扭曲椭圆管内超临界CO2冷却换热的数值模拟

为了提高CO₂热泵的传热性能，基于Fluent的数值模拟方法研究了不同质量流量下，扭距为100 mm及无扭曲状态下的水平椭圆管管内超临界CO₂冷却换热特性及二次流的变化规律，并针对竖直椭圆管引入局部换热系数和压降，研究了长短轴比b/a及扭距对扭曲管换热性能的影响。结果表明，低质量流量下扭曲椭圆管内浮升力明显大于椭圆管扭曲结构所产生的浮升力,对于低质量流量G<200 kg/(m²·s²)下的超临界CO₂流体，椭圆管具有更大强度的浮升力所造成的二次流，强化传热更明显；对于高质量流量G>200 kg/(m²·s²)下的超临界CO₂流体时，扭曲椭圆管具有更大强度自身结构所产生的周期性二次流来强化传热；管内的传热系数及压降随着扭曲程度及压扁程度的增大而增大。为扭曲椭圆管在CO₂热泵中的应用提供了重要的理论与数据支持。

Numerical simulation of cooling heat transfer of supercritical carbon dioxide in twisted elliptical tubes

In order to enhance the heat transfer performance of CO₂ heat pump, based on the numerical simulation method of Fluent, the law of supercritical CO₂ cooling and heat transfer characteristics and secondary flow in the horizontal elliptical tube whose torque is 100 mm or one infinity number under different mass flow are studied. In addition, concerning part coefficient of heat transfer and pressure drop brought by vertical elliptical tube, the influence of the length of the axial ratio b/a and the torque on the heat transfer performance is studied. Simulation results show that, the effect of buoyancy on the twisted elliptical tube is significantly larger than that of elliptical tube under low mass flow, and for the elliptical tube when supercritical CO₂ is under the low mass flow G<200 kg/(m²·s²), the elliptical tube has a greater intensity of secondary flow caused by buoyancy, and the enhanced heat transfer is more pronounced; when supercritical CO₂ is under the high mass flow G>200 kg/(m²·s²) , the twisted elliptical tube has a greater intensity of periodic secondary flow caused by self-structure, and the enhanced heat transfer is more pronounced; the heat transfer coefficient and pressure drop increase with the increasing degree of twist and flattening. It provides important theory and data support for the application of the twisted elliptical tube in CO₂ heat pump.