CO2热泵系统具有环保、紧凑的特点,且在低温环境下的制热性能优异。CO2热泵系统放热侧通常工作在近临界区域附近,研究近临界CO2的冷却传热特性是二氧化碳热泵系统设计的一个关键技术问题。本文在管径为2mm的水平圆管中进行近临界CO2的冷却传热实验,实验流量范围200~400kg·m-2·s-1。结果表明,相同压力下CO2换热系数在准临界温度附近变化最为剧烈,随着压力远离临界压力,CO2换热系数在准临界温度附近的变化趋势变缓。在平均温度远离准临界温度的区域,CO2换热系数的变化趋势变为平缓,并且相同流量下不同压力的CO2换热系数在相同温度下接近相同。此外,本文拟合了CO2在温度28~55℃,压力7.5~12MP范围内的传热关联式。在准临界温度以下区域,关联式91.3%的预测值与实验值之间的偏差在±15%以内；在准临界温度以上区域,关联式93.9%的预测值与实验值之间的偏差在±15%以内。

The CO2 heat pump system has the characteristics of environmental protection, compactness, and excellent heating performance in low temperature environment. The exothermic side of CO2 heat pump system usually works near the critical point, so studying the cooling heat transfer characteristics of near-critical CO2 is a key technical problem in the design of CO2 heat pump system. In this paper, the cooling heat transfer experiment of near-critical CO2 is carried out in a horizontal circular tube with a diameter of 2mm, and the experimental flow range is 200~400 kg∙m-2∙s-1. The results show that the CO2 heat transfer coefficient changes most violently near the quasi-critical temperature under the same pressure, and the change trend of the CO2 heat transfer coefficient near the quasi-critical temperature slows down as the pressure moves away from the critical pressure. In the region where the average temperature is far from the quasi-critical temperature, the change trend of the CO2 heat transfer coefficient becomes flat, and the CO2 heat transfer coefficient of different pressures at the same flow rate is close to the same at the same temperature. In addition, the heat transfer correlation formula of CO2 in the range of temperature 28~55 ℃ and pressure 7.5~12MPa is fitted in this paper. In the region below the quasi-critical temperature, 91.3% of the predicted values have a ±15% deviation from the experimental values. In the region above the quasi-critical temperature, 93.9% of the predicted values have a ±15% deviation from the experimental values.

国家重点研发计划项目（2023YFB4102205）；中央高校基本科研业务费专项资金资助（2022ZFJH04）