以清洁能源和超临界压力流体利用中的强化换热为背景，通过实验研究、数值模拟、理论分析等方法，系统地研究了超临界压力流体在蛇形管内的流动换热规律，为超临界压力流体的强化换热设计及优化提供理论基础和技术支持。 对超临界压力CO$_2$在竖直蛇形管由层流向湍流转捩的早期不稳定性进行了实验和模拟研究。结果表明：外壁温在较低热流密度下稳定，随热流密度升高出现不稳定，波动值先增加后降低。在相同流动换热条件下，向下流动时开始出现不稳定的位置最早，向上流动次之，纯强迫对流最晚。向上和向下流动中浮升力沿径向分量增强离心力的作用，使不稳定的出现比强迫对流更早；向下流动中浮升力沿流向分量与流向相反，引起逆向压力梯度，使不稳定出现最早。 开展了超临界压力CO$_2$在竖直蛇形管的湍流对流换热的实验研究与分析。结果表明：壁温沿蛇形管呈现沿程整体上升和周期下降的规律，离心力的反向改变极大地强化局部换热。壁温在第二个相反U型段连接处，出现明显的局部谷值。这是由蛇形管本身的结构特点与物性达到局部峰值的位置随热流密度升高向上游移动，二者耦合的结果。与直管中流动换热向上恶化而向下强化不同，蛇形管中向上和向下流动的对流换热系数分布接近，没有出现换热恶化。 研究了超临界压力CO$_2$在蛇形管的湍流换热恶化抑制和强化换热特性。对于直管向上流动换热，浮升力、热加速使换热恶化的条件下，蛇形管可抑制传热恶化，综合换热指数PEC范围为3-6。对直管向下流动换热，浮升力使换热强化时，蛇形管在此基础上进一步强化换热，PEC范围为1.3-2.2。直管向上流动，浮升力和热加速在影响换热的转折点附近出现不稳定时，蛇形管能抑制不稳定。直管向上和向下流动，在一定流量和热流密度区间，浮升力、热加速在不同位置起相反作用，出现局部恶化与强化共存，蛇形管消除局部恶化与强化共存，PEC范围0.8-1.2。 利用激光多普勒测速和数值模拟研究了超临界压力R-23在蛇形通道的强化换热机理。结果表明：靠近准临界点和热流密度增加时，二次流发展更强，切向流发展较弱，因此综合强化换热效果更好 。蛇形通道中涡的周期性出现、变小和变大加强了边界层流体的扰动，湍动能增加，有助于抑制传热恶化。且二次流的发展阻止了直管中浮升力影响速度分布，改变湍动能而发生恶化的作用机制，因而传热恶化从根本上被抑制。

Based on the background of the enhanced heat transfer in the utilization of clean energy and supercritical pressure fluid, the flow and heat transfer of supercritical pressure fluid in the serpentine tube were systematically studied by experimental research, numerical simulation, theoretical analysis and other methods. This study can provide theoretical and technical support for the design and implementation of enhanced heat transfer for supercritical pressure fluids. The early instability of supercritical pressure CO$_2$ in the transition from laminar to turbulent flow in a vertical serpentine tube was studied experimentally and by simulation. The outer wall temperature remains stable at low heat flux, but becomes unstable with increasing heat flux, and the fluctuation value first increases, then decreases. At the same heat flux, the position where the instability appears is the earliest for downward flow, the second for upward flow, and the last for forced convection. The fluctuation is a typical early instability of the transition from laminar to turbulent flow in a curved pipe. The radial component of buoyancy force in upward and downward flow enhances the effect of centrifugal force, so that instability occurs earlier than that in forced convection; in downward flow, the component of buoyancy force along the flow direction is opposite to the flow direction, causing a reverse pressure gradient, making the instability appears the earliest. The experimental research and analysis were carried out on turbulent convection heat transfer in a vertical serpentine tube of supercritical pressure CO$_2$. The wall temperature along the serpentine tube presents an overall increase and periodic decreases along the flow. The reverse change of the centrifugal force greatly strengthens the local heat transfer.There is an obvious local valley of the wall temperature at the connection of the second opposite U-shaped segment. This is the coupling result of, the structural feature of the serpentine tube itself, and the position, where the thermo-physical properties reach a local peak, moves upstream with increasing heat flux. Different from the heat transfer performance in the straight tube, that is, deterioration in upward flow and enhancement in downward flow, the heat transfer coefficients of the upward and downward flow in the serpentine tube are close, and there is no heat transfer deterioration. The research was carried out on the suppression of deterioration and the turbulent heat transfer enhancement characteristics of supercritical pressure CO$_2$ in the serpentine tube. When the buoyancy force and thermal acceleration make the heat transfer deteriorated in upward flows in the straight tube, the deterioration is suppressesed in the serpentine tube, and the comprehensive heat tranfer number PEC is in the range of 3-6. When the buoyancy force enhances the heat transfer in downward flows in the straight tube, the heat transfer is enhanced on the basis in the serpentine tube, and PEC is in the range of 1.3-2.2. When the buoyancy force and thermal acceleration make the flow unstable and are close to the turning point of the heat transfer influence in upward flows in the straight tube, the instability is suppressed in the serpentine tube. When the buoyancy force and thermal acceleration antagonize at different positions, local deterioration and enhancement coexist in upward and downward flows in the straight pipe in a certain range of flow rate and heat flux, the coexistence of local deterioration and enhancement is eliminated in the serpentine tube, and PEC is in the range of 0.8-1.2. The enhanced heat transfer mechanism in the serpentine channel of supercritical pressure R-23 was studied by means of Laser Doppler Velocimetry and numerical simulation. When approaching the pseudocritical point and with the heat flux increasing, the secondary flow development is stronger, the tangential flow development is weaker, while the secondary flow development has a better effect on enhancing heat transfer, so the comprehensive heat transfer is better enhanced. The periodic appearance, diminishment and enlargement of vortices in the serpentine channel enhance the disturbance of the boundary layer fluid, increase the turbulent kinetic energy, and thus suppress the deterioration. The secondary flow development prevents the buoyancy from affecting the velocity distribution and changing the turbulent kinetic energy to deteriorate heat transfer in the straight pipe, so the heat transfer deterioration is suppressed fundamentally.