Abstract:

The heat transfer characteristic of supercritical CO₂ in tubes is the key factor affecting the overall performance of heat exchangers. In recent years, square microchannels have shown broad application prospects in compact and efficient printed circuit heat exchangers. The SST k-ω turbulent model was used to simulate the heat transfer characteristics of supercritical CO₂ in square microchannels under uniform heating conditions. The effects of flow channel shape, heat flux, mass flow rate and inclination angle on heat transfer performance in microchannels were studied by comparing three average heat transfer coefficients, buoyancy parameter and secondary flow intensity. The results show that the overall heat transfer performance of horizontal square microchannels is better than that of semicircular microchannels with the same hydraulic diameter. The temperature distribution, velocity distribution and turbulent kinetic energy distribution of typical sections in the fluid domain can well explain the non-uniform heat transfer phenomenon in horizontal microchannels. The overall heat transfer level of square microchannels can be improved by decreasing the heat flux, increasing the mass flow rate or decreasing the angle between the flow direction and the gravity direction. The simulation results have certain theoretical significance for the design and optimization of microchannel heat exchangers using supercritical CO₂ as working medium.

Key words: supercritical CO₂, numerical simulation, heat transfer, buoyancy effect, second flow intensity

摘要：

采用SST k-ω湍流模型对加热条件下超临界CO₂在方形微通道内的流动换热特性进行了数值模拟。通过对比三种壁面平均传热系数、浮升力参数和二次流强度的沿程变化研究了管型、热通量、质量流量和倾斜角度对微通道内流动换热性能的影响。结果表明：水平方形微通道的整体换热性能优于相同水力直径的半圆形微通道。流体域典型截面的温度分布、速度分布和湍动能分布等信息可以很好地解释水平方向流动时上、下壁面传热差异的现象。减小热通量、增大质量流量或减小流体流动方向与重力方向之间的夹角，可提高方形微通道的整体换热水平。该模拟结果对以超临界CO₂为工质的微通道换热器的设计和优化具有一定的理论指导意义。

关键词: 超临界二氧化碳, 数值模拟, 传热, 浮升力效应, 二次流强度