部。